U.S. patent application number 12/760867 was filed with the patent office on 2010-10-21 for apparatus and methods thereof for power consumption measurement at circuit breaker points.
This patent application is currently assigned to PANORAMIC POWER LTD.. Invention is credited to David Almagor, Adi Shamir, Dan Wijsboom.
Application Number | 20100264906 12/760867 |
Document ID | / |
Family ID | 42342603 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100264906 |
Kind Code |
A1 |
Shamir; Adi ; et
al. |
October 21, 2010 |
Apparatus and Methods Thereof for Power Consumption Measurement at
Circuit Breaker Points
Abstract
Apparatus and methods are provided for the measurement of power
consumption at points of interest, such as circuit breakers,
machines, and the like. Accordingly, means are provided for
measurement of power consumption for each electrical sub-network
that is controlled by a circuit breaker. Each apparatus is enabled
to communicate its respective data, in an environment of a
plurality of such apparatuses, to a management unit which is
enabled to provide finer granularity power consumption profiles.
Challenges of measuring relatively low supply currents, wireless
operation in an environment of a large number of apparatuses, and
self-powering are addressed.
Inventors: |
Shamir; Adi; (Kidron,
IL) ; Wijsboom; Dan; (Ganei Tikva, IL) ;
Almagor; David; (Caesarea, IL) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN LLP
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Assignee: |
PANORAMIC POWER LTD.
Kidron
IL
|
Family ID: |
42342603 |
Appl. No.: |
12/760867 |
Filed: |
April 15, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61169750 |
Apr 16, 2009 |
|
|
|
61272216 |
Sep 2, 2009 |
|
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Current U.S.
Class: |
324/127 ;
702/62 |
Current CPC
Class: |
G01R 21/06 20130101;
H01F 38/38 20130101; Y02B 90/20 20130101; Y04S 20/30 20130101; G01R
15/183 20130101; G01R 15/186 20130101; H01F 38/32 20130101; H02M
3/1582 20130101; G01R 22/063 20130101 |
Class at
Publication: |
324/127 ;
702/62 |
International
Class: |
G01R 15/18 20060101
G01R015/18; G01R 21/06 20060101 G01R021/06; G06F 19/00 20060101
G06F019/00 |
Claims
1. An apparatus comprising: at least one analog section having a
current transformer having a transformer core configured to mount
around an alternating current (AC) power line making it a primary
winding of the current transformer, the analog section harvesting
energy from a secondary winding wound around the transformer core,
and storing harvested energy for use by components of the
apparatus, the analog section providing an analog signal responsive
to AC in the power line and a pulse having a frequency responsive
to the alternating current in the AC power line; a microcontroller
coupled to the at least one analog section to receive energy for
the operation of at least the microcontroller, and to receive the
analog signal and the pulses; a memory coupled to the
microcontroller; and a transmitter coupled to the microcontroller
to transmit, under the control of the microcontroller, information
responsive to at least one of the analog signal and the pulses as
an indication of the power consumption of a load connected to the
power line.
2. The apparatus of claim 1, further comprising: a resonance
capacitor coupled in parallel to the secondary winding of the
current transformer.
3. The apparatus of claim 1, further comprising one of: a diode
bridge coupled in parallel to the secondary winding of the current
transformer; or a voltage multiplier coupled in parallel to the
secondary winding of the current transformer.
4. The apparatus of claim 1, wherein the transformer core comprises
a first section having the secondary winding wound thereon, the
first section and the second section fitting together such that the
power line is surrounded by the transformer core by the first
section and second section to achieve an essentially uninterrupted
magnetic path around the power line.
5. The apparatus of claim 1, wherein the number of turns in the
secondary winding is greater than 500.
6. The apparatus of claim 1, further comprising, in the analog
section, a sense capacitor and circuitry for periodically
discharging the sense capacitor for prevention of saturation of the
core.
7. The apparatus of claim 1, wherein the microcontroller operates
in a continuous mode when sufficient energy is available from the
analog section, and in the continuous mode, performs continuous
measurements of the analog signal, stores information responsive to
the continuous measurements and cause the transmission of the
information using the transmitter.
8. The apparatus of claim 7, wherein the continuous measurements
include at least one of: peak detection, phase detection, power
disruption.
9. The apparatus of claim 1, further comprising a receiver coupled
to the microcontroller.
10. The apparatus of claim 9, wherein the receiver is enabled to
perform at least one of: sense for a carrier signal, receive an
acknowledge signal, receive a synchronization information.
11. The apparatus of claim 1, wherein the memory contains
calibration information of the apparatus.
12. A system for power management comprising: at least one
self-powered power sensor (SPPS) coupled around an alternating
current (AC) power line; a communication bridge adapted to
communicate with the at least a SPPS and further coupled to a
network; a management server coupled to the network and adapted to
receive information from the communication link respective of the
at least one SPPS; and a database coupled to the network for
storing at least the information; the SPPS having at least one
analog section comprising a current transformer comprising a
transformer core configured to mount around an alternating current
(AC) power line making it a primary winding of the current
transformer, the analog section harvesting energy from a secondary
winding wound the transformer core, and storing it for use by
components of the apparatus and periodically providing a pulse
having a frequency responsive to the alternating current in the AC
power line; a microcontroller coupled to the at least one analog
section to receive harvested energy, to receive at least an analog
signal responsive to the alternating current in the AC power line,
and the pulse; a memory coupled to the microcontroller; and, a
transmitter enabled to periodically transmit, under the control of
the microcontroller, information respective of the power
consumption of the power line.
13. The system of claim 12, further comprising: a client node
coupled to the network and enabled to display at least information
respective of the power consumed through the AC power line
associated with the at least one SPPS.
14. A method for sensing power consumption comprising: receiving a
pulse from a current to pulse converter of an analog section of a
self-powered power sensor (SPPS); counting the number of pulses
received; activating a transmitter of the SPPS for transmission;
transmitting information respective of the number of pulses counted
upon determination that the SPPS has accumulated sufficient power
for transmission; and deactivating the transmitter of the SPPS; the
SPPS having at least one analog section comprising a current
transformer comprising a transformer core configured to mount
around an alternating current (AC) power line making it a primary
winding of the current transformer, the analog section harvesting
energy from a secondary winding wound around the transformer core,
and storing it for use by components of the apparatus and
periodically providing a pulse having a frequency responsive to the
alternating current in the AC power line; a microcontroller coupled
to the at least one analog section to receive harvested energy, to
receive at least an analog signal responsive to the alternating
current in the AC power line, and the pulse; a memory coupled to
the microcontroller; and, a transmitter enabled to periodically
transmit, under the control of the microcontroller, information
respective of the power consumption of the power line.
