Active EMI filter for switching noise of high frequency inverters

In high frequency inverter fed ac motor systems, high frequency leakage current generated by high dv/dt at switching times flows to the ground wire through the stray capacitor between motor windings and core. This paper proposes an active EMI filter to compensate common mode current using high frequency transistors as active elements and a high frequency common mode CT. It works just as a power active filter in the harmonic compensation in the power system. The leakage current is actively suppressed to under 1/50 of the uncompensated circuit. The proposed method is also effective to decrease the EMI, more than 40 dB mu V.