Switching Circuits For Extracting Power From An Electric Power Source And Associated Methods

• US 20120043818A1
• Filed: 08/17/2011
• Published: 02/23/2012
• Est. Priority Date: 08/18/2010
• Status: Active Grant

• Current Assignee: Volterra Semiconductor Corporation (Analog Devices, Inc.)
• Original Assignee: Volterra Semiconductor Corporation (Analog Devices, Inc.)
• Inventors: McJimsey, Michael D., Jergovic, Ilija, Ikriannikov, Alexandr, Yao, Kaiwei, Lidsky, David B., Stratakos, Anthony J., Der Minassians, Artin, Zuniga, Marco A., Borisavljevic, Ana
• Granted Patent: US 8,872,384 B2
• Time in Patent Office: Days
• US Class Current: 307/77
• CPC Class Codes: H01L 2224/16225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/13091 Metal-Oxide-Semiconductor Field-Effect Transistor [MOSFET]
• CPC Class Codes: H02J 1/102 being switching converters H02J1/108, H02J1/12 take precedence
• CPC Class Codes: H02J 1/106 for load balancing, symmetrisation, or sharing
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H03K 17/102 in field-effect transistor switches
• CPC Class Codes: H03K 17/122 in field-effect transistor switches
• CPC Class Codes: H03K 17/145 in field-effect transistor switches
• CPC Class Codes: H03K 17/693 Switching arrangements with several input- or output-terminals, e.g. multiplexers, distributors logic circuits H03K19/00; code converters H03M5/00, H03M7/00
• CPC Class Codes: H03K 2217/0036 Means reducing energy consumption
• CPC Class Codes: H03K 2217/0054 Gating switches, e.g. pass gates
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

An electric power system includes N electric power sources and N switching circuits, where N in an integer greater than one. Each switching circuit includes an input port electrically coupled to a respective one of the N electric power sources, an output port, and a first switching device adapted to switch between its conductive and non-conductive states to transfer power from the input port to the output port. The output ports of the N switching circuits are electrically coupled in series and to a load to establish an output circuit. Each of the N switching circuits uses an interconnection inductance of the output circuit as a primary energy storage inductance of the switching circuit.

Claims

1. An electric power system, comprising:

N electric power sources, N being an integer greater than one;

N switching circuits, each switching circuit including an input port electrically coupled to a respective one of the N electric power sources, an output port, and a first switching device adapted to switch between its conductive and non-conductive states to transfer power from the input port to the output port, the output ports of the N switching circuits electrically coupled in series and to a load to establish an output circuit;

wherein each of the N switching circuits uses an interconnection inductance of the output circuit as a primary energy storage inductance of the switching circuit.

2. The electric power system of claim 1, each of the N electric power sources being a photovoltaic device.

3. The electric power system of claim 2, at least one of the photovoltaic devices being a plurality of electrically coupled photovoltaic cells.

4. The electric power system of claim 2, at least one of the photovoltaic devices being a junction of a multi junction photovoltaic cell.

5. The electric power system of claim 2, each of the N switching circuits further including a controller adapted to control switching of the first switching device of the switching circuit to at least substantially maximize an amount of electric power extracted from a respective photovoltaic device electrically coupled to the input port of the switching circuit.

6. The electric power system of claim 5, wherein for each of the N switching circuits:

the input port includes a first and second input terminal;

the first switching device is electrically coupled between the first input terminal and an intermediate switching node; and

the switching circuit further includes a device selected from the group consisting of a diode and a second switching device electrically coupled between the second input terminal and the intermediate switching node, the device adapted to provide a path for current through the output circuit when the first switching device is in its non-conductive state.

7. The electric power system of claim 5, wherein the controller of each of the N switching circuits is adapted to at least substantially maximize an average value of a voltage at the intermediate switching node of the switching circuit.

8. The electric power system of claim 5, wherein the controller of each of the N switching circuits is adapted to repeatedly sample an average value of a voltage at the intermediate switching node of the switching circuit and control switching of the first switching device of the switching circuit at least partly based on at least two successive samples of the average value of the voltage at the intermediate switching node.

