Power System Wind Energy

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International Journal of Emerging

Electric Power Systems

Volume 8, Issue 3 2007 Article 6

A Novel Modulated Power Filter Compensator

for Distribution Networks with Distributed

Wind Energy

Adel M. Sharaf Weihua Wang

Ismail H. Altas

University of New Brunswick, Dept. of Electrical and Electronics Engineering,

[email protected] of New Brunswick, Dept. of Electrical and Computer Engineering, [email protected] Technical University, Dept. of Electrical and Electronics Engineering, ihal-

[email protected]

Copyright c2007 The Berkeley Electronic Press. All rights reserved.


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A Novel Modulated Power Filter Compensator

for Distribution Networks with Distributed

Wind Energy

Adel M. Sharaf, Weihua Wang, and Ismail H. Altas

Abstract

During the last two decades, renewable wind energy has become increasingly popular as aconsequence of strong ecological concerns and appealing advantages with regard to economical

energy solutions in remote communities. Furthermore, with very large wind farms emerging, the

dispersed renewable wind energy is required to be fully connected to the electrical distribution net-

works. However, the integration of dispersed renewable wind energy will pose a great challenge

to the power quality in the distribution networks when the weak nature of the grid in remote areas

and the uncertainty of wind are taken into consideration.

This paper presents a novel Modulated Power Filter Compensator (MPFC) for the distribution

networks with dispersed renewable wind energy interfaced. A tri-loop error driven controller is

used to adjust the PWM switching of the modulated power filter compensator. Full power factor

correction and power quality improvement is validated under different operation conditions, like

load switching and wind velocity excursions. The MPFC device is a member of novel FACTS

based compensators developed by the first author.

KEYWORDS: Modulated Power Filter Compensator, reactive power compensation, power qual-

ity, renewable wind energy

I. H. Altas wishes to thank the Scientific and Technological Research Council of Turkey for the

financial support during this work. He is currently a visiting scholar at the University of New

Brunswick.


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I. INTRODUCTION

Wind is an abundant renewable source of energy, which is usually obtained by

converting part of the kinetic energy in the moving air into electricity. Wind

renewable energy is also a clean energy source, that is, operating without

producing carbon dioxide, sulfur dioxide, particulates or any other type of air

pollution[1-2]. Demand for electrical energy from renewable sources is rapidly

increasing as industrialized societies are becoming more aware of and concerned

about fossil fuel shortage and environmental impacts [3]. Besides hydro-power,

which is already well established, wind energy is by far one of the most

technically advanced and promising renewable energy sources. In many countries,

the potential for wind energy production exceeds by far the local consumption ofelectricity. By 2005, the worldwide capacity had been increased to 58,982

megawatts and the World Wind Energy Association expects 120,000 MW to be

installed globally by 2010. Germany is the leading producer of wind power with a

capacity of 18,428 megawatts in 2005, which accounts for 6% of German

electricity in the same year [4].

Recently, with the technological improvement in new materials, fabrication

technology, as well as new wind blade, gear box and induction generator designs

and manufacturing methods, both the size of wind turbine blades and the volume

of commercial production have been steadily increasing to the point where typical

peak output is currently in the range of several megawatts [5-6]. In this case, thegrid integration of large wind renewable energy becomes significant and arouses

great interest from the society [2].

However, increased penetration of dispersed and distributed wind energy

creates a new serious uncontrollable scenario in electric power grid system. On

one hand, dynamic variations and wind velocity excursions cause excessive

changes in prime mover power and the corresponding electrical power injected

into the grid utility network. Depending on intensity and rate of wind changes,

difficulties with generator output frequency variations and severe generator

voltage stabilization could result in possible loss of excitation and frequent

shutdowns as well as severe power quality issues, such as voltage distortions and

variations in its output electrical energy [7]. On the other hand, based on

economic and aesthetic considerations, wind farms and distributed wind

generation schemes are usually planned and installed in rural, mountain and

coastal areas with annual favorable wind utilization regimes, where the

1

Sharaf et al.: MPFC for Distribution Networks with Distributed Wind Energy

Published by The Berkeley Electronic Press, 2007


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distribution/utilization electric grid networks are usually of radial structure and are

electrically weak with low short circuit ratios [7-8].

