Control circuits for power converters
A control circuit for controlling one or more power switches of a power converter includes a voltage control loop and a current control loop. The control circuit is configured to generate a current reference for the current control loop using the voltage control loop and an AC reference signal. The control circuit is configured to operate in at least a first mode in which a parameter of the voltage control loop is sampled only at every other zero crossing of the AC reference signal and the sampled parameter is used to generate the current reference for the current control loop. The power converter may be an AC-DC converter or a DC-AC converter (i.e., inverter). Alternatively, the voltage control loop may be sampled at every zero crossing of the AC reference signal, and/or more frequently during transient load conditions.
1. A power converter comprising:
an inverter for coupling to a utility grid, the inverter comprising a power circuit having at least one power switch; and
a control circuit for controlling the at least one power switch, the control circuit including a voltage control loop and a current control loop, the control circuit configured to generate a current reference for the current control loop using the voltage control loop and an AC reference signal, the control circuit configured to operate in at least a first mode in which a parameter of the voltage control loop is sampled only once per full cycle of the AC reference signal and the sampled parameter is used to generate the current reference for the current control loop.
2. The power converter of claim 1 wherein the control circuit is configured to sample the voltage control loop parameter at a fixed time during each full cycle of the AC reference signal.
3. The power converter of claim 2 wherein the fixed time is during a zero crossing of the AC reference signal.
4. The power converter of claim 3 wherein the AC reference signal is an AC voltage of the utility grid.
5. The power converter of claim 4 wherein the control circuit includes a phase lock loop (PLL) for monitoring the AC voltage of the utility grid.
6. The power converter of claim 5 wherein the voltage control loop is configured to regulate a DC input voltage of the inverter and the current control loop is configured to shape an AC output current of the inverter.
7. The power converter of claim 1 wherein the control circuit is configured to implement average current mode (ACM) control using the voltage control loop and the current control loop.
8. The power converter of claim 1 wherein the voltage control loop includes a proportional-integral controller and the sampled parameter is an output of the proportional-integral controller.
9. The power converter of claim 1 wherein the sampled parameter is an error signal produced by the voltage control loop.
10. The power converter of claim 9 wherein the voltage control loop includes a proportional-integral controller for processing the sampled parameter.
11. The power converter of claim 1 wherein the inverter is a grid-tie inverter.
12. The power converter of claim 1 wherein the inverter is a solar inverter configured to implement a maximum power tracking function.
13. The power converter of claim 1 wherein the AC reference signal is an AC voltage of the utility grid.
14. The power converter of claim 13 wherein the control circuit is configured to sample the voltage control loop parameter at a fixed time during each full cycle of the AC reference signal.
15. The power converter of claim 4 wherein the control circuit is configured to implement average current mode (ACM) control using the voltage control loop and the current control loop.
16. The power converter of claim 4 wherein the voltage control loop includes a proportional-integral controller and the sampled parameter is an output of the proportional-integral controller.
17. The power converter of claim 4 wherein the sampled parameter is an error signal produced by the voltage control loop.
18. The power converter of claim 17 wherein the voltage control loop includes a proportional-integral controller for processing the sampled parameter.