Modified Strategy of Direct Torque Control Applied to Asynchronous Motor Based on PI Regulators
Direct Torque Control (DTC) is known to generate a fast and robust response in asynchronous engines. Yet, during steady state, observable flux, torque and current pulsations arise. This paper presents a study of modified direct torque control applied to a
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Abstract. Direct Torque Control (DTC) is known to generate a fast and robust response in asynchronous engines. Yet, during steady state, observable flux, torque and current pulsations arise. This paper presents a study of modified direct torque control applied to a three-phase high performance asynchronous motor. The proposed strategy is based on PI regulators instead of the hysteresis comparators to control both the stator flux and torque whose parameters are determined from modulus and symmetrical optimum criterions. Since the performance of a feedback control system relies on the accuracy of the response signal, an estimator of stator flux and torque is presented. The control system benefits from the advantages of field oriented control (FOC) and conventional direct torque control (DTC) while avoiding some of the disadvantages of either of the two control methods. Performances of the asynchronous motor control are checked by simulations under MATLAB/SIMULINK software. Keywords: Modified DTC Conventional DTC FOC Asynchronous motor Modulus criterion Symmetrical optimum criterion PI regulator Torque/Flux estimator
1 Introduction The three-phase asynchronous motor is the most used electric motor worldwide for industrial applications. Simple in terms of design, robust and economical to use. It is the most promising drive solution at the level of low cost and high quality. Due to those advantages, numerous efforts by researchers have been made to develop the strategy of control for this type of electric motors. Among those strategies; there is the vector control strategies which consist of field oriented control (FOC), direct torque control (DTC), etc. In general, the vector control methods were based on the same idea that transforms the motor’s three phase variables into two phase variables to separate of the motor parameters as flux-component and torque-component [1]. In the same way, the FOC is a strategy that assigns high performance and quick dynamic response over a wide speed range to asynchronous motors by decoupling their variables; but it uses a rather high number of regulation loops which leads to a slow dynamics of the flux [2]. © Springer Nature Switzerland AG 2019 Y. Farhaoui and L. Moussaid (Eds.): ICBDSDE 2018, SBD 53, pp. 20–26, 2019. https://doi.org/10.1007/978-3-030-12048-1_4
Modified Strategy of Direct Torque Control
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The direct torque control (DTC) method was proposed in 1980 by Takahashi [3], this method has become one of the high performance control strategies for motors to provide a very fast torque and flux control. It is based on comparing the reference values of the stator flux and torque to their estimated ones, the resultant errors are fed into a two level and three level hysteresis comparators to regulate the stator flux and the torque respectively, controlling the motor in the two directions of rotation. So, with this method, it is possible to directly control the inverter states by selecting the appropriate state through the “optimal switching table” in order to reduce the
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