Inverter for a distributed power generator

• US 8,670,249 B2
• Filed: 02/19/2010
• Issued: 03/11/2014
• Est. Priority Date: 02/20/2009
• Status: Active Grant

• Current Assignee: SPARQ Systems, Inc.
• Original Assignee: SPARQ Systems, Inc.
• Inventors: Khajehoddin, Sayed Ali, Jain, Praveen, Bakhshai, Alireza
• Primary Examiner(s): Laxton, Gary L
• Application Number:
  US12/709,166
• Publication Number:
  US 20100236612A1
• Time in Patent Office: 1,481 Days
• Field of Search: 363/40, 363/41, 363/78, 363/79, 363/80, 363/95, 363/97, 363/98, 363/131, 363/132, 363/39, 323/266, 323/906
• US Class Current: 363/39
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H01L 31/02021 for solar cells electrical connection means, e.g. junction boxes, specially adapted for structural association with photovoltaic modules H02S40/34
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 1/14 Arrangements for reducing ripples from dc input or output
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

Provided is a maximum power point (MPP) tracker for a PV cell inverter, and a PV cell inverter. The MPP tracker decouples output power oscillations from the input power generation and extracts maximum available power from the PV cell. The PV cell inverter uses the MPP tracker and generates a sinusoidal output current from the MPP tracker output. The sinusoidal output current may be fed to a power distribution grid. The PV cell inverter may use a pulse width modulation technique to cancel harmonics in the sinusoidal output current. The circuits use a minimum number of components and avoid use of large electrolytic capacitors.

Claims

1. A circuit for use with an inverter and a distributed power generator, comprising:

a high side input point and a low side input point for the distributed power generator;

and

(i) a parallel input capacitor connected across the high side input point and the low side input point;

a first regulating circuit connected in parallel with the parallel input capacitor, the first regulating circuit having a high side output point and a low side output point for connection to an input of the inverter; and

a first controller that controls the first regulating circuit so that voltage oscillation at twice a grid frequency across the parallel input capacitor is substantially removed;

wherein the parallel input capacitor has a small value such that voltage oscillation at twice the grid frequency at the first regulating circuit high side and low side output points is not substantially removed;

or

(ii) a series input inductor having a first terminal and a second terminal, the first terminal connected to one of the high side input point and the low side input point;

a second regulating circuit connected between the second terminal of the series input inductor and the other of the high side input point and the low side input point, the second regulating circuit having a high side output point and a low side output point for connection to an input of the inverter; and

a second controller that controls the second regulating circuit so that current oscillation at twice a grid frequency through the series input inductor is substantially removed;

wherein the series input inductor has a small value such that current oscillation at twice a grid frequency at the second regulating circuit high side and low side output points is not substantially removed.

2. The circuit of claim 1, wherein the first regulating circuit regulates voltage across the parallel input capacitor between a lower limit and an upper limit.

3. The circuit of claim 1, wherein the first regulating circuit that regulates voltage across the parallel input capacitor comprises:

a switch connected between the high side input point and a node;

an output inductor connected between the node and the high side output point; and

a diode connected between the node and the low side output point.

4. The circuit of claim 2, wherein the upper limit is a reference voltage and the lower limit is selected so that a switching frequency of a switch and the voltage oscillation across the parallel input capacitor does not exceed selected values.

5. The circuit of claim 4, wherein the reference voltage is obtained from a maximum power point tracking (MPPT) algorithm.

6. The circuit of claim 1, wherein the first controller or the second controller is a hysteresis controller.

7. The circuit of claim 1, wherein the second regulating circuit regulates current through the series input inductor between a lower limit and an upper limit.

8. The circuit of claim 1, wherein the second regulating circuit that regulates current through the series input inductor comprises:

a switch connected between the second terminal of the series input inductor and the other of the high side input point and the low side input point; and

a diode connected in series between the second terminal of the series input inductor and a corresponding high side output point or low side output point.

