Static Var Compensator Having Active Filter Function for Lower Order Harmonics

In this paper, various harmonic characteristics of SVC's (Static Var Compensators) are discussed, comparison being made between symmetrical and asymmetrical modulation strategies which influence a quality of output waveform. It appears that the asymmetrical modulation strategy is the better approach in higher power factor applications such as ac motor drives. However, in a case requiring a passive filter, for example, with an extremely large scale SVC, a symmetrical modulation strategy is superior. Therefore, In this research, a symmetrical modulation is preferred for a NPC-PWM inverter. Since the harmonics, due to the switching appear in a limited narrow frequency band, such output harmonics can be easily eliminated using a simple passive filter. Furthermore, harmonics such as the fifth and the seventh can be suppressed using the proposed SVC scheme, in which the feedback signals for the fifth and seventh harmonics are injected into the SVC. Using these feedback signals, the harmonics in the power system can be significantly reduced. This result is confirmed by simulation. Thus, in addition to the proper operation of the SVC, It is possible to perform an active filtering function.