SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 9 –November 2014
Analysis of FL Controller Based UPFC with Multilevel
Series Converter
Rajesh.Nenavath*1, Dr. Sai Prasad Reddy*2
M-Tech Student Department of EEE, VBIT, Aushapur, Ghatkesar, R.R (Dt), Telangana, India,
Associate Professor, Department of EEE, VBIT, Aushapur, Ghatkesar, R.R (Dt), Telangana, India
ABSTRACT
The last two decades as the more increase in
population occurred in usage of electric power is increasing
day by day but the industries are not concentrating quality
of power. For that to maintain the quality power here the
new FACTS device is called UPQC reduces the both
voltage sag and swell and then improve the quality of
power. In the growth of electricity demand increased
number of non linear loads in power grids is providing a
best quality power should be considered. This paper
proposed voltage sag and swell of the power quality issues
are studied Unified Power Quality Controller is used to
mitigate the voltage distortions and improve the power
quality. Various FACTS devices DPFC, UPFC which
structure is similar to the Unified Power Quality and flow
Controllers. Instead of DPFC, in UPFC and UPQC have
common dc-link between both shunt and series converters
through the line.
Key Words: Power Quality, Sag and Swell Mitigation,
UPFC, UPQC.
I.
INTRODUCTION
In the past, equipment used to control industrial process
was mechanical in nature, being rather tolerant of voltage
disturbances, such as voltage sags, spikes, harmonics, etc.
In order to improve the efficiency and to minimize costs,
modern industrial equipment typically uses a large amount
of electronic components, such as programmable logic
controllers (PLC), adjustable speed drives (ASD), power
supplies in computers, and optical devices. Nevertheless,
such pieces of equipment are more susceptible to
malfunction in the case of a power system disturbance than
traditional techniques based on electromechanical parts [1].
Minor power disruptions, which once would have been
noticed only as a momentary flickering of the lights, may
now completely interrupt whole automated factories
because of sensitive electronic controllers or make all the
computer screens at an office go blank at once. In order to
restart the whole production, computers, etc, a considerable
time might be necessary (in the range of some hours),
implying on significant financial losses to an industry [2-4].
It is thus natural that electric utilities and end-users of
electrical power are becoming increasingly concerned
about the quality of electric power in distribution systems.
The term “power quality” has become one of the most
common expressions in the power industry during the
current decade [5,6]. The term includes a countless number
of phenomena observed in power systems. Although such
disturbances have always occurred on the power systems, a
great attention has been dedicated to minimize their effects
to the end-users, notably large industrial plants [7].
Regarding
transmission
systems,
they
were
overdimensioned in the past, with large stability margins.
Therefore, dynamic compensators, such as synchronous
ISSN: 2348 – 8379
condensers, were seldom required. Over the last 10-20
years, this situation has been changed since the
construction of generation facilities and new transmission
lines has become unfeasible due to financial and
environmental constraints. Therefore, better utilization of
existing power systems has become imperative [8]. The
interconnection of separate power systems allows better
utilization of power generation capability, but the
interconnected system must be able to recover from faults
and supply the necessary power at load changes. From the
economical point of view, the most important factor has
been the progressive deregulation of the electrical energy
transmission/distribution market worldwide. The utilities
are aware of the importance of delivering to their customers
a voltage with “good quality” in order to satisfy and
consequently retain them. Simultaneously to the changes in
the operation and requirements of transmission and
distribution systems, the power semiconductor technology
has experienced a very fast development. Until the
beginning of the nineties, the sole semiconductor device
applied to high power applications was the thyristor,
employed in High Voltage Direct Current (HVDC)
transmission systems and Static Var Compensators (SVC)
[9,10]. Nevertheless, the voltage and current ratings of
commercially available power semiconductor devices have
continuously been increased, improving the performance
and reducing the necessity of series and parallel
connections for achieving the desired rating, making their
applications more compact with decreasing costs.
II. RELATED WORK
In resume, FACTS devices replace conventional equipment
employed for voltage and power flow control by equivalent
equipment based on power electronics with superior
performance. Custom Power devices form a generation of
power electronic controllers applied to distribution systems
that enables utilities providing a good power (voltage)
quality to critical customers. Regarding power electronics,
emergent semiconductor devices with turn-off capability,
such as the Integrated Gate Commutated Thyristor (IGCT)
[24,25] are also a driving force for improving performance
and reducing installation costs of FACTS and Custom
Power Devices. The main goal is obtaining components
that can be switched at high frequencies with lower losses.
In a longer time perspective, it is also expected that
semiconductor devices based on new materials, e.g. Silicon
Carbide (SiC) [26,27] will allow the operation of these
devices at considerably higher temperatures (around
400°C), alleviating thus cooling requirements and reducing
installation costs.
CONTRIBUTIONS OF THE WORK
Although the term “power quality” encompasses all
disturbances encountered in a power system, it has been
found that voltage sags and interruptions are the most
relevant types of phenomena in distribution systems
affecting the quality of the service provided by a utility.
