WO2008154031A2 - Power converter and power combiner for power-limited power sources - Google Patents

Power converter and power combiner for power-limited power sources Download PDF

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Publication number
WO2008154031A2
WO2008154031A2 PCT/US2008/007334 US2008007334W WO2008154031A2 WO 2008154031 A2 WO2008154031 A2 WO 2008154031A2 US 2008007334 W US2008007334 W US 2008007334W WO 2008154031 A2 WO2008154031 A2 WO 2008154031A2
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WO
WIPO (PCT)
Prior art keywords
terminal
power
output
capacitor
switch
Prior art date
Application number
PCT/US2008/007334
Other languages
French (fr)
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WO2008154031A3 (en
Inventor
Fouad Kiamilev
Nicholas Andrew Waite
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University Of Delaware
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Publication date
Application filed by University Of Delaware filed Critical University Of Delaware
Priority to CN200880020138A priority Critical patent/CN101682258A/en
Priority to EP08794352A priority patent/EP2158669A2/en
Priority to JP2010512187A priority patent/JP2010529831A/en
Publication of WO2008154031A2 publication Critical patent/WO2008154031A2/en
Publication of WO2008154031A3 publication Critical patent/WO2008154031A3/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/1563—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators without using an external clock
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0016—Control circuits providing compensation of output voltage deviations using feedforward of disturbance parameters
    • H02M1/0022—Control circuits providing compensation of output voltage deviations using feedforward of disturbance parameters the disturbance parameters being input voltage fluctuations

Definitions

  • This invention relates to a power source power converter and to a power combiner that combines the output power of multiple power sources into a single output.
  • Small power sources such as photovoltaic cells, and in particular solar cells, are being used to power portable devices or to charge a battery pack.
  • the well-known boost chopper power converter circuit has been used in conjunction with such power sources in portable applications.
  • This type of power converter takes input current at a low voltage, e.g., a single silicon solar cell has an output of about 0.5 volts, and produces an output current at a higher voltage that can be used to operate handheld electronics or charge a battery pack.
  • the outputs of the individual sources have to be combined.
  • the power sources such as like-type silicon solar cells have been connected in some series-parallel combination to provide the voltage and current outputs required for the particular application.
  • one type of solar cell battery charger connects the solar cells in series to approximate the battery voltage. The output is then fed into the battery through a diode.
  • this architecture is inefficient and the rechargeable batteries quickly wear out.
  • Another approach simulates the AC outlet that users can plug into with a solar cell powered equivalent.
  • This architecture is inherently inefficient since the battery chargers incorporated in most consumer electronics are not designed for efficient operation with limited sources of power.
  • Recent solar cell architectures use multiple cells that efficiently absorb different portions of the solar spectrum and thereby achieve higher overall conversion efficiency than traditional solar cells using a single type of cell.
  • the voltages of the different cells are regulated at specific temperature-compensated values to achieve maximum efficiency. Since the cells and their characteristics are not identical, the traditional approach of combining their output by connecting the cells in some series-parallel combination will not work and a different type of power combiner is needed.
  • This invention provides a hysteretic input-regulating boost power converter for converting the power provided by a power source, the power converter comprising a hysteretic voltage comparator, wherein the power converter provides an output current at an output voltage that is greater than and not dependent on the input voltage.
  • a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal;
  • a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
  • a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
  • first and second input terminals for connection to a power source providing an input voltage
  • a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal
  • a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
  • a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
  • an output rectifier having a first terminal connected to the first terminal of the transformer secondary winding and a second terminal;
  • This invention also provides a power combiner that combines the output power of multiple power sources into a single output.
  • the power combiner comprises a parallel arrangement of circuits, wherein a different one of the circuits is allocated to each of the multiple power sources.
  • Each of these circuits is a complete input-regulating high-output impedance power converter circuit or forms a complete input-regulating high-output impedance power converter circuit when connected to the one or more elements that these circuits share. When elements are shared, no more than one circuit is connected to the shared elements at any given time. The output power of these circuits is fed into a single output.
  • the power combiner utilizes one embodiment of the power converter circuit of the invention, the power combiner comprising:
  • each power converter circuit comprising:
  • a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal;
  • a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
  • a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
  • an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal; and (b) an output having a first terminal connected to the second terminal of the output rectifier of each power converter circuit and a second terminal connected to the second terminal of the switch of each power converter circuit.
  • the power combiner utilizes another embodiment of the power converter circuit of the invention, the power combiner comprising:
  • each power converter circuit allocated to each of the power sources, each power converter circuit comprising: (i) first and second input terminals for connection to the power source designated for the power converter circuit;
  • a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
  • a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
  • the power combiner comprises:
  • the power combiner comprises:
  • each said circuit comprising:
  • an inductor having a first terminal connected to the second terminal of the switch in each said circuit and a second terminal connected to the second terminal of the capacitor in each said circuit;
  • an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal;
  • an output having a first terminal connected to the second terminal of the output rectifier and a second terminal connected to the first terminal of the inductor; and (e) a controller that periodically cycles through and opens and closes all the switches and processes each of the power sources, wherein no more than one switch is closed at any given time.
  • the power converter and power combiner are useful with power sources such as fuel cells and photovoltaic cells, particularly solar cells, i.e., with power sources that have power-limited outputs.
  • the power combiner is useful when the solar cell unit is comprised of multiple cells and especially when the multiple cells are of different types.
  • FIGURES Figure 1 is a schematic diagram of one embodiment of the power converter of the invention.
  • Figure 2 is a schematic diagram of another embodiment of the power converter of the invention.
  • Figure 3 is a circuit diagram for the embodiment of the power converter used in Example 1.
  • Figure 4 is a schematic diagram of an embodiment of the power combiner of the invention in which the circuits allocated to each of the power sources are complete hysteretic input-regulating high-output impedance power converter circuits.
  • FIG. 5 is a schematic diagram of an embodiment of the power combiner of the invention in which the circuits allocated to each of the power sources share elements and when connected to the shared elements form complete input-regulating high-output impedance power converter circuits
  • Figure 6 is a circuit diagram for the embodiment of the power converter used in Example 2.
  • Figure 7 is a circuit diagram of the embodiment of the power combiner of the invention used in Example 3.
  • the circuits allocated to each of the power sources are complete hysteretic input-regulating high- output impedance power converter circuit.
  • Figure 8 is a circuit diagram of one embodiment of the power combiner of the invention used in Example 4.
  • the circuits allocated to each of the power sources share elements and when each is connected to the shared elements each forms a complete input-regulating high-output impedance power converter circuit.
  • Figure 9 shows the charging characteristics obtained by simulation of the circuit shown in Figure 8.
  • Figure 10 is a circuit diagram of another embodiment of the power combiner of the invention used in Example 5. The circuits allocated to each of the power sources share elements and when connected to the shared elements form a complete input-regulating high-output impedance power converter circuits. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • the power converter of the invention can be used in conjunction with a power-limited power source to provide an output voltage sufficient to operate handheld electronics or charge a battery pack.
  • the power converter uses hysteresis, input-side regulation and self-induced oscillation to reduce parts count and power consumption and is a hysteretic input-regulating high-output impedance power converter.
  • the power converter has a circuit 10 comprising the following elements.
