Harmonic distortion reduction technique for uninterruptible power supplies with DC voltage boost technique

This paper presents a new control strategy for UPS inverter, which is based on the addition of the DC voltage boost compensation for keeping the fundamental output voltage at the preset value and suppressing the generation of low-order harmonics caused by nonlinear load. This solution involves the combination of a total harmonic distortion (THD) reduction controller and a power factor correction (PFC) controller, such that the harmonics contaminated in the output voltage can be eliminated despite the highly distorted load current while maintaining an acceptable dynamic performance. Thus, the proposed strategy is viewed as a refinement term added to the outer voltage control loop. Besides, the DC voltage of the inverter under linear loads is adaptively reduced so that low switching losses is achieved, when compared with conventional constant DC voltage approaches. The new strategy is quite simple and requires only the measurement of the output voltage to compute the THD. Simulation results are presented to exhibit the improved performance of the proposed approach especially under rectifier loads.