9. The electric power system of claim 8, wherein a starting time of the controller of each of the N switching circuits is loosely controlled.

10. The electric power system of claim 8, wherein a starting time of the controller of at least one of the N switching circuits varies from a starting time of the controller of the other N−

1 switching circuits.

11. The electric power system of claim 8, wherein the controller of at least one of the N switching circuits is adapted to sample the average value of the voltage at the switching node of the switching circuit at a different rate than the controller of the other N−

1 switching circuits.

12. The electric power system of claim 8, wherein for each of the N switching circuits, the controller is adapted to repeatedly sample the average value of the voltage at the intermediate switching node at a frequency that is less than a frequency at which the first switching device switches between its conductive and non-conductive states.

13. The electric power system of claim 8, wherein for each of the N switching circuits, the controller is adapted to repeatedly sample the average value of the voltage at the intermediate switching node at a frequency that is less than one tenth of the frequency at which the first switching device switches between its conductive and non-conductive states.

14. The electric power system of claim 8, wherein for each of the N switching circuits, the controller is adapted to repeatedly sample the average value of the voltage at the intermediate switching node at a frequency that is sufficiently slow such that transient voltage excursions on the output port settle between successive samples of the average value of the voltage at the intermediate switching node.

15. The electric power system of claim 8, wherein for each switching circuit, the controller is configured to repeatedly sample the average value of the voltage at the intermediate switching node at a sampling rate that is sufficiently fast such that Δ

I/I_R is less than Δ

D/D_R, wherein;

Δ

I is a change in current out of the output port between first and second successive samples of the average value of the voltage at the intermediate switching node, the second sample occurring after the first sample;

I_R=I_max−

I_min;

I_max is a maximum expected value of current out of the output port;

I_min is a minimum expected value of current out of the output port;

Δ

D is a change in duty cycle of the first switching device between the first and second successive samples of the average value of the voltage at the intermediate switching node; and

D_R is a difference between a maximum expected duty cycle and a minimum expected duty cycle of the first switching device.

16. The electric power system of claim 8, wherein for each switching circuit, the controller is configured to repeatedly sample the average value of the voltage at the intermediate switching node at a sampling rate that is sufficiently fast such that a percentage change in current out of the output port is less than a percentage change in duty cycle of the first switching device between successive samples of the average value of the voltage at the intermediate switching node.

17. The electric power system of claim 5, each of photovoltaic devices comprising a plurality of photovoltaic cells electrically coupled in series.

18. The electric power system of claim 5, each of the photovoltaic devices being a photovoltaic sub-module of a photovoltaic panel, each photovoltaic sub-module including a plurality of photovoltaic cells electrically coupled in series.

19. The electric power system of claim 5, at least one of the photovoltaic devices comprising a plurality of electrically coupled photovoltaic cells.

20. The electric power system of claim 5, at least one of the photovoltaic devices being a junction of a multi junction photovoltaic cell.

21. The electric power system of claim 2, wherein a frequency at which the first switching device of each of the N switching circuit switches between its conductive and non-conductive states is loosely controlled.

22. The electric power system of claim 2, wherein a switching frequency of each first switching device varies from a switching frequency of each other first switching device.

23. The electric power system of claim 2, wherein each of the N switching circuits is configured such that each first switching device switches out of phase with each other first switching device.

24. The electric power system of claim 2, further comprising a diode electrically coupled in series with the output circuit.

25. The electric power system of claim 2, wherein for each switching circuit, the output port comprises a first and a second output terminal, and the switching circuit is operable to allow current to flow between the first and second output terminals in only a single direction.

26. The electric power system of claim 2, wherein each of the N switching circuits is configured such that its first switching device switches between its conductive and non-conductive states at a frequency of at least 200 kilohertz.

27. The electric power system of claim 26, further comprising at least one multi-layer ceramic capacitor electrically coupled across the input port of each of the N switching circuits, and wherein ripple current flowing through the input port of each of the N switching circuits is filtered primarily by the at least one multi-layer ceramic capacitors electrically coupled across each of the switching circuit'"'"'s input port.

