U.S. patent application number 14/975351 was filed with the patent office on 2016-04-14 for high-current battery management system.
The applicant listed for this patent is Rocketship, Inc.. Invention is credited to Zack D. Bomsta, Michael S. Horito.
Application Number | 20160105054 14/975351 |
Document ID | / |
Family ID | 52105106 |
Filed Date | 2016-04-14 |
United States Patent
Application |
20160105054 |
Kind Code |
A1 |
Horito; Michael S. ; et
al. |
April 14, 2016 |
HIGH-CURRENT BATTERY MANAGEMENT SYSTEM
Abstract
An apparatus includes a microcontroller and isolation circuitry
including multiple transistor-based switches arranged electrically
in parallel to isolate a battery from a load source, wherein the
battery is capable of providing high levels of current. The
apparatus includes a first buss bar to which first pins of the
multiple switches are connected, wherein the first buss bar is to
be connected to the battery and a second buss bar to which second
pins of the multiple switches are connected, wherein the second
buss bar is to be connected to the load source. A microcontroller
is programmed to control the multiple switches substantially
simultaneously to isolate the battery from the load source upon
detecting a predetermined condition.
Inventors: |
Horito; Michael S.; (Provo,
UT) ; Bomsta; Zack D.; (Provo, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rocketship, Inc. |
Provo |
UT |
US |
|
|
Family ID: |
52105106 |
Appl. No.: |
14/975351 |
Filed: |
December 18, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US2014/040997 |
Jun 5, 2014 |
|
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|
14975351 |
|
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61836233 |
Jun 18, 2013 |
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Current U.S.
Class: |
320/134 |
Current CPC
Class: |
H01M 10/4257 20130101;
Y02E 60/10 20130101; H02J 7/0029 20130101; H01M 2220/20 20130101;
B60L 58/15 20190201; H01M 2010/4278 20130101; Y02T 10/70 20130101;
H01M 2010/4271 20130101; H02J 7/0072 20130101; H02J 7/0091
20130101; H01M 10/425 20130101; H02J 7/00306 20200101; H01M 10/4207
20130101; H02J 7/0031 20130101; H01M 10/482 20130101 |
International
Class: |
H02J 7/00 20060101
H02J007/00; B60L 11/18 20060101 B60L011/18 |
Claims
1. An apparatus comprising: an isolation circuitry including
multiple, transistor-based switches arranged electrically in
parallel to isolate a battery from a load source, wherein the
battery is capable of providing high levels of current; a first
buss bar to which first pins of the multiple switches are
connected, wherein the first buss bar is to be connected to the
battery; a second buss bar to which second pins of the multiple
switches are connected, wherein the second buss bar is to be
connected to the load source; and a microcontroller programmed to
control the multiple switches substantially simultaneously to
isolate the battery from the load source upon detecting a
predetermined condition.
2. The apparatus of claim 1, further comprising a heat-conducting
bar made of a heat-conducting metal and thermally coupled to the
multiple switches, to equalize a temperature across the multiple
switches.
3. The apparatus of claim 1, further comprising: a switching driver
circuit operatively coupled to the microcontroller and to turn on
and off the multiple switches responsive to signals from the
microcontroller; and a plurality of metal traces connecting gates
of the multiple switches to the switching driver circuit that are
of equal length, such that a signal from the switching driver
circuit arrives at the multiple switches at substantially the same
time.
4. The apparatus of claim 1, wherein the multiple switches are
arranged in a first subarray and a second subarray, wherein a
number of the multiple switches in the first subarray are equal to
those in the second subarray.
5. The apparatus of claim 4, wherein the first buss bar and the
second buss bar each include a first conductive path and a second
conductive path that connect, wherein the multiple switches of the
first subarray are located in a line along an edge of the first
conductive path and the multiple switches of the second subarray
are located in a line along an edge of the second conductive
path.
6. The apparatus of claim 5, wherein a first switch in the first
subarray and a first switch in the second subarray are located so
as to be equidistant from the load source along, respectively, the
first buss bar and the second buss bar in order to synchronize a
time for current to arrive at each of the first switches.
7. The apparatus of claim 5, further comprising: a current
measuring circuit to: determine a first current of the first
conductive path; determine a second current of the second
conductive path; and notify the microcontroller of the first
current and the second current; and wherein the microcontroller is
further to generate an alert indicative of the first current and
the second current differing beyond a pre-defined threshold amount
indicative of degradation of one or more of the multiple
switches.
8. The apparatus of claim 1, wherein the predetermined condition
comprises one of: a short circuit in the load source, overheating
of the battery, overheating of the isolation circuitry, a
low-voltage threshold of the battery, or a user-initiated shut
off.
9. The apparatus of claim 1, further comprising a metal oxide
varistor (MOV) coupled to the first buss bar or to the second buss
bar in parallel with the multiple switches, to provide voltage
suppression by shunting current caused by high voltages away from
the multiple switches.
10. The apparatus of claim 1, further comprising: a printed circuit
board located between the first buss bar and the second buss bar
and to which is attached the microcontroller; and a thermal sensor
attached to the printed circuit board and operatively coupled to
the microcontroller, wherein the thermal sensor is to: measure a
temperature level of the second buss bar; and responsive to
detecting a temperature above a pre-determined threshold
temperature, send a signal as an over-temperature indicator to the
microcontroller; and wherein the microcontroller is to switch off
the multiple switches responsive to the signal.
11. The apparatus of claim 1, further comprising measurement
circuitry to: measure, to a high level of accuracy, a resistance of
one buss bar selected from the first buss bar and the second buss
bar; determine a current level through the one buss bar in view of
a voltage measured across the one buss bar and the resistance of
the one buss bar; and detect a high current surge condition in view
of the current level being over a predetermined threshold high
current.
12. The apparatus of claim 11, wherein the load source is a
vehicle, and wherein the measurement circuitry is further to
distinguish the high current surge condition in view of the current
level being below the predetermined threshold high current.
13. An apparatus comprising: an isolation circuitry including
multiple, transistor-based switches arranged electrically in
parallel to isolate a battery from a load source, wherein the
battery is capable of providing high levels of current of at least
400 amperes; a switching driver circuit operatively coupled to the
isolation circuitry such as to switch off the multiple switches
simultaneously; and a microcontroller operatively coupled to the
switching driver circuit, wherein the microcontroller is to direct
the switching driver circuit to turn off the multiple switches
responsive to detecting a predetermined condition.
14. The apparatus of claim 13, wherein the multiple switches are
arranged in a first subarray and a second subarray, wherein a
number of the multiple switches in the first subarray are equal to
those in the second subarray, wherein a first switch in the first
subarray and a first switch in the second subarray are located so
as to be equidistant from the load source.
15. The apparatus of claim 13, wherein the multiple switches
operate within a range of switching rates, and wherein the
switching driver circuit is to switch off the multiple switches at
a slowest rate within the range of switching rates without
exceeding a maximum allowable power dissipation caused by
switching.
16. The apparatus of claim 13, wherein the battery includes a
plurality of banks of cells, further comprising an
analog-to-digital converter (ADC) to measure a voltage of a bank of
the plurality of banks of cells and to send the voltage to the
microcontroller, wherein the microcontroller is further to:
determine a number of charge cycles in which the voltage has cycled
between a specified first voltage and a specified second voltage;
determine an amount of time in which the bank is at a critical
voltage level that depends on a type of the battery; and generate
an alert indicative of degradation of the bank responsive to
passing a threshold number of charge cycles and a pre-defined
amount of time at the critical voltage.
17. The apparatus of claim 13, wherein the predetermined condition
comprises a high pre-set current level over a short period of time,
wherein an amount of the high pre-set current level depends on the
load source.
18. The apparatus of claim 13, wherein the predetermined condition
comprises a reserve voltage below which the microcontroller is to
generate an alert to reset the battery in order to access reserve
capacity.
19. The apparatus of claim 13, wherein the predetermined condition
comprises a low-voltage threshold below which the microcontroller
is further to: shut off the multiple switches to protect the
battery from over-discharging; and require charging the battery
above the low-voltage threshold before accepting a reset to begin
drawing on the battery again.
20. The apparatus of claim 13, wherein the microcontroller is
further to: retrieve a critical low voltage for the battery; track
an amount of time at which the battery is at or below the critical
low voltage; responsive to the battery being at or below the
critical low voltage for a predetermined minimum period of time,
cause the battery to enter a hibernation mode of extremely low
current consumption when compared with normal operation of the
battery; and require recharging the battery above the critical low
voltage before accepting a reset to again draw power from the
battery.
