Maximum Power Point Tracking Controllers And Associated Systems And Methods

• US 20140103894A1
• Filed: 10/16/2012
• Published: 04/17/2014
• Est. Priority Date: 10/16/2012
• Status: Active Grant

• Current Assignee: Volterra Semiconductor Corporation (Analog Devices, Inc.)
• Original Assignee: Volterra Semiconductor Corporation (Analog Devices, Inc.)
• Inventors: McJimsey, Michael D., Stratakos, Anthony J., Jergovic, Ilija, Zhang, Xin, Yao, Kaiwei, Ng, Vincent W., Nguyen, Phong T., Minassians, Artin Der
• Granted Patent: US 9,141,123 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: G01R 21/06 by measuring current and voltage G01R21/08 - G01R21/133 take precedence
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• 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 3/356165 using additional transistors in the feedback circuit
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A maximum power point tracking controller includes an input port for electrically coupling to an electric power source, an output port for electrically coupling to a load, a control switching device, and a control subsystem. The control switching device is adapted to repeatedly switch between its conductive and non-conductive states to transfer power from the input port to the output port. The control subsystem is adapted to control switching of the control switching device to regulate a voltage across the input port, based at least in part on a signal representing current flowing out of the output port, to maximize a signal representing power out of the output port.

Claims

1. A maximum power point tracking controller, comprising:

an input port for electrically coupling to an electric power source;

an output port for electrically coupling to a load;

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

a control subsystem adapted to control switching of the control switching device to regulate a voltage across the input port, based at least in part on a signal representing current flowing out of the output port, to maximize a signal representing power out of the output port.

2. The maximum power point tracking controller of claim 1, the control subsystem further adapted to control switching of the control switching device based partially on the signal representing current flowing out of the output port and a difference between the voltage across the input port and a reference voltage.

3. The maximum power point tracking controller of claim 2, the control subsystem further adapted to vary a magnitude of the reference voltage to maximize the signal representing power out of the output port.

4. The maximum power point tracking controller of claim 3, the control subsystem further adapted to control switching of the control switching device based partially on an error signal given by −

Kv*(Vin−

Vref)+Ki*Io, where Kv is a first scaling factor, Ki is a second factor, Vin is the voltage across the input port, Vref is the reference voltage, and Io is the signal representing current flowing out of the output port.

5. The maximum power point tracking controller of claim 4, the control switching device being electrically coupled between a first terminal of the input port and a first terminal of the output port, the maximum power point tracking controller further comprising a freewheeling device electrically coupled between the first terminal of the output port and a second terminal of the output port, the freewheeling device adapted to provide a path for current flowing between the first and second terminals of the output port when the control switching device is in its non-conductive state.

6. The maximum power point tracking controller of claim 5, the control subsystem comprising a multiplier adapted to determine the signal representing power out of the output port from a product of a scaled signal representing average voltage across the output port and a scaled signal representing average current flowing out of the output port.

7. The maximum power point tracking controller of claim 6, the control subsystem further comprising:

a voltage scaling subsystem adapted to generate the scaled signal representing average voltage across the output port by scaling a signal representing average voltage across the output power port to be within a first predetermined range; and

a current scaling subsystem adapted to generate the scaled signal representing average current flowing out of the output port by scaling a signal representing average current flowing out the output port to be within a second predetermined range.

8. The maximum power point tracking controller of claim 7, the current scaling subsystem further adapted to prevent a magnitude of the scaled signal representing average current flowing out of the output port from falling below a minimum threshold value.

9. The maximum power point tracking controller of claim 8, the current scaling subsystem further adapted to add a positive offset value to the scaled signal representing average current flowing out of the output port when the signal representing average current flowing out the output port is within a first range of values.

10. The maximum power point tracking controller of claim 7, the control subsystem further comprising a current filter subsystem adapted to generate the signal representing average current flowing out of the output port by filtering the signal representing current flowing out the output port.