28. An electric power system, comprising:

N electric power sources, N being an integer greater than one; and

N switching circuits, each switching circuit including;

an input port electrically coupled to a respective one of the N electric power sources,

an output port, and

a first switching device adapted to switch between its conductive and non-conductive states to transfer power from the input port to the output port;

wherein each of the N switching circuits uses an interconnection inductance of a respective input circuit formed from a series connection of at least its input port and its respective one of the N electric power sources as a primary energy storage inductance of the switching circuit.

29. The electric power system of claim 28, each of the N electric power sources being a photovoltaic device.

30. The electric power system of claim 29, each of the N switching circuits further comprising a controller adapted to control switching of the first switching device of the switching circuit to at least substantially maximize an amount of electric power extracted from a photovoltaic device electrically coupled to the input port of the switching circuit.

31. The electric power system of claim 29, at least one of the photovoltaic devices being a junction of a multi junction photovoltaic cell.

32. The electric power system of claim 29, at least one of the photovoltaic devices being a plurality of electrically coupled photovoltaic cells.

33. The electric power system of claim 29, at least one of the photovoltaic devices being a plurality of photovoltaic cells electrically coupled in parallel.

34. The electric power system of claim 29, each of the photovoltaic devices being a photovoltaic sub-module of a photovoltaic panel, each photovoltaic sub-module including a plurality of photovoltaic cells electrically coupled in series.

35. The electric power system of claim 29, wherein for each of the N switching circuits:

the first switching device is electrically coupled across the input port; and

the switching circuit further includes a device selected from the group consisting of a diode and a second switching electrically coupled between the input and output ports, the device adapted to provide a path for current between the input and output ports when the first switching device is in its non-conductive state.

36. The electric power system of claim 29, wherein each of the N switching circuits further includes a controller adapted to control switching of the first switching device of the switching circuit to at least substantially maximize an average value of current flowing through the output port of the switching circuit.

37. The electric power system of claim 29, wherein each of the N switching circuits further includes a controller adapted to repeatedly sample an average value of current flowing through the output port of the switching circuit and control switching of the first switching device of the switching circuit at least partly based on at least two successive samples of the average value of current flowing through the output port.

38. The electric power system of claim 37, wherein a starting time of the controller of each of the N switching circuits is loosely controlled.

39. The electric power system of claim 37, wherein a starting time of the controller of at least one of the N switching circuits varies from a starting time of the controller of the other N−

1 switching circuits.

40. The electric power system of claim 37, wherein for each of the N switching circuits, the controller is adapted to repeatedly sample the average value of current flowing through the output port at a frequency that is less than a frequency at which the first switching device switches between its conductive and non-conductive states.

41. The electric power system of claim 37, wherein for each of the N switching circuits, the controller is adapted to repeatedly sample the average value of current flowing through the output port at a frequency that is less than one tenth of the frequency at which the first switching device switches between its conductive and non-conductive states.

42. The electric power system of claim 37, wherein for each of the N switching circuits, the controller is adapted to repeatedly sample the average value of current flowing through the output port at a frequency that is sufficiently slow such that transient current excursions on the output port settle between successive samples of the average value of current flowing through the output port.

43. The electric power system of claim 30, wherein a frequency at which the first switching device of each of the N switching circuit switches between its conductive and non-conductive states is loosely controlled.

44. The electric power system of claim 30, wherein a switching frequency of each first switching device varies from a switching frequency of each other first switching device.

45. An electric power system, comprising:

N photovoltaic devices, N being an integer greater than one;

N switching circuits, each switching circuit including an input port electrically coupled to a respective one of the N photovoltaic devices, an output port, and a first switching device adapted to switch between its conductive and non-conductive states to transfer power from the input port to the output port, the output ports of the N switching circuits electrically coupled in series and to a load to establish an output circuit; and

a system control device including;

a transistor electrically coupled in series with the output circuit,

a current sense subsystem configured to generate a current sense signal representing a magnitude of current flowing through the output circuit, and

a control subsystem in communication with the transistor and the current sense subsystem, the control subsystem configured to control the transistor based at least in part on the current sense signal to control current through the output circuit.

