The Comparison of Two SVPWM Methods for Low-Speed Control of PMSM in Servo System

Abstract

Two space vector pulse width modulation (SVPWM) methods for low-speed control of PMSM are described in this paper. One is the traditional modulation method using 180-degree space vectors. Another is a novel hybrid modulation method using 120-degree space vectors and 180-degree space vectors, which has no need to set up the dead time and can avoid the effects as well. When the PMSM runs at ultra-low speed condition, the dead time effects in traditional six-sector modulation method is significant and the speed stability is poor. To avoid the distortion of motor current caused by dead time effects and improve the low-speed control performance of PMSM in servo system, the twelve-sector modulation method using hybrid vectors is proposed. From the analysis of principles to the derivation of formulas, from the construction of SIMULINK models to the analysis of simulation results, the similarities and differences between the two kinds of modulation methods are compared in detail. The simulation results of the two methods are supported by experimentation. The experimental system is consisted of a digital signal processor (DSP), a field programmable gate array (FPGA), a PWM inverter and a permanent magnet synchronous motor (PMSM).