21. The apparatus of claim 13, wherein the load source is a
vehicle, and wherein the microcontroller is further to: restrict
amperes available to the vehicle, as drawn through the multiple
switches, to an amount insufficient to turn on the vehicle; and
reverse the restriction in amperes responsive to receiving a signal
indicating presence of an authorized operator.
22. An apparatus comprising: an isolation circuitry including
multiple, transistor-based switches arranged electrically in
parallel on a circuit board, wherein the isolation circuitry is to
isolate a load source from a battery that is capable of providing
high levels of current; a surge detection circuit including an
operation amplifier to detect a surge in current by measuring a
voltage difference between source and drain of a subset of the
multiple switches; a surge measuring circuit to measure a magnetic
field and to determine a current level of the surge in current; and
a microcontroller operatively coupled to the surge detection
circuit and the surge measuring circuit, wherein the
microcontroller is to: receive a first signal from the surge
detection circuit, wherein the first signal is indicative of
detecting the surge in current; turn on the surge measuring circuit
responsive to the first signal; receive the current level of the
surge from the surge measuring circuit; and send a second signal to
switch off the multiple switches responsive to determining that the
current level is above a pre-defined threshold current level
indicating a short circuit.
23. The apparatus of claim 22, wherein the surge measuring circuit
includes a Hall Effect sensor attached to the circuit board with
which to measure the magnetic field.
24. The apparatus of claim 22, wherein the surge detection circuit
further includes a digital-to-analog (ADC) circuit to generate the
first signal responsive to the surge detection circuit detecting
the surge in current.
25. The apparatus of claim 22, wherein the microcontroller is
further to set the pre-defined threshold current level according to
a size of the battery or a size of the load source.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of
PCT/US2014/40997, filed Jun. 5, 2014, which claims the benefit of
U.S. Provisional Patent Application No. 61/836,233, filed Jun. 18,
2013, wherein the entire disclosure of both applications are
incorporated herein by this reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present disclosure relates generally to the management
and protection of batteries, and more specifically to a
high-current battery management system.
[0004] 2. Description of Related Art
[0005] Lead Acid batteries are the common battery of choice for
starting internal combustion engines (ICE) vehicles. Lead acid
batteries are robust in that they can handle a fair number of
charge-discharge cycles and can operate in most non-extreme
environmental temperature ranges. While they do degrade when
over-discharged, the effect is not as drastic as other chemistries.
Furthermore, lead-acid batteries are comparatively low cost
compared to other types of batteries.
[0006] However, other chemistries, such as lithium iron phosphate
(LFP) have advantages over lead-acid batteries. Although there are
several chemistries that can have these advantages over lead-acid
batteries, LFP is generally referred to herein by way of example
only, and is not meant to be limiting. Batteries using other
chemistries, such as LFP, typically consist of a battery pack made
up of multiple cell banks arranged electrically in series to
achieve the voltage output desired. Furthermore, a cell bank can
consist of one cell, or multiple cells arranged electrically in
parallel to achieve the capacity level, or ampere-hour (Ah),
desired.
[0007] Advantages of using another chemistry, such as LFP, over
lead-acid particularly for starting ICE vehicles, include by way of
example, substantially longer cycle lives, so the batteries can
last much longer (around three to six times longer by most
estimations). Batteries other than lead-acid batteries also have
higher energy density, which allows the battery to be more compact
than a lead-acid battery while still maintaining the same capacity
(e.g., number of Ah). An LFP battery pack could be less than one
half the size of a lead-acid battery and still contain the same
amount of capacity.
[0008] The advantages of other-than-a-lead-acid battery also
includes less internal resistance, so less capacity is needed to
achieve the desired cranking amperes ("amps"). A lead-acid battery
with higher internal resistance requires that the battery bank be
over-sized in order to achieve the necessary high surge current
required to start an engine. One explanation for why this works is
the surge current can be distributed between cells connected
electrically in parallel, reducing the voltage drop as current
passes over the internal resistance according to Ohm's law (V=IR)
over each individual cell's internal resistance. Another
explanation is the fact that putting multiple cells or banks in
parallel reduces the overall effective internal resistance of the
power source according to the parallel impedance equation:
1 Z eq = 1 Z 1 + 1 Z 2 + + 1 Z n . ##EQU00001##
[0009] The lower internal resistance of the LFP battery results in
the capability of the battery to provide the required high surge
current with much less capacity. Because less capacity is needed,
the volumetric size of the battery can be reduced even further
(approximately 50%-75% smaller). For example, because a lead-acid
battery has much higher internal resistance, a typical semi-truck
may require a lead-acid bank with a capacity of up to 280 Ah to
achieve the necessary cranking amps required to start the engine.
This would require three to four lead-acid batteries taking up
approximately six to eight cubic feet. An LFP battery with much
lower internal resistance would only require a capacity of 46 Ah to
start the same engine, and take up approximately a cubic foot in
comparison.
[0010] Other advantages of other-than-lead-acid batteries further
include being of lighter weight, making it easier to handle and
less weight for the vehicle to carry. The lead-acid batteries for a
semi-truck weigh approximately 200 pounds (lbs.) total while an LFP
battery for starting the same vehicle may weigh only about 20
lbs.
[0011] Also, an LFP battery includes no hydrogen off-gassing (so
less chance for explosion) and no sulphation, so no corrosion or
corrosive leakage. Off-gassing, also referred to as outgassing, is
the emission of especially noxious gases that is dissolved,
trapped, frozen or absorbed in some material. Off-gassing can
include sublimation and evaporation which are phase transitions of
a substance into gas as well as desorption, seepage from cracks or
internal volumes and gaseous products of slow chemical reactions.
Sulphation is the normal movement of the sulfate radical SO4, from
the sulfuric acid electrolyte H2SO4, to the battery plates during
the discharge and re-charging cycle of a rechargeable battery.
[0012] An LFP battery, however, is not as robust as a lead-acid
battery when it comes to over-discharging or overheating.
Additionally, lower internal resistance and the habit to have a
smaller capacity battery also creates both a safety concern as well
as a need to protect and optimize the operational life of the
battery.
[0013] As mentioned above, today's lead-acid battery banks used for
starting a semi-truck are over-sized in order to achieve the
desired cranking amps. This results in a large amount of excess
capacity in the battery bank. Because LFP requires less capacity to
achieve needed cranking amps, LFP batteries have considerably less
excess capacity available for other things. For example, it is
common for drivers to turn off their engines while stopping for
rest, yet continue to use running lights, cab lights, fans, radios
and other appliances. Because the lead-acid battery bank contains a
large amount of excess capacity, it can provide this power for a
certain length of time. However, because the LFP battery has much
less capacity, there is much less excess capacity to use for such
loads. If the driver were to use the same appliances, they would
increase the risk of running down the battery and over-discharging
it and increasing the likelihood of a dead battery. Once
over-discharged, an LFP battery degrades much faster than a
lead-acid battery, reducing the operational life to less than that
of a lead-acid battery.
[0014] Additionally, if the battery system were to experience a
short circuit, the effect would be even more catastrophic than if a
lead-acid battery system short circuits. The lower internal
resistance allows for higher surge currents that can cause much
greater damage than seen in lead-acid batteries. For example, if a
cable were to wear through its protective sheathing and contact any
metal on the truck, such as the frame or other wiring, the entire
battery system could instantaneously become red hot and the metals
reach their melting point. The LFP battery could also begin to
overheat at a rate much higher and to temperatures much higher than
in lead-acid batteries. Typically, the result would lead to a fire
in the vehicle, either from the battery itself bursting into
flames, or other parts of the vehicles become overheated and
combusting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The disclosure will be understood more fully from the
detailed description given below and from the accompanying drawings
of various embodiments of the disclosure. The drawings, however,
should not be taken to limit the disclosure to the specific
embodiments, but are for explanation and understanding only.
[0016] FIG. 1 is a perspective view of a buss bar according to one
embodiment.
[0017] FIG. 2 is a perspective view a circuit board with a bottom
buss bar attached, according to one embodiment.
[0018] FIG. 3 illustrates a battery management system (BMS)
assembly as in FIG. 2, with subarrays of metal-oxide semiconductor
field-effect transistors (MOSFETs) and a top buss bar attached,
according to one embodiment.
[0019] FIG. 4 illustrates a BMS assembly as in FIG. 3, but with
bottom and top buss bars according to another embodiment.
[0020] FIG. 5 illustrates a BMS assembly as in FIG. 3, with a heat
tie added on top of the MOSFET arrays according to one
embodiment.
[0021] FIG. 6 illustrates an underside of the BMS assembly of FIG.
5 with metal oxide varistors (MOVs) and cell balancing circuitry,
according to one embodiment.
[0022] FIG. 7 is a block diagram of circuitry of a battery
management system (BMS) located at least in part on the circuit
board of FIGS. 2-6, according to one embodiment.