15. The method of claim 14, further comprising: activating a
receiver of the SPPS to sense another transmission carrier signal;
enabling the transmission of the information if a receiver of the
SPPS does not detect another transmission carrier signal; and
deactivating the receiver.
16. The method of claim 15, further comprising: receiving a signal
from a source.
17. The method of claim 16, wherein the signal comprises at least
one of: an acknowledge signal, synchronization information.
18. A method for sensing power consumption comprising: receiving a
first signal responsive of a primary current sensed by sensing
resistor of an analog section of a self-powered power sensor
(SPPS); activating a transmitter of the SPPS for transmission;
transmitting information respective of the first signal upon
determination that the SPPS has accumulated sufficient power for
transmission; and deactivating the transmitter of the SPPS; the
SPPS having at least one analog section comprising a current
transformer comprising a transformer core configured to mount
around an alternating current (AC) power line making it a primary
winding of the current transformer, the analog section harvesting
energy from a secondary winding wound around the transformer core,
and storing it for use by components of the apparatus and
periodically providing a pulse having a frequency responsive to a
current in the AC power line; a microcontroller coupled to the at
least one analog section to receive harvested energy, to receive at
least an analog signal responsive to the current in the AC power
line, and the pulse; a memory coupled to the microcontroller; and,
a transmitter enabled to periodically transmit, under the control
of the microcontroller, information respective of the power
consumption of the power line.
19. The method of claim 18, further comprising: activating a
receiver associated with the SPPS to sense another transmission
carrier signal; enabling the transmission of the information if a
receiver of the SPPS does not detect another transmission carrier
signal; and deactivating the receiver.
20. The method of claim 19, further comprising: receiving a second
signal from a source.
21. The method of claim 20, wherein the second signal comprises at
least one of: an acknowledge signal, synchronization
information.
22. An apparatus comprising: at least one analog section comprising
a current transformer comprising a transformer core configured to
mount around an alternating current (AC) power line making it a
primary winding of the current transformer, the analog section for
harvesting energy from a secondary winding wound the transformer
core, and storing it for use by components of the apparatus and
periodically switching to allow sampling of a current flowing
through the current transformer by a sense resistor; a
microcontroller coupled to the at least one analog section to
receive harvested energy, at least an analog signal responsive to
the alternating current in the AC power line by the sense resistor;
a memory coupled to the microcontroller; and a transmitter enabled
to periodically transmit, under the control of the microcontroller,
information responsive to the power consumption of a load connected
to the power line.
23. The apparatus of claim 22, wherein the switching comprises use
of a first switch operative in the positive phase of the AC cycle
and a second switch operative in the negative phase of the AC
cycle.
24. The apparatus of claim 22, wherein the sense resistor is
coupled to a secondary winding of the current transformer, and has
a resistance which is smaller than the resistance of the secondary
winding.
25. An apparatus comprising: at least one analog section comprising
a current transformer comprising a transformer core configured to
mount around an alternating current (AC) power line making it a
primary winding of the current transformer, the analog section
harvesting energy from a secondary winding wound around the
transformer core, and storing it for use by components of the
apparatus using a first secondary winding of the current
transformer and a sense resistor coupled to a second secondary
winding for sensing the current of the transformer; a
microcontroller coupled to the at least one analog section to
receive harvested energy and at least an analog signal responsive
to the alternating current in the AC power line by the sense
resistor; a memory coupled to the microcontroller; and a
transmitter enabled to periodically transmit, under the control of
the microcontroller, information respective of the power
consumption of a load connected to the power line.
26. The apparatus of claim 25, wherein the sense resistor has a
resistance which is smaller than the resistance of the second
secondary winding of the current transformer.
27. The apparatus of claim 25, further comprising: a resonance
capacitor coupled in parallel to the secondary winding of the
current transformer.
28. The apparatus of claim 25, further comprising one of: a diode
bridge coupled in parallel to the secondary winding of the current
transformer; or a voltage multiplier coupled in parallel to the
secondary winding of the current transformer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/169,750 filed Apr. 16, 2009 and U.S.
Provisional Patent Application No. 61/272,216 filed Sep. 2,
2009.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention generally relates to the measurement of power
consumption and more specifically to non-intrusive and self-powered
measurement of electrical current flow through a power line to
enable analysis of power consumption on a per circuit breaker
basis.
[0004] 2. Prior Art
[0005] In a typical electricity distribution system, power is
provided through a main circuit breaker and a device for
measurement of the power consumption of the entire electrical
network connected thereto. However, typically, the main power line
is then connected to a plurality of circuit breakers, each feeding
a smaller section of the electrical network with its specific power
requirements. The circuit breaker is adjusted to the amount of
maximum current that may be used by this electrical sub-network. In
industrial and commercial applications, hundreds of such circuit
breakers may be installed, each controlling a section of the
electrical network. Even in smaller locations, such as a house, it
is not unusual to find tens of circuit breakers controlling various
electrical sub-networks.
[0006] Non-intrusive measurement of current through a power line
conductor has well known principles. A current transformer (CT) of
sorts is created that comprises the primary winding as the power
line conductor and the secondary providing an output current
inversely proportionate to the number of windings. Typically such
systems are used for measuring currents in very high voltage or
current environments, for example, as shown in Gunn et al. in U.S.
Pat. No. 7,557,563. These types of apertures are useful for main
power supplies. Using such devices, or power meters for that
matter, is deficient for the purposes of measuring relatively low
currents in an environment of a plurality of circuit breakers.
Providing wireless telemetry on a singular basis, such as suggested
by Gunn et al., and other prior art solutions, suffers from
deficiencies when operating in a noisy environment.
[0007] There is a need in the art that is now developing, resulting
from the move toward energy conservation to enable analysis of
power consumption on a finer granularity. This would require
analysis on at least a per circuit breaker basis and such solutions
are not available today. It would be further advantageous if a
solution may be provided for installation in a circuit breaker
closet for existing circuit breakers. It would be therefore
beneficial to overcome the limitations of the prior art by
resolving these deficiencies.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a circuit breaker equipped with a compatible
self-powered power sensor deployed in accordance with the
invention.
[0009] FIG. 2 is a block diagram of a first embodiment of a
self-powered sensor in accordance with the invention.
[0010] FIG. 3 is a circuit diagram of a first embodiment of the
analog portion of the self-powered sensor in accordance with the
invention.
[0011] FIG. 4 is a circuit diagram of a second embodiment of the
analog portion of the self-powered sensor in accordance with the
invention.
[0012] FIG. 5 is a circuit diagram of a third embodiment of the
analog portion of the self-powered sensor in accordance with the
invention.
[0013] FIG. 6 is a schematic diagram of a core with the secondary
winding.
[0014] FIG. 7 is a schematic diagram of the two parts comprising
the core.
[0015] FIG. 8 is a schematic diagram of a housing of a self-powered
power sensor implemented in accordance with the invention.
