I
ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-04, Issue-01, January 2016
An Adaptive SRF Based Cascaded Multilevel Active
Filter for Power Line Conditioners
N Lakshmi Silpha1, M Ramanjaneyulu2
M.Tech Scholar, Department of EEE, VRS & YRN College of Engineering & Technology, Chirala, India 1.
Associate Professor, Department of EEE, VRS & YRN College of Engineering & Technology, Chirala, India 2
Abstract— This project presents a synchronous
reference frame (SRF) controlled five-level cascaded
multilevel inverter based shunt active filter for power line
conditioners (PLCs) to improve the power quality in the
distribution system. The SRF based compensation is
developed by sensing load currents only, which require for
harmonics and reactive power compensation due to nonlinear loads. A cascaded multilevel Voltage Source
Inverter (VSI) based shunt Active Power Filter (APF) for
current harmonics and reactive power compensation due
to nonlinear loads. The proposed approach comprises Low
Pass Filter (LPF) in conjunction with Proportional
Integral (PI) controller which is used to estimate the peak
reference current and maintain the DC bus capacitor
voltage of the cascaded inverter nearly constant. The
simulation results are determined by using MATLAB
Simulink.
Keywords: Shunt Active Power Filter (APF), Active Power
Line Conditioner (APLC), synchronous reference frame
(SRF), power line conditioners (PLCs),Voltage sourse
inverter(VSI),Convetional PI,PID
I. INTRODUCTION
Power quality may also be defined as the degree to which
both utilization and delivery of electric power affects the
performance of electrical equipment. From a customer
perspective, a power quality problem is defined as any power
problem manifested in voltage, current or frequency deviations
that result in power failure or disoperation of customer of
equipment. With the advent of power semi-conductor
switching devices like thyristors, GTO’ (Gate turnoff
thyristors), IGBT’s (Insulated gate bipolar transistor) and many
more devices, control of electric power has become a reality.
Such power electronic controllers are widely used to feed
electric power to electrical loads such as adjustable speed
drives (ASD’s), furnaces, computer power supplies, HVDC
(High voltage DC) systems.
Isolated power systems are commonly found in rural
and remote areas of the world. Isolated power systems are
characterized by limiting generating capacity. Non-linear
loads result in harmonic or distortion current and create
reactive power problems .Traditionally passive filters have
been used to compensate harmonics and reactive power; but
passive filters are large in size, aging and tuning problems
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exist and can resonate with the supply impedance. Recently
active power line conditioners (APLC) or active power filters
(APF) are designed for compensating the current-harmonics
and reactive power simultaneously Non-linear loads result in
harmonic or distortion current and create reactive power
problems .Traditionally passive filters have been used to
compensate harmonics and reactive power; but passive filters
are large in size, aging and tuning problems exist and can
resonate with the supply impedance. Recently active power
line conditioners (APLC) or active power filters (APF) are
designed for compensating the current-harmonics and reactive
power simultaneously.
In the proposed system the compensation process is
based on sensing load currents only, which require current
harmonics and reactive power elimination due to the loads.
The cascaded H-bridge active filter has been applied for power
quality applications due to increase the number of voltage
levels, low switching losses and higher order of harmonic
elimination. The main objective of the proposed system is to
suppress the harmonics by using shunt active power filter
designing based on SRF controller in electrical power system
with non-linear loads in order to improve the power quality in
the distribution system. In this project the concept of design of
SRF controller for shunt APLC system and the basics of
power quality were discussed i.e. power quality standards,
need for improvement of power quality, sources of power
quality problems and simple prevention techniques.
Simulink and Mat lab provide an ideal integrated
environment for developing models, performing dynamic
system simulations, and designing and testing new ideas. The
enhancement of power quality in isolated power systems is
studied by using with and without shunt compensators. The
corresponding simulation results are presented and compared.
