A Study of a Full Fuzzy Self-tuning Controller for Induction Motor V/f Speed Control
| Autor: | Te-Hung Hsu, 徐德宏 |
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| Rok vydání: | 2003 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 91 This thesis proposes a full fuzzy self-tuning controller which is embedded in the modified V/f (Voltage/frequency) speed control structure of a three-phase induction motor. Results of simulation and experiment validate the performances of the proposed controller. The V/f control is a conventional method for controlling an induction motor speed since the construction is simple and the motor parameters are not required. However, this method uses a constant ratio of the voltage to the frequency, which is effective under steady state only. The speed responses are usually unstable during the changing of a speed command owing to the nonlinear characteristic of the induction motor system. Therefore, the modified V/f control is recently adopted; it utilizes a compensation voltage which is in proportion to the slip speed to improve the transient response. The compensation voltage increases the ratio of the voltage and frequency during an acceleration period and decreases the ratio during a deceleration period. An induction motor is the system of a high order nonlinear mathematical model with parameters that are difficult to obtain. Hence, the designing of a conventional controller is hard. In general, a fuzzy controller can work without mathematical model and parameters of the controlled systems. However, the number of input variables and control rules will be increased for a higher performance and the implementation will become complicated too. Therefore, a standard fuzzy controller with a modified algorithm is proposed. This method can simplify the design procedure of the controller and make the implementation more concise. In addition, the algorithm is independent of the number of input variables and control rules. Since a controller with constant parameters cannot perform well in a nonlinear system, a self-tuning function is incorporated with the modified fuzzy algorithm. The algorithm will automatically change the positions of output membership functions according to the positions of the input values on the phase plane. The proposed controller is named a full fuzzy self-tuning controller. To identify the characteristics of the proposed controller, the V/f speed control of a three-phase induction motor by a PID controller, a fuzzy controller and the full fuzzy self-tuning controller are simulated and tested respectively. The speed responses to different types of changes in the input command and the load torque illustrate that the performances of the full fuzzy self-tuning controller are better than those of the other two controllers. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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