[0016] FIG. 9 is a flowchart of the operation of a self-powered
power sensor deployed in accordance with the invention.
[0017] FIG. 10 is a schematic diagram of a system configured in
accordance with the invention.
[0018] FIG. 11 is a block diagram of a second embodiment of a
self-powered sensor in accordance with the invention.
[0019] FIG. 12 is a circuit diagram of a fourth embodiment of the
analog portion of the self-powered sensor in accordance with the
invention.
[0020] FIG. 13 is a circuit diagram of a fifth embodiment of the
analog portion of the self-powered sensor in accordance with the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Apparatus and methods are provided for the measurement of
power consumption at points of interest, such as circuit breakers,
machines and the like. Accordingly, means are provided for
measurement of power consumption for each electrical sub-network
that is controlled by a circuit breaker. Each apparatus is enabled
to communicate its respective data, in an environment of a
plurality of such apparatuses, to a management unit which is
enabled to provide finer granularity power consumption profiles.
Challenges of measuring relatively low supply currents, wireless
operation in an environment of a large number of apparatuses, and
self-powering are addressed.
[0022] Reference is now made to FIG. 1 where an exemplary and
non-limiting system 100 is equipped with a compatible self-powered
power sensor (SPPS) 110 deployed in accordance with the invention.
The SPPS 110 is designed to fit either above or below the circuit
breaker 120 which is of standard size such that it fits into
current circuit breaker closets without modification. The SPPS 110
housing is designed, as discussed in further detail below, to wrap
around the power line 130 leading to or going out of the circuit
breaker 120. The SPPS 110 is designed to enable easy installation
at an existing location or otherwise during construction when the
entire electrical network is put in place.
[0023] The SPPS contains an electrical circuit the exemplary and
non-liming circuit 200 which is shown in block diagram form in FIG.
2. The circuit 200 comprises an analog section 210 that is coupled
to a microcontroller 220. The analog section comprises a current
transformer 212 to transform current from the power line, for
example power line 130, to a lower current. The power sensed there
from is used for two purposes, the first is to provide the power
needed for the operation of the SPPS 110 and the second is to sense
the actual power consumption of the load connected to the power
line 130. The current to pulse converter (C2PC) 214 is used to
generate periodically a pulse that is provided to the
microcontroller unit (MCU) 220 and enables the measurement of the
power consumption. The more frequent the pulses the higher the
power consumption. The energy harvester 216 stores energy to be
used as the power supply for the circuitry of SPPS 110. It is
further enabled to receive a discharge signal from the
microcontroller 220 to enable intentional discharge of the energy
harvester 216 and prevent overcharge. In one embodiment of the
invention a Zener diode (not shown) is used to clamp the voltage to
the desired level thereby preventing overcharge.
[0024] The circuit 200 further comprises a MCU 220 that is
comprised of several components. An analog-to-digital (A/D)
converter 225 that is coupled to a signal processor 224 which is
further coupled to the media access control (MAC) 222 that supports
the communication protocol of the SPPS. The MAC 222 provides the
data-link layer of the 7 layer standard model of a communication
system. This involves the creation in hardware, software, firmware
or combination thereof, of data frames, timing their transmission,
received signal strength indication (RSSI), acknowledgements, clock
synchronization etc. A counter 227 is excited by an interrupt
signal received from the analog section 210 and enables the
counting of the number of pulses that, as noted above, is
proportionate to the power consumed for a given unit of time.
Another A/D converter 226 is used to measure the output of the
energy harvester 216, and in one embodiment, under control of MCU
220, to cause a discharge thereof as may be needed and as further
explained below. In another embodiment, further explained herein
below, it can be used to detect that the load connected to the
measured power line was turned off. A memory 230 is coupled to the
MCU 220 that can be used as scratch pad memory 230 as well as
memory for storage of the plurality of instructions that when
executed by the MCU 220 executes the methods discussed herein.
Memory 230 may comprise random access memory (RAM), read only
memory (ROM), non-volatile memory (NVM), other memory types and
combinations thereof.
[0025] A radio frequency (RF) transceiver 240 is coupled to the MCU
220 and to an antenna 250 to provide one or two-way communication
with a management unit, discussed in more detail below. In one
embodiment of the invention the RF transceiver 240 supports
transmission only, i.e., uplink communication. However, the RF
transceiver 240 may comprise a receiver portion to support features
such as, and without limitation, sensing for a carrier signal,
clock synchronization, acknowledgement, firmware download, and
configuration download. Typically, this should be an unlicensed
industrial scientific medical (ISM) band transceiver, operative,
for example and without limitation, at 2.4 Ghz. In one embodiment
some form of spread-spectrum modulation technique may be used, for
example and without limitation, direct sequence spread spectrum
(DSSS), to enable better coexistence with other systems working in
the same environment. The communication rate, discussed in more
detail below, should be high enough to enable coexistence of a
couple of hundred SPPSs in the same electrical closet. The power
consumption of the RF transceiver 240 should be low enough to
adhere with the energy harvesting limitations. Yet another
requirement of the RF transceiver 240 is to support a communication
range sufficient to operate in an electrical closet, e.g., 3-4
meters metallic reach environment. In another embodiment of the
invention the range may reach up to a few tens of meters in an
indoor environment. This enables the placing of SPPSs on individual
devices, e.g., on machines in a production line of a factory, and a
minimum number of bridge units in the area. The RF transceiver 240
preferably uses a standard PHY layer supporting, for example and
without limitations, IEEE 802.15.4, and/or communication protocol,
for example and without limitation, Zigbee. Use of such standards
enables easy integration with existing systems that already include
wireless hardware, for example and without limitations, smart
meters.
[0026] According to the principles of the invention, each time a
pulse arrives from the C2PC 214 an interrupt signal is sent to the
MCU 220. Responsive to receiving the interrupt pulse the MCU 220
wakes up and increases the counter 227 value. The energy stored in
each pulse is larger than the energy required for wakeup and
counting, hence enough energy is still available for charging the
energy harvester 216 and/or enable transmission using the RF
transceiver 250. The value of the counter 227 is proportional to
the total charge which went through the primary line 130, i.e.,
current integrated over time. The value in the counter 227, as well
as other parameters, are saved in the system's memory 230. The MCU
220 is enabled to periodically check for a condition to transmit.
Such a condition may be one or more of the following conditions:
sufficient amount of energy exists, upon a certain time lapse from
a previous transmission, upon collection of certain data such as
significant or otherwise interesting data, and other relevant
conditions. According to the principles of the inventions detection
of the existence of sufficient amount of energy for transmission,
for example, through the A/D converter 226 connected to the energy
harvester 216, it is possible to detect if its voltage reached a
predetermined value.