11. The maximum power point tracking controller of claim 10, the control subsystem further comprising a voltage filter subsystem adapted to generate the signal representing average voltage across the output port by filtering a signal representing voltage across the output port.

12. The maximum power point tracking controller of claim 3, the control subsystem further adapted to inhibit a reduction in the magnitude of the reference voltage when the voltage across the input port falls below a threshold value.

13. The maximum power point tracking controller of claim 3, the control subsystem further adapted to inhibit a reduction in the magnitude of the reference voltage when doing so would cause the voltage across the input port to fall below a threshold value.

14. The maximum power point tracking controller of claim 3, the control subsystem further adapted to inhibit an increase in the magnitude of the reference voltage when the voltage across the input port rises above a threshold value.

15. The maximum power point tracking controller of claim 3, the control subsystem further adapted to:

change the magnitude of the reference voltage by a first step size, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is below a first threshold value; and

change the magnitude of the reference voltage by a second step size, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is greater than or equal to a second threshold value;

the second step size being smaller than the first step size.

16. The maximum power point tracking controller of claim 15, the first threshold value being the same as the second threshold value.

17. The maximum power point tracking controller of claim 3, the control subsystem further adapted to:

change the magnitude of the reference voltage by a first step size, to maximize the signal representing power out of the output port, when a difference in the signal representing power out of the output port between successive changes in magnitude of the reference voltage is below a first threshold value; and

change the magnitude of the reference voltage by a second step size, to maximize the signal representing power out of the output port, when a difference in the signal representing power out of the output port between successive changes in magnitude of the reference voltage is greater than or equal to a second threshold value;

the second step size being greater than the first step size.

18. The maximum power point tracking controller of claim 17, the first threshold value being the same as the second threshold value.

19. The maximum power point tracking controller of claim 3, the control subsystem further adapted to:

change the magnitude of the reference voltage at a first rate, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is within a first range of values; and

change the magnitude of the reference voltage at a second rate, to maximize the signal representing power out of the output port, when the command to control the duty cycle of the control switching device is within a second range of values;

the second rate being greater than the first rate.

20. The maximum power point tracking controller of claim 19, the first range of values representing a command that the duty cycle of the control switching device be between zero and one hundred percent, and the second range of values representing a command that the duty cycle of the control switching device be less than zero or greater than one hundred percent.

21. The maximum power point tracking controller of claim 3, the control subsystem further adapted to increase the magnitude of the reference voltage in response to the magnitude of the voltage across the input port falling below a threshold value.

22. The maximum power point tracking controller of claim 3, the control subsystem further adapted to set an initial magnitude of the reference voltage based at least partially on an initial value of the voltage across the input port, at start-up of the switching circuit.

23. The maximum power point tracking controller of claim 22, the control subsystem further adapted to set the initial magnitude of the reference voltage to a fraction of the voltage across the input port, at start-up of the switching circuit.

24. The maximum power point tracking controller of claim 3, the control subsystem further adapted to decrease the magnitude of the reference voltage in response to the signal representing current flowing out of the output port indicating that a magnitude of current flowing out of the output port has fallen below a first threshold level.

25. The maximum power point tracking controller of claim 24, the control subsystem further adapted to operate the control switching device at a fixed duty cycle in response to the signal representing current flowing out of the output port indicating that a magnitude of current flowing out of the output port has fallen below a second threshold level, where the second threshold level is lower than the first threshold level.

26. The maximum power point tracking controller of claim 1, the control switching device and the control subsystem being part of a common integrated circuit.

27. The maximum power point tracking controller of claim 1, wherein:

the control switching device comprises a dynamically sized field effect transistor;

the maximum power point tracking controller further comprises a current reconstructor subsystem adapted to generate the signal representing current flowing out of the output port, the current reconstructor subsystem having a gain at least partially dependent on a size of the dynamically sized field effect transistor; and

the control subsystem is adapted to decrease a size of the dynamically sized field effect transistor if a magnitude of the signal representing current flowing out of the output port falls below a threshold value, thereby increasing the gain of the current reconstructor subsystem.