  • a first input terminal 11 and a second input terminal 12 provide for connection to a power source PS.
  • a capacitor 13 has a first terminal connected to the first input terminal and a second terminal connected to the second input terminal.
  • a hysteretic voltage comparator 14 has a first terminal connected to the first terminal of the capacitor, a second terminal 15 for inputting a reference voltage and a third terminal that is an output terminal.
  • Switch 16 has a first terminal connected to the third terminal of the hysteretic voltage comparator 14 to thereby receive the output signal from the hysteretic voltage comparator 14. The output signal serves to open and close the switch 16.
  • the switch 16 also has a second terminal connected to the second terminal of the capacitor and a third terminal.
  • An inductor 17 has a first terminal connected to the first terminal of the capacitor 13 and a second terminal connected to the third terminal of the switch 16.
  • An output rectifier 18 has a first terminal connected to the second terminal of the inductor 17 and a second terminal connected to the first output terminal 19.
  • the second output terminal 20 is connected to the second terminal of the switch 16.
  • the second input terminal, the second terminal of the capacitor, the second terminal of the switch and the second output terminal are all connected to ground.
  • This power converter operates in the following fashion.
  • the power source PS charges the capacitor 13 until the voltage on capacitor 13 exceeds the high threshold voltage of hysteretic voltage comparator 14. This causes hysteretic voltage comparator 14 to close switch 16.
  • Transformer 17F has a primary winding having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch.
  • the secondary winding has a first terminal connected to the first terminal of output rectifier 18 and a second terminal connected to the output terminal 20.
  • the second terminal of the output rectifier is connected to the first output terminal 19.
  • the circuit elements can take various forms.
  • the capacitor 13 can be a single capacitor or two or more capacitors arranged in parallel and/or series configurations.
  • the hysteretic voltage comparator 14 can be comprised of a commercially available externally referenced integrated circuit comparator or a self-referencing circuit.
  • the switch 16 can be comprised of a bipolar transistor or a field effect transistor and resistors to set the high and low switching threshold voltages.
  • the inductor 17 can be a single inductor or coupled inductors to provide further flexibility in operational range.
  • the output rectifier 18 can be in form of a diode or, if pulse outputs are not desired, the pulses can be easily filtered to DC by using a capacitor in conjunction with the diode.
  • a synchronous rectifier structure can be used in place of the diode.
  • Other forms for these elements will be apparent to those skilled in the art.
  • the power converter does not require a programmed controller; however, the use of such a controller is not precluded.
  • a single controller circuit can be used to operate multiple power converters, e.g., the multiple power converters in the power combiner.
  • the hysteretic input-regulating boost power converter power of the invention has many advantages. It has a wide operating range, high efficiency, simple and low-cost implementation. It makes efficient use of the inductor, which is one of the largest components in the circuit, by its inherently fixed-on-time switching set by the inductor-capacitor (L-C) time constant and hysteresis voltage.
  • the power consumption of the power converter is in the microwatt range and that makes it efficient for use with power sources such as solar cells that produce only a few milliwatts of power. It can also optimally match its power source by dynamically adjusting the hysteretic voltage comparator's internal or external reference voltage to achieve maximum power point (MPP) tracking of solar and other photovoltaic cells. MPP is the point at which the current and voltage output of these cells are jointly maximized, i.e., the cell is operating at maximum efficiency. For these cells temperature tracking of the cell voltage is very important in order to achieve optimum power output and can be achieved by using temperature-variable resistors or diodes in the reference circuit or an externally-derived varying reference voltage.
  • a controller When a controller is used to operate one or more power converters it does so such that the photovoltaic cell power source of each power converter is essentially performing at its MPP.
  • the power converter's output is flexible. There is no feed back to regulate its impedance so at the output terminal it appears to be an inductor/diode series combination with naturally high impedance. As a result it is possible to track the output voltage across a wide range without losing power.
  • the power converter produces saw-tooth current pulses which are ideal for pulse-charging a battery. The size and chemistry of the battery has no effect on the power converter's efficiency. Pulse-charging of batteries is known to improve the batteries lifetimes.
  • the pulses can be easily filtered to DC by using a capacitor to allow conventional methods of charging.
  • the components used in one embodiment of the power converter shown schematically in Figure 1 are shown in the circuit diagram of Figure 3.
  • the comparable elements of Figure 3 are labeled with the same numbers as used in Figure 1 and the circuit components making up the elements are indicated.
  • Capacitor 13 consists of capacitor C5.
  • the comparator 14 is implemented in this embodiment with a 1.8 V low power LMV7271 comparator (National Semiconductor, Santa Clara, CA), resistors R11 , R12 and R13 and capacitor C14.
  • the five terminals of the LMV7271 comparator are indicated in Figure 2 using the manufacturer's terminal numbers.
  • the VDD input provides the power needed to operate the comparator.
  • the high and low voltage switching thresholds are set by the resistors R11 , R12 and R13 and the input voltage reference VREF that is applied to terminal 15.
  • the switch 16 is implemented with a ZXTN23015CPH bipolar transistor BT (Zetex Semiconductors pic, Chadderton, Oldham, UK), its base-feed network of capacitor C9 and resistor R10 and the anti-electromagnetic interference (EMI) network of capacitor C7 and resistor R8.
  • the inductor 17 is inductor L4.
  • the output rectifier is implemented with a low-leakage Schottky diode D3 and filter capacitor C15. This embodiment has only 14 or 15 components depending on whether the filter capacitor C15 is used.
  • the invention also provides a power combiner that combines the output power of multiple power sources into a single output with minimal loss.
  • the power combiner can be used to provide the single output with the power from one or more power sources.
  • the power combiner can be used to combine the power from power sources that are alike or different. For example, when used with multiple like-type photovoltaic cells the power combiner can be used to combine the power from individual cells or from parallel or series combinations of these cells.
  • the power combiner of the invention is especially useful when combining the outputs of individual power sources that are not alike, e.g., when combining the power from multiple cells of a solar cell wherein the cells are of different types.
  • the various cells can be chosen so that each converts different ranges of the solar spectrum and thereby provides more efficiency.
  • the voltage across each cell is regulated at a particular temperature-compensated value to provide optimum operation of that cell.
  • the power combiner circuit operates with the same energy conversion efficiency regardless of the number or types of cells attached to its inputs.
  • the power combiner of the invention is simple, efficient and not costly to produce.
  • the power combiner of the invention combines the output power of multiple power sources and is comprised of multiple circuits, wherein a different one of the circuits is allocated to each of the multiple power sources. For example, if there are n power sources there will be n circuits, one for each of the power sources.
  • the multiple circuits can be different or identical. As used herein, "identical circuits" indicates that the circuits have the same components. Even though the components are the same, their values and the operation of the circuits can differ, e.g., the hysteretic voltage comparators internal or external reference voltages can be different in order to achieve MPP tracking.
  • each circuit is a complete input- regulating high-output impedance power converter circuit.
  • the high-output impedance of the power converter of the invention enables the direct connection of multiple power converters in parallel to add their power.
  • the power combiner is further comprised of a single output .
  • each circuit is a complete hysteretic input-regulating high- output impedance power converter circuit.
  • One such embodiment is shown schematically in Figure 4. It uses identical circuits, each with a hysteretic input-regulating high-output impedance power converter circuit as shown schematically in Figure 1.
