a hybrid control scheme for fault ride-through capability using line-side converter and an energy...

International Electrical Engineering Journal (IEEJ)

Vol. 5 (2014) No.4, pp. 1305-1312

ISSN 2078-2365

http://www.ieejournal.com/

1305

Rajkumar and Suganthi Hybrid Control Scheme for Fault Ride-Through Capability using Line-Side Converter and an Energy Storage System for

PMSG Wind Turbine Systems

A Hybrid Control Scheme for Fault Ride-Through

Capability using Line-Side Converter and an

Energy Storage System for PMSG Wind Turbine

Systems

S.Rajkumar1, S.T.Suganthi2

1 Department of EEE,SNS College of Technology, Coimbatore-35 2 Department of EEE,SNS College of Technology,Coimbatore-35

[email protected],

[email protected]

Abstract— As the wind power installations are increasing in

number, Wind Turbine Generators (WTG) are required to have

Fault Ride-Through (FRT) capabilities. Lately developed grid

operating codes demand the WTGs to stay connected during

fault conditions, supporting the grid to recover faster back to its

normal state. In this paper, the generator side converter

incorporates the maximum power point tracking algorithm to

extract maximum energy from wind turbine system. A hybrid

control scheme for energy storage systems (ESS) and braking

choppers for fault ride-through capability and a suppression of

the output power fluctuation is proposed for permanent-magnet

synchronous generator (PMSG) wind turbine systems. During

grid faults, the dc-link voltage is controlled by the ESS instead of

the line-side converter (LSC), whereas the LSC is exploited as a

STATCOM to inject reactive current into the grid for assisting in

the grid voltage recovery. A simple model of the proposed system

is developed and simulated in MATLAB environment. The

effectiveness of the system is validated through extensive

simulation results

Index Terms- Boost converter, Braking Chopper(BC),dc-link control,

energy storage system(ESS),ride through, STATCOM, Permanent

Magnet Synchronous Generator.

I. INTRODUCTION

The development of various wind turbine (WT)

configurations in the last decade has been very dynamic and

has resulted in larger ratings and higher operating speed

ranges allowing them to be tied up to the grid more easily.

Variable speed operation of wind energy conversion systems

(WECS) make them more ‘grid-friendly’. Permanent magnet

synchronous generators (PSMG) based WECS are emerging

as strong competitors to the other variable speed technologies.

The power converter, whose rating is the same as that of the

generator, connected between PMSG and grid allows full

controllability of the system during normal operation and fault

conditions. Further, PMSG operates at higher efficiency and

better power factor than its counterparts especially when it

functions as a direct driven generator [1-3]. WECS based on

PMSG can be connected to the grid by using a voltage source

converter (VSC) on the grid side and by using either a diode

converter with a buck-boost converter or a VSC on the

machine side. Evidently, using VSC on both machine and grid

sides offer full control of active and reactive powers resulting

in the best performance [4-6] in terms of power output, quality

of power and performance during faults.

Different strategies have been presented by various

authors, to enhance fault ride through (FRT) capabilities of

PMSG based WECS. Many devices, such as static var

compensator (SVC), dynamic voltage restorers (DVR), Static

Synchronous Compensators (STATCOM) etc have been

shown to improve FRT of WECS, but they will also increase

the overall cost of the system [7-8]. In [9], a nonlinear

controller design for power converter based WT system is

presented which ensures that current levels remain within

design limits, even at greatly reduced voltage levels. A back to

back connected voltage source- converter (VSC) configuration

is discussed in [10] where the machine side converter (MSC)

controls the speed of the generator by using a flux vector

control technique and the grid side converter (GSC) controls

the power flow by PWM technique Transient analysis of a

grid connected wind driven PMSG is presented in [11] and a

comparison is presented with the other generators at fixed and

variable speeds. An electromagnetic braking resistor

controlled using power electronic switch is used to dissipate


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the excess energy in the DC link Circuit, preventing DC link

over voltage in [12]. Flexible active power control of

distributed generation systems during Grid Faults is discussed

in [13]. Reactive power as well as real power manipulation

using current control is described in [14]. Control of grid

converter in synchronously rotating reference frame is

described in [15-16].

In this paper, the generator side converter

incorporates the maximum power point tracking algorithm to

extract maximum energy from wind turbine system. In

addition, FRT technique of the PMSG wind turbine system is

proposed during the grid fault. By switching the control mode,

the ESS is operated to control the dc-link voltage of the back-

to-back converters during the grid voltage sags. Meanwhile,

the LSC is utilized to supply the reactive current to the grid for

satisfying the reactive current requirements of the grid code.

By this, the grid voltage can be recovered rapidly without an

external STATCOM after fault clearance. Also, the generator

active power can be absorbed fully by the ESS and the BC

during the voltage sags. In addition, the output power

fluctuation of wind turbine systems operating in steady state is

smoothened by the ESS. With this control scheme, the system

can still operate well even though the grid voltage is fully

interrupted. The validity of the proposed control algorithm is

verified by simulation and experimental results.

II. SYSTEM DESCRIPTION

Fig. 1 presents a block diagram of the simulation

model used for the FRT and Maximum Power point tracking.

In this paper, the wind turbine converts the power of the wind

to mechanical power in the rotor shaft. This is then converted

to electricity using a permanent magnet synchronous generator

(PMSG). The output voltage is rectified using a three-phase

diode bridge rectifier. The dc-to-dc converter is used to

control the dc voltage Vdc . The MPPT controller delivers a

voltage reference that is compared to the actual value of Vdc.

The result is fed into a PI controller whose output is compared

to a triangular waveform to determine when to turn the dc -dc

boost converter switch ON or OFF.The ESS consists of a

Electric Double Layer capacitor bank and a bidirectional

DC/DC converter and is also connected to the dc-link. Super

capacitors are suitable for wind power applications, as they

present the features of high efficiency, high power density,

long cycle life and easy maintenance . A BC is connected in

parallel with the dc-link. The BC will be activated to dissipate

the excessive power beyond the capacity of the ESS in cases

of deep voltage sags or high wind speed variations. The

control objective of the DC/DC converter is to maintain the

dc-link voltage magnitude at a constant level, by absorbing

any mismatch between the generated power and the power

transferred to the grid. In normal conditions, the LSC controls

the dc-link voltage , and the ESS is able to smoothen the

power ripples. In grid fault conditions, on the other hand, the

LSC functions as a STATCOM, and the ESS controls the dc-

link voltage. The FRT control scheme is designed according to

the grid code requirements on FRT.

III. MODELLING OF PROPOSED CONTROL SCHEME

A. Maximum Power Extraction Algorithm

Due to its monotonic characteristics, wind turbines can be

controlled to yield maximum power using search control

methods. Before explaining the maximum power tracking

controller, it is important to understand the basic physics of

the system. The generated mechanical power is given by [17-

19]

Pmech=Tmech(t)ωR(t) (1)

Where, Tmech is the mechanical torque. For simplification, the

generated electric power of a one-phase generator is given by

Pe(t)=Va(t)Ia(t) (2)

Fig 1:Block diagram of the proposed MPPT and FRT Method

Va and Ia are the generator voltage and current respectively.

Assuming no losses in the system, then

Tmech(t).ωR(t)= Va(t)Ia(t) (3)

The basic electrical and motion equations are

Te = kIaIf (4)

Ia=(Va-Ea)/Ra (5)

Ea=kIaωe (6)

Where, ωe = (p/2) ωR and p is the number of poles of the

generator.

Maximum power is at

=0 (7)



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Fig. 2. Typical power versus speed characteristics of a wind turbine.

The power extracted from the wind can be controlled by

varying the dc bus voltage, which is a function of If and ωe.

Considering the wind turbine characteristics given in Figure 2,

we know that the maximum power point is obtained whe

ω = 0 (8)

This equation can be written as:

=

=0 (9)

According to equation (9),maximum power point is when:

=0 (10)

The function Pmech (Vdc) has a single point where

maximum power extraction is achieved. It also means that the

maximum power can be tracked by searching the rectified dc

power, rather than environmental conditions, such as wind

speed and direction. The MPPT algorithm is as follows. One

initiates the maximum power searching process by setting an

arbitrary dc side voltage reference Vref. The controller then

measures both the dc side current and voltage, and calculates

the initial electric power Po = VdcIdc. Next, the reference

voltage Vref is increased by ΔVdc so that.

Vref(k)= Vref(k-1)+ ΔVdc (11)

Then the dc power is calculated with P(k) =

Vdc(k)Idc(k).

If P(k) is bigger than P(k - 1), the maximum power

point has not been reached therefore, the voltage reference

needs to be increased by ΔVdc and the dc power needs to be

compared. This process will repeat until maximum power is

reached.

And if P(k) is less than P(k - 1), the dc voltage

reference is then decreased by ΔVdc. In order to search for

maximum power at any wind speed four conditions must be

met.

1. If P(k)≥ P(k-1) and Vdc(k)≥ Vdc(k-1), the dc side

voltage reference need to be increased by ΔVdc. This condition

is met when the turbine operates on the low speed side of the

power curve, shown on Fig 3.

2. If P(k)≥ P(k-1) and Vdc(k)< Vdc(k-1), the wind

turbine is being operated in the high speed side and the dc

reference voltage needs to be decreased by ΔVdc.

3. When P(k)< P(k-1) and Vdc(k)≥ Vdc(k-1), the

maximum power point is passed and a step back must be

taken, decreasing the reference voltage by ΔVdc. This

condition is met when the turbine is operated in the high

speed side of the dome and the power is decreasing.

4. When P(k)< P(k-1) and Vdc(k)< Vdc(k-1), the

power is decreasing on the low speed side, therefore the

voltage reference is to be increased by ΔVdc.

Fig 3 Maximum Power Tracking Process

In Figure 3, the power-speed plot is shown for three different

wind speeds, where υ1 < υ 2 < υ 3. The arrows show the

trajectory in which the turbine will be operated using the

maximum power tracking algorithm explained above. If the

wind speed is υ1, the controller will search for the maximum

power. If the wind changes to υ3 the turbine is no longer being

operated at the maximum power point so the controller will

search for the new maximum power point.

Fig 4. Flowchart for MPPT Algorithm



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After reaching the maximum point it will operate the

wind turbine at the optimal point until wind changes, thus

searching for maximum power at any wind speed. In order to

optimize the maximum power search algorithm presented

above, a step that combines speed of convergence and

accuracy of results was developed. The variable step method

is based on the Newton Raphson method. The value of the

root can be calculated as,

Xn+1=Xn -

(12)

Where Xn is the current known value of X, ƒ(Xn)

represents the value of the function at Xn, and ƒ’(Xn) is the

derivative at Xn. The function ƒ (Xn) can be expressed as:

ƒ(Xn)= ƒ(Vdc(k)) =

=

= Slope(k) (13)

And ƒ’(Xn) as

ƒ’(Xn)=ƒ’(Vdc(k)=

=

(14)

Using (12,)(13) and (14), ΔVdc can be express as follows:

ΔVdc =

=

(15)

This variable step will allow the maximum power

tracker to converge faster to the maximum power point and

will decrease power oscillations due to large values of ΔVdc

when maximum power is achieved. For protection the value of

ΔVdc is limited. The ΔVdc limit can be changed based on the

generator size and design parameters.

B. DC/DC Converter Controller

Fig 5 Typical DC-to-DC Converter Controller

The maximum power tracker will generate a reference voltage

that will be used to control the dc voltage at the rectifier dc

side terminals. The dc-to-dc converter uses a simple feedback

controller. The dc voltage reference is compared to the actual

dc voltage, and the error signal is fed to a PI controller. The

output signal is compared with a fixed frequency repetitive

triangular waveform to deliver a signal that will turn ON or

OFF the switch. This is shown in Fig 5.

C. Control of ESS and BC

The ESS and the BC are used to suppress the

generator output power fluctuation in normal conditions by

absorbing or releasing the pulsated power component from or

to the grid, in which the power command, P*ESS, is obtained

through a high-pass filter to the generator power [20]. The

ESS power is regulated by an outer PI regulator, whereas the

EDLC current is controlled by an inner PI regulator.

Fig. 6. Control block diagram of the ESS and BC.



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D. DC-Link Voltage Control

During grid sags, the dc-link voltage of the back-to-

back converters is controlled by the ESS instead of the LSC.

Hence, an outer PI voltage controller is employed, which

produces a current reference for an inner PI current controller.

Fig. 6 shows the overview control block diagram of the ESS

and the BC in both normal and grid sag conditions.

Neglecting the power losses of the converters and considering

the active power negligible flowing into the grid, the dynamic

equation of the dc-link voltage is expressed as

Pgen-PBC-PESS=0.5C(dV2

dc/dt) (16)

where C is the dc-link capacitance, Pgen is the generator

power, PBC is the power dissipated by the BC, and PESS is the

power of the ESS computed from the ESS voltage, VESS, and

the EDLC current, IESS, as

PESS=VESS*IESS (17)

From (16 ) in order to keep the dc-link voltage constant, the

ESS and the BC should be able to absorb the generator

powerfully.

From the control block diagram shown in Fig. 6, the output of

the dc-link voltage controller, I∗ ESS, is given as

I*ESS=Kp2(Vdc*-Vdc)+

(Vdc*-Vdc) +

(18)

where Kp2 and KI2 are PI controller gains of the dc-link

voltage control. In Fig. 6, IESS_max represents the maximum

current of the ESS.

By expanding a Taylor series of the dc-link voltage at

operating point Vdc0, the following can be obtained:

V2

dc=V2

dc0+2Vdc0(Vdc-Vdc0) (19)

From (16)–(19), the dc-link voltage equation can be rewritten

in the “s” domain as

CVdc0sVdc=-VESSKp2(Vdc*-Vdc)-VESS

(Vdc*-Vdc) (20)

The transfer function of the voltage controller is derived as

[21]

∗ =

(21)

where ξ is the damping ratio, and ωn is the natural frequency.

It is indicated in (21) that the transfer function has a zero and

two poles, which are always located in the left-half plane.

Hence, control stability is achieved.

E. EDLC Current Control

To establish the current control law for the dc/dc converter, a

voltage across the inductance, VLf , is investigated.

The dynamic equation of the inductance voltage is expressed

as [22], [23]

VLf=Lf

=DESSVdc-VESS (22)

VLf=Lf

=DESSVdc-VESS (22)

where Lf is the boost inductance, and DESS is the duty cycle.

As shown in Fig. 6, the output of the current controller, V ∗Lf ,

is given as

V*Lf=Kpc(I*ESS-IESS)+

(I*ESS-IESS) (23)

where Kpc and KIc are PI controller gains of the current

control.

The duty cycle is calculated by

DESS=(VESS+V*Lf)/Vdc (24)

Then, the gating signals for switches S1 and S2 are generated

by comparing the duty cycle with the carrier wave of 2 kHz as

shown in Fig. 6.

F.BC Control

During the grid disturbance, the ESS may not absorb the full

generator power, and then the BC will be activated to dissipate

the rest of power, PBC as

PBC=Pgen-PESS (25)

The BC is controlled by the switch S3 shown in Fig. 6.The

duty ratio DS3 for the switch depends on PBC, which is

expressed as

DS3=

PBC (26)

where Rbc is the braking resistance.



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G.Control of LSC

The LSC controls the dc-link voltage, Vdc, to be

constant under normal conditions. Cascaded control structure

with an inner current control loop and the outer dc-link

voltage control loop is applied . During grid voltage sags,

however, the dc-link voltage is controlled by the ESS. Hence,

the LSC is exploited as a STATCOM to supply the reactive

current to the grid according to the requirements of the grid

code. For this, the control strategy of the LSC is a voltage-

controlled current source, in which the LSC is operated as a

current source .

In the case of unbalanced grid sags, the dual-current

controllers for positive- and negative-sequence components

are adopted for the LSC. The control block diagram of the

LSC is shown in Fig. 7. In normal operation, the current

references for positive- and negative-sequence current

controllers are calculated from the output of the dc-link

voltage controller as shown in Fig. 7 . During grid sags, dc-

link voltage control by the LSC is deactivated, and the LSC

injects the reactive current component. Hence, the reference of

the active current component, Ip*

qe is set to zero

Ip*

qe =0 (27)

Fig. 7. Control block diagram of LSC

The dq-axis current references In*

dqe, of negative-sequence

components are set to zero to eliminate the unbalanced current

components flowing into the grid, which are expressed as

In*

qe =0 (28)

In*

de =0 (29)

A proportional-integral (PI) controller is usually used

for dc-link voltage control. Hence, an error accumulation in

the integral regulator should be considered for fast transition

when the dc-link voltage controller is reactivated after fault

clearance. The PI controller is implemented in a discrete time

domain. The actual dc-link voltage is able to track its

reference by ESS control during the sag. Hence, an initial

accumulated error, ΔVdc_I_int, of the integral regulator is set

to zero as

ΔVdc_I_int = 0. (30)

IV SIMULATION RESULTS

To perform the feasibility of the proposed scheme, Matlab simulations have been performed for a PMSG wind turbine system. The system parameters for the simulation are listed in Appendix .

Fig 8 shows the variation of the wind speed and its

corresponding output voltage of the PMSG. With the increase

in wind speed the power fed to the grid also increases which is

indicated by an increase in magnitude of PMSG phase voltage.

At t =2.4 s, wind speed is changed from 8 to 12 m/s in step,

whereas tip-speed ratio is maintained at Cp maximum in

steady state conditions.

Fig 8 (a) wind Speed (b) Phase voltage



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Fig 9 (a) Grid voltage (b) Grid Current

Fig 9 shows the performance of the LSC at voltage sags. Fig.

9(a) shows the grid voltage, where three grid-phase voltages

drop to 20%, 20%, and 50%, respectively, during 0.5 s. Fig

9(b) shows the grid current which increased during the fault

condition

Fig 10(a) Grid Voltage (b) DC-Link Voltage

The two-phase grid voltage interruption is considered

as shown in Fig. 10(a) .With the proposed system, the dc-link

voltage is controlled well by the ESS, which is shown in

Fig.10(b). The increase in the dc-link voltage is less than

1.5%.

Fig. 11 shows the performance of the ESS and the

BC. The dc link voltage is controlled well as shown in Fig.

11(a), in which its transient value is less than 2.5%. Fig. 11(b)

shows the ESS powers, in which the control performance is

good for normal conditions. When the grid fault occurs, the

power controller is deactivated, and the power is absorbed by

the ESS as seen in Fig. 11(b) to maintain the dc-link voltage.

The current control performance is shown in Fig. 11(c). Since

the ESS is not able to absorb the full generator power, the rest

of the power is dissipated by the BC. The BC current is shown

in Fig. 11(d). When the EDLC absorbs the power from the

wind system, the EDLC voltage is increased as shown in Fig.

11(e).

Fig. 11. Performance of ESS and BC under unbalanced sag (a) DC-link voltage. (b) ESS power. (c) EDLC current. (d) Braking chopper current. (e)

EDLC voltage.

CONCLUSION

This paper has proposed the maximum power point

tracking algorithm to extract maximum energy from wind

turbine system and combines the ESS and the BC for the

LVRT in PMSG wind turbine systems which is an cost

effective solution. The maximum power was tracked by

searching the rectified dc power, rather than environmental

conditions, such as wind speed and direction. Controlling the

dc-link voltage by the ESS, the LSC is able to comply with the

reactive current requirements of the grid code. By this, the

grid voltage can be recovered rapidly without an external

STATCOM after fault clearance. Also, the output power

fluctuation of the wind turbine system operating in steady state

is smoothened by the ESS. This control scheme offers an FRT



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capability for the wind turbines even though the grid voltage is

fully interrupted.

Appendix:

PMSG parameters: Stator resistance Rs=2.1Ω, Stator

Inductance: 0.00083mH, inertia J= 0.01197 kgm2, magnetic

flux Φ=0.118 Wb and number of poles=4.

Converter parameters: Low voltage side capacitor C1=500μF,

High voltage side capacitor C0=3600μF, Inductor L=200mH,

Switching frequency fd=20kHz, system frequency f=50Hz.

ESS and BC parameters: ESS power ratingPESS-rated -0.6 KW,

Capacitance of EDLCCEDLC-100 F, Operating VoltageVESS-

440 V,Power rating of BCPbc-rated-1.13 KW,Resistance Rbc-1.5

Ω

REFERENCES

[1] Rahul Nema, Anurag Trivedi “Application of Super Capacitor

Based Energy Storage System for Power Quality Improvement

of a Decentralized Power Plant” IEEJ Trans vol 04 no 1 pp 846-

855

[2] H. Li and Z. Chen, “Overview of different wind generator

systems and their comparisons”, in IET Renewable Power

Generation, Vol. 2, No. 2, pp. 123-138, 2008.

[3] Rajveer Mittal, K.S. Sandhu and D.K. Jain., “An Overview of

Some Important Issues Related to Wind Energy Conversion

System (WECS)”, International Journal of Environmental

Science and Development, Vol. 1, No. 4, pp. 351-362, October

2010.

[4] Z. Chen and E. Spooner, “A Modular Permanent Magnet

Generator for Variable Speed Wind Turbines” in proceedings of

IEE EMD, pp. 453- 457, 1995

[5] Alejandro Rolán, Álvaro Luna, Gerardo Vázquez, Daniel Aguilar

and Gustavo Azevado, “Modelling of a Variable Speed Wind

Turbine with a Permanent Magnet Synchronous Generator”, in

proceedings of IEEE International Symposium on Industrial

Electronics ISIE, pp. 734-739, July 2009.

[6] Rajveer Mittal, K.S. Sandhu and D.K. Jain., “Low Voltage Ride

Through of Grid Interfaced Wind Driven PMSG”, ARPN

Journal of Engineering and Applied Sciences, Vol. 4, No. 5, pp.

73-83, 2009

[7] B. Singh, R.Saha, A. Chandra, K. Al. Haddad, “Static

Synchronous Compensators”, IET Power Electronics, Vol. 2,

Issue.4, pp. 297-324, 2009

[8] Yingdong Wei, Lucheng Hong, Qirong Jiang and Zhiyong Wang,

“ A New Dynamic Strategy for Ride Through Capability of

Wind Turbine Generator”, Power and Energy Society General

Meeting, pp. 1-6, 2011

[9] A. Mullane, G. Lightbody and R. Yacamini, "Wind-turbine fault

ride through enhancement," IEEE transactions on Power

Systems, Vol.20, No.4, pp. 1929- 1937, Nov. 2005.

[10] Remus Teodorescu and Frede Blaabjerg, "Flexible Control of

Small Wind Turbines with Grid Failure Detection Operating in

Stand Alone and Grid Connected Mode," IEEE Transactions on

Power Electronics, vol. 19, No.5, pp.1323-1332, September

2004.

[11] Mazen Abdel-Salam, Adel Ahmed and Mahmoud Mahrous,

“Transient Analysis of Grid Connected Wind Driven PMSG,

DFIG and SCIG at Fixed and Variable Speeds”, Innovative

Systems Design and Engineering, Vol. 2, No. 3, 2011

[12] J. F. Conroy and R. Watson, “Low Voltage Ride Through of a

Full Converter Wind Turbine with Permanent Magnet

Generator”, IET Renewable Power Generation, Vol. 1, No. 3,

pp. 182-189, 2007

[13] P. Rodriguez, A.V. Timbus, R. Teodorescu, M. Liserre and F.

Blaabjerg, "Flexible Active Power Control of Distributed Power

Generation Systems During Grid Faults," IEEE Transactions on

Industrial Electronics, vol.54, no.5, pp.2583-2592, Oct. 2007.

[14] P. Rodriguez, A.V. Timbus, R. Teodorescu, M. Liserre and F.

Blaabjerg, "Independent PQ Control for Distributed Power

Generation Systems under Grid Faults," In Proc. of IEEE 32nd

Annual Conference on Industrial Electronics, pp.5185-5190,

Nov. 2006.

[15] P. N. Enjeti and S. A. Choudhury, “A New Control Strategy to

Improve the Performance of a PWM AC to DC Converter Under

Unbalanced Operating Conditions,” IEEE Transactions on

Power Electronics, Vol. 8, pp. 493–500, Oct. 1993.

[16] P. Rioual, H. Pouliquen, and J. Louis, “Regulation of a PWM

Rectifier in the Unbalanced Network State Using a Generalized

Model,” IEEE Transactions on Power Electronics, vol. 11, pp.

495–502, May 1996.

[17] Spera DA. Wind turbine technology: fundamental concept of

wind turbine engineering. New York: ASHE Press; 1994.

[18] Bhadra SN, Kastha D, Banerjee S. Wind electrical systems.

Oxford, UK: Oxford University Press; 2005.

[19] Mohammad H. Rashid. Power electronics-circuit. Devices and

application. 3rd ed; 2004.

[20] T. H. Nguyen, D.-C. Lee, S.-H. Song, and E.-H. Kim,

“Improvement of power quality for PMSG wind turbine

systems,” in Proc. IEEE ECCE, Sep. 2010, pp. 2763–2770.

[21] T. H. Nguyen and D. C. Lee, “Ride-through technique for

PMSG wind turbine using energy storage systems,” J. Power

Electron., vol. 10, no. 6, pp. 733–738, Nov. 2010.

[22] R. J. Wai and L. C. Shih, “Design of voltage tracking control for

DCDC boost converter via total sliding-mode technique,” IEEE

Trans. Ind. Electron., vol. 58, no. 6, pp. 2502–2511, Jun. 2011.

[23] E. Babaei, M. E. S. Mahmoodieh, and M. Sabahi, “Investigating

buck DCDC converter operation in different operational modes

and obtaining the minimum output voltage ripple considering

filter size,” J. Power Electron., vol. 11, no. 6, pp. 793–800, Nov.

2011.

[24] Shuhui Li and Tim A. Haskew, “Characteristics Study of Vector

– Controlled Direct Driven Permanent Magnet Synchronous

Generator in Wind Power Generation”, in proceedings of IEEE

Power and Energy Society General Meeting - Conversion and

Delivery of Electrical Energy in the 21st Century, pp. 01-09,

2008.