From the distribution grid point of view, reactive power compensation is animportant issue. Excessive reactive current increases distribution losses, reduces

system power factor and causes large variations in bus voltages. Moreover, power

quality, voltage swells and sags issues as well as harmonic propagation are other

aspects that require attention with dispersed wind energy interface and wind farm

installations. Proper studies of impact and penetration levels of the wind farms

protection gear mal-operation, islanding hazards and other issues of degraded

power quality and harmonics with possibility of harmonic resonances are required

to be dealt with. [9]

Consequently, it is necessary to provide effective technical solutions for both

power quality and security aspects related to electric grid integration withdistributed wind farms and dispersed wind energy schemes. Fortunately, the new

emerging FACTS technologies can perform new stabilization and control

functions due to rapid power control provided by fast switching devices and

especially voltage source converters [10]. The applications of FACTS based

schemes for standalone wind energy were studied in [3, 11-12]. By far, the Static

VAR Compensator (SVC) has been the extensively utilized FACTS based devices

that can maintain a constant voltage by continuously adjusting reactive power

flow through the grid-connected WECS. To ensure proper operation of the SVC,

various mathematical models and control strategies have been developed.

Numerous studies have been performed dealing with the steady state and transientcondition using a number of simulation platforms [13]. E.S. Abdin proposed two

controllers for the SVC and the digital simulation results have validated good

damping and fast system recovery from different types of large disturbances and

excursions [14]. A Harmonic mitigation scheme using an Active Power Filter for a

wind energy generation system was also investigated in [15]. A Unified Power

Flow Controller (UPFC) for power flow control and voltage regulation under

different types of wind speed changes was studied in [7].

This paper focuses on the impact of a dispersed renewable wind energy scheme

integrated into distribution network on operation, voltage and frequency

stabilization, as well as the need of novel FACTS stabilization devices and control

strategies such as the low cost Modulated Power Filter Compensator (MPFC)

developed by the first author. Comparing with the conventional FACTS devices,

the novel MPFC has the advantage of simple structure and low cost, since no line

commuted converter is involved in the MPFC scheme. In this paper, the

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International Journal of Emerging Electric Power Systems, Vol. 8 [2007], Iss. 3, Art. 6

http://www.bepress.com/ijeeps/vol8/iss3/art6


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effectiveness of the proposed MPFC scheme for both power quality improvement

and power factor correction is fully validated using MATLAB/SIMULINK

software environment.

II. Wind Energy Conversion Schemes (WECS)

1. Wind turbine modelThe wind turbine model is developed based on the steady-state power

characteristics of the turbine. The stiffness of the drive train is infinite and the

friction factor and the inertia of the turbine must be combined with those of the

generator coupled to the turbine [16]. The mechanical power captured by a windturbine depends on its power utilization coefficient Cp for a given wind velocity v,

and can be represented by:

Pm =1/2Cp*S**v3

(1)

where, S is the area swept by the rotor blades, v is the wind velocity and is

its density. Coefficient Cp is a nonlinear function of two magnitudes: the pitch

angle of rotor blades and tip speed ratio , which is the quotient between the

tangential speed of the rotor blade tips and the undisturbed wind velocity [17]. A

general equation used to model Cp (, ), based on the modeling turbinecharacteristics [1], is given by:

3

21 3 4 6( , )

i

c

p

i

CC C C C e C

= +

(2)

and with

31 1 0.0350.08 1i

= + + . (3)

The coefficients C1 to C6 are: C1= 0.5176, C2= 116, C3= 0.4, C4 = 5, C5 = 21 and

C6 = 0.0068. In this research, a constant pitch angle is used and the value is

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assigned as 0. The based wind speed is selected at 12 m/s and the base rotational

speed is set at 1.2 times of the generator synchronous speed. The turbine power

characteristics of the model employed in this paper is shown in Figure 1.

2. Electrical generatorTo convert mechanical energy to electrical energy, generally three-phase

synchronous or asynchronous generators are used. For the wind energy systems,

asynchronous generators are preferred due to their operating characteristics and

compatibility with variable wind speed ranges. The output voltage of the

generator is dependent on the construction of the generator, the rotation speed of

the rotary field, the excitation, and the load characteristics.

