Improved Indirect Rotor Flux Oriented Control of PWM inverter fed Induction Motor Drives

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In today’s high-power electrical drives using vector
controlled induction machines, voltage source inverters (VSI)
based on PWM technology and current source inverters (CSI)
based on based on PWM technology are the most important
alternatives for motor supply (cyclo-converters being confined
to very low speed applications). In this paper an Induction
motor modeled in the rotor flux reference frame, the rotor
flux orientation is obtained, a high performance current fed
Indirect Rotor Flux Oriented Controller also proposed and a
comparative performance analysis of the VSI & CSI drive
topologies in Flux-Feed forward Vector Control (Indirect
Vector Control) is also presented. To verify the design of
controllers and system performance, the drive system
simulation is carried out using MATLAB/Simulink. The
steady state and dynamic performance of the drive system for
different operating conditions are studied. The simulation
results are provided to demonstrate the effectiveness of the
proposed drive system

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Improved Indirect Rotor Flux Oriented Control of PWM inverter fed Induction Motor Drives

  1. 1. ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010 Improved Indirect Rotor Flux Oriented Control of PWM inverter fed Induction Motor Drives I. Gerald Christopher Raj 1, Dr. P. Renuga 2, and M. Arul Prasanna 1 1 PSNA College of Engineering and Technology/Department of EEE, Dindigul, Tamilnadu, India Email: gerald.gera@gmail.com, arulresearch2006@gmail.com 2 Thiagarajar College of Engineering /Department of EEE, Madurai, Tamilnadu, India Email: preee@tce.eduAbstract— In today’s high-power electrical drives using vector transformer are d-q axis current components and the rotorcontrolled induction machines, voltage source inverters (VSI) position θ and the output is the current reference vectorbased on PWM technology and current source inverters (CSI) based on the stator coordinate. There is no interlinkage fluxbased on based on PWM technology are the most importantalternatives for motor supply (cyclo-converters being confined feedback loop, but the flux is controlled by the feedto very low speed applications). In this paper an Induction forward control utilizing the machine parameters [4]-[6],motor modeled in the rotor flux reference frame, the rotor [8], [9].flux orientation is obtained, a high performance current fed The vector controlled drives employ mostly a VoltageIndirect Rotor Flux Oriented Controller also proposed and a Source Inverter (VSI) to control the motor armature,comparative performance analysis of the VSI & CSI drive despite the inherent advantages of the Current Sourcetopologies in Flux-Feed forward Vector Control (IndirectVector Control) is also presented. To verify the design of Inverter (CSI) topology. This is partly due to the currentcontrollers and system performance, the drive system source nature of the topology and the complexity of thesimulation is carried out using MATLAB/Simulink. The controls required, the voltage source being a moresteady state and dynamic performance of the drive system for universal power supply and being easier to control [10]-different operating conditions are studied. The simulation [12]. The VSI has drawbacks that complicate controlresults are provided to demonstrate the effectiveness of the circuit implementation and may reduce the drive reliability,proposed drive system. including:Index Terms— CSI, Indirect, Rotor flux Orientation, Vector - the requirement for additional circuit to protect thecontrol, VSI. converter against internal and external short circuit, - the high dv/dt of the pulse width modulated inverter I. INTRODUCTION output which is known to have resulted in motor winding failures, It is well known that the instantaneous torque producedby an ac machine is controllable when vector control is - the possibility of internal short circuits resulting fromapplied. There are essentially two general methods of improper gating, particularly under