Comparison of common-mode voltages in frequency converters with alternative space vector modulation methods

This paper presents a comparison of common- mode voltages (CMV) for three power electronic converters: two-level voltage source inverter (2LVSI), three-level voltage source inverter (3LVSI) and matrix converter (MC). In addition, a comparison of common-mode currents (CMC), a source for circulating-type bearing currents and shaft grounding currents is presented. The work is done by computer simulations with Matlab Simulink. The simulation results show that the number of CMV pulses and CMV peak amplitudes are reduced by the influence of optimal modulation methods. However, the step size of the CMV can only be affected with the converter topology. Using given comparison criteria, an optimal modulation method for each topology was chosen and the CMCs for these methods were simulated with a simplified common-mode circuit. The simulations of the CMCs show that the best results are achieved with the 3LVSI, which has the CMV step lowest in magnitude.