MODLING & PERFORMANCE ANALYSIS OF MULTI PHASE INDUCTION GENERATOR

Prashant Singh Rajpoot1, Sharad Chandra Rajpoot 2, Sudama Gupta3 Amar Singh Rathore 4

1M Tech. Scholar, Electrical & Electronics Engineering Department, Dr. C. V. Raman Institute Of science&Techno-logy Kargi Road Kota Bilaspur, Chhattisgarh, India, prashantrajpoot141@gmail.com . 2 M Tech. Scholar, Electrical & Electronics Engineering Department, Dr. C .V. Raman Institute &science Technology Kargi Road Kota Bilaspur, Chhattisgarh, India,ms.sharad90@gmail.com . 3M Tech. Scholar, Electrical & Electronics Engineering Department, Dr. C. V. Raman Institute Of science & Techno-logy Kargi Road Kota Bilaspur, Chhattisgarh, India. sudama21@gmail.com . 4B.E., Scholar,Electrical,EngineeringDepartment,L.C.I.T.Bilaspuras,Chhattisgarh,India,amar.as767@gmail.com

ABSTRACT— In this paper mainly the compensation of multiphase machines over predictable three phase machines have been existing with the help of previous investigate works carry out in this field. Induction generators are gradually more being use in non-conventional energy system such as wind, micro/mini hydro, etc. The compensation of using an induction generator instead of a synchronous generator are reduced unit price and size, severity, brushless (in squirrel cage construction), nonappearance of separate dc source, ease of repairs, self-protection against severe overload and short circuits, etc. In inaccessible systems, squirrel cage induction generators with capacitor excitation, recognized as self-excited induction generators , are very popular. Here a model has been developed in common reference frame and is appropriate for study of generator performance with an arbitrary angle of displacement connecting the two three-phase windings sets. Steady state analysis is in work on six-phase induction generator and for special value of the capacitors of dissimilar rating machines are simulated with MATLINK/SIMULINK. the six-phase SEIG is analyzed, finally in terms of d-q model and the equations developed in the d-q model have been modified in MATLAB/SIMULINK. The resultant voltage and current waveforms for dissimilar loading conditions have been analyze by use power GUI device in MATLAB.KEY WORD:- MATLAB/SIMULINK PROGRAME, MULTI INDUCTION MACHINE.

1.1INTRODUCTION- Multiphase Induction machine is now days broadly considered as potentially viable solutions for numerous variable-speed drive applications. With an improved importance on renewable electric energy production, where interfacing with the grid normally takes place by means of power electronic converters, or if the generators are utilize for stand-alone application, the merit of multiphase equipment that make them feasible for drive applications can also be successfully demoralized in generating applications.[1]

The rising concern for the environment and resources has motivated the world towards rationalizing make use of conventional energy wealth and exploring the non-conventional energy sources to congregate the ever-increasing power demand. A number of renewable energy source like

mini /micro hydro, wind, solar, industrial dissipate, geothermal, etc. were deliberate. Since small hydro and wind power sources are existing in plenty, their consumption was fairly hopeful to accomplish the future power requirements. Amassing small hydro and wind energy for electric power production is an part of research significance and at current, the emphasis is being given to the price effective consumption of these power resources for quality and dependable power supply.[3]The synchronous generator have been use for power production but induction generators are gradually more being use and further researched these days because of their relative a features over conservative synchronous generators. These features are brush less and strong construction, poor cost, repairs and operational simplicity, self-protection against fault, good dynamic response, and capacity to produce power at reliable speed. The later aspect facilitates the induction generator operation in isolated mode to provide supply far remote areas where expansion of grid is not expensively viable; in coincidence with the synchronous generator to fulfill the improved local power requirement, and in grid-connected method to supplement the real power require of the grid by integrate power from resources sited at special sites.[2]Six-phase self excited induction generator can operate with a single three phase synchronous .phase modifier, so that loss of excitation or fault at one winding does no direct to the system shutdown. The generator can also supply two part three phase loads, which represents an additional benefit. The outputs of the two three phase windings can be use to supply a single three phase load throughout an interconnect to six phase to three phase transformer, in which case breakdown of one three phase winding does not lead to the system shutdown and the load can be still supplied from the remaining strong winding.[4] The six stator phases are separated into two star-connected three-phase sets (labeled abc and xyz further on, respectively), with magnetic axes for the two three phase set displaced by an angle of 30 degree electrical. Neutral points of two three phase stator winding sets are kept isolated in arrange to prevent physical fault propagation from one three phase set to other one, and to check the flow of triple n harmonics. [5] The study spread over the last two decades specify the technical and economic feasibility of using the number of

phases higher than three in ac device in general and induction machine in particular. The examine in this area is still in immaturity, yet some tremendously significant findings have been reported in the literature indicating general feasibility of multi-phase systems. Therefore, here the mathematical modeling, and a detailed analysis of multi-phase (six-phase)

induction generator are presented.[6]

