108
CHAPTER 5
DESIGN OF UPQC FOR POWER QUALITY
ENHANCEMENT USING CONVENTIONAL
PI CONTROLLER
5.1
INTRODUCTION
The advancement of power electronics and digital control
technology has led to increase in the use of the renewable energy sources and
non linear loads in the distribution systems. On the other hand, with the
proliferation of the power electronic devices, nonlinear loads and unbalanced
loads have degraded the power quality in the power distribution network
(Bollen 1999). Owing to increasing demand and the rapid development of the
high power semiconductor technology, the custom power solutions are taking
place rapidly. But in a real time power system, the use of non linear loads
leads to the load current harmonics, load voltage harmonics, neutral current
distortion and load unbalance. So, the various custom power devices are
proposed to enhance the power quality in the system by eliminating the above
effects. The term custom power pertains to the use of power electronic
controllers in a distribution system to deal with various power quality
problems.
5.1.1
Types of Custom Power Devices
There are many types of custom power devices. Some of these
devices include APF, Solid State Fault Current Limiter (SSFCL), Solid-State
Transfer Switches (SSTS), Static VAR Compensator (SVC), Dynamic
109
Voltage Restorer (DVR), Distribution Static Synchronous Compensators
(DSTATCOM) and UPQC.
The compensation type devices are used for active filtering, load
balancing, power factor correction and voltage regulation. The best protection
for sensitive loads from sources with inadequate quality is UPQC. UPQC is
the combination of DSTATCOM and DVR. It injects series voltage and shunt
currents to the system (Khadkikar et al 2006). It is a special versatile custom
power device which consists of two inverters connected back-to-back and
deals with load current and load voltage imperfections and balances the
unbalance loads (Yash Pal et al 2012). UPQC is the best solution to
compensate various power quality problems under non linear load and
unbalance conditions (Han et al 2006).
5.1.2
Advantages and Configuration of UPQC
In this proposed method, UPQC is used to compensate load current
distortion, load voltage distortion, neutral current distortion and balance an
unbalance load. The use of UPQC for non linear and voltage sensitive loads
has the following advantages over other custom devices,
It compensates load current and load voltage distortion and
also balances unbalance loads at single installation.
The voltage injected by UPQC to maintain the load end
voltage at the desired value is taken from the same DC link,
thus no additional DC link voltage support is required for the
series compensator.
UPQC maintains load end voltage at the rated value even in
the presence of supply voltage sag.
110
It consists of series inverter and shunt inverter i.e. it is the
combination of DVR and D-STATCOM which is shown in Figure 5.1.
Figure 5.1 Configuration of UPQC
DVR
compensates the
load
voltage
distortion by
series
compensation whereas the D-STATCOM compensates the load current
distortions by providing shunt compensation. In the proposed method, the
reference signal for UPQC is extracted by using SRF controller along with
PLL (Fatiha Mekri et al 2008). PI conventional controller is used to maintain
the voltage across the dc-link capacitor. Fuzzy-Hysteresis Current Controller
(FHCC) and Fuzzy Hysteresis Voltage Controller (FHVC) are used for
generating switching signals to the shunt and series inverter of UPQC
respectively.
5.2
EFFECTS OF NON LINEAR LOADS WITHOUT UPQC
The three phase diode bridge rectifier connected to 3P4W
distribution causes the load current and load voltage distortion. The effect of
the distortion is shown in Figure 5.2. The distribution system is considered as
an unbalance by connecting three single phase diode rectifier with different
values of loads along with one three phase diode bridge rectifier.
111
Figure 5.2 Effects of non linear loads at PCC
The different loads are connected to the PCC. PCC is also called as
Point of Common Connection. The load currents get distorted due to non
linear loads and the other linear loads connected to the point are also getting
degraded.
5.2.1
MATLAB Model of Distribution System without UPQC
The effects of load currents, load voltages and neutral current are
analyzed by modeling the 3P4W distribution system with diode bridge
rectifier loads. The various system parameters considered for the simulation
are shown in Table 5.1. The MATLAB model of system is shown in
Figure 5.3.
Table 5.1 Simulation parameters of 3P4W distribution system
System parameters
Values
Three phase source voltage V LN
220/110 V
Supply Frequency
50 Hz
Leakage Reactance of the Transformer
0.35mH
Diode bridge rectifier as non linear load
Three single phase diode rectifier load
Single three phase diode rectifier load
112
Figure 5.3 MATLAB model of 3P4W distribution systems without UPQC
The 3P4W distribution system is simulated with diode bridge
rectifier using simulink model. The voltage and current scopes are connected
in each phases to display the load voltage, load current and neutral
waveforms.