fast transients, thisvector control. One called the direct or feed-back method reduces the converter reliabilitywas invented by Blaschke [1], and the other, known as the To overcome these problems this paper proposes aindirect or feed forward method, was invented by Hasse voltage-regulated CSI fed Indirect Rotor-Flux-Oriented[2]. The methods are different essentially by how the unit Control (IRFOC) of induction motor drive which offers thevector (cos θ and sin θ) is generated for the control. It same features as its VSI counterpart, together with theshould be mention here that the orientation of ids with rotor added advantages inherent in the CSI topology, namelyflux ψr or stator flux ψs is possible in vector control [3]. suppression of high dv/dt across motor windings, built-inThe rotor flux orientation gives natural decoupling control, short-circuit protection, natural power reversibility andwhereas stator flux orientation gives a coupling effect high reliability with minimum torque ripple. In section IIwhich has to be compensated by a decoupling the basic concept of flux feed forward control for VSI &compensation current. Therefore the ac machine controlled CSI drive topologies explained. The section III dealsby the vector control scheme is equivalent to a separately induction motor model in rotor flux frame and the currentexcited dc machine. model of rotor flux estimation. The simulation circuit Nowadays, the flux-feed forward vector control system models and results are discussed in section IV.is preferred to the flux-feedback type because it requires noflux detector or flux calculator. The indirect vector control II. FLUX-FEED FORWARD VECTOR CONTROLcircuit inputs the amplitude of the torque componentcurrent reference vector and the amplitude of the Fig. 1 shows the block diagram of flux feed forwardinterlinkage flux reference vector and calculates the current vector control of induction motor fed from voltage sourcereference vector based on the rotor coordinate, utilizing the inverter. Here both inverter output voltage and frequencymachine parameters. The inputs of the coordinate 7© 2010 ACEEEDOI: 01.IJEPE.01.03.67
  2. 2. ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010 This converts the CSI into a voltage source, but preserves the inherent features of the CSI topology listed above closely as possible. III. INDUCTION MOTOR MODEL AND ROTOR FLUX ESTIMATION Figure 1. Flux-feed forward vector control with VSI The model of three-phase squirrel-cage induction motor in the rotating rotor flux reference frame can be expressed as (1) . (2) Figure 2. Flux-feed forward vector control with CSI (3)can be controlled by its PWM scheme. For the rotor fluxcontrol the calculated ψr is compared with its reference ψr* (4)to generate d-axis stator current reference ids*. The q-axisstator current reference iqs* is generated according to thetorque reference Te*. The feedback dq-axis stator currents The investigated induction motor’s parameters are givenare compared with their references, and errors are send to in Table 1. The rotor flux can be calculated from thecurrent controllers to generate stator voltage reference in following expressions.dq-axis voltages in synchronous reference frame then they .are transformed to three-phase stator voltages Vabc* in Wherestationary reference frame. The rotor flux angle θ is used 34.7in transformation blocks for field orientation. Fig. 2 shows the block diagram of flux feed forward 0.1557vector control of induction motor fed from current source 0.8 34.7 35.5inverter. Here the inverter output frequency is controlled byPWM scheme but the inverter output current is adjusted by The rotor flux angle ‘θ’ can be calculated from thethe dc current of the rectifier. The q-axis (torque- following expressions.producing) stator current reference iqs* and d-axis (flux-producing) current reference ids* are generated in the same (5)manner as in the case of VSI fed drives. Where The general control system block diagram of theproposed CSI induction motor drive is shown in Fig. 3.Here the gating patterns are generated in a manner such The dq-axis current components can be obtained fromthat the inverter output voltage is regulated. the following expressions. (6) (7) The transformation of the three-phase (abc-axis) current components of an induction motor to the equivalent two- phase (dq-axis) current components can be performed by 2 4 2 3 3 . 