Research On Sensorless Direct Torque Control Of Permanent Magnetic Synchronous Motor

Sensorless direct torque control(DTC) of Permanent magnet synchronous motor(PMSM)occupies an important position in modern AC motor control.DTC avoids the complex rotating coordinate transformation. Instead, it directly controls flux and torque of motor in the static coordinates.The kind of control system rarely relies on motor parameters with simple architecture. In addition, its dynamic response of torque is fast and it is robust to the parameters, external interference, measurement errors and noise as well. However, the distortion of stator flux and torque ripple is relatively severe. The key technique of sensorless DTC is to achieve the high accuracy of estimation of flux and torque. The intergal model of voltage and current is capable of estimating stator flux without accurate rotor position, but the performance of estimation is not good. In terms of fast dynamic torque response and current harmonic of DTC in steady state, the paper proposes rotor positon/speed observers with excellent dynamic and steady accuracy. Sensorless DTC system is improved through estimating stator flux and torque by current-position model.The contribution of paper is discussed as below:(1)An adaptive discrete sliding mode observer(ADSMO) based on extended EMF is proposed which can be used for interior PMSM in medium-high speed.The paper proposed the methodology of adaptive pamameter tunning based on discrete reaching rate. Besides, the paper proposed adaptive notich filter(ANF) PLL in order to reduce the harmonic error of position estimation when PLL extracts the location signals. Position observation accuracy in speed and load transient condition is increased by 21.7% and 32.5%, respectively. Position observation accuracy in speed steady condition is increased by 28.2%.(2) A dynamic phase compensation observer(DPCO) is porposed which combinated voltage model and current model of stator flux without speed, instead, the device calculates estimated rotor position using concept of active flux. Dynamics is improves through phase error between estimated and actual stator current to compensate estimated position so as to further reduce the error of estimated flux. Position observation accuracy in speed and load transient condition is increased by 29.4% and 36.9%, respectively. Position observation accuracy in speed steady condition is increased by 25.6%.(3)Combining the advantages of entended EMF model and active flux model, the active EMF model is established in stationary reference coordinate. A dynamic error angel compensation observer(DEACO) is proposed based on active EMF and its dynamics is improved using dynamic position compensater. Position observation accuracy in speed and load transient condition is increased by 32.56% and 38.69%, respectively. Position observation accuracy in speed steady condition is increased by 21.46%.(4)A new method is proposed for the on-line compensation of the current zerocrossing zone disturbance voltage(CZDVC), which is suitable for the high frequency signal injection sensorless control. An analytical model is established to reveal the essential characteristics of the current zero-crossing effect in the high frequency injection method. The model is then applied to a special off-line running debugging experiment, in order to obtain the inductance and voltage distortion coefficient of the motor. By this method, the precision of rotor position estimation in the current zero crossing region can be improved without the complexity of the look-up table. Position observation accuracy in speed steady condition is increased by 23.9%.(5)A novel harmonic compensation and an adaptive notch filter(ANF) phase lock loop(PLL) are proposed to reduce harmonic flux and current resulting of torque ripple and to reduce the harmonic error of position observation when extracting position signal, respectively. The total harmonic distortion rate(THD) of current decreased from 24.67% to 4.38%. THD of harmonic error of observer dropped from 24.88% to 5.35%.(6)The proposed novel position observers are directly used as feedback of sensorless DTC speed closed-loop control system, and the difference between speed command and actual speed is used as the speed control precision. The closed-loop control system of sensorless DTC with the proposed observers is improved. In speed and load transient, speed control precision is increased by 35.8% and 29.6% while transient stability time is decreased by 24.4% and 20.2%, respectively. In speed steady state, speed control precision is increased by 27.5 and 18.7%, respectively.