28. An electric power system, comprising:

an electric power source; and

a maximum power point tracking controller, including;

an input port electrically coupled to the electric power source,

an output port for electrically coupling to a load,

a control switching device adapted to repeatedly switch between its conductive and non-conductive states to transfer power from the electric power source to the output port, and

a control subsystem adapted to control switching of the control switching device to regulate a voltage across the input port, based at least in part on a signal representing current flowing out of the output port, to maximize a signal representing power out of the output port.

29. The electric power system of claim 28, the electric power source comprising a photovoltaic device.

30. The electric power system of claim 29, the photovoltaic device comprising a plurality of interconnected photovoltaic cells.

31. The electric power system of claim 29, the photovoltaic device comprising a multi-junction photovoltaic cell.

32. The electric power system of claim 29, the control subsystem adapted to control switching of the control switching device based partially on the signal representing current flowing out of the output port and a difference between the voltage across the input port and a reference voltage.

33. The electric power system of claim 32, the control subsystem further adapted to vary a magnitude of the reference voltage to maximize the signal representing power out of the output port.

34. The electric power system of claim 33, the control subsystem further adapted to control switching of the control switching device based partially on an error signal given by −

Kv*(Vin−

Vref)+Ki*Io, where Kv is a first scaling factor, Ki is a second scaling factor, Vin is the voltage across the input port, Vref is the reference voltage, and Io is the signal representing current flowing out of the output port.

35. The electric power system of claim 34, the control switching device being electrically coupled between a first terminal of the input port and a first terminal of the output port, the maximum power point tracking controller further comprising a freewheeling device electrically coupled between the first terminal of the output port and a second terminal of the output port, the freewheeling device adapted to provide a path for current flowing between the first and second terminals of the output port when the control switching device is in its non-conductive state.

36. The electric power system of claim 35, the control subsystem comprising a multiplier adapted to determine the signal representing power out of the output port from a product of a scaled signal representing average voltage across the output port and a scaled signal representing average current flowing out of the output port.

37. The electric power system of claim 36, the control subsystem further adapted to prevent a magnitude of the scaled signal representing average current flowing out of the output port from falling below a minimum threshold value.

38. The electric power system of claim 29, the control switching device and the control subsystem being part of a common integrated circuit.

39. The electric power system of claim 38, the common integrated circuit and the photovoltaic device being co-packaged.

40. The electric power system of claim 28, further comprising one or more additional maximum power point tracking controllers electrically coupled in series with the output port and the load, each additional maximum power point tracking controller adapted to transfer power from a respective additional electric power source to the load.

41. A method for operating a maximum power point tracking controller including an input port for electrically coupled to an electric power source and an output port for electrically coupling to a load, comprising the steps of:

repeatedly switching a control switching device of the maximum power point tracking controller between its conductive and non-conductive states to transfer power from the input port to the output port; and

controlling switching of the control switching device, based at least in part on a signal representing current flowing out of the output port, to regulate a magnitude of a voltage across the input port such that a signal representing power out of the output port is maximized.

42. The method of claim 41, further comprising controlling switching of the control switching device partially based on the signal representing current flowing out of the output port and a difference between the magnitude of the voltage across the input port and a reference voltage.

43. The method of claim 42, further comprising varying a magnitude of the reference voltage to maximize the signal representing power out of the output port.

44. The method of claim 43, further comprising controlling switching of the control switching device partially based on an error signal given by −

Kv*(Vin−

Vref)+Ki*Io, where Kv is a first scaling factor, Ki is a second scaling factor, Vin is the voltage across the input port, Vref is the reference voltage, and Io is the signal representing current flowing out of the output port.

45. The method of claim 44, further comprising determining the signal representing power out of the output port by multiplying a signal representing average voltage across the output port by a signal representing average current flowing out of the output port, using a multiplier.

