POWER CONDITIONING UNITS

• US 20100309692A1
• Filed: 05/27/2010
• Published: 12/09/2010
• Est. Priority Date: 01/13/2006
• Status: Active Grant

• Current Assignee: Tesla Inc.
• Original Assignee: Enecsys Limited
• Inventors: Rodriguez, Cuauhtemoc, Amaratunga, Gehan Anil Joseph, Chisenga, Lesley
• Granted Patent: US 8,405,367 B2
• Time in Patent Office: Days
• US Class Current: 363/37
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• 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 3/381 Dispersed generators
• CPC Class Codes: H02J 3/40 Synchronising a generator for connection to a network or to another generator
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 5/45 using semiconductor devices only
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

We describe a power conditioning unit with maximum power point tracking (MPPT) for a dc power source, in particular a photovoltaic panel. A power injection control block has a sense input coupled to an energy storage capacitor on a dc link and controls a dc-to-ac converter to control the injected mains power. The power injection control block tracks the maximum power point by measuring a signal on the dc link which depends on the power drawn from the dc power source, and thus there is no need to measure the dc voltage and current from the dc source. In embodiments the signal is a ripple voltage level and the power injection control block controls an amplitude of an ac current output such that an amount of power transferred to the grid mains is dependent on an amplitude of a sinusoidal voltage component on the energy storage capacitor.

Claims

1. A power conditioning unit with maximum power point tracking (MPPT), for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit comprising:

an input for receiving power from said dc power source;

an output for delivering ac power to said ac mains power supply;

an energy storage capacitor for storing energy from said dc power source for delivering to said ac mains power supply output;

a dc-to-ac converter coupled to said output for converting energy stored in said energy storage capacitor to ac power for said ac mains power supply output;

a power injection control block having a sense input coupled to said energy storage capacitor and having an output coupled to said dc-to-ac converter, to control said dc-to-ac converter to control power injected into said ac mains power supply; and

wherein said power injection control block is configured to track a maximum power point of said dc power source without measuring a dc voltage or dc current provided from said dc power source.

2. A power conditioning unit as claimed in claim 1 wherein a voltage on said energy storage capacitor has a sinusoidal voltage component at twice a frequency of said ac mains, wherein said sense input senses a value of said sinusoidal voltage component, and wherein said power injection control block is configured to control an amplitude of an ac current provided to said ac mains power supply output such that an amount of power transferred to said ac mains power supply output is dependent on an amplitude of said sinusoidal voltage component on said energy storage capacitor.

3. A power conditioning unit as claimed in claim 2 wherein said power injection control block is configured to control said amplitude of said ac current provided said ac mains to substantially maximise said value of said sinusoidal voltage component.

4. A power condition unit as claimed in claim 3 wherein said power injection control block is configured to generate a template of said ac current provided said ac mains, to adjust an amplitude of said template responsive to said value of said sinusoidal voltage component, and to control said power injection control block responsive to a difference between said template and a value dependent on said value of said sinusoidal voltage component to control said amplitude of said value of said sinusoidal voltage component.

5. A power conditioning unit as claimed in claim 2 wherein said power injection control block is configured to determine a power transferred from said dc source to said ac mains power supply using a squared value of said sinusoidal voltage component, and to control said dc-to-ac converter responsive to said determined power transferred.

6. A power conditioning unit as claimed in claim 1 wherein said power injection control block is galvanically isolated from said dc power source.

7. A power conditioning unit as claimed in any claim 1 wherein said power injection control block is configured to multiply a voltage sensed from said energy storage capacitor by a sinusoidal template to generate a template signal, and to compare said template signal with a signal sensed from said output to control said dc-to-ac converter.

8. A power conditioning unit as claimed in claim 1 further comprising a dc voltage amplifier coupled between said input and said energy storage capacitor to increase a voltage from said dc power source by a substantially constant amplification factor.

