U.S. patent application number 15/363512 was filed with the patent office on 2018-04-19 for chargers with voltage amplitude modulation.
The applicant listed for this patent is StoreDot Ltd.. Invention is credited to Daniel Aronov, Yegal Darhovsky, Leonid SPINDLER.
Application Number | 20180109117 15/363512 |
Document ID | / |
Family ID | 61904776 |
Filed Date | 2018-04-19 |
United States Patent
Application |
20180109117 |
Kind Code |
A1 |
SPINDLER; Leonid ; et
al. |
April 19, 2018 |
CHARGERS WITH VOLTAGE AMPLITUDE MODULATION
Abstract
Chargers and methods are provided which increase the charging
efficiency of the chargers by implementing voltage amplitude
modulation (VAM) instead of voltage frequency modulation. The
charging voltage amplitude is modulated using feedback from at
least one energy storage device that is being charged by the
charger, while maintaining a charging voltage frequency constant at
a LLC resonance frequency of the charger. A buck/boost
configuration may be used to reduce maximal voltage levels and
further optimize the charger's design.
Inventors: |
SPINDLER; Leonid; (Kfar
Saba, IL) ; Darhovsky; Yegal; (Beer-Sheva, IL)
; Aronov; Daniel; (Netanya, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
StoreDot Ltd. |
Herzeliya |
|
IL |
|
|
Family ID: |
61904776 |
Appl. No.: |
15/363512 |
Filed: |
November 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62409417 |
Oct 18, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 10/0525 20130101; H01M 10/44 20130101; H02J 7/02 20130101;
Y02B 40/00 20130101; Y02B 70/10 20130101; H02M 1/4233 20130101;
Y02P 80/10 20151101; H02J 7/022 20130101; H02J 2207/20
20200101 |
International
Class: |
H02J 7/00 20060101
H02J007/00; H01M 10/0525 20060101 H01M010/0525 |
Claims
1. A method of increasing a charging efficiency of a charger, the
method comprising modulating a charging voltage amplitude using
feedback from at least one energy storage device that is being
charged by the charger, while maintaining a charging voltage
frequency constant at a LLC resonance frequency of the charger.
2. The method of claim 1, further comprising using a buck/boost PFC
(power factor correction) unit for enabling charging with voltage
amplitude modulation below a maximum input voltage to the
charger.
3. The method of claim 1, further comprising implementing a bypass
of a PFC unit of the charger when an input voltage to the charger
is equal to the modulated voltage.
4. The method of claim 1, wherein the at least one energy storage
device comprises at least one fast charging lithium ion
battery.
5. A charger for an energy storage device, comprising a PFC unit
configured to implement charging voltage amplitude modulation,
while maintaining a charging voltage frequency constant at a LLC
resonance frequency of the charger, according to a feedback to the
PFC unit from at least one energy storage device that is being
charged by the charger.
6. The charger of claim 5, wherein the PFC unit is configured in a
buck/boost configuration to enable the charging with voltage
amplitude modulation below a maximum input voltage to the
charger.
7. The charger of claim 6, configured to charge at least one fast
charging lithium ion battery as the at least one energy storage
device.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 62/409,417 filed on Oct. 18, 2016, which is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Technical Field
[0002] The present invention relates to the field of chargers for
energy storage devices, and more particularly, to charger designs
which increase the charger's efficiency.
2. Discussion of Related Art
[0003] Typical charging processes (of various energy storage cells,
such as batteries, supercapacitor packs) are carried out by
chargers in either a constant current mode or a constant voltage
mode. Chargers operate at maximum power in the constant current
mode, with the cell voltage near its maximum, and a softly switched
LLC (i.e., with a capacitance C.sub.r, a serial inductance L.sub.r
and a parallel inductance L.sub.m) resonant converter is typically
used to handle high power and produce variable voltage gains in
different operating frequencies while providing soft switching for
all involved semiconductor devices. Such charger has one or more
LLC resonance frequencies.
[0004] Typical softly switched LLC resonant converters have a
half-bridge or full-bridge converter connected via a switching
circuit to a resonant LLC tank circuit to which the load is
connected. Switching operations (square waves delivered to the LLC
tank) are synchronized to zero crossing of the voltage or current
(ZVS or ZCS, respectively), to reduce switching losses. The LLC
tank delivers only fundamental sinusoidal waveforms and thus forces
the voltage or current to be sinusoidal. A rectifier is used to
convert the sinusoidal LLC tank output (alternating current--AC) to
direct current (DC) output to the charger cell(s).
