Voltage-Level based SMPC with CMV Minimization for a Four-Level Inverter

The switching action of devices in pulse width modulated multilevel inverter (MLI) produces common-mode voltage (CMV), causing shaft and bearing breakdown in electric drive systems (EDSs). To minimize the CMV, an optimal voltage level (OVL) based sequential model predictive control (SMPC) method is proposed in this article. In this approach, the system models are developed by following the per-phase philosophy, which allows the direct estimation of OVL from the reference load currents. The selected OVL controls the load currents while producing the lowest CMV, thereby obviating the necessity for weighting factor dependent cost function. The proposed SMPC method is applied to an MLI with four levels (4L-MLI). The discrete-time models of 4L-MLI ac currents are formulated by using Euler method, whereas the flying capacitor voltage models are developed by using Heun’s method. The effectiveness of the proposed method is demonstrated on a 4 kV system through MATLAB simulations under steady state and transient scenarios.