Modeling, Simulation and Implementation of a Five

Modeling, Simulation and Implementation of a Five-Phase Induction Motor Drive System Atif Iqbal, Senior Member IEEE, Sk. Moin Ahmed, Student Member IEEE, Mohd. Rizwan Khan, Mohd. Arif Khan ABSTRACT- This paper presents a comprehensive simulation model of a five-phase induction motor drive system. Both openloop and closed-loop control is elaborated. The complete component modeling is developed using ‘simpower system’ blocksets of Matlab/Simulink. To address the real time implementation issues, dead banding of the inverter switches are also incorporated in the simulation model. To validate the modeling procedure, experimental implementation is done in TMS320F2812 DSP platform with a custom built five-phase drive system. Excitation, acceleration and loading transients are investigated. The developed simulation model is fully verified by the real time implementation.

I. INTRODUCTION

T

HREE-phase Induction motors have well known advantages of simple construction, reliability, ruggedness, low maintenance and low cost which has led to their wide spread use in many industrial applications. The major problem of this machine is their complicated control for speed regulation in industrial drive applications [1-7]. However, with the advent of cheap and fast switching power electronics devices not only the control of induction machine became easier and flexible but also the number of phases of machine became a design parameter. Multi-phase machines (more than three-phases) are found to possess several advantages over three-phase machines such as lower torque pulsation [8-10], higher torque density [11-13], fault tolerance [14-16], stability [17-18] and lower current ripple [19]. Thus multi-phase order machines are normally considered for niche application areas such as ship propulsion, ‘more electric aircraft’, electric/hybrid electric vehicles etc. Detailed reviews on the research on multi-phase machines are presented in [2025]. The induction motor control methods can be broadly classified into scalar and vector control. In the scalar control only the magnitude and frequency of voltage, current and flux linkage space vectors are controlled. In contrast in vector control not only magnitude and frequency but also instantaneous positions of voltage, current and flux space vectors are controlled. Thus in vector control scheme the controller acts on the position of the space vectors and Atif Iqbal and SK Moin Ahmad are with Electrical & Computer Engineering Programme, Texas A&M University at Qatar, Doha, QATAR, (e-mail - [email protected], [email protected]). M Rizwan Khan is with Electrical Engg. Deptt., Aligarh Muslim University, Aligarh, India (e mail: [email protected]) Mohd Arif Khan is with Deptt. of Electrical & Electronics Engg., Krishna Institute of Engg. & Technology, Ghaziabad INDIA, (e-mail: [email protected]).

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provides their correct orientation for both steady state and transient condition. Recently scalar control of a five-phase induction machine is presented in [26] and the field oriented control for five-phase machine is illustrated in [27-28]. This paper focuses on the development of flexible simulation model of open-loop constant v/f control scheme of a five-phase induction motor. A simple approach of utilizing the built in blocks of the Matlab/simulink is used. Step by step model development is illustrated incorporating the real time implementation issues such inclusion of dead band in the switching signals of the inverter. Various simulation results are presented followed by their experimental validation. Experimental results are presented for both open-loop and closed-loop control. Thus the major contribution of the paper is the development of a simple and flexible simulation model such that other control strategies can also be implemented using this model and can finally be implemented experimentally. II DRIVE CONTROL SCHEME In numerous industrial applications, the dynamic performance of the drive is not so important especially where sudden change in speed is not required. In such cases the cheap solution is to use open-loop or closed-loop constant v/f control scheme. A block diagram representation of this control technique is depicted in Fig. 1. The block with dashed line is applicable in conjunction with closed-loop v/f control. The basic principle behind this control strategy is to keep the flux constant under all operating conditions. The control algorithm calculates the voltage amplitude, proportional to the command speed value, and the angle is obtained by the integration of this speed. These information are required to implement space vector PWM of the inverter feeding the motor drive system. * The reference speed ω determines the inverter frequency which simultaneously defines the reference voltage required. The voltage boost is then added to this voltage signal to implement the constant v/f scheme. This scheme is well documented in the literature for three-phase drive system. and a detailed discussion is presented in [1-4]. The same is not true for a five-phase drive system. Thus this paper focuses on a five-phase drive system extending the control concept of a three-phase drive system. The control law is given by equation (1) where V0 is called voltage boost. The control law is shown in Fig. 2. This is required to offset the effect of the stator resistance drop especially at low speed. The resulting torque-speed characteristics using this control law approaches those obtainable with true constant flux operation.

