A Four-Level Rectifier-Inverter System for Drive Applications

Multilevel converters are based on the neutral point clamped inverter topology proposed by Nabae et al. [1]. Subsequently, Bhagwat and Stefanovic [2] demonstrated the possible advantages of a multilevel converter topology. However, by using dc power supplies (i.e., batteries), voltage balancing of the dc link capacitors was not demonstrated for possible drive applications. Three distinct topologies have been proposed so far to realize the multilevel inverter (MLI) [3,4], viz., the diode clamped MLI, the “flying capacitor" MLI, and MLIs with separate dc sources. So far, attention has been largely restricted to high-power, high-voltage applications such as static var compensation [5] in which the voltage balancing of the dc capacitors is less difficult. However, recently a three-level rectifier-inverter drive system was investigated in [6, 7, 8], and a partially active three-level rectifier topology was proposed in [9].