46. The method of claim 45, further comprising filtering the signal representing current flowing out of the output port to generate the signal representing average current flowing out of the output port.

47. The method of claim 46, further comprising filtering a signal representing voltage across the output port to generate the signal representing average voltage across the output power port.

48. The method of claim 47, further comprising preventing a magnitude of the signal representing average current flowing out of the output port from falling below a minimum threshold value.

49. The method of claim 43, further comprising:

storing a first sample of the signal representing power out of the output port when a duty cycle of the control switching device is one hundred percent duty cycle;

decreasing the magnitude of the reference voltage by a first amount;

storing a second sample of the signal representing power out of the output port, after the step of decreasing the magnitude of the reference voltage by the first amount;

comparing the first sample of the signal representing power out of the output port to the second sample of the signal representing power out of the output port;

increasing the magnitude of the reference voltage when the first sample of the signal representing power out of the output port is greater than the second sample of the signal representing power out of the output port; and

decreasing the magnitude of the reference voltage when the second sample of the signal representing power out of the output port is greater than the first sample of the signal representing power out of the output port.

50. The method of claim 43, further comprising inhibiting a reduction in the magnitude of the reference voltage when the voltage across the input port falls below a threshold value.

51. The method of claim 43, further comprising inhibiting an increase in the magnitude of the reference voltage when the voltage across the input port rises above a threshold value.

52. The method of claim 43, further comprising:

changing the magnitude of the reference voltage by a first step size, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is below a first threshold value; and

changing the magnitude of the reference voltage by a second step size, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is greater than or equal to a second threshold value;

the second step size being smaller than the first step size.

53. The method of claim 43, further comprising:

changing the magnitude of the reference voltage at a first rate, to maximize the signal representing power out of the output port, when a command to control a duty cycle of the control switching device is within a first range of values; and

changing the magnitude of the reference voltage at a second rate, to maximize the signal representing power out of the output port, when the command to control the duty cycle of the control switching device is within a second range of values;

the second rate being greater than the first rate.

54. The method of claim 53, the first range of values representing that the duty cycle of the control switching device is commanded to be between zero and one hundred percent, and the second range of values representing that the duty cycle of the control switching device is commanded to be less than zero or greater than one hundred percent.

55. The method of claim 43, further comprising increasing the magnitude of the reference voltage in response to the magnitude of the voltage across the input port falling below a threshold value.

56. The method of claim 43, further comprising setting an initial magnitude of the reference voltage based at least partially on an initial value of the voltage across the input port, at start-up of the switching circuit.

57. The method of claim 56, further comprising setting the initial magnitude of the reference voltage to a fraction of the voltage across the input port, at start-up of the switching circuit.

58. The method of claim 43, further comprising decreasing the magnitude of the reference voltage in response to a magnitude of current flowing out of the output port falling below a first threshold level.

59. The method of claim 58, further comprising operating the control switching device at a fixed duty cycle in response to a magnitude of current flowing out of the output port falling below a second threshold level, where the second threshold level is lower than the first threshold level.

60. The method of claim 41, further comprising:

generating the signal representing current flowing out of the output port using a current reconstructor subsystem; and

decreasing a size of a dynamically sized field effect transistor of the control switching device when a magnitude of the signal representing current flowing out of the output port falls below a threshold value, thereby increasing a gain of the current reconstructor subsystem.

61. A method for transferring electric power between an electric power source and a load using a maximum power point tracking controller, comprising the step of controlling switching of a control switching device of the maximum power point tracking controller, based at least in part on a signal representing current flowing through energy storage inductance of the maximum power point tracking controller, to regulate a voltage across the electric power source, such that:

(a) the voltage across the electric power source is greater than or equal to a voltage across the load, and (b) a signal representing power transferred to the load is maximized.

62. The method of claim 61, further comprising controlling switching of the control switching device partially based on the signal representing current flowing out of the output port and a difference between the magnitude of the voltage across the electric power source and a reference voltage.