5.2.2
Effects of Load Currents, Load Voltages and Neutral Current
The three phase load voltages (VLa, VLb and VLc ) and load currents
(ILa, ILb and ILc ) waveforms which are measured in the simulink model are
shown in Figure 5.4 and 5.5 respectively. The waveforms are distorted due to
the impact of harmonics generated by non linear loads.
113
(a) Phase A load voltage
(b) Phase B load voltage
(c) Phase C load voltage
Figure 5.4 Waveform and THD analysis of load voltage without UPQC
114
(a) Phase A load current
(b) Phase B load current
(c) Phase C load current
Figure 5.5 Waveform and THD analysis of load current without UPQC
115
The load voltages and currents are highly distorted and especially
third order harmonic component is more dominant. The FFT analysis shows
that THD values of load voltages are: VLa is 20.22%, VLb is 22.64% and VLc is
13.37%. Similarly the THD values of load currents are: ILa is 34.37%, ILb is
38.43% and ILc is 34.09%. The magnitudes of load currents are 35.82A,
32.93A and 18.61A which are due to the unbalance of load in each phase.
This leads to the flow of current in the neutral with distortion which is shown
in Figure 5.6. These distortions in the load voltage and load currents degrade
the performance of the distribution system.
Figure 5.6 Waveform of neutral current without UPQC
The magnitude of the neutral current is high and the waveform is
distorted because of unbalance loading in the phase conductors and the impact
of non-linear loads. To make the system balanced, the magnitude of the
neutral current should be reduced.
5.3
BLOCK DIAGRAM OF THE PROPOSED METHOD
In order to enhance the performance of the distribution system the
UPQC model is proposed. UPQC is a combination of 3-leg shunt and series
active filter where shunt active filter compensates the current harmonics and
series active filter compensates the voltage harmonics. The block diagram of
conventional PI controller based UPQC is shown in Figure 5.7.
116
Figure 5.7 Block diagram of the proposed UPQC
The block diagram consists of two back to back connected series
and shunt inverters, the PI controller to maintain the regulated voltage across
the dc-link capacitor, SRF controller to extract the reference voltage and
current signals to compensate the distortion, PLL which is used to
synchronize the phase angle with SRF, FHVC and FHCC to generate the
switching signals to the series and shunt inverters respectively (Bhim Singh &
Venkateswaralu 2010). The equivalent model of UPQC is shown in Figure 5.8.
In the equivalent model, Vs represents the source voltage, V se represents the
voltage compensation by series active filter, Ish is the current compensation by
the shunt active filter, VL is the voltage across the load terminal. Due to
voltage and current distortion, the system may consist of harmonic
components.
117
Figure 5.8 Equivalent model of UPQC
To obtain the sinusoidal load voltage with amplitude V, the output
voltage compensation provided by the series active filter is given by,
Vse
(V VLf ) Sin( t
)
(5.1)
where VLf
phase angle of fundamental component derived from PLL. The shunt-APF
acts as a controlled current source (I sh) and its output components include
harmonics and reactive compensation in order to compensate the load current.
5.3.1
Design of PI Controller
The PI controller is a generic control loop feedback mechanism
widely used in industrial control systems and other applications. PI controller
algorithm involves two separate parameters, the Proportional (P) and the
Integral (I). The proportional value determines the reaction to current error
where as the integral value determines the reaction based on the sum of recent
errors. The equation form of PI controller is given by,
Y (t )
t
K P .e(t ) K I e(t )dt
o
(5.2)
118
KP and KI represent the proportional gain and integral gain
respectively; y(t) represents the output of the controller. The voltage error
value e is fed to the PI controller. The transfer function model of PI controller
is shown in Figure 5.9.
Figure 5.9 Transfer function model of PI controller
To maintain the DC-link voltage at the reference value, the DC-link
capacitor needs a certain amount of real power, which is proportional to the
difference between the actual and reference voltages. The power required by
the dc-link capacitor can be expressed as,
t
Pdc
K P (Vref
Vact ) K I (Vref
Vact )dt
(5.4)
0
If the values of KP and KI are large, DC-bus voltage regulation is
dominant and steady state dc-bus voltage error is low. On the other hand, if
KP and KI are small, the real power unbalance gives little effect to the
transient performance. Therefore, proper selection of K P and KI are essentially
important to satisfy the control performance and maintain power required by
capacitor. In the first approach, KP and KI values are chosen based on trial and
error method.