1.2 SELF-EXCITED INDUCTION GENERATOR (SEIG)The increasing rate of the depletion of conventional energy sources has given rise to an increased emphasis on renewable energy sources such as wind, mini/ micro-hydro, etc. Generation of electrical energy mainly so far has been from thermal, nuclear and hydro plants. They have continuously degraded the environmental conditions. An increasing rate of the depletion of conventional energy sources and the degradation of environmental conditions has given rise to an increased emphasis on renewable energy sources, particularly after the increases in fuel prices during the 1970s. Use of an induction machine as a generator is becoming more and more popular for the renewable sources. Reactive power consumption and poor voltage regulation under varying speed are the major drawbacks of the induction generators, but the development of static power converters has facilitated the control of the output voltage of induction generators. [8]

1.3 CLASSIFICATION OF INDUCTION GENERATORSOne the basis of rotor construction, induction generators are two types (i.e., the wound rotor induction generator and squirrel cage induction generator). Depending upon the prime movers used (constant speed or variable speed) and their locations (near to the power network or at isolated places), generating schemes can be broadly classified as under

1-Constant - speed constant - frequency (CSCF),2-Variable - speed constant - frequency (VSCF),3-Variable - speed variable - frequency (VSVF);

(a) Constant – Speed Constant – Frequency:- In this scheme, the prime mover speed is held constant by continuously adjusting the blade pitch and/or generator characteristics. An induction generator can operate on an infinite bus bar at a slip of 1% to 5% above the Synchronous speed. Induction generators are simpler than Synchronous generators. They are easier to operate, control and maintain, do not have any synchronization problems and are economical.

(b)Variable – Speed Constant – Frequency:- The variable speed operation of wind electric system yields higher output for both low and high speeds. This results in higher Annual energy yields per rated installed capacity. Both horizontal axis wind turbines exhibit under variable speed op-eration.

(c)-Variable – Speed Variable – Frequency:-With variable prime mover speed, the performance of synchronous generators can be affected. For variable speed corresponding to the changing derived speed, SEIG can be conveniently used for resistive heating loads, which are essentially frequency insensitive. This scheme is gaining importance for stand-alone wind power applications.

1.4 SELF EXCITATION PROCESS &VOLTAGE BUILD UP IN SEIG

Self-excitation phenomenon in induction machines although known for more than a half century’s still a subject of considerable attention. The interest in this topic is primarily due to the application of SEIG in isolated power systems. When an induction machine is driven at a speed greater than the synchronous speed (negative slip) by means of an external prime mover, the direction of induced torque is reversed and theoretically it starts working as an induction generator. From the circle diagram of the induction machine in the negative slip region, it is seen that the machine draws a current, which lags the voltage by more than 90.[10] The process of voltage buildup in an induction generator is very much similar to that of a dc generator. There must be a suitable value of residual magnetism present in the rotor. In the absence of a proper value of residual magnetism, the voltage will not build up. So it is desirable to maintain a high level of residual magnetism, as it does ease the process of machine excitation. The operating conditions resulting in demagnetization of the rotor (e.g., total collapse of voltage under resistive loads, rapid collapse of voltage due to short circuit, etc. should be avoided) When an induction generator first starts to run, the residual magnetism in the rotor circuit produces a small voltage. This small voltage produces a capacitor current flow, which increases the voltage and so forth until the voltage is fully built up. The no-load terminal voltage of the induction generator is the intersection of the generator’s magnetization curve with capacitor load line. The magnetization curve of the induction generator can be obtained by running the machine as a motor at no load and measuring the armature current as a function of terminal voltage. To achieve a given voltage level in an induction generator, an external capacitor must be able to supply the magnetizing current of that level.[7]

