Induction Motor Drive Predictive Control Method Analysis and Comparison with Fundamental Direct Torque Control Method

The authors propose new modiflcation of the direct torque control method based on voltage vector prediction. The principle of the method is explained and the mathematical description of the system is provided. The control algorithm is implemented in simulation envi- ronment MatLab/Simulink and its behaviour is tested on the mathematical model of an induction motor drive. Then, the control algorithm is verifled on the real drive with induction motor with dSPACE control system. The results from the simulations and measurements are presented and compared with those when using the fundamental direct torque control method. 1. INTRODUCTION In 1986 Isao Takahashi and Toshihiko Noguchi presented a new control strategy of induction mo- tor control algorithm called direct torque control (DTC) (1). The method is based on transistor switching according to table uses hysteresis torque and magnetic ∞ux controllers. One of the dis- advantages is the relatively high torque ripple. A lot of modiflcations were performed since then. The most important are DTC with space vector modulation (2), multilevel inverter application (3) and predictive algorithms of DTC (4,5). The method described in the paper presents another modiflcation using prediction of voltage vector. It is based on the calculations of changes in stator and rotor magnetic ∞uxes and motor parameters. 2. PRINCIPLE OF VOLTAGE VECTOR PREDICTIVE DTC The basic theory of the proposed method flrstly predicts the stator magnetic ∞ux for the next cycle and then the voltage vector that should be switched on the inverter. The calculations are based on the every cycle motor state values (measured or estimated), motor parameters and reference values. Because the requirement of the method is the rotor ∞ux value knowledge, the estimator have to calculate with adequate precision and parameters of the induction machine must be known. The block diagram of the controlled system is depicted in Fig. 1 on the left hand side. The calculation of voltage for the next cycle is based on the induction motor stator voltage Equation (1). After discretisation it results in (2)