Analytical investigation of the switching frequency harmonic characteristic for common mode reduction modulator

Common mode voltage (CMV) generated by two-level voltage source rectifier/inverter adjustable speed drive (ASD) system is troublesome and requires extra hardware fixes, which increase production costs and can lead to increased installation costs. The use of the common mode reduction modulator (CMRM) to control the common mode voltage has received some attention over the past few years. It is attractive for its software selectivity, no additional components, etc. From a product design viewpoint, there is a need to analytically analyze and quantify the switching frequency harmonic characteristics for the CMRM. A complete design-oriented analytical analysis of the switching frequency harmonic characteristic of CMRM for a two-level voltage source rectifier/inverter ASD system is presented in this paper. An analytical harmonic flux formula for CMRM is derived, followed by a per carrier cycle and per fundamental cycle calculation of the harmonic flux RMS value. The analytical solution has been verified against both the simulated and the experimental tested load current harmonic components.