0 0.2 0.4 0.6 0.8 1 1.2 1.4-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.2 pu

Max. power at base wind speed (12 m/s) and beta = 0 deg

6 m/s7.2 m/s

8.4 m/s

9.6 m/s

10.8 m/s

12 m/s

13.2 m/s

14.4 m/s

Turbine speed (pu of nominal generator speed)

Turbineoutputpower(pu

ofnominalmechanicalpower)

Turbine Power Characteristics (Pitch angle beta = 0 deg)

Fig.1 Power characteristics of the wind turbine model under study

It is common sense that the asynchronous machine can go over to generating

power, if its shaft is rotated at super-synchronous speed in the same direction as

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that of the air gap flux, so that the slip become negative and a negative or

regeneration torque is created.

Asynchronous generators with squirrel cage are by far the most common typeof generator for mechanical-electrical energy conversion in wind power plants,

since they are remarkable for their extremely simple but robust construction.

Because of their high operating security, they can be possibly with rough

handling.

However, the asynchronous generator can only deliver real power to the grid,

but it need reactive power supported by the grid or capacitor bank in parallel

connected to its stator terminals. As a result, it may potentially bring heavy

reactive power burden to the grid.

Fig.2 Control block diagram of inverter in WECS grid integration interface

3. Power electronics based interfaceThe Wind Energy Conversion Schemes (WECS) can be connected as stand-alone

for supplying power to the loads in remote areas, or connected to the electric grid

system [1, 16]. WECS are further classified based on their output AC voltage and

frequency into three schemes, such as Variable Voltage-Variable Frequency

(VV-VF), Constant Voltage-Variable Frequency (CV-VF), and constant

voltage-constant frequency (CV-CF) [18].

Without power electronics based interface, the WECS is only suitable for

extremely rigid grid coupling. [1] When it comes to grid integration of dispersed

renewable energy, classic AC-DC-AC converters are normally used to adjust the

generator output voltage and frequency.

In this paper, the three phase full wave uncontrolled bridge functions as the

rectification stage and a pulse-width-modulated (PWM) switching strategy is

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employed to guarantee a nearly stable voltage and minimal frequency excursions

caused by the stochastic temporal nature of wind variations and changes in prime

mover power from wind generation scheme. The d-q transformation basedProportional and Integral (PI) controller shown in Figure 2 is designed to generate

proper pulses to modulate the switching of the inverter.

The phase locked loop (PLL) is responsible for strict synchronizing the inverter

output voltage with the grid voltage [19]. The synchronization signal is obtained

from the grid side voltage of the WECS grid integration interface.

III. SYSTEM DESCRIPTION

1. Sample Study System ConfigurationA sample distribution network with dispersed renewable wind energy is studied

under a sequence of excursions, such as load switching and wind speed variations.

Figure 3 depicts a single-line diagram of the sample study system.

L.L.1

138/11kV

5MVA

Wind Turbine

L.L.2 L.L.3

11/4.16kV

600kVA

Induction

Motor

N.L.L

4.16/11kV

3.6MVA

AC

DC

DC

AC

I.G.

Infinite Bus

138kV/60HZ

bus2bus1 bus3 bus4 bus5 bus6

T2

T1

T3

MPFC

Fig. 3 Single-line Diagram of the Sample Study Distribution System

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The system shown in Figure 3 is an 11 kV distribution network with dispersed

renewable wind energy, 4 linear loads at power factor 0.8 lagging, motorized load

and converter type nonlinear load. Except the wind energy interfaced at bus 2 andthe one at the main in-feed point representing an infinite bus as 138 kV, there is no

other generation unit in the system. In this case, bus3, bus4, bus5 and bus 6 are

meshed in radial structure. Two step-down transformers are used at the main

in-feed point and at the bus 5 where a 4160V/600kVA motor is connected and a

step-up transformer is employed for WECS grid integration. The detail parameters

of the system under study are given in Table 1.

The FACTS-based devices were also proposed to be located at the dominant

load bus with nonlinear and motorized loads, other than the WECS grid

connection interface where traditional reactive compensation schemes are

connected. The new idea achieves combined voltage stabilization for the WECSwind interface and the power factor correction at the key nonlinear load bus with

improved power quality and reduced harmonics. This arrangement can reduce the

number of reactive power compensation devices in the distribution networks and

hence reduce the cost.

