Distributed power generation interface
Described herein are methods, systems, and apparatus for a controller for a power circuit that interfaces distributed power generation with a power distribution grid, comprising: a first portion, including a maximum power point tracker, that receives signals corresponding to the distributed power generation voltage and current, and outputs to the power circuit a signal for controlling the voltage of the distributed power generation; a second portion, including a current reference generator, a current controller, and a dc voltage controller, that receives signals corresponding to a dc voltage of the power circuit, the power distribution grid voltage and current, and the inverter current, and outputs signals for controlling the power circuit output voltage; wherein the current reference generator includes nonlinear circuit elements and generates a current reference signal from the dc voltage of the power circuit and the grid voltage and current; such that substantially harmonic-free power is injected into the power distribution grid. The distributed power generation may be, for example, a photovoltaic module or a wind turbine.
1. A method for controlling a power circuit that interfaces distributed power generation with a power distribution grid, comprising:
generating a current reference signal;
minimizing a difference between an output grid current and the current reference signal, and outputting a first control signal;
rejecting harmonics, dc, or harmonics and dc in output power delivered to the power distribution grid by receiving only a signal corresponding to the power distribution grid current, and outputting a second control signal; and
generating at least one gating signal that controls the power circuit output current using the first and second control signals;
wherein substantially harmonic-free, dc-free, or harmonic-free and dc-free power is delivered to the power distribution grid using the second control signal corresponding to the power distribution grid current.
2. The method of claim 1 , wherein the power circuit includes a current source inverter.
3. The method of claim 1 , wherein the power circuit includes a voltage source inverter.
4. The method of claim 1 , wherein the distributed power generation includes at least one PV module.
5. The method of claim 1 , including generating an instantaneous power reference signal, and generating the current reference signal from the instantaneous power reference signal and the grid voltage and current using nonlinear elements.
6. The method of claim 5 , including using a phase angle of the grid voltage to generate the instantaneous power reference signal.
7. The method of claim 6 , including using an enhanced phase locked loop (EPLL) to provide the phase angle of the grid voltage.
8. The method of claim 5 , including using real and reactive power commands to control real and reactive power delivered to the power distribution grid.
9. The method of claim 8 , including setting the real and reactive power commands externally.
10. The method of claim 8 , including generating the real power command using a PI controller operating on a dc-link voltage error, on a dc-link current error, or on a dc-link energy error.
11. The method of claim 8 , including generating the reactive power command using a PI controller operating on a voltage magnitude error.
12. The method of claim 1 , including generating parallel and orthogonal signals corresponding to the grid voltage.
13. The method of claim 12 , including generating a real current component of the current reference signal from an error between a reference energy signal and an actual energy signal corresponding to the dc voltage of the power circuit, multiplied with the parallel signal.
14. The method of claim 12 , including generating a reactive component of the current reference signal from an error between a reference reactive power signal and an actual reactive power signal corresponding to the output power of the power circuit, multiplied with the orthogonal signal.
15. The method of claim 12 , including using an EPLL to generate the parallel and orthogonal signals corresponding to the grid voltage.
16. The method of claim 1 , including using a semi-state feedback control structure combined with a resonant-type output feedback portion in a current controller.
17. The method of claim 16 , including using a feed forward soft start controller.
18. The method of claim 17 , wherein the current controller comprises:
(i) one or more resonant-type harmonic controllers acting on grid current;
(ii) an integrating controller acting on grid current;
(iii) a wide band harmonic controller in parallel with a resonant-type controller;
(iv) a wide band harmonic controller in series with a resonant-type controller; or
(v) a wide band feed forward harmonic compensator acting on the grid voltage signal; or
(vi) two or more of (i) to (v).
19. The method of claim 17 , wherein the current controller comprises a wide band harmonic controller having a proportional, proportional-derivative, lead, or lead-lag configuration.
20. The method of claim 17 , wherein the current controller comprises a wide band feed forward harmonic compensator having a proportional, proportional-derivative, lead, or lead-lag configuration.
21. The method of claim 1 , including using a semi-state feedback combined with one or more resonant-type output feedback portions in a current controller.
22. The method of claim 21 , wherein each resonant-type output feedback portion corresponds to a harmonic of the grid voltage.
23. The method of claim 1 , wherein controlling power delivered to the power distribution grid includes using a maximum power point tracker.