134 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 13, NO. 1, JANUARY 1998 On-Line Fuzzy Tuning of Indirect Field-Oriented Induction Machine Drives Li Zhen and Longya Xu, Senior Member, IEEE Abstract—This paper presents an on-line fuzzy tuning scheme for indirect field-orientation (IFO)-controlled induction machine drives. A fuzzy controller is used to regulate the speed, and an- other two fuzzy compensators are combined to correct detuning of field orientation. Since detuning effects of the IFO induction machine drive is minimized by the new fuzzy control scheme, the induction machine can achieve good performance in terms of overshoot, steady-state error, torque disturbance, and variable- speed tracking. Efficiency and torque/ampere capability are also enhanced. The results obtained by laboratory implementation are presented to verify the effectiveness of the proposed on-line fuzzy-tuning scheme. Index Terms—Field-orientation control, fuzzy logic, induction machine drive, on-line tuning. I. INTRODUCTION I NDIRECT field-oriented (IFO) induction machine drives are finding numerous industrial applications in recent years. In a typical IFO induction machine drive, either a synchronous- frame proportional and integral (PI) current regulator or a feedforward current regulator is often used to achieve ideal current regulation. In addition, a slip calculator is applied to accomplish feedforward field-oriented control. However, changes in the rotor time constant often cause field- orientation detuning and degrade system performance, espe- cially for large high-efficiency induction machine systems. When detuning occurs, the efficiency and torque capability of the drive are greatly reduced in steady state [1]. Furthermore, due to the inverter current limits, torque/ampere capability of the drive is significantly less, resulting in unsatisfactory drive performance, particularly for fast dynamic speed commands. Many on-line rotor time-constant identification schemes and on-line tuning schemes have been studied in the last decade [2]–[4]. The various proposed methods have shown some improvement of the variable-speed drive. However, these methods usually need either more machine parameters or have hardware complications. This paper introduces an on-line fuzzy-tuning scheme for IFO induction machine drives. A conventional synchronous PI current regulator and feedforward slip calculator are used to implement decoupled flux and torque control. To prevent detuning of field orientation, two fuzzy slip compensators are designed to handle machine parameter deviations. That is, one fuzzy compensator is used to on-line tune in the slip Manuscript received April 19, 1996; revised February 25, 1997. Recom- mended by Associate Editor, D. Torrey. L. Zhen is with Industrial Devices Corporation, Novato, CA 94947 USA. L. Xu is with the Department of Electrical Engineering, Ohio State Uni- versity, Columbus, OH 43210 USA (e-mail: longya@ee.eng.ohio-state.edu). Publisher Item Identifier S 0885-8993(98)00479-7. calculator when the machine is working in the speed-tracking mode, and another is used to compensate when the machine is working in the constant-speed mode. Compared to a conven- tional IFO drive, the new on-line tuning scheme does not need any machine parameter estimation and additional hardware. Since detuning effects of the IFO induction machine drive are corrected by the fuzzy compensators, good performance of the IFO drive is achieved in terms of overshoot, steady-state error, torque disturbance, and variable-speed tracking. The results obtained by laboratory implementation are presented to verify the effectiveness of the proposed on-line fuzzy-tuning scheme. II. DETUNING OF IFO DRIVE SYSTEMS Assuming that the induction machine is supplied from a current-regulated voltage-source inverter with rotor flux ori- entation, the - equations of the machine in the synchronous reference frame are (1) (2) (3) (4) (5) From these equations, an important slip relation can be derived (6) Equation (6) means that field-orientation control of an induc- tion machine is equivalent to a correct slip control of the same machine. Note that in (6), is the key parameter to determine field orientation. Unfortunately, is a parameter, which is temperature and saturation dependent. Therefore, the desired independent control of flux and torque is often lost because of variation. Although a properly designed speed regulator can partially handle a slightly detuned case for speed control, for a fast dynamic speed command, the drive performance will degrade. Generally, for a large machine, detuning of the IFO-controlled induction machine results in a high-slip high-current low-flux condition if the actual value of is large than the predicted value. Conversely, detuning results in a low-slip low-flux 0885–8993/98$10.00  1998 IEEE