  • the power combiner 25 is shown with only two power sources and two power converter circuits, but any number can be used.
  • Comparable circuit elements are labeled with the same numbers used for the schematic drawing of Figure 1.
  • the second input terminal 12A or 12B the second terminal of the capacitor and the second terminal of the switch are all connected to ground.
  • the second output terminal 22 is accordingly connected to ground.
  • Power source PSA is connected to power converter circuit 10A using input terminal 11A and ground terminal 12A.
  • the various circuit elements capacitor 13A, voltage comparator 14A with terminal 15A for inputting a reference voltage, switch 16A, inductor 17A and output rectifier 18A all are connected as described previously for the power converter of the invention and the circuit 10A operates in the manner described previously.
  • Power source PSB is connected to power converter circuit 10B using input terminal 11 B and ground terminal 12B.
  • Power converter circuit 10B has the same elements, i.e., 13B through 18B,as power converter circuit 10A . They all are also connected as described previously for the power converter of the invention and the circuit 10B operates in the manner described previously.
  • the second terminal of the output rectifier of each power converter circuit is connected to the common output terminal 21 and current flows out of the output rectifier of each of the power converter circuits and out of the power combiner through output terminal 21.
  • a similar preferred embodiment of this type of power combiner could be constructed using the hysteretic input-regulating high- output impedance power converter circuit as shown schematically in Figure 2.
  • the circuits allocated to the various power sources are not complete power converter circuits but rather share one or more elements.
  • the circuits may be different or identical.
  • the circuit and the shared elements form a complete input-regulating high-output impedance power converter circuit. No more than one circuit is connected to the shared elements at any given time. Sharing certain elements results in a reduction in the number of components needed and the cost and size of the power combiner.
  • an inductor is a typical element and often the largest size component in a power converter circuit. Sharing an inductor can therefore enable the use of a higher quality inductor to improve the efficiency of the power combiner and still reduce overall size and cost.
  • the power combiner further comprises a controller that periodically cycles through and opens and closes all the switches and processes each of the power sources, wherein no more than one switch is closed at any given time.
  • circuits are identical with each circuit comprising a capacitor and a switch and with the shared elements comprising an inductor and an output rectifier.
  • Circuit 31 A is comprised of input terminals 32A and 33A, capacitor 34A and switch 35A.
  • Power source PSA is connected to circuit 31 A using first input terminal 32A and second input terminal 33A.
  • Capacitor 34A has a first terminal connected to the first input terminal 32A and a second terminal connected to the second input terminal 33A.
  • Switch 35A has a first terminal connected to the first terminal of the capacitor 34A and a second terminal.
  • Circuit 31 B is comprised of input terminals 32B and 33B, capacitor 34B and switch 35B.
  • Power source PSB is connected to circuit 31 B using first input terminal 32B and second input terminal 33B.
  • Capacitor 34B has a first terminal connected to the first input terminal 32B and a second terminal connected to the second input terminal 33B.
  • Switch 35B has a first terminal connected to the first terminal of the capacitor 34B and a second terminal.
  • Also shown in Figure 5 are the shared elements, an inductor 36 and an output rectifier in the form of diode 37.
  • Inductor 36 has a first terminal connected to the second terminal of all the switches, i.e., in the power combiner shown in Figure 5, switches 35A and 35B, and a second terminal connected to the second terminal of all the capacitors, i.e., in the power combiner shown in Figure 5, capacitors 34A and 34B.
  • the diode 37 has a first terminal connected to the second terminal of inductor 36 and a second terminal that is connected to the first output terminal 38.
  • the second output terminal 39 is connected to the first terminal of the inductor.
  • a controller 40 periodically cycles through and opens and closes all the switches thereby processing all the power sources.
  • switch 35A When processing power source PSA, switch 35A is closed and all other switches are open, i.e., in the power combiner shown in Figure 5 switch 35B is open.
  • the energy stored in capacitor 34A is then transferred to the shared inductor 36.
  • Switch 35A is then opened and all other switches are kept open. Therefore no more than one switch is ever closed at any time.
  • the voltage across the inductor builds up until it causes the diode 37 to turn on and conduct current into the common output terminal 38.
  • the common output terminal 38 can be directly connected to and charging a rechargeable battery.
  • the power combiner produces saw-tooth current pulses which are ideal for pulse-charging a battery. If it is desired to not use the current pulses directly, the pulses can be easily filtered to DC by using a capacitor to allow conventional methods of charging.
  • the second terminals of all the switches 35A and 35B 1 the first terminal of the inductor 36 and the second output terminal 39 are all connected to ground.
  • the positions of the capacitors and the switches can be interchanged in the circuits so that, in the case of circuit 31 A, the first terminal of capacitor 34A is connected to the first input terminal 32A and to ground and the second terminal of capacitor 34A is connected to the second input terminal 33A and to one terminal of switch 35A.
  • the other terminal of switch 35A is connected to the second terminal of the inductor 36.
  • the configuration shown in Figure 5 is preferred since in that configuration the switching voltages are referenced to ground.
  • the switch cycling process can be carried out at a fixed frequency. In more sophisticated modes, cycling can be carried out with varying times spent at different power sources, e.g., at different solar cells.
  • the controller can sense the voltage of each storage capacitor, it can skip over solar cells that have little or no stored energy and it can spend more time "draining" the storage capacitors of solar cells that have accumulated more stored energy.
  • the power combiner shown in Figure 5 requires n storage capacitors, n switches, one inductor, one diode and one controller chip.
  • the controller is implemented as a single silicon chip that also includes all the switches used in the circuits.
  • This implementation would require n storage capacitors, the controller chip with the switches, one inductor and one diode for operation with n power sources.
  • the only component that scales in number with the number of power sources is the storage capacitor.
  • the shared-element architecture is smaller and less costly than that in which a complete power converter is dedicated to each power source.
  • the circuit elements for the power combiner can take the same various forms indicated previously for the circuit elements of the power converter.
  • the power combiner of the invention can be embedded in a photoelectric generating module.
  • the power combiner is useful in combining the power from an array of solar cells on a solar panel and can be an integral part of and embedded in each panel. The panels can then connect to one another both mechanically and electrically.
  • input-regulating has its usual meaning, i.e., the power converter senses the input voltage and maintains it at a certain level.
  • 'high output impedance has its usual meaning, i.e., the output looks like a current source.
  • Example 1 This Example demonstrates the operation of one embodiment of the power converter of the invention.
  • the diode D3 was a ZLLS400 rectifier (Zetex Semiconductors pic, Chadderton, Oldham, UK).
  • the comparator was a LMV7271 comparator (National Semiconductor, Santa Clara, CA) and the bipolar transistor used in the switch was a ZXTN23015CPH bipolar transistor (Zetex Semiconductors pic, Chadderton, Oldham, UK).
  • the power source was modeled as a current source of 2mA and the input voltage to the power converter was 0.32 volts. The simulated efficiency of the power converter was 75%.
  • Example 2 This Example demonstrates the construction and operation of an embodiment of the power converter of the invention shown in Figure 6 which is similar to that as simulated in Example 1.
  • U1 was a LMV7271 comparator (National Semiconductor, Santa Clara, CA) and Q1 was a Si5856DC MOSFET + Schottky diode (Vishay Semiconductor, Vishay Intertechnology, Inc., Malvern, PA).
