A closed-loop selective harmonic compensation for active filters

This paper proposes a control algorithm for parallel active power filters, based on current-controlled PWM converters, which allows precise compensation of selected harmonic currents produced by distorting loads. The approach is based on the measurement of line currents and performs the compensation of the selected harmonics using closed-loop synchronous frame controllers. Because of the closed-loop operation, full compensation of the desired harmonics is achieved even in the presence of a significant delay in the VSI current control. Because of the selective approach, active filter interactions with a possible dynamic component of the load are minimized. The complexity of the synchronous frame controllers are avoided using equivalent stationary frame controllers with the same dynamic performance. Experimental results of a converter prototype confirm the theoretical expectations.