46. The electric power system of claim 45, the control subsystem operable to control the transistor such that current is allowed to flow through the output circuit in only a single direction.

47. The electric power system of claim 45, the control subsystem further configured to control the transistor at least in part based on the current sense signal to interrupt current flowing through the output circuit if the magnitude of current flowing through the output circuit exceeds a threshold value.

48. The electric power system of claim 45, the control subsystem further configured to monitor and transmit to an external system a characteristic of the electric power system.

49. The electric power system of claim 48, the characteristic of the electric power system being a voltage across at least the output ports of the N switching circuits electrically coupled in series.

50. The electric power system of claim 48, the characteristic of the electric power system being the magnitude of current flowing through the output circuit.

51. The electric power system of claim 48, the characteristic of the electric power system being a temperature of one or more components of the electric power system.

52. The electric power system of claim 48, the control subsystem operable to modulate the transistor to generate a communication signal including the characteristic of the electric power system.

53. The electric power system of claim 45, each of the N switching circuits further including a controller adapted to control switching of the first switching device of the switching circuit to at least substantially maximize an amount of electric power extracted from the respective one of the N photovoltaic devices electrically coupled to the input port of the switching circuit.

54. The electric power system of claim 45, at least one of the N electric power sources being a junction of a multi junction photovoltaic cell.

55. An electric power system, comprising:

first and second electric power sources electrically coupled in series, the first electric power source capable of generating a maximum current having a first value, the second electric power source capable of generating a maximum current having a second value that is smaller than the first value; and

first and second switching circuits operable to perform maximum power point tracking;

wherein the first and second electric power sources and the first and second switching circuits are electrically coupled such that the first and second switching circuits are collectively operable to at least substantially maximize an amount of electric power extracted from both of the first and second electric power sources.

56. The electric power system of claim 55, wherein the first switching circuit comprises a circuit having a boost-type topology and an input port electrically coupled across the first electric power source.

57. The electric power system of claim 56, wherein:

the first switching circuit further comprises an output port electrically coupled across the series combination of the first and second electric power sources; and

the second switching circuit comprises an input port electrically coupled across the series combination of the first and second electric power sources.

58. The electric power system of claim 57, wherein the second switching circuit further comprises:

first and second switching devices electrically coupled in series across the input port of the second switching circuit; and

an output port,

the second switching device also electrically coupled across the output port and adapted to provide a path for current through the output port of the second switching circuit when the first switching device is in its non-conductive state, and

the second switching circuit using an interconnection inductance of a circuit including its output port as a primary energy storage inductance of the second switching circuit.

59. The electric power source of claim 56, wherein:

the second switching circuit comprises a circuit having a buck-type topology, an input port, and an output port, the input port of the second switching circuit being electrically coupled across the series combination of the first and second electric power sources; and

the first switching circuit further comprises an output port electrically coupled in parallel with the output port of the second switching circuit.

60. The electric power system of claim 56, wherein:

the second switching circuit comprises a circuit having a buck-type topology, an input port, and an output port, the input port of the second switching circuit being electrically coupled across the second electric power source; and

the first switching circuit further comprises an output port electrically coupled in series with the output port of the second switching circuit.

61. The electric power system of claim 55, wherein the first switching circuit comprises a circuit having a buck-boost topology including an input port electrically coupled across the first electric power source.

62. The electric power system of claim 61, wherein:

the first switching circuit further comprises an output port electrically coupled across the second electric power source; and

the second switching circuit comprises an input port electrically coupled across the second electric power source.

63. The electric power system of claim 62, wherein the second switching circuit further comprises:

first and second switching devices electrically coupled in series across the input port of the second switching circuit; and

an output port,

the second switching device also electrically coupled across the output port of the second switching circuit and adapted to provide a path for current through the output port when the first switching device is in its non-conductive state, and

the second switching circuit using an interconnection inductance of a circuit including its output port as a primary energy storage inductance of the second switching circuit.

