February, 004, China Railways Induction Motor with Constant Switching Frequency Without Speed ​​Sensor Direct Torque Control SONG Changlin \ TANG Puhua 2 LI Zhi 1 (1. School of Electrical Engineering, Southwest Jiaotong University, Chengdu 6100312, China. Numerical Control Research Center of Sichuan University of Technology, Sichuan Province, China Chengdu, Chengdu 610039, China) Relational real-time calculation of the voltage to be applied to the stator windings of the motor in the next control cycle to achieve dynamic decoupling control of the induction motor. The method of space voltage vector modulation is used to make the inverter switching device operate at a constant frequency. status. Compared with the traditional direct torque control method, it has better control performance at low speed, and has the advantages of quick response and no influence of motor parameters due to high speed and traditional direct torque control methods. It also introduces the speed sensorless method of this method. Implementation, simulation results verify that the method described in this paper is effective.
212: A does not discuss the method of determining the hysteresis width of the magnetic flux chain. The main disadvantages of traditional direct torque control with double hysteresis are: low speed control performance is not ideal, switching frequency is not constant, torque ripple is large, and there is distortion of the magnetic flux path in overvoltage sectors 14' in order to achieve high performance. Direct torque control, a commonly used method, uses neural fuzzy and space voltage vector modulation techniques to achieve a constant switching frequency, divides a control cycle into three equal segments, and uses effective voltage vectors and zeros in three equally divided segments within one control cycle. The combination of voltage vectors reduces the torque ripple. The space voltage vector modulation can realize the combination of seven voltage vectors in one control cycle, compared with the traditional direct torque control, which has the characteristics of simple control, fast dynamic response, and no influence of motor parameters on the direct torque control of induction motors. Wide attention has been paid to 11'231. Traditional direct torque control uses torque hysteresis and flux hysteresis to achieve control of the inverter switching devices. This is the advantage of traditional direct torque control and its disadvantages. The hysteresis width of the torque is related to the parameters of the motor, speed, and switching frequency. There is no report on the determination method of the torque hysteresis width in the existing direct torque control. The voltage component Va of the shaft is substituted into the equation (2). The voltage component of the P-axis can be calculated to obtain a set of voltage calculation formulas in the stationary control system in the next control cycle. In X, the denominator of the formula, when Xs, it will lead to the failure of the calculation. Therefore, using the same derivation method to obtain another set of voltage calculations in the stationary coordinate system, a b2 = 2-2% of the milk level, Tuen '10 0 4:-level / 2 less 2. In order to achieve the entire 360 ​​° range All can be solved correctly. The P and the stationary coordinate system are divided into 4 solution intervals. As shown in the figure, the mechanical angular velocity of the rotor of the rotor can be calculated by the following formula, so as to realize the estimation of the motor speed.
3 simulation The simulation results of the traditional direct torque control method can be seen at the start, the rise of the flux chain is slower, and the flux trajectory distortion occurs in the over-voltage sector, the motor output torque also has a larger pulse. Also, based on the stator flux trajectory shown in (a), it can be inferred that a direct torque control method with a constant switching frequency has a fast flux response characteristic, and the flux linkage trajectory does not have any distortion over the entire 360° interval. Due to the fast response of the flux linkage, this method is very suitable for the application of controlling the power factor by controlling the amplitude of the flux linkage. From (b) the change of torque input, this shows that the decoupling control of the flux linkage and torque has been well achieved, and the stator current also has a very fast response speed, and the fluctuation is small, as shown in (). This is the control effect that traditional direct torque control and vector control systems cannot achieve. From the speed curve shown in (d), a smooth torque output can also be achieved during the forward rotation to the reverse rotation. This shows that at low speeds, very (a) stator flux can also be obtained. Trajectory) 〉Motor Output Torque Without Speed ​​Sensor Direct Torque Control with Constant Switching Frequency Simulation Results At the same maximum switching frequency, the method described in this article also has the characteristics of small current ripple and small torque ripple due to the control Only stator resistance parameters of the motor are used to make the control performance of the system have good robustness to the motor parameters. Under the condition of stator field orientation, a calculation method of slip speed was deduced to realize the speed estimation. This method can have the characteristics of fast torque response of traditional direct torque control. u. High precision, easy f present characteristics.
The direct torque control method with the constant switching frequency proposed in this paper has a constant switching frequency compared with the traditional direct torque control. There is no distortion of the flux linkage in the overvoltage sector, which effectively improves the control performance of the low-speed system. From the graphs of estimated speed and measured speed, it can be inferred that the estimated speed has higher accuracy. When running at rated speed, it can meet the application requirement of 0.5% speed accuracy, and the estimation error is relatively small at the speed zero crossing point. Big. From the slip speed calculation formula, it is analyzed that the accuracy of the speed estimation will be affected by the motor parameters to a certain extent, and this effect is mainly reflected in the low operating speed.
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