[0023] FIG. 8 is a circuit diagram of a MOSFET array attached
between the top and bottom buss bars of FIGS. 1-6, according to one
embodiment.
[0024] FIG. 9 is a circuit diagram of the MOSFET switching driver
of the battery management system of FIG. 7, according to one
embodiment.
[0025] FIG. 10 is a circuit diagram of the surge detection circuit
of the battery management system of FIG. 7, according to one
embodiment.
[0026] FIG. 11 is a circuit diagram of the surge measuring circuit
of the battery management system of FIG. 7, according to one
embodiment.
[0027] FIG. 12 is a circuit diagram of the buss bar temperature
sensor of the battery management system of FIG. 7, according to one
embodiment.
[0028] FIG. 13 is a circuit diagram of the cell bank voltage sensor
of the battery management system of FIG. 7, according to one
embodiment.
[0029] FIG. 14 is a circuit diagram of a voltage divider that
measures the charge of an entire battery bank (e.g., cell pack) of
the battery management system of FIG. 7, according to one
embodiment.
[0030] FIG. 15 is a circuit diagram of charge shunt circuitry of
the battery management system of FIG. 7, according to one
embodiment.
DESCRIPTION OF EMBODIMENTS
[0031] For safety reasons, a battery management system (BMS) can
protect the battery from a short circuit or overheating by
isolating the battery from the load source. Additionally, in order
to optimize the battery life, the BMS can also detect a low voltage
and isolate the battery to prevent the battery from being
over-discharged. Current LFP batteries for starting vehicles do not
have such a BMS that performs this protection and isolation, which
are therefore not available to average consumers.
[0032] The BMS can be coupled to a battery cell pack such that the
BMS resides in a single enclosure, generally referred to as a
battery. "Cell pack" is one or more cell banks connected in series
to achieve a desired voltage output. A cell bank is one or more
cells connected in parallel to achieve a desired capacity. In the
alternative, the BMS can be external to the battery in its own
independent enclosure and connected to the internal battery cell
pack from the outside of the battery. This later configuration can
be useful in aftermarket applications with a battery that was
manufactured with no BMS. In either case, the BMS can be connected
in line at the negative terminal of the battery such that the BMS
can control the return current to the battery and shut off power
from the battery, if necessary.
[0033] One challenge with creating a BMS for this scenario is the
ability to cut a high current. A vehicle, such as a large
semi-truck, can draw around 400 amps while turning over the engine.
However, there is a momentary spike in the current draw when the
ignition is initially attempted. This current spike can reach as
high as 2,500 amps, an extremely high current. This means the BMS
should be able to allow at least this much current to pass for a
specified period of time without shutting off, to allow the vehicle
to start properly. When an unexpected high current is detected and
determined to be outside of specified safe operating ranges, the
BMS is to cut the current at this very high level. Shutting off a
high current like this is normally achieved with mechanical relays
or insulated-gate bipolar transistors (IGBTs). These mechanical
relays and IGBTs, however, are expensive and bulky, making it
difficult to fit the battery configured with mechanical relays or
IGBTs into the same size compartment as a standard vehicle starting
battery. Use of mechanical relays or IGBTs also increases cost
beyond prices comparable to existing vehicle starting
batteries.
[0034] Using a plurality of solid state semiconductor,
transistor-based switches arranged electrically in parallel in a
BMS is a less expensive and a compact alternative. These
transistor-based switches can include, for example, bipolar
junction transistors (BJTs), metal-oxide semiconductor field-effect
transistors (MOSFETs), junction field-effect transistors (J-FETs),
meta-semiconductor field-effect transistors (MESFETs), or
modulated-doping field-effect transistors or modulation-doped
field--effect transistors (MODFETs), and the like. For ease of
explanation. the present disclosure will sometimes refer to all of
these as "switches."
[0035] Transistor-based switches, and particularly MOSFETs, are
commonly used in low current situations such as cellphones, laptops
and other portable rechargeable devices (on the order of
milliamps). Switches such as MOSFETs are significantly less
expensive and less bulky than mechanical relays or IGBTs. However,
MOSFETs are not available that can handle currents in the thousands
of amps, and in these situations, designers usually employ
electromechanical relays or IGBTs, which are designed for higher
power applications. In one embodiment, MOSFET-based switches are
significantly less expensive, and less bulky, and by using an array
of transistor-based switches connected electrically in parallel it
is possible to handle high current situations when the current load
can be distributed and shared properly. For example, to use
MOSFET-based switches in high current applications, the MOSFETs are
to be protected from overloading so that the MOSFETs can reliably
be used to isolate the battery from the system, as will be
described in more detail.
[0036] Unfortunately, when transistor-based switches such as
MOSFETS are manufactured, each batch of the switches has a
different Vgs (gate to source voltage) or turn on voltage. Matching
switches from the same batch is only achievable during the silicon
wafer manufacturing process and ensuring that switches are selected
from the same batch is difficult and costly and therefore not a
preferred option. The difference in turn on times between batches
can only be slight (measured in nanoseconds and even picoseconds),
but is significant enough to make it difficult to switch the
switches on/off at the same time. This time difference can cause
the faster switch in the array to carry the entire load and burn
up.
[0037] By maintaining turn on times that are as close to the same
as possible among all the switches in the array, the switches can
distribute the current simultaneously when cutting the current.
Maintaining a similar turn on voltage across the array of switches
is difficult but manageable if approached differently from common
practices and recommendations for utilizing switches, as will be
explained.
[0038] Additionally, when starting a vehicle with an electric
starter motor, a very large inductive load is put on the battery
that requires high current. Suddenly switching the current off with
this very large inductive load creates a very fast and very large
voltage spike (measured in kilovolts (kV)) that can overload the
transistor-based switches, causing them to burst. If the inductive
current is kept at or below recommended operating currents, the
transistor-based switches can handle them fine without overheating,
provided the proper thermal heat sinking is used. While
transistor-based switches are sensitive to overcurrent and
overvoltage conditions, transistor-based switches can be employed
in a BMS as disclosed herein when these conditions are properly
controlled.
[0039] In one embodiment, a rechargeable battery system of the
present disclosure includes a battery pack and a battery management
system (BMS). The battery pack has rechargeable battery cells that
are connected in a way that allows the battery cells to be
discharged when the battery system is in operation. The BMS is
connected to the battery to allow data gathering from the battery,
and to provide selective isolation between the battery and a load
source. The BMS can be configured to perform cell balancing within
the battery bank. Cell balancing allows each of the rechargeable
battery cells to be maintained in a similar electrical state.
[0040] In still other embodiments, the BMS can include isolation
circuitry. The isolation circuitry can be configured to
electrically isolate the battery when a threatening electrical
system event, for example a short circuit, is detected within or
even outside of the battery system. For example, a battery system
is designed with a battery pack containing rechargeable battery
banks and cells, and a BMS can be connected to the battery
pack.
[0041] For example, a BMS can include isolation circuitry including
multiple, transistor-based switches arranged electrically in
parallel to isolate a battery from a load source, wherein the
battery is capable of providing high levels of current of at least
400 amperes. The BMS can further include a switching driver circuit
operatively coupled to the isolation circuitry such as to switch
off the multiple switches simultaneously. The BMS can further
include a microcontroller operatively coupled to the switching
driver circuit and configured to direct the switching driver
circuit to turn off the multiple switches responsive to detecting a
predetermined condition
[0042] In one embodiment, the microcontroller directs the switching
driver circuit to switch off the multiple switches at substantially
the same time, and other circuit design techniques can be used to
synchronize the timing of turning the multiple switches on and off.
The structure and programmed control provide this timing in order
to distribute the load evenly, to prevent damage caused by
overvoltage, as will be discussed in more detail.
[0043] In another embodiment, a BMS can include isolation circuitry
including multiple, transistor-based switches arranged electrically
in parallel to isolate a battery from a load source, wherein the
battery is capable of providing high levels of current. The BMS can
further include a first buss bar to which first pins of the
multiple switches are connected, wherein the first buss bar is to
be connected to the battery and a second buss bar to which second
pins of the multiple switches are connected, wherein the second
buss bar is to be connected to the load source. A microcontroller
of the BMS can be programmed to control the multiple switches
substantially simultaneously responsive to detecting a
predetermined condition. For example, the microcontroller can
receive a signal indicating any number of conditions, such as a
short circuit in the load source, overheating of the battery,
overheating of the isolation circuitry, a low-voltage threshold of
the battery, or a user-initiated shut off, among other as will be
discussed.