9. A power conditioning unit as claimed in claim 8 further comprising a voltage amplifier control block to drive said dc voltage amplifier with a substantially constant duty cycle pulse width modulation control signal, and to provide on-off control of a dc output from said dc voltage amplifier.

10. A power conditioning unit as claimed in claim 1 wherein an energy flow from said dc power source to said energy storage capacitor is substantially proportional to an amount of energy stored in said energy storage capacitor, and wherein an amount of energy drawn from said energy storage capacitor and provided to said output is controlled by said power injection control block such that said amount of energy stored in said energy storage capacitor is dependent on said ac power delivered to said ac mains power supply, wherein said power injection block is able to track said maximum power point by controlling said ac power delivered to said ac mains power supply.

11. A power conditioning unit as claimed in claim 1 wherein said power injection control block is configured to track said maximum power point by sensing at said sense input a signal responsive to power drawn from said dc power source, and to control said power injection into said ac mains power supply to substantially maximise said sensed signal.

12. A power conditioning unit as claimed in claim 11 wherein said sensed signal comprises a signal dependent on level of ripple voltage on said energy storage capacitor.

13. A power conditioning unit with maximum power point tracking (MPPT), for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit comprising:

an input for receiving power from said dc power source;

an output for delivering ac power to said ac mains power supply;

an energy storage capacitor for storing energy from said dc power source for delivering to said ac mains power supply output;

a dc-to-ac converter coupled to said output for converting energy stored in said energy storage capacitor to ac power for said ac mains power supply output;

a power injection control block having a sense input coupled to said energy storage capacitor and having an output coupled to said dc-to-ac converter, to control said dc-to-ac converter to control power injected into said ac mains power supply; and

wherein, in operation, a voltage on said energy storage capacitor has a sinusoidal voltage component at twice a frequency of said ac mains;

wherein said power injection control block is configured for controlling an amplitude of an ac current provided to said ac mains power supply output such that an amount of power transferred to said ac mains power supply output is dependent on an amplitude of said sinusoidal voltage component on said energy storage capacitor, and

wherein said power injection control block is configured to track a maximum power point of said dc power source by controlling said dc-to-ac converter.

14. A power conditioning unit as claimed in claim 13 wherein said power injection control block is configured to track a maximum power point of said dc power source without measuring a dc voltage or dc current provided from said dc power source.

15. A power conditioning unit as claimed in claim 13 wherein said power injection control block is configured to determine a power transferred from said dc source to said ac mains power supply using a squared value of said sinusoidal voltage component, and to control said dc-to-ac converter responsive to said determined power transferred.

16. A power conditioning unit as claimed in claim 13 wherein said power injection control block is galvanically isolated from said dc power source.

17. A power conditioning unit as claimed in claim 13 wherein said power injection control block is configured to multiply a voltage sensed from said energy storage capacitor by a sinusoidal template to generate a template signal, and to compare said template signal with a signal sensed from said output to control said dc-to-ac converter.

18. A power conditioning unit as claimed in claim 13 further comprising a dc voltage amplifier coupled between said input and said energy storage capacitor to increase a voltage from said dc power source by a substantially constant amplification factor.

19. A power conditioning unit as claimed in claim 18 further comprising a voltage amplifier control block to drive said dc voltage amplifier with a substantially constant duty cycle pulse width modulation control signal, and to provide on-off control of a dc output from said dc voltage amplifier.

20. A power conditioning unit as claimed in claim 13 wherein an energy flow from said dc power source to said energy storage capacitor is substantially proportional to an amount of energy stored in said energy storage capacitor, and wherein an amount of energy drawn from said energy storage capacitor and provided to said output is controlled by said power injection control block such that said amount of energy stored in said energy storage capacitor is dependent on said ac power delivered to said ac mains power supply, wherein said power injection block is able to track said maximum power point by controlling said ac power delivered to said ac mains power supply.

21. A power conditioning unit as claimed in claim 13 wherein said power injection control block is configured to track said maximum power point by controlling said power injection control block to substantially maximise said amplitude of said sinusoidal voltage component.

