Research on Ultra-low speed control of PMSM in servo system

Two new methods to improve the ultra-low speed control performance of ac servo system are described in this paper. One is improved M/T method, which could minimize the influence of speed detection dead time and smooth the measurement. Another is instantaneous speed detection based on constant jerk model, which assumes the rotor jerk is constant at the interval of sampling period. The instantaneous speed is calculated by analytic geometry. This method can minimize both the speed detection dead time and detection delay, which is the premise of low-speed control. The effectiveness of these methods has been confirmed by experimentation. The experimental system is composed of a digital signal processor (DSP), a field programmable gate array (FPGA), a PWM inverter and a permanent magnet synchronous motor (PMSM).