Calculation of Current Total Harmonic Distortion for a Single-Phase Current Source Multilevel Inverter

Abstract

The focus of this paper is a theoretical calculation of current Total Harmonic Distortion (THD) for a current source single-phase multilevel PWM inverter with CL-filter. Analytical approach to current ripple mean square / current THD calculation was introduced in the 1980s for a 2-level voltage source inverter with inductance dominated RL-load. This paper presents a generalization of this approach for a single-phase multilevel current source PWM inverter with an arbitrary number of current levels accounting for the CL-filter effect. The output of this research is a closed-form analytical current THD solution. Though one of the assumptions is large switching-to-fundamental frequencies ratio, the formulas are practically accurate for the said ratio larger than 20-25. The formulas become quite compact and simple without a loss of accuracy when using a Bessel function approximation. They demonstrate a single-phase PWM current source inverter current THD dependence on CL-filter parameters and current modulation index.