2.1 ANALYTICAL MODEL OF SIX-PHASE INDUCTION GENERATOR

A schematic representation of the stator and rotor windings for a two pole, six-phase induction machine is given in Fig.1.The six stator phases are divided into two wye-connected three-phase sets, labeled abc and xyz (called set I and II respectively), whose magnetic axes are displaced by an arbitrary angle . The windings of each three-phase set are uniformly distributed and have axes that are displaced 120 degree apart. The three-phase rotor windings ar, br, cr are also sinusoidally distributed and have axes that are displaced by

120 degree apart. In developing the equations, which describe the behavior of a multi-phase machine, it is assumed that there

Fig. 1. A two-pole six-phase induction machine with Displacement between the two stator winding sets[11]is no physical fault propagation from one three-phase set to other three-phase set as neutral of both the stator winding sets are separate. The following voltage equations are written for a multiphase induction machine in arbitrary reference frame: vq1 = - r1 iq1 + ωk λd1 + p λq1 (1)

vd1 = - r1 id1 -ωk λq1 + p λd1 (2)

vq2 = - r2 iq2 + ωk λd2 + p λq2 (3)

vd2 = - r2 id2 -ωk λq2 + p λd2 (4)

0 = rr iqr + (ωk -ωr) λdr + p λqr (5)

0 = rr idr - (ωk -ωr) λqr + p λdr (6)

where, ωk is the speed of the reference frame, p denotes differentiation w.r.t. time, ωr is the rotor speed. Here, rotor quantities are referred to stator. The expressions for stator and rotor flux linkages are λq1=-Ll1 iq1-Llm(iq1 +iq2) + Lm (-iq1 -iq2 + I qr) (7)

λd1=-Ll1id1- L lm (id1 +id2) + Lm (-id1 -id2 + idr) (8)

λq2=-Ll2 iq2-Llm(iq1 +iq2) + Lm (-iq1 -iq2 + iqr) (9)

λd2=-Ll2id2-Llm(id1 +id2) + Lm (-id1 -id2 + idr) (10)

λ qr = L lr iqr+ Lm (-iq1 -iq2 + iqr) (11)

λdr = Llr idr+ Lm(-id1 -id2 + idr) (12)

L lm=(N1/N2)L lm (13)

where, N1 and N2 are the number of turns of the abc and xyz winding sets respectively, and Llm is the common mutual leakage inductance between the two sets of stator winding, Lm

is the mutual inductance between stator and rotor. Llm is given by:

Llm=L lax cosα + Llay cos (α+2 /3) + Llaz cos(α-2 /3) (14)These equations suggest the equivalent circuit as shown in Fig.2.

Fig. 2. The q- and d- axis equivalent circuit of a six-phase induction machine in arbitrary reference frame[9]The common mutual leakage inductance Llm in Fig. 2 represents the fact that the two sets of stator windings occupy the same slots and are, therefore, mutually coupled by a component of leakage flux. This mutual leakage inductance, Llm has an important effect on the harmonic coupling between the two stator-winding sets and depends on the winding pitch and the displacement angle between the two stator-winding sets. In the above expressions, the prime quantities are referred to stator. As for as steady state analysis, the voltages equations in phasor form can be obtained by replacing p by j.vq1 = - r1 iq1 + ωk λd1 + j λq1 (15)

vd1 = - r1 id1 - ωk λq1 + j λd1 (16)

vq2 = - r2 iq2 + ωk λd2 + j λq2 (17)vd2 = - r2 id2 - ωk λq2 + j λd2 (18)0=rr iqr+ (ωk -v)λdr + jλqr (19)0=rr idr - (ωk -v) λqr + jλdr (20)

Also r = v Where v = Actual speed/ Synchronous speed = (1- s)

2.2 MODELING OF SHUNT EXCITATION CAPACITOR The voltage current equations of the excitation capacitor can be transformed from the three-phase quantities into d-q axis ones by using Krause transformation and are given by

p vq1 = (iq1c /Csh1) -ωb vd1 (33)p vd1 = (id1c /Csh1) +ωb vq1 (34)p vq2 = (iq2c /Csh2) -ωb vd2 (35)p vd2 = (id2c /Csh2) +ωb vq2 (36)Where, iq1c, id1c and iq2c, id2c are q-axis and d-axis components of currents flowing into the exciter capacitor, Csh1 and Csh2

connected across the three-phase winding set I and II respectively.For steady state analysis, replacing p by jω, from eqns.(33),(34),(35),(36) it can written as jω(- r1 iq1 + ωk λd1 + jωλq1) = (iq1c /Csh1) -ωb( - r1 id1 -ωk λq1 + jωλd1) (37) jω(- r1 id1 -ωk λq1 + jωλd1) = (id1c /Csh1) +ωb(- r1 iq1 + ωk λd1 + jωλq1) (38)jω(- r2 iq2 + ωk λd2 + jωλq2 ) = (iq2c /Csh2) -ωb(- r2 id2 -ωk λq2 + jωλd2) (39)jω(- r2 id2 -ωk λq2 + jωλd2) = (id2c /Csh2) +ωb(- r2 iq2 + ωk λd2 + jωλq2) (40)