9. The circuit of claim 7, wherein the upper limit is a reference current and the lower limit is selected so that a switching frequency of a switch and the current oscillation through the series input inductor does not exceed selected values.

10. The circuit of claim 9, wherein the reference current is obtained from a maximum power point tracking (MPPT) algorithm.

11. The circuit of claim 1, wherein the distributed power generator is a photovoltaic cell.

12. An inverter for a distributed power generator, comprising:

the circuit of claim 1; and

an output circuit connected to the high side output point and the low side output point of the first regulating circuit or the second regulating circuit that generates a substantially sinusoidal output current.

13. The inverter of claim 12, wherein the distributed power generator is a photovoltaic cell.

14. The inverter of claim 12, wherein:

the output circuit that generates a substantially sinusoidal output current comprises a current source inverter or a voltage source inverter.

15. The inverter of claim 14, further comprising a compensator that controls the current source inverter or the voltage source inverter to substantially reduce harmonics in the inverter output current arising from inverter input voltage or input current oscillations at twice the grid frequency.

16. The inverter of claim 15, wherein the compensator comprises a pulse width modulator and the compensator modifies a pulse width modulation (PWM) reference signal in proportion to a ratio of average and instantaneous values of the voltage source inverter input voltage or the current source inverter input current.

17. The inverter of claim 16, wherein the distributed power generator is a photovoltaic cell.

18. A method for obtaining power from a distributed power generator, comprising:

(i) connecting a parallel input capacitor across the output voltage of the distributed power generator;

connecting a first regulating circuit in parallel with the parallel input capacitor, the first regulating circuit having a high side output point and a low side output point; and

controlling the first regulating circuit so that voltage oscillation at twice a grid frequency across the parallel input capacitor is substantially removed;

wherein the parallel input capacitor has a small value such that voltage oscillation at twice the grid frequency at the first regulating circuit high side and low side output points is not substantially removed;

or

(ii) connecting a first terminal of a series input inductor to a first output terminal of the distributed power generator;

connecting a second regulating circuit across a second terminal of the series input inductor and a second output terminal of the distributed power generator, the second regulating circuit having a high side output point and a low side output point; and

controlling the second regulating circuit so that current oscillation at twice the grid frequency through the series input inductor is substantially removed;

wherein the series input inductor has a small value such that current oscillation at twice a grid frequency at the second regulating circuit high side and low side output points is not substantially removed.

19. The method of claim 18, wherein:

(i) controlling the first regulating circuit includes regulating the voltage across the parallel input capacitor between an upper limit and a lower limit;

or

(ii) controlling the second regulating circuit includes regulating the current through the series input inductor between an upper limit and a lower limit.

20. The method of claim 19, wherein:

(i) the upper limit is a reference voltage and the lower limit is selected so that a switching frequency of the first regulating circuit and the voltage oscillation cross the parallel input capacitor do not exceed selected values;

or

(ii) the upper limit is a reference current and the lower limit is selected so that a switching frequency of the second regulating circuit and the current oscillation through the series input inductor do not exceed selected values.

21. The method of claim 18, wherein the distributed power generator is a photovoltaic cell.

22. The method of claim 18, further comprising:

producing substantially sinusoidal output current from output power of the first regulating circuit or second regulating circuit high side output point and low side output point using a current source inverter or a voltage source inverter.

23. The method of claim 22, further comprising connecting the sinusoidal output current to a power distribution grid.

24. The method of claim 22, wherein the distributed power generator is a photovoltaic cell.

25. The method of claim 22, further comprising controlling the current source inverter or the voltage source inverter to substantially reduce harmonics in the inverter output current arising from inverter input voltage or input current oscillations at twice the grid frequency.

26. The method of claim 25, further comprising:

controlling the voltage source inverter or the current source using a pulse width modulator; and

modifying a pulse width modulation (PWM) reference signal in proportion to a ratio of average and instantaneous values of the voltage source inverter input voltage or the current source inverter input current.

27. The method of claim 25, wherein the distributed power generator is a photovoltaic cell.