[0027] Upon determination that a transmission is to take place the
MCU 220 prepares a message to be transmitted. The message is
typically a single packet of data that may contain various types of
information and include the SPPS's unique identification (UID)
which enables a management unit to positively associate the current
data received with previous data handled by the management unit
with respect of the SPPS. The value of counter 227 value,
potentially multiplied by a calibration factor converting that
value into a normalized charge unit relative to other sensors, for
example, Ampere-Hour (AH), may be attached as part of the packet.
The calibration factor may be programmed to the SPPS 110 in the NVM
of memory 230 during calibration of the circuit 200, as part of
final inspection during manufacturing. This ensures compensation
against inaccuracies typical to the manufacturing process. The
calibration factor may be a fixed value for all units or a specific
calibration factor unique to each unit. The later is useful for
overcoming production tolerances of the SPPS. Other information may
include, without limitations, various SPPS status information,
hardware version, software version, alerts such as overload, phase
information, average current, temperature, time duration
information, power off indication, e.g., upon identification that
the load was turned off, and other system parameters. Such
parameters may be saved until such time of transmission in memory
230, and more specifically in a NVM portion of memory 230. A cyclic
redundancy code (CRC) calculation, forward error correction (FEC),
and/or data redundancy may be further added to a packet for data
validation at the receiver side. In one embodiment, when the
voltage of the harvesting circuitry is determined to be decreasing
at a high rate, i.e., the power line load was turned off, the
device transmits a message containing the last counter value as no
energy may be available until the load is switched on again.
[0028] When condition(s) to transmit is (are) met, the MCU can
implement a carrier sense multiple access (CSMA) mechanism for the
purpose of collision avoidance. The following steps are therefore
taken. First, the receiver of the RF transceiver 240 is switched
on. Second the receiver senses whether there are currently other
transmissions. This is particularly important in the environment in
which the SPPS operates, which is an environment rich with SPPSs,
possibly a few hundreds of them. Third, upon determination that the
air is free, the receiver is disabled and the transmitter of the RF
transceiver 240 is enabled for transmission to send the information
message; otherwise, the receiver us disabled and the circuit 200 is
caused to sleep for a random time interval, after which the circuit
200 wakes-up and the sequence of steps is repeated until the
desired transmission is completed. In one embodiment of the
invention, after completion of transmission the transmitter is
disabled and the receiver is enabled to receive an acknowledgement
signal from the management unit. In another embodiment of the
circuit 200 the information messages are short enough and the
intervals between transmissions are long enough so that collisions
are highly unlikely. In such an embodiment the transmission of the
information message may take place without pre-sensing of the air,
thereby conserving energy. In yet another embodiment of the
invention, after transmission the receiver is activated to receive
a clock synchronization signal. This allows synchronization between
the clocks of MCU 220 and the management server 1050 (see FIG. 10),
and as further explained herein below.
[0029] In yet another embodiment of the invention sufficient
amounts of energy are available in the circuit 200 for continuous
or longer operation. This is possible in cases where the primary
current is above a certain value. The MCU 220 can then remain on
and perform signal processing on the non-rectified signal coming
directly from the current transformer 212. The gathered information
may be therefore transmitted more frequently. This is useful for
example for measurements relating to peak values, average currents,
phase calculation, frequency shift calculation, transient and
irregular current over short period of time, and total harmonic
distortion (THD). The reservoir voltage of energy harvester 216 is
constantly measured by means of A/D converter 226 of MCU 220, in
order to prevent overcharge. If necessary a discharge of the energy
harvester 216 is performed through an I/O port. The voltage
information further provides an indication of the available energy
for keep-alive transmissions when no primary current exists. This
may happen when the circuit breaker 120 tripped or was otherwise
shutdown, or otherwise when no power is consumed by the electrical
sub-network protected by the circuit breaker 120. In a further
embodiment of the invention a 3-phase SPPS is implemented
comprising three analog sections 210 each coupled to a single MCU
220, which is further coupled to the transceiver (240) and an
antenna (250). The circuit is configured to handle three analog
sections such that the single MCU 220 can handle the entire
operation of a 3-phase SPPS. While a 3-phase SPPS is described it
should be understood that a system comprising a plurality of analog
sections maybe implemented, for a single phase or multiple phase
SPPS, thereby reducing the costs of such a multi-power-line-sensor
SPPS.
[0030] Reference is now made to FIG. 3 depicting an exemplary and
non-limiting circuit diagram 300 of a first embodiment of the
analog portion 210 of the self-powered circuit 200 in accordance
with the invention. The primary winding of the current transformer
310 is the power line 130 and its AC current induces voltage and
current in the current transformer 310. The induced current
resonates with the resonance capacitor 320 to produce sufficient
voltage to pass through the diode bridge 330. In the case where
Schottky diodes are used this voltage is approximately 0.3V. At the
output of the diode bridge a rectified DC current is provided which
charges the sense capacitor 340 until it reaches a certain
threshold V.sub.1H. The comparator 360 detects V.sub.1H on the
sense capacitor 340, and produces a control signal to the DC/DC
controller 370 which in turn activates the DC/DC switch 375 and
boosts the voltage on the high capacitance reservoir capacitor 380
to a high voltage V.sub.2, typically up to 12V. The control signal
is also used as an interrupt to wake up the MCU 220 and raise a
counter 227. Each discharge of the sense capacitor 340 represents a
quantum of AH flowing through the main circuit. The frequency of
the pulses is proportional to the primary current and the number of
pulses is therefore proportional to the total AH flowing through
the main circuit. The sense capacitor 340 is discharged through the
DC/DC inductor 350 into the reservoir capacitor 380. The DC/DC
control signal from the DC/DC controller 370 causes suspension of
the discharge of the sense capacitor 340, once the comparator 360
detects a low threshold V.sub.1L, for example 0.5V, on the sense
capacitor 340. The voltage of the reservoir capacitor 380 is
regulated by the linear regulator 390 into a steady DC voltage, for
example 3.3V or 2V as the case may be, which is supplied to the MCU
220, RF Transceiver 240, DC/DC controller 370 and the comparator
360.
[0031] Upon startup of circuit 300 the reservoir capacitor 380 is
charged by the sense capacitor 340 until enough energy is stored in
the reservoir capacitor 380 that provides a sufficient voltage to
activate the comparator 360 and the DC/DC controller 370. The
advantages of using a DC/DC converter are twofold: enabling the
boosting of the reservoir capacitor 380 into a high voltage, hence
enabling an energy reservoir sufficient for many RF transmission
cycles; and, enabling a relatively low V.sub.1H/V.sub.1L range,
hence enabling the circuit 300 to operate at very low primary
currents by producing, typically, only up to 1V at the sense
capacitor 380. The voltage of the reservoir capacitor 380 is
provided to the A/D converter 226 of the MCU 220 thereby enabling
an intentional discharge to prevent overcharge. Discharge is
achieved by the MCU 220 through control of the I/O terminal of
transistor 395. In another embodiment, as also previously
discussed, a Zener diode (not shown) is used for the purpose of
overcharge control. In another embodiment the A/D converter 226 is
configured to detect if the load connected to the primary line was
turned off and hence consumes zero current. In this case the
voltage on the reservoir capacitor 380 drops at a high rate as no
energy is supplied to the circuit 200. The transmitter therefore
transmits a single message indicating that power was turned off.
