A PWM Method for Overvoltage Suppression in Long Cable Motor Drive Systems

Abstract

In motor drive systems employing long cables, the LC network formed by the distributed capacitance of the cable and the inductance of the motor induces voltage oscillations at the motor terminals. When the next switching pulse is applied before the preceding oscillation has fully damped, the newly induced oscillation superimposes on the residual oscillation. This superposition generates an overvoltage that exceeds the dielectric withstand ratings recommended by NEMA MG1-2009 Part 31. To suppress this overvoltage this paper proposes a PWM method that defines a threshold voltage Vth derived from the required oscillation damping time Tth and categorizes the operating conditions into six modes from Mode 0 to Mode 5 based on the real-time computed voltage margin Vmrg. Each mode applies an appropriate combination of SVPWM, up-clamping DPWM, vector splitting and pairing to secure the minimum zero vector dwell time while minimizing the distortion of the pole voltage reference. The effectiveness of the proposed method is verified through MATLAB/Simulink simulations and hardware experiments using a DSP based inverter platform confirming that the intended zero voltage dwell time is secured in the line-to-line voltage waveform.