[0044] In yet another embodiment, the BMS can further include a
surge detection circuit including an operation amplifier to detect
a surge in current by measuring a voltage difference between source
and drain of a subset of the multiple switches. The BMS can further
include a surge measuring circuit to measure a magnetic field and
to determine a current level of the surge in current. The
microcontroller can be operatively coupled to the surge detection
circuit and the surge measuring circuit, wherein the
microcontroller is to: receive a first signal from the surge
detection circuit, wherein the first signal is indicative of
detecting the surge in current; turn on the surge measuring circuit
responsive to the signal; receive the current level of the surge
from the current measuring circuit; and send a second signal to
switch off the multiple switches responsive to determining that the
current level is above a pre-defined threshold current level
indicating a short circuit. In one embodiment, the surge measuring
circuit includes a Hall Effect sensor attached to a circuit board
with which to measure the magnetic field.
[0045] These and other features will now be explained in more
detail that help to prevent individual transistor-based switches
from overcurrent and overvoltage conditions by synchronizing turn
on times, and other solutions that reduce the effects of voltage
spikes, short circuits and the like.
[0046] FIG. 1 is a perspective view of a buss bar 100 according to
one embodiment. The buss bar 100 can include a single conductive
path (or two co-conductive paths) as in FIG. 4, or as in FIG. 1, a
first conductive path 102a and a second conductive path 102b that
connect to each other. As shown in FIG. 1, the first conductive
path 102a and the second conductive path 102b can form a horseshoe
shape, although other shapes are envisioned that likewise provide
two conductive paths, such as a V-shape, a square or rectangular
shape and the like. The buss bar 100 can also include a number of
apertures through which to connect the buss bar 100 to a battery
pack or to a load source, e.g., a vehicle when the battery pack (or
battery) is to turn on and power the vehicle. In the description
herein, battery pack and battery can be used interchangeably to
refer to a source of stored power deliverable as current to a load
source. In some cases, however, the term battery can be considered
to include a battery pack made up of banks of storage cells.
[0047] FIG. 2 is a perspective view a circuit board 200 with a
bottom buss bar 100a attached to the circuit board 200, according
to one embodiment. A number of electrical and sensing components
can be attached to the circuit board 200 that perform or help
perform a number of isolation and protection functions as well as
communication and monitoring functions. For example, a first metal
trace 202a and a second metal trace 202b (one for each sub-array of
switches that is arranged along each conductive path 102a and 102b,
respectively) can be formed on the circuit board 200. Additional
components, which will be discussed in more detail with reference
to FIGS. 7-14, include but are not limited to a switching driver
circuit 204, a microcontroller 206, Hall Effect sensors 210a and
210b, a satellite board connector 214, a data port 216 (e.g., a
universal serial bus (USB) connector), wireless circuitry 220,
global positioning system (GPS) circuitry 224, a reset button 228
to allow the user to reconnect the battery to the system if
pre-determined requirements are met, a light emitting diode (LED)
(or other type of) display 230 to provide status indications and
instructions to an operator, and a temperature sensor 234.
[0048] The satellite board connector 214, the data port 216, the
wireless circuitry 220 and the GPS circuitry 224 can also act as a
communication interface in various embodiments that enables
communications via one or more communications networks. A
communication network can include wired networks, wireless
networks, or combinations thereof. Such a communication interface
over the communications network(s) can enable communications via
any number of communication standards, such as 802.11, 802.17,
802.20, WiMax, 3G, 4G, long term evolution (LTE) or other cellular
telephone or communication standards.
[0049] FIG. 3 illustrates a battery management system (BMS)
assembly 300 as in FIG. 2, further illustrating an array 304 of
solid state semiconductor switches such as multiple
transistor-based switches 302, which sometimes are referred to as
switches 302 for ease of explanation. The array 304 of switches 302
can further be broken down into two subarrays of switches. These
two subarrays can include a first subarray 308a and a second
subarray 308b of transistor-based switches 302 connected to the
circuit board 200 and between the bottom buss bar 100a and a second
(or top) buss bar 100b. In a typical configuration, the bottom buss
bar 100a is to be connected to the battery and the top buss bar
100b is to be connected to the load source, although these can be
switched in another embodiment. In one embodiment, the first
subarray 308a and the second subarray 308b each include an equal
number of switches, thus balancing the current load on the first
switches closest to the load source across multiple subarrays of
switches.
[0050] In other words, when the current travels through a buss bar,
the current arrives at the first switch on the buss bar (the one
closest to the load source) sooner than it arrives at the last
switch in the line. Although seemingly negligible, this time
difference can cause the first switch to overload and burst before
the current is equalized across the array of switches in high
current applications. Accordingly, this time difference can be
reduced by arranging multiple subarrays 308a and 308b of equal
numbers of electrically parallel switches 302 along each of the
multiple electrically parallel conductive paths of the buss bars.
The relief to each first switch of each subarray is proportional to
the number of subarrays of switches arranged in parallel, so it is
envisioned that more than two subarrays 308a and 308b could be
employed.
[0051] With further reference to FIG. 3, the switches 302 of the
first subarray 308a can be arranged in a line along an edge of the
first conductive path 102a and of the second subarray 308b can be
arranged in a line along an edge of the second conductive path
102b. In one embodiment, the edges can oppose each other so that at
least the first switch from each of the two different subarrays are
located equidistant from the battery (along the bottom buss bar
100b) and are located equidistant from the load source (along the
top buss bar 100a). In this way, first current moving between the
first subarray 308a and the battery can arrive at substantially the
same time as second current moving between the second subarray 308b
and the battery. Similarly, third current moving between the first
subarray and the load source can arrive at substantially the same
time as fourth current moving between the second subarray 308b and
the load source. This works to further synchronize the time at
which the switches are loaded. This method alone (synchronizing the
time at which the current reaches the switches), however, may not
necessarily be enough to protect the switches from overloading,
particularly in ultra-high current situations.
[0052] FIG. 4 illustrates a BMS assembly 400 as in FIG. 3, but with
a bottom buss bar 400a and a top buss bar 400b according to another
embodiment. In this embodiment, each buss bar 400a and 400b can be
considered to have a single conductive path, or two co-conductive
paths. The co-conductive paths of each buss bar 400a and 400b are
still connected, however, and provide opposing edges along which to
position the first subarray 308a and the second subarray 308b of
switches 302, respectively.
[0053] In one embodiment, the source pin of each transistor-based
302 switch is connected to the bottom buss bar 100a or 400a and the
drain pin of each switch 302 is connected to the top buss bar 100b
or 400b. In another embodiment, these connections are switched. The
circuit board 200 can include holes through which each source pin
can pass to connect to the bottom buss bar 100a located beneath the
circuit board 200. In one embodiment, the first pins of the
switches are of equal length and the second pins of the switches
are equal length, to further synchronize the timing of current
arriving at the switches 302 of respective subarrays 308a and
308b.
[0054] In one embodiment, the metal traces 202a and 202b (of FIG. 2
and now hidden in FIG. 3) can connect gates of the transistor-based
switches 302 to a switching driver circuit 204 and be electrically
equidistant from the switching driver circuit 204, which controls
switching the semiconductor switches on and off as directed by a
microcontroller 206 (see also FIG. 7). This is referred to as trace
matching, and can be tuned such that the arrival of an on/off
signal at any two switches 302 is as close to the exact moment as
possible, where even a few nanosecond can be too much time. This is
the case particularly with high current, where a difference of too
much time could cause one switch to quickly conduct too much
current (an overcurrent situation), overloading the switch and
causing it to burst before other switches in the array can divert
some of that current. However, synchronizing the timing of the
signal with metal tracing alone is not necessarily enough to
protect the switches from overcurrent.
[0055] FIG. 5 illustrates a BMS assembly 500 as in FIG. 3, with a
heat tie 502 added on top of the subarrays 308a and 308b of
transistor-based switches 302 according to one embodiment. The heat
tie 502, also referred to as a heat conducting bar, can be
thermally coupled to the switches to equalize the temperature
across the switches 302. In one embodiment the heat tie 502 is made
of an appropriately-sized heat conducting material meant to
equalize heat across the heat tie and thus across the switches.
Equalizing the temperature across the switches 302 allows the
temperature of each switch to be as close to the same as the
temperature of any other switch. This is beneficial because
temperature impacts the turn on voltage (V.sub.t), which can be
expressed as:
V T = V FB + 2 .phi. F + 2 s 5 qN a ( 2 .phi. F + V SB C ox .