The message may further contain the last counter value sampled
prior to the reservoir energy depletion. The non-rectified output
of the current transformer 370 is coupled to the A/D converter 245
of the MCU 380, for example using a small sense resistor (not
shown) thus enabling additional signal processing and measurements
when enough energy exists in the circuit 300. For example, and
without limitations, phase measurement or detection of irregular
behavior may be achieved at such times. By limiting the voltage of
the sense capacitor, the voltage on the CT 310 coil is kept low
hence the magnetic core can be operated below its natural
saturation point which increases the measurement accuracy.
[0032] The resonance capacitor 320 resonates with the current
transformer coil in order to produce a sufficiently large voltage
to pass through the diode rectifier. Since the magnetization curve
of a typical core is non linear at low primary currents, the
effective inductance of the core varies with primary current. In
one embodiment of the invention, it is beneficial to select the
resonance capacitor's value so that maximum resonance is achieved
at low primary currents. This produces the required voltage swing
to pass through the diode bridge even at very low primary
currents.
[0033] FIG. 4 depicts an exemplary and non-limiting circuit diagram
400 of a second embodiment of the analog portion 205 of the
self-powered sensor 110 in accordance with the invention. The
circuit is simpler then the circuit 300 as it does not use a DC/DC
controller. In this embodiment, when the sense capacitor 440
reaches 3V, the comparator 450 activates the switches 452 and 454.
Activation of the switch 452 enables charging the reservoir
capacitor 470 directly from the sense capacitor 440. The switch 454
changes the comparator 450 thresholds. When the sense capacitor 440
is discharged to 2.2V the comparator disengages the capacitors,
i.e., transfer of energy to the reservoir capacitor 470 ceases. The
voltage on the reservoir capacitor 470 is regulated to, for
example, 2V, the voltage which is the V.sub.CC voltage of the MCU
220 and the RF transceiver 240. In many cases, the internal voltage
regulator of the MCU 220 may be used since the voltage range is
minimal. When the voltage of the reservoir capacitor 470 voltage is
above, for example, 2V, the MCU 220 is capable of waking up and
drawing current for pulse counting and transmission as described
above. The MCU 220 enables the reservoir capacitor 470 to be
charged to a peak voltage of, for example, 2.2V. Overcharge is
prevented by intentional discharge as described in the previous
embodiment. In this case, since no DC/DC is used, it is critical to
keep the voltage of the reservoir capacitor 470 lower than the low
threshold of the sense capacitor 440, for example, 2.2V, in order
to prevent charge from flowing backwards. In another embodiment, as
also previously discussed, a Zener diode (not shown) is used for
the purpose of overcharge control. An optional small auxiliary
battery 460 is used in order to feed the comparator 450, provide
initial operating energy when the reservoir capacitor 470 is not
fully charged, and provide enough energy for low frequency, for
example once per day, keep-alive transmissions when no primary
current exists. Keep alive transmissions are important in order to
notify the system of the existence of the sensor even when no
primary current exists.
[0034] FIG. 5 depicts an exemplary and non-limiting circuit diagram
500 of a third embodiment of the analog portion 205 of the
self-powered sensor 110 in accordance with the invention. In this
embodiment of the analog portion 205 there is only one large sense
capacitor 540 and no reservoir capacitor nor a DC/DC controller.
The reason for using lesser components in the circuits shown in
FIGS. 4 and 5 is to reduce the component count and thereby reduce
the bill-of-materials (BOM) of the solution. In the circuit 500 the
sense capacitor 540 also functions as the energy source for,
typically, a single transmission. Therefore, the sense capacitor
540 of this embodiment is designed with a rather large capacitance,
for example 1 mF. According to the principles of operation of the
circuit 500 the comparator 550 detects when the sense capacitor 540
is charged, for example, up to 4V, and opens the switch 552 towards
the linear regulator 570. The linear regulator 570 provides a
regulated voltage, for example a 3V output, thereby allowing the
MCU 220 to draw current resulting in discharge of the sense
capacitor 540. Due to the activation of switch 554, discharge to a
lower reference voltage, for example 3V, is detected by the
comparator 550 and discharge is stopped. The MCU 220 is enabled to
perform operations which discharge the sense capacitor 540 to
perform the counting operation and transmission when needed. The
MCU 220 is further enabled to measure the voltage of the sense
capacitor and discharges it down to a lower voltage, for example
3V, intentionally when performing operations that do not consume
the entire energy. An optional battery 560 is used to provide a
reference voltage to the comparator 550, as well as to allow
keep-alive transmissions when the primary current is below a
minimum detectable current. In another embodiment, as also
previously discussed, a Zener diode (not shown) is used for the
purpose of overcharge control. In another embodiment, as also
previously discussed, a linear regulator is not used and the MCU's
internal regulator regulates the input voltage.
[0035] In another embodiment of the invention, power measurement is
done by measuring the voltage change rate on the sense capacitor,
e.g., capacitors 540, 440 or 340. The sense capacitor voltage is
measured by A/D 226. The MCU 220 then lets the capacitor discharge
through a resistor, for example resistor 395, for a fixed period of
time, during which the MCU 220 can be set to a low power mode. The
voltage level of the sense capacitor is measured after the elapse
of the fixed period of time, and the voltage difference (.DELTA.V)
between the two measurements is calculated. .DELTA.V consists of a
negative fixed part, i.e., the voltage discharge through resistor
395, plus a positive variable part proportionate to the charge rate
of the capacitor due to the primary current flow.
