Compensation for neutral point potential in a three-level inverter using motor currents of a permanent magnet synchronous motor and its characteristics

A three-level inverter has several advantages of large capacity, large voltage, and low current waveform distortion. However, there is an important problem of neutral point potential variation in three-level inverters. The variation causes an unbalance in the dc link voltage levels and current waveform distortion. In this paper, we propose a new method to control the neutral point potential. First, the neutral point potential variation in a three-level inverter for permanent magnet synchronous motor drive is analyzed by state variable method and is calculated on the basis of the analytic results. Second, using the estimated value, proposed compensation for the variation can be done. Third, analytic and experimental results of the proposed method are compared with the results of feedforward compensation by simply adjusting the vector output intervals. (C) 2002 Wiley Periodicals, Inc.