64. The electric power system of claim 61, wherein:

the first switching circuit further comprises an output port; and

the second switching circuit comprises an output port and an input port electrically coupled in series with the second electric power source and the output port of the first switching circuit.

65. The electric power system of claim 64, wherein the second switching circuit further comprises:

first and second switching devices electrically coupled in series across the input port of the second switching circuit; and

an output port,

the second switching device also electrically coupled across the output port of the second switching circuit and adapted to provide a path for current through the output port when the first switching device is in its non-conductive state, and

the second switching circuit using an interconnection inductance of a circuit including its output port as a primary energy storage inductance of the second switching circuit.

66. The electric power system of claim 61, wherein:

the first switching circuit includes an output port; and

the second switching circuit comprises a circuit having a buck-boost type topology, an output port electrically coupled in series with the output port of the first switching circuit, and an input port electrically coupled across the second electric power source.

67. The electric power system of claim 55, wherein:

each of the first and second switching circuit comprises;

an input port,

an output port, and

a first and second switching device electrically coupled in series across the input port,

the second switching device also electrically coupled across the output port and providing a path for current through the output port when the first switching device is in its non-conductive state;

the input port of the first switching circuit is electrically coupled across the first electric power source;

the input port of the second switching circuit is electrically coupled across the second electric power source; and

the output port of the first switching circuit is electrically coupled in series with the output port of the second switching circuit.

68. The electric power system of claim 67, each of the first and second switching circuits using an inductance of a circuit including the output ports of the first and second switching circuit as a primary energy storage inductance.

69. The electric power system of claim 55, each of the first and second electric power sources comprising at least one photovoltaic device.

70. The electric power system of claim 69, the first electric power source comprising a first photovoltaic junction, and the second electric power source comprising a second and third photovoltaic junction electrically coupled in series.

71. The electric power system of claim 70, the first, second, and third photovoltaic junctions being part of a common multi junction photovoltaic cell.

72. The electric power system of claim 55, each of the first and second switching circuits comprising:

a switching device, and

a controller adapted to control switching of the switching device to perform maximum power point tracking;

wherein the switching device of the first switching circuit switches out of phase with respect to the switching device of the second switching circuit.

73. The electric power system of claim 55, each of the first and second switching circuits comprising:

a switching device, and

a controller adapted to control switching of the switching device to perform maximum power point tracking;

wherein a starting time of the controller of each of the first and second switching circuits is loosely controlled.

74. The electric power system of claim 55, each of the first and second switching circuits comprising:

a switching device, and

a controller adapted to control switching of the switching device to perform maximum power point tracking;

wherein a switching frequency of the switching device of each of the first and second switching circuits is loosely controlled.

75. An electric power system, comprising N photovoltaic strings, N being an integer greater than one, each photovoltaic string including a plurality of photovoltaic devices and a plurality of DC-to-DC converters with output ports electrically coupled in series with a string optimizer, each DC-to-DC converter adapted to at least substantially maximize power extracted from a respective one of the plurality of photovoltaic devices, and each string optimizer adapted to interface its respective string with a common bus.

76. The electric power system of claim 75, each string optimizer comprising a boost converter adapted to interface its respective string with the common bus.

77. The electric power system of claim 76, each boost converter adapted to operate in a continuous conduction operating mode.

78. The electric power system of claim 76, each boost converter adapted to operate in a discontinuous conduction operating mode.

79. The electric power system of claim 76, wherein the boost converter of each string optimizer is adapted to:

operate in a continuous conduction operating mode in a first operating mode of the string optimizer; and

operate in a discontinuous conduction operating mode in a second operating mode of the string optimizer.

80. The electric power system of claim 76, wherein each boost converter uses an interconnection inductance of a circuit of its respective photovoltaic string as a primary energy storage inductance of the boost converter.

81. The electric power system of claim 76, at least one of the boost converters being a multi-phase boost converter.

82. The electric power system of claim 76, at least one of the boost converters being a multi-phase boost converter where energy storage inductors of two or more phases of the boost converter are magnetically coupled.

