Capacitor Voltage Balancing Control of Four-Leg Inverter for Two Vector-Controlled Induction Motor Drives

Recently, the four-leg inverter and the four switch inverter, which have fewer of switches, have been studied for their advantages of low cost and compactness super((1)-(12)). In particular, the four-leg inverter super((13)-(15)) can drive two motors independently. Applications of the four-leg inverter are factory automation, electric vehicles and crane trucks. The inverter consists of four legs and two capacitors connected in a series. However, many of conventional studies on the four-leg inverter and the four switch inverter have used open-loop control systems such as the volts per hertz (V/f) control system. This paper proposes capacitor voltage balancing control of the four-leg inverter for two vector-controlled induction motor drives. In this a study, the source of the capacitor voltage fluctuation caused by the current flow through the capacitors is analyzed by using the space vector and a compensation method is described. The capacitor voltage fluctuation compensation method and the independent drives of the two induction motors fed by the four-leg inverter with the vector control method are demonstrated with experimental results.