[0036] Key to the operation of the SPPS 110 is that it is capable
of addressing several critical challenges to its successful
operation. Three key issues are the minimum power detection of the
current transformer 212, the power balance of the circuit 200, and
wireless coexistence in an environment of a plurality of SPPSs 110
that may include several hundreds of SPPSs. In order for an SPPS
110 to be a useful device it is necessary that it be capable of
detecting as low as possible currents flowing through the primary
lead 130. The design must take into consideration the limited space
typically available for an apparatus such as, but not limited to,
SPPS 110 that must fit dimension restrictions of the circuit
breaker 120. In other embodiments of the invention other size
restrictions may apply, however these should not be viewed as
limiting the scope of the invention. Inductance of the secondary
winding is approximately:
L = .mu. 0 .mu. r N 2 A 1 ##EQU00001##
[0037] Where N is the number of windings, .mu..sub.r is the
relative permeability of the magnetic material, such as, and not
limited to, strip wound iron, .mu..sub.0 is the permeability of
free space, A is the cross section of the core, further discussed
with respect of FIGS. 6 and 7 below, and l is the effective length
of the core. For N=1500, .mu..sub.r=1000,
.mu..sub.0=4.pi.10.sup.-7, A=40 mm.sup.2, and l=20 mm, the
inductance is L=5.5 Hy. The current ratio between the secondary
current I.sub.s and the primary current I.sub.p is approximately,
for an ideal transformer, I.sub.p/I.sub.s=N. The voltage on the
secondary coil is given by
V.sub.s=I.sub.s.omega.L=I.sub.p.omega.L/N, and at f=50 Hz
.omega.=2.pi.f=314 rad/sec. Therefore,
V.sub.s=I.sub.p.omega.L/N=1.15 I.sub.p. Assuming a 1V drop over the
diode rectifier, for example diode rectifier 330, and charge
voltage of 1V then at least 2V are needed in order for the system
to operate. Hence, there is a minimum detectable current of
2/1.15=1.7 A peak=1.2 A RMS. Using the resonance capacitor, for
example resonance capacitor 320, the impedance is decreased by a
factor of 1/(X.sub.L-X.sub.C) where X.sub.L is the impedance of the
core and X.sub.C Is the impedance of the resonance capacitor.
Taking an accumulative tolerance of .+-.20% for the capacitance and
inductance, results in a worst case of 40% increase in signal, and
hence the minimum detectable current is, in this exemplary case,
1.2.times.0.4=0.48 A, which represents a minimum detectable power
of 105VA at 220V. At 110V 60 Hz, the minimum detectable current in
the exemplary case is 5/6.times.0.48=0.4 A and a minimum detectable
power of 44VA. Since L is proportional to N.sup.2 and to A and V is
proportional to 1/N, the minimum detectable current may be
decreased by increasing either N or A. However, it is essential to
ensure that the entire core, and its respective secondary winding,
fit in the size constraints of SPPS 110, and an increase of N or A
may have a material effect thereon.
[0038] Furthermore, to make the SPPS 110 an operative device it is
essential to ensure that a sufficient amount of power may be made
available through the operation of the circuits discussed
hereinabove. Following is an exemplary and non-limiting analysis
thereof. Firstly it is essential to understand the energy
requirements of each of the key components: the transmission cycle,
the counting cycle and the logic operation. Failure to address
these issues may result in non-operative circuits. In all cases the
assumption is for a 3V operation. For the transmission cycle a
transmission current of 20 mA is used for a period of 5 mSec. A
processing current of 1 mA is used during a 10 mSec period of
wakeup and processing. Therefore the total energy requirements for
the transmission cycle is: 3V.times.(20 mA.times.5 msec+1
mA.times.10 msec)=0.33 mJ. For the counting cycle a processing
current of 1 mA is used for a wakeup and processing period of 5
mSec. Therefore the energy requirements for this counting cycle
are: 3V.times.1 mA.times.5 msec=15 .mu.J. Lastly, the logic
operation requires a continuous current of 50 .mu.A, resulting in a
continuous power consumption of: 3V.times.0.05 mA=150 .mu.W. The
total energy has to be supplied reliably by the power supply
circuit, for example, circuit 300. It is therefore necessary that
the sense capacitor, for example sense capacitor 340, and the
reservoir capacitor, for example reservoir capacitor 380, provide
sufficient energy for the performance of the desired operations.
The above assumptions are typical for common low power MCUs and
radio frequency integrated circuits (RFICs).
[0039] To address the energy balance of the circuit 200 it is
necessary to ensure that the sense capacitor, for example sense
capacitor 320, is capable of supplying sufficient energy for the
counting cycle and that the reservoir capacitor, for example
reservoir capacitor 380, is capable of supplying enough energy for
several transmission cycles. Both are addressed in the following
exemplary and non-limiting calculations. If the sense capacitor
C.sub.1 is equal to 1 mF and is charged to V.sub.1=1V and
discharged to V.sub.2=0.5V, then the total discharge energy is:
E=0.5 C.sub.1.times.(V.sub.1.sup.2-V.sub.2.sup.2)=375 .mu.J. It has
been shown hereinabove that the counting cycle requires 15 .mu.J
which is less than 3% of the available energy. The remaining energy
is accumulated for the purposes of transmission, for example, in
the reservoir capacitor. Assuming a reservoir capacitor, for
example capacitor 320, having a value of 0.375 mF, the capacitor
being charged to V.sub.1=5V and discharged to V.sub.2=3V, then the
total energy is: E=0.5
C.sub.2.times.(V.sub.1.sup.2-V.sub.2.sup.2)=3 mJ. A previous
calculation has shown that the transmission cycle consumes around
0.33 mJ and hence roughly nine transmission cycles are possible
under these conditions. Now it is possible to determine the number
of counting cycles it takes to charge the reservoir capacitor with
the required amount of energy. The available energy is 360 .mu.J
and with a 50% DC/DC controller efficiency there are 180 .mu.J at
every sense capacitor pulse. By dividing the amount of energy
required for several transmission cycles, e.g., 3 mJ, by the amount
of energy charged each cycle, e.g., 0.18 mJ, it is determined that
approximately 17 sense capacitor cycles are needed to charge the
reservoir capacitor with the required energy.
[0040] In order to ensure proper operation of the circuit 200 it is
necessary to ensure a positive energy balance for continuous system
operation even at the lowest primary currents. It is therefore
necessary to calculate the power in to the system versus the power
out of the system, the later having to be smaller than the earlier.
For the power in, at a primary current I.sub.p=0.5 A and N=1500
results in a secondary current of I.sub.s=0.33 mA. Using the same
figures as above, i.e., a sense capacitor of 1 mF, discharge
voltage down to 0.5V and charge voltage of 1V, the charge time is
T=C.DELTA.V/I.sub.s=1.5 Sec. The available energy of 375 .mu.J
therefore provides 375/1.5=0.25 mW. Assuming 80% DC/DC efficiency,
the available power in is 200 .mu.W. The power out is a combination
of the continuous logic operation, the counting process and the
transmissions. The continuous logic operation requires 150 .mu.W as
shown above. The counting processing requires 15 .mu.J for a period
of 375 mSec which is equivalent to 40 .mu.W. Assuming a
transmission once every one minute then 360 .mu.J are required
every 60 seconds which are 6 .mu.W. The total power consumption is
therefore 196 .mu.W which is less than the 200 .mu.W available as
explained herein above. It should be noted that a higher primary
current results in an improved power balance that enables an
increase of the transmission frequency, performing continuous
signal processing, storing energy for times when no primary current
exists, and combinations thereof.