119
5.3.2
Synchronous Reference Frame Controller
The control scheme for series and shunt active filters are provided
by using SRF controller. Although there are many control approaches
available for the generation of reference signals. SRF controller is more
preferable due to its robustness, simplicity and easy to design (Akagi 2006). It
is also used to decompose the load currents IL into four parts, i.e. fundamental
frequency positive sequence active current, fundamental frequency positive
sequence reactive current, current at harmonic frequencies and fundamental
frequency negative sequence current. With these current components,
selective compensation of different combinations based on the priority can be
made, which supports the limited rating of the inverter.
The reference signal using SRF is extracted by transforming the threephase components into two phase components and again by transforming into
three phase components after analysis using Par
al 2005). PLL plays an important role in the design of SRF. PLL is used to
achieve synchronization with distorted voltage and current (Awad et al 2003).
Three-phase distorted voltages are given to conventional PLL which generates
two quadrature unit vectors (sin
cos t) to maintain synchronization with
sinusoidal voltage and current. In the proposed method, conventional PLL is
replaced by Modified PLL (Svensson et al 2002). During unbalanced and nonlinear load conditions the load voltage and load current consist of fundamental
positive, negative and zero sequence components. In UPQC applications, the
fundamental positive sequence component of the signals must be separated to
compensate the load voltage and load current harmonics. In this process, the
conventional PLL has poor performance under unbalanced and distorted
system conditions. In order to improve the performance of filtering, a modified
PLL is employed and is shown in Figure 5.10. To determine the transformation
a
by applying three-phase instantaneous load voltages, i.e. VLab and VLcb, where
VLab = VLa-VLb and VLcb=VLc-VLb.
120
Figure 5.10 Modified PLL model
The measured load voltages are multiplied by auxiliary feedback
currents (Iax1 and Iax2) with unity magnitude, in which Iax1 leads 120º to Iax2 in
order to obtain three-phase auxiliary instantaneous active power (P3ax). The
o
ded to the output of
the PI controller to stabilize the output. The transformation angle is obtained
the system fundamental frequency. Therefore, the integrator in order to reach the system fundamental frequency. Thus
proper tuning of PI controller provides good performance under distorted and
unbalanced load condition. The output of the modified PLL is shown in
Figure 5.11.
Figure 5.11 Output of modified PLL
121
Thus the proposed SRF control strategy produces an effective
response by extracting the load current and load voltage distortion and also
balances the unbalance system.
5.3.3
Control Strategy for Series Active Inverter
The proposed control strategy is aimed to compute mainly the three
phase reference voltages at the load terminals i.e. V La*, VLb* and VLb*. The
series filter is controlled such that it injects voltages through the series
transformer which cancels out the distortions and/or unbalance present in the
load voltages, thus making the voltages at the PCC (VLa, VLb and VLb)
perfectly balanced and sinusoidal with the desired amplitude. The flow chart
of series active filter controller is shown in Figure 5.12.
Figure 5.12 Flowchart of controller for series active filter
122
The three-phase load voltages VLa, VLb and VLc are transformed
into Vd, Vq and Vo using the following Park transformation equation,
Vd
2
VLa sin t
3
2
VLb sin( t
3
2 / 3)
2
VLc sin( t
3
Vq
2
VLa cos t
3
2
VLb cos( t
3
2 / 3)
2
VLc cos( t
3
Vo
1
VLa
3
Vd
Vq
Vo
1
VLb
3
1
V Lc
3
2 / 3) (5.5)
2 / 3) (5.6)
(5.7)
sin( t ) sin( t 2 / 3) sin( t 2 / 3) VLa
2
cos t cos( t 2 / 3) cos( t 2 / 3) VLb
3
1
1
1
VLc
2
2
2
(5.8)
As per the SRF controller (Yash Pal et al 2012), distorted free,
balanced and constant magnitude three-
to extract the fundamental components of the instantaneous voltages which
two phase into threephase components and are given as,
1
VLa
2
Vsd sin( t )
3
VLb1
2
Vsd sin( t
3
2 / 3)
(5.10)
VLc1
2
Vsd sin( t
3
2 / 3)
(5.11)
(5.9)
123
transformation is given as,
1
V
V
V
1
La
1
Lb
1
Lc
2
3
2
1
2
1
2
sin( t )
cos( t )
0
sin( t
2 / 3) cos( t
2 / 3) V sd
sin( t
2 / 3) cos( t
2 / 3)
(5.12)
0
The error signal (voltage compensation signal) is obtained by
comparing the extracted reference voltage V La1, VLa1 and VLa1 with the actual
load voltage and are given by,
VLa* = VLa-VLa1
(5.13)
VLb* = VLb-VLb1
(5.14)
VLc* = VLc-VLc1
(5.15)
The MATLAB control scheme for series active filter is shown in
Figure 5.13.