  • the power source was a pair of parallel-connected monocrystalline silicon solar cells. Best observed efficiency under real solar conditions was about 80%.
  • This Example demonstrates the power combiner for an embodiment in which identical circuits are allocated to the two power sources and the circuits are complete hysteretic input-regulating power converter circuits.
  • the circuit diagram is shown in Figure 7. Operation of this power combiner circuit was simulated using SIMETRIX circuit simulation software (Catena Software LTD, Berkshire, UK). The two power sources were simulated with output powers of 640 mV and 2 V. The efficiency of the power combiner was found to be 83%.
  • This Example demonstrates the power combiner for an embodiment in which the identical circuits allocated to the two power sources are not complete power converter circuits but rather share elements.
  • the shared elements are an inductor and a diode.
  • the circuit diagram for the power combiner is shown in Figure 8. Operation of this power combiner circuit was simulated using SIMETRIX circuit simulation software (Catena Software LTD, Berkshire, UK). The input power of the two power sources was 8.737 mW and 8.6 mW. The output waveforms are shown in Figure 9. The output power was 14.86 mW and the efficiency of the power combiner was 87.5%.
  • This Example demonstrates the power combiner for an embodiment in which the identical circuits allocated to the two power sources are not complete power converter circuits but rather share elements.
  • the circuit is identical to the circuit used in Example 4 except that the shared elements are an inductor and a synchronous rectifier.
  • the circuit diagram for the power combiner is shown in Figure 10. Operation of this power combiner circuit was simulated using SIMETRIX circuit simulation software (Catena Software LTD, Berkshire, UK). The efficiency of the power combiner was 94.1 % showing the advantage of using the synchronous rectifier in place of the diode.

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  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)
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  • Photovoltaic Devices (AREA)

Abstract

This invention relates to a hysteretic input-regulating high-output impedance power converter for converting the energy output of power-limited power sources such as solar cells to provide output current at voltages useful to operate electronics or charge batteries. This invention also relates to a power combiner that combines the output of multiple power sources into a single output. The power combiner is comprised of multiple circuits, one for each power source. These circuits are either complete input-regulating high-output impedance power converter circuits or, when connected to shared elements, form complete input-regulating high-output impedance power converter circuits. The power combiner can be used to combine the power from power sources that are alike or different.

Description

TITLE
POWER CONVERTER AND POWER COMBINER FOR POWER- LIMITED POWER SOURCES
This invention was made with Government support under Agreement W911 NF-05-9-0005 awarded by the Government. The Government has certain rights in the invention.
FIELD OF THE INVENTION
This invention relates to a power source power converter and to a power combiner that combines the output power of multiple power sources into a single output.
BACKGROUND OF THE INVENTION
Small power sources such as photovoltaic cells, and in particular solar cells, are being used to power portable devices or to charge a battery pack. The well-known boost chopper power converter circuit has been used in conjunction with such power sources in portable applications. This type of power converter takes input current at a low voltage, e.g., a single silicon solar cell has an output of about 0.5 volts, and produces an output current at a higher voltage that can be used to operate handheld electronics or charge a battery pack. When it is desired to use the power of multiple power sources the outputs of the individual sources have to be combined. Traditionally, the power sources such as like-type silicon solar cells have been connected in some series-parallel combination to provide the voltage and current outputs required for the particular application. For example, one type of solar cell battery charger connects the solar cells in series to approximate the battery voltage. The output is then fed into the battery through a diode. However, this architecture is inefficient and the rechargeable batteries quickly wear out. Another approach simulates the AC outlet that users can plug into with a solar cell powered equivalent. This architecture is inherently inefficient since the battery chargers incorporated in most consumer electronics are not designed for efficient operation with limited sources of power.
Recent solar cell architectures use multiple cells that efficiently absorb different portions of the solar spectrum and thereby achieve higher overall conversion efficiency than traditional solar cells using a single type of cell. The voltages of the different cells are regulated at specific temperature-compensated values to achieve maximum efficiency. Since the cells and their characteristics are not identical, the traditional approach of combining their output by connecting the cells in some series-parallel combination will not work and a different type of power combiner is needed.
Thus there is a continuing need for an efficient power converter and for an efficient power combiner, especially one that can combine the outputs of different types of photovoltaic cells. There is a particular need for such power converters and power combiners for operating portable electronic devices and charging batteries for such devices.
SUMMARY OF THE INVENTION
This invention provides a hysteretic input-regulating boost power converter for converting the power provided by a power source, the power converter comprising a hysteretic voltage comparator, wherein the power converter provides an output current at an output voltage that is greater than and not dependent on the input voltage.
In one embodiment the power converter has a circuit comprising:
(i) first and second input terminals for connection to a power source providing an input voltage;
(ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal; (iii) a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
(iv) a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
(v) an inductor having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch;
(vi) an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal; and
(vii) first and second output terminals, wherein the first output terminal is connected to the second terminal of the output rectifier and the second output terminal is connected to the second terminal of the switch.
In another embodiment the power converter has a circuit comprising:
(i) first and second input terminals for connection to a power source providing an input voltage; (ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal;
(iii) a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
(iv) a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
(v) a transformer with a primary winding having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch and a secondary winding having a first terminal and a second terminal;
(vi) an output rectifier having a first terminal connected to the first terminal of the transformer secondary winding and a second terminal; and
(vii) first and second output terminals, wherein the first output terminal is connected to the second terminal of the output rectifier and the second output terminal is connected to the second terminal of the transformer secondary winding.
This invention also provides a power combiner that combines the output power of multiple power sources into a single output. The power combiner comprises a parallel arrangement of circuits, wherein a different one of the circuits is allocated to each of the multiple power sources. Each of these circuits is a complete input-regulating high-output impedance power converter circuit or forms a complete input-regulating high-output impedance power converter circuit when connected to the one or more elements that these circuits share. When elements are shared, no more than one circuit is connected to the shared elements at any given time. The output power of these circuits is fed into a single output.
In one embodiment in which the circuits allocated to the various power sources are complete power converter circuits and are identical, the power combiner utilizes one embodiment of the power converter circuit of the invention, the power combiner comprising:
(a) a power converter circuit allocated to each of the power sources, each power converter circuit comprising:
(i) first and second input terminals for connection to the power source designated for the power converter circuit;
(ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal; (iii) a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal; (iv) a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
(v) an inductor having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch; and
(vi) an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal; and (b) an output having a first terminal connected to the second terminal of the output rectifier of each power converter circuit and a second terminal connected to the second terminal of the switch of each power converter circuit.
In another embodiment in which the circuits allocated to the various power sources are complete power converter circuits and are identical, the power combiner utilizes another embodiment of the power converter circuit of the invention, the power combiner comprising:
(a) a power converter circuit allocated to each of the power sources, each power converter circuit comprising: (i) first and second input terminals for connection to the power source designated for the power converter circuit;
(ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal;
(iii) a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
(iv) a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
(v) a transformer with a primary winding having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch and a secondary winding having a first terminal and a second terminal; (vi) an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal; and
(b) an output having a first terminal connected to the second terminal of the output rectifier of each power converter circuit and a second terminal connected to the second terminal of the transformer secondary winding of each power converter circuit.
