Digital controller for a power converter

1. A second-order controller for a power inverter control system, comprising:

an input that receives an error signal corresponding to the power inverter output voltage or current;

first and second control loops that operate substantially independently;

wherein the first control loop is an amplitude control loop and the second loop is a phase control loop;

wherein the phase control loop receives a signal corresponding to a fundamental system frequency of the output voltage or current and produces a phase signal, and adjusts the phase signal according to the error signal and a cosine of the phase signal;

wherein the amplitude control loop adjusts the error signal according to a sine of the phase signal to produce an output signal that controls the power inverter.

2. The second-order controller of claim 1 , wherein:

the amplitude control loop operates at an amplitude that is proportional to an amplitude of an input signal at the fundamental system frequency and at a selected harmonic of the fundamental system frequency; and

the phase control loop operates at the fundamental system frequency and at a selected harmonic of the fundamental system frequency.

3. The second-order controller of claim 1 ; wherein the phase control loop is adaptable to the fundamental system frequency or to a selected harmonic of the fundamental system frequency.

4. The second-order controller of claim 1 , implemented in a digital domain.

5. The second-order controller of claim 1 , implemented in an analogue domain.

6. The second-order controller of claim 3 , implemented in a digital domain.

7. The second-order controller of claim 3 , implemented in an analogue domain.

8. The second-order controller of claim 4 , wherein:

the second-order controller requires a number of bits to satisfy a stability criterion;

wherein the number of bits is less than a number of bits required by a second-order controller having a combined amplitude and phase control loop to satisfy a stability criterion.

9. The second-order controller of claim 4 , wherein:

the second-order controller is stable over a range of sampling frequencies;

wherein the range of sampling frequencies is broader than a range of sampling frequencies over which a second-order controller having a combined amplitude and phase control loop is stable.

10. A n-order controller for a power inverter control system, comprising;

at least one controller according to claim 1 ;

wherein n is three or more.

11. The second-order controller of claim 1 , wherein the power inverter control system includes one or more of a distributed generation (DG) system, a microinverter for a photovoltaic system, a grid-connected inverter, a grid-isolated inverter, an uninterruptible power supply (UPS), an off-grid DG system, a permanent magnet synchronous motor drive, an active power filter, and a flexible ac transmission system.

12. A second-order control method for a power inverter control system, comprising:

receiving an error signal corresponding to the power inverter output voltage or current;

operating first and second control loops substantially independently;

wherein the first control loop is an amplitude control loop and the second loop is a phase control loop;

wherein the phase control loop receives a signal corresponding to a fundamental system frequency of the output voltage or current and produces a phase signal, and adjusts the phase signal according to the error signal and a cosine of the phase signal;

wherein the amplitude control loop adjusts the error signal according to a sine of the phase signal to produce an output signal that controls the power inverter.

13. The second-order control method of claim 12 , comprising:

operating the amplitude control loop at an amplitude that is proportional to an amplitude of an input signal at the fundamental system frequency and at a selected harmonic of the fundamental system frequency; and

operating the phase control loop at the fundamental system frequency and at a selected harmonic of the fundamental system frequency.

14. The second-order control method of claim 12 , wherein operating the phase control loop includes adapting to the fundamental system frequency or to a selected harmonic of the fundamental system frequency.

15. The second-order control method of claim 12 , including operating the method in a digital domain.

16. The second-order control method of claim 12 , including operating the method in an analogue domain.

17. The second-order control method of claim 14 , including operating the method in a digital domain.

18. The second-order control method of claim 14 , including operating the method in an analogue domain.

19. The second-order control method of claim 15 , wherein:

operating requires a number of bits to satisfy a stability criterion;

wherein the number of bits is less than a number of bits required by a second-order controller having a combined amplitude and phase control loop to satisfy a stability criterion.

20. The second-order control method of claim 15 , including:

operating such that the method is stable over a range of sampling frequencies;

wherein the range of sampling frequencies is broader than a range of sampling frequencies over which a second-order controller having a combined amplitude and phase control loop is stable.

21. An n-order control method for a power inverter control system, comprising;

operating at least one controller according to claim 12 ;

wherein n is three or more.

22. The second-order control method of claim 12 , including controlling a power inverter in a system comprising one or more of a distributed generation (DG) system, a microinverter for a photovoltaic system, a grid-connected inverter, a grid-isolated inverter, an uninterruptible power supply (UPS), an off-grid DG system, a permanent magnet synchronous motor drive, an active power filter, and a flexible ac transmission system.