##EQU00002##
[0056] The .phi..sub.F parameter can be significantly affected by
temperature and which represents half the surface potential of the
switches. The equation for .phi.F, expressed as
.phi.F.sub.=(kT/q)ln(N.sub.A/N.sub.i)
[0057] shows the dependency on temperature T. As T increases,
.phi..sub.F also increases, causing the turn on voltage to
increase. This means that if one switch is cooler than another,
then the one switch will turn on more quickly as the turn-on signal
(gate voltage) does not have to rise to as high of a value to
overcome the turn-on voltage. Accordingly, temperature differences
between the switches affect the ability of the BMS to turn on or
off the switches at substantially the same time, and avoid an
overcurrent condition on any individual switch that could cause the
switch to burn out. Only equalizing the temperature across all the
switches, however, may not necessarily protect against all
overcurrent situations.
[0058] FIG. 6 illustrates an underside of the BMS assembly 500 of
FIG. 5 with metal oxide varistors (MOVs) 607a and 607b and bank
balancing circuitry 603, according to one embodiment. The bank
balancing circuitry 603 will be discussed in more detail with
reference to FIG. 7. Where slower switching alone may not reduce
the voltage spike enough to protect the switches 302 from
overvoltage and damage, any remaining voltage spikes can be shunted
away from the switches 302 to further protect the switches from
damage.
[0059] The MOVs 607a and 607b can be used to provide voltage
suppression to protect the switches 302 from overvoltage by
shunting the current caused by high voltages away from the switches
302. An MOV is a variable resistor, which increases in resistance
at low voltages and decreases in resistance at high voltages. By
placing the MOV electrically in parallel with the switches, the
high resistance during normal operation will not shunt a
significant amount of current away from the switches. However,
because resistance of the MOV decreases at high voltages, a voltage
spike can effectively turn the MOV into a short circuit and shunt
the current away from the switches 302 so as not to overload the
switches. Using only MOVs to suppress voltage spikes may not
necessarily be sufficient to protect the switches from overvoltage
situations. For example, combining the MOVs 607a and 607b with slow
switching of the switches 302 can be used to more reliably protect
the switches from overvoltage.
[0060] FIG. 7 is a block diagram of circuitry of a battery
management system (BMS) 700 located at least in part on the circuit
board of FIGS. 2-6, according to one embodiment. Additional or
fewer components are contemplated in additional embodiments, and as
will be apparent herein. The BMS 700 can include the MOSFET
subarrays 308a and 308a and attached bottom buss bar 100a or 400a
and top buss bar 100b or 400b that can be coupled between a battery
705 and a load 715. The battery 705 can include multiple cell
banks, including in the illustrated embodiment, Bank_1, Bank_2,
Bank_3 and Bank_4, to increase voltage output. A more-detailed
circuit diagram of the array 304 of switches 302, the bottom buss
bar 100a or 400a, and the top buss bar 100b or 400b is shown in
FIG. 8, according to one embodiment.
[0061] The microcontroller 209 can receive sensor signals and other
information with which to manage and monitor the battery and other
potentially unsafe conditions. Voltage and current levels along
with other parameters and features can be stored in a memory 207
for later retrieval by the microcontroller 209. The memory 207 can
be computer-readable media. A "computer-readable medium,"
"computer-readable storage medium," "machine readable medium,"
"propagated-signal medium," and/or "signal-bearing medium" can
include any device that includes, stores, communicates, propagates,
or transports software for use by or in connection with an
instruction executable system, apparatus, or device. The
machine-readable medium can selectively be, but not limited to, an
electronic, magnetic, optical, electromagnetic, infrared, or
semiconductor system, apparatus, device, or propagation medium.
[0062] Accordingly, the BMS 700 and methods disclosed herein can be
realized in hardware, software, including firmware, or a
combination of hardware and software. The BMS 700 and methods can
be realized in a centralized fashion in at least one BMS or in a
distributed fashion where different elements are spread across
several interconnected BMSs. Any kind of computer system or other
apparatus adapted for carrying out the methods described herein is
suited. The BMS 700 and methods can also be embedded in a computer
program product, which includes all the features enabling the
implementation of the operations described herein and which, when
loaded in a BMS of sufficient capability, is able to carry out
these operations. Computer program in the present context means any
expression, in any language, code or notation, of a set of
instructions intended to cause a BMS having an information
processing capability to perform a particular function, either
directly or after either or both of the following: a) conversion to
another language, code or notation; b) reproduction in a different
material form.
[0063] With continued reference to FIG. 7, the BMS 700 can further
include the switching driver circuit 204 operatively coupled
between the microcontroller 209 and the switches 302 of the
subarrays 308a and 308b. A more-detailed circuit diagram of the
switching driver circuit 204 is shown in FIG. 9, according to one
embodiment. An on/off signal from the microcontroller 209 comes
into the switching driver circuit 204 and a battery on/off signal
is output from the switching driver circuit 204, to turn off the
switches 302 as discussed herein. The switching driver circuit 204
can amplify the signal from the microcontroller 209 and slow the
switching speeds to reduce current spikes.
[0064] For example, when suddenly switching off high currents with
a large inductive load, as is done with a high-current battery for
example, the battery can experience very large voltage spikes (in
the kV range). These spikes can overload the switches 302 and cause
the switches to burst. The size of the voltage spike depends on the
equation for the voltage across an inductor, expressed as:
.upsilon. = t ( Li ) = L i t . ##EQU00003##
[0065] which states that the voltage is equal to the rate of change
of the current times the inductance. The faster the current
changes, the higher the voltage spike.
[0066] To reduce the rate of change of current (when the switches
are switched off), and thereby reduce overvoltage due the voltage
spike, switching circuitry in the switching driver circuit 204 can
be designed or programmed to turn the switches 302 on and off at
speeds as slow as possible, to reduce the change in current over
time without exceeding the maximum allowable power dissipation
caused by switching (switching causes the highest power dissipation
in most types of transistors including MOSFETS). In one embodiment,
for example, component values of a resistive-capacitive (RC)
circuit of the switching driver circuit 204 can be set to a
specific rise time for the turn on/off signal. This setting is well
below the manufacturers recommendations. It is commonly held that
transistor-based switches such as MOSFETs should switch off as fast
as possible, so switching as slow as possible is a counter
intuitive approach. Only slowing the switching speed, however, may
not necessarily protect all of the switches from overvoltage due to
voltage spikes.
[0067] The BMS 700 can further include a surge detection circuit
713 located on the circuit board 200 and operatively coupled to the
microcontroller 209 to provide a first-stage surge detection. In
one embodiment, the surge detection circuit 713 also operates as a
current sensing circuit. A more-detailed circuit diagram of the
surge detection circuit 713 is illustrated in FIG. 10, according to
one embodiment. A dual operational-amplifier (op-amp) circuit 1010
can send an I_SENSE_ON signal to indicate to the microcontroller
209 to turn on a surge measuring circuit 710. The op-amp circuit
101 can provide initial, low-power current sensing by measuring a
voltage difference between source and drain of a subarray of
electrically parallel switches, e.g., subarray 308a and/or subarray
308b, and calculating the current based on the switches' specific
voltage-current characteristics. The calculated current can be sent
to the microcontroller 209 through the Vdrain_G6 pin.
[0068] A digital-to-analog converter (ADC) 709 may be included to
help convert the current to a digital signal readable by the
microcontroller 209. In different embodiments, the ADC 709 can be
integrated into the microcontroller 709 (as shown) or into the
surge detection circuit 713, or can be a stand-alone ADC 709 on the
circuit board 200.
[0069] Upon detecting a sufficient surge in current, the I_SENSE_ON
signal can alert the microcontroller that a current over a
predetermined threshold (e.g., 10, 15 or 25 amps or the like) has
been detected. The microcontroller 209 can then turn on Hall Effect
sensors 210a and 210b to more accurately measure how much current
the surge contains, to help distinguish between, for example, an
engine start and a short circuit as will be discussed in more
detail.
[0070] For example, the BMS 700 can further include the surge
measuring circuit 710, which can include a left Hall Effect sensor
210a and a right Hall Effect sensor 210b, attached to the circuit
board 200 and operatively coupled to the microcontroller 209. A
more-detailed circuit diagram of the left Hall Effect sensor 210a
of the surge measuring circuit 710 is illustrated in FIG. 11,
according to one embodiment. A Hall Effect voltage (V.sub.hall),
which represents the magnitude of the magnetic field created by the
buss bar current that is sensed, is output to the microcontroller
209. The microcontroller 209 can then determine whether or not the
V.sub.hall value is within operating ranges and take appropriate
action that may be necessary, such as switching off the
transistor-based switches 302.
[0071] The BMS 700 can further include the temperature sensor 234,
locatable between the circuit board 200 (FIGS. 2-6) and at least
one buss bar, and which is also operatively coupled to the
microcontroller 209. A more-detailed circuit diagram of the
temperature sensor 234 is illustrated in FIG. 12, according to one
embodiment. The buss bar temperature is output from the temperature
sensor 234 to the microcontroller 209.
