08-16-2017, 09:13 PM
matlab simulink OF dtc-svm five phases induction motor
ABSTRACT:This paper proposes design and simulation of a direct torque controlled induction motor drive system based on space vector modulation technique for ripple reduction.Direct Torque Control is a control technique used in AC drive systems to obtain high performance torque control. The principle is based on simultaneously decoupling the stator flux and electromagnetic torque. DTC drives utilizing hysteresis comparators suffer from high torque ripple and variable switching frequency.The proposed SVM basedDTC reduces torque ripples and preserve DTC transient merits suchas fast torque response. The basis of the SVM-DTC methodology is the calculation of the required voltage space vector to compensate the flux and torque errors and its generation using the SVM at each sample period.The performance of thismethod is demonstrated by simulation using Matlab/Simulink software. Simulation results presented in this paper show the torque,flux linkage and stator current ripple decreases with the proposed SVM-DTC algorithm.
INTRODUCTION
Induction Motors(IMs) are widely used in industrial, commercial and domestic applications as they are simple,rugged, lowcost and easy to maintain. Since IMs demands well control performances: precise and quick torque and flux response, large torque at low speed, wide speed range, the drive control system is necessary for IMs.Though DC motor is able to provide desired performance, its maintenance and unsafe in explosive environment restricts its use. In 1970s, field oriented control
(FOC) scheme proved success for torque and speed control of induction motor. Decoupling of two components of stator currents (flux and torque producing components) is achieved as DC machines to provideindependent torque control. Hence the scheme proves itself superior to the DC machine. The problem faced by FOC scheme is complexity in its implementation due to dependence of machine parameters, reference frame transformation. Later DTC was introduced. The method requires only the stator resistance to estimate the stator flux and torque. In conventional DTC, electromagnetic torque and flux are independently controlled by selection of optimum inverterswitching modes. The selection of optimum inverter switching modes is made to limit the electromagnetic torque and flux linkage errors within the torque and flux hysteresis bands. The basic DTC scheme consists of two comparators with specified bandwidth, switching table, voltage source inverter, flux and torque estimation block. Like every control method has some advantages and disadvantages, DTC method has too.Some of the advantages are lower parameters dependency, making the system more robust and easier implements and the disadvantages are difficult to control flux and torque at low speed, current and torque distortion during the change of the sector , variable switching frequency, a high sampling frequency needed for digital implementation of hysteresis controllers, high torque ripple. The torque ripple generates noise and vibrations, causes errors in sensor less motor drives, and associated current ripples are in turn responsible for the EMI. The reason of the high current and torque ripple in DTC is the presence of hysteresis comparators together the limited number of available voltage
vectors. If a higher number of voltage vectors than those used in conventional DTC is used, the favourable motor control can be obtained. Because of complexity of power and control circuit, this approach is not satisfactory for low or medium power applications. An another solution to minimize torque ripple is the space vector modulated DTC scheme. The objective of the DTC-SVM scheme, isto estimate a reference stator voltage vector V*and modulate it by SVM technique, in orderto drive the power gates of the inverter with a constant switching frequency, so that in everysampling time, inverter can produce a voltage
CONCLUSION
This project has reviewed Direct Torque Control strategies for SVPWM inverter-fed ACmotor drives. The DTC represents a viable alternative to Field Oriented Control (FOC)being also a general philosophy for controlling the AC drives DTC strategies have been divided into two groups: hysteresis-based switching tableDTC, and constant switching frequency schemes operating with space vector modulators(SVM-DTC). Constant switching frequency SVM-DTCschemes improve considerably the driveperformance in terms of reduced torque and flux pulsations, reliable start up and lowspeed operation, well-defined harmonic spectrum as well as radiated noise. Therefore,SVM-DTC is an excellent solution for general purpose IM drives in a very wide powerrange. In conclusion, it is believed that the DTC principle will continue toplay a strategic role in the development of high performance drives.