[0041] FIGS. 6 and 7 show schematic diagrams 600 and 700 of a core
with the secondary winding and the core separated into two parts.
The core is comprised of two parts 610 and 620 that are separable
from each other, however, as shown in FIG. 7, are designed so as to
ensure that when they are assembled they provide good magnetic flow
through the core by reducing the air-gap between the two parts to
minimum, for example 10 .mu.m. While an exemplary shape of the two
portions of the core is shown these are merely for explanation
purposes and other designs are possible to achieve the required
results. It is essential, as explained herein above, that the core
fit in the dimensions allotted in the SPPS 110 so that it can
properly fit in an electricity closet in conjunction with a circuit
breaker. The secondary windings 630 of the current transformer 212
are wound on one of the sections of the core, for example, section
610 which is the stationary section that is placed in the exemplary
and non-limiting housing 800 shown with respect of FIG. 8. In this
example, these may be two windings connected in series, of two
independent secondary windings (see FIG. 6). The moveable section
of the core, for example section 620, is placed in section 810 of
the housing 800 which is separable from section 820 of the housing,
in which section 610 is placed. When separating section 810 from
section 820 it is possible to place them around power line 130 so
that when the sections 810 and 820 are reconnected the power line
130 is placed within the core perimeter thereby completing the
current transformer 212. Each SPPS 110 is assigned a unique
identification (ID), for example a MAC address that maybe 16 bytes
in length, that is placed on the housing 800 at, for example,
location 840. At installation of the SPPS the MAC address is read
by a technician installing the system for configuration purposes.
In one embodiment machine readable code is provided, e.g., barcode,
to enable automatic reading using a reader. While a core comprising
of two sections is described hereinabove, it should be noted that
other implementations for a core are possible without departing
from the scope of the invention. In one embodiment a single section
core is used and in such a case the primary line must be inserted
through the hole in the core. It may require disconnection of the
line and threading it through the core for mounting the SPPS
device.
[0042] An exemplary and non-limiting flowchart 900 depicted in FIG.
9 describes the operation of a SPPS deployed in accordance with the
invention. In S910 the SPPS, for example, SPPS 110, checks if
counting pulse was received and if so execution continues with
S920; otherwise, execution continues with S910. In S920 a count is
performed in accordance with the principles described herein above,
which may include the discharge of the sense capacitor, for example
capacitor 320. In S930 it is checked whether there is sufficient
energy to perform a transmission and is so execution continues with
S940; otherwise, execution continues with S910. In S940 it is
checked whether it is time to transmit by the SPPS 110 and if so
execution continues with S950; otherwise, execution continues with
S910. In S950 SPPS 110 senses the environment for another
transmission to avoid transmission collisions as discussed herein
above. In S960 it is checked if it is possible to transmit and if
so execution continues with S980; otherwise, in S970 a random wait
period is determined and execution then continues with S930. In
S980 the information gathered by the SPPS 110 is transmitted, the
information transmitted contains data as discussed herein above. In
S990 it is checked whether the operation should continue and if so
execution continues with S910; otherwise, execution terminates. An
optional step may be added after transmission is complete for the
purpose of reception of feedback information from the unit
receiving the information sent by the transmitter. Such feedback
information may include, but is not limited to, acknowledge
information and/or synchronization information.
[0043] Reference is now made to FIG. 10 where an exemplary and
non-limiting system 1000, configured in accordance with the
principles of the invention, is shown. The system comprises a
plurality of SPPS 1010 communicatively coupled to a communication
link 1020. The SPPS 1010 may be placed in an electrical closet
before or after respective circuit breakers or, at the input to
specific power consuming units. The management server is equipped
with a transceiver enabling the communication with the plurality of
SPPS 1010 using one or more of the communication schemes discussed
herein above. The communication bridge 1020 is configured to
communicate with those SPPSs 1010 it is configured to operate with,
using for identification their respective MAC addresses. The
communication bridge 1020 is coupled to a network 1020 which may
be, but is not limited to, a local area network (LAN), a wide area
network (WAN), a metro area network (MAN), the Internet, the world
wide web (WWW), the likes and combinations thereof. The
communication link can be, but is not limited to, a WLAN (Wireless
LAN), for example 802.11 also known as WiFi, a wireless sensor area
network, for example 802.15.4 also known as Zigbee, power line
communication (PLC), or a cellular to modem network such as GPRS or
CDMA. In one embodiment of the invention the communication bridge
aggregates the data from the plurality of sensors 1010-1 to 1010-N
prior to sending it to the network. To the network there are
coupled a database 1040 to accumulate data collected by the
communication bridge 1020. The communication bridge 1020 may be
placed in each closet and aggregate a plurality of SPPS 110
communications. In one embodiment the communication bridge 1020 is
responsible for the phase calculation discussed in more detail
herein below. Further coupled to the network is a management server
1050 that based on the data accumulated in database 1040 may
provide a client 1060 processed information respective of the
collected data as well as communicate with other application
software, for example building management systems (BMSs). In one
embodiment of the invention the minimum number of winding in the
secondary coil is 500.
[0044] In one embodiment of the invention the communication bridge
1020 is enabled to provide information with respect to a phase and
enable the system to calculate a phase shift. Knowledge of the
phase shift between current and voltage is used to calculate the
power factor (cos .phi.), hence determine more accurately the real
active power flowing through the power line. When it is determined
that there is sufficient energy in energy reservoir 216 then MCU
220 may become operative in continuous mode, for as long as such
sufficient energy is available, or until operation is complete.
Using AD converter 225 MCU 220 detects the peak current of the
current transformer 212. The time of the peak relative to a clock
synchronized between the sensor and the bridge unit is recorded
and, when appropriate, transmitted to the communication bridge
1020, according to the principles discussed hereinabove.
communication bridge 1020 is further enabled to detect the peak of
the power supply voltage nearest to the sensors by at least a peak
detector (not shown) coupled to the communication bridge 1020 and
to a reference power line. The time of the peak of is recorded by
the communication bridge 1020 continuously. As the clocks of the
communication bridge 1020 and circuit 200 are synchronized, as
further discussed hereinabove, it is now possible for the
communication bridge 1020, upon receiving information from the
circuit 200 respective of the measure peak and time, to determine
the phase shift between the reference power line voltage and the
current measurement made by the circuit 200. It should be noted
that the use of a peak detector enables the system to become
agnostic to the differences in the utility grid frequency, e.g., 60
Hz for the USA versus 50 Hz in Europe, as well as to any other
error or change in the supply voltage frequency.