63. The method of claim 62, further comprising varying a magnitude of the reference voltage to maximize the signal representing power transferred to the load.

64. A multiplier, comprising:

a first and a second input port;

an output port;

a first field effect transistor electrically coupled in series with the first input port;

a second field effect transistor electrically coupled in series with the second input port;

a third field effect transistor electrically coupled in series with the output port; and

control circuitry adapted to control each of the first, second, and third field effect transistors such that a magnitude of current flowing into the output port is proportional to a product of (a) a magnitude of current flowing into the first input port, and (b) a magnitude of current flowing into the second input port.

65. The multiplier of claim 64, a gate of the first field effect transistor being electrically coupled to a gate of the third field effect transistor.

66. The multiplier of claim 65, further comprising:

fourth and fifth field effect transistors forming a current minor configured such that a magnitude of a drain-to-source current flowing through the fifth field effect transistor is equal to Iref, and a magnitude of a drain-to-source current flowing through the fourth field effect transistor is equal to Iref/m; and

a first amplifier adapted to control the gate of the first field effect transistor such that a voltage across the first field effect transistor is equal to a voltage across the fourth field effect transistor.

67. The multiplier of claim 66, a gate of the second field effect transistor being electrically coupled to a gate of the fourth field effect transistor and a gate of the fifth field effect transistor.

68. The multiplier of claim 67, wherein the second field effect transistor has a channel resistance equal to R/m, and the fourth and fifth field effect transistors each have a channel resistance equal to R, when the second, fourth, and fifth transistors are driven by a common gate-to-source voltage.

69. The multiplier of claim 68, further comprising a second amplifier and a sixth transistor configured to control the magnitude of current flowing into the output port such that a voltage across the second field effect transistor is equal to a voltage across the third field effect transistor.

70. An electronic filter, comprising:

an integrator subsystem adapted to operate in a bipolar domain to filter an alternating current component of an input signal; and

transconductance circuitry adapted to operate in a unipolar domain to generate an output current signal proportional to an average value of the input current signal.

71. The electronic filter of claim 70, wherein:

the integrator subsystem is adapted to generate an integrator signal representing the average value of the input current signal; and

the transconductance circuitry comprises a first transconductance amplifier adapted to generate the output current signal, from the integrator signal.

72. The electronic filter of claim 70, the integrator subsystem comprising:

an integrator having an inverting input terminal and a non-inverting input terminal; and

a resistive device electrically coupled across the input terminals of integrator;

the non-inverting input terminal of the integrator being electrically coupled to a reference node of the electronic filter via a voltage source,

the inverting input terminal of the integrator being electrically coupled to a first node, and

the electronic filter arranged such that the input current signal flows out of the first node.

73. The electronic filter of claim 72, the transconductance circuitry further comprising a second transconductance amplifier adapted to generate a direct current component of the input current signal, from the integrator signal.

74. A method for filtering an input signal, comprising:

filtering an alternating current component of the input signal in a bipolar domain; and

generating a direct current component of the input signal in a unipolar domain.

75. The method of claim 74, further comprising mirroring the direct current component of the input signal in the unipolar domain to generate an output signal representing an average value of the input signal.

76. A signal scaling system, comprising:

a transconductance subsystem adapted to convert an input voltage signal to an output current signal, the transconductance subsystem including a programmable resistor adapted to set a gain of the transconductance subsystem; and

control logic adapted to set a resistance of the programmable resistor to adjust the gain of the transconductance subsystem such that a magnitude of the output current signal is at least as large as a first threshold value.

77. The signal scaling system of claim 76, the transconductance subsystem further including:

a transistor electrically coupled to the programmable resistor; and

an amplifier adapted to control the transistor to regulate a voltage across the programmable resistor in response to the input voltage signal.

78. The signal scaling system of claim 77, the control logic further adapted to set a gain of the transconductance subsystem to a minimum value in response to a first external signal.