ω*

ωs

∫

θs

ω*

ωm Fig. 1. Constant V/F control scheme for a five-phase drive.

⎛V ⎞ V = k ⎜⎜ n ⎟⎟ f + V0 ⎝ fn ⎠

Fig. 3. Simulink diagram of constant v/f control of Induction motor Drive.

(1)

V

Vn

V0 0

fn

f

Fig. 2. Illustration of control law for a five-phase drive.

III SIMULINK MODEL OF THE CONTROL SCHEME This section describe the step by step development of simulink model to implement constant v/f control scheme. The purpose here is to replicate the model in such way as to matches the real time DSP (TMS320F2812) implementation requirement. In case of real time implementation 3.3 V input to the DSP corresponds to the rated speed of the motor. Thus by simply augmenting the control voltage, the speed of the motor can be varied from zero to the rated value (only base speed is considered here) keeping constant v/f. The user defined control voltage corresponding to the reference speed and the voltage corresponding to the actual speed from the motor model is given as the inputs to the variable voltage variable frequency (VVVF) generation block. This control voltage is to be converted to appropriate gating signal of the inverter. Appropriate dead band is created using a dead band genarator block. This will ensure the safe operation of the inveter. Although this is not very important from the simualtion point of view but the real time implemntation sitautaion is simulated using this technqiue. The gating signals thus generted is fed to IGBT power modules which ultimelty run the induction machine. The complete simulink block diagram is illustrated in Fig. 3 The expanded form the simulation blocks is depicted in Fig. 4. Each sub blocks are discussed in the subsequent section.

Fig. 4. Expanded form of Simulink model of constant v/f control of Induction Motor.

III.1.ELECTRICAL MOTOR MODEL The built in induction motor in simpower blockset cannot be used as it corresponds to three-phase only. The mathematical model of five-phase motor given in [27-28] is used to simulate the five-phase induction machine, the data is provided in Appendix 1. The transformed equations of a five-phase induction machine are given as vds = Rsids − ωaψ qs + pψ ds

vdr = Rr idr − (ωa − ω )ψ qr + pψ dr

vqs = Rsiqs + ωaψ ds + pψ qs v xs = Rsixs + pψ xs v ys = Rsi ys + pψ ys

vqr = Rr iqr + (ωa − ω )ψ dr + pψ qr v xr = Rr ixr + pψ xr v yr = Rr i yr + pψ yr

vos = Rsios + pψ os

vor = Rr ior + pψ or

ψ ds = ( Lls + Lm )ids + Lmidr ψ qs = ( Lls + Lm )iqs + Lmiqr

ψ dr = ( Llr + Lm )idr + Lmids ψ qr = ( Llr + Lm )iqr + Lmiqs

ψ xs = Llsixs ψ ys = Llsi ys

ψ xr = Llr ixr ψ yr = Llr iyr

ψ os = Llsios

ψ or = Llr ior

(2)

(3)

[

Te = PLm i dr i qs − i ds i qr

]

(4)