Figure 5.13 MATLAB scheme for series active inverter
Thus the generated voltage compensation signal is given to the
FHVC to generate switching pulses to the inverter of series active filter which
compensates load voltage distortion.
124
5.3.4
Control Strategy for Shunt Active Inverter
The proposed control algorithm uses SRF controller which
decomposes the load current into different components. The shunt active filter
injects the current such that the harmonic component in the load currents gets
eliminated. The flow of shunt active filter is shown in Figure 5.14.
Figure 5.14 Flowchart of controller for shunt active filter
The important feature of shunt active filter is that it controls the
DC-link voltage across the capacitor in addition to load current compensation.
The three-phase load currents ILa, ILb and ILc are transformed into Id, Iq and Io
using the following Park transformation equation,
125
Id
2
I La sin t
3
2
I Lb in ( t
3
Iq
2
I La cos t
3
2
I Lb cos( t
3
Io
1
I La
3
Id
Iq
Io
1
I Lb
3
2 / 3)
2 / 3)
2
I Lc sin( t
3
2
I Lc cos( t
3
2 / 3) (5.16)
2 / 3) (5.17)
1
I Lc
3
(5.18)
sin( t ) sin( t 2 / 3) sin( t 2 / 3) I La
2
cos t cos( t 2 / 3) cos( t 2 / 3) I Lb
3
1
1
1
I Lc
2
2
2
(5.19)
As per the SRF controller (Yash Pal et al 2012), distorted free,
balanced and constant magnitude three-
to extract the fundamental components of the instantaneous load current. The
actual voltage across dc-link capacitor is compared with the reference voltage
(Vdc=240V) and the error signal is given to PI controller. The output of PI
controller is considered as current loss I
loss.
The PI controller stabilizes the
error signal and then added with the fundamental DC components of load
current (Id), to get the reference direct axis component (Id*).
Id* = Id + Iloss
(5.20)
sformation is used to convert these two
phase into three-phase components and given as,
I 1La
2
I d sin( t )
3
(5.21)
126
I 1Lb
2
I d sin( t
3
2 / 3)
(5.22)
I 1Lc
2
I d sin( t
3
2 / 3)
(5.23)
The matrix
1
I
I
I
1
La
1
Lb
1
Lc
2
3
2
1
2
1
2
sin( t )
cos( t )
0
sin( t
2 / 3) cos( t
2 / 3) I d
sin( t
2 / 3) cos( t
2 / 3)
(5.24)
0
The error signal (current compensation signal) is obtained by
comparing the extracted reference current ILa1, ILa1 and ILa1 with the actual
load current and given by,
ILa* = ILa-ILa1
(5.25)
ILb* = ILb-ILb1
(5.26)
ILc* = ILc-ILc1
(5.27)
The MATLAB control scheme for shunt active filter is shown in
Figure 5.15.
Figure 5.15 MATLAB scheme for shunt active inverter
127
Thus the generated current compensation signal is given to the
FHCC to generate switching pulses to the inverter of shunt active filter which
compensates load current distortion and load unbalance.
5.4
FUZZY-HYSTERESIS CONTROLLER
The hysteresis band controller for active power filter can be carried
out to generate the switching pattern for inverter (Ram Kumar & Surya
Kalavathi 2013). There are various current control methods proposed for such
active power filter configurations, but in terms of quick current controllability
and easy implementation, hysteresis current control method has the highest
rate among other current control methods. Hysteresis band current controller
has properties like robustness, excellent dynamics and fastest control with
minimum hardware. In the case of positive input current, if the error between
the desired reference value and the actual value exceeds the upper hysteresis
band limit (+h), then the upper switch of the inverter arm is OFF and the
lower switch is ON and vice versa.
