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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-
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
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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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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
Rated frequency 60 Hz
Connection Y/Y
Primary voltage (L-L/rms) 138 kV
Secondary voltage (L-L/rms) 11 kV
Transformer (T2)
Rated power 3.6 MVA
Rated frequency 60 Hz
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
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
Real Power/p.u.
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-0.5
0
0.5Reactive 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. 7 System dynamic responses at bus 2
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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
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
Fig. 8 System dynamic responses at bus 3
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
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
Fig. 9 System dynamic responses at bus 4
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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
Voltage (L-L rms)/p.u.
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
0.5Reactive 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. 10 System dynamic responses at bus 5
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
0.250.5
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
0.5Reactive 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. 11 System dynamic responses at bus 6
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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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Voltage Stabilization of Stand Alone Hybrid (Wind/Small Hydro) Schemes',
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KICHIRO YAMAMOTO,TAKAMICHI SARUBAN, and TAKAHIRO
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