In an embodiment in which the circuits allocated to the various power sources share one or more elements to form power converter circuits, the power combiner comprises:
(a) a parallel arrangement of circuits, wherein a different one of the circuits is allocated to each of the multiple power sources; (b) one or more shared elements that are shared by the circuits, wherein when a circuit is connected to the one or more shared elements the circuit and the shared elements form a complete input-regulating high-output impedence power converter circuit; and (c) a single output;
In one such embodiment in which the circuits allocated to the various power sources share one or more elements to form power converter circuits, the power combiner comprises:
(a) a parallel arrangement of circuits, wherein a different one of the circuits is allocated to each of the multiple power sources, each said circuit comprising:
(i) a first input terminal and a second input terminal for connection to the power source designated for the circuit: (ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal;
(iii) a switch having a first terminal connected to the first terminal of the capacitor and a second terminal;
(b) an inductor having a first terminal connected to the second terminal of the switch in each said circuit and a second terminal connected to the second terminal of the capacitor in each said circuit; (c) an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal;
(d) an output having a first terminal connected to the second terminal of the output rectifier and a second terminal connected to the first terminal of the inductor; and (e) a controller that periodically cycles through and opens and closes all the switches and processes each of the power sources, wherein no more than one switch is closed at any given time.
The power converter and power combiner are useful with power sources such as fuel cells and photovoltaic cells, particularly solar cells, i.e., with power sources that have power-limited outputs. The power combiner is useful when the solar cell unit is comprised of multiple cells and especially when the multiple cells are of different types.
BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic diagram of one embodiment of the power converter of the invention.
Figure 2 is a schematic diagram of another embodiment of the power converter of the invention. Figure 3 is a circuit diagram for the embodiment of the power converter used in Example 1.
Figure 4 is a schematic diagram of an embodiment of the power combiner of the invention in which the circuits allocated to each of the power sources are complete hysteretic input-regulating high-output impedance power converter circuits.
Figure 5 is a schematic diagram of an embodiment of the power combiner of the invention in which the circuits allocated to each of the power sources share elements and when connected to the shared elements form complete input-regulating high-output impedance power converter circuits
Figure 6 is a circuit diagram for the embodiment of the power converter used in Example 2.
Figure 7 is a circuit diagram of the embodiment of the power combiner of the invention used in Example 3. The circuits allocated to each of the power sources are complete hysteretic input-regulating high- output impedance power converter circuit.
Figure 8 is a circuit diagram of one embodiment of the power combiner of the invention used in Example 4. The circuits allocated to each of the power sources share elements and when each is connected to the shared elements each forms a complete input-regulating high-output impedance power converter circuit.
Figure 9 shows the charging characteristics obtained by simulation of the circuit shown in Figure 8. Figure 10 is a circuit diagram of another embodiment of the power combiner of the invention used in Example 5. The circuits allocated to each of the power sources share elements and when connected to the shared elements form a complete input-regulating high-output impedance power converter circuits. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The power converter of the invention can be used in conjunction with a power-limited power source to provide an output voltage sufficient to operate handheld electronics or charge a battery pack. The power converter uses hysteresis, input-side regulation and self-induced oscillation to reduce parts count and power consumption and is a hysteretic input-regulating high-output impedance power converter.
One embodiment of the power converter circuit is shown in the schematic drawing of Figure 1. The power converter has a circuit 10 comprising the following elements. A first input terminal 11 and a second input terminal 12 provide for connection to a power source PS. A capacitor 13 has a first terminal connected to the first input terminal and a second terminal connected to the second input terminal. A hysteretic voltage comparator 14 has a first terminal connected to the first terminal of the capacitor, a second terminal 15 for inputting a reference voltage and a third terminal that is an output terminal. Switch 16 has a first terminal connected to the third terminal of the hysteretic voltage comparator 14 to thereby receive the output signal from the hysteretic voltage comparator 14. The output signal serves to open and close the switch 16. The switch 16 also has a second terminal connected to the second terminal of the capacitor and a third terminal. An inductor 17 has a first terminal connected to the first terminal of the capacitor 13 and a second terminal connected to the third terminal of the switch 16. An output rectifier 18 has a first terminal connected to the second terminal of the inductor 17 and a second terminal connected to the first output terminal 19. The second output terminal 20 is connected to the second terminal of the switch 16. Preferably, the second input terminal, the second terminal of the capacitor, the second terminal of the switch and the second output terminal are all connected to ground. This power converter operates in the following fashion. The power source PS charges the capacitor 13 until the voltage on capacitor 13 exceeds the high threshold voltage of hysteretic voltage comparator 14. This causes hysteretic voltage comparator 14 to close switch 16. An increasing current flows from capacitor 13 through the inductor 17 and switch 16 to ground, discharging the energy from capacitor 13 and storing it in the magnetic field of inductor 17. When the voltage on capacitor 13 has fallen to the low threshold voltage of hysteretic voltage comparator 14, the switch 16 is opened. The energy stored in the inductor 17 acts as a current source and raises the voltage at output rectifier 18 until it surpasses the level at the output terminal 19 Current flows through the output rectifier 18 and out of the converter through output terminal 19. When the energy stored in inductor 17 is exhausted, the rectifier ceases conduction and the power converter is returned to its original state. The cycle repeats when capacitor 13 is again charged to a sufficient level. The voltage at the output terminal is greater than the voltage of the power source at the input terminal.
Another embodiment of the power converter circuit is shown in the schematic drawing of Figure 2. Comparable elements are labeled with the same numbers used for the schematic drawing of Figure 1. Elements 11- 16 all are in the same configuration as shown in Figure 1. However, in this embodiment a flyback converter is used. Transformer 17F has a primary winding having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch. The secondary winding has a first terminal connected to the first terminal of output rectifier 18 and a second terminal connected to the output terminal 20. The second terminal of the output rectifier is connected to the first output terminal 19. When the output rectifier is a diode as indicated in Figure 2, the diode can be "flipped", i.e., have its N side connected to the terminal.
The circuit elements can take various forms. The capacitor 13 can be a single capacitor or two or more capacitors arranged in parallel and/or series configurations. The hysteretic voltage comparator 14 can be comprised of a commercially available externally referenced integrated circuit comparator or a self-referencing circuit. The switch 16 can be comprised of a bipolar transistor or a field effect transistor and resistors to set the high and low switching threshold voltages. The inductor 17 can be a single inductor or coupled inductors to provide further flexibility in operational range. The output rectifier 18 can be in form of a diode or, if pulse outputs are not desired, the pulses can be easily filtered to DC by using a capacitor in conjunction with the diode. Alternatively, a synchronous rectifier structure can be used in place of the diode. Other forms for these elements will be apparent to those skilled in the art. The power converter does not require a programmed controller; however, the use of such a controller is not precluded. A single controller circuit can be used to operate multiple power converters, e.g., the multiple power converters in the power combiner. The hysteretic input-regulating boost power converter power of the invention has many advantages. It has a wide operating range, high efficiency, simple and low-cost implementation. It makes efficient use of the inductor, which is one of the largest components in the circuit, by its inherently fixed-on-time switching set by the inductor-capacitor (L-C) time constant and hysteresis voltage.
