Energy efficiency of two-level and multilevel inverters - a drive system comparison

Multilevel inverter topologies are an alternative for a wide range of low voltage electrical drives. They can reduce power semiconductor losses, voltage transients at the motor windings, harmonic losses in the cables and common mode disturbance currents. In the voltage range below 1000 V highly optimized switches with lower losses are available. The paper compares the component losses (power semiconductor losses in the frequency inverter, losses of the output filter, harmonic cable and motor losses) and the efficiency of a drive system with two-level and different multilevel NPC inverters. Higher inverter levels reduce the power losses of the inverter and the output filter. For a 22 kW induction motor a losses reduction of 800 W is simulated, if a five-level inverter is used. A five-level inverter requires power semiconductor devices with 300 V blocking voltage. New wide-bandgap semiconductors (SiC, GaN) with low blocking voltage have the potential to reduce the conduction and switching losses in multilevel inverters. This would lead to a reduction of cooling effort and to smaller inverter size. Moreover, the sine filter at the inverter output can be chosen smaller which is accompanied by lower power losses inside the filter. The application of multilevel inverters also in the so called low voltage range can make a contribution to efficiency improvement in electrical drives.