[0072] The BMS 700 can further include the bank balancing circuitry
603 and corresponding bank voltage sensors 703 operatively coupled
between the microcontroller 209 and the banks within the battery
705. A more-detailed circuit diagram of the bank voltage sensors
703 is illustrated in FIG. 13, according to one embodiment. A
voltage output for each bank of the battery 705 is sent to the
microcontroller 209. An example voltage divider 1400 as illustrated
in FIG. 14 can be used to measure a charge the entire battery pack,
e.g., battery 705. Dividing the voltage down to a lower voltage can
allow the microcontroller 209 or the ADC 709 to properly handle or
operate on the lower voltages.
[0073] Furthermore, a more-detailed circuit diagram of the bank
balancing circuitry 603, with separate circuits 603a, 603b, 603c
and 603d to balance, respectively, Bank_1, Bank_2, Bank_3 and
Bank_4 within the battery 705 is illustrated in FIG. 15 according
to embodiment. Each balancing circuit receives a corresponding bank
control signal from the microcontroller 209.
[0074] With it now possible to consistently protect the array 304
of transistor-based switches from damage due to overcurrent or
overvoltage situations, the array 304 can be reliably used as an
isolation circuit. A microcontroller 209 can be operatively coupled
to the isolation circuitry to control when current is allowed to
pass and when it is cut off, or in other words, when the battery
should be connected to a loud source (or other electrical system)
and when it should be isolated from the load source. Voltage
sensors, temperature sensors and other such sensors or sensing
devices that can detect an event and send a signal to the
microcontroller 209 can be used to help the microcontroller 209
know when to allow current to pass though the battery 705, and
whether to cut off current through the battery due to an unsafe
condition as defined by the micro-controller's programming. In the
case of a starter battery, we protect against certain events that
could create a dangerous situation or reduce the life of a battery
as now explained in more detail with reference to FIGS. 1-15.
[0075] Measuring Current Surges and Detecting a Short Circuit
[0076] Current surges can be created in a number of ways. Some may
be part of normal operation conditions, such as starting a vehicle,
while others are caused by an unsafe operating condition, such as a
short circuit in the system. These surges are to be detected and
measured so as to determine a current condition of an electrical
system, and take favorable action, if necessary. When the current
surges, there is also a large surge in the magnetic field of the
buss bar 100. The Hall Effect sensors 210a and 210b can be used to
detect this surge. The term "Hall Effect" refers to a potential
difference observed between the edges of a conducting strip
carrying a longitudinal current when placed in a magnetic field
perpendicular to the plane of the strip, which in the present
disclosure is the plane of the buss bars 100 and 400.
[0077] In one embodiment, each Hall Effect sensor 210a and 210b is
placed near the edge of a conducting path of the buss bar (e.g., of
102a or 102b) where the magnetic field is strongest so the Hall
Effect sensors can be more effective. Each Hall Effect sensor can
measure the current in the conductive path. Each Hall Effect sensor
then reports the current to the microcontroller 209. The
microcontroller 209 can then determine whether or not a
short-circuit condition exists by analyzing the magnitude and
duration of the surge. If the surge satisfies the conditions for a
short circuit, the microcontroller can signal the switching driver
circuit 204 to activate the isolation circuitry, and therefore
disconnect the battery 705 from the load 715.
[0078] Hall Effect sensors require a relatively large current
(several mA) to function. If used continuously to monitor the
current, the Hall Effect sensors 210a and 210b can drain the
battery in a relativity short amount of time. To prevent this, a
low-power consuming method, such as the op-amp-based amplifier in
combination with the ADC 709 can be used as the surge detection
circuit 713 (FIGS. 7 and 10). This surge detection circuit can also
act as a current sensing circuit and can monitor the relative
current by measuring the voltage difference across the drain and
source of the electrically parallel array 304 of switches. While
this method consumes very little power and can detect a surge in
current, it cannot accurately measure the surge at high levels.
[0079] In one embodiment, the surge measuring circuit 710 remains
off until the microcontroller 209 signals the microcontroller 209
to turn on, thereby saving power. When the surge detection circuit
713 detects a surge, the surge detection circuit 713 signals the
microcontroller 209, which in turn directs the surge measuring
circuit 710 to turn on. The microcontroller 209 can turn on the
Hall Effect sensors 210a and 210b to measure the magnetic field,
determine the current level, and report back to the microcontroller
209. The microcontroller 209 can then determine (from its
programming) whether the surge constitutes a short circuit and,
therefore, whether the isolation circuitry is to be activated. For
example, a pre-defined threshold level of current can be set for a
particularly-sized battery 705 or load 715 (or a certain
combination thereof) that is compared to the determined surge in
current to determine whether the surge constitutes a short circuit.
In this way, the low-current consuming surge detection circuit 713
can save power by anticipating a potentially high current situation
where the BMS 700 might need to turn on the Hall-effect sensors to
measure the surge in current. This approach allows for constant
monitoring of current levels without draining the battery 705 and
can be done quickly enough to isolate the battery 705 before a
short circuit can cause significant damage.
[0080] In many low-power current sensing circuits, a series
resistor is used for current measurement by measuring the voltage
across the resistor and calculating the current using ohms law. In
the present BMS 700, a series resistor may not be practical because
of the very large currents present. Every conductor, however, has a
resistance, although in some cases the resistance is small, it
could be treated as a series resistor. The resistance of such a
conductor can be measured using a very accurate device because the
resistance is so small, so that determining a current flow through
the conductor can be performed at a proper granularity and with
accuracy.
[0081] Accordingly, the buss bar 100a, 100b, 400a or 400b can be
considered as a series resistor, and the current can be calculated
by measuring the voltage across the buss bar and using ohms law. In
the present BMS 700, the measurement can be done with measurement
circuitry including the ADC 709, which the microcontroller 209 can
use to measure an accurate voltage across the buss bar. In one
embodiment, the measurement circuitry is integrated with or
operatively coupled to the microcontroller 209. Because the
resistance is small and slightly varied with each buss bar used as
a conductor, the resistance is preferably measured in production
during calibration and stored in the memory 207 or other firmware,
so as to be available to the microcontroller 209 during operation.
During operation, the microcontroller can determine the current
flowing through the switches 302, using Ohm's Law, from the
measured voltage and the stored resistance. The measurement
circuitry can also include a ranging circuit to supply the ADC 709
with the correct range of voltages that corresponds to the possible
current magnitudes. In one embodiment, this ranging circuit can
include an op amp, voltage divider, and overvoltage protection.
[0082] The resistance measurement circuitry (and/or the
microcontroller 209) can also be programmed to distinguish between
a high current surge situation that occurs, for example, when
starting a vehicle, and a high current surge caused by an actual
short circuit. The resistance measurement circuitry can do this by
monitoring the time at which the current surge (and a current surge
of a particular threshold level) is at an expected level for
starting a vehicle. When a short circuit is detected, the switching
driver circuit 204 is directed to send a signal to the switch gates
to turn off the switches 302 before damage can occur, and prevents
the switches from being turned on until the short-circuit is
removed.
[0083] Voltage Measurement and Low Voltage Detection
[0084] A lithium iron phosphate (LFP) cell or cell bank produces an
output voltage of approximately 3.3 volts. This output voltage
commonly has a narrow range of safe operating voltages,
approximately between three (3) and four (4) volts. Operating
outside of this operating voltage range will cause the cells to
degrade to the point where they will no longer hold a charge and
become unusable. The BMS can, therefore, detect when the voltage is
outside of the optimal range and isolate the battery from being
overcharged or over discharged. The voltage of each bank of cells
can be monitored independently as well as the entire pack voltage
collectively, to be able to pinpoint individual banks that can be
overcharged or over discharged. An ADC can be used to detect
voltage levels.
[0085] As the voltage drops while the battery 705 is being
discharged, the microcontroller 209 can be programmed to recognize
where the voltage is in relation to the operating range.
Additionally, multiple pre-programmed or preset lockouts can be
programmed to desired voltage thresholds. When the microcontroller
209 determines that one of these thresholds has been met, the
microcontroller can direct the isolation circuitry to activate. The
ability to program these presets is advantageous because it allows
for quick and easy custom configurations for diverse applications
such as use of different chemistries, automotive and marine engine
starting, auxiliary power units, emergency power storage, and
others. When a voltage threshold has been met, a signal can be sent
to activate the isolation circuitry until a specified condition is
met.
[0086] The most common presets can include, but not be limited
to:
[0087] Reserve Voltage:
[0088] Reserve voltage is when the voltage level of the battery 705
drops to a dangerously low level but not yet outside of the safe
operating range. This is set to reserve enough battery capacity to
start the vehicle without dropping below the operating voltage
range. The reserve voltage can be reset manually (via the reset
button 228) or wirelessly, for example, by a mobile device.
