International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN: 2250 155X Vol.2, Issue 1 Mar 2012 54-65 TJPRC Pvt. Ltd., 54 DESIGN, SIMULATION AND ANALYSIS OF SENSORLESS VECTOR CONTROLLED INDUCTION MOTOR DRIVE 1 T.H. PANCHAL AND HORMAZ AMROLIA 1,2 Institute of Technology, Nirma University, Ahmedabad, India ABSTRACT The applications where vector control is required but retrofitting of shaft for speed encoder is not possible, sensorless vector control can be used. The paper presents a scheme for sensorless vector control of induction motor. The proposed scheme utilizes easy and simple approach for speed estimation. The scheme is very efficient and a wide range of speed control is available. Speed reversal can be achieved without any instability of system. The proposed scheme had been simulated using MATLAB software. Index Terms-- Flux estimation, Induction Motor, SensorlessVector control, Speed estimation. I. INTRODUCTION The advent of vector control of Induction motor drive has revolutionized the area of drives. Induction Motors can be controlled as a separately excited dc motor using vector control i.e. flux and torque can be controlled separately. Thus the problem regarding the decoupling of current components is rectified using vector control thus improving the response of the drive system [1].
55 Design, Simulation And Analysis Of Sensorless Vector Controlled Induction Motor Drive Vector control drives are efficient and have speed accuracy higher than the scalar drives. But the major disadvantage of vector drives is that they are costly and cannot be used for multi motor drive system. To nullify the cost and reliability issuesnew field of drives has been developed i.e. Sensorless vector Controlled Drives. In these drives thecontroller itself estimates the flux and speed thus eliminating the speed sensor and problems regarding it. Fig.1 shows the block diagram for proposed scheme. II. FLUX ESTIMATION As mentioned in the block diagram the estimation of flux is mandatory for the calculation of speed of motor. This is the key step or the foundation for speed estimation for the drive. There are various methods for calculation of flux in which two are common and most popular viz. 1) Voltage Model estimation 2) Current model Estimation (1) (2) The above equations can be modified and can be written as - (3)
T.H. Panchal and Hormaz Amrolia 56 (4) Integrating (3) & (4) the flux can be obtained which is further utilized for estimation of speed. III. SPEED ESTIMATION Using above equations the flux is estimated which is utilized for the next step i.e. speed estimation of the motor. A simple and basic approach i.e. torque-speed relation is used to obtain speed. Figure 1 : General block diagram The flux estimated using equations (3) & (4) is usedto determine the electromagnetic torque produced (5) The torque obtained using equation (5)is used to estimate the speed from the relation
57 Design, Simulation And Analysis Of Sensorless Vector Controlled Induction Motor Drive (6) The speed can be obtained integrating equation (6). The speed obtained is then used to estimate the rotor position (7) (8) (9) IV. SPEED CONTROLLER Every closed loop control requires a controller that accepts the feedback signals,compares it with reference and maintains zero error [3]. The controller designed calculates the speed error and produces a reference torque signal which is provided with hysteresis limits that controls the current. The torque produced is utilized to obtain reference torque component ( ). In a similar fashion reference flux component is obtained ( Figure 2 : General block diagram for speed controller
T.H. Panchal and Hormaz Amrolia 58 (10) (11) The reference value of the 2-Φ currents (, ) are transformed to 3-Φ values (,, ) and are compared withthe actual currents (,, ). These compared values will provide the pulses to inverter accordingly. V. SIMULATION RESULTS The simulation had been carried out on Matlab software. The equations presented in the paper were used to simulate the system. The results shown are for the motor having parameters V = 440 V, F = 60 Hz, P = 50 HP, p=4. Fig.3 shows waveforms of reference and calculated speeds and shows calculated speed, flux and stator currents at ω = 0.5 rad/s.
59 Design, Simulation And Analysis Of Sensorless Vector Controlled Induction Motor Drive Figure 3 Reference and calculated speeds at ω = 0.5 rad/s Speed, Flux and stator currents at ω = 0.5 rad/s Fig.4 shows waveforms of reference and calculated speeds and shows calculated speed, flux and stator currents at ω = 10 rad/s.
T.H. Panchal and Hormaz Amrolia 60 Figure 4 : Reference and calculated speeds at ω = 10 rad/s. Speed, Flux and stator currents at ω = 10 rad/s Fig.5 shows waveforms of reference and calculated speeds and shows calculated speed, flux and stator currents at ω = 60 rad/s.
61 Design, Simulation And Analysis Of Sensorless Vector Controlled Induction Motor Drive Figure 5 : Reference and calculated speeds at ω = 60rad/s Speed, Flux and stator currents at ω = 60 rad/s Fig.6 shows waveforms of reference and calculated speeds and shows calculated speed, flux and stator currents at ω = 130 rad/s.
T.H. Panchal and Hormaz Amrolia 62 Figure 6 : Reference and calculated speeds at ω = 130rad/s Speed, Flux and stator currents at ω = 130 rad/s Fig.7 shows waveforms of reference and calculated speeds and shows calculated speed, flux and stator currents at ω = 180 rad/s.
63 Design, Simulation And Analysis Of Sensorless Vector Controlled Induction Motor Drive Figure 7 : Reference and calculated speeds at ω = 180rad/s Speed, Flux and stator currents at ω = 180 rad/s Fig.8 shows waveforms of reference and calculated speeds and shows calculated speed, flux and stator currents during speed reversal.
T.H. Panchal and Hormaz Amrolia 64 Figure 8 : Reference and calculated speeds for speed reversal Speed, Flux and stator currents for speed reversal Fig.9 shows waveforms of reference and calculated speeds and shows calculated speed, flux and stator currents at ω = 200 rad/s.
65 Design, Simulation And Analysis Of Sensorless Vector Controlled Induction Motor Drive Figure 9 : Reference and calculated speeds at ω = 200 rad/s Speed, Flux and stator currents at ω = 200 rad/s VI. CONCLUSIONS The above results conclude that the controller tracks the reference speed precisely. The control strategy does not show any instability for low and high speeds as well as operation during speed reversal. A wide range of speed control is available. The calculations carried out for the estimations are simple and can be easily implemented using a DSP. VII. REFERENCES 1. B.K.Bose, Power Electronics and Ac Drives, PHI publications, Chapter 8. 2. P.Vas, Sensorless Vector and Direct Torque Control, Oxford Universitypress,Chapter 2 and Chapter 4. 3. Slobodan N. Vukosavić, Digital Control of Electrical Drives, Springer, Chapter 2. 4. P.C.Krause, Analysis of Electric Machinary and Drive Systems, IEEE Press, Chapter 3. 5. E.D.Mitronikas, A.N.Safacas, "A Hybrid Sensorless Stator-Flux Oriented Control Method for Induction Motor Drives", in 2004 35th Annual IEEE Power Electronics Specialists Conference, Aacken, Germany, 2004, pp. 3481-3485.