SUMMARY OF THE INVENTION
[0005] The following is a simplified summary providing an initial
understanding of the invention. The summary does not necessarily
identify key elements nor limit the scope of the invention, but
merely serves as an introduction to the following description.
[0006] One aspect of the present invention provides a method of
increasing a charging efficiency of a charger, the method
comprising modulating a charging voltage amplitude using feedback
from at least one energy storage device that is being charged by
the charger, while maintaining a charging voltage frequency
constant at a LLC resonance frequency of the charger.
[0007] These, additional, and/or other aspects and/or advantages of
the present invention are set forth in the detailed description
which follows; possibly inferable from the detailed description;
and/or learnable by practice of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a better understanding of embodiments of the invention
and to show how the same may be carried into effect, reference will
now be made, purely by way of example, to the accompanying drawings
in which like numerals designate corresponding elements or sections
throughout.
[0009] In the accompanying drawings:
[0010] FIG. 1 is a high level comparative schematic block diagram
of a charger according to some embodiments of the invention,
compared with a charger according to the prior art.
[0011] FIGS. 2A and 2B exemplify schematically block diagrams of
prior art chargers with examplary values for voltage ranges and
current profiles.
[0012] FIG. 2C illustrates schematically aspects of prior art
chargers.
[0013] FIG. 3 is a high level schematic block diagram of chargers,
according to some embodiments of the invention.
[0014] FIG. 4 is a high level flowchart illustrating a method,
according to some embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] In the following description, various aspects of the present
invention are described. For purposes of explanation, specific
configurations and details are set forth in order to provide a
thorough understanding of the present invention. However, it will
also be apparent to one skilled in the art that the present
invention may be practiced without the specific details presented
herein. Furthermore, well known features may have been omitted or
simplified in order not to obscure the present invention. With
specific reference to the drawings, it is stressed that the
particulars shown are by way of example and for purposes of
illustrative discussion of the present invention only, and are
presented in the cause of providing what is believed to be the most
useful and readily understood description of the principles and
conceptual aspects of the invention. In this regard, no attempt is
made to show structural details of the invention in more detail
than is necessary for a fundamental understanding of the invention,
the description taken with the drawings making apparent to those
skilled in the art how the several forms of the invention may be
embodied in practice.
[0016] Before at least one embodiment of the invention is explained
in detail, it is to be understood that the invention is not limited
in its application to the details of construction and the
arrangement of the components set forth in the following
description or illustrated in the drawings. The invention is
applicable to other embodiments that may be practiced or carried
out in various ways as well as to combinations of the disclosed
embodiments. Also, it is to be understood that the phraseology and
terminology employed herein is for the purpose of description and
should not be regarded as limiting.
[0017] Unless specifically stated otherwise, as apparent from the
following discussions, it is appreciated that throughout the
specification discussions utilizing terms such as "processing",
"computing", "calculating", "determining", "enhancing" or the like,
refer to the action and/or processes of a computer or computing
system, or similar electronic computing device, that manipulates
and/or transforms data represented as physical, such as electronic,
quantities within the computing system's registers and/or memories
into other data similarly represented as physical quantities within
the computing system's memories, registers or other such
information storage, transmission or display devices. Any of the
disclosed modules or units may be at least partially implemented by
a computer processor.
[0018] Chargers and methods are provided which increase the
charging efficiency of the chargers by implementing voltage
amplitude modulation (VAM) instead of voltage frequency modulation.
The charging voltage amplitude is modulated using feedback from at
least one energy storage device that is being charged by the
charger, while maintaining a charging voltage frequency constant at
a LLC resonance frequency of the charger. A buck/boost
configuration may be used to reduce maximal voltage levels and
further optimize the charger's design.
[0019] FIG. 1 is a high level comparative schematic block diagram
of a charger 100 according to some embodiments of the invention,
compared with a charger 90 according to the prior art. Charger 100
comprises a PFC (power factor correction) unit 110 configured to
implement charging voltage amplitude modulation according to a
feedback to PFC unit 110 from at least one energy storage device
(cell load, e.g., a battery, a capacitor, e.g., lithium ion
batteries) 80 that is being charged by charger 100. Disclosed
chargers 100 enable operation at the resonance frequency f.sub.s of
converter 96, which provides the maximal efficiency during the
whole charging process. PFC unit 110 may be configured in a
buck/boost configuration to enable the charging voltage amplitude
modulation below a maximum input voltage to the charger.
