LC Filter Design for Wide Band Gap Device Based Adjustable Speed Drives

This paper presents a simple design procedure for LC filters used in wide band gap device based adjustable speed drives. Wide band gap devices offer fast turn-on and turn-off times, thus producing high dV/dt into the motor terminals. The high dV/dt can be harmful for the motor windings and bearings and must therefore be reduced. This may be accomplished by a sine LC filter with DC link feedback, which reduces both the differential mode and common mode dV/dt. Wide band gap devices are capable of switching at frequencies much higher than traditional Si based devices. This makes it possible to design the LC filter with a higher cut off frequency and without damping resistors. The selection of inductance and capacitance is chosen based on capacitor voltage ripple and current ripple. The filter adds a base load to the inverter, which increases the inverter losses. It is shown how the modulation index affects the capacitor capacitor and the inverter current.