22. A method of maximum power point tracking (MPPT) in a power conditioning unit for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit including an energy storage capacitor for storing energy from said dc power source for delivering to said ac mains power supply output, the method comprising:

tracking a maximum power point of said dc power source by controlling a dc-to-ac converter converting energy stored in said energy storage capacitor to ac power for said ac mains power supply input, wherein said tracking is performed without measuring a dc voltage or dc current provided from said dc power source.

23. A method as claimed in claim 22 wherein, in operation, a voltage on said energy storage capacitor has a sinusoidal voltage component at twice a frequency of said ac mains, and wherein said controlling comprises controlling an amplitude of an ac current provided to said ac mains power supply output such that an amount of power transferred to said ac mains power supply output is dependent on an amplitude of said sinusoidal voltage component on said energy storage capacitor.

24. A method as claimed in claim 23 further comprising determining a power transferred from said dc source to said ac mains power supply using a squared value of said sinusoidal voltage component, and wherein said tracking is responsive to said determined transferred power.

25. A method as claimed in claim 22 wherein said tracking is performed by a power injection control block controlling power injected into said ac mains power supply.

26. A method of maximum power point tracking (MPPT) in a power conditioning unit for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit including an energy storage capacitor for storing energy from said dc power source for delivering to said ac mains power supply output, wherein, in operation, a voltage on said energy storage capacitor has a sinusoidal voltage component at twice a frequency of said ac mains, the method comprising:

controlling an amplitude of an ac current provided to said ac mains power supply output such that an amount of power transferred to said ac mains power supply output is dependent on an amplitude of said sinusoidal voltage component on said energy storage capacitor, wherein said controlling is performed by controlling a dc-to-ac converter converting energy stored in said energy storage capacitor to ac power for said ac mains power supply input; and

tracking a maximum power point of said dc source by controlling said dc-to-ac converter.

27. A method as claimed in claim 26 wherein said tracking is performed without measuring a dc voltage or dc current provided from said dc power source

28. A method as claimed in claim 26 further comprising determining a power transferred from said dc source to said ac mains power supply using a squared value of said sinusoidal voltage component, and wherein said tracking is responsive to said determined transferred power.

29. A method as claimed in claim 26 wherein said tracking is performed by a power injection control block controlling power injected into said ac mains power supply.

30. A method as claimed in claim 29 further comprising galvanically isolating said power injection control block from said dc power source.

31. A method of maximum power point tracking (MPPT) in a power conditioning unit for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit including an energy storage capacitor for storing energy from said dc power source for delivering to said ac mains power supply output, the method comprising:

tracking a maximum power point of said dc power source by controlling a dc-to-ac converter converting energy stored in said energy storage capacitor to ac power for said ac mains power supply input, wherein said tracking comprises;

sensing, at a circuit node coupled to said energy storage capacitor, a signal responsive to a level of power drawn from said dc power source; and

controlling said dc-to-ac converter to adjust an amplitude of an ac output to substantially maximise said sensed signal.

32. A method as claimed in claim 31 wherein said controlling comprises controlling a switching rate of said dc-to-ac converter.

33. A method as claimed in claim 32 wherein said controlling comprises sensing said ac current provided to said ac mains power supply, determining a control signal dependent on a change in said sensed signal responsive to said level of power, determining a difference between said sensed ac current and said control signal and adjusting said ac current responsive to said difference to increase said sensed signal responsive to said level of power.

34. A method as claimed in claim 31 wherein said sensed signal responsive to said level of power comprises a signal dependent on a level of sinusoidal ripple on said energy storage capacitor.

35. A method as claimed in claim 31 wherein said sensing comprises sensing at a dc link of said power conditioning unit, wherein said power conditioning unit further comprises a dc-to-ac converter coupled to said dc power source, wherein said dc link is coupled between said dc-to-dc converter and said dc-to-ac converter, and wherein said energy storage capacitor is coupled to said dc link.