3. RESULTS & DISCUSSIONS The theoretical studies using MATLAB/SIMULINK (MATLAB 7.0.1 and SIMULINK 6.1) have been carried out on a six-phase self excited induction generator. The parame-ters of the test machine are given in Appendix-I. The perfor-mances of SEIG under following operating conditions have been presented, * Voltage and current build-up of six-phase SEIG at no-load * Steady-State response under resistive loading without Series Compensation* Steady-State response under R-L loading without series compensation * Steady-State response under resistive loading with Series Compensation* Steady-State response under R-L loading with series Com-pensationVoltage Build-up at No-Load Fig. 3 shows the analytical waveform of voltage and current during no-load voltage build up for the two three-phase winding sets. In the present study, the per phase value of the shunt excitation capacitance is selected as 108 μF. The steady state no-load voltage generated is about 163 V and the value

of current is about 2.1 A at an input Shaft Power Psh = 300. It is observed that the SEIG terminal voltage and current build-up from their initial value of few volts and few amperes to their steady state values. The rate of no-load voltage and current build-up depend upon the value of shunt excitation capacitance and the level of residual magnetism in the rotor circuit of the SEIG. Steady State Response of Resistive Load without Series Compensation Fig. 4 displays the simulated steady state response of six-phase SEIG terminal voltage and load current, with a resistive load of 600 ohms. On the application of the resistive load, the terminal voltage is reduced to approximately 107.8 V. This decrease in terminal voltage also causes a decrease in excitation capacitor current, which further affects the voltage regulation of the generator. The poor voltage regulation of the SEIG is due to lack of reactive power that can be compensated through series capacitor connected in each line.Steady State Response with RL Load without Series CompensationThe reactive load test is performed with a balanced three-phase RL load comprising a 200 ohm resistance in series with 500mH inductor. The generated voltage and lagging load current waveform are shown in Fig. 12. As it is evident, the generator voltage has dropped to 52 V.For the RL load comprising of 200 ohm resistance in series with different values of inductor, i.e., 1H and 1.5 H. The generated voltage and load current waveforms are shown in Figs. 13 & 14 and voltage has dropped to 62.5 V and 68.5 V. the load consisting of different values of resistances, i.e., 400 ohm and 600 ohm in series with constant value of inductor 500mH, the generator voltage is dropped to 55.35 V and 58.9 V. The voltage and current waveforms are shown in Figs. 15 & 16.

Steady State Response of Resistive Load with Series CompensationThe Steady state response of six-phase SEIG feeding a resistive load of 200 ohm, when series capacitors of 72 µF are connected in each line between load and SEIG as short shunt is illustrated in Fig.17.The application of series capacitor results in an over-voltage across the generator terminals. A careful selection of the value of shunt and series capacitors may avoid the excessive voltage at SEIG terminals. The selection of series capacitance should be justified not only on the basis of full load voltage regulation but also from the view point of load voltage profile and maximum utilization of the machine as the generator.Steady State Response with RL Load with Series CompensationSeries capacitors of value 72 µF each were connected in series with the generator terminals as short shunt scheme. The voltage and current responses are shown in Fig.18. Multiphase Induction machines are nowadays widely considered as potentially viable solutions for numerous variable-speed drive applications. With an increased emphasis on renewable electric energy generation, where interfacing with the grid

typically takes place by means of power electronic converters, or if the generators are used for stand-alone applications, the advantages of multiphase machines that make them viable for drive applications can also be effectively exploited in generating applications.