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 9 –November 2014
This thesis exploits this fact, evaluating the solutions based
on Custom Power for improving the power quality of
the distribution systems regarding the occurrence of
voltage sags and interruptions.
A considerable amount of FACTS and Custom Power
devices employs forcedcommutated voltage-source
converters as their essential parts. The thesis also
investigates the use of these converters for voltage and
power flow control in transmission systems and
mitigation of voltage sags in distribution systems.
CAUSE OF POWER QUALITY PROBLEMS
Some typical disturbances to power systems, which may
cause power quality problems, are listed below:





effectiveness of the proposed UPQC-S approach are
validated by simulation as well as experimental results.
1.1.U.P.F.C:
The UPFC is a combination of a static compensator and
static series compensation. It acts as a shunt compensating
and a phase shifting device simultaneously.
Lightning and natural phenomena.
Energization of capacitor banks and transformers.
Switching or start-up of large loads e.g. motors.
Operation of non-linear and unbalanced loads
Failure of equipment, e.g. transformers and
cables.

Wrong maneuvers in distribution substations and
plants.
Although all disturbances mentioned above are of concern
in the power quality context, there is no doubt that the most
problematic issue is the occurrence of faults, which is the
most exploited topic along this work. System faults can
produce voltage variations at different points of the system
with different magnitudes and time scales, depending on
how far the analyzed point is from the fault location, the
fault clearing procedure, and system impedances. The large
majority of faults on a utility system are single phase-toground temporary faults. Nevertheless, most of the threephase breakers and reclosers on utility distribution system
work on all three phases in order to prevent single phasing
of three-phase loads such as large three-phase motors. It
can thus be said that the single-phase fault will have the
same effect downstream to the fault as a three-phase fault
after the actuation of the protection scheme. Operating the
circuit breakers and reclosers only on the faulted phase is a
usual practice if the feeder serves only single-phase loads,
which is common in the USA. Faults in transmission
systems usually do not cause sustained interruptions, as the
transmission systems are mostly meshed. In the case of a
fault, the electric power flow is transferred to another path
through the action of the protection system. On the other
hand, faults in distribution systems are prone to cause
sustained interruptions because distribution systems are
radially operated or with very slow redundancy capability
(in the range of hours). Nevertheless, faults.
Proposed work
1) The series inverter of UPQC-S is utilized for
simultaneous voltage sag/swell compensation and
load reactive power compensation in coordination
with shunt inverter.
2) In UPQC-S, the available VA loading is utilized to its
maximum capacity during all the working conditions
contrary to UPQC-VAmin where prime focus is to
minimize the VA loading of UPQC during voltage
sag condition.
3) The concept of UPQC-S covers voltage sag as well as
swell scenario.
In this paper, a detailed mathematical formulation of PAC
for UPQC-S is carried out. The feasibility and
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Fig.2.1. Principle configuration of an UPFC.
The UPFC consists of a shunt and a series transformer,
which are connected via two voltage source converters with
a common DC-capacitor. The DC-circuit allows the active
power exchange between shunt and series transformer to
control the phase shift of the series voltage. The series
converter needs to be protected with a Thyristor bridge.
III. METHODOLOGIES
SYSTEM
OF PROPOSED
The concept of PAC of UPQC suggests that with proper
control of the power angle between the source and load
voltages, the load reactive power demand can be shared by
both shunt and series inverters without affecting the overall
UPQC rating. The phasor representation of the PAC
approach under a rated steady-state condition is shown in
Fig.3. According to this theory, a V Sr-> vector with proper
magnitude V Sr and phase angle ϕsr when injected through
series inverter gives a power angle δ boost between the
source Vs and resultant load VL’ voltages maintaining the
same voltage magnitudes. This power angle shift causes a
relative phase advancement between the supply voltage and
resultant load current IL’ , denoted as angle β.
For a rated steady-state condition
|VS | = |VL | = |V L | = |V’L | = k
(1)
Using Fig. 3, phasor _VSr can be defined as
(2).
(3).
Fig. 3.1. Concept of PAC of UPQC.
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 9 –November 2014
a.
Voltage SAG/SWELL Compensation Utilizing
UPQC-P and UPQC-Q
simultaneous compensation, as noticed from Fig.3.1.2., the
series inverter should now supply a component which
would be the vector sum of VSr1-> and V Sr2->. This resultant
series inverter voltage V Sr->f will maintain the load voltage
magnitude at a desired level such that the drop in source
voltage will not appear across the load terminal.
For load reactive power compensation using PAC concept
(4).
(5).
For voltage sag compensation using active power control
approach
For simultaneous
compensation
load
reactive
power
and
(6).
sag
(7).
Fig. 3.1.1. voltage sag and swell compensation using
UPQC-P and UPQC-Q, Phasor representation, (a) Voltage
sag (UPQC-Q), (c) Voltage Swell (UPQC-P), (d) Voltage
Swell (UPQC-Q).
The voltage sag on a system can be compensated through
active power control and reactive power control methods.