[0089] Low Voltage Lockout:
[0090] A low voltage lockout can be reached when the voltage level
of the battery 705 has dropped below the operating voltage. The
battery can remain at this low level for long periods without
degradation of the cells and this level is specific to each type of
battery chemistry. The microcontroller 209 can be programmed with a
low voltage lockout to allow reset only when the battery is
recharged to a level within the safe operating range. The reset can
happen manually through the rest button 228, a wireless signal or
the like. The microcontroller 209 can also be programmed to
automatically reset the battery 705 when the battery 705 is safely
within the safe operating range.
[0091] Critical Voltage:
[0092] At and below a critical voltage level, the battery 705 can
still be usable, but cell degradation can start to occur, reducing
the operational life of the battery. This level is specific to each
type of battery chemistry. The longer the battery stays below this
level and the lower the voltage gets, the greater the degradation
that occurs. The microcontroller 209 can track the length of time
the voltage stays in this state. The microcontroller 209 can be
programmed with this critical voltage and only allow reset when the
battery is recharged to operating levels.
[0093] Temperature Monitoring of the BMS
[0094] A temperature sensor 234 (or thermal sensor) located near or
against a buss bar 100a, 400a or 100b, 400b can be used to monitor
temperature levels of the BMS. The temperature sensor relays the
temperature to the microcontroller 209. In one embodiment, when a
specified high temperature is reached, the microcontroller 209 can
direct the switching driver circuit 204 to send a signal to the
transistor-based switch gates to turn off the switches 302 before
damage can occur, and prevents the switches from being turned on
until the temperature has returned to a specified level within the
safe operating range.
[0095] Temperature Monitoring of Banks of Cells
[0096] A thermal sensor (not shown), such as a thermistor, can be
located in or around each cell pack (or bank of the battery 205)
when the cell pack is manufactured. In one embodiment, the thermal
sensor is located centrally in the bank as that is where heat will
concentrate the most. The thermal sensor can then relay the
temperature of the cell pack to the microcontroller 209, allowing
the temperature of the cell pack to be monitored to determine
whether the cell pack is within acceptable operating temperature
ranges. When a specified high temperature is reached, the switching
driver circuit 204 can send a signal to the transistor-based switch
gates to switch off the switches 302 before damage can occur, and
prevent the switches from being turned on until the temperature has
returned to safe operating levels.
[0097] Current Leakage Detection
[0098] The BMS 700 can detect when there is a low amount of current
being drawn from the battery while the engine is not running (for
example, when the lights are left on, etc.). In this situation, the
BMS can alert the user and even be programmed to isolate the
battery so further leakage cannot occur. It can determine whether
or not the engine is on by monitoring the charge current from the
alternator and use this information to detect a slow steady power
draw on the battery when the engine is not running.
[0099] Cell Bank Balancing
[0100] When the output voltage of the cells of a battery bank is
outside of the operating range, cell degradation starts to occur.
It is advantageous that each cell bank be fully charged. However,
cells can charge and discharge at different rates, resulting in
different charge levels in each bank. During the charging process,
some cells reach full charge before others and begin to overcharge.
Overcharging can start to degrade the battery cells. It is
therefore advantageous during charging to detect when the voltage
reaches its optimum, fully-charged level and to protect each cell
bank from being overcharged or left undercharged. Cell balancing is
beneficial because it prevents unbalanced cell banks that lead to
overcharging of the bank and damage to cells, as well as preventing
inability for the battery to be fully charged.
[0101] The BMS 700 can use either passive or active cell balancing.
With passive cell balancing, the bank balancing circuitry 603
includes charge shunt circuitry to ensure the cells in the battery
705 are charged uniformly. When battery cells are discharged, the
cells do not always discharge uniformly. This can cause an
imbalance when recharged. To prevent an imbalance in charging, the
cell balancing circuitry 603 can be used to redirect the current
from a fully charged bank of cells to a bank of resistors that
dissipate the charge to ground until all of the cell banks have
reached full charge. A bank voltage sensor 703 can be used to
monitor the cells of the battery 705 and a voltage divider circuit
1400 (FIG. 14) can be used to create a measurable signal for the
ADC and measure the charge level of each cell bank.
[0102] The BMS 700 can alternatively, or additionally, have active
balancing as a part of the cell balancing circuity 603. Active
balancing redirects the current from a fully charged cell bank to
another bank that isn't fully charged and continues doing this
until all banks are fully charged. This is advantageous because the
battery can be fully charged using less power and in less time.
[0103] Additionally, the BMS 700 has features programmed into its
firmware, e.g., on the circuit board 200 and within the
microcontroller 209 and other components, to provide functionality
that does not exist with current starter batteries as detailed
below.
[0104] Data Logging
[0105] Tracking Health Indicators:
[0106] Replacement of batteries is typically done either when the
battery no longer holds a charge (a dead battery) or on a schedule.
The health of a lead-acid battery is difficult to determine and
therefore when the battery should be replaced cannot be accurately
determined. A dead battery can cause considerable inconvenience and
cost, especially in the trucking industry. Efforts are made,
therefore, to prevent the battery from failing in the field. A
schedule can be created that calls for changing the battery well
before its possible end of life, regardless of how much life can be
left. In most instances, there is considerable life left in the
battery, but because it is indiscernible how much, the trucking
industry (among other industries) prefers to remove doubt and
replace the battery. This has a considerable cost that the industry
has no choice but to accept. A lithium battery that includes or is
managed by a BMS can be diagnosed and its operational life can be
determined with a certain degree of accuracy, thereby optimizing
the use of the battery. Tracked health indicators can be reported
back to the user to signal when it is time to replace a battery,
e.g., through the display 230.
[0107] Transistor-Based Switch Degradation:
[0108] Switching transistor-based switches 302 such as MOSFETs at
high currents cause the switches to breakdown over time, although
tests show these last for at least hundreds of short circuit events
using the methods described in this application. When a switch in a
particular subarray fails, the load decreases in that subarray. If
the switches in that subarray continue to fail, the load will
continue to decrease. If a switch in another subarray fails, the
load balance will fluctuate. The BMS 700 can detect the breakdown
(degradation) of the switches by monitoring these changes in load
balances between the individual conductor paths (with the different
subarrays of the buss bars) using the current sensing capability of
the surge detection circuit 713 to determine current levels in each
conductive path. The microcontroller 209 can receive the current
levels in each conductive path and compare the two current levels.
When a difference between the two current levels are beyond a
pre-defined threshold amount, for example 1, 2 or 5 amps (or some
other threshold), the microcontroller 209 can generate an alert
indicative of a certain level of switch degradation, e.g., an
audible alert or a visual alert through the display 230.
[0109] Battery Cell Degradation:
[0110] As a battery cell reaches its cycle life limit (or when it
is used outside of its operating conditions), the battery cell will
start to lose its ability to hold a charge. The charging holding
capability of each cell bank can be monitored to detect when this
degradation starts to occur or detect a level of cell degradation.
Determining cell degradation in this way can be performed by one or
a combination of methods, as follows:
[0111] (1) In one embodiment, the ADC 709 can be used to measure
the cell voltage and determine the number of charge cycles the
battery has experienced (which is limited) by counting the times
the voltage has fluctuated from high to low and back. Beyond a
certain number of charge cycles, the battery 705 begins to
degrade.
[0112] (2) In another embodiment, the microcontroller 209 can
monitor the cell banks of the battery 705 for a critical voltage
level and for an amount of time spent at the critical voltage
level. The critical low voltage level is a low voltage level that
can be defined for banks of batteries depending on type and size of
battery. The microcontroller 209 can monitor and determine a length
of time a battery bank has been at critical voltage levels to
detect cell degradation. The longer the battery has been kept at
critical levels, the more degradation that occurs. This degradation
occurs even if the battery is not being used. Understanding this
information can help to determine whether the battery has been
maintained properly over its life.
[0113] (3) The microcontroller 209 can also track a number of times
the battery 705 has been charged and discharged, including how
often the battery has been discharged in a normal fashion (for
example in starting the vehicle) and how often the battery 705 has
been deep cycled (e.g., running other things that bring the charge
down further than with just a regular vehicle start). Based on this
(and potentially other) information, the microcontroller 209 can
determine not only if battery capacity is decreasing over time, but
also whether there is a problem with the charging system (e.g., an
alternator) and whether an electrical system is using more or less
power than normal (e.g., lights burned out or short circuits
present).
