u Predictive modulation schemes to reduce common-mode voltage in three-phase inverters-fed AC drive systems

Pulse width modulation controlled inverters produce common-mode voltage, which has been reported to cause many system drawbacks. This voltage along with high dv/dt raises leakage currents which can result in serious problems such as motor damage and electromagnetic interference to the surrounding equipment. Also common-mode voltage is responsible for bearing failure and overvoltage stress to the winding insulation of an AC motor. Therefore knowledge of reducing common-mode voltage is essential to provide a correct insight into the design of the drive system. Previous methods for common-mode voltage reduction cause extra harmonic in output currents, since they are based on voltage control. This study proposes new modulation strategies based on predictive current control (PCC) for three-phase pulse width modulation inverters-fed AC motor drive systems which mitigate the common-mode voltage and moreover, decrease the harmonic contents of output currents. As PCC can be employed in low voltage and medium voltage drive applications, the proposed strategies have been implemented on two-level and three-level neutral-point clamped inverter. A comparative study of proposed techniques with traditional ones has been carried out from the output current total harmonic distortion point of view. Simulation results and mathematical analyses, along with experimental tests for two-level inverter using Texas Instrument DSP model TMS320F28335, confirm that the new strategies improve behavior of drive systems in comparison with previous methods.