Performance of a Two-Stage Actively Damped LC Filter for GaN/SiC Motor Inverters

In this paper, the filter performance of a wide-bandgap (WBG) three phase motor inverter with integrated sinusoidal output voltage LC filter is analyzed. To ensure a well damped system behaviour at low losses, an active damping scheme based on filter capacitor feedback is used. Unfortunately, the nonlinear DC-Bias dependent capacitance of the used ceramic capacitors (X7R is used to minimize filter volume) significantly affects the active damping. A symmetrical filter structure sufficiently reduces the capacitors voltage dependency. However, the paper shows that the symmetrical structure also causes negative effects in respective to the filters noise suppression performance. Modifications in the filter topology are reported and analyzed for reducing the impaired noise suppression. The proposed filter scheme finally results in a well damped system behaviour fulfilling established EMC standards according output noise demonstrated by experimental results of a 2 kW/400 V laboratory prototype.