Sensorless Control of Induction Motor Drive Using SVPWM - MRAS Speed Observer

Transcription

1 Journal of Eerging Trends in Engineering and Applied Sciences (JETEAS) 2 (3): Journal Scholarlink of Eerging Research Trends Institute in Engineering Journals, 2011 and Applied (ISSN: ) Sciences (JETEAS) 2 (3): (ISSN: ) jeteas.scholarlinkresearch.org Sensorless Control of Induction Motor Drive Using SPWM - MRAS Speed Observer K. Suan and. Aditya C..S.R College of Engineering, Hyderabad, India Corresponding Author: K. Suan Abstract This paper proposes a novel Space ector Pulse width odulation (SPWM) for sensor less control of induction otor using odel erence adaptive syste (MRAS). The steady state ripples in the torque are present in the conventionally used MRAS sensor less control of induction otor which utilizes norally used voltage source inverters. Also perforance of the steady state speed is not as perfect as required having disturbances in steady state region. Hence to iprove the perforance of MRAS based speed observer a novel ethod of SPWM based on erence voltage vector that utilizes the control variables as stator flux coponents is proposed. By using the proposed SPWM control of induction otor the speed disturbances which are obtained are iniized and the speed perforance is iproved. Also the ripples present in the electroagnetic torque are reduced. This is proved by the siulation results for conventional MRAS speed observer and proposed SPWM based MRAS speed observer. Keywords: sensor less control, odel erence adaptive syste, erence voltage vector, SPWM I TRODUCTIO Induction otors have been widely used in high perforance ac drives, requiring inforation. Introducing a shaft speed sensor decreases syste reliability, and different solutions for sensor less ac drives have been proposed. The MRAS speed estiators are the ost attractive approaches (Hori and Uchida, 1991) due to their design siplicity. The MRAS is based on principle, in which the outputs of two odels one independent of the rotor speed (erence odel) and the other dependent (adjustable odel)- are used to for an error vector. The error vector is driven to zero by an adaptation echanis which yields the estiated rotor speed. Depending on the choice of output quantities that for the error vector, several MRAS structures are possible. The ost coon MRAS structure is that based on the rotor flux error vector (Holtz 1996) which provides the advantage of producing rotor flux angle estiate for the fieldorientation schee. Other MRAS structures have also been proposed recently that use the back EMF and the reactive power as the error vectors estiators. It is the intention of this paper, theore, to present a direct coparison between two different MRAS approaches: the rotor flux based and the back EMF based MRASS (Lassaâd and Ben Haed, 2007). The rotor flux based MRAS approach studied in this paper basically follows that of, while the back EMF based approach is the odified for of the one developed in. To allow for a fair coparison, no on-line paraeter ethods will be incorporated and sae current controllers and a PWM generation technique will be used in both approaches. In order to copare the perforances of the two estiators. Several perforance easures are evaluated in coputer 509 Siulations. The studies include the level of difficulties in tuning the adaptive Gain constants and the tracking perforances of both speed estiators. To obtain accurate estiation of the speed, a siple online identification approach has been incorporated. Based on the theory of MRAS, siultaneous estiation of rotor speed has been described in this paper. Coparing to other adaptation techniques, this ethod is siple and needs a low coputation power and has a high speed adaptation even at zero speeds. This ethod because eliinates the produced error in the speed adaptation, is ore stable and robust. Coputer siulations results are presented to show its effectiveness. In SPWM ethods, the voltage erence is provided using a revolving erence vector. In this case agnitude and frequency of the fundaental coponent in the line side are controlled by the agnitude and frequency, respectively, of the erence voltage vector. Space vector odulation utilizes dc bus voltage ore efficiently and generates less haronic distortion in a three phase voltage source inverter. Space ector Pulse Width Modulation Space ector Modulation (SM) was originally developed as vector approach to Pulse Width Modulation (PWM) for three phase inverters. It is a ore sophisticated technique for generating sine wave that provides a higher voltage to the otor with lower total haronic distortion. The ain ai of any odulation technique is to obtain variable output having a axiu fundaental coponent with iniu haronics. Space ector PWM (SPWM)

