Model Predictive Control With Double Virtual Vector Modulation for Suppressing Common Mode Voltages in Dual Three-Phase Drives

A model predictive control (MPC) method coupled with a novel asymmetrical modulation of a unique set of virtual voltage vectors to suppress the high-frequency common-mode (CM) voltage in dual three-phase drives is presented in this article. The MPC method is based on an ultralocal model and a disturbance observer for model-free implementation offering a highly robust control performance. Synthesizing the control voltage with only one of the identified virtual vectors suppresses the net CM voltage, but will result in high current ripples under heavy loads. The current quality performance issue is addressed in this article using an asymmetrical modulation strategy consisting of two virtual vectors and one null vector to balance the tradeoff between CM voltage suppression and current ripple in the entire operating region. Furthermore, a simplified switching sequence is developed for ease of implementation on a low-cost processor. The validity and performance of the proposed model-free predictive control and modulation method are verified and compared with conventional linear control with interleaved space vector modulation through simulations and experiments on an asymmetrical dual three-phase permanent magnet synchronous motor (PMSM) drive.