Nonlinear loads such as diode/thyristor rectifiers, switched
mode power supply (SMPS), welding equipment,
incandescent lighting, and motor drives are degrading power
quality in transmission and distribution grid systems. These
non-linear loads result in harmonic or distortion current and
create reactive power problems. To solve the rated power
problem of active power filters, more than one active power
filter can be connected in cascade, where each of the active
power filters operates at different switching frequencies and
contains a different power rating.
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-04, Issue-01, January 2016
II. HARMONICS AND POWER QUALITY
A. Sources Of Harmonic Current
The main sources of harmonic current are at present the
phase angle controlled rectifiers and inverters. These are often
called static power converters. These devices take AC power
and convert it to another form, sometimes back to AC power
at the same or different frequency, based on the firing scheme.
The firing scheme refers to the controlling mechanism that
determines how and when current is conducted. One major
variation is the phase angle at which conduction begins
and ends.
A typical such converter is the switching-type power
supplies found in most personal computers and
peripheral large increase of this type of equipment over the
past fifteen years is largely responsible for the increased
attention to harmonics. A capacitor, where the voltage value
on the cap at any time depends on how much energy is being
taken out by the rest of the power supply. When the input
voltage value is higher than voltage on the capacitor, the
diode will conduct current through it. This results in a current
waveform and harmonic spectrum. Obviously, this is not a
pure sinusoidal waveform with only a 50 Hz frequency
component.
B. Power Quality
The power quality is the most important factor in
power sector. The fact that power quality has becomes an
issue recently, does mean that it was not important in the past.
Actually good power supply means quality of power supply is
of good health for the electrical equipment. On industrial side
it is very important to minimize losses. Sometimes it is also
called quality of supply. Different definitions are there but we
have IEEE and IEC definitions, given as follows.
1. The definition of power quality given in the IEEE
dictionary: Power quality is the concept of powering sensitive
equipment in a manner that is suitable to the operation of that
equipment.
2. According to IEC the electromagnetic capability is the
ability of an equipment or system to function satisfactorily in
its electromagnetic environment without introducing
intolerable electromagnetic disturbance to anything in that
environment. The following definition of power quality was
adopted for describing the scope of project group of IEC: set
of parameters defining the properties of the power supply as
delivered to the user in normal operating conditions in terms
of continuity of supply and characteristics of voltage.
Power quality is the combination of the voltage
quality and current quality. Thus the power quality is
concerned with the deviation of voltage or current from ideal.
. Here quality of the supply or power quality include in
technical part voltage quality and in non-technical part
sometimes referred to as “quality of the service.” Power
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quality is combination of voltage quality and current quality.
Power quality is the quality of the electrical power supplied to
electrical equipment. Poor power quality can result in mal
operation of the equipment .The electrical utility may define
power quality as reliability and state that the system is 99.5%
reliable.
C. Voltage Source Converters (Vsc)
A voltage-source converter is a power electronic
device, which can generate a sinusoidal voltage with any
required magnitude, frequency and phase angle. Voltage
source converters are widely used in adjustable-speed drives,
but can also be used to mitigate voltage dips. The VSC is used
to either completely replace the voltage or to inject the
‘missing voltage’. The ‘missing voltage’ is the difference
between the nominal voltage and the actual.
III. DESIGN OF SHUNT APLC SYSTEM
A cascaded active filter for power line conditioning
system is connected in the distribution network at the PCC
through filter inductances and operates in a closed loop.
Three phase active power filter comprises of 24-power
transistors with freewheeling diodes; each phase consists of
two-H-bridges in cascaded connection and every H-bridge
having a dc capacitor. The shunt APLC system contains a
cascaded multilevel inverter, RL-filters, a compensation
controller (synchronous reference frame controller) and
switching signal generator (triangular-periodical current
controller) as shown
Figure1.Shunt active power line conditioners system
Three phase supply source connected with the nonlinear load. Due to the nonlinear load, load current contains
fundamental component and harmonic current components.
