Performance of medium voltage multi-level inverters

There are many ways to build medium voltage inverters. This paper studies the characteristics of two types of nonregenerative medium voltage source inverters that are in the market place today. Each inverter that was investigated has major differences in circuit topologies, which in turn led to differences in performance characteristics. The operational characteristics and the mechanical construction of a 5 level neutral point clamped medium voltage PWM inverter are described. Particular detail is given in describing the current harmonics present at different speeds of motor operation. The second part of the paper studies a medium voltage drive which was invented by P. Hammond (see IEEE Trans. Ind. Appl., vol.33, no.1, 1997). The inverter was built by Robicon and retrofitted with GE signal electronics. The performance of that GE-Robicon hybrid inverter prototype was measured and is described in this paper