Analysis and Comparison of Peak-to-Peak Current Ripple in Two-Level and Multilevel PWM Inverters

Three-phase multilevel (ML) inverters are used in many medium- and high-power applications such as motor drives and grid-connected systems. Despite the fact that numerous pulsewidth modulation (PWM) techniques for ML inverters have been developed, the impact of these modulation schemes on the peak-to-peak output current ripple amplitude has not been addressed yet. In this paper, analysis and comparison of current ripple for two-level (2L) and three-level (3L) voltage source inverters are given. Reference is made to optimal and popular modulation, so-called centered PWM, easily obtained by both carrier-based modulation (phase disposition, with proper common-mode voltage injection) and space vector modulation (nearest three vectors). It is shown that the peak-to-peak current ripple amplitude in 3L inverters can be determined on the basis of the ripple in 2L inverters, obtaining the same results as by directly analyzing the output voltage waveforms of the 3L inverters. This procedure can be readily extended to higher level numbers. The proposed analytical developments are verified by both numerical simulations and experimental tests.