Multilevel DC link inverter for brushless permanent magnet motors with very low inductance

Due to their long effective air gaps, permanent magnet motors tend to have low inductance. The use of ironless stator structure in present high power PM motors (several tens of kWs) reduces the inductance even further (<100 /spl mu/H). This low inductance imposes stringent current regulation demands for the inverter to obtain acceptable current ripple. An analysis of the current ripple for these low inductance brushless PM motors shows that a standard inverter with the most commonly used IGBT switching devices cannot meet the current regulation demands and will produce unacceptable current ripples due to the IGBT´s limited switching frequency. This paper introduces a new multilevel DC link inverter, which can dramatically reduce the current ripple for brushless PM motor drives. The operating principle and design guidelines are included.