High-Performance Control Strategies and Applications of a New Hybrid Cascaded Multilevel Inverter

Multilevel inverters have been receiving increasing attention in recent years. Use of multilevel inverters has become popular for motor drive applications. Various topologies and modulation strategies have been investigated in the literature. This paper is devoted to the investigation of a new hybrid multilevel inverter system typically suitable for high-performance high-power applications. In this new topology, 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 the floating ultra capacitors to store the braking energy of motors, which will be reused. The efficiency of the system can be improved. Compared with the traditional H-bridge inverter, this new scheme can reduce the DC sources while maintaining the same voltage output. When the motor is at steady state, the conditioning inverter can provide reactive power to the motor, so that the power factor of the main inverter can be improved. At the same time, the floating capacitor´s voltage can be kept balanced by proper control. This scheme has a wide range of practical applications, especially in the electric vehicle motor drive and marine propulsion system.