voltage and frequency controller for an autonomous micro hydro generating system

7/29/2019 Voltage and Frequency Controller for an Autonomous Micro Hydro Generating System

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Abstract-- This paper presents an investigation on a voltage

and frequency controller (VFC), which functions as an improved

electronic load controller (IELC) for parallel operated isolated

asynchronous generators (IAGs) in an autonomous micro hydro

power generation system. In such type of micro hydro scheme

whole generating system is isolated from the grid and supply

electricity to the remote communities. The single point operation

of these generators is realized, in such a manner that excitation

capacitors, speeds, voltage, currents of generators remain

constant under various operating loads conditions. The proposed

controller consists of a 3-leg IGBT (Insulated Gate BipolarTransistor) based voltage source converter (VSC) and a DC

chopper with an auxiliary load at the DC bus of the VSC. The

IELC controls the reactive and active power simultaneously for

controlling the voltage and frequency under varying consumer

loads. Along with voltage and frequency control through single

point operation of IAGs driven by uncontrolled micro hydro

turbines, the IELC meets the power quality standard an IEEE-

519 and it keeps the total harmonic distortion (THD) of the

terminal voltage and generator currents within the limit of 5%.

Here the proposed electrical system along with its controller is

modeled in MATLAB along with Simulink and PSB (Power

System Block-set) toolboxes. Simulation results are presented to

demonstrate the capability of proposed controller for an isolated

generating system.

Key-words Parallel Operation of Isolated AsynchronousGenerators, Voltage and Frequency Controller, Single PointOperation

I. INTRODUCTIONRecently, problems such as air pollution and global

warming have become serious concerns because of increasedconsumption of the fossil fuels. Therefore, there have beenmany studies related to the natural energy generation systemeffective to cope with these problems. The small size hydroand wind power generating units are the most usefulgeneration systems harnessing these renewable energy inremote and isolated areas where grid supply is not accessible.The squirrel cage asynchronous generator with its leastmaintenance and simplified controller appears to be a good

Bhim Singh and Gaurav Kumar Kasal are with the Dept. of ElectricalEngineering, Indian Institute of Technology, Delhi, New Delhi 110016India (e-mail: [email protected] , [email protected]).

Ambrish Chandra and Kamal Al- Haddad are with the Dept. of ElectricalEngineering, cole de Technologie Superieure, 1100 Notre Dame Ouest,Montreal, Quebec H3C1K3, Canada (email: [email protected],[email protected])

solution for such applications. For its simplicity, robustness,and small size per generated kilowatt, an asynchronousgenerator is favored for small hydro and wind powergenerating systems [1-5]. However, the major drawbacks ofthe IAGs are reactive power consumption and poor voltageand frequency regulation under varying loads and speed. Butthe development of static power converters has facilitated thecontrol of the output voltage and some investigations onvoltage and frequency have been carried out in the area ofrenewable energy application [6-16] of IAGs. Moreover, these

small potential of renewable energy may be located nearbylocality but dispursed in low powers. Apart from it, the loadsmay also be more than the capacity of single unit. Thereforeparallel operation of these generators becomes necessary.However, a single controller may also be used for severalgenerators to control voltage and frequency of such system.

The study of such a system is relevant to full fill theincreased load demand and the parallel operation of IAGs ismore effective than other electrical generators because of noneed of synchronization, and no problem due to hunting.However, only few attempts have been made in the area ofmodeling, steady state analysis [17-20] and voltage regulation[21,22] of parallel operated IAGs. Therefore, here an attempt

is made to investigate a voltage and frequency controller forparallel operated IAGs driven by uncontrolled pico hydroturbines.

II. SYSTEM CONFIGURATION AND CONTROL STRATEGYFig. 1 shows the system configuration of parallel operated

IAGs, with an individual excitation capacitor, a voltage andfrequency controller (consisting 3-leg CC-VSC and DCchopper) and consumer loads. The delta connected 3-phasecapacitor banks are used for generators excitation and valueof excitation capacitors is selected to generate the ratedvoltage at no load. The constant power generation of IAGsand demand of varying consumer loads is met by the CC-VSCwith self supporting DC bus with chopper and an auxiliaryload. The IAGs generate constant power and when the powerof consumer loads changes, the DC chopper of IELC absorbsthe difference in the power (generated consumed) into anauxiliary load. Thus generated voltage and frequency are notaffected and remain constant during the change in consumerloads.

