Operation of fault-tolerant inverters with DC-link midpoint connection for adjustable speed drives

Some fault-tolerant three-phase inverters are based upon a reconfiguration to an inverter with only two active phases and a DC-link midpoint connection after any semiconductor failure. Thus, the maximum output voltage is halved and the DC-link midpoint capacitor voltage ripple depends on output frequency and output current of the inverter. These limiting effects on the operation range of adjustable speed drives as well as software and hardware based countermeasures are presented in this paper.