2 ethod is an advanced; coputation intensive PWM ethod and possibly the best techniques for variable frequency drive application (Erfidan et al., 2004). The space vector concept, which is derived fro the rotating field of induction otor, is used for odulating the inverter output voltage. In this odulation technique the three phase quantities can be transfored to their equivalent two-phase quantity either in synchronously rotating frae (or) stationary frae. Fro these two-phase coponents, the erence vector agnitude can be found and used for odulating the inverter output. The process of obtaining the rotating space vector is explained in the following section, considering the stationary erence frae. Considering the stationary erence frae let the three-phase sinusoidal voltage coponent be, a = Sinωt (1) b = Sin(ωt-2π/3) (2) c = Sin(ωt-4π/3) (3) When this three-phase voltage is applied to the AC achine it produces a rotating flux in the air gap of the AC achine. This rotating resultant flux can be represented as single rotating voltage vector. The agnitude and angle of the rotating vector can be found by eans of Clark s Transforation as explained below in the stationary erence frae. To ipleent the space vector PWM, the voltage the stationary dq erence frae that consists of the horizontal (d) and vertical (q) axes as depicted in Figure-1. Fro Figure-1, the relation between these two erence fraes is below equivalent to an orthogonal projection of [a b c] t onto the two-diensional perpendicular to the vector [1 1 1] t (the equivalent d-q plane) in a three-diensional coordinate syste. As a result, six non-zero vectors and two zero vectors are possible. Six non-zero vectors ( 1-6 ) shape the axes of a hexagonal as depicted in Figure-2, and supplies power to the load. The angle between any adjacent two non-zero vectors is 60 degrees. Meanwhile, two zero vectors ( 0 and 7 ) and are at the origin and apply zero voltage to the load. The eight vectors are called the basic space vectors and are denoted by ( , 6 7 ). The sae transforation can be applied to the desired output voltage to get the desired erence voltage vector in the d-q plane. The objective of SPWM technique is to approxiate the erence voltage vector using the eight switching patterns. One siple ethod of approxiation is to generate the average output of the inverter in a sall period T to be the sae as that of in the sae period Figure-2. Basic switching, vectors and sectors Figure-1. The relationship of abc erence fra and stationary dq erence frae. and f denotes either a voltage or a current variable. As described in Figure-1. This transforation is Switching States For 180 ode of operation, there exist six switching states and additionally two ore states, which ake all three switches of either upper ars or lower ars ON. To code these eight states in binary (one-zero representation), it is required to have three bits (2 3 = 8). And also, as always upper and lower switches are coutated in copleentary fashion, it is enough to represent the status of either upper or lower ar switches. In the following discussion, status of the upper bridge switches will be represented and the lower switches will it s copleentary. Let "1" denote the switch is ON and "0" denote the switch in OFF. Table-1 gives the details of different phase and line voltages for the eight states (Rathnakuar et al,. 2005) 510

3 MRAS Based On Rotor Flux-Linkage Estiation The proposed MRAS is using state observer odel with current error feedback and rotor current odel as two odels for flux estiation. Figure 5 shows the block diagra of the proposed MRAS. The erence odel is given by: Table-1. Switching patterns and output vectors. The adjustable odel is given by: Model Reference Adaptive Syste The Model Reference Adaptive Systes (MRAS) approach uses two odels. The odel that does not Involve the quantity to be estiated (the rotor speed re in our case) is considered as the erence odel. The odel that has the quantity to be estiated involved is considered as the adaptive odel (or adjustable odel). The output of the adaptive odel is copared with that of the erence odel, and the difference is used to drive a suitable adaptive echanis whose output is the quantity to be estiated (rotor speed in our case). The adaptive echanis should be designed to assure the stability of the control syste. Figure 3 illustrates the basic structure of MRAS. Different approaches have been developed using MRAS, such as rotor-flux-linkage estiation-based MRAS, back-emf based MRAS (reactive-power-based MRAS) (Lassaâd and Ben Haed, 2007). The Overall syste of the proposed sensor less control algorith is shown in Figure 2. Where estiated values of rotor fluxes in state observer odel estiated values of rotor fluxes in rotor current odel. Rotor speed is obtained fro the adaptation echanis as follows(marwali and Ali Keyhani, 1997) The presence of the pure integrators brings the probles of initial conditions and drift. In (Marwali and Ali Keyhani, 1997), To reduce the effect of the derivative ters, a siilar approach as that used to eliinate the pure integration proble a low pass filter was used to replace the pure integrator, but the perforance in the low speed range is not satisfying, for reasons which will be explained later. Figure 3. Block diagra of the proposed MRAS Figure 5. MRAS based on rotor Flux-linkage estiation Figure 4. Configuration of overall syste 511 MRAS Based on Back-EMF Estiation This paper proposes a novel sensor less control algorith based on the MRAS for the speed sensor less control of a induction otor. The proposed MRAS is using the state observer odel of and the agnet flux odel of and as two odels for the back-emf estiation. The rotor speed is generated fro the adaptation echanis using the error