Even though fixed hysteresis band method is very simple and easy
to implement, but it has several known disadvantages like uncontrollable high
switching frequency and induced important switching losses. To improve this
control, a fuzzy hysteresis band control technique is proposed as a function of
the active filter and supply parameters to minimize the influence of current
distortions on modulated waveform. The hysteresis band can be modulated at
different points of fundamental frequency of the cycle to control the PWM
switching pattern of the inverter (Rama Rao & Subhransusekhar 2010).
128
5.4.1
Design of Hysteresis Band Current and Voltage Controller for
Shunt and Series Active Inverter
The hysteresis band current controller is derived based on the
switching intervals T1 and T2 shown in Figure 5.16.
dI La
dt
dI La
dt
1
(0.5Vdc VLa )
Lf
1
(0.5Vdc VLa )
Lf
(5.28)
(5.29)
Figure 5.16 Hysteresis band controller
From Figure 5.16,
dI La
T1
dt
dI 1La
T1
dt
dI La
T2
dt
1
dI La
T2
dt
T 1 T2
Tc
1
fc
2HB
2HB
(5.30)
(5.31)
(5.32)
129
T1 and T2 are the respective switching intervals and fc is the
switching frequency. Adding Equations (5.30) and (5.31) and substituting in
Equation (5.32), it can be written as,
dI La
T1
dt
dI La
T2
dt
1
1 dI La
f c dt
(5.33)
0
subtracting Equation (5.31) from Equation (5.30),
dI La
T1
dt
dI La
T2
dt
(T1
dI 1La
T2 )
dt
4HB
(5.34)
substituting Equation (5.29) in Equation (5.34),
(T1
dI
T2 ) La
dt
(T1
1
dI La
T2 )
dt
4 HB
(5.35)
substituting Equation (5.29) in Equation (5.33) and solving,
(T1 T2 )
dI 1La dt
f c dI La dt
(5.36)
substituting Equation (5.36) in Equation (5.35),
HB
4 L2f
0.125Vdc
1
(VLa L f
fc L f
Vdc2
1
dI La
dt
(5.37)
In general,
HB j
4 L2f
0.125Vdc
1
(VLj L f
fc L f
Vdc2
where j=a, b, c for each phase.
dI 1Lj dt
(5.38)
130
Lf represents the filter inductance whose value is taken as 0.66mH
(Kerrouche & Fateh et al 2009). Thus the expression for Hysteresis Band
(HB) for current controller is obtained. Similarly, the expression for HB for
voltage controller can be obtained as,
HB j
5.4.2
4 L2f
0.125Vdc
1
(VLj L f
fc Lf
Vdc2
dVLj1 dt
(5.39)
Fuzzy-Hysteresis Band Current and Voltage Controller
The Equation (5.38) implies that the HB of current controller is a
function of load voltage (VLa), slope of reference current (dI La1/dt), dc-link
capacitor voltage (Vdc), switching frequency (fc) and the value of filter
inductance. FLC is used to determine the hysteresis band width according to
the load voltage V La and the rate of change of reference current dILa1/dt. So,
these two parameters are taken as two input variables and HB is considered
as an output variable. In a hysteresis controller, the reference compensation
current is compared with the actual current that is being injected by the
compensation circuit. A positive pulse is produced if the actual current tends
to decrease below the lower hysteresis limit, while a negative pulse is
produced if the current exceeds the upper hysteresis limit. Thus, in a
hysteresis current controller the actual compensation current is forced to stay
within a particular hysteresis band. The set of linguistic values are
associated with each variable. Each input variable is transformed into
linguistic size with seven fuzzy subsets, PL: positive large, PM: positive
medium, PS: positive small, ZE: zero, NL: negative large, NM: negative
medium, NS: negative small and for the output variables are: PVS: positive
131
very small, PS: positive small, PM: positive medium, PL: positive large,
PVL: positive very large. The rules of inference of fuzzy hysteresis current
controller is framed using the linguistic variables and is arrayed in Table 5.2.
The parameters of the FLC are the same as used in chapter 3.