83. The electric power system of claim 76, wherein energy storage inductors of at least two of the boost converters are magnetically coupled.

85. The electric power system of claim 75, each string optimizer being a multi-phase boost converter, and wherein for each boost converter, a switching device of a first power stage switches out of phase with respect to a switching stage of a second phase.

86. The electric power system of claim 85, wherein at least two switching devices of each multi-phase boost converter are adapted to switch out of phase with respect to at least two switching devices of each other multi-phase boost converter.

87. The electric power system of claim 85, further comprising an inverter electrically coupled to the common bus.

88. The electric power system of claim 87, the inverter lacking maximum power point tracking capability.

89. The electric power system of claim 87, the inverter lacking global maximum power point tracking capability.

90. The electric power system of claim 75, wherein the N photovoltaic strings are disposed on a tracking device operable to track movement of the sun.

91. The electric power system of claim 90, each of the string optimizers being housed in a common enclosure separate from the tracking device.

92. The electric power system of claim 90, wherein each of the plurality of photovoltaic devices is a single photovoltaic cell.

93. The electric power system of claim 75, wherein the N photovoltaic strings are distributed among at least two tracking devices, each tracking device operable to track movement of the sun.

94. The electric power system of claim 75, each of the plurality of photovoltaic devices being part of a common photovoltaic panel.

95. The electric power system of claim 75, further comprising an additional photovoltaic string electrically coupled to the common bus, the additional photovoltaic string including a plurality of photovoltaic devices electrically coupled in series with an additional string optimizer, the additional string optimizer adapted to interface the additional photovoltaic string with the common bus.

96. The electric power system of claim 75, each string optimizer operable to regulate a voltage on the common bus.

97. The electric power system of claim 75, at least one of the string optimizers being adapted to regulate a current through its respective string.

98. The electric power system of claim 97, at least one of the string optimizers being adapted to regulate a current through its respective string to a current greater than a photogenerated current of a strongest photovoltaic device of the string.

99. The electric power system of claim 97, at least one of the string optimizers being adapted to regulate a current through its respective string to a current that is adjusted at least partially according to the irradiance of the sun.

100. The electric power system of claim 97, at least one of the string optimizers being adapted to regulate a current through its respective string to a current that is adjusted according to a photogenerated current of a reference photovoltaic device of the string.

101. The electric power system of claim 97, at least one of the string optimizers being adapted to regulate a current through its respective string to a current that at least substantially maximizes an amount of electric power transferred from its respective string to the common bus.

102. The electric power system of claim 75, at least one of the string optimizers adapted to regulate a voltage across the series coupled output ports of the DC-to-DC converters of the string.

103. The electric power system of claim 75, at least one of the string optimizers operable to at least substantially maximize an amount of electric power transferred from its respective string to the common bus.

104. The electric power system of claim 75, wherein each of the plurality of DC-to-DC converters comprises:

an input port electrically coupled to a respective one of plurality of photovoltaic devices; and

a first and second switching device electrically coupled in series across the input port,

wherein the second switching device is also electrically coupled across the output port of the DC-to-DC converter and provides a path for current through the output port when the first switching device is in its non-conductive state.

105. The electric power system of claim 104, wherein each of the plurality of DC-to-DC converters uses an interconnection inductance of a circuit including the output ports of the plurality of DC-to-DC converters as a primary energy storage inductance of the DC-to-DC converter.

106. The electric power system of claim 75, wherein at least one of the string optimizers and the DC-to-DC converters are operable to exchange information.

107. The electric power system of claim 106, the information comprising a command from a string optimizer to a switching circuit.

108. The electric power system of claim 107, wherein the command is selected from the group consisting of a command to start-up the switching circuit, a command to shut-down the switching circuit, and a command for the switching circuit to enter a bypass mode.

109. The electric power system of claim 106, the information comprising information selected from the group consisting of switching circuit status information and switching circuit fault information.

84. The electric power system of 75, each string optimizer comprising a first switching device adapted to switch between its conductive and non-conductive states to interface its respective string with the common bus, each first switching device switching out of phase with respect to each other first switching device.