The power consumption of the power converter is in the microwatt range and that makes it efficient for use with power sources such as solar cells that produce only a few milliwatts of power. It can also optimally match its power source by dynamically adjusting the hysteretic voltage comparator's internal or external reference voltage to achieve maximum power point (MPP) tracking of solar and other photovoltaic cells. MPP is the point at which the current and voltage output of these cells are jointly maximized, i.e., the cell is operating at maximum efficiency. For these cells temperature tracking of the cell voltage is very important in order to achieve optimum power output and can be achieved by using temperature-variable resistors or diodes in the reference circuit or an externally-derived varying reference voltage. When a controller is used to operate one or more power converters it does so such that the photovoltaic cell power source of each power converter is essentially performing at its MPP. The power converter's output is flexible. There is no feed back to regulate its impedance so at the output terminal it appears to be an inductor/diode series combination with naturally high impedance. As a result it is possible to track the output voltage across a wide range without losing power. The power converter produces saw-tooth current pulses which are ideal for pulse-charging a battery. The size and chemistry of the battery has no effect on the power converter's efficiency. Pulse-charging of batteries is known to improve the batteries lifetimes. If it is desired to not use the current pulses directly, the pulses can be easily filtered to DC by using a capacitor to allow conventional methods of charging. The components used in one embodiment of the power converter shown schematically in Figure 1 are shown in the circuit diagram of Figure 3. The comparable elements of Figure 3 are labeled with the same numbers as used in Figure 1 and the circuit components making up the elements are indicated. Capacitor 13 consists of capacitor C5. The comparator 14 is implemented in this embodiment with a 1.8 V low power LMV7271 comparator (National Semiconductor, Santa Clara, CA), resistors R11 , R12 and R13 and capacitor C14. The five terminals of the LMV7271 comparator are indicated in Figure 2 using the manufacturer's terminal numbers. The VDD input provides the power needed to operate the comparator. The high and low voltage switching thresholds are set by the resistors R11 , R12 and R13 and the input voltage reference VREF that is applied to terminal 15. The switch 16 is implemented with a ZXTN23015CPH bipolar transistor BT (Zetex Semiconductors pic, Chadderton, Oldham, UK), its base-feed network of capacitor C9 and resistor R10 and the anti-electromagnetic interference (EMI) network of capacitor C7 and resistor R8. The inductor 17 is inductor L4. The output rectifier is implemented with a low-leakage Schottky diode D3 and filter capacitor C15. This embodiment has only 14 or 15 components depending on whether the filter capacitor C15 is used. The majority of these are small resistors and capacitors. The invention also provides a power combiner that combines the output power of multiple power sources into a single output with minimal loss. The power combiner can be used to provide the single output with the power from one or more power sources. The power combiner can be used to combine the power from power sources that are alike or different. For example, when used with multiple like-type photovoltaic cells the power combiner can be used to combine the power from individual cells or from parallel or series combinations of these cells. The power combiner of the invention is especially useful when combining the outputs of individual power sources that are not alike, e.g., when combining the power from multiple cells of a solar cell wherein the cells are of different types. The various cells can be chosen so that each converts different ranges of the solar spectrum and thereby provides more efficiency. The voltage across each cell is regulated at a particular temperature-compensated value to provide optimum operation of that cell. The power combiner circuit operates with the same energy conversion efficiency regardless of the number or types of cells attached to its inputs. The power combiner of the invention is simple, efficient and not costly to produce.
The power combiner of the invention combines the output power of multiple power sources and is comprised of multiple circuits, wherein a different one of the circuits is allocated to each of the multiple power sources. For example, if there are n power sources there will be n circuits, one for each of the power sources. The multiple circuits can be different or identical. As used herein, "identical circuits" indicates that the circuits have the same components. Even though the components are the same, their values and the operation of the circuits can differ, e.g., the hysteretic voltage comparators internal or external reference voltages can be different in order to achieve MPP tracking.
In one type of embodiment, each circuit is a complete input- regulating high-output impedance power converter circuit. The high-output impedance of the power converter of the invention enables the direct connection of multiple power converters in parallel to add their power. The power combiner is further comprised of a single output . In one preferred embodiment, each circuit is a complete hysteretic input-regulating high- output impedance power converter circuit. One such embodiment is shown schematically in Figure 4. It uses identical circuits, each with a hysteretic input-regulating high-output impedance power converter circuit as shown schematically in Figure 1. For simplicity, the power combiner 25 is shown with only two power sources and two power converter circuits, but any number can be used. Comparable circuit elements are labeled with the same numbers used for the schematic drawing of Figure 1. In each circuit the second input terminal 12A or 12B, the second terminal of the capacitor and the second terminal of the switch are all connected to ground. The second output terminal 22 is accordingly connected to ground. Power source PSA is connected to power converter circuit 10A using input terminal 11A and ground terminal 12A. The various circuit elements capacitor 13A, voltage comparator 14A with terminal 15A for inputting a reference voltage, switch 16A, inductor 17A and output rectifier 18A all are connected as described previously for the power converter of the invention and the circuit 10A operates in the manner described previously. Power source PSB is connected to power converter circuit 10B using input terminal 11 B and ground terminal 12B. Power converter circuit 10B has the same elements, i.e., 13B through 18B,as power converter circuit 10A . They all are also connected as described previously for the power converter of the invention and the circuit 10B operates in the manner described previously. The second terminal of the output rectifier of each power converter circuit is connected to the common output terminal 21 and current flows out of the output rectifier of each of the power converter circuits and out of the power combiner through output terminal 21. A similar preferred embodiment of this type of power combiner could be constructed using the hysteretic input-regulating high- output impedance power converter circuit as shown schematically in Figure 2.
In another type of preferred power combiner embodiment, the circuits allocated to the various power sources are not complete power converter circuits but rather share one or more elements. The circuits may be different or identical. When a circuit is connected to the one or more shared elements, the circuit and the shared elements form a complete input-regulating high-output impedance power converter circuit. No more than one circuit is connected to the shared elements at any given time. Sharing certain elements results in a reduction in the number of components needed and the cost and size of the power combiner. For example, an inductor is a typical element and often the largest size component in a power converter circuit. Sharing an inductor can therefore enable the use of a higher quality inductor to improve the efficiency of the power combiner and still reduce overall size and cost.
The power combiner further comprises a controller that periodically cycles through and opens and closes all the switches and processes each of the power sources, wherein no more than one switch is closed at any given time.
In one such embodiment the circuits are identical with each circuit comprising a capacitor and a switch and with the shared elements comprising an inductor and an output rectifier.
