International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017
p-ISSN: 2395-0072
www.irjet.net
Speed Sensor less DTC of VSI fed Induction Motor with Simple Flux Regulation for Improving State Estimation at Low Speed K. Farzand Ali1, S.Sridhar2 PG Scholar, Dept. Of Electrical & Electronics Engineering, JNTUACEA, Anantapuramu, A.P., India Asst. Professor, Dept. Of Electrical & Electronics Engineering, JNTUACEA, Anantapuramu, A.P., India 1
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---------------------------------------------------------------------***--------------------------------------------------------------------Abstract – In this paper constant switching frequency sensor, estimating the speed is more preferable as it controller is used in order to replace 3-level hysteresis reduces the drive cost, size, and maintenance torque comparator without increasing the complexity of the requirements while increasing the system robustness and control structure. The main objective of this paper is to reliability. Processing requirements lower in DTC, improve speed and torque estimations of direct torque whereas in FOC higher. No coordinate transforms are control of induction motor at low speed region with the needed in DTC, all calculations are done in stationary improved flux regulation. It forms a simple structure of a coordinate frame. look-up table based DTC drive by utilizing CSFC. With DTCDTC scheme has high efficiency & low losses. CSFC, constant switching frequency is maintained, and at Switching losses are minimized because the transistors the same time, poor stator flux regulation at low speed are switched only when it is needed to keep torque and operation i.e. flux droop problem that normally occurs in flux within their hysteresis bands. In DTC, the step DTC with the hysteresis controller (DTC-HC) at low speed is response has no overshoot. Typical control cycle time is solved; and also the stator flux and torque estimations at 10-30 microseconds in DTC, where as in FOC it is 100-500 low speed are also improved. By using an extended Kalman microseconds. filter (EKF) based estimator the speed feedback for the The main problems that are normally associated closed loop speed control system is estimated, in the with DTC utilizing hysteresis torque controller (DTC-HC) proposed system. Simulation work was carried out for the are poor stator flux regulation at low speed operation, also proposed work using MATLAB/SIMULINK software and referred as flux droop, high torque ripples and variable results were presented for low speed operation. switching frequency. Problems of high torque ripples and variable switching frequency can be achieved by space Key Words: Constant switching frequency controller, vector modulation, known as the DTC-SVM. With DTCdirect torque control, extended Kalman filter, flux SVM, voltage vector is generated within the sampling time, regulation, induction motor. which is then synthesized using the space vector modulator, thus, hysteresis comparators are not needed 1. INTRODUCTION for the flux and torque control. Nevertheless, the complexity of DTC structure and high computational effort Induction motor drives have been a mature increase significantly. Additionally, DTC-SVM cannot technology for many years, but investigations into sensor achieve stability at a zero speed operation. Flux droop less concepts are still taking place. The basic aim of sensor problem, needs a separate treatment and cannot be less control research is to achieve dynamic system directly solved with the implementation of DTC-SVM. With performance equivalent to an encoded scheme without the DTC-SVM, the torque and stator flux are indirectly disadvantages associated with using a speed encoder. controlled through the application of computed stator Direct Torque Control was first introduced by Takahashi voltage space vectors. In order to solve this problem, it in 1986. It offers fast instantaneous torque and flux needs modifying the predefined lookup table of DTC-HC by control with simple implementation. DTC controls the adding more reverse voltage vectors to improve the flux torque and speed of the motor, which is directly based on regulation. However this leads to an increase in the size of the electromagnetic state of the motor. The main the lookup table and require more precise stator flux advantages of DTC compared to FOC are less machine position estimation. parameter dependence, simpler implementation and In this paper, an alternative DTC variation with a quicker dynamic torque response. And also it doesn’t constant switching frequency controller (DTC-CSFC) that require the complex field orientation block, speed retains the simple structure of DTC is presented. DTCencoder, current regulator and PWM modulator. Even CSFC has been initially proposed, analyzed and proved for though DTC drives are inherently sensor less, the rotor its capability in minimizing the torque ripple and speed information is still needed for the speed control, operating at constant switching frequency. In this paper, which is common in most industrial applications. the performance of DTC-CSFC near and at zero frequency However, rather than installing a mechanical speed is studied. With DTC-CSFC, flux regulation can be achieved © 2017, IRJET
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