79. The signal scaling system of claim 78, the control logic further adapted to increment the gain of the transconductance subsystem in response to a second external signal, until the magnitude of the output current signal is at least as large as the first threshold value.

80. The signal scaling system of claim 79, the control logic further adapted to detect when the magnitude of the output current signal exceeds a second threshold value, where the second threshold value is greater than the first threshold value.

81. The signal scaling system of claim 80, the control logic further adapted to generate a signal indicating that the magnitude of the output current signal exceeds the second threshold value.

82. The signal scaling system of claim 81, the transconductance system further comprising a current minor adapted to generate the output current signal in response to current flowing through the programmable resistor.

83. A signal level shifter for shifting complementary input voltage signals in a first power supply domain to complementary output voltage signals in a second power supply domain, comprising:

a transconductance stage in the first power supply domain and adapted to generate complementary current signals in response to the complementary input voltage signals; and

a load circuit in the second power supply domain adapted to generate the complementary output voltage signals in response to the complementary current signals, the load circuit comprising first and second inverter circuits adapted to generate the complementary output voltage signals in response to the complementary current signals.

84. The signal level shifter of claim 83, wherein:

a high side rail of the first inverter circuit is electrically coupled to a high side rail of the second power supply domain by a first transistor;

a high side rail of the second inverter circuit is electrically coupled to the high side rail of the second power supply domain by a second transistor; and

the first and second transistors are cross-coupled.

85. The signal level shifter of claim 84, each of the inverter circuits comprising:

a high side transistor electrically coupled between the high side rail of the inverter circuit and an output node of the inverter circuit; and

a low side transistor electrically coupled between the output node of the inverter circuit and a reference rail of the second power supply domain;

the high side transistor operable to pull the output node of the inverter circuit up to at least fifty percent of an electrical potential of the high side rail of the inverter, with respect to the reference rail of the second power supply domain, when the low side transistor is in its conductive state.

86. The signal level shifter of claim 85, the transconductance stage operable to drive current into the high side rails of the first and second inverter circuits, when an electrical potential of a reference rail of the second power supply domain is below an electrical potential of a reference rail of the first power supply domain.

87. A system for determining a signal representing power in a maximum power point tracking (MPPT) controller, comprising:

a voltage filter subsystem adapted to generate a signal representing average voltage across an output port of the MPPT controller by filtering a signal representing voltage across the output port;

a current filter subsystem adapted to generate a signal representing average current flowing out of the output port by filtering a signal representing current flowing out the output port;

a voltage scaling subsystem adapted to generate a scaled signal representing average voltage across the output port by scaling the signal representing average voltage across the output port to be within a first predetermined range;

a current scaling subsystem adapted to generate a scaled signal representing average current flowing out of the output port by scaling the signal representing average current flowing out the output port to be within a second predetermined range; and

a multiplier adapted to determine the signal representing power from a product of the scaled signal representing average voltage across the output port and the scaled signal representing average current flowing out of the output port.

88. The system of claim 87, the multiplier comprising:

a first input port adapted to receive the scaled signal representing average voltage across the output port;

a second input port adapted to receive the scaled signal representing average current flowing out of the output port;

an output port adapted to provide the signal representing power;

a first field effect transistor electrically coupled in series with the first input port;

a second field effect transistor electrically coupled in series with the second input port;

a third field effect transistor electrically coupled in series with the output port; and

control circuitry adapted to control each of the first, second, and third field effect transistors such that a magnitude of current flowing into the output port is proportional to a product of (a) a magnitude of current flowing into the first input port, and (b) a magnitude of current flowing into the second input port.

89. The system of claim 88, a gate of the first field effect transistor being electrically coupled to a gate of the third field effect transistor.

