A Discussion of Parallel Connection of Five-Level Pulse Width Modulated Inverters

Abstract

The five-level PWM inverters have many advantages such as an ability to operate the motor or the static var compensator (SVC) with nearly sinusoidal current waveforms. For these reasons, actual consideration of applications have just begun with great interest. In the discussion of applications, still larger capacity inverters are also expected. In order to increase the capacities of switching device, a certain technique and controlling methods are proposed for the parallel connections of the five-level PWM inverters. In high-power applications, however, the carriers should be synchronized to modulating sinusoidal waves. In addition, each three phase waveform should be built in a bilateral symmetry for each half-wave as well as the horizontal axis symmetry. Moreover, for the current sharing reactor, lower order harmonic application is prohibited. To improve the harmonic characteristic of the parallel connected three phase five-level inverters, various modulation strategies are devised and discussed.