The only difference between the five-phase machine model, given with (2)-(4), and the corresponding three-phase machine model is the presence of x-y component equations in (2) and (3). Rotor x-y components are fully decoupled from d-q components and one from the other. Since rotor winding is short-circuited, x-y components cannot appear in the rotor winding. Zero sequence component equations for both stator and rotor can be omitted from further consideration due to short-circuited rotor winding and star connection of the stator winding. Finally, since stator x-y components are fully decoupled from d-q components and one from the other and vector control is applied (i.e. only d-q axis current components are generated), the equations for x-y components can be omitted from further consideration as well. This means that the model of the five-phase induction machine in an arbitrary reference frame becomes identical to the model of a threephase induction machine. The inputs to the motor are the five-phase voltage supply obtained from voltage source inverter. The load is assumed as constant torque type and is hence simulated using a step signal of the value equal to the rated torque. The Fig. 5 depicts the motor model at the end of the paper. III.2.INVERTER WITH DEADBAND MODEL Although the inverter can be simulated using the developed equations;

v/f control scheme, of five-phase induction machine is studied. The resulting speed response is illustrated in Fig. 10. The machine is at first started at no-load condition and the reference speed is given as 1500 rpm. Once the machine attains the steady state speed, rated load of 8.33 Nm is applied to the machine at t = 6.75 sec. The drop in speed due to the loading is clearly visible in the speed response. The actual speed follows the reference except the offset and drop in speed due to loading is observed. This response is typical of constant v/f control scheme. The offset can be eliminated using closedloop constant v/f control method. V

EXPERIMENTAL RESULTS

A DSP based five-phase induction motor drive system is developed in the laboratory. Texas Instrument TMS320F2812 DSP platform is used to generate the control signals. The main control code is written in C++ which runs in a PC. A control cable is connected to the DSP board through RS232 port which sends the control signals generated by PC to the DSP. The DSP board is connected to the control card of the inverter through a cable. The PWM signals thus generated is used to appropriately switch the power semiconductor switches (IGBT). The intelligent power module based on IGBT is rated to run a motor of upto 3 hp with 400 V line voltages. Five-phase motor is coupled with eddy current loading system. The complete set-up of five-phase induction motor drive systems is shown in Fig. 11.

v a = (4 5)v A − (1 5)(v B + v C + v D + v E )

v b = (4 5)v B − (1 5)(v A + v C + v D + v E )

v c = (4 5)v C − (1 5)(v A + v B + v D + v E ) v d = (4 5)v D − (1 5)(v A + v B + v C + v E ) v e = (4 5)v E − (1 5)(v A + v B + v C + v D )

(5)

Where suffix with small letter indicates phase-to-neutral voltages and the suffix with capital letters represents leg voltages. The component modeling is done using the simpower system block sets. The IGBT based power module is utilized. Each IGBT block represents one inverter leg incorporating both the upper and lower power switch along with the snubber circuit. The deadband is also incorporated in this model to simulate the real time implementation issues. get the accurate results. The deadband model is shown in Fig. 6.: IV SIMULATION RESULTS The simulation is carried out to implement the open-loop constant v/f control technique using the developed simulation model. The reference speed of 400 rpm is given initially then the reference speed is step raised to 675 rpm, 950 rpm and 1500 rpm at t = 3.75, 6.25 and 8.75 sec, respectively. Finally the reference speed is step down to 600rpm at t = 12sec. The actual speed very well follows the reference as illustrated in Fig. 9 (a) under no-load condition. An inherent steady state error in the reference and actual speed is observed in Fig. 9 (a). In Fig. 9 (b) a regular stepping of reference speed is shown. The loading rejection capability for open-loop constant

(a)

(b) Fig. 9. Speed response for open-loop constant v/f control at no-load.