A schematic diagram of one such embodiment of the power combiner architecture in which elements are shared is shown in Figure 5. For simplicity, the power combiner 30 is shown with only two power sources PSA and PSB, but the power from any number of power sources can be combined. Circuit 31 A is comprised of input terminals 32A and 33A, capacitor 34A and switch 35A. Power source PSA is connected to circuit 31 A using first input terminal 32A and second input terminal 33A. Capacitor 34A has a first terminal connected to the first input terminal 32A and a second terminal connected to the second input terminal 33A. Switch 35A has a first terminal connected to the first terminal of the capacitor 34A and a second terminal. Circuit 31 B is comprised of input terminals 32B and 33B, capacitor 34B and switch 35B. Power source PSB is connected to circuit 31 B using first input terminal 32B and second input terminal 33B. Capacitor 34B has a first terminal connected to the first input terminal 32B and a second terminal connected to the second input terminal 33B. Switch 35B has a first terminal connected to the first terminal of the capacitor 34B and a second terminal. Also shown in Figure 5 are the shared elements, an inductor 36 and an output rectifier in the form of diode 37. Inductor 36 has a first terminal connected to the second terminal of all the switches, i.e., in the power combiner shown in Figure 5, switches 35A and 35B, and a second terminal connected to the second terminal of all the capacitors, i.e., in the power combiner shown in Figure 5, capacitors 34A and 34B. The diode 37 has a first terminal connected to the second terminal of inductor 36 and a second terminal that is connected to the first output terminal 38. The second output terminal 39 is connected to the first terminal of the inductor. A controller 40 periodically cycles through and opens and closes all the switches thereby processing all the power sources. When processing power source PSA, switch 35A is closed and all other switches are open, i.e., in the power combiner shown in Figure 5 switch 35B is open. The energy stored in capacitor 34A is then transferred to the shared inductor 36. Switch 35A is then opened and all other switches are kept open. Therefore no more than one switch is ever closed at any time. The voltage across the inductor builds up until it causes the diode 37 to turn on and conduct current into the common output terminal 38. The common output terminal 38 can be directly connected to and charging a rechargeable battery. The power combiner produces saw-tooth current pulses which are ideal for pulse-charging a battery. If it is desired to not use the current pulses directly, the pulses can be easily filtered to DC by using a capacitor to allow conventional methods of charging. In one preferred embodiment, the second terminals of all the switches 35A and 35B1 the first terminal of the inductor 36 and the second output terminal 39 are all connected to ground. The positions of the capacitors and the switches can be interchanged in the circuits so that, in the case of circuit 31 A, the first terminal of capacitor 34A is connected to the first input terminal 32A and to ground and the second terminal of capacitor 34A is connected to the second input terminal 33A and to one terminal of switch 35A. The other terminal of switch 35A is connected to the second terminal of the inductor 36. However, the configuration shown in Figure 5 is preferred since in that configuration the switching voltages are referenced to ground.
In a simple mode, the switch cycling process can be carried out at a fixed frequency. In more sophisticated modes, cycling can be carried out with varying times spent at different power sources, e.g., at different solar cells. If the controller can sense the voltage of each storage capacitor, it can skip over solar cells that have little or no stored energy and it can spend more time "draining" the storage capacitors of solar cells that have accumulated more stored energy. With n power sources, the power combiner shown in Figure 5 requires n storage capacitors, n switches, one inductor, one diode and one controller chip. In one embodiment the controller is implemented as a single silicon chip that also includes all the switches used in the circuits. This implementation would require n storage capacitors, the controller chip with the switches, one inductor and one diode for operation with n power sources. The only component that scales in number with the number of power sources is the storage capacitor. For a large number of power sources the shared-element architecture is smaller and less costly than that in which a complete power converter is dedicated to each power source. The circuit elements for the power combiner can take the same various forms indicated previously for the circuit elements of the power converter.
Multiple electronic devices that use the charger architecture of either the power converter of the invention or the power combiner of the invention can be connected together with conventional wiring to share power from the power converter or the power combiner. As long as one or more of the devices are equipped with solar cells and a power converter or a power combiner, all the connected devices will be charged. If more than one of the devices are equipped with solar cells and power converters or power combiners, the combined power of all the devices so equipped can be directed to charging the batteries of the devices that need charging.
The power combiner of the invention can be embedded in a photoelectric generating module. For example, the power combiner is useful in combining the power from an array of solar cells on a solar panel and can be an integral part of and embedded in each panel. The panels can then connect to one another both mechanically and electrically.
As used herein, "input-regulating" has its usual meaning, i.e., the power converter senses the input voltage and maintains it at a certain level.
As used herein, 'high output impedance" has its usual meaning, i.e., the output looks like a current source.
EXAMPLES
Example 1 This Example demonstrates the operation of one embodiment of the power converter of the invention. The circuit diagram of this embodiment is shown in Figure 3. Operation of this power converter circuit was simulated using SIMETRIX circuit simulation software (Catena Software LTD, Berkshire, UK). The components used were C5 = 15OuF, C7 = 30OpF, C9 = 10OpF, C14 = 0.47uF, R8 = 1 kΩ, R10 = 750 Ω, R11 = 47 kΩ , R12 = 68 kΩ, R13 = 3.3 MΩ, and L4 = 10OuH. The diode D3 was a ZLLS400 rectifier (Zetex Semiconductors pic, Chadderton, Oldham, UK). As indicated above, the comparator was a LMV7271 comparator (National Semiconductor, Santa Clara, CA) and the bipolar transistor used in the switch was a ZXTN23015CPH bipolar transistor (Zetex Semiconductors pic, Chadderton, Oldham, UK). The power source was modeled as a current source of 2mA and the input voltage to the power converter was 0.32 volts. The simulated efficiency of the power converter was 75%.
Example 2 This Example demonstrates the construction and operation of an embodiment of the power converter of the invention shown in Figure 6 which is similar to that as simulated in Example 1. The components used were C1 = 8OuF, C2=10uF, C3=10uF, C4=300pF, R1=200 Ω, R2=2 MΩ , R3=100 kΩ, R4 = not present, R5=200Ω , R6= 0.5Ω R7= 1 QΩ L1 = 20 uH, Q2=NST3946DVX6T1 dual bipolar transistor (ON Semiconductor). U1 was a LMV7271 comparator (National Semiconductor, Santa Clara, CA) and Q1 was a Si5856DC MOSFET + Schottky diode (Vishay Semiconductor, Vishay Intertechnology, Inc., Malvern, PA). The power source was a pair of parallel-connected monocrystalline silicon solar cells. Best observed efficiency under real solar conditions was about 80%.
Example 3
This Example demonstrates the power combiner for an embodiment in which identical circuits are allocated to the two power sources and the circuits are complete hysteretic input-regulating power converter circuits. The circuit diagram is shown in Figure 7. Operation of this power combiner circuit was simulated using SIMETRIX circuit simulation software (Catena Software LTD, Berkshire, UK). The two power sources were simulated with output powers of 640 mV and 2 V. The efficiency of the power combiner was found to be 83%. Example 4
This Example demonstrates the power combiner for an embodiment in which the identical circuits allocated to the two power sources are not complete power converter circuits but rather share elements. The shared elements are an inductor and a diode. The circuit diagram for the power combiner is shown in Figure 8. Operation of this power combiner circuit was simulated using SIMETRIX circuit simulation software (Catena Software LTD, Berkshire, UK). The input power of the two power sources was 8.737 mW and 8.6 mW. The output waveforms are shown in Figure 9. The output power was 14.86 mW and the efficiency of the power combiner was 87.5%.
Example 5
This Example demonstrates the power combiner for an embodiment in which the identical circuits allocated to the two power sources are not complete power converter circuits but rather share elements. The circuit is identical to the circuit used in Example 4 except that the shared elements are an inductor and a synchronous rectifier. The circuit diagram for the power combiner is shown in Figure 10. Operation of this power combiner circuit was simulated using SIMETRIX circuit simulation software (Catena Software LTD, Berkshire, UK). The efficiency of the power combiner was 94.1 % showing the advantage of using the synchronous rectifier in place of the diode.

