Power conversion system with transient event ride-through capability and method thereof

1. A power conversion system, comprising:

a DC bus for receiving direct current (DC) power;

a line side converter coupled to the DC bus for converting the DC power on the DC bus to alternating current (AC) power; and

a voltage source controller for providing control signals to the line side converter to enable the line side converter to regulate the AC power, the voltage source controller comprising:

a signal generator to generate the control signals for the line side converter based at least in part on a power command signal and a power feedback signal;

an active power regulator for generating an internal frequency command signal based on the power command signal and the power feedback signal, and for generating a phase angle command signal by integrating the internal frequency command signal;

a current limiter to, during a transient event, adjust the phase angle command signal based at least in part on an electrical current threshold; and

a voltage limiter for adjusting the phase angle command signal based at least in part on a DC bus voltage feedback signal and a DC boundary voltage threshold during the transient event,

wherein the voltage source controller is configured to use the phase angle command signal when generating the control signals.

2. The power conversion system of claim 1 , wherein the power conversion system further comprises a maximum power point tracking (MPPT) device for generating an MPPT power reference signal, wherein the voltage source controller further comprises a power command adjustment unit configured to constrain the power command signal according to the MPPT power reference signal.

3. The power conversion system of claim 1 , wherein the voltage source controller further comprises a freezing unit for determining whether the power conversion system is entering the transient event or recovering from the transient event by detecting a feedback voltage at the output of the line side converter, and generating a status signal used to freeze one or more integrating elements of the active power regulator until the power conversion system is determined to be recovered from the transient event.

4. The power conversion system of claim 1 , the current limiter is configured to calculate a voltage magnitude threshold based at least in part on the electrical current threshold and an impedance at the output terminal of the line side converter, and further to calculate a phase angle limit signal for the phase angle command signal based at least in part on the calculated voltage magnitude threshold and a feedback grid voltage.

5. The power conversion system of claim 1 , wherein the power conversion system further comprises a phase locked loop (PLL) circuit for generating a frequency reference signal or a phase angle reference signal of a grid voltage, and the active power regulator is further configured for generating the phase angle command signal by adjusting the internal frequency command signal according to the frequency reference signal or adjusting the phase angle command signal according to the phase angle reference signal.

6. The power conversion system of claim 1 , wherein the voltage limiter is further configured to provide a frequency correction signal for the internal frequency command signal or a phase angle correction signal for the phase angle command signal based on the DC bus voltage feedback signal and the DC boundary voltage threshold.

7. The power conversion system of claim 1 , wherein the voltage source controller further comprises a reactive power regulator for generating a voltage magnitude command signal based on a reactive power command signal and a reactive power feedback signal obtained by measuring the AC power output from the line side converter, and wherein the voltage source controller is configured to use the voltage magnitude command signal when generating the control signals provided to the line side converter.

8. The power conversion system of claim 7 , wherein the voltage source controller further comprises a freezing unit for determining whether the power conversion system is entering the transient event or recovering from the transient event by receiving a feedback voltage at the output of the line side converter, and for generating a status signal to freeze one or more integrating elements of the reactive power regulator until the power conversion system is determined to be recovered from the transient event.

9. The power conversion system of claim 7 , wherein the current limiter is configured to calculate a voltage. magnitude threshold based at least in part on the electrical current threshold and an impedance at the output terminal of the line side converter, and further to calculate a voltage magnitude limit on the voltage magnitude command signal based at least in part on the calculated voltage magnitude threshold and a feedback grid voltage.

10. The power conversion system according to claim 7 , wherein the current limiter is configured to calculate a voltage magnitude threshold based at least in part on the electrical current threshold and an impedance at the output terminal of the line side converter, to calculate a phase angle limit based at least in part on the voltage threshold and a feedback grid voltage, and to calculate a voltage magnitude limit on the voltage magnitude command signal based at least in part on the phase angle limit, the calculated voltage magnitude threshold.

11. A method of operating a line side converter in a power conversion system, the method comprising:

generating control signals for the line side converter based at least in part on a power command signal and a power feedback signal, said generation comprising:

generating an internal frequency command signal based on the power command signal and the power feedback signal;

integrating the internal frequency command signal to generate a phase angle command signal for use when generating the control signals;

limiting, during a transient event, the phase angle command based at least in part on an electrical current threshold and a DC bus boundary voltage threshold;

generating the control signals based on the limited phase angle command; and

applying the control signals to the line side converter.

12. The method of claim 11 , further comprising:

freezing one or more integrating elements of the power conversion system upon determination that the power conversion system is experiencing the transient event; and

resetting the one or more integrating elements of the power conversion system upon determination that the power conversion system has recovered.

13. The method of claim 11 , further comprising:

calculating a voltage magnitude threshold based at least in part on the electrical current threshold and an impedance at the output terminal of the line side converter;

calculating a phase angle limit signal based at least in part on the calculated voltage threshold and a feedback grid voltage;

providing a limit on the phase angle command signal using the phase angle limit signal.

14. The method of claim 11 , further comprising:

using a phase locked loop (PLL) circuit for generating a frequency reference signal or a phase angle reference signal of a grid voltage;

adjusting the internal frequency command signal according to the frequency reference signal or adjusting the phase angle command signal according to the phase angle reference signal.

15. The method of claim 11 , further comprising:

generating a voltage magnitude command signal based on a reactive power command signal and a feedback reactive power signal obtained by measuring the AC power output from the line side converter, and using the voltage magnitude command signal when generating the control signals.

16. The method of claim 11 , further comprising:

calculating a voltage magnitude threshold based at least in part on the electrical current threshold and an impedance at the output terminal of the line side converter;

calculating a voltage magnitude limit based at least in part on the calculated voltage magnitude threshold and a feedback grid voltage;

providing a limit on the voltage magnitude command signal using the voltage magnitude limit.

17. The method of claim 11 , further comprising:

calculating a voltage magnitude threshold based at least in part on the electrical current threshold and an impedance at the output terminal of the line side converter;

calculating a phase angle limit based at least in part on the voltage magnitude threshold and a feedback grid voltage;

calculating a voltage magnitude limit based at least in part on the phase angle limit;

providing a limit on the voltage magnitude command signal using the voltage magnitude limit.

18. A solar power conversion system, comprising:

a photovoltaic (PV) power source for outputting direct current (DC) power;

a DC bus for receiving the DC power from the PV power source;

a line side converter electrically coupled to the DC bus for converting the DC power on the DC bus to alternating current (AC) power; and

a voltage source controller configured to:

generate a phase angle command based at least in part on a power command signal and a power feedback signal;

limit, during a transient event, the phase angle command based at least in part on an electrical current threshold and a DC boundary voltage limit;

generate the control signals based on the limited phase angle command; and

apply the control signals to the line side converter to limit the electrical current of the line side converter when the power conversion system is experiencing the transient event.