Fig.3.1.1. shows the phasor representations for voltage sag
compensation using active power control as in UPQC-P
[see Fig. 3.1.1.(a)] and reactive power control as in UPQCQ [see Fig. 3.1.1. (b)]. Fig. 3.1.1.(c) and (d) shows the
compensation capability of UPQC-P and UPQC-Q to
compensate a swell on the system. For a voltage swell
compensation using UPQC-Q [see Fig.3.1.1.d(d)], the
quadrature component injected by series inverter does not
intersect with the rated voltage locus. Thus, the UPQC-Q
approach is limited to compensate the sag on the system.
a. PAC Approach under voltage SAG
condition
Consider that the UPQC system is already working under
PAC approach, i.e., both the inverters are compensating the
load reactive power and the injected series voltage gives a
power angle δ between resultant load and the actual source
voltages. If a sag/swell condition occurs on the system,
both the inverters should keep supplying the load reactive
power, as they were before the sag.
(8).
Series Inverter Parameter Estimation under Voltage
Sag
In this section, the required series inverter parameters to
achieve simultaneous load reactive power and voltage sag
compensations are computed. Fig. 6 shows the detailed
phasor diagram to determine the magnitude and phase of
series injection voltage.
The voltage fluctuation factor kf which is defined as the
ratio of the difference of instantaneous supply voltage and
rated load voltage magnitude to the rated load voltage
magnitude is represented as
∗
Kf =
−
∗
(9)
Representing (9) for sag condition under PAC
Kf =
=
Let us define
1 + kf = no
Fig.3.1.2. Phasor representation of the proposed UPQC-S
approach under voltage sag codition.
Let us represent a V Sr1-> vector responsible to compensate
the load reactive power utilizing PAC concept and vector
VSr2-> responsible to compensate the sag on the system
using active power control approach. Thus, for
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(10).
(11).
(12).
(13).
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 9 –November 2014
Therefore, the reactive power shared by the series inverter
and hence by the shunt inverter changes.
(14).
IV. SIMULATION RESULTS
(15).
(16).
Equations (15) and (17) give the required magnitude and
phase of series inverter voltage of UPQC-S that should be
injected to achieve the voltage sag compensation while
supporting the load reactive power under PAC approach.
Fig. 3.1.4. current based phasor representation of the
proposed UPQC-S approach under voltage sag condition.
The performance of the proposed concept of simultaneous
load reactive power and voltage sag/swell compensation
has been evaluated by simulation. To analyze the
performance of UPQC-S, the source is assumed to be pure
sinusoidal. Furthermore, for better visualization of results
the load is considered as highly inductive. The supply
voltage which is available at UPQC terminal is considered
as three phase, 60 Hz, 600 V (line to line) with the
maximum load power demand of 15 kW + j 15 kVAR (load
power factor angle of 0.707 lagging). The simulation
results for the proposed UPQC-S approach under voltage
sag and swell conditions are given in Fig.4.2. Before time
t1 , the UPQC-S system is working under steady state sate
condition, compensating the load reactive power using both
the inverters. A power angle δ of 21◦ is maintained between
the resultant load and actual source voltages. The series
inverter shares 1.96 kVAR per phase (or 5.8 kVAR out of
15 kVAR) demanded by the load. Thus, the reactive power
support from the shunt inverter is reduced from 15 to 9.2
kVAR by utilizing the concept of PAC. In other words, the
shunt inverter rating is reduced by 25% of the total load
kilovoltampere rating. At time t1 = 0.6 s, a sag of 20% is
introduced on the system (sag last till time t = 0.7 s).
Between the time period t = 0.7 s and t = 0.8 s, the system
is again in the steady state. A swell of 20% is imposed on
the system for duration of t2 = 0.8–0.9 s. active and
reactive power flows through the source, load, and UPQC
are given in Fig.4.3. The distinct features of the proposed
UPQC-S approach.
Upfc fig 10 a&b
Vabc,iabc
Fig. 3.1.5. Detailed phasor diagram to estimate the shunt
inverter parameters for the proposed UPQC-S approach
under voltage sag condition.
Upfcfig 9b
Vabc,Iabc
Upfc fig 9a
Vabc,,iabc
(17).
Upfc fig 8c series
(18).
upfc 8a
(19).
V. CONCLUSION
(20).
(21).
(22).
(23)
(24).
UPQC-S CONTROLLER
A detailed controller for UPQC based on PAC approach is
described. Furthermore, the power angle δ is maintained at
constant value under different operating conditions.
ISSN: 2348 – 8379
To improve the electric power quality in the flow of power
transmission system we will get some distortions voltage
sag and swell to mitigate using a new FACT devices called
UPFC and UPQC are presented. The power quality is to
balance the line parameters like the line impedance,
transmission angle, and bus voltage magnitude. However
the UPFC and UPQC offer some advantages such has high
capability of power flow control, reliability and low cost.
The systems under this study a single machine have
multiple levels of converters with and without the FACTS
devices. In future instead FACTS devices you can use
FUZZY controller it gives better accuracy then compare to
this propose work.
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SSRG International Journal of Electrical and Electronics Engineering (SSRG-IJEEE) – volume 1 Issue 9 –November 2014
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