Fig. 10. Speed response for constant v/f control at rated load operating at 1500rpm

The experimental results obtained using front end software of VI Micro Systems, Chennai, India, are depicted in Fig. 1214. The experimental results are taken for the same conditions as that of simulation study. The typical behavior of five-phase induction machine is observed. The experimental results obtained very well validate the simulation results and thus the simulation approach. The steady-state offset speed error is completely eliminated in the closed-loop constant v/f control method, as depicted in Fig. 14. However, a small overshoot in the speed response is observed, this is due to the PI controller setting. The drive is fully capable of rejecting the load disturbance as depicted in Fig. 14 (b). The dip in speed due to loading is quickly recovered by the corrective PI controller action. The rise in the speed is also observed due to un-loading of the machine and this is also corrected in very small time. Thus it can be concluded that the PI controller is optimaly tuned to reject the disturbances. VI. CONCLUSION This paper presents a complete simulation model to simulate a five-phase induction motor drive system for

Fig. 13. Speed response of a five-phase IM for open loop constant v/f control at rated load operating at 1500rpm

constant v/f speed control method. The simulation model is developed using simpower system block sets of the Matlab/Simulink software. Step by step model development is elaborated. Dead banding in the simulation procedure is presented. A detailed simulation results are presented to validate the modeling procedure. Experimental set up is discussed and the experimental results are provided to exactly match the results obtained using simulation. This proves the successful implementation of the control scheme.

Fig. 11. Five-phase induction motor experimental rig.

Fig. 14. Speed response for closed-loop constant v/f control of a five-phase Induction motor. Fig. 12.(a) Speed response of a five-phase IM for open loop constant v/f control at no-load (three step rising and one step fall).

Acknowledgment: Authors greatfully acknowledges the support provided by AICTE, New Delhi, India through research grant no. 8023/BOR/RPS86/2006-07

VII. REFERENCES [1] D. Novotony, and T.A. Lipo, Vector control and dynamics of ac drives,

Fig. 12.(b) Speed response of a five-phase IM for open loop constant v/f control at no-load(step rising)

Clarendon Press, Oxford, UK, 2000. [2] A.M. Trzynadlowski, The field oriented Principle in Control of Induction motors, Kuluwer Press, 1994. [3] I. Boldea and S.A. Nasar, Vector Control of AC Drives, CRC Press, London, 1992. [4] D.C. White and H.H. Woodson, Electromechanical energy conversion, John Wiley and Sons, New York, 1959. [5] S.A. Nasar and I. Boldea, The Induction Machine Handbook, CRC Press, London, 2002. [6] S. E. Lyshevski, Electromechanical Systems, Electric Machines & Applied Mechatronics, CRC Press, 2000. [7] H.A. Toliyat, DSP based Electromechanical Motion Control, CRC Press, 2003.

[8] E.E. Ward and H.Harer, “Preliminary investigation of an inverter fed fivephase induction motor”, Proc. IEE 116 (6), 1969, pp. 980-984. [9] S. Williamson and A.C. Smith, “Pulsating torque and losses in multi-phase induction machines”, IEEE Trans. Ind. Appl. , vol. 39, no. 4, pp. 986-993, July/Aug. 2003. [10] J.M. Apsley, S. Williamsons, A.C. Smith and M. Barnes, “Induction motor performance as a function of phase number”, Proc. Int. Electr. Eng.Electr. Power Appl., vol. 153, no. 6, pp. 898-904, Nov. 2006. [11] H.A. Toliyat, T.A. Lipo and J.C. White, “Analysis of concentrated winding machine for adjustable speed drive applications-Pat II: Motor design performance”, IEEE Tras. Energ Conv., vol. 6, no. 4, pp. 684-692, Dec. 1991. [12] R. Lyra and T.A.Lipo, “Torque density improvement in a six-phase induction motor with third harmonic current injection”, IEEE Trans. Ind. Appl. Vol. 38, no. 5, pp. 1351-1360, Sept./Oct. 2002. [13] H.A. Toliyat, S.P. Waikar and T.A. Lipo, “Analysis and simulation of fivephase synchronous reluctance machines including third harmonic of airgap MMF”, IEEE Trans. Ind. Appl. vol. 34, no. 2, pp. 332-339, Mar./Apr. 1998. [14] N. Bianchi, S. Bolognani, and M.D. Pre, “Strategies for the fault tolarent current control of a five-phase permanent magnet motor”, IEEE Trans. Ind. Appl. , vol. 43, no. 4., pp. 960-970, Jul. /Aug. 2007, [13] R.J.Kerkman,B.J.Seibel, and T.M.Rowan, “A new flux and stator resistance identifier for AC drive systems”.IEEE Trans.Indust.Appl.32, 585-593(1996). [15] G. K. Singh and V. Pant, “Analysis of multi-phase induction machine under fault condition in a phase redundant AC drive system”, Elect. Mach. Power System, vol. 28, no. 6, pp. 577-590, 2000. [16] J.M. Apsley and Williamson, “Analysis of multi-phase inductions with winding faults”, Proc. IEEE IEMDC, San Antonio, TX, pp. 249-255, 2005. [17] M.J. Duran, F. Salas and M.R. Arahal, “Bifurcation Analysis of fivephase induction motor drives with third harmonic injection”, IEEE Trans. On Ind. Elect. vol. 55, no. 5, pp. 2006-2014, May 2008. 1 In1 2 In2 3 In3 4 In4

