Research And Implementation Of PMSM Servo System Based On DTC

The rapid development of motor control theory, power electronic device and permanent magnetic materials has made DTC a control algorithm with high performance due to the simple structure and fast response.Many related literatures have been read and the development of DTC is described in this paper. Strategies are presented to solve the problems in conventional DTC.In order to solve the problem of flux increments asymmetry, a novel DTC algorithm based on sectors subdivision was studied. Flux and torque increments asymmetry in sector boundaries was confirmed through analysis and increments of flux and torque are proportion to the sampling period and voltage vector amplitude in a sampling period. A strategy which subdivides six vectors into twelve to enlarge the choosing scale was applied. Simulation results show that this method can effectively decrease the flux asymmetry and inprove the flux trajectories.In order to solve the problems of large ripples and inconstant inverter switching frequency in conventional DTC, a novel DTC method based on SVM was studied. In this method, flux and torque hysteresis controllers in conventional DTC were improved, using the setpoints and actual values of flux and torque to calculate the voltage vector, compensating for flux error in one cycle, to achieve accurate control for flux and torque. Simulation studies show SVM method can effectively decrease flux and torque ripples and make the inverter has constant switching frequency.Finally, the hardware experiment of SVM-DTC was accomplished with the waveforms of PWM, line voltage, phase voltage and three-phase current detected which ensure the validity of the agriothm. However, the performance is not so good as the simulation results due to the ageing of motor and the overamplification of transformer.