3 2 4 3 3 The three-phase current components ias, ibs, and ics are in stationary reference frame which does not rotate in space whereas the two phase current components ids, iqs are in the synchronous reference frame whose direct and quadratureFigure 3. Proposed Rotor Flux-feed forward vector control with CSI axes rotate in space at the synchronous speed 8© 2010 ACEEEDOI: 01.IJEPE.01.03.67
  3. 3. ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010 IV. ANALYSIS AND SIMULATION RESULTS 2 2 The proposed control algorithm is derived from the basic 3 3 . principle of rotor field orientation control. Consequently, 4 4 so it is still vector control method. It should be noted that the purpose of this control method is aimed to reduce the 3 3 money cost in hardware, and simplify the control design. The rotor flux can also be calculated from the following The drive architectures of Fig. 1, Fig. 2 and Fig. 3 haveequations been completely implemented and assessed in the Mat lab- Simulink environment along with their respective control cos (8) systems. The simulation is based on the parameters shown in Table I and Table II. Fig. 5 to 9 shows the dynamic sin (9) responds of VSI vector control and proposed CSI vector control scheme in case of no load and 200 Nm load. (10) Rotor Flux vector estimation using current model In the low-speed region, the rotor flux components canbe synthesized more easily with the help of speed andcurrent signals. The rotor circuit equations can be given as 0 (11) 0 (12) Adding the terms Figure 4. Simulink diagram of actual induction motor model in rotor flux (13) frame Table I Induction Motor Parameters (14) 50HP, 460V, 4Pole, 60Hz, Squirrel-cage motor Respectively, on both sides of the above equations (11), Values in SI Units Nominal Parameters(12) the equations becomes Rs=0.087 Stator resistance (Ohm) (15) Rr=0.228 Rotor resistance (Ohm) Lsl=0.8e-3 Stator leakage inductance (H) Lrl=0.8e-3 Rotor leakage inductance (H) (16) Lm=34.7e-3 Magnetizing inductance (H)After simplification P=4 Number of poles (17) J=1.662 Moment of inertia (kg.m2) Bm=0.1 Torque speed coefficient (18) Table II The above two equations give rotor fluxes as functions Gains of Controllerof stator currents and speed. After knowing these signals,the fluxes and corresponding unit vector signals can be Kp = 100 Proportional Gainestimated. Flux estimation by this requires a speed encoder,but the advantage is that the drive operation can be Ki = 2500 Integral Gainextended down to zero speed. TL= 350 Torque Limit (N.m) 9© 2010 ACEEEDOI: 01.IJEPE.01.03.67
  4. 4. ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010a) Fig. 6 shows the proposed flux feed forward vector controlled drive’s modeling results at no load TL = 0 N.m. Fig. 6(a) shows the phase A stator current response when the speed reference suddenly changed at .2 sec. Fig. 6(b) shows the electromagnetic torque response with refer to the speed reference. Fig. 7 shows the proposed flux feed forward vector controlled drive’s modeling rotor speed response with refer to the speed command. The speed command suddenly increased at 0.2 sec. and suddenly decreased at 1.5 sec. the motor speed follows the reference speed.b) Figure 7. Simulated waveforms of PWM current source inverter fed induction motor drive’s rotor speed response with refer to the rotor speed Figure 5. Simulated waveforms of PWM voltage source inverter fed reference-speed command change at 0.2sec. and 1.5sec. induction motor drive with no load TL = 0 N.m a) phase A stator current. a) b) Electromagnetic Torquea)b) b) Figure 6. Simulated waveforms of PWM current source inverter fedinduction motor drive with no load TL = 0 N.m a) phase A stator current b) Electromagnetic Torque Fig. 5 shows the VSI fed flux feed forward vectorcontrolled drive’s modeling results at no load TL = 0 N.m. Figure 8. Simulated modeling waveforms of PWM VSI fed inductionFig. 5(a) shows the phase A stator current response when motor drive with load torque TL =200 N.m a) Phase A stator current b) Electromagnetic Torque with ripplesthe speed reference suddenly changed at .2 sec. Fig. 5(b)shows the electromagnetic torque response with refer to thespeed reference. 10© 2010 ACEEEDOI: 01.IJEPE.01.03.67
