15 th International Power Electronics and Motion Control Conference, EPE-PEMC 2012 ECCE Europe, Novi Sad, Serbia Stator Voltage Vector Direct Torque Control of Induction Machine Petar R. Matić 1 , Aleksandar Ž. Rakić 2 , Slobodan N. Vukosavić 2 1 Faculty of Electrical Engineering, University of Banja Luka, Banja Luka, Republic of Srpska, Bosnia and Herzegovina 2 Faculty of Electrical Engineering, University of Belgrade, Belgrade, Serbia Abstract — This paper presents improved high speed Induction Motor (IM) torque control algorithm that achieves full inverter voltage utilization in field weakening and smooth speed transition from the base speed to high speed region. The Stator Voltage Vector Direct Torque Control (SVV DTC) algorithm simultaneously controls IM torque and rotor flux by regulating stator voltage angle and amplitude in the base speed region, and by regulating only the voltage angle in the field weakening region. Fast torque dynamics is obtained in wide speed range by using torque regulator with variable gain. The main benefit from the proposed algorithm is in field weakening range, in which the machine is supplied by maximal available voltage without outer flux trajectory reference. This approach enables full utilisation of both magnetic material of the machine and power capabilities of the inverter, which is not possible with traditional vector drives with current regulators. Transition from base speed region to field weakening is obtained by simply limiting the output voltage. Experimental results gathered on the high speed low cost IM drive confirm the effectiveness of the proposed SVV DTC approach. Keywords — Direct Torque Control, Stator Voltage Vector Control, High Speed Induction Motor I. INTRODUCTION Decoupled control of torque and flux in Induction Motor (IM) drives is commonly achieved through the Field Oriented Control (FOC), which is based on decoupling of the torque-producing and flux-producing components of stator current vector, or through Direct Torque Control (DTC), which is based on direct control of stator voltage without inner current control loop [1-2]. Contemporary drives should provide fast and well damped torque response with full utilization of available motor and inverter overloading capabilities. In IM drives torque and flux are coupled and they are controlled simultaneously by using fast current regulated inverters (in FOC drives), or by employing hysteresis controllers or decoupling circuits (in DTC drives). In both cases respective flux components are kept constant below the base speed (base speed region), and decreased above the base speed in field weakening region [3-7]. The Stator Voltage Vector (SVV) DTC approach presented in this paper is focused on high speed induction motors for which full utilization of available inverter voltage is required. Medium and high-speed induction machines gain more attention due to better efficiency, larger power-to-weight ratio, and smaller size and cost. They can be used without mechanical gear in wide speed range, typically from 1 to 5 (or 6), and mainly operate in field weakening regime [8-11]. In order to achieve maximum torque capability in field weakening, full utilization of available inverter voltage is mandatory [11-15]. The absence of an explicit current controller in DTC schemes results in a better DC bus utilization then in FOC. For the proper operation of the current loops within FOC schemes, a minimum voltage margin has to be preserved both in the constant flux and the field weakening regime. The voltage margin is obtained by reducing the flux or using overmodulation. Therefore, the FOC scheme in field weakening results in suboptimal flux amplitudes or current harmonics in overmodulation [16-19]. Fundamental frequencies of high speed machines are in range of few hundreds of hertz. High fundamental frequencies in high speed drives can not be followed with the increase of Pulse Width Modulation (PWM) frequency because that would increase switching losses and demand more CPU calculating power. Time consuming real-time algorithms with need for precise knowledge of flux position and fast current regulation can not be implemented in those drives. This is especially true when the ratio between sampling and fundamental frequency is low or single phase AC tachogenerator is used for sensing the speed [20, 21]. As a result, to make cheap high speed IM drive a simple control algorithm should be used. Basic U/f control which fully utilize the available voltage in field weakening is often preferred, even the torque dynamic response is not satisfying [22]. Flux and torque are coupled in field weakening due to voltage limit. Torque control in the field weakening regime is usually accomplished by using outer flux trajectories calculated from the steady state relations. These trajectories use the same FOC or DTC rule as used in the base speed range, with the flux reduction designed so as to provide the necessary voltage margin in order to enable fast torque transients. Since the IM dynamics is not considered, the DC bus voltage is not fully exploited, the torque per ampere ratio and the peak torque drive capabilities are suboptimal, while the flux and torque loops are coupled both in steady state and in transients. If the machine is supplied by full constant voltage in field weakening, the outer flux trajectory reference is not necessary since rotor flux automatically adjusts by torque control loop in field weakening [23-25]. The SVV DTC control scheme proposed in this paper aims to improve torque performance of high speed IM drive by obtaining fast and well damped torque response both in base speed and field weakening, with full utilization of inverter voltage. In the Section II mathematical model of IM supplied from voltage source is derived. The operating point model in which voltage amplitude and phase angle are control variables is