Inverter Modeling and Current Control System Design for Improving Current Response of PM Synchronous Motor in Overmodulation Range

In this paper, we propose the method of inverter modeling for linearization of PMSM current control system in the overmodulation range. Because of the nonlinear characteristic and the large amount of harmonic components when an inverter is operating in the overmodulation range, it´s quite difficult to use the usual linear current controller design methods. For counteracting this problem, we considered an inverter in the overmodulation range to be equivalent to the nonlinear amplifier plus the harmonics disturbance generator. The problem of nonlinear amplifier is usually carried out by the amplitude compensation method, however, the problem of nonlinear amplifier is not only the nonlinear amplitude relation but also the nonlinear phase relation too. From our study in this paper, we show that the effect from the harmonic disturbance in overmodulation range causes the nonlinear relation phase shift between the commanded voltage and the output voltage of an inverter. Although this phase shift effect may be compensated by PI controller in the steady state condition, but in the transient condition, this phase shift between voltages causes the transient response of currents to be different from the case when an inverter is operating in the linear range. By using the proposed phase compensation method, the transient response of currents in the overmodulation range becomes same as the response in the linear range as verified by the simulation results. With the proposed phase compensation method, we can deal with an inverter in the overmodulation range in the same way as the linear range without any change in current controller design methods