[0045] Reference is now made to FIG. 11 where an exemplary and
non-limiting second embodiment of a SPPS 1100 is shown. A key
difference may be observed in the microcontroller 220 that does not
receive a pulse as an interrupt signal as was shown in the
previously described embodiments, for example in FIG. 2. Similar
components to those of FIG. 2 are not further discussed herein,
unless necessary for clarity. The notable change is in the analog
section 1110 that comprises a current transformer 212, an energy
harvester 216, a switch 1114 and a sense resistor 1112. In normal
operation the switch 1114 is positioned to enable energy harvesting
by the energy harvester 216. Periodically, for example under the
control of the microcontroller 220, the switch 1114 is activated to
short the secondary winding of transformer 212 through the sense
resistor 1112, typically having a low resistance. The voltage on
the sense resistor 1112 is sampled by the ADC 225. In order for the
system 1100 to identify a voltage peak the process is repeated
several times in each cycle. The switch 1114 is toggled between the
two positions to enable energy harvesting most of the time in a
first position, and measurement of the voltage periodically when in
the second position. The sampling is averaged over a number of
cycles and divided by the resistance value of the sense resistor
1112 to provide the current value. The current value is then
multiplied by a time interval to obtain the total charge value, for
example, in Ampere Hours. A calibration factor, as discussed herein
above, can also be used with respect of system 1100.
[0046] The analog section may be implemented as shown in the
exemplary and non-limiting circuit diagram 1200 of FIG. 12.
Normally, the switches 1210 and 1220, connected between the
resonance capacitor 320 and the bridge rectifier 330 are off, so
that the harvesting capacitor 380 is charged. The voltage of the
harvesting capacitor 380 is limited to avoid overcharge as
discussed in detail herein above with respect to other embodiments
of the invention. From an energy harvesting point of view, FIG. 12
represents an embodiment close to the one shown in FIG. 5 but
embodiments similar to the ones shown in FIGS. 3 and 4, in terms of
the harvesting circuitry, are also possible. To perform a
measurement the microcontroller 220 switches the transistors 1210
and 1220 using their respective I/O ports. According to the
principles of the invention switches 1210 and 12220 are operated
simultaneously in opposite phases. Although measurement is
preformed on a single resistor 300 rather than two, the use of the
two switches and two resistors is in order to prevent DC load on
the transformer 212. This is required to avoid saturation and
distortion of the measurement results. It would be appreciated by
those skilled in the art that one switch conducts in the positive
part of the cycle, and the other switch conducts in the negative
part of the cycle. It should be noted however that topologies using
a single switch which can symmetrically conduct in both directions
are possible, for example, by using a pair of MOSFET transistors
connected in series. When the switches are active the current flows
through the appropriate sense resistor instead of charging the
harvesting capacitor 380. According to the invention, the sense
resistors have a low impedance relative to the self resistance of
the transformer coil. This enables a close to short circuit current
flow, keeping the voltage across the resistor low enough thus
maintaining minimal flux across the core and avoiding saturation of
the transformer 212. In one embodiment of the invention, after
switching on the sense resistors, the MCU 220 waits a certain time
interval, typically a couple of hundreds of milliseconds, or switch
to an off/power save mode, before performing the measurement, in
order to allow for the resonance capacitor to discharge. This
ensures high accuracy and better linearity of the measurement
results. In accordance with the principles of the invention, in
cases where it is possible to use two coils, a first secondary coil
used to measure the voltage using the ADC 225 while the second
secondary coil (see prior descriptions of FIGS. 6 and 8) is used
for the purpose of energy harvesting, thereby eliminating the need
for switching at the expense of a potential increase in size of the
SPPS. The value of the sense resistor may be easily calculated.
Assuming the SPPS is designed for a maximum primary current of 30 A
then with N=1000 the maximum short circuit current of the secondary
winding would be 30 mA. If the maximum input to the ADC 225 is 1V
then the sense resistor 1112 is to be 30.OMEGA.. The resistance of
a thin, e.g., 0.1 mm, copper wire with 1000 windings at typical
dimensions of the SPPS is approximately 100.OMEGA.. Referring to
the energy balance calculation explained hereinabove with respect
to different embodiments, a similar amount of energy calculated
before for the purpose of pulse counting, can be used here for the
purpose of A/D activation and sampling, thus this embodiment does
not significantly differ from the previous ones in terms of energy
consumption. Therefore a sufficient amount of energy is available
for proper system operation even when a very low primary current
exists.
[0047] In yet another exemplary embodiment of the analog section
circuit 1300, shown in FIG. 13, a voltage doubler 1340 is used. In
fact, the bridge rectifier described herein above with respect to
all of the other embodiments can be replaced by a voltage
multiplier. A person skilled in the art would readily note that the
voltage multiplier may be a voltage doubler, tripler, quadrupler or
any other type of passive voltage multiplier topology, without
departing from the scope of the invention. The exemplary and
non-limiting circuit 1300 shows a simple implementation of a
voltage doubler 1340. The voltage on the harvesting capacitor 380
is double the voltage on the transformer 310 after resonance. In
some cases the use of a voltage multiplier is advantageous at the
lower current range. Also, specifically referring to the sense
resistor topology, the voltage multiplier simplifies the grounding
of the circuit as a common ground can be connected to the
harvesting capacitor and the sensing resistor, whereas when using
the bridge rectifier a differential voltage measurement needs to be
made.
[0048] The principles of the invention, wherever applicable, are
implemented as hardware, firmware, software or any combination
thereof. Moreover, the software is preferably implemented as an
application program tangibly embodied on a program storage unit or
computer readable medium. The application program may be uploaded
to, and executed by, a machine comprising any suitable
architecture. Preferably, the machine is implemented on a computer
platform having hardware such as one or more central processing
units ("CPUs"), a memory, and input/output interfaces. The computer
platform may also include an operating system and microinstruction
code. The various processes and functions described herein may be
either part of the microinstruction code or part of the application
program, or any combination thereof, which may be executed by a
CPU, whether or not such computer or processor is explicitly shown.
In addition, various other peripheral units may be connected to the
computer platform such as an additional data storage unit and a
printing unit. The circuits described hereinabove may be
implemented in a variety of manufacturing technologies well known
in the industry including but not limited to integrated circuits
(ICs) and discrete components that are mounted using surface mount
technologies (SMT), and other technologies. The scope of the
invention should not be viewed as limited by the types of packaging
and physical implementation of the SPPS 110 or the communication
bridge 1020.
[0049] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the principles of the invention and the concepts
contributed by the inventor to furthering the art, and are to be
construed as being without limitation to such specifically recited
examples and conditions. Moreover, all statements herein reciting
principles, aspects, and embodiments of the invention, as well as
specific examples thereof, are intended to encompass both
structural and functional equivalents thereof. Additionally, it is
intended that such equivalents include both currently known
equivalents as well as equivalents developed in the future, i.e.,
any elements developed that perform the same function, regardless
of structure.
* * * * *