Analysis and implementation of a three-level active filter with a reduced number of power semiconductors

A three-phase two-leg voltage source inverter is proposed to achieve three-level pulsewidth mudulation operation. A shunt active power filter based on the proposed inverter is implemented to achieve harmonic elimination, reactive power compensation and DC-link voltage regulation. Four active switches are used in each inverter leg. The proposed inverter is operated as a controllable current source to supply the necessary active power for the compensation of inverter losses, to suppress current harmonics, and to compensate the reactive power drawn by the nonlinear loads. The balanced and sinusoidal line currents are drawn from the AC source. There are two control loops in the control algorithm to keep the DC-link voltage constant and to track line current commands. The effectiveness of the control scheme is verified through simulation and experimental results based on a laboratory prototype.