International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 02 | Feb -2017
p-ISSN: 2395-0072
www.irjet.net
VECTOR CONTROL METHODS FOR VARIABLE SPEED OF AC MOTORS Mr. Tausif Ahmad Shekh Muktar 1 , Mr. Ankit R. Umale2 , Prof: Rahul K. Kirpane3 BE, Electrical Engineering Department, DES’sCOET, Maharashtra, Indi BE, Electrical Engineering Department, DES’sCOET, Maharashtra, India 3 Assistant Professor, Electrical Engineering Department, DES’sCOET, Maharashtra, India ---------------------------------------------------------------------***--------------------------------------------------------------------1
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Abstract - This research paper gives the information and
result about the vector controlling methods, using vector control methods what parameters are obtained. These vector controlling is used for A.C .motors. The three phase alternating current (AC) induction motor are mechanically simple, rugged, highly reliable, lower in cost per horsepower than DC motors and capable of more torque and efficiency than single-phase A.C. motors. Vector control, also called field-oriented control (FOC), is a variable-frequency drive (VFD) control method in which the stator currents of a three-phase AC electric motor are identified as two orthogonal elements that can be visualized with a vector. One element defines the magnetic flux of the motor, the second the torque. The control system of the drive analyzed the equivalent current element places from the flux and torque places set by the drive’s speed control. Normally proportional-integral (PI) controllers are used to keep the measured current elements at their reference values. The pulse-width modulation (PWM) of the variable frequency drive defines the transistor switching according to the stator voltage references that are the output of the PI current controllers. Doubly Fed Induction Generator (DFIG) wind turbines are nowadays increasingly used in large wind farms because of their ability to supply power at constant voltage and frequency. Modern control techniques such as vector control and MFC (magnitude and frequency control) are studied and some of proposed systems are simulated in MATLAB-SIMULINK environment. Key Words: Doubly Fed Induction Generator (DFIG), Alternating Current (AC), Pulse Width Modulation (PWM), Proportional Integral (PI), Wind Energy, Spectral Analysis, Electrical Drives (E.D).
1. INTRODUTION The control strategy of the machine is distributed in two ways, one is scalar control and the second is vector control. The limitations of scalar control give a importance to vector control. However the scalar control strategy is uncertain to implement but the natural coupling effect gives sluggish response. The inherent problem is presence solved by the vector control. The vector control is invented in the beginning of 1970s. Using this control strategy an induction motor can be performed like dc machine. Because of dc machine like performance vector control is also known as orthogonal, decoupling or Tran‘s vector control. FOC is used to control AC synchronous and
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induction motors. It was originally developed for high performance motor applications that are required to operate smoothly over the full speed range, generate full torque at zero speed, and have high dynamic performance including fast acceleration and deceleration. However, it is becoming gradually attractive for lower performance applications as well due to FOC’s motor size, cost and power consumption reduction superiority. It is predictable that with increasing computational power of the microprocessors it will eventually nearly universally displace single-variable scalar volts-per-Hertz (V/f) control Altered vector control strategies have been proposed to control the active and reactive power of an induction motor. The basic of the vector control theory is d-q theory. To understand vector control theory information about d-q theory is essential. 1.1 D-Q THEORY
The d-q theory is also known as reference frame theory. The history states in 1920, R. H. Park suggested a new theory to overcome the problem of time varying limitations with the ac machines. He expressed a change of variables which replace the variables related to the stator windings of a synchronous machine with variables related with fictitious winding which rotates with the rotor at synchronous speed. Basically he changed the stator variables to a synchronously rotating reference frame fixed in the rotor. With such transformation (Park‘s transformation) he presented that all the time varying inductances that occur due to an electric circuit in relative motion and electric circuit with varying magnetic reluctances can be eliminated. Later in 1930s H. C. Stanley showed that time varying parameters can be eliminated by transforming the rotor variables to the variables associated with fictitious stationary windings. In this case the rotor variables are transformed to the stationary reference frame fixed on the stator. Later G. Kron proposed transformation of stator and rotor variables to a synchronously rotating reference frame which moves with rotating magnetic field. Latter, Krause and Thomas had shown that the time varying Inductances can be eliminated by mentioning the stator and rotor variables to an arbitrary reference frame which may rotate at any speed.
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