Investigation of Control Method for a New Hybrid Cascaded Multilevel Inverter

In recent years, multilevel inverters are becoming more and more popular in the medium-high voltage AC drive system. Various multilevel inverter topologies have been proposed to enhance the performance of motor drive system. This paper presents a hybrid cascaded multilevel inverter scheme, in which the H-bridge inverter (main inverter) and the 3-level diode clamped inverter (conditioning inverter) are connected together to drive the motors, but only the main inverter needs DC voltage source. The conditioning inverter is supplied by ultra capacitors to store the braking energy of motors which will be reused. Additionally, compared with the traditional H-bridge inverter, this scheme can reduce the DC sources while maintaining the same voltage output. Further more, when the motor is at steady state, the conditioning inverter can provide reactive power to the motor and the capacitor´s voltage can be kept balanced. This scheme has a wide range of practical applications, especially in the electric vehicle motor drive and marine propulsion system.