Research On No Sensors And No Flux Cloused-loop System For Pmsm-DTC In Low Speed Situation

The Direct Torque Control(DTC) technology is the new technology which arising after the Space Vector Pulse Width Modulation(SVPWM). This technology was applied in the Induction motor first, and then turned into the Permanent magnet synchronous motor(PMSM). Because of the advantages of the PMSM, which are small, light, high efficiency, and the simple structure, quick dynamic response of the DTC control system, the PMSM-DTC developed rapidly. But, the motor parameters such as speed and position were sensed through the Mechanical sensors, and the control signals were generated by the Hysteresis comparator, which made the torque ripple apparently, especially in the low speed situation.In order to solve the problem mentioned above, this paper proposed a new control system, which is no sensor and no closed-loop flux direct control system. First, this system using the Extended Kalman Filter(EKF) instead of the mechanical sensors to observe the parameters that the control system needs, and then, to simplify the system structure, this paper removed the flux closed-loop without reducing the performance of the torque response. At last, to lower the torque ripple from the generating principle of it, this paper proposed a voltage tracking filter which aimed to make the voltage that injected to the motor to be Sinusoidal. In that way, the Magnetic field caused by the sinusoidal voltage would be circular rotating, which could drive the rotor running smoothly. The major works are as follows:(1) Studied the control systems of the PMSM briefly.(2) Analyzed the reasons of the torque ripple in the low speed situation, and found the way to solve this problem.(3) Studied the sensor-less technology and designed the EKF for the PMSM-DTC to observe the speed and position of the motor.(4) Proposed a no flux closed-loop system structure for the PMSM-DTC, and to avoid the saturation of the flux in the stator, this paper found a way to limit the Amplitude of the flux.(5) In order to reduce the torque ripple of the motor from the beginning, this paper proposed a voltage tracking filter to compensate the voltage that from the inverter output to make the motor stator voltage wave to be sinusoidal.(6) Build up the module of the system mentioned above using the MATLAB/simulink, and verified the principle through the simulation.The simulation results show that, the designed EKF for the motor tracking the speed and position well; the no flux closed-loop DTC system simplified the traditional PMSM-DTC structure without reducing the torque performance and the dynamic characteristic of the system; the proposed voltage tracking filter compensated the output of the inverter to make the motor stator voltage sinusoidal indeed, which achieved the goal we want.