u(1)-10*u(5)

1 s

fluxalphas

Integrator

u(2)-10*u(6)

1 s

Fluxbitas

Integrator1 1 s

u(3)-10*u(7) Fluxxs

[18] [19]

M.R. Arahal and M.J. Duran, “PI tuning of Five-phase drives with third harmonic injection”, Control Engg. Practice, 17, pp. 787-797, Feb. 2009. D. Dujic, M. Jones, and E. Levi, “Analysis of output current ripple rms in multiphase drives using space vector approach”, IEEE Trans. On Power Elect., vol. 24, no. 8, pp. 1926-1938, Aug. 2009.

[20] G.K.Singh; Multi-phase induction machine drive research – a survey, Electric Power System Research, vol. 61, pp. 139-147, 2002. [21] M.Jones, E.Levi; A literature survey of state-of-the-art in multiphase ac drives, Proc. 37th Int. Universities Power Eng. Conf. UPEC, Stafford, UK, pp. 505-510, 2002. [22] R. Bojoi, F. Farina, F. Profumo and Tenconi,“Dual three induction machine drives control-A survey”, IEEE Tran. On Ind. Appl.,vol. 126, no. 4, pp. 420-429, 2006. [23] E. Levi, R.Bojoi, F. Profumo, H.A. Toliyat and S. Williamson, “Multiphase induction motor drives-A technology status review”, IET Elect. Power Appl. vol. 1, no. 4, pp. 489-516, July 2007. [24] E.Levi, “ Guest editorial”, IEEE Trans. Ind. Electronics, vol.55, no. 5, May 2008, pp. –1891-1892. [25] E. Levi, “Multi-phase Machines for Variable speed applications” IEEE Trans. Ind. Elect., vol. 55, no. 5, pp. 1893-1909, May 2008. [26] C. C. Scharlau, L. F.A. Pereira, L.A. Pereira and S. Haffner, “Performance of five-phase induction machine with optimized air gap field under open loop v/f control”, IEEE Trans. Energy Conv., vol. 23, no. 4, Dec. 2008. [27] L. Zheng, J.E. Fletcher, B.W. Williams and X. He, “Dual-plane vector control of five-phase induction machine for an improved flux pattern”, IEEE Trans. On Ind. Elect., vol. 55, no. 5, pp. 1996-2005, May 2008. [28] H. Xu, H.A. Toliyat and L.J. Peterson, “Five-phase induction motor with DSP based control system”, IEEE Trans. Power Elect., vol. 17, no. 4, pp. 524-533, Jul. 2002. APPENDIX 1: RS = 10 ohm, Rr = 6.3 ohm, Ls = Lr = 0.46 H, Lm = 0.4 H, P= 4.

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-6.3*u(6)

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flr

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Fig. 5. Simulink model of a five-phase induction machine.

-KGain1

we To Workspace