Fig.3:No Load Voltage build up and Capacitor Current Waveforms of abc phases

Figure 3:No Load Voltage build up and Capacitor Current Waveforms of xyz phases

Figure 4: Voltage and Current Waveforms for Resistive Load with R = 600 ohms of abc phases

Figure5: Voltage and Current Waveforms for RL Load comprising of R = 600 ohms and L = 500mH of xyz phases

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Figure6:-Voltage and Current Waveforms for RL Load with Series Compensation of abc phases

Fig:-Voltage and Current Waveforms for RL Load with Series Compensation of xyz phases

I. 5. CONCLUSIONS & FUTURE SCOPEIn the present pepar, a simple and unified mathematical model for six-phase self-excited induction generator (SEIG) has been developed and the simulated results for six-phase SEIG under different load conditions are presented. With inclusion of series capacitors, the voltage regulation profile of SEIG improves because series capacitors provide the additional VAR requirement with increase of load current. However, an appropriate combination of series and shunt capacitors are necessary to achieve the desired level of voltage regulation, while keeping the machine voltage and current with in specified limits. With proper choice of series and shunt capacitor, the quality of output voltage and current waveforms can also be controlled.

7. REFERENCES[1]. Singh G. K., Yadav K. B. and Saini R. P., “Modeling and Analysis of Multi-Phase (Six Phase) Self-Excited Induction Generator,” in Proc.IEEE Conf. ICEMS’2005, The Eighth International Conference on Electrical Machines and Systems, 2005, China, pp. 1992-1927.[2]. R.C. Bansal ,“Three-Phase Self Excited Induction Generators Overview”, IEEE Transactions on energy conversion, vol. 20,no.2, Jun 2005,pp.292-299.[3]. G.K. Singh, “Self-excited induction generator research—a survey”,Electric Power Systems Research 69 (2004), pp. 107–114[4]. Seyoum D., Grantham C. and Rahman F., “The Dynamics of an Isolated Self-Excited Induction Generator Driven by a Wind Turbine,” in Proc.IECON’01, The 27th Annual Conference of IEEE Industrial Electronics Society, 2001, pp. 1364-1369.[5].K.B.Yadav,G.K.Singh,R.P.Saini,“A Self-Excited six phase Induction generator for stand alone renewable energy generation,” Internationl Aegean Conference on Electrical machines & Power Electronics(ACEMP’07),pp.692-695, 10-12 Sept 2007.Bodrun,Turkey.[6] .Ojo O. and Davidson I. E., “PWM-VSI Inverter-Assisted Stand-Alone Dual Stator Winding Induction Generator,” IEEE Trans. Energy Conversion,2000, vol. 36, pp. 1604-1611.[7]. Duro Basic, Jian Guo Zhu & Gerard Boardman, “Transient Performance Study of a Brushless Doubly Fed Twin Stator Induction Generator”, IEEE Transactions on Energy Conversion, vol. 18, no. 3, September 2003.[8].G. K. Singh, K. B. Yadav, and R. P. Saini, “Analysis of a Saturated Multi-Phase (Six-Phase) Self-Excited Induction Generator”,International Journal of Emerging Electric Power Systems, Vol. 7 [2006],Iss. 2, Art. 5[9].A.K. Al Jabir & A.I.Aloalah, “Capacitance requirement for isolated Self-Excited induction generator”, IEE Proceedings, Vol. 137, Pt. e, No.3, May 1990.[10]. L. Shridhar, B. Singh, C. S. Jha, B. P. Singh, and S. S. Murthy, “Selection of capacitors for the self regulated short shunt self-excited generator,” IEEE Trans. Energy Convers., vol. 10, no. 1, pp. 10–17,Mar. 1995.

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[11]. Klingshirn E. A., “High Phase Order Induction Motors—Part I: Experimental Results,” IEEE Trans. Power App. Syst., Jan. 1983, vol.PAS-102, pp. 54-59.

1Prashant Singh Rajpoot M Tech. Scholar, Electrical & Electronics Engineering Department, Dr. C. V.Raman Institute Of science&Technology Kargi Road KotaBilaspur,Chhattisgarh,India. , prashantrajpoot141@gmail.com

2 Sharad Chandra Rajpoot M Tech. Scholar, Electrical & Electronics Engineering Department,

Dr. C .V. Raman Institute &science Technology Kargi Road Kota Bilaspur, Chhattisgarh,India,ms.sharad90@gmail.com .

3Sudama Gupta M Tech. Scholar, Electrical & Electronics Engineering Department, Dr. C.V. Raman Institute Of science &Technology Kargi Road,KotaBilaspur,Chhattisgarh,India.sudama21@gmail.com

. 4Amar Singh Rathore B.E., Scholar,Electrical,EngineeringDepartment,L.C.I.T.Bilaspuras,Chhattisgarh,India,amar.as767@gmail.com