Novel PWM inverters having their own active filter

For larger scale inverters, since the low frequency switching devices such as GTOs are used. we could not avoid the harmonic generations, especially the lower order harmonics. In order to improve these demerits, various multiple connections of inverters using transformers have been generally reported so far. In this paper a novel circuit configuration is proposed, in which the main fundamental converter constituted by the larger scale GTO inverter supplies an active power at low frequency, and with respect to the harmonics, the reduced scale IGBT inverter supplies a reactive power at high frequency. By means of transformers, these two inverters are connected in series and an improved output current waveform can be obtained. In such manner of using the IGBT inverter having the functions of an active filter some effective control strategies are proposed and the validity is confirmed by simulations and experiments