90. The system of claim 89, further comprising:

fourth and fifth field effect transistors forming a current minor configured such that a magnitude of a drain-to-source current flowing through the fifth field effect transistor is equal to Iref, and a magnitude of a drain-to-source current flowing through the fourth field effect transistor is equal to Iref/m; and

a first amplifier adapted to control the gate of the first field effect transistor such that a voltage across the first field effect transistor is equal to a voltage across the fourth field effect transistor.

91. The system of claim 90, a gate of the second field effect transistor being electrically coupled to a gate of the fourth field effect transistor and a gate of the fifth field effect transistor.

92. The system of claim 91, wherein the second field effect transistor has a channel resistance equal to R/m, and the fourth and fifth field effect transistors each have a channel resistance equal to R, when the second, fourth, and fifth transistors are driven by a common gate-to-source voltage.

93. The system of claim 92, further comprising a second amplifier and a sixth transistor configured to control the magnitude of current flowing into the output port such that a voltage across the second field effect transistor is equal to a voltage across the third field effect transistor.

94. The system of claim 88, the current scaling subsystem comprising:

a transconductance subsystem adapted to convert the signal representing average current flowing out the output port to the scaled signal representing average current flowing out of the output port, the transconductance subsystem including a programmable resistor adapted to set a gain of the transconductance subsystem; and

control logic adapted to set a resistance of the programmable resistor to adjust the gain of the transconductance subsystem such that a magnitude of the scaled signal representing average current flowing out of the output port is at least as large as a first threshold value.

95. The system of claim 94, the transconductance subsystem further including:

a transistor electrically coupled to the programmable resistor; and

an amplifier adapted to control the transistor to regulate a voltage across the programmable resistor in response to the signal representing average current flowing out of the output port.

96. The system of claim 95, the control logic further adapted to set a gain of the transconductance subsystem to a minimum value in response to a first external signal.

97. The system of claim 96, the control logic further adapted to increment the gain of the transconductance subsystem in response to a second external signal, until the magnitude of the scaled signal representing current flowing out of the output port is at least as large as the first threshold value.

98. The system of claim 97, the transconductance system further comprising a current mirror adapted to generate the scaled signal representing average current flowing out of the output port in response to current flowing through the programmable resistor.

99. The system of claim 94, the current filter subsystem comprising:

an integrator subsystem adapted to operate in a bipolar domain to filter an alternating current component of the signal representing current flowing out the output port; and

transconductance circuitry adapted to operate in a unipolar domain to generate the signal representing average current flowing out of the output port from an average value of the signal representing current flowing out the output port.

100. The system of claim 99, wherein:

the integrator subsystem is adapted to generate an integrator signal representing the average value of the signal representing current flowing out the output port; and

the transconductance circuitry comprises a first transconductance amplifier adapted to generate the signal representing average current flowing out of the output port, from the integrator signal.

101. The system of claim 100, the integrator subsystem comprising:

an integrator having an inverting input terminal and a non-inverting input terminal; and

a resistive device electrically coupled across the input terminals of integrator;

the non-inverting input terminal of the integrator being electrically coupled to a reference node via a voltage source,

the inverting input terminal of the integrator being electrically coupled to a first node, and

the current filter subsystem arranged such that the signal representing current flowing out the output port flows out of the first node.

102. The system of claim 101, the transconductance circuitry further comprising a second transconductance amplifier adapted to generate a direct current component of the signal representing current flowing out the output port, from the integrator signal.

103. A method for determining a signal representing power in a maximum power point tracking (MPPT) controller, comprising the steps of:

filtering a signal representing current flowing out of an output port of the MPPT controller to obtain a signal representing average current flowing out of the output port;

filtering a signal representing voltage across the output port to obtain a signal representing average voltage across the output port;

scaling the signal representing average current flowing out of the output port to obtain a scaled signal representing average current flowing out of the output port;

scaling the signal representing average voltage across the output port to obtain a scaled signal representing average voltage across the output port; and

multiplying the scaled signal representing average current flowing out of the output port by the scaled signal representing average voltage across the output port to obtain the signal representing power.