experimental evaluation of isolated 3-phase self-excited...

134 Umesh C. Rathore, Sanjeev Singh

International Journal of Electronics, Electrical and Computational SystemIJEECS

ISSN 2348-117XVolume 6, Issue 6

June 2017

Experimental Evaluation of Isolated 3-Phase Self-ExcitedInduction Generator with Anti-Windup Control

Umesh C. RathoreDepartment of Electrical EngineeringABV Government IET, Pragatinagar,

Shimla, Himachal Pradesh-171202

Sanjeev SinghDepartment of Electrical & Instrumentation Engg.Sant Longowal Institute of Engg. & Technology

Longowal, Sangrur, Punjab-148106

ABSTRACTThree-phase self-excited induction generators are best suited for renewable energy conversion systems especially in smallhydro power generation systems feeding isolated load. However, suitable control is required to keep the voltage andfrequency constant under variable loading conditions. Mostly electronic load controllers are used in pico-hydro powergeneration system along with dump load to maintain the voltage and frequency of generated output under permissiblelimits under varying load conditions. The aim of author in this paper is to investigate the anti-windup control in dump loadcontrol circuit in three-phase self-excited induction generator (SEIG) feeding isolated load in constant power prime-moverdriven pico-hydro power generation system. This paper experimentally evaluates the performance of constant powerprime-mover driven pico-hydro power generation system using 3-φ SEIG feeding isolated load under different operatingconditions. The performance of complete system is first simulated in MATLAB/Simulink environment without and withanti-windup control and then results are validated using an experimental set-up to demonstrate the effectiveness of theproposed system.

Keywords

Self-excited induction generator, electronic load controller, dump load, anti-windup control, Pico-hydro

INTRODUCTIONWith the advancement in renewable energy conversion technology along with widespread use ofcomputational devices, induction generators are widely being used due to their increased efficiency, bettercontrol and better co-ordination with power system especially in isolated mode of operation. For the isolateddomestic electrical load, installing the pico-hydro power plants (<100kW) involving self-exciting inductiongenerators is cost effective and reliable solution under the varying load conditions. Among the various typesof induction generators, self excited induction generator (SEIG) is suitable for micro or pico hydro powerplants feeding an isolated load. In stand-alone mode of operation of SEIG, the reactive power must be fedexternally using capacitors to establish the required magnetic field [1-4]. The main aim of the controlstrategies in self-excited induction generator is to regulate and maintain the required voltage and frequency ofthe generated output. This control is achieved using various types of controllers involving power electronicsbased devices. These controllers are called electronic load controllers. The main function of the electronicload controller in constant power prime-mover driven isolated pico-hydro power plant using SEIG is tomaintain the output load constant as seen by the induction generator under different consumer load conditionsso as to maintain the desired speed and hence the frequency constant [1-6]. The electronic chopper in thecontroller circuit regulates the real & reactive power so that load seen by the generator is always constant. Thechopper circuit consists of an insulated gate bipolar transistor (IGBT) or MOSFET; which is used aselectronic switch operated by a close loop controller based driver circuit. In electronic load controller circuit, aproportional-integral controller is used in the PWM generation circuit to control the operation of chopperswitch.




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A proportional–integral controller is still most widely used and preferred in control schemes because it isinherently more robust and simpler than modern controllers that require an exact model. However, one of themost critical issues in control system is the integrator-windup phenomenon. This integral windup leads tolarge overshoots, longer settling time and unstable conditions in the system being controlled. In three-phaseSEIG system feeding isolated load, this integral windup phenomenon occurs during the voltage build upprocess in self-excited induction generator or when the consumer load across SEIG is maximum. Therefore, toavoid this, a pulse block circuit is used to control the PWM pulse to chopper circuit [1-7]. However, numerousanti-windup control schemes have been developed in the recent times. The various anti-windup controlschemes are categorized as conditional-integration scheme; back-calculation scheme; and hybrid scheme.

This paper presents the anti-windup control scheme for PI controller used in electronic load controller circuitin 3-phase SEIG feeding isolated load in constant power prime-mover driven pico-hydro power generationsystem. The performance of the 3-phase SEIG is evaluated using MATLAB/Simulink environment and resultsare validated using a hardware set-up comprising of 2.2kW, 4 poles, 415v, 3-phase squirrel cage inductionmachine operated as 3-phase SEIG driven by a 5HP, 1500 RPM DC shunt motor acting as constant powerprime-mover emulating the pico-hydro power generation system conditions.

ANTI-WINDUP CONTROLProportional-integral (PI) controller is most widely used in various control applications in which controlapplication depends upon the feedback error signal which is the difference of process value and referencedesired value. Generally in various process applications, a large step change in the process value will causethe generated command in the form of current or voltage signal from the controller to exceed the prescribedmaximum value, determined by the allowable current of the system. This results in PI controller outputvariable to saturate by the current and voltage limiters. This results in wind-up phenomenon problem becausethe integral state accumulates control errors even while the output variable saturates. This integral windupleads to a large overshoot, long settling times, and an unstable response. Therefore, a design method for alimitation compensator considering output variable saturation is required.

An anti-windup control scheme generally consists of a linear feedback controller that satisfies the desirednon-saturation specification and an anti-windup compensator that operates during saturation condition. It onlyconsiders situations where the input limit is crossed and stops the integrator without exceeding the limit andprevents excessive overshoots in the control action. There are several anti-windup control methods whichhave been developed in recent times for various control applications [7-12]. In anti-windup control, when theplant input variable is different from the PI controller output variable, a realizable command, instead of thecommand, is applied to the controller.

P Controller

I Controller+

-

++

+ +

ProcessRef.

Feedback

+

-

Fig 1: Back calculation anti-windup control scheme




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The realizable command is derived from both the command and the difference between the controller outputvariable and the plant input variable. For ideal anti-windup PI control, it is desirable that the controlperformance satisfies the specifications determined by the PI gains in the linear region. The anti-windupcontrol schemes can also be classified as conditional-integration scheme; back-calculation scheme; and hybridscheme [8]. In the most commonly used back calculation anti-windup method as shown in Fig. 1, the gain ischosen to be large so that the anti-windup signal drives the integrator to a large negative value that increasesthe response time. A back-calculation or tracking-type controller dynamically reduces the integral term oncethe controller saturates. The overall control performance can be determined by the choice of back-calculationparameters.

VOLTAGE AND FREQUENCY CONTROL IN 3-PHASE SEIG SYSTEMDifference between induction generator and induction motor lies in their rotor speed. In induction generator;the rotor speed is more than the synchronous speed, while in induction motor the rotor speed is slightly lessthan the synchronous speed. Induction generator consumes reactive power rather than supplying it andsupplies only the real power (kW) to the system to which it is connected. The kVAr required by the inductiongenerator and loads on the system must be supplied from external source such as static capacitors [1]. Voltageand frequency are the two important parameters in power generation system and these have to be kept underpermissible limit under different loading conditions. In pico-hydro power generation system using 3-phaseself-excited induction generator, the generated voltage in SEIG depends upon the SEIG speed, excitationcapacitance and the amount of load connected across the SEIG. The frequency of the generated signal dependsupon the speed of prime-mover. The Fig. 2 shows per phase equivalent circuit model of self-excited inductiongenerator [1].

Vph

I2

Im

I1 jX1 R 1

Xm

jX2

R2(1-s)/ s

R2

Fig 2: Per phase equivalent circuit model of SEIGWhere

Vph = SEIG phase voltage

I1, I2 = Stator and rotor circuit currents

R1, X1 = Stator circuit resistance & reactance in ohm

R2, X2 = Rotor circuit resistance & reactance in ohm

s = Slip

Im = Magnetizing circuit current in amperes

Rm = Magnetizing reactance in ohm

In induction generator, the speed of rotor is slightly higher than the synchronous speed of the inductionmachine operated as induction generator. Therefore, the slip in inductor generator is negative. The mechanicalpower developed in the shaft for negative slip in the case of induction generator and which is converted into




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electricity is the difference between the power that goes through air gap and the power dissipated in the rotorand is given as [1]: = 3 − 3 = = 3 1 −= (1 − ) (1)

The air gap power in an induction machine is given as = 3 (2)Neglecting the magnetizing reactance as shown in Fig. 2, and putting the value of I2 in equation (2), the valueof air gap power is given as: = 3 = 3 /( + / ) + ( + ) (3)= (1 − ) (4)

From equations (3) and (4), the value of per phase generated voltage in SEIG is given as:

= + + ( + )3 1 − (5)Where slip ‘s’ of SEIG is given as:= − = ℎ −ℎ (6)The value of slip is negative for induction generator as rotor speed is higher than the synchronous speed. Fromabove equations, it is observed that SEIG voltage and frequency are affected by the rotor speed. The type ofload on the SEIG affects its voltage and also the frequency of the generated voltage. Therefore, suitablecontrol is required to maintain the voltage and frequency in SEIG system under permissible limits under alloperating conditions. The voltage in the SEIG system feeding isolated load is maintained or controlled usingthe voltage regulators such as static compensators (STATCOM) and the frequency in SEIG system is keptconstant using load controllers by keeping the load on the SEIG constant using automatically controlled dumpload especially in constant power prime-mover driven SEIG feeding isolated load. Voltage regulationbecomes poor at very high resistive and inductive loads. With the change in load, the control of reactivepower using STATCOM maintains the terminal voltage constant. Individual capacitors are also connected ineach inductive load individually to maintain the effective load as seen by SEIG as resistive load for bettervoltage regulations in case of highly inductive load.

CONTROL SCHEME FOR ISOLATED 3-PHASE SEIG IN PICO-HYDRO POWER GENERATIONSYSTEMThe main aim of the control strategies in self-excited induction generator is to regulate and maintain therequired voltage and frequency of the generated output. This control is achieved using various types ofcontrollers involving power electronics based devices. These controllers are called electronic load controllers[3-4]. The main function of the electronic load controller in constant power prime-mover driven isolated pico-hydro power plant using SEIG is to maintain the output load constant as seen by the induction generator underdifferent consumer load conditions so as to maintain the desired speed and hence the frequency constant. TheSEIG feeds two loads connected in parallel. The main load is consumer load and other load is dump orauxiliary load where power dissipated is generally wasted but can be used for other useful purposes such aspumping of water etc. The electronic chopper in the controller circuit regulates the real & reactive power so




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that load seen by the generator is always constant. Conventional diode rectifier based ELC circuit consists ofan uncontrolled 3- phase rectifier using diodes, a filtering capacitor, an IGBT or MOSFET based choppercircuit and resistive dump load as shown in Fig. 3.

RotorPico

HydroTurbine

iR

iY

iB

SEIG

idR

idY

idB

iecY

iecB

iecR

isR

isY

isB

ConsumerLoad

ilR

ilY

ilB

Capacitor BankFor Excitation

Vdc

S

RdDump Load

Cdc+

-

D1 D3

D2

D5

D6D4

Electronic Load Controller

ChopperControlCircuit

Vref.

Vfb.

Gating Signal

Fig 3: Conventional ELC for isolated 3-phase SEIG in pico-hydro power generation system

The uncontrolled rectifier converts generated AC voltage at terminals of SEIG into DC voltage and filteringcapacitor removes ac ripples from rectified output [3]. The chopper circuit consists of an insulated gate bipolartransistor (IGBT) or MOSFET; which is used as electronic switch operated by a close loop controller baseddriver circuit. The control circuit of electronic load controller consists of a feedback control circuit used togenerate the duty cycle of the chopper switch to regulate the dump load such that the load seen by the self-excited induction generator is always constant at different consumer load. The various components of thecontrol circuit consists of SEIG output voltage sensing circuit, comparator circuit, error amplifier,Proportional-Integral controller circuit, PWM generator circuit, gate pulse isolation and conditioning circuit.The schematic representation of the control circuit is as shown in Fig. 4.

Proportional-Integral

Controller(PI)

PWMGeneration

Circuit

Opto-IsolatorCircuit

Gate-DriverCircuit

SignalConditioning

Circuit

+_

Vref.

Vfb

Vfb

Vref.+

_

PWM Pulse ToChopper IGBT

Pulse Control Circuit

FeedbackSignal

Fig 4: Schematic layout of the control circuit in electronic load controller




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Depending upon the control circuit configuration and requirement, the system voltage can either be sensedbefore the rectifier circuit or after the rectifier circuit. In case the SEIG output voltage is sensed before therectifier circuit, it is first stepped down using the step down transformer and then it is rectified using rectifiercircuit and after filtering, it is used as feedback signal in the comparator circuit to compare with referencevoltage and whose output is the error signal which is then fed to the Proportional-Integral (PI) controller [4].The gain of the PI controller can be varied by using the externally connected potentiometers. TheProportional-Integral controller output is then compared with the saw-tooth carrier wave to generate the PWMoutput. The parameters of saw-tooth waveform such as magnitude and frequency can be varied by using theresistance and capacitor components as per the desired parameters. Hardware point of view, the PI controllerand PWM generation circuit are available on a single integrated circuit chip. The commonly used IC chip forthis purpose is IC-3525. The PWM controller has two push-pull amplifiers at its output stage giving twooutputs. One output gives a duty cycle variation of 0 to 45% and the second output gives duty cycle variationof 50-95%. Therefore, to get the wide range of duty cycle for IGBT, the two outputs of the PWM controllerare connected in parallel so that the duty cycle can be varied between 10-100%. During the period of voltagebuild up across SEIG and when consumer load is full across SEIG, the chopper switch has to be kept underOFF condition. Since the IC-3525 gives an output pulse of 10% duty cycle even when the feedback signal isless than the reference signal, the PWM controller output is ANDed using IC-HD14081B with another signalfor pulse block or release to get the desired output. Before applying the PWM pulse signal to IGBT, it is firstisolated using opto-coupler and then conditioned to a level for safe operation of the IGBT [3-4].

SIMUATED PERFORMANCE OF ISOLATED 3-PHASE SEIG SYSTEMThe performance of 3-φ SEIG feeding isolated load is simulated first using MATLAB/Simulink [14]. Themodel for simulation consists of a 3φ, 3HP, 4 pole, and 415V induction machine used as self excited inductiongenerator. The feedback signal for the controller circuit which depends upon the generated voltage in SEIG iscompared with the reference voltage to generate an error signal for chopper control circuit which contains a PIcontroller as shown in Fig. 5. The magnitude of feedback voltage depends upon the amount of consumer loadconnected to the SEIG terminals. The duty cycle of the PWM pulse output from controller circuit variesaccording to the error signal. It has maximum ON time when consumer load is minimal so that dump load isON in the circuit and vice-versa so that load seen by the SEIG under different consumer load conditionsremains same. Self excited induction generator is first run at no load at a speed slightly greater than thesynchronous speed till the rated voltage builds up at required excitation current by switching ON the capacitorbank in delta mode. Once the voltage builds up and remains fairly constant for a few minutes, the electronicload controller circuit is switched ON and connected to the SEIG system in parallel to the consumer load andself-excited induction generator. Since consumer load is zero at this moment, the controller action generatesPWM pulse with maximum ON time to switch chopper circuit and connects dump load and maximum currentflows through ELC circuit.

Fig 5: Chopper control circuit subsystem model with PI controller

Ch_Pulse1

Vdc_ref .

587

Step

Scope 2

Scope 1

Scope

RepeatingSequence

RelationalOperator

>=

LogicalOperator

AND

DiscretePI Controller

PI

Vdc1




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After few seconds, a set of consumer load consisting of resistive load and non-linear rectifier load underbalanced and un-balanced conditions across SEIG is connected. Due to electronic load controller action, thecurrent through ELC decreases proportionally due to the change in duty cycle of PWM pulse controlling thechopper switch and the load current flows through load circuit as per the connected load [2-7]. The simulatedrecorded parameters such as stator voltage (Vst), stator current (Ist), speed (N), frequency (f), dump load circuitvoltage (Vdl) and current (Idl), consumer load circuit voltage (Vload) and current (Iload) are shown in Figs. 6 to 8.

Fig 6: SEIG parameters under different loading conditions

Fig 7: Dump load circuit parameters in SEIG system under different loading conditions

Fig 8: Consumer load circuit parameters in SEIG system under different loading conditions




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SIMUATED PERFORMANCE OF ISOLATED 3-PHASE SEIG SYSTEM WITH ANTI-WINDUPCONTROLNow the performance of 3-phase self-excited generator is evaluated using an anti-windup control methodusing PI controller [12-13] in the chopper control circuit of electronic load controller in the system. Anti-windup (back calculation) feature of the PI controller is used in the chopper control circuit. The schematicrepresentation of the control scheme is shown in Fig. 9. The pulse block feature using AND gate is alsoeliminated.

Fig 9: Chopper control with PI controller using anti-windup controlThe consumer load block include different load on each phase such as resistive, resistive-inductive andrectifier load to emulate the actual consumer loading conditions as prevalent in remote location fed by 3-phaseSEIG system in pico-hydro power plants. The rectifier load emulates the load of various electronic gadgets ascommonly used in every house-hold these days. The simulated performance of the SEIG system recorded inthe forms of stator circuit, load circuit, ELC circuit and dump load parameters such as voltage and currents atvarious loading condition along with SEIG speed and generated frequency is as shown in Figs. 10 to 15. Fromthe simulated performance of 3-phase SEIG it is observed that anti-windup control gives satisfactoryperformance at the time of sudden switching of ELC circuit and dump load as well at various instances ofswitching of consumer load as system parameters such as generated voltage current, SEIG speed andfrequency of the generated voltage are not perturbed by the sudden change in loading conditions.

Fig 10: SEIG stator voltage and current at different loading conditions




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Fig 11: Load voltage and current at different loading conditions

Fig 12: ELC circuit voltage and current at different loading conditions

Fig 13: Dump load circuit voltage & current at the time of switching of ELC circuit




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Fig 14: Dump load circuit voltage and current at the time of switching of consumer load

Fig 15: SEIG speed and frequency of generated voltage

HARDWARE IMPLEMENTATION OF THE CONTROL SCHEME IN ISOLATED 3-PHASE SEIGSYSTEMThe simulated results are validated using a hardware set-up comprising of 2.2kW, 4 poles, 415v, 3-phasesquirrel cage induction machine operated as 3-phase SEIG driven by a 5HP, 1500 RPM DC shunt motoracting as constant power prime-mover emulating the pico-hydro power generation system conditions. Theother prime components used are suitable capacitor banks in delta and star connection mode to providerequired excitation current to the SEIG for required voltage build-up under different operating conditions [15].Electronic load controller circuit in hardware setup is used to maintain the desired voltage and frequency ofthe generated voltage of SEIG. In small hydro power plants such as uncontrolled pico-hydro power plants,power input to the uncontrolled hydro turbine is fixed or constant. Therefore, the generated output of thegenerator will be constant as well according to the capacity of the generator. Since these pico-hydro powerplants are connected to isolated consumer load which is variable in nature, there need to be a controllingarrangement so that the output power of the generator remains constant at different consumer load. Under thiscondition, it requires a controllable auxiliary or dump load connected in parallel with the consumer load sothat total power consumed by the SEIG remains constant. This is achieved using the electronic load controllerwhich maintains the required voltage and frequency of the generated output under different loadingconditions. The basic conventional electronic load controller consists of an uncontrolled rectifier with anIGBT based chopper switch and an auxiliary load which is also known as dump load. The whole controlmechanism involves the variation of duty cycle of chopper switch using a suitable feedback based close-loopcontrol system. The varying duty cycle of chopper connects or disconnects the dump load according to the




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amount of consumer load connected so that the sum of consumer plus dump load remains constant forconstant power output of SEIG thus maintaining the required voltage and frequency of the generated outputunder permissible limits. Fig. 16 shows the complete hardware setup used for experimentation and electronicload controller part used for the voltage and frequency control in the SEIG system.

Fig. 16 Complete hardware setup for SEIG system feeding isolated load

Experimental methodologyThe operating sequence of the experimentation starts with running the induction machine first as inductionmotor for few hours to initiate the residual magnetic field. Then the induction machine is driven with prime-mover (DC shunt machine in the used set-up) at its rated speed for few minutes. The speed of prime-mover isthen increased to run the 3-phase induction motor at above the synchronous speed (1500 RPM for 4-polemachine). In this set-up, induction machine is driven at 1540 RPM for few minutes without connecting thecapacitor bank across SEIG terminals. A small 3-phase voltage (1 to 6V approximately) is generated acrossthe induction machine (SEIG) terminal due to residual magnetic field inside the induction machine. All themeasurement and recording devices are also connected in the system to measure and record the self-excitedinduction generator system parameters under various operating conditions. Then the excitation capacitance isconnected across the SEIG system in steps till the required no load voltage is generated across the SEIGterminals and then all the parameters such as generated voltage, excitation capacitance value, generatedcurrent, excitation circuit current and SEIG speed are also recorded [15-16]. Then the performance of SEIG isevaluated under different load conditions. Firstly resistive load is connected in steps and SEIG parameters arerecorded. The speed and excitation capacitances are varied at different load conditions to get the desired SEIGparameters. Now along with resistive load, some inductive load is also added and at the same time extracapacitance is added to counter the inductive load effect to maintain the required SEIG parameters underpermissible limit. All the parameters are recorded under different R-L load conditions. To evaluate theperformance of SEIG under dynamic load conditions, a three phase induction motor is connected as loadalong with other resistive load on SEIG and all the parameters are recorded under this dynamic loadconditions. The power quality parameter such as THD (total harmonic distortion) is also recorded underdifferent operating conditions.




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Experimental resultsSEIG at no-loadThe various recorded parameters of SEIG under no-load conditions are tabulated in Table 1.

Table1. SEIG parameters under no-load conditions

Parameters Parameter Values

Line Voltage(V)

VRY 6.8 415 420 419

VYB6.8 415 420 419

VBR6.8 414 421 420

Line Current(A)

IR 0 2.67 2.62 2.62

IY0 2.67 2.62 2.62

IB0 2.67 2.62 2.62

THD (%)

V 0.72 1.80 1.9 1.88

I33 2.95 2.9 2.97

C/Ph (∆) in μF 0 11 11 12

Speed (RPM) 1505 1510 1516 1470

F (Hz) 50.1 50.2 50.4 48.7

SEIG at loadThe type of load on 3-phase SEIG consists of resistive, resistive –inductive, and dynamic load in the form ofinduction motor used for water pumping application etc. The load may be balanced/unbalanced, linear or non-linear type. The performance of the 3-phase SEIG is evaluated experimentally under all these loadingconditions. Domestic consumer electrical load in remote mountainous regions generally comprises of lightingand heating load using incandescent and compact fluorescent lamps. Apart from this; for a very short periodelectronic gadgets and house-hold single phase appliances are also used. To emulate these loading conditions,a three phase lamp load with multiple loading steps for each phase has been used to connect the lamp load oneach phase in the experimental set-up. With greater emphasis on the maximum use of compact fluorescentlamps (CFLs) from energy conservation point of view, CFLs have also been used along with conventionalincandescent lamps to evaluate the performance of SEIG. For consumer load purposes, incandescent lamps of100W & 200W ratings and compact fluorescent lamps (CFLs) of 20 W capacities are also used to emulate theactual domestic lighting load used in remote mountainous region. For non-linear load, a 3-phase and 1-phaseuncontrolled rectifier with DC load is used. A 3-phase inductive load panel of 5kVA capacity with multiplesteps is also used to analyze the performance of SEIG with inductive load. Tables 2 and 3 show the SEIG andload side parameters under various loading conditions.




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Table 2. SEIG parameters under different loading conditions

SEIG Parameters Parameter Values

Line Voltage (V)

VRY 415 413 415 407

VYB 414 413 415 408

VBR 414 414 416 408

Line Current (A)IR 2.65 2.78 2.63 3.2IY 2.65 2.78 2.61 3.2IB 2.66 2.79 2.58 3.2

Consumer Load (W)R 100 120 120 100Y 100 200 0 100B 100 200 0 100

VAr (Q) -Watt 0 0 0 400

DC Load -Watt 0 0 0 350

THD (%)V 1.2 2.29 0.7 1.17

I 3.1 4.73 3.5 2.89

C/Ph (∆) in μF 11 11 11 16

Speed (RPM) 1501 1510 1505 1498

F (Hz) 50 50.2 50.1 49.8

Table 3. Load side parameters under different loading conditions

Load Side Parameters Parameter Values

Line Voltage (V)

VRY 414 408 407 408

VYB 414 408 407 409

VBR 415 409 408 408

Line Current (A)

IR 0.50 0.56 1.16 1.2

IY 0.54 0.56 1.16 1.2

IB 0.52 0.56 1.16 1.2

Consumer Load (W)

R 120 100 120 100

Y 200 100 120 100

B 120 100 0 100

VAr (Inductive)Q 0 320 320 425IL 0 0.76 0.76 0.99

DC Load W 0 0 350 350

THD (%)V 1.95 0.59 1.31 1.3

I 0.87 8.41 15.81 15.4

C/Ph (∆) in μF 12 13 15 16

Speed (RPM) 1495 1519 1504 1503

F (Hz) 49.3 50.2 50.1 50.1




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For DC load, a three phase rectifier is used to connect the DC load which is equally distributed on the threephases of SEIG. Similarly, a three phase inductive load panel is used for connecting inductive load on SEIG.From the experimental evaluation of 3-phase SEIG, it is observed that a minimum value of excitationcapacitance is required to build up the voltage at SEIG terminals on no load. In this case for 3 HP, 4-poleSEIG the terminal voltage built-up at 10-12µF/phase in delta connected capacitor bank and it is 32-36µF/phase in star connected mode. When the electrical load on SEIG is increased, its terminal voltageslightly falls along with the slight drop in the speed of induction generator. However, the decrease in terminalvoltage due to increase in load can be compensated by increasing the speed of prime mover. With the furtherincrease in electrical load, requirement of excitation capacitance increases at rated speed. Since domesticelectrical load is of single-phase type and 3-phase, 4-wire system is used for electrifying the villages whichresults in the un-balancing of load in each phase. Therefore, unequal loading has been done for SEIG in theexperiment. The requirement of the excitation capacitance increases when inductive load is added tocompensate for the lagging reactive power caused by the inductive load.

CONCLUSIONThe simulated performance of 3-phase SEIG feeding isolated load using anti-windup control in constantpower prime-mover driven pico-hydro power generation system has been evaluated in this paper. Thesimulated results are validated using a hardware set-up comprising of 2.2kW, 4 poles, 415v, 3-phase squirrelcage induction machine operated as 3-phase SEIG driven by a 5HP, 1500 RPM DC shunt motor acting asconstant power prime-mover emulating the pico-hydro power generation system conditions. The results showthe efficacy of electronic load controller using anti-windup control in maintaining the SEIG systemparameters under required limits at various loading conditions including the abrupt change in load or at thetime of starting of SEIG voltage build up process. During these load changing conditions, the anti-windupcontrol feature of PI controller helps in countering the integral windup phenomenon and also there is no needfor pulse block circuit during the starting period.

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