2. Modulated Power Filter Compensator (MPFC)The proposed MPFC is a member of novel FACTS based devices and

compensators develped by the First Author. Figure 4 displays the function model

of the proposed MPFC. The MPFC is composed of a capacitor, an inductor, aresistor, two PWM wave controlled IGBT switches and a three phase diode bridge.

The capacitor rating at 225F per phase is connected to the AC side of the diode

bridge, while a 0.15 ohms resistor and a 0.1 mH inductor are located at DC side of

the diode bridge. The two IGBT switches are controlled by two complementary

pulses and the topology of the MPFC circuit and hence the equivalent admittance

can be changed with different states of the complementary pulses. If S1 is open

and S2 is closed, the resistor and inductor will be connected into the circuit; if S1

is closed and S2 is open, the resitor and inductor will be shorted.

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Tab. 1 Power system configuration

Wind Turbine Model Transformer (T3)

Nominal wind speed 15 m/s

Nominal mechanical

Output power 3.6 MW

Based rotational speed

(p.u. of synchronous speed) 1.2

Induction Generator

Rated power 0.6MVA

Rated frequency 60 Hz

Connection Y/Y

Primary voltage (L-L/rms) 11 kV

Secondary voltage (L-L/rms) 4.16 kV

Distribution Feeder

Length 3 km/section

Resistance 0.25 ohms/kmInductance 0.93 mH/km

Hybrid Loads

Nominal power (based) 3.6 MVA

Nominal voltage 4160 V

Nominal frequency 60 Hz

Local capacitor bank 441F

Stator resistance 0.019 p.u

Stator inductance 0.06 p.u.

Rotor resistance 0.019 p.u.

Rotor inductance 0.06 p.u.

Transformer (T1)

Linear loads

Active power 1.2 MW

Reactive power 0.9 MVAR

Nonlinear loads

Active power 1.6 MW

Reactive power 1.2 MVAR

Rated power 5 MVA


Connection Y/Y

Primary voltage (L-L/rms) 138 kV

Secondary voltage (L-L/rms) 11 kV

Transformer (T2)

Rated power 3.6 MVA


Connection Y/

Primary voltage (L-L/rms) 4.16 kV

Secondary voltage (L-L/rms) 11 kV

Motorized loadNominal power (based) 0.6 MVA

Nominal voltage 4160 V

Nominal frequency 60 Hz

Stator resistance 0.019 p.u

Stator inductance 0.06 p.u.

Rotor resistance 0.019 p.u.

Rotor inductance 0.06 p.u.

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Fig. 4 The functional model of modulated power filter compensator (MPFC)

3. Novel tri-loop dynamic error driven PI controllerThe MPFC is controlled by a novel tri-loop dynamic error driven PI controller

developed by the first author [3]. The tri-loops compute the global error (et) using

the phase to phase Root-Mean-Square (RMS) voltage, phase RMS current, and

current harmonics, as shown is figure 5. The main loop is the voltage stabilization

loop, which functions as tracking the error of the root mean squared value of load

voltage at the radial distribution bus 5 and maitaining the voltage at 1.0 per unit.

The second loop is the load bus current dynamic error tracking loop, which is an

auxiliary loop to compensate for any sudden electrical load excursions or wind

velocity variations. The third loop is the current harmoics dynamic tracking loop,

a supplementary loop used for sensing and minimizing the harmonic component

of the current.The scaling and time delay of these loops were selected by an

offline guided trial and error method to insure fast response [16].

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Fig.5 Tri-loop dynamic error driven PI controller

The total error signal (et) of the three basic loops is fed to the PI controller

whose proportional and integral gains are 1 and 10, respectively. The output signal

of the PI controller is assigned as the reference voltage of the Pulse Width

Modulation (PWM) and it is compared with a fixed carrier signal to produce two

complementary pulses. In other words, the modulation index can be adaptively

controlled in this controller. The full parameters of the novel tri-loop dynamiccontroller are given in Table 2.

