Closed-Loop Harmonic Suppression for Grid Connected 3-Phase PWM Inverters

Harmonic currents disturb the operation of ac grids with electronically controlled and distributed sources and loads. Harmonic suppression methods in grid-connected inverters exhibit finite attenuation of low-order harmonics, weak suppression of high-order harmonics, and dynamic coupling between current controllers and harmonic controllers, which all impair overall performance. The developed harmonic controller suppresses residual harmonics to at least sixty decibels below rated current. The structure includes a new error-free harmonic estimator and an original controller that eliminates mutual coupling with the fundamental current controller. The system is experimentally tested in industrial inverter units connected to an ac grid rich in harmonics with artificially introduced unbalances.