4 between the estiated quantities obtained by the two odels as follows in Figure.6 (Toufouti, Meziane, Benalla, 2006). The erence odel is given by: The adjustable odel is given by: I TERPRETATIO OF RESULTS To validate the perforances of the proposed controller, we provide a series of siulations and a coparative study between the perforances of the proposed control strategy. A 1.5kW induction otor with controller is siulated using the nonlinear controller The results with the above schee in steady state operation are shown below. It shows the behavior of the Electroagnetic torque, Stator current, THD response of stator current at steady state The adaptive echanis is given by : Where Ki, and Kp, are the gain constants, i, and p are the estiated values of back-emf in the state observer odel. Figure 7 shows the block diagra of the proposed MRAS algorith has a robust perforance through cobining the state observer odel and the agnet flux odel. a)electroagnetic torque Figure 6: The MRAS speed observer This schee does not have pure integrators in the Reference odel. b) stator current Figure 7: MRAS based on back EMF 512 c) THD response of stator current

5 It can be observed fro the results that the value of Total haronic Distortion (THD) is just 24.58% which is very low. So by using SPWM MRAS speed Observer technique Total Haronic Distortion is also iniized CO CLUSIO This work has dealt with the sensor less control of induction otor with svpw. Its principles and basic concepts have been introduced and thoroughly explained. This paper is focused on the analysis of SPWM-MRAS speed control schees. The siulation shows a SPWM-MRAS has better perforance. T. Erfidan, S. Urugun, Y. Karabag and B. Cakir New Software ipleentation of the Space ector Modulation. Proceedings of IEEE Conference. pp Y. Hori C. Ta, T. Uchida (1991): MRAS-based speed Sensor less control for induction otor drives using instantaneous reactive power. IECON, Pp Zhou K., Wang D., Relationship Between Space- ector Modulation and Three Phase Carrier-Based PWM: A Coprehensive Analysis, IEEE Transactions on Industrial Electronicsol. 49, No. 1, February 2002, page REFERE CES D. Rathnakuar, J. Lakshana Perual and T. Srinivasan A New software ipleentation of space vector PWM. Proceedings of IEEE Southeast conference. pp D.W. Jin Y.A. Kwon. (1999): A novel MRAS based speed sensorless control of induction otor. IECON, 2: J. Holtz, (1996): Methods for speed sensorless control of ac drives, in Sensorless Control of AC Motors, K. Rajashekara, Ed. Piscataway, NJ: IEEE Press. Mohaad N. Marwali and Ali Keyhani (1997): A Coparative Study of Rotor Flux Based MRAS and Back EMF Based MRAS Speed Estiators for Speed Sensorless ector Control of Induction Machines IEEE Industry Applications Society Annual Meeting New Orleans, Louisiana, October 5-9 R. Blasco-Gienez., G.M. Asher, M. Suner, and K. J. Bradley (1996): "Dynaic Perforance Liitations for MRAS based sensorless induction otor drives. Part 2: Online paraeter tuning and dynaic perforance studies", IEE Proc. Elect. Power Applol. 143, (2), pp R.Toufouti S.Meziane,H. Benalla,(2006): Direct Torque Control for Induction Motor Using Fuzzy Logic ICGST Trans. on ACSEol.6, Issue 2, pp S.Lassaâd and M.Ben Haed (2007): An MRAS - based full Order Luenberger Observer for Sensorless DRFOC of Induction Motors ICGST-ACSE Journal, olue 7, Issue