An Improved Speed ​​Sensorless Induction Motor Direct Torque Control
In the past few years, speed sensorless induction motors have attracted considerable interest because of their significant advantages, such as good mechanical stability, simple structure, and easy maintenance, etc. 13. The article introduced a new type of technology. The direct torque and flux control of a SVM (DTC-SVM) speed sensorless induction motor. It uses closed-loop digital control similar to the DTC method for both flux linkage and torque. But the voltage is generated in a DTCSVM unit. In this method, the transient performance and robustness of the DTC are preserved, and the steady state torque ripple is reduced. In the article, a simple and convenient speed observer is used, which can achieve accurate observation of the full speed range.
1 Speed ​​sensorless induction motor A block diagram of a speed sensorless induction motor is given.
It operates with direct stator flux linkage and torque control. It is considered that the rotor flux is constant during a working cycle. The regulator can generate fund projects: Liu Xianxing (1966―), a male funded project of the Jiangsu University Youth Fund, and a man, doctor and associate professor of Zhenjiang City, Jiangsu Province. He is mainly engaged in the research of AC speed control and switched reluctance motors.
Torque. Since only the DC bus voltage and the bilinear current are measured, the induction motor model is: Here, Us is the stator voltage, is, ir is the stator and rotor current, X, X is the stator and rotor flux linkage, R., Rr, L; Lr, Lm is the motor parameter, called model speed (arbitrary speed), called the rotor speed.
Here p is the number of magnetic pole pairs.
Stator flux and torque closed-loop control is achieved through the DTC-SVM unit. In order to reduce the torque and flux fluctuations and implied current noise, compared to the traditional DTC, we used the torque and flux PI controller Wang Deming (1956-), male, Zhenjiang City, Jiangsu Province, Professor, Ph.D., mainly engaged in and SVM. Research on power transmission and intelligent control.
2 Speed ​​Observer 141 For speed observers operating in the full speed range, model adaptive speed observations are used here. The analysis is as follows: Full-range flux link observers are used here to achieve full speed range speed observations. The model is mentioned earlier. Rotor flux model (Equation 12).
The adaptive model is a current model in a stationary coordinate system: the estimator calculates stator flux X, rotor flux X, electromagnetic torque Me, and rotor speed call. They are based on the five equations (1)~() of the induction motor. The inputs to the state estimator are stator voltage Us and current is vector. They are all stationary coordinate systems. The flux estimator counts as: We calculate and correct the rotational speed through a PI adjustment method: it is a full-scale full-speed range stator and rotor flux observer (see), which contains two models that one wants to produce accurate values, in particular Open loop current model at low speed and adjustable voltage model running at full speed range.
The rotor flux current model estimator is derived from the stator current calculation where 1 = rotor time constant.
For the rotor flux linkage, the d, q components of the rotor flux are shown in the proposed DTC-SVM. The controller contains two PI controllers, one for the flux linkage and torque regulator, and one SVM unit. It accepts stator flux and torque errors as inputs and generates the inverter's control signal, where 0e = arctan(Xw/X).
The output of the open-loop current model (written as "l") is the stator flux X calculated in the stator coordinate system where Xr is the sum and the measured stator voltage and current. For the stator structure, the stator flux X can be simplified as follows to correct the stator flux estimation value to compensate for the measurement (or estimation) error of the pure integrator and stator resistance Rs associated with low speed and provide full speed range integrity Observer, voltage model is adjusted by a PI compensator.
However, for the SVM method, the idea is to generate a target voltage vector by synthesizing a plurality of voltage vectors in a flux chain sector. Within each sector, the target voltage vector has a different decomposition formula. Within each sector, the formula for the on-time duration of two basic voltage vectors that approximately represent the target vector voltage can be found.
Here, we divide the eight voltage vectors into: Sa (rice uses the symmetric regular rice sample method, ie: Sa-Sb-S7-S7-Sb rotor flux linkage X is calculated in the stator system because the control adopts DTC- SVM structure, so we carry out such a conversion, that is, when the given voltage is too large, SVM's PI regulator saturates, can not guarantee the normal six-pulse, (turning to page 133) of which the top of a decline in the curve represents The system speed output can be seen from the figure as the speed decreases with time, the slowest rising curve at the bottom represents the system torque output, and the slowly rising curve at the middle represents the input to the system (inverter). Torque signal curve.
From the relation between tension and torque T=D, when the tension is fixed, the input torque should increase as the diameter of the coil increases, and the coil diameter increases with time, so the input torque should be It increases over time, as evidenced by the curves on the graph. From the simulation result curve, it can be seen that the adaptive tension control achieves a better control effect.
5 Conclusion The slitter is an electric drive system widely used in paper or film production lines. Many existing systems often use DC motors due to the introduction of production lines. Compared with the AC asynchronous motor, the DC motor has the disadvantages of large volume, easy failure, complicated control circuit, and difficulty in maintenance. The simulation results of the paper show that under the control of the AC vector inverter and the asynchronous motor, the adaptive tension control can achieve a better control effect and a higher degree of automation. Therefore, it is feasible to change the existing DC motor system to AC asynchronous motor drive. For the current use of DC motor system upgrades provide ideas.
Matlab is an excellent system simulation tool software. The paper uses its Simulink environment and S-function to construct a tension adaptive simulation system for slitting machine. Its characteristics are as follows: (1) The adaptive controller is designed by S-function, and it is represented by an S-function module under Simulink. The structure of the entire system is simple and clear.
Finally, it should be noted that the adaptive control process discussed in the article is implemented in a stable operating state of the system. During the acceleration process and parking down process, the traditional DTC method is adopted in the tension model (Continued on page 139) (up from page 130). The saturation point of the PI regulator is set to 1.5V, lK, and although the voltage amplitude cannot be controlled effectively, the phase of the voltage can still be controlled.
The simulation waveform of the load when the motor is at no load and t = 0.6s is shown in Fig.
6 Conclusions The new direct torque and flux linkage control methods introduced in the article use a combination of DTC and SVM, and the speed observation model is simple and effective. It can run in the full speed range, and the effect can be basically comparable to a speed sensor. Simulation results show that The torque fluctuation is small, the dynamic performance is good, and the response speed is fast. The result shows that the control strategy is correct and feasible, and has great practical significance.
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