The IELC consists of an IGBT based current controlled 3-leg VSC with a, DC bus capacitor, DC chopper and ACinductors. The output of the VSC is connected through theAC filtering inductors to the IAGs terminals. The DC bus

Voltage and Frequency Controller for anAutonomous Micro Hydro Generating System

Bhim Singh, Senior Member IEEEand Gaurav Kumar Kasal

Ambrish Chandra, Senior Member IEEEand Kamal-Al-Haddad Fellow IEEE

2008 IEEE.


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capacitor is used to filter voltage ripples and provides self-supporting DC bus. The DC chopper is used to control surpluspower into the controller due to change in consumer loads.

Fig.2 shows the control scheme of the controller to regulatethe voltage and frequency of the IAGs. The control scheme is

based on the generation of reference source currents (havetwo components in-phase and quadrature with AC voltage).The in-phase unity amplitude templates (ua, ub and uc) arethree-phase sinusoidal functions, which are derived bydividing the AC voltages va, vb and vc by their amplitude Vt.Another set of quadrature unity amplitude templates (wa, wband wc) is sinusoidal function obtained from in-phase vectors(ua, ub and uc). To regulate AC terminal voltage (Vt), it is

sensed and compared with the reference voltage (Vtref). Thevoltage error is processed in the PI voltage controller. Theoutput of the PI (Proportional Integral) controller for ACvoltage control loop decides the amplitude of reactive current(Ismq

*) to be generated by the controller. Multiplication ofquadrature unity amplitude templates (wa, wb and wc) with theoutput of PI based AC voltage controller (Ismq

*) yields thequadrature component of the reference source currents (isaq

*,isbq

* and iscq*). For a constant power generation, active power

component of source currents are fixed at rated value, whichis the amplitude of in-phase component of source currents(Ismd

*). Multiplication of in-phase unit amplitude templates(ua, ub and uc) with in phase component of source current

(Ismd*) yields the in-phase component of the reference sourcecurrents (isad

*, isbd*and iscd

*). The sum of instantaneousquadrature and in-phase components of currents is the

Fig.1 Schematic diagram of a proposed parallel operated IAG system with anim roved electronic load controller ca tion.

Fi .2 Schematic dia ram of control scheme for an im roved electronic load controller


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reference source currents (isa*, isb

* and isc*), and these arecompared with the sensed source currents (isa, isb and isc).These current error signals are these amplified and fed to thehystresis controller for generating the PWM signals forIGBTs of VSC.

The excess generated power other than consumer loads isabsorbed in the DC chopper fed auxiliary load resistor (Rd)using DC bus PI voltage controller. The DC bus voltage of

VSC of the controller is compared with its reference voltagevalue. The DC bus error voltage is processed in a PIcontroller. The output of the PI controller is compared withtriangular carrier wave to generate gating signal to the DCchopper switch (IGBT).

III. CONTROL ALGORITHMModeling of the control scheme for 3-leg voltage source

converter and a DC chopper switch for voltage and frequencycontrol is given as follows:

A. In Phase Component o f Reference Source CurrentFor the constant power application, IAGs should generate

constant active power to feed either consumer loads orauxiliary load (Rd) in the controller. For regulating theconstant power, in-phase component of reference sourcecurrent is set equal to the rated amplitude of active powercomponent of current as:

Ismd* = 2(Prated)/ 3 (Vrated) (1)

where Prated is the total generated power (Pgen1 + Pgen2) ofIAGs and Vrated is rated voltage at their terminals.

The instantaneous line voltages at the IAGs terminals (va, vband vc) are considered sinusoidal and their amplitude iscomputed as:

Vt = {(2/3) (va2 +vb

2 +vc2)} 1/2 (2)

The unity amplitude templates having instantaneous value

in phase with instantaneous voltage (va, vb and vc), which arederived as:ua = va/Vt ; ub = vb/Vt ; uc = vc/Vt (3)

Instantaneous values of in-phase components of referencesource currents are estimated as:

i*sad = I*

smd ua; i*

sbd = I*smd ub; i*

scd = I*smd uc (4)

B. Quadrature Component of Reference Source CurrentThe AC voltage error Ver at the n

th sampling instant is:Ver(n) = Vtref(n) Vt(n) (5)

where Vtref(n) is the amplitude of reference AC terminal voltageand Vt(n) is the amplitude of the sensed three-phase ACvoltage at the IAGs terminals at nth instant.

The output of the PI controller (I*smq(n)) for maintainingconstant AC terminal voltage at the nth sampling instant isexpressed as:I*smq(n) = I*smq(n-1) + Kpa { Ver(n) Ver(n-1)} + Kia Ver(n) (6)

where Kpa and Kia are the proportional and integral gainconstants of the proportional integral (PI) controller (valuesare given in Appendix). Ver (n) and Ver(n-1) are the voltageerrors in nth and (n-1)th instant and I*smq(n-1) is the amplitudeof quadrature component of the reference source current at(n-1)th instant.

The instantaneous quadrature components of the referencesource currents are estimated as:

i*saq = I*

smq wa; i*sbq = I

*smq wb; i

*scq = I

*smq wc (7)

where wa, wb and wc are another set of unit vectors having aphase shift of 90 leading the corresponding unit vectors ua, uband uc which are given as follows:

wa = -ub /3 + uc /3 (8)wb = 3 ua / 2 + (ub uc) / 23

(9)wc = -3 ua / 2 + (ub uc) / 23 (10)

C. Reference Source CurrentTotal reference source currents are sum of in-phase and

quadrature components of the reference source currents as:i*sa = i

*saq +i

*sad (11)

i*sb = i*

sbq +i*

sbd (12)i*sc = i

*scq +i

*scd (13)

D. PWM Current ControllerThe reference source currents (i*sa, i

*sb and i

*sc) are

compared with the sensed source currents (isa, isb and isc).).The current errors are computed as:

isaerr = i*sa isa (14)isberr = i

*sb isb (15)

iscerr = i*

sc isc (16)After amplification these current errors signal are compared

with fixed frequency triangular wave to generate the switchingsignals of IGBTs of VSC.

E. Control for DC Bus ChopperTo maintain the DC bus voltage of VSC constant, the DC

voltage error Vdcer(n) at nth sampling instant ia calculated as:

Vdcer(n) = Vdcref(n) Vdc(n) (17)where Vdcref(n) is the reference DC voltage and Vdc(n) is the

sensed DC link voltage of the CC-VSC.

The output of the PI voltage controller at the nth

samplinginstant is expressed as:V*con(n) = V*con(n-1) + Kpp { Vdcer(n) Vdcer(n-1)} + Kpi Per(n) (18)where Kpp and Kpi are the proportional and integral gain

constants of the DC bus voltage controller. The PI controlleroutput (V*con(n)) is compared with the triangular carrier (Vtri)waveform and its output is fed to the gate of the chopperswitch (IGBT) of the controller.

IV. MATLABBASED MODELINGFigs 3-4 show the MATLAB based model of the proposedcontroller along-with parallel operated isolated asynchronousgenerators system. The main generating system consists of

parallel operated isolated asynchronous generators, excitationcapacitors, voltage and frequency controller along-withbalanced/unbalanced, linear/non-linear consumer loads. Fig. 3shows the complete model of the proposed electricalgenerating system while Figs 4(a) and 4(b) shows thesubsystem VSC control and chopper control. The universalbridge is used to model the voltage source converter for thecontroller and three phase diode bridge rectifier for non-linearconsumer load. The proposed system is modeled using15kW, 415V, 50Hz, Y-connected and 7.5kW, 415V, 50Hz, Y-connected asynchronous machines to operate as IAGs.


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Individual delta connected capacitor banks having rating of9kVAR and 5kVAR are used for generating the rated voltageat no-load. Simulation is carried out in MATLAB version 7.1using (ode 23tb/TR-BDF-2) solver and other relevant data aregiven in Appendix.

V. RESULTS AND DISCUSSION

The developed model of proposed controller for paralleloperated IAGs system feeding linear/ non- linear,balanced/unbalanced loads is simulated and waveforms of thegenerators voltage (vabc) and currents (iabc1) and (iabc2),capacitor current (icca1 , icca2), load current (ilabc), controllercurrent (icabc), terminal voltage (vt), DC link voltage (vdc),frequency (f) and speeds of both generators (1 and 2) etcare shown in Figs. 5-6. For the simulation, a 7.5 kW, 415V,

50Hz and 15kW, 415V, 50Hz asynchronous machines havebeen used as IAGs for parallel operation and parameters aregiven in Appendix

A. Performance with Balanced/Unbalanced Linear LoadsFig. 5 shows the performance of the proposed controller

system with balanced/unbalanced delta connected resistiveload. At 2.5 sec balanced three-single phase loads each of7kW is applied between each phase to phase and then thecurrents (icabc) drawn by the controller are suddenly reduced toregulate the generators currents, which in turn maintain thesystem frequency constant. With opening of a single phaseload at 2.6 sec and then other phase at 2.7sec, the load

becomes unbalanced and an action of the controller isobserved, which shows the load balancing aspect of thesystem. At 2.8 sec the consumer load is fully removed, theauxiliary load absorbs the full active power generated by thegenerators, which shows that the controller maintains thegenerators power, frequency and voltage constant.

B. Performance with Balanced/Unbalanced Non-linear LoadsFig.6 shows the performance of parallel operated IAGs-

controller system feeding balanced/unbalanced non-linearloads using three phase diode rectifier with resistive load andL-C filter at its DC side. At 2.6 sec, a balanced non-linearload is applied then the controller currents (icabc) are reducedwith in a cycle for regulating the power, frequency and thesebecome non-linear for eliminating harmonic currents. Onremoval of one phase of the load at 2.75 sec the load becomesunbalanced but the generators currents remain balanced,which shows the load balancing aspects of the controller.

C. Power Quality AspectsFig. 7 and Fig. 8 demonstrate performance of the controller

as a harmonic eliminator. Here it is observed that due to thenon-linear load, harmonics are injected in the supply. Atapplication of around full load, load currents which are havingtotal harmonic distortion (THD) of around 26.30%, arecompensated by the controller and THD of terminal voltage,generator-1 current and generator-2 current are observed

order of 1.01%, 2.59% and 1.53% respectively as shown inFig.7. At opening of one phase of the load, the load becomesunbalanced and its current THD is observed to be order of37.53% as it is shown in harmonic spectra given in Fig.8.Under this condition, the THD of terminal voltage, generator-1 current and generator-2 current are observed of the order of1.27%, 1.59% and 1.39% respectively, which is much lessthan 5%, the limit imposed by IEEE 519 Standard.

VI. CONCLUSION

Fig. 3 MATLAB based simulation model of proposed electric system

Fig. 4(a). Subsystem of VSC control.

Fig 4(b) Subsystem of chopper control


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The performance of the proposed controller has beendemonstrated for parallel operated isolated asynchronousgenerators in constant power application driven byuncontrolled micro hydro turbines. It has been observed thatthe controller is having capability of voltage and frequencyregulation along with harmonic compensation and loadbalancing. Moreover, it has resulted in a single pointoperation of the generators through regulating the voltage,frequency, the load and capacitors to constant value.

VII.APPENDIXA.. The Parameters of 15kW, 415V, 50Hz, Y-Connected, 4-Pole

Asynchronous Machine are Given Below.

Rs = 0.58, Rr =0.78, Xlr= Xls= 2.52, J = 0.23kg-m2,

Lm = 0.22 Im


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E. Prime Mover Characteristics for 15kW MachineTsh = K1-K2r ; K1 = 6500, K2 = 40

F. Prime Mover Characteristics for 7.5 kW MachineTsh = K1-K2r,; K1 = 3310, K2 = 10.

VIII.REFERENCES[1] S.N. Bhadra, D. Kastha, S.Banerjee, Wind Electrical Systems 1st Ed.Oxford University Press, New Delhi 2004.[2] M. Godoy Simoes, Felix A. Farret, Renewable Energy Systems 1st Ed.

CRC Press Florida, 2004.[3] L.L. Lai and T.F. Chan, Distributed Generation Induction and

Permanent Magnet Generators 1st Ed. Jon Wiley and Sons Ltd, 2007.[4] Jean-Marc Chapallaz, Dos Ghali Peter Eichenberger, Gehard Fischer,

Manual on induction motors used as generators Deutsches ZentrumFur Entwicklingstechnologien- GATE 1992.

[5] B. Singh, Induction generator a prospective, Electric Machines andPower Systems, vol. 23, pp163-177, 1995.

[6] E. Suarez and G. Bortolotto, Voltage frequency control of a self excitedinduction generator,IEEE Trans Energy Convers. vol. 14, no. 3, pp.394-401, Sept 1999.

[7] B. Singh, S.S. Murthy and Sushma Gupta, Transient analysis of selfexcited induction generator with electronic load controller supplying staticand dynamic loadsIEEE Trans. on Industry Applications, vol. 41, no. 5,pp.1194-1204, Sept 2005.

[8] B. Singh, S.S. Murthy, S. Gupta, Analysis and implementation of anelectronic load controller for a self-excited induction generator in IEEProc - Generation Transmission and Distribution, vol 151, no.1, pp. 51-60, Jan2004.

[9] R. Bonert and S. Rajakaruna, Self-excited induction generator withexcellent voltage and frequency control IEE Proc-Generation,Transmission and Distribution, v 145, no. 1, pp 33-39, Jan. 1998,

[10] B. Singh, S.S Murthy and S. Gupta, Analysis and design of electronicload controller for self-excited induction generators, IEEE Transactionson Energy Conversion, vol 21, no. 1,, pp 285-93, March 2006.

[11] Bhim Singh, S.S Murthy, and S. Gupta A voltage and frequencycontroller for self-excited induction generators, Electric PowerComponents and Systems, vol 34, no. 2, pp 141-157,Feb 2006.

[12] B. Singh, S.S. Murthy, S. Gupta, An improved electronic load controllerfor self-excited induction generator in micro-Hydel applications inIEEE

Industrial Electronics Conference (IECON), vol. 3, 2-6 Nov. 2003, pp2741 - 2746.

[13] H.S. Timorabadi Voltage source inverter for voltage and frequencycontrol of a stand-alone self-excited induction generator, in Proc.

Fig. 6 Transient waveforms of parallel operated IAGs with an improved electronic load controller feeding non-linear load


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Canadian Conference on Electrical and Computer Engineering, May2006, pp2241-2244.

[14] J.M. Ramirez and Emmanuel. Torres M An Electronic Load Controllerfor the Self-Excited Induction Generator IEEE Transaction on EnergyConversion, vol. 22, no. 2, pp 546 548, June 2007.

[15] J.A. Barrado and R. Grino, Voltage and frequency control for a selfexcited induction generator using a 3-phase 4-wire electronic converters,in Proc of 12th International IEEE Power Electronics and MotionControl Conference, Aug 2006, pp. 1419-1424.

[16] T. Ahmad, M. Nakaoka and K. Nishida Advanced active power filter forrenewable energy application of stand alone induction generator, 32ndannual Conf IECON2005, Nov 2005, pp756-761.

[17] L. Wang and C.H. Lee, Dynamic analysis of parallel operated self excitedinduction generator feeding an induction motor load, IEEE Trans. EnergyConversion, vol. 14, vol.3, pp 479-485, 1999.

[18] C. Chakraborty, S.N. Bhadra, A.K. Chattopadhyay, Analysis of paralleloperated self- excited induction generators, in proc of IEEE

International Conf on Power Electronics Drives and Energy Systems,Dec 1996, New Delhi, India, pp 463-469.

[19] L. B. Shilpkar, Bhim Singh, K.S.P. Rao, Transient analysis of paralleloperated self-excited induction generators, in Proc. of IEEE InternationalConf on Power Electronics Drives and Energy Systems , Dec 1996, NewDelhi, India, pp 470-476.

[20] Chandan Chakraborty, S.N. Bhadra, Muneaki Ishida and A.K.Chattopadhyay, Performance of parallel operated self excited inductiongenerators with the variation of machine parameters, in Proc. of IEEEConference on Power Electronics and Drive Systems, July. 1999, pp. 86-91.

[21] A.H. Al-Bahrani and N.H. Malik, Voltage control of parallel operatedself excited induction generators,IEEE Trans. Energy Conversion, vol.8,no.2, pp. 236-242, June 1993.

[22] I. Tamrakar, L. B. Shilpkar, B. G. Fernandes and R. Nilsen Voltage andfrequency control of parallel operated synchronous generator and inductiongenerator with STATCOM in micro hydro scheme, in Proc IET Gener.Transm. Distrib, vol.1, no. 5, pp 743-750, Sept 2007.

IX. AUTHORSBIOGRAPHYBhim Singh (SM99) was born in Rahamapur, India, in 1956. He received theB.E (Electrical) degree from the University of Roorkee, Roorkee, India, in1977 and the M.Tech and Ph.D. degree from the Indian Institute of Technology(IIT) Delhi, New Delhi, India, in 1979 and 1983, respectively. In 1983, he

joined the Department of Electrical Engineering, University of Roorkee, as alecturer, and in 1988 became a Reader. In December 1990, he joined theDepartment of Electrical Engineering , IIT Delhi, as an Assistant Professor. He

Fig.7 Waveforms and harmonic spectra of generated voltage (va) Generator-1 current (ia1) Generator-2 current (ia2) Consumer load current (ilc) under the conditionof balanced non-linear load.


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became an Associate Professor in 1994 and Professor in 1997. His area ofinterest includes power electronics, electrical machines and drives, active

filters, FACTS, HVDC and power quality.Dr. Singh is a fellow of Indian National Academy of Engineering (INAE), theInstitution of Engineers (India) (IE (I)), and the Institution of Electronics andTelecommunication Engineers (IETE), a life member of the Indian Society forTechnical Education (ISTE), the System Society of India (SSI), and theNational Institution of Quality and Reliability (NIQR) and Senior Member ofInstitute of Electrical and Electronics Engineers (IEEE).

Gaurav Kumar Kasal was born in Bhopal, India, in Nov, 1978. He receivedthe B.E (Electrical) and M.Tech degree from the National Institute ofTechnology (NIT) Allahabad and National Institute of Technology (NIT)Bhopal, India respectively in 2002 and 2004. Since Dec 2004, he has beenpursuing the Ph. D. degree with the Department of Electrical Engineering,Indian Institute of Technology (IIT) Delhi, New Delhi, India. His field ofinterest includes power electronics and drives, renewable energy generationand applications, flexible AC transmission system.

Ambrish Chandra (SM99) was born in India in 1955. He received B.E.degree from the University of Roorkee (presently IIT), India, M. Tech. degreeform I.I.T., New Delhi, India, and Ph.D. degree from University of Calgary,Canada, in 1977, 1980, and 1987, respectively. He worked as a Lecturer and

later as a Reader at University of Roorkee. Since 1994 he is working as aProfessor in Electrical Engineering Department at cole de technologiesuprieure, University of Qubec, Montreal, Canada. His main researchinterests are renewable energy, power quality, active filters, static reactivepower compensation, and flexible AC transmission systems (FACTS). Dr.Chandra is a senior member of IEEE and member of the Ordre des ingnieursdu Qubec, Canada.

Kamal Al-Haddad (S82M88SM92) was born in Beirut, Lebanon, in

1954. He received the B.Sc.A.and M.Sc.A. degrees from the University ofQubec Trois-Rivires, Trois-Rivires, QC, Canada, in 1982and 1984,respectively, and the Ph.D. degree from the Institut National Poly thechnique,Toulouse, France,in 1988.From 1987 to 1990, he was a Professor in theEngineering Department, Universit du Qubec Trois Rivires. In 1990, he

joined the Electrical Engineering Department, cole de Technologie Suprieure,Universit du Qubec, Montreal, QC, Canada, as a Professor. Hisfields ofinterest are static power converters, harmonics and reactive power control, andswitch-mode and resonant converters, including the modeling, control, anddevelopment of industrial prototypes for various applications. He is a coauthor ofthe Power System Blockset software of Matlab. Dr. Al-Haddad has held theCanada Research Chair In Energy Conversion and Power Electronics since2002. He is a member of the Order of Engineers of Quebec, Canada, and theCanadian Institute of Engineers.

Fig.8 Waveforms and harmonic spectra of generated voltage (va) Generator-1 current (ia1) Generator-2 current (ia2) Consumer load current (ilc) under the conditiof un-balanced non-linear load.


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voltage and frequency controller for an autonomous micro hydro generating system

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