[0114] The microcontroller 209 can then generate an alert (such as
an audible alert of a visual alert on the display 230, or a data
download to a smart phone or another computer) indicative of
degradation of a bank of cell in the battery 705, responsive to
detecting one of the above three conditions. In this way, the BMS
700 can more accurately detect battery cell degradation and timing
of battery replacement.
[0115] Event Logging:
[0116] As events such as these occur, the events can be recorded
and reported back to the user to help understand how the battery is
being used and how it is performing. Examples of such events
include, but are not limited to: (1) short circuits; (2) high
temperature levels; (3) low voltage levels; and (4) time spent at
critical voltage, for example.
[0117] Communications & Control
[0118] Additional features allow for communication with and
external control of the BMS 700 using either wired (such as a USB
port) or wireless methods (such as Wifi, Bluetooth, GSM and other
technologies that can transmit to a remote location) or a
combination of both. Components for these features can be placed on
the circuit board 200 or on a satellite board connectable to the
circuit board 200 through the satellite board connector 214. The
ability to monitor and control a vehicle battery while it is
installed in the vehicle provides a powerful advantage. This
ability enables the user to accurately diagnose problems as well as
identify potential problems before the problems occur. When the
microcontroller 209 receives signals and reports from the various
methods of monitoring the battery pack as described herein, the
microcontroller 209 can record that information forming a battery
history and saving that history for later retrieval.
[0119] The BMS 700 further provides for downloading or transmission
of logged data (health indicators and events, for example) from the
BMS 700 to a user, who can be at a remote location through wired or
wireless means as disclosed herein. Such data communication allows
the tracking of battery usage history. When the battery 705 is
operational, the data can be used to diagnose the health of the
battery and determining the optimal time for replacement. In the
case of a failed battery, the data can be used to determine the
cause of the failure. And, during testing, the data can be used to
see the performance of the BMS 700 and a coupled battery.
[0120] Updating of Firmware:
[0121] Before the battery system with the BMS 700 is put into
service, its firmware is loaded. Also, from time to time,
improvements to the firmware can be made. Loading and updating
firmware can be done through a data port, such as the USB port 216
or wirelessly via the wireless circuitry 220.
[0122] GPS Locating Circuitry:
[0123] The GPS circuitry 224 allows a vehicle's location and travel
routes to be tracked and monitored. This information, combined with
wireless communication can allow the vehicle's location to be
reported to a remote location away from the vehicle when the
battery system happens to be lost, located in a stolen vehicle, or
has some other need to retrieve its global coordinates.
[0124] User Initiated Control:
[0125] The BMS 700 can also provide for user-initiated isolation of
the battery 705 from the system (e.g., from an electrical system or
other load source) as well as user-initiated re-connection of the
battery 705 to the system. In one embodiment, the user can shut
down the BMS 700 to perform the isolation. For example, the user
can initiate isolation manually with a reset button (e.g., the
reset button 228 acting as a toggle switch or another button) or
remotely with a mobile device or other remote control device. This
also allows the user to shut down the engine remotely in the case,
for example, the vehicle is being used without proper authorization
or has a hazardous condition (e.g., is on fire) and needs to be
shut down. The battery 705 may also be isolated from the system by
proximity of a paired electronic or mobile device, such as a cell
phone using a certain setting. Accordingly, various embodiments
allow for putting the battery 705 in isolation (or taking the
battery out of isolation) depending on the situation and user
preference.
[0126] For example, a user may want to trigger isolation (or return
from isolation) to perform any of the following functions:
[0127] (1) It is common in the trucking industry for vehicles to be
stolen along with any cargo. Accordingly, the user may want to
intentionally prevent the passing of high current (e.g., sufficient
current to start a vehicle) by placing the BMS 700 into an
anti-theft or "locked" mode, when the user is away from the vehicle
or plans to leave the vehicle. The BMS 700 can go into locked mode
in response to a deactivation signal or other indicator.
[0128] In one embodiment, the user can put the BMS 700 into locked
mode through a smart phone application that communicates through
the Internet and with the wireless circuitry 220, for example.
Alternatively, or additionally, the microcontroller 209 can track a
location of the user through the user's smart phone in comparison
with the location of the vehicle (through the GPS circuitry 224),
and be pre-programmed to put the BMS 700 in locked mode after the
user has passed a certain distance from the vehicle. Similarly, the
microcontroller 209 can bring the BMS 700 out of locked mode when
the user returns within that distance of the vehicle.
[0129] In another embodiment, the wireless circuitry 220 includes
near-field communication capability (such as Bluetooth.RTM. by the
Bluetooth.RTM. special interest group) and can sense when the user
leaves the vicinity of the vehicle. The microcontroller 209,
operatively coupled to the wireless circuitry 220, can then detect
the user has left the vehicle and be pre-programmed to place the
BMS 700 into locked mode. To put the BMS 700 back into operation
mode upon return to the vehicle, the wireless circuitry 220 detects
that the user is back in range, and makes the BMS 700 fully
operational with high current capability.
[0130] When in locked mode, the microcontroller 209 can detect and
prevent the passing of high current. By intentionally isolating the
battery from the system, the vehicle cannot be started. In locked
mode, for example, the BMS 700 can allow a low specified number of
amps to be drawn from the battery to allow for continuous
functioning of basic appliances such as a clock, a radio, security
features, and the like. In locked mode, however, the BMS 700 can
detect a sudden high current surge (through a start attempt) and
isolate the battery. The BMS 700 can also alert the user through
one of the communication interfaces when such an event occurs. When
the user returns to the vehicle, the BMS 700 can be reactivated
such as discussed above, which reconnects the battery 705 to the
electrical system of the vehicle. Isolation and re-connection can
additionally be protected by a passcode.
[0131] (2) The user may want to access the reserve power in the
battery 705. To do the user can provide a reset command, for
example, by way of a reset button on the battery 705 or a remote
reset that can be sent via a mobile application or the like,
wirelessly.
[0132] (3) Also, if for some reason the BMS 700 has been isolated
the battery 705 from the load source due to a harmful condition,
and the condition has been repaired or resolved, the BMS 700 can
then be reactivated. For example, the BMS 700 can be reactivated in
response to sensing the proximity of a remote device, such as a
mobile electronic device of the like.
[0133] Remote display of the BMS 700 status and other logged data
may be provided to a remote device, such as on a mobile device or
remotely operating computing device. A remote display has the
advantage of not having to be at the battery to see its status and
read data from the battery. For example, a fleet manager could
obtain all the data from the batteries in the fleet at a single
location, without having to go to each vehicle.
[0134] The status display can be as simple as an LED display 230,
or other more complex display types. This allows the user to
observe the status directly on the battery 705.
[0135] Power Savings
[0136] The BMS 700 may be designed to save power when not in
operation. During an event, such as turning on a vehicle, powering
up a load source, detecting a short circuit or a voltage or current
spike, for example, the BMS 700 can be in full power mode. When
full functionality of the BMS 700 is not needed, the BMS 700 can go
into one of three lower power states as follows.
[0137] Sleep Mode:
[0138] The BMS 700 may spend most of the time in this mode in which
the BMS is operational, but draws little current and has little
energy leakage. The sleep mode may include when the Hall Effect
sensors 210a and 210b are turned off because they are not needed,
as previously explained.
[0139] Hibernation Mode:
[0140] The BMS 700 can go into hibernation mode when the current
consumption from the battery 705 is reduced by a factor on the
order of a hundred times. In other words, current consumption is
much less than would otherwise be consumed. In one embodiment, both
the Hall Effect sensors 210a and 210b and the microcontroller 209
are powered off during hibernation mode. Hibernation mode can be
entered at times other than after detecting a critical voltage
threshold. For example, after detecting a period of non-use of the
battery 705 by the load source, and to preserve energy of battery
705, the BMS 700 can enter hibernation mode.
[0141] Low Power State:
[0142] The BMS 700 can enter a low power state when the
microcontroller 209 powers down one or more of the auxiliary
circuitry on the circuit board 200, and puts itself into an
ultra-low power state. The microcontroller 209 can also be
activated periodically to monitor vital signs or can be activated
when an event occurs that requires the BMS 700 take action in
response to the event.
[0143] The above-disclosed subject matter is to be considered
illustrative, and not restrictive, and the appended claims are
intended to cover all such modifications, enhancements, and other
embodiments, which fall within the true spirit and scope of the
present disclosure. Thus, to the maximum extent allowed by law, the
scope of the present embodiments are to be determined by the
broadest permissible interpretation of the following claims and
their equivalents, and shall not be restricted or limited by the
foregoing detailed description. While various embodiments have been
described, it will be apparent to those of ordinary skill in the
art that many more embodiments and implementations are possible
within the scope of the above detailed description. Accordingly,
the embodiments are not to be restricted except in light of the
attached claims and their equivalents.
* * * * *