Multilevel inverter modulation schemes to eliminate common-mode voltages

It is well known that conventional two-level pulsewidth modulated (PWM) inv erters generate high-frequency common-mode voltages with high dv/dt, Simila rly, commonly used multilevel inverter modulation schemes generate common-m ode voltages. Common-mode voltages may cause motor shaft voltages and beari ng currents and conducted electromagnetic interference (EMI). Premature mot or bearing failures and electronic equipment malfunctions have been reporte d to be directly related to bearing currents and EMI, In this paper, approa ches to eliminating common-mode voltage when using multilevel PWM inverters are presented. It is shown that inverters, which have an odd number of lev els, will generate zero common-mode voltage by switching among certain stat es, Therefore, motor bearing currents will be eliminated and conducted EMI will be reduced. Both sinusoidal PWM and space-vector modulation (SVM) sche mes are discussed and detailed comparative simulation results between conve ntional and novel modulation schemes are provided. The value of the propose d technique is demonstrated experimentally by applying the novel SVM approa ch to a conventional multilevel inverter.