A new control method for PWM voltage-source converters under unbalanced input voltage condition

The advanced features of three-phase PWM voltage-source converter are not necessarily achieved under unbalanced input voltage conditions due to the generation of even-order harmonics at dc output and the odd-order harmonics in input currents. Both the 2^nd harmonic voltage component onto the dc link and the negative sequence part of the input currents can disturb the performance of the attached inverter load and reduce the dc link capacitor lifetime. This paper presents a kind of new observer-based unbalance estimation and control method that compensates source voltage unbalances. The 2^nd harmonics were eliminated and the unbalanced input currents were compensated by this new control method, respectively. The presented method also compensates the detrimental impact of delay effects and reduces the PWM switching frequency. Analytical and simulation results are presented to illustrate the effectiveness of the new observer-based control method.