04-05-2012, 03:30 PM
DESIGN OF A HYBRID PID PLUS FUZZY CONTROLLER FOR SPEED CONTROL OF INDUCTION MOTORS
ABSTRACT
In this paper, a Ziegler-Nichols (Z-N) based PID plus fuzzy logic control (FLC) scheme is proposed for speed control of a direct field-oriented induction motor (DFOIM). The Z-N PID is adopted because its parameter values can be chosen using a simple and useful rule of thumb. The FLC is connected to the PID controller for enhancing robust performance in both dynamic transient and steady-state periods. The FLC is developed based on the output of the PID controller, and the output of the FLC is the torque command of the DFCIM. The complete closed-loop speed control scheme is implemented for the laboratory 0.14-hp squirrel-cage induction motor. Experimental results demonstrate that the proposed Z-N PID+FLC scheme can lead to desirable robust speed tracking performance under load torque disturbances.
Ziegler-Nichols(Z-N)) method is adopted for designing a PID controller (denoted as “the Z-N PID”) because its design rule is simple and systematic. We design a FLC carrying out fuzzy tuning of the output of the Z-N PID controller to issue adequate torque commands. Based on a simulation model of the DFOIM drives incorporating the proposed controller, experiments are set up in an Matlab/Simulink environment and implemented in real time using the MRC-6810 analog-to-digital (AD)/ digital-to-analog (D/A)servo control card together with a DSP electronic controller. The results show that the incorporation of the proposed controller into the DFOIM drives can yield superior and robust variable-speed tracking performance.
The fuzzy inference engine, based on the input fuzzy sets in combination with the expert’s experience, uses adequate IF-THEN rules in the knowledge base to make decisions and produces an implied output fuzzy set u. A computer simulation model is developed using the Matlab/Simulink software. A computer simulation model is developed using the Matlab/Simulink software The control system is implemented in real time using the MRC-6810 AD/DA servo control card as the interface between software and hardware. No torque disturbance is applied to the shaft.
It is noted that the proposed controller yields much smaller tracking errors than the FLC and NFC. In addition, the proposed controller takes shorter time to resume the command speed following than the FLC and the NFC when the load disturbance takes place. Accordingly, it is suggested that the proposed controller has a robust performance. The proposed controller has exhibited the combined advantages of a PID controller and a FLC. Specifically, it can improve the stability, the transient response and load disturbance rejection of speed control of a DFOIM. The fuzzy logic and only with three membership functions are used for each input and output for low computational burden, which can achieve satisfactory results. Simulation and experiment results have illustrated that the proposed controller scheme has a good and robust tracking performance.