Table 5.2 Rules of fuzzy inference current controller
dILa1/dt
NB NM
NS
ZE
NB
NB
NB
NB
NB NM NS
NM
NB
NB
NB NM
NS
NB
NB NM
ZE
NB NM
PS
NM
PM
PB
Vs VLa
PS
PM PB
ZE
NS
ZE
PS
NS
ZE
PS
PM
NS
ZE
PS
PM PB
NS
ZE
PS
PM
PB
PB
NS
ZE
PS
PM
PB
PB
PB
ZE
PS
PM
PB
PB
PB
PB
The simplified model of FHCC for phase A is shown in Figure
5.17. Similar FHCC model is also obtained for phases B and C.
Figure 5.17 Simplified model of FHCC for phase A
132
Thus the switching pulses are generated using FHCC for the shunt
active inverter of UPQC. The six output pulses are given to the three-leg
shunt inverter for current compensation. In order to compensate the load
voltage distortion, a fuzzy hysteresis based voltage controller is designed. The
Equation (5.39) shows that the HB of voltage controller is a function of load
voltage (VLa), slope of reference voltage (dVLa1/dt), dc-link capacitor voltage
(Vdc), switching frequency (fc) and the value of filter inductance. Fuzzy logic
controller is used to determine the hysteresis voltage band width according to
the load voltage VLa and the rate of change of reference voltage dVLa1/dt. So,
these two parameters are taken as two input variables and HB is considered as
an output variable. The simplified model of FHVC for phase A is shown in
Figure 5.18. Similarly FHCC model is also obtained for phases B and C.
Figure 5.18 Simplified model of FHVC for phase A
The switching pulses are generated using FHVC for the series
active inverter of UPQC. The six output pulses are given to the three-leg
series inverter, which injects the compensating voltage using series
transformer thereby maintaining the load voltage nearly sinusoidal. Also the
proposed method balances the unbalance loads by diverting the neutral
current equally to all the phase using star-point of series transformer.
133
5.5
EFFECT OF CONVENTIONAL PI-FUZZY HYSTERESIS
CONTROLLER ON LOAD VOLTAGES AND CURRENTS
To validate the effect of conventional PI-fuzzy hysteresis
controller, a MATLAB simulink model of the proposed system is simulated
and is shown in Figure 5.19. The parameters of the simulation are supply
voltage Vs=110V, supply frequency=50Hz, dc-link capacitor voltage Vdc=240V,
dc-link capacitance C=2500µF, filter inductance Lf =0.66mH, filter resistance
Rf
s=20
KHz, proportional gain KP=0.35 and
integral gain KI=9.02 and the load values are the same as in Table 5.1.
Figure 5.19 MATLAB model of UPQC using conventional PI controller
The waveform of the load voltages after compensation are shown in
Figure 5.20 (a, b & c) and load currents are shown in Figure 5.21 (a, b & c).
The distortions in the load voltages are reduced. The THD values of load
voltages are reduced from 20.2% to 1.98% for phase A, 22.6% to 2.64% for
phase B and 13.3% to 1.84% for phase C.
134
(a) Phase A load voltage
(b) Phase B load voltage
(c) Phase C load voltage
Figure 5.20 Waveform of load voltages with PI-fuzzy hysteresis controller
135
Similarly, the distortion in the load currents are reduced and the
THD values are reduced from 34.3% to 4.89% for phase A, 38.4% to 4.08%
for phase B and 34.09% to 3.52% for phase C respectively.
(a) Phase A load current
(b) Phase B load current
Figure 5.21 (Continued)
136
(c) Phase C load current
Figure 5.21 Waveform of load currents with PI-fuzzy hysteresis
controller
The magnitudes of the fundamental load currents before
compensation are 35.82A, 32.93A and 18.61A and after compensation they
are 26.50A, 25.8A and 24.62A, which are nearly balance. The effect of
neutral current and DC-link capacitor voltage after compensation are shown
in Figures 5.22 and 5.23.
Figure 5.22 Waveform of neutral current with PI-fuzzy hysteresis
controller
137
Figure 5.23 Voltage across DC-link capacitor using conventional PI
controller
5.5
SUMMARY
In this chapter, conventional PI with fuzzy hysteresis controller
based UPQC is proposed to reduce the harmonic distortion in load voltages
and currents. The various advantages of UPQC and its configurations are
discussed. The effect of PI controller for maintaining DC voltage is analyzed
and simulated. In order to synchronize phase angle with the load parameters,
PLL is designed. SRF controller is also simulated in MATLAB which is used
to extract the reference voltage and current signals. The proposed method
used FLC to optimize the hysteresis band. The load voltage and current
distortion get reduced to a great extent when compared with the results of
without compensation. The magnitude of the neutral current is also reduced
and the system becomes nearly balanced.