For harmonic compensation, the active filter must provide the
compensation current ic (t) = iL (t) − is (t). At that time,
source current will be in phase with the utility voltage and
become sinusoidal.
The Shunt APLC block diagram is designed using
synchronous reference frame theory where the sensitive load
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-04, Issue-01, January 2016
currents are ILa, ILb, and ILc. A three-phase stationary
coordinate load current iLa, iLb, iLc are convert to id-iq
rotating coordinate current, as follows
d= [iLa
iq=
+iLb
[iLa
+iLc
+iLb
]
+iLc
]
The measured currents of load are transferred into dq0
frame using sinusoidal functions through dq0 synchronous
reference frame conversion. The sinusoidal functions are
obtained through grid voltage using PLL. Here the currents are
divided into AC and DC components.
Figure. 2 Synchronous reference frame controller
~
i1d  i1d  i1d
IV. SIMULATION STUDY
~
i1q  i1q  i1q
The active part of current is id and iq is the reactive one. AC
and DC elements can be derived by a low pass filter.
Controlling algorithm corrects the system’s power factor and
compensates the all current harmonic components by
generating the reference current as
i *fq  i1q i
System currents are
isd  i1q , isq  0
The desired reference current signals in d-q rotating frame
is converted back into a − b − c stationery frame. The inverse
transformation from d − q rotating frame to a − b – c
stationery frame is achieved by the following equations.
Isa*= id
MATLAB is a high-performance language for technical
computing. It integrates computation, visualization, and
programming in an easy-to-use environment where problems
and solutions are expressed in familiar mathematical notation.
SIMULINK is software for modeling, simulating, and
analyzing Dynamic systems. It supports linear and nonlinear
systems, modeled in continuous time, sampled time, or a
hybrid of the two. Systems can also be multi rate, i.e., have
different parts that are sampled or updated at different rates.
SIMULINK enables you to pose a question about a system,
model it, and see what happens. With SIMULINK, one can
easily build models from scratch, or take an existing model
and add to it. Thousands of engineers around the world use
SIMULINK to model and solve real problems in a variety of
industries.
A. Simulink model for without SHUNT APLC System
+ iq
Isb*= id
+ iq
Isc*= id
+ iq
*
*
*
The Resulted reference current ( i fa ,i fb and i fc ) are
compared with the output current of shunt inverter
( i fa , i fb ,
and i fc ) in periodical carrier current controller.
Figure. 3 Simulink model for without SHUNT APLC System
Figure show Simulink model without SHUNT APLC, it
consist of three phase AC source and Non-linear load. The
source is directly connected to the load; observe the wave
forms of three phase AC source input voltage and current,
Non-linear load current and voltage, load power factor wave
forms also observed.
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-04, Issue-01, January 2016
Fig: 6 Non- linear load current without SHUNT APLC
Figure. 4 Three phase input source current without SHUNT
APLC
Fig 7 P.F OF the system without SHUNT APLC
Figure. 5 Three phase input source voltage without
SHUNT APLC
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-04, Issue-01, January 2016
B. MATLAB/SIMULINK MODEL OF SHUNT APLC
Figure. 11 Power factor of the system with SHUNT APLC
Figure. 8 MATLAB/SIMULINK Model of SHUNT APLC
System
Figure. 12 Gate pulses for Inverter in SHUNT APLC
V. CONCLUSION
In this chapter, simulation block diagrams of with and
without SRF based SHUNT APLC are presented, simulation
results of input source voltage and current, non-linear load
voltage and current, load power factor, total harmonic
distortion of with and without UPQC are presented. THD
value of system with SHUNT APLC System is 1.38% is better
than THD value of without SHUNT APLC is 19.45%. The
input source current wave form of without SRF based SHUNT
APLC is distorted waveform but with SHUNT APLC System
is sinusoidal waveform.
Figure. 9 Three phase source current with SHUNT APLC
It can be adaptive by training intelligently in neural
network or Fuzzy logic control. This efