Electrical Power and Energy Systems 53 (2013) 857–866

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Electrical Power and Energy Systems

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Dynamic stability study of an isolated wind-diesel hybrid power systemwith wind power generation using IG, PMIG and PMSG: A comparison

0142-0615/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.ijepes.2013.06.014

⇑ Corresponding author.E-mail address: bitt1979@gmail.com (P. Sharma).

Pawan Sharma ⇑, Waldemar Sulkowski, Bjarte HoffDepartment of Technology, Narvik University College, Narvik, Norway

a r t i c l e i n f o

Article history:Received 6 February 2013Received in revised form 16 May 2013Accepted 9 June 2013

Keywords:IGPMIGPMSGWind-diesel hybrid systemSynchronous generatorSTATCOM

a b s t r a c t

This paper presents a comparative study of reactive power control for isolated wind-diesel hybrid powersystem in three different cases with wind power generation by induction generator (IG), permanent-mag-net induction generator (PMIG) and permanent-magnet synchronous generator. The synchronous gener-ator (SG) is used with diesel engine set. A mathematical model of the system based on small signalanalysis, is developed considering reactive power flow balance equations. The variable reactive powerneeded by the system is provided by a static synchronous compensator (STATCOM) when wind powergeneration is done by IG and PMIG. When permanent-magnet synchronous generator (PMSG) is usedfor wind power generation, the variable reactive power demand is fulfilled by a voltage source converter(VSC) which is on the load side. A new mathematical approximation model for VSC connected with PMSGis proposed such that the voltage source converter fulfills the increased reactive power requirement ofload and also increases its active power equal to the increased input wind power. Proportional and inte-gral (PI) gains of the STATCOM and VSC controllers are optimized using integral square error criterion(ISE). The dynamic responses of the system for small (1%) step increase in load reactive power withand without 1% step increase in input wind power are shown. The paper also shows the dynamicresponses of the system for random step change in load reactive power plus random step change in inputwind power. The MATLAB/SIMULINK environment is used for simulation.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

To enhance capacity, reliability and for economic reasons, thepower supply of local diesel based grids are integrated with therenewable energy sources like solar, wind, mini/micro hydro, etc.[1–5]. The diesel engine generators (having SG as generator) arecommonly integrated with wind power generators having IG asthe electro-mechanical conversion device. The IG has main advan-tage of no synchronization due to variation in wind speed in theoperating range [5]. But their performance is poor in terms of volt-age regulation as they require magnetizing current from the sourcefor excitation and decreases both the power factor and efficiency ofthe IG [6]. The power factor, voltage regulation and efficiency canbe improved by the use of PMIG and PMSG [6].

In PMIG, a second rotor mounted with permanent magnets(PMs) provides the flux in the IG’s new PM counterpart. This PM ro-tor is mounted on a freely rotating shaft to provide alternating flux.The poles of the PM rotor now coincide with the magnetic poles in-duced in the stator field. The main rotor operates in asynchronousmode as it still follows the rotating stator field with slip [7]. Themachine reactive power need gets significantly reduced as the re-

quired magnetizing current reduces due to permanent-magnetsand the direct driven PMIG can be used omitting the need for agearbox and all its maintenance issues [7]. The other major advan-tage is that even if the voltage of the power grids is unbalanced, thePMIG can operate at high efficiency over a wide range of slip andthe built-in – permanent-magnet rotor is minimally affected bythe negative sequence rotating field [8]. The size of the machinegets reduced due to high power density with reduction in inrushcurrents and improves both its steady state and transient perfor-mances [9–12].

PMSG has advantages such as higher efficiency, better thermalcharacteristics owing to the absence of field losses, solid fieldstructure, high power to weight ratio and improved dynamic sta-bility [13–23]. The surface mounted permanent-magnet (SPM)generators are becoming popular for wind turbine applicationsthat are designed for low speed direct driven gearless operationas compared to interior permanent-magnet generators [24]. Thewind turbine coupled to PMSG produces power at different fre-quencies depending upon the wind turbine speed and input windpower. To generate power at the desired frequency and voltage le-vel, AC/DC/AC converters are used with PMSG [14–18]. As nopower electronics is required for grid interface for PMIG, thereforea decrease in the cost of about 20% can be realized compared tocost of wind power generation by PMSG [7].

Nomenclature

KA, KE, KF gains of voltage regulator, exciter, and stabilizer con-stants, respectively

DEfd, DEq small deviation in the voltages of the exciter, andinternal armature e.m.f. of the synchronous generator(SG) under steady state, respectively

DE0q small deviation in the internal armature e.m.f. of the SGunder transient condition

KP, KI proportional and integral (PI) gains of the static syn-chronous compensator (STATCOM) and converter con-trollers, respectively

g performance index used in the parameter optimizationbased on the integral square error (ISE) criterion

PWG, QWG active and reactive power generated by wind genera-tors, respectively

PDG, QDG active and reactive power generated by diesel genera-tor, respectively

Qcom, reactive power generated by STATCOMDPIW small deviation in the input wind powerDa small deviation in the phase angle at STATCOMT1, Ta, Td main time constant, transport lag, and average dead

time of zero crossings of the STATCOM controller,respectively

Req, Xeq, Xm equivalent resistance, reactance and magnetizingreactance of the permanent-magnet induction genera-tor/induction generator, respectively

s slip of PMIG/IGT 0do direct-axis open-circuit transient time constant of the

SGV system bus voltageDV, DVa, DVf small deviation in the system bus voltage, exciter

amplifier voltage, and exciter feedback voltage, respec-tively

Xd;X0d direct-axis reactance of SG under steady state and tran-

sient-state conditions, respectivelyVin voltage injected to the transformer of the converter-2

for the wind power generationdin angle of the injected voltage, Vin, with respect to the sys-

tem bus voltage, VXT total reactance of the coupling transformer and filter

inductance of the converter-2 for the wind power gen-eration

858 P. Sharma et al. / Electrical Power and Energy Systems 53 (2013) 857–866

The isolated wind-diesel system has active and reactive powerbalances under steady state conditions. The disturbance in the loadand/or in the input wind power may cause mismatch in the gener-ated and consumed active and reactive power. The mismatch in thereactive power can cause variation in the system bus voltage. Toeliminate mismatch between generation and consumption of reac-tive power, a variable source of reactive power like STATCOM is re-quired [25]. The STATCOM employs a voltage source converter thatinternally generates inductive/capacitive reactive power [26–44].A small size of STATCOM is required when PMIG is used for windpower generation in isolated wind-diesel system as compared toIG for supply of variable reactive power [25]. In case of wind powergeneration by PMSG, the VSC (which is connected on the load side)meets the variable reactive power requirements of load.

This study presents a systematic approach for state space mod-eling of the wind-diesel system for automatic reactive power con-trol. The state equations are derived based on small signal analysis.A new mathematical approximation model (based on power flowequations) for voltage source converter connected with PMSG isproposed. The STATCOM and VSC controller PI gains are optimizedusing ISE criterion for minimum deviation in system bus voltage.The dynamic responses of the system are investigated in threecases when the wind power is generated by three different gener-ators i.e. IG, PMIG, and PMSG while SG is used for power generationwith diesel engine set.

2. Mathematical modeling of the hybrid power system

A wind-diesel hybrid power system considered for study isshown in Fig. 1. The dotted blocks distinguish two cases whenPMIG or IG is used for wind power generation and then STATCOMis required as a reactive power compensator. Small change in fre-quency is due to small change in real power [45,46] while a smallchange in the voltage is due to the small change in reactive power[47]. The active and reactive power balance equations of the sys-tem under steady state conditions are given below:

PWG þ PDG ¼ PL ð1ÞQ DG þ Qcom þ Q WG ¼ QL ð2Þ

When PMSG is used for wind power generation, no compensa-tor is needed, therefore, Qcom = 0 in Eq. (2). Due to disturbance inload reactive power, DQL, the system bus voltage may changewhich results an incremental change in reactive power of othercomponents. The net reactive power surplus is DQDG + DQcom + -DQWG � DQL and it will change the system bus voltage as givenby the following transfer function equation [25]:

DVðsÞ ¼ KV

1þ sTV½DQ DGðsÞ þ DQcomðsÞ þ DQ WGðsÞ � DQ LðsÞ� ð3Þ

where KV and TV are the system gain and time constants, andDQcom(s) = 0 in the case of PMSG for wind power generation. Allthe connected loads experience an increase with the increase in sys-tem bus voltage due to load voltage characteristics given below[47]:

DV ¼@Q L

@Vð4Þ

The composite loads can be expressed in exponential voltageform [47] as

QL ¼ c1Vq ð5Þ

where C1 is the constant of the load and the exponent q, dependsupon the type of load. The load voltage characteristics DV can befound empirically as follows [47]:

DV ¼DQL

DV¼ q � Q

0L

V0 ð6Þ

In Eq. (3), KV = 1/DV and TV is the time constant of the systemwhich is proportional to the ratio of electromagnetic energy ab-sorbed in the winding to the reactive power absorbed by the sys-tem. An IEEE type-1 excitation control system as shown in Fig. 2is considered for the SG connected with the diesel engine set ofthe system as given by Ref. [47].

The small deviation in voltage behind transient reactance,DE0qðsÞ, in SG by solving the flux linkage equation for small pertur-bation as in Ref. [47]:

DE0qðsÞ ¼1

ð1þ sTGÞ½K1DEfdðsÞ þ K2DVðsÞ� ð7Þ

Fig. 1. Single line diagram of isolated wind-diesel power system.

Fig. 2. IEEE type-1 excitation system; SF = 0.

P. Sharma et al. / Electrical Power and Energy Systems 53 (2013) 857–866 859

where

K1 ¼ X0d=Xd ð8Þ

and

K2 ¼ ½ðXd � X0dÞ cos d�=Xd ð9Þ

The small deviation in synchronous generator reactive power interms of state variables is given in Eq. (10) [47]

DQ DGðsÞ ¼ K3DE0qðsÞ þ K4DVðsÞ ð10Þ

where

K3 ¼ V cos d=X0d ð11Þ

Fig. 3. Approximate equivalent circuit diagram of wind generator with dotted blockis also included when PMIG used and only solid block included when IG is used.

and

K4 ¼ ½E0q cos d� 2V �=X0d ð12Þ

The approximate equivalent circuit of IG and PMIG is given inFig. 3. The effect of permanent-magnets is to provide reactivepower as function of voltage as given in [48]

XC ¼ ðaV3 þ bV2 þ cV þ dÞ1=3

ð13Þ

In Eq. (13), the values of a, b, c, and d are selected such that theeffect of XC is equivalent to the permanent-magnets in providingreactive power at different voltages. In case of IG, XC, becomesinfinity. The small perturbations of the reactive power deliveredby PMIG, for 1% step increase in load reactive power, DQL, withoutany change in the input wind power [48] is given by

DQWGðsÞ ¼ K5DVðsÞ ð14Þ

where

K5 ¼2XeqV

R2Y þ X2

eq

þ V2

XC� 2

Vþ ð3aV2 þ 2bV þ cÞ

ð3X3CÞ

( )ð15Þ

For 1% step increase in load reactive power, DQL, plus 1% stepincrease in input wind power, DPIW, the reactive power deliveredby PMIG [48] is given by

DQWGðsÞ ¼ K6DPIWðsÞ þ K7DVðsÞ ð16Þ

where

860 P. Sharma et al. / Electrical Power and Energy Systems 53 (2013) 857–866

K6 ¼2XeqRY V2

R2Y þ X2

eq

� �f2RY PIW � Pcorelossð Þ þ V2g

ð17Þ

K7 ¼ Kc1 þV2

XC

2V�

3aV2 þ 2bV þ c� �

3X3C

� �8<:

9=;

24

35 ð18Þ

RY ¼ RP þ Req ð19Þ

RP ¼r02sð1� sÞ ð20Þ

and

Kc1 ¼2XeqV

R2Y þ X2

eq

1þ 2RY RPV2

R2Y þ X2

eq

� �f2RY PIW � Pcorelossð Þ þ V2g

24

35 ð21Þ

The STATCOM is based on a solid state synchronous voltagesource that is analogous to an ideal synchronous machine whichgenerates a balanced set of three sinusoidal voltages, at the funda-

(a) (b)Fig. 4. STATCOM configuration: (a) schematic diagram and (b) equivalent circuit.

Fig. 5. Transfer function block diagram o

mental frequency, with rapidly controllable amplitude and phaseangle. The configuration of a STATCOM is shown in Fig. 4. It con-sists of a voltage source converter (VSC), a coupling transformer,and a d.c. capacitor as shown in Fig. 4a. The real current of theSTATCOM is negligible and is assumed to be zero. Control of reac-tive current is possible by variation of d and a as shown in Fig. 4b.Here d is the phase angle of the system bus voltage, V where STAT-COM is connected and a is the angle of the fundamental outputvoltage, kVdc of the STATCOM [49]. The magnitude of the funda-mental component of the converter output voltage is kVdc, whereVdc represent the voltage across the capacitor. The reactive powerinjection to the system bus has the form: [49],

Qcom ¼ kV2dcB� kVdcVB cosða� dÞ þ kVdcVG sinða� dÞ ð22Þ

The system bus voltage V is taken as reference voltage, thereforethe angle d is zero. Also G is negligible as G + jB represent the trans-former admittance. Therefore, considering the value of G and d tobe zero in the system, Eq. (22) can be written as

Qcom ¼ kV2dcB� kVdcVB cos a ð23Þ

The flow of reactive power depends upon the variables V and a,therefore for small perturbation, the linearized STATCOM equationis written as

DQcom ¼@Q com

@aDaþ @Qcom

@VDV ð24Þ

Substituting the value of partial derivatives from Eq. (23) in Eq.(24), we get

DQcomðsÞ ¼ K8DaðsÞ þ K9DVðsÞ ð25Þ

f wind-diesel hybrid power system.

Fig. 6. Small signal model of used STATCOM scheme.

Table 1Optimum PI gain values of controllers gains.

Gains STATCOM controller Converter-2 controllers

IG PMIG C1 C2

KP 44.64 47.3 11.5 6KI 7090.9 7120.4 5150 2100

0 0.002 0.004 0.006 0.008 0.01-1

-0.5

0

0.5

1 x 10-3

PMSGPMIGIG

0 0.002 0.004 0.006 0.008 0.01

0

0.01

0.02PMSGPMIGIG

0.01PMSG

Time in sec

Time in sec

ΔV (

pu)

ΔQ W

G (

pu)

(b)

(c)

(a)

P. Sharma et al. / Electrical Power and Energy Systems 53 (2013) 857–866 861

where,

K8 ¼ kVdcVBsina ð26ÞK9 ¼ �kVdcB cos a ð27Þ

where k ¼ p6 �

ffiffi6p

p and p, is the pulse number of the inverter with mod-ulation index unity [49].

When PMSG is used for wind power generation as shown inFig. 5, the AC/DC converter (converter-1) is able to satisfy the reac-tive power requirement on the turbine generator side, so it keepsthe voltage across the capacitor constant. The converter-2 (theVSC on the load side) pumps the active power of wind turbine tothe local diesel based grid and also balances the reactive power re-quired by the system. Therefore, the reactive power compensatorsuch as STATCOM is not required as the converter-2 inherentlyhas two controls for active and reactive powers. A new mathemat-ical approximation model for converter-2 of PMSG is proposedsuch that the converter-2 fulfills the increased reactive powerrequirement of load and also increases its active power equal tothe increased input wind power by adjusting its internal voltage,Vin, and angle, din.

The power equations (based on power flow equations) of theconverter-2 are as follows:

PWG ¼VinV sin din

XTð28Þ

Q WG ¼VinV cos din � V2

XTð29Þ

The small deviations in the active and reactive powers of thewind generator will be given as follows:

10 20 30 40 50 60 70 800

1

2

3

4 x 10-3(a)

0 2000 4000 6000 8000 100002

2.2

2.4

2.6

2.8

3

3.2 x 10-4(b)

Perf

orm

ance

Ind

ex

KI

Optimum value = 7090.9

Perf

orm

ance

Ind

ex

KP

Optimum value = 44.64

Fig. 7. Optimization of STATCOM controller gains of PI gains when IG is used withWECS: (a) KP vs. g and (b) KI vs. g.

0 0.002 0.004 0.006 0.008 0.01-0.01

-0.005

0

0.005 PMIGIG

0 0.002 0.004 0.006 0.008 0.010

0.005

0.01

0.015

0.02PMIGIG

Time in sec

Time in sec

ΔQ D

G (

p.u.

)ΔQ

com

(p.

u.)

(d)

Fig. 8. Dynamic responses of wind-diesel system for 1% step increase in loadreactive power.

DPWGðsÞ ¼ K 001DdinðsÞ þ K 002DVinðsÞ þ K 003DVðsÞ ð30ÞDQWGðsÞ ¼ K 004DdinðsÞ þ K 005DVinðsÞ þ K 006DVðsÞ ð31Þ

where

0 0.002 0.004 0.006 0.008 0.01-1

-0.5

0

0.5

1 x 10-3

PMSGPMIGIG

0 0.002 0.004 0.006 0.008 0.01-5

0

5

10

15

20 x 10-3

PMSGPMIGIG

0 0.002 0.004 0.006 0.008 0.01-5

0

5

10 x 10-3

PMSGPMIGIG

0 0.002 0.004 0.006 0.008 0.010

0.005

0.01

0.015

0.02

PMIGIG

Time in sec

Time in sec

Time in sec

Time in sec

ΔV (

pu)

ΔQ W

G (

pu)

ΔQ D

G (

p.u.

) ΔQ

com

(p.

u.)

(b)

(c)

(d)

(a)

Fig. 9. Dynamic responses of wind-diesel system for 1% step increase in loadreactive power plus 1% step increase in input wind power.

0 0.002 0.004 0.006 0.008 0.01-6

-4

-2

0

2

4 x 10-3

PMSGPMIGIG

0 0.002 0.004 0.006 0.008 0.01-0.02

00.020.040.060.08

PMSGPMIGIG

0 0.002 0.004 0.006 0.008 0.01-0.04

-0.02

0

0.02

0.04PMSGPMIGIG

0 0.002 0.004 0.006 0.008 0.010

0.02

0.04

0.06

0.08

0.1PMIGIG

Time in sec

Time in sec

Time in sec

Time in sec

ΔV (

pu)

ΔQ W

G (

pu)

ΔQ D

G (

p.u.

)ΔQ

com

(p.

u.)

(b)

(c)

(d)

(a)

Fig. 10. Dynamic responses of wind-diesel system for 5% step increase in loadreactive power plus 1% step increase in input wind power.

0 0.2 0.4 0.6 0.8 1 1.20

0.002

0.004

0.006

0.008

0.01

ΔQ L

or ΔP

IW (

pu)

Time in sec

Fig. 11. Type of random step change in load reactive power and input wind power.

862 P. Sharma et al. / Electrical Power and Energy Systems 53 (2013) 857–866

K 001 ¼VinV cos din

XTð32Þ

K 002 ¼V sin din

XTð33Þ

K 003 ¼Vin sin din

XTð34Þ

K 004 ¼ �VinV sin din

XTð35Þ

K 005 ¼V cos din

XTð36Þ

K 006 ¼ðVin cos din � 2VÞ

XTð37Þ

Vin ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiððPWGXTÞ2 þ ðQWGXT þ V2Þ2Þ

V2

sð38Þ

and

din ¼ sin�1 PWGXT

VinV

� �ð39Þ

Using these equations, a simulation model of the system isdeveloped and the transfer function block diagram of the systemis shown in Fig. 5. Here, the dotted blocks are shown whenPMIG/IG is used for wind power generation. The STATCOM blockshown in Fig. 5 is redundant when PMSG is used. The small signal

model used for STATCOM block is shown in Fig. 6 where Td, Ta areaverage dead time of zero crossings in a 3 phase system and firingdelay time, respectively.

3. Simulation results

The simulation results discussed in this section are based on thetypical data of the wind-diesel system with three different types ofwind generators, IG, PMIG and PMSG, as given in Appendix A. Theoptimization of STATCOM and converter 2 controllers PI gains, isperformed by using the ISE criterion and ISE criterion [47] is givenby

P. Sharma et al. / Electrical Power and Energy Systems 53 (2013) 857–866 863

g ¼Z 1

0½DVðtÞ�2dt ð40Þ

For IG with WECS, the optimized values of PI gains, is shown inFig. 7.

The optimized values of the PI controller gains are given inTable 1. Using the optimum values, different dynamic responses

0 0.2 0.4 0.6-6

-5

-4

-3

-2

-1

0

1

2

3

4 x 10-4

0 0.2 0.4 0.6-6

-4

-2

0

2

4

6

8

10

12

14 x 10-3

0.6 0.602 0.604 0.606 0.608 0.61-4

-2

0

2

4 x 10-4

0.6 0.602 0.604 0.606 0.608 0.61-5

0

5

10x 10-3

ΔV (

pu)

ΔQ W

G (

pu)

0 0.2 0.4 0.6-3

-2

-1

0

1

2

3

4x 10-3

0.6 0.602 0.604 0.606 0.608 0.61-3-2-101234 x 10-3

ΔQ D

G (p

u)

Tim

Tim

Tim

(a)

(b)

(c)

Fig. 12. Dynamic responses of wind-diesel system for random step change

of the system are obtained as shown in Figs. 8–10 and 12. Fig. 11shows the type of random step change in load reactive power,DQL and random step change in input wind power, DPIW.

Fig. 8 shows the deviation in system bus voltage DV, deviationsin diesel reactive power generation DQDG, wind reactive powergeneration DQWG, and reactive power generation by STATCOM

0.8 1 1.2 1.4

PMSG

PMIG

IG

0.8 1 1.2 1.4

PMSG

PMIG

IG

0.8 1 1.2 1.4

PMSG

PMIG

IG

e in sec

e in sec

e in sec

in load reactive power plus random step change in input wind power.

0 0.2 0.4 0.6 0.8 1 1.2 1.4-5

0

5

10

15

20x 10-3

PMIG

IG

0.6 0.602 0.604 0.606 0.608 0.61

468

10121416 x 10-3

ΔQ co

m (p

u)

Time in sec

(d)

Fig. 12 (continued)

864 P. Sharma et al. / Electrical Power and Energy Systems 53 (2013) 857–866

DQcom, for 1% step increase in load reactive power DQL. It is ob-served that the voltage deviation (first peak and subsequentswings) stabilizes fast in case of wind power generation by PMIGand IG than that of PMSG, which is due to the fast action of theSTATCOM. The converter-2 inherently have two controls for activeand reactive powers, therefore the peak deviations in system busvoltage is higher. It is shown that DG provides the required loadreactive power only under transient conditions as shown inFig. 8c. The STATCOM is providing the required load reactive powerunder transient and steady state conditions as shown in Fig. 8d.The needed load reactive power under steady state conditions isfulfilled by the converter 2 when PMSG is used as shown inFig. 8b. The deviations DV and DQDG, therefore, become zero understeady state conditions.

Fig. 9 shows deviations DV, DQDG, DQWG, and DQcom, for 1% stepincrease in load reactive power plus 1% step increase in input windpower, DPIW. The increase in the input wind power only increasesthe active power of the converter-2 by the same amount but thereis no change in its reactive power under steady state conditions.This is in contrast to the case of wind power generation by IG orPMIG where the reactive power is absorbed with the increase inthe input wind power. Therefore, the converter-2 fulfills the in-creased reactive power requirement of load and also increases itsactive power equal to the increased input wind power under stea-dy state conditions by adjusting its internal voltage, Vin and angle,din. It is shown that DG provides the required load reactive poweronly under transient conditions.

Fig. 10 shows the deviations DV, DQDG, DQWG, and DQcom, inreactive powers for 5% step increase in load reactive power plus1% step increase in input wind power. It is found that though theincrease in the disturbance increases the first peak of the systemvariables but the settling time remains almost the same. Fig. 12shows the deviations DV, DQDG, DQWG, and DQcom for random stepchange in load reactive power plus random step change in inputwind power. It is clear from the Fig. 12 that the peak deviations de-pend upon the disturbance on the instant (at 0.6 s, in Fig. 12, this isshown).

4. Conclusions

This paper presents a dynamic performance study of an isolatedwind-diesel hybrid power system with reactive power control hav-ing SG and IG, PMIG and PMSG for electric power generation fromdiesel engine set and wind turbine, respectively. The reactive

power control is being achieved by using STATCOM and convertercontrols. A new mathematical approximation model for VSC con-nected with PMSG is proposed. In the system, an equal size of1500 kW wind power generation with IG, PMIG and PMSG genera-tors is considered for comparison of performance. The PI gains ofSTATCOM and converter 2 controllers for minimum deviation insystem bus voltage is optimized using ISE criterion.

It is found that the dynamic performance of wind power gener-ation by IG and PMIG are comparable under transient conditionswith equal settling times. The size of the STATCOM gets reducedwhen PMIG is used instead of IG for wind power generation asPMIG requires less reactive power at rated voltage. When PMSGis used for wind power generation, the converter-2 fulfills the in-creased load reactive power requirement and also increases its ac-tive power equal to the increased input wind power under steadystate conditions by adjusting its internal voltage and angle. Henceno needs of any reactive power compensator like STATCOM. Theincrease in the input wind power only increases the active powerof the converter-2 by the same amount but there is no change inits reactive power under steady state conditions. This is in contrastto the case of wind power generation by IG or PMIG where thereactive power is absorbed with the increase in the input windpower.

Appendix A.

The data of the wind-diesel hybrid power system are as follows:

Generation wind capacity (kW)

Wind Diesel Total

Capacity (kW)

1500 1500 3000 Load (kW) 1500 1000 2500

The base power = 2500 kV A, base voltage = 400 V.The data of the wind-diesel system are given as follows:

System parameters

SG IG PMIG PMSG

PDG (p.u.)

0.4 – – – QDG (p.u.) 0.2 – – – Eq (p.u.) 1.1136 – – 1.1136 E0q (p.u.) 0.9603 – – –

d (�)

21.05 – – – din 1.67

P. Sharma et al. / Electrical Power and Energy Systems 53 (2013) 857–866 865

Appendix A. (continued)

System parameters

SG IG PMIG PMSG

X0d (p.u.)

0.15 – – – Xd (p.u.) 1.0 – – 1.0 T 0do 5 – – – PWG (p.u.) – 0.6 0.6 0.6 QWG (p.u.) – �0.2906 0 0.55 g% – 90 90 – r1 ¼ r02 (p.u.) – 0.19 0.19 – x1 ¼ x02Þ (p.u.) – 0.56 0.56 – s% – 4.0 4.0 – PL (p.u.) – – – – QL (p.u.) – – – – Power factor – 0.8 0.8 –

The parameters of the IEEE Type-1 Excitation are given below:KA = 40, KE = 1.0, KF = 0.5, TA = 0.05 s. SF = 0, TE = 0.55 s.

The parameters of the STATCOM are given below: T1 = 30 ms,Ta = 0.25 m, Td = 1.67 ms.

For wind-diesel system, the values of the constants are asfollows:

Constants

IG PMIG PMSG

K1

0.15 0.15 – K2 0.793277 0.793277 – K3 6.22178 6.22178 – K4 �7.8249 �7.8249 – K5 0.1016 �0.666 – K6 0.444 0.444 – K7 �0.09747 �0.8651 – K8 5.152869 3.36 – K9 �3.8347 �2.5 – K 001 – – 20.53 K 002 – – 0.5828 K 003 – – 0.5986 K 004 – – �0.5986 K 005 – – 19.9915 K 006 – – �19.61 KV 0.6667 0.6667 0.667 TV 7.34e�4 7.34e�4 5.34e�4

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