110. An electric power system, comprising N photovoltaic strings, N being an integer greater than one, each photovoltaic string including a plurality of photovoltaic devices and a plurality of DC-to-DC converters with output ports electrically coupled in series with a string inverter, each DC-to-DC converter adapted to at least substantially maximize power extracted from a respective one of the plurality of photovoltaic devices, and each string inverter adapted to interface its respective string with a common alternating current bus.

111. An electric power system, comprising N switching circuits, N being an integer greater than one, each switching circuit including an input port, an output port including a first and second output terminal, and a first switching device adapted to switch between its conductive and non-conductive states, the output ports of the N switching circuits being electrically coupled in series with a load to establish an output circuit, wherein:

each switching circuit is adapted to cause its first switching device to switch between its conductive and non-conductive states to transfer power from the input port to the output port in a first operating mode of the switching circuit; and

each switching circuit is adapted to shunt its first and second output terminals in a second operating mode of the switching circuit.

112. The electric power system of claim 111, each of the N switching circuits further comprising a controller adapted to control switching of the first switching device of the switching circuit in the first operating mode of the switching circuit to at least substantially maximize an amount of electric power extracted from an electric power source electrically coupled to the input port of the switching circuit.

113. The electric power system of claim 111, each of the N switching circuits further comprising a second switching device electrically coupled between the first and second output terminals of the switching circuit and adapted to operate in its conductive state during the second operating mode of the switching circuit.

114. The electric power system of claim 111, wherein each of the N switching circuits is adapted to operate in the second operating mode upon occurrence of an event selected from the group consisting of (1) voltage across the input port of the switching circuit being below a threshold value, (2) voltage across the input port of the switching circuit being above a threshold value, (3) power transferred from the input port to the output port of the switching circuit being below a threshold value, (4) a magnitude of current through the input port of the switching circuit being below a threshold value, (5) a magnitude of current flowing between the first and second output terminals of the switching circuit exceeding a threshold value, and (6) a temperature of the switching circuit exceeding a threshold value.

115. An electric power system, comprising:

a photovoltaic device; and

a switching circuit including;

an input port electrically coupled to the photovoltaic device,

an output port for electrically coupling to a load,

a first switching device adapted to switch between its conductive and non-conductive states to transfer power from the input port to the output port, and

a controller adapted to cause the first switching device to switch between its conductive and non-conductive states at a frequency that at least substantially maximizes an amount of electric power delivered to the load;

wherein the frequency is greater than 200 kilohertz.

116. The electric power system of claim 115, wherein ripple current flowing through the input port is filtered primarily by one or more multi-layer ceramic capacitors.

117. A system for extracting power from N electric power sources, where N is an integer greater than one, the system comprising:

N switching circuits, each switching circuit including;

an input port for electrically coupling to a respective one of the N electric power sources,

an output port for electrically coupling to a load,

a first switching device configured to switch between its conductive state and its non-conductive state to transfer power from the input port to the output port,

a controller configured to control switching of the first switching device to at least substantially maximize an amount of power extracted from the respective one of the N electric power sources electrically coupled to the input port of the switching circuit; and

at least one additional switching device configured to electrically couple output ports of at least two of the N switching circuits either in series or in parallel.

118. The system of claim 117, wherein each of the N switching circuits has a buck-type topology.

119. The system of claim 117, wherein each of the N switching circuits has a boost-type topology.

120. An electric power system, comprising N photovoltaic strings electrically coupled in parallel, N being an integer greater than one, each string including:

a plurality of photovoltaic devices; and

a plurality of switching circuits, each switching circuit including;

an input port electrically coupled to a respective one of the plurality of photovoltaic devices,

an output port, and

first and second switching devices electrically coupled in series across the input port, the second switching device also electrically coupled across the output port and adapted to provide a path for current through the output port when the first switching device is in its non-conductive state,

wherein the output ports are electrically coupled in series in each of the N photovoltaic strings, and

wherein each of the switching circuits uses an interconnection inductance of a circuit including its output port as a primary energy storage inductance of the switching circuit.