A Model Predictive Control Scheme for Zero Common Mode Voltage in Two-Parallel Three-Phase Two-Level Converters

This paper aims to eliminate the common mode voltage (CMV) in two-parallel converters. The presented analysis reveals that unwanted commutation causes deviations from ideal switching states, leading to unexpected instantaneous CMV. The unwanted switching states during the commutation process originate from the mismatch between the switching states applied and the output current of the individual converter. The existing PWM schemes rely on the fixed vector sequence, and its instantaneous output vector and the resulting switching states cannot be adjusted online. This paper first comprehensively analyzes the commutation process and establishes a general model describing the actual CMV during the commutation process. Significantly, the presented model dictates the optimal combination of the current polarity and the applied switching states. The complete elimination of the CMV solely depends on the combination of the current polarity and the switching state applied. To achieve the required combination, a current prediction model is presented to facilitate the identification of the current polarity. Moreover, a singlevector model predictive control (MPC) scheme is proposed to instantaneously adjust the switching states matched to the current polarity for CMV elimination. Finally, simulations were built, and the simulation results confirm that the proposed method excludes unwanted switching states, achieving complete CMV elimination.