Wide-speed-range optimal PAM control for permanent magnet synchronous motors

Generally, PWM voltage source inverter (VSI) has been used for the variable speed permanent magnet synchronous motor (PMSM) drives. However, the PWM-VSI fed PMSMs has two disadvantages. Firstly, PMSMs cannot operate at the speed at which the motor terminal voltage exceeds voltage constraint imposed by the DC-link voltage. Secondly, the distortion of the voltage commands increase at the low speed, because the DC-link voltage is significantly higher than the motor line voltage. Because of this, the armature currents are distorted and then the torque ripple increases. Consequently, higher DC-link voltage influences the speed control performance at the low speed range. This paper proposes an optimal PAM control which can adjust the inverter DC-link voltage by using the buck-boost DC-DC converter. Further, considering the electrical vehicle application, the converter enables bi-directional power flow. At low speed range, the proposed system can reduce the total harmonic distortion (THD) of the voltage commands, and then the armature currents waveforms would be improved. Also, the allowable speed range would be extended. In order to verify the proposed method, simulation results are presented.