Claims

CLAIMSWhat is claimed is:
1. A power converter for converting the power provided by a power source, wherein the power converter is a hysteretic input-regulating high-output impedance power converter and provides an output current at an output voltage that is greater than and not dependent on the input voltage.
2. The power converter of claim 1 , said power converter comprising a hysteretic voltage comparator
3. The power converter of claim 2, said power converter having a circuit comprising:
(i) first and second input terminals for connection to a power source providing an input voltage;
(ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal;
(iii) a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
(iv) a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
(v) an inductor having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch;
(vi) an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal; and
(vii) first and second output terminals, wherein the first output terminal is connected to the second terminal of the output rectifier and the second output terminal is connected to the second terminal of the switch.
4. The power converter of claim 3, wherein the output rectifier is a diode or a synchronous rectifier structure.
5. The power converter of claim 4, wherein the output rectifier is further comprised of a capacitor having a first terminal connected to the second terminal of the output rectifier and a second terminal connected to the second terminal of the switch.
6. The power converter of claim 3, wherein the second input terminal, the second terminal of the capacitor, the second terminal of the switch and the second output terminal are all connected to ground.
7 The power converter of claim 2, said power converter having a circuit comprising:
(i) first and second input terminals for connection to a power source providing an input voltage;
(ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal;
(iii) a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
(iv) a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
(v) a transformer with a primary winding having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch and a secondary winding having a first terminal and a second terminal;
(vi) an output rectifier having a first terminal connected to the first terminal of the transformer secondary winding and a second terminal; and
(vii) first and second output terminals, wherein the first output terminal is connected to the second terminal of the output rectifier and the second output terminal is connected to the second terminal of the transformer secondary winding.
8. The power converter of claim 7, wherein the output rectifier is a diode or a synchronous rectifier structure.
9. The power converter of claim 8, wherein the output rectifier is further comprised of a capacitor having one terminal connected to the second terminal of the output rectifier and a second terminal connected to the second terminal of the switch.
10. The power converter of claim 7, wherein the second input terminal, the second terminal of the capacitor, the second terminal of the switch and the second output terminal are all connected to ground.
11. A power combiner that combines the output power of multiple power sources into a single output, said power combiner comprising a parallel arrangement of circuits, wherein a different one of the circuits is allocated to each of the multiple power sources and each of these circuits is a complete input-regulating high-output impedance power converter circuit or forms a complete input-regulating high-output impedance power converter circuit when connected to one or more shared elements that these circuits share.
12. The power combiner of claim 11 , wherein each of said circuits is a complete input-regulating high-output impedance power converter circuit.
13. The power combiner of claim 12, further comprising a controller to operate the power converter circuits
14. The power combiner of claim 12, wherein each of said circuits is a complete hysteretic input-regulating high-output impedance power converter circuit comprising a hysteretic voltage comparator.
15. The power combiner of claim 14, said power combiner comprising:
(a) a power converter circuit allocated to each of the power sources, each power converter circuit comprising:
(i) first and second input terminals for connection to the power source designated for the power converter circuit;
(ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal;
(iii) a hysteretic voltage comparator having at least three terminals, wherein a first terminal is an input terminal connected to the first terminal of the capacitor, a second terminal is an input terminal for inputting a reference voltage and a third terminal is an output terminal;
(iv) a switch having a first terminal connected to the third terminal of the hysteretic voltage comparator to thereby receive the output signal from the hysteretic voltage comparator, a second terminal connected to the second terminal of the capacitor and a third terminal, whereby the output signal from the hysteretic voltage comparator serves to open and close the switch such that when the voltage on the capacitor exceeds the high threshold voltage of the hysteretic voltage comparator the switch is closed and when the voltage on the capacitor decreases to the low threshold voltage of the hysteretic voltage comparator the switch is open;
(v) an inductor having a first terminal connected to the first terminal of the capacitor and a second terminal connected to the third terminal of the switch; and
(vi) an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal; and
(b) an output having a first terminal connected to the second terminal of the output rectifier of each power converter circuit and a second terminal connected to the second terminal of the switch of each power converter circuit.
16. The power combiner of claim 15, wherein the output rectifier of each power converter circuit is a diode or a synchronous rectifier structure.
17. The power combiner of claim 16, further comprising a capacitor having a first terminal connected to the first terminal of the output and a second terminal connected to the second terminal of the output.
18. The power combiner of claim 15, wherein the second input terminal rectifier of each power converter circuit, the second terminal of the capacitor rectifier of each power converter circuit, the second terminal of the switch rectifier of each power converter circuit and the second output terminal are all connected to ground.
19. The power combiner of claim 11 , wherein each of said circuits, when connected to the one or more shared elements, forms a complete input-regulating high-output impedance power converter circuit and wherein no more than one circuit is connected to the one or more shared elements at any given time.
20. The power combiner of claim 19, wherein said shared elements are an inductor and an output rectifier.
21. The power combiner of claim 20, each said circuit comprising a capacitor and a switch.
22. The power combiner of claim 19, further comprising a controller that periodically cycles through and connects and disconnects the circuits to the shared elements and thereby processes each of the power sources,.
23. The power combiner of claim 21 , further comprising a controller that periodically cycles through and connects and disconnects the circuits to the shared elements and thereby processes each of the power sources, wherein no more than one switch is closed at any given time.
24. The power combiner of claim 23, wherein each of said circuits comprises:
(i) a first input terminal and a second input terminal for connection to the power source designated for the circuit; (ii) a capacitor having a first terminal connected to the first input terminal and a second terminal connected to the second input terminal; and (iii) a switch having a first terminal connected to the first terminal of the capacitor and a second terminal; wherein the shared elements comprise: (a) an inductor having a first terminal connected to the second terminal of the switch in each said circuit and a second terminal connected to the second terminal of the capacitor in each said circuit;
(b) an output rectifier having a first terminal connected to the second terminal of the inductor and a second terminal, wherein the single output has a first terminal connected to the second terminal of the output rectifier and a second terminal connected to the first terminal of the inductor.
25. The power combiner of claim 24, wherein the second terminal of the switch in each said circuit, the first terminal of the inductor and the second terminal of the output are all connected to ground.
26. The power combiner of claim 24, wherein the output rectifier is a diode.or a synchronous rectifier structure.
27. The power combiner of claim 26, further comprising a capacitor having a first terminal connected to the output terminal and a second terminal connected to ground.
28. The power converter of claim 2, wherein the power source is a photovoltaic cell and the hysteretic voltage comparator has a reference voltage adjusted so that the photovoltaic cell is operating essentially at its maximum power point.
29 The power combiner of claim 13, wherein the power sources are photovoltaic cells and the controller adjusts operation of each photovoltaic cell such that it is is operating essentially at its maximum power point.
30. The power combiner of claim 22, wherein the power sources are photovoltaic cells and the controller adjusts operation of each photovoltaic cell such that it is is operating essentially at its maximum power point.
1. The power combiner of claim 23, wherein the controller and the switch from each circuit are contained in a silicon chip.
PCT/US2008/007334 2007-06-13 2008-06-12 Power converter and power combiner for power-limited power sources WO2008154031A2 (en)

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EP2158669A2 (en) 2010-03-03

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