Induction motor torque control in field weakening regime by voltage angle control.pdf

Induction Motor Torque Control in Field Weakening Regime by Voltage Angle Control Petar Mati?*, Aleksandar Raki??, Slobodan N. Vukosavi?? * Faculty of Electrical Engineering, Banjaluka, RS, Bosnia and Herzegovina, e-mail: pero@ieee.org ?Faculty of Electrical Engineering, Belgrade, Serbia, e-mail: rakic@etf.rs; boban@ieee.org Abstract — This paper presents a novel algorithm for the induction motor torque control in field weakening region. Proposed method insures maximum DC bus utilization and offers DTC performance through the stator voltage angle control. The algorithm is simple, without the outer flux loop nor the inner current loop. Dynamic response is preserved over wide speed range by means of gain-scheduling. The paper comprises the implementation details and experimental results. Keywords — Induction Motor, Vector Control, Direct Torque Control, Field Weakening. I. INTRODUCTION Decoupled torque and flux control of an induction machine (IM) is commonly achieved through the Field Oriented Control (FOC) or the Direct Torque Control (DTC). In the former, the stator current component aligned with the rotor flux controls the flux amplitude, while the perpendicular component controls the torque. The later method is based on setting the stator voltage vector according to the torque and flux references and it does not have an inner current loop [1-3]. In both cases stator or rotor flux is kept constant below the nominal speed and decreased proportionally to the rotor speed above the nominal speed, in the field weakening region. The FOC control schemes require current controller and coordinate transformations. They can be based on rotor flux or stator flux reference frames. In most cases, the stator current controller is located in synchronous dq reference frame and it requires both direct and inverse Park transforms. The benefit of first DTC schemes [2, 3] was sought in relieving the controller from numerical tasks of per