Advantageously, with respect to prior art chargers 90 which
implement frequency modulation, charger(s) 100 operating at the
resonance frequency of the LLC achieve higher efficiency, as
exemplified below.
[0020] In the prior art, chargers 90 for energy storage device
typically receive network AC power (e.g., from a power source 82),
rectify the AC to DC via a rectifier 92 (e.g., a bridge). The DC is
then boosted to a voltage level which is above the maximal network
voltage (see example below) by PFC unit 93 in boost configuration
93A and is converted to frequency modulated AC by a converter 96
according to feedback from energy storage device 80 that is being
charged by the frequency modulated AC via a rectifier 97. Due to
the frequency modulation, prior art chargers 90 inherently cannot
be operated at the resonance frequency, which is optimized for
maximal efficiency.
[0021] In contrast, disclosed chargers 100 are configured to
modulate the amplitude of the DC from PFC unit 110 to yield
amplitude modulated AC from converter 96 at its resonance
frequency, to yield maximal efficiency during the charging.
Moreover, PFC unit 110 may be configured in buck/boost
configuration 112 which may provide DC levels which may be
occasionally lower ("buck") than the maximal level of AC power
source 82.
[0022] It is emphasized that disclosed chargers 100 may be
implemented in various ways and the feedback for amplitude
modulation may be implemented in respective configurations, as
appreciated by a person skilled in the art.
[0023] FIGS. 2A and 2B exemplify schematically block diagrams of
prior art chargers 90A, 90B with examplary values for voltage
ranges and current profiles. The indicated voltage levels (VAC for
AC voltage and VDC for DC voltage) are provided to illustrate a
possible range of voltages under various circumstances (depending
on the AC power source and charger configuration). The main AC
voltage is typically filtered by a RFI/EMI
(radiofrequency/electromagnetic interference) filter 91, rectified
by a bridge 92 (e.g., a half bridge or a full bridge) and boosted
by PFC 93 to a voltage level beyond the maximal voltage level of
the AC power source (e.g., 380V in FIG. 2A, 400V-600V in FIG. 2B),
over one or more illustrated capacitors 94A, 94B, respectively. The
boosted voltage level is converted back to AC by LLC converter 96
and delivered via a rectifier 97 to a voltage/current controller 98
which charges energy storage device(s) 80 such as batteries. In
order to implement ZVS, ZCS (as explained above) or ZPS (zero power
switching, as explained below), prior art chargers 90B provide
feedback 95 from charged energy storage device(s) 80 (e.g., cells,
batteries, etc.) which is used to modulate the switching frequency
during the charging process.
[0024] FIG. 2C illustrates schematically aspects of prior art
chargers 90 which are overcome by embodiments of the disclosed
invention. In particular the switching with respect to LLC tank in
converter 96 of charger 90C (having a full-bridge LLC converter
with full-bridge rectifier) is discussed below. It is noted that
similar principles are applicable in various charger
topologies.
[0025] In zero power switching (ZPS), the MOSFETs
(metal-oxide-semiconductor field-effect transistors) of the
switching network are driven by PWM (pulse-width modulation)
signals to generate a square wave for resonant tank circuit 96.
However, tank circuit 96 supports only fundamental sinusoidal
waveforms which are then rectified by output rectifier 97 to
provide the desired DC output voltage. A transformer 96A may be
coupled to LLC tank 96 as the parallel inductance, permitting
operation in a galvanically-isolated environment. Converters 96
converters are characterized by two operating frequencies, with
respect to which power transfer and output voltage are managed (via
feedback 95), namely f.sub.s-the switching frequency, as imposed by
the control electronics (the frequency at which the MOSFETs are
operated), which dynamically variable; and f.sub.r-the natural
resonant frequency of the LLC tank in converter 96, which is fixed
by choice of the LLC components. As a result, prior art charger
configurations necessarily operate at least some of the time with
f.sub.s.noteq.f.sub.r, i.e., at sub-optimal conditions, resulting
in switching losses expressed in Equations 1, with P.sub.conduction
denoting the conduction losses and P.sub.switching denoting the
switching losses.