Tab. 2 Parameters of the novel tri-loop dynamic controller

Tri-loop weighting gains PI controller

RMS voltage loop gain (v) 0.8

RMS current loop gain (i) 0.4

Harmonics loop gain (h) 0.5

Loop2 Time Delay 0.001 seconds

Proportional gain (Kp) 1

Integral gain (Ki) 10

Maximum limit 1

Minimum limit 0

IV. DIGITAL SIMULATION AND RESULTS

The proposed novel FACTS based schemes for distribution networks with

distributed/dispersed renewable wind energy are digitally simulated under

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MATLAB/SIMULINK software environment. The built-in functional blocks in

SIM-POWER toolbox facilitate the simulation of large and complicated power

system. Discrete simulation mode with a sample time of 0.1 milliseconds will beapplied to the simulation of the controller to accelerate the simulation speed.

The digital simulation is carried out with and without the controlled MPFC

located at Bus5 for 0.8 seconds in order to show its performance in volatge

stabilization, harmonic reduction, and reactive power compensation. The dynamic

performance of the proposed MPFC is tested under the following disturbance

sequence:

At t = 0.1second, induction motor is removed at bus 5 for a duration of 0.1

seconds;

At t = 0.3second, linear load is removed at bus 4 for a duration of 0.1 seconds;At t = 0.5 second, wind speed suddenly decreased to 9 m/s for a duration of 0.1

seconds;

At t = 0.6second, wind speed suddenly increased to 21 m/s for a duration of 0.1

seconds;

At t = 0.7 the system was recovered to its initial state.

The dynamic responses of voltage, current, real power, reactive power and

power factor at each bus are shown from Figure 6 to Figure11.

From the simulation results, significant transients can be observed, when the

system is suffering from the disturbances. The transients are dramaticallymitigated by using proposed MPFC, since both the amplitude and duration of the

oscillation has been reduced.

Besides transient mitigation, the proposed MPFC is also powerful for power

factor correction and regulating voltage profile along the feeder, since reasonalble

amount of reactive power can be injected into the grid according to its demand. It

can be observed that all power factors along the feeder are improved above 0.85

and unit power factors are even achieved at bus 3, bus 4 and bus 5. A plot for

steady-state voltage profile is depicted in Figure 12. From Fig.12, it can be

noticed that the largest voltage drop is only 5.5% in case of with MPFC

compensation, while the largest voltage drop comes to 14.0% in case of without

MPFC compensation.

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80.5

0.751

1.25

Voltage (L-L rms)/p.u.

with compensation

without compensation

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

1.5

Current (rms)/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

1.3Real Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-0.5

0

0.5Reactive Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Time/Second

Power Factor

Fig. 6 System dynamic responses at bus 1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80.5

0.751

1.25


with compensation


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

1.5

Current (rms)/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Real Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-0.5

0


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Time/Second

Power Factor


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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80.5

0.751

1.25


with compensation


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Current (rms)/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.250.5

0.751

Real Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-1

0

1Reactive Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Time/Second

Power Factor


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80.5

0.751

1.25


with compensation


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Current (rms)/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.5

1Real Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-1

0

1Reactive Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Time/Second

Power Factor


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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80.50.75

11.25


w ith compensation

w ithout compensation

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

1.5Current (rms)/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.250.5

0.75

Real Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

-0.5

0


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Time/second

Power Factor


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80.5

0.751

1.25


with compensation


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.250.5

0.751

Current (rms)/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.25

0.5Real Power/p.u.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.25


0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.51

Time/Second

Power Factor


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1 2 3 4 5 60.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1

1.02

Bus Number

Voltage(RMS/p.u)

With Compensation

Without Compensation

Fig.12 Steady-state voltage profile along the feeder

Comparison of harmonics at each bus is made in case of with and without

MPFC. Voltage and current harmonic analysis in term of the total harmonic

distortion (THD) and magnitude of certain low order harmonics are displayed in

Table 3 and Table 4 respectively. It is obvious that the voltage harmonics are

significantly reduced to a level within the limit set by the IEEE Std.519-1992

regarding the THD of bus voltage at low voltage system (less than 69 kV) [20].

However, the proposed MPFC scheme is not very effective for the current

harmonics elimination.

Furthermore, the dynamic performances of the WECS are also studied both in

case of with MPFC and without MPFC. The output voltage of the WECS is

depicted in Figure 13. The WECS can be highly regulated by the proposed MPFC

scheme, because sufficient reactive power can be fed to the induction generator

used in the WECS.