  5. 5. ACEEE Int. J. on Electrical and Power Engineering, Vol. 01, No. 03, Dec 2010a) and transient state conditions. At very low speed, proposed indirect rotor-flux-oriented control (IRFOC) of induction motor drive is particularly sensitive to an accurate rotor resistance value in the rotor flux. To overcome this problem, the implementation of online tuning rotor resistance variation of the induction motor is essential in order to maintain the dynamic performance of the drive. So the implementation of online rotor resistance tuning is the main future scope of this paper. REFERENCES [1] F.Blaschke, “The principle of field orientation as applied tob) the new transvector closed-loop control system for rotating field Machines,” Siemens Review, vol.34, pp.217-220, May 1972. [2] Hasse, K., “Zum dynamischen Verhalten der Asynchronmaschine bei Betrieb mit variabler Ständerfrequenz und Ständerspannung” ETZ-A 89, 1968, pp. 387-391 [3] R. W. De Doncker and D. W. ovotny, “The universal field oriented controller”, IEEE IAS Annu. Meet. Conf. Rec.,pp. 450-456, 1988. [4] R. Krishnan and P. Pillay, “Sensitivity analysis and comparison of parameter compensation scheme in vector controlled induction motor drives,” in IEEE-IAS Ann. Meeting Conf. Rec., 1986, pp. 155-161. Figure 9. Simulated modeling waveforms of PWM CSI fed induction [5] J. Holtz, “Sensorless Control of Induction Motor Drives,”motor drive with load torque TL =200 N.m a) Phase A stator current b) Proceedings of the IEEE, Vol. 90, No. 8, Aug. 2002, pp. 1359 Electromagnetic Torque with reduced ripples – 1394. [6] G. Pellegrino, R. Bojoi and P. Guglielmi, Performance Fig. 8.a) shows the phase A stator current with ripples, Comparison of Sensorless Field Oriented Controlso these ripples developed high electromagnetic torque Techniques for Low Cost Three-Phase Induction Motorripples shown in Fig. 8.b). The ripples are minimized in the Drives”, Industry Applications Conference, 42nd IASproposed system. Fig. 9.a) shows the ripple free phase A Annual Meeting. 2007. [7] P.Vas, Vector Control of AC Machines, Clarendon Press,stator current, so the developed electromagnetic torque has Oxford, 1990.low ripples shown in Fig. 9.b). [8] B.K. Bose, Modern Power Electronics and AC Drives, 2001, Pearson Education. CONCLUSIONS [9] P. C. Krause, O. Wasynczuk, and S. D. Sudhoff, Analysis of Electric Machines and Drive Systems, 2nd edition, Wiley- In this paper, the control of a high performance PWM IEEE Press, New York, 2002current source inverter fed induction motor drive has been [10] Miki, O. Nakao and S. Nishiyama, "A new simplified currentdiscussed. The control system has been realized in the control method for fielddented induction drives", IEEErotor-flux-oriented reference frame. The proposed CSI Trans. Ind. Appl., vol. 27, no. 6, pp. 1081-570, Nov./Dec.drive topology exhibits the same high performance features 1991.as the corresponding VSI topology, both in terms of [11] B. Wu, S.Dewan and G. Slemon, "PWM-CSI inverter forwaveform quality and dynamic performance. It has induction motor drives", IEEE Trans. Ind. Appl., vol. 28, no.additional control flexibility (waveform and efficiency 1, pp. 317-325, Jan./Feb. 1992.improvements) and the inherent advantages of the CSI [12] H. Inaba, K. Hirasawa, T. Ando, M. Hombu and M. Nakazato, "Development of a high-speed elevator controlledtopology (short-circuit protection, low output dv/dt.). The by current source inverter system with sinusoidal input andtests with the simulation model of Indirect Rotor Flux output", IEEE Trans. Ind. Appl., vol. 28, no. 4, pp. 893-643,Oriented Controller (Feed-Forward Vector Controller) for July/August 1992induction motor show excellent performance in both steady 11© 2010 ACEEEDOI: 01.IJEPE.01.03.67

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