P.sub.loss,MOSFET=P.sub.conduction+P.sub.switching;P.sub.conduction=I.su-
p.2.sub.MOSFET,rms*R.sub.DS,on, Equations 1
[0026] The reason for prior art losses is that the LLC topology
only provides optimum efficiency performance when P.sub.switching
is almost eliminated, around the resonant frequency (f.sub.r)
between its resonant inductor (L.sub.r) and capacitor (C.sub.r).
However, in order to be adapted to the wide voltage gain variation
range, the switching frequency (f.sub.s) must swing in a wide range
and deviate from f.sub.r, especially in case of energy storage
chargers, since the load (energy storage device(s) 80) varies as
function of charging state, temperature, time, charging/discharging
rate, etc. of energy storage device(s) 80, as indicated in graphs
99A and 99B in FIG. 2C, the former showing the increasing internal
resistance with time and temperature for a typical energy storage
device and the latter showing the DC voltage gain of LLC converter
96 adapted to a wide output voltage range. As shown, the desired
output voltage window [V.sub.min, V.sub.max] on the gain axis is
mapped to an ultra-wide switching frequency range in the frequency
axis (denoted ZCS region). Therefore, it is extremely difficult to
optimally design LLC converter 96 in prior art chargers 90.
[0027] FIG. 3 is a high level schematic block diagram of charger
100, according to some embodiments of the invention. In chargers
100, an amplitude modulation feedback 105 is implemented to
modulate the DC voltage amplitude instead of modulating the AC
frequency as in prior art chargers 90. In contrast to prior art
configurations illustrated in FIGS. 2A and 2B, feedback 105 enables
operating converter 96 at its resonance frequency f.sub.r and
achieve thereby higher efficiency of charger 105. Charger 100 is
illustrated by a non-limiting example of voltage amplitude
modulation (VAM) LLC resonant converter 96 for two batteries in
serial connection as energy storage device 80. The illustrated
topology is derived from the LLC topology with input voltage
modulation stage via buck or/and boost topology PFC converter.
[0028] Chargers 100 may comprise PFC unit 110, receiving DC from
bridge 92 which rectifies AC from main 82 after EMI/RFI filter 91.
PFC unit 110 may use feedback 105 from load 80 (any energy storage
device, e.g., fast charging lithium ion batteries) to modify the
amplitude of DC provided to converter 96 while charger 100 operates
continuously with the resonance frequency (f.sub.r) of converter
96. Load 80 is charged with DC supplied via controller 98 after
being rectified by rectifier 97. In certain embodiments, converter
96 implemented with transformer 96A, and the output voltage range
from transformer 96A is limited by the amplitude control range and
may be regulated to meet the final required output voltage. In
certain embodiments, PFC unit 110 may be in a buck/boost
configuration (and not only in boost configuration as in prior art
chargers 90) to provide lower DC amplitude in at least some
sub-range of its operation.
[0029] Charger 100 may be configured to implement controlled LLC
topology with minimum losses by simultaneously maintaining a
constant frequency and apply ZPS on the semiconductor elements
(with the LLC topology operating at its resonant frequency). The
voltage is controlled via its amplitude (in chargers 100) instead
of via its frequency (in prior art chargers 90). An additional
advantage of disclosed designs is that the LLC is much simpler, as
only one frequency is implemented and calibrated. The inventors
have found out that advantageously, chargers 100 provide optimum
efficiency of the LLC power circuit, ZPS turning-on and turning-off
the MOSFETs, reduced circulating current and conduction losses,
reduced EMI/RFI (due to the use of a constant frequency), reduced
size of magnetic components, simpler LLC converter 96 may be used
(e.g., transformer 96A is simpler due to lack of skin effect and
lower losses of the ferrite), the bypass voltage during the
charging may result in almost 100% efficiency, as well as provision
of the other advantages of ZPS use.
[0030] In chargers 100, the switching frequency of LLC converter 96
may be fixed and equal to the resonant frequency between the
transformer's primary leakage inductance and the resonant
capacitance, as expressed in Equation 2.
f.sub.s=f.sub.r=(1/2.pi.)/(L.sub.rC.sub.r).sup.1/2 Equation 2
In such case, the resonant tank has unity gain and best optimized
operation and efficiency, therefore, the turns ratio of transformer
96A may be designed so that converter 96 operates at this point at
nominal input and output voltages defined by PFC converter output
and transformer respectively. Moreover, using such schemes, only
one high voltage capacitor 104 may be required for 450V output
compared to two high voltage capacitors 94B for 600V that must be
used in standard schemes of prior art chargers 90B with feedback 95
(see FIG. 2B).
[0031] It is emphasized that energy storage device 80 may be of any
kind, and charger 100 may serve for any number of batteries in
serial or/and parallel connection, with the charger's voltage being
defined by the buck or/and boost topology PFC output and the
transformer. Moreover, buck and boost topology PFC converter 100
may be configured to use any AC input voltage, like European (220V
AC), USA (110V AC), etc., as exemplified in FIG. 3. For example,
when input to PFC 110 is in the range of 310V-325V (using e.g.,
Europe main) there is a bypass voltage effect (no need for buck or
boost), since the input voltage falls in the output range. In this
case, the efficiency is almost 100%.
[0032] Table 1 provides and examplary simulation-based illustration
of advantages of charger(s) 100 over prior art chargers 90 for
charging two serially connected batteries as energy storage device
80, using a charging current of 30 A. In this example the batteries
can be charged up to V.sub.out=8.8V and discharged down to
V.sub.out=6V. The data compares two different topologies based on
standard design frequency modulation LLC (prior art charger 90,
where V.sub.in,LLC=450V is constant, and f.sub.s is modified) and
VAM (voltage amplitude modulation) LLC as implemented in
embodiments of charger 100, where V.sub.in,LLC is modified and the
frequency is fixed at f.sub.s=f.sub.r=70 kHz).
[0033] Table 1 illustrates that, as in LLC-based chargers the
minimized losses (P.sub.switching) are proportional to
I.sub.MOSFET,rms, the current of 0.36 Ampere used by charger 100 is
highly advantageous with respect to the current of 2.06 Ampere used
by prior art charger 90. This is due to the keeping of the
frequency at the resonance frequency, as indicated in the shaded
table entries comparing prior art chargers 90 and disclosed
chargers 100.
[0034] FIG. 4 is a high level flowchart illustrating a method 200,
according to some embodiments of the invention. The method stages
may be carried out with respect to charger 100 described above,
which may optionally be configured to implement method 200. Method
200 may comprise stages for producing, preparing and/or using
charger 100, such as any of the following stages, irrespective of
their order.
[0035] Method 200 may comprise increasing a charging efficiency of
a charger 202 by performing input voltage amplitude modulation
(VAM) (stage 204). Method 200 may comprise modulating a charging
voltage amplitude using feedback from at least one energy storage
device (such as fast charging lithium ion battery(ies)) that is
being charged by the charger (stage 210), while maintaining a
charging voltage frequency constant at a LLC resonance frequency of
the charger (stage 212).
[0036] Method 200 may further comprise configuring the PFC unit in
buck/boost configuration to receive the feedback (stage 220) and
using a buck/boost PFC unit to enable charging with voltage
amplitude modulation below a maximum input voltage to the charger
(stage 222). Method 200 may further comprise implementing a bypass
when input voltage is equal to the modulated voltage (stage
224).
[0037] In the above description, an embodiment is an example or
implementation of the invention. The various appearances of "one
embodiment", "an embodiment", "certain embodiments" or "some
embodiments" do not necessarily all refer to the same embodiments.
Although various features of the invention may be described in the
context of a single embodiment, the features may also be provided
separately or in any suitable combination. Conversely, although the
invention may be described herein in the context of separate
embodiments for clarity, the invention may also be implemented in a
single embodiment. Certain embodiments of the invention may include
features from different embodiments disclosed above, and certain
embodiments may incorporate elements from other embodiments
disclosed above. The disclosure of elements of the invention in the
context of a specific embodiment is not to be taken as limiting
their use in the specific embodiment alone. Furthermore, it is to
be understood that the invention can be carried out or practiced in
various ways and that the invention can be implemented in certain
embodiments other than the ones outlined in the description
above.
[0038] The invention is not limited to those diagrams or to the
corresponding descriptions. For example, flow need not move through
each illustrated box or state, or in exactly the same order as
illustrated and described. Meanings of technical and scientific
terms used herein are to be commonly understood as by one of
ordinary skill in the art to which the invention belongs, unless
otherwise defined. While the invention has been described with
respect to a limited number of embodiments, these should not be
construed as limitations on the scope of the invention, but rather
as exemplifications of some of the preferred embodiments. Other
possible variations, modifications, and applications are also
within the scope of the invention. Accordingly, the scope of the
invention should not be limited by what has thus far been
described, but by the appended claims and their legal
equivalents.
* * * * *