Finally, the critical control signals of the tri-loop dynamic error driven

controller are displayed, including the phase portrait of the three weighted errors

in the three basic error driven loops (Figure 14) and the total error (e t) (Figure 15).

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-2

-1

0

1

2

Time/second

Voltage/p.u.

WECS Output Voltage in case of with MPFC

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-4

-2

0

2

Time/second

Voltage/p.u.

WECS Output Voltage in case of without MPFC

Fig.13 The output voltage of the WECS under study

Tab.3 Voltage harmonics in the distribution networks under study

Bus

No.

Case*

THD Fundamental

p.u.

3rd

p.u.

5th

p.u.

7th

p.u.

9th

p.u.

A 9.00% 0.971 0.013 0.061 0.033 0.0011

B 4.90% 1.016 0.003 0.005 0.010 0.002

A 10.4% 0.942 0.016 0.069 0.036 0.0012

B 4.60% 1.000 0.004 0.003 0.028 0.001

A 11.9% 0.929 0.019 0.078 0.042 0.0023

B 4.29% 0.994 0.004 0.004 0.032 0.001

A 12.0% 0.888 0.019 0.067 0.027 0.0044

B 3.51% 0.989 0.005 0.019 0.007 0.0003

A 12.8% 0.852 0.019 0.065 0.024 0.0085

B 3.32% 0.993 0.006 0.035 0.019 0.0007A 14.3% 0.824 0.020 0.073 0.024 0.0126

B 3.57% 0.962 0.007 0.012 0.013 0.002

*Case A: Distribution network without MPFC/Case B: Distribution network with MPFC

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Tab.4 Current harmonics in the distribution networks under study

Bus

No.

Case*

THD Fundamental

p.u.

3rd

p.u.

5th

p.u.

7th

p.u.

9th

p.u.A 28.36% 0.761 0.013 0.06 0.03 0.0011

B 2.50% 0.777 0.003 0.005 0.010 0.016

A 7.15% 0.650 0.018 0.038 0.013 0.0022

B 28.88% 0.693 0.002 0.005 0.012 0.002

A 44.63% 0.829 0.019 0.092 0.060 0.0113

B 9.28% 0.856 0.009 0.073 0.080 0.002

A 44.59% 0.686 0.017 0.090 0.060 0.0134

B 11.8% 0.809 0.009 0.070 0.081 0.002

A 44.54% 0.562 0.019 0.065 0.021 0.0085

B 12.3% 0.794 0.010 0.076 0.081 0.002

A 43.02% 0.376 0.014 0.091 0.061 0.0116

B 25.1% 0.433 0.002 0.118 0.073 0.0005

*Case A: Distribution network without MPFC/Case B: Distribution network with MPFC

0

0.2

0.4

0.6

0.8

0

0.20.4

0.6

0.80

0.1

0.2

0.3

0.4

0.5

Ev*GamaV

The Phase Portrait of Tri-loop Errors

Ei*Gamai

Eh*Gamah

Fig. 14 The phase portrait of weighted errors of the three basic error driven loops

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

Time/second

The total error (Et)/ p.u.

Fig. 15 The total error signal of the tri-loop error driven controller

V. Conclusion

This paper presents a novel PWM switching modulated power filter compensator(MPFC) scheme for use in a weak distribution networks with dispersed renewable

wind energy integrated. The MPFC is controlled by a novel tri-loop dynamic error

driven PI controller. The digital simulation models of the proposed MPFC scheme

have been fully validated for effective power quality (PQ) improvement and

power factor correction. The proposed scheme can be extended and tested in other

distributed/dispersed renewable energy interface systems and can be easily

modified for other specific compensation and voltage stabilization duties.

VI. Reference

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[2] Mohamed S. ElMoursi and Adel M. Sharaf, 'Novel STATCOM Controllers for

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[4] The World Wind Energy Association (WWEA) web site,

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YAMAEMORI, 'Compensation for Harmonic Currents and Reactive Power in

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[20] IEEE Std. 519-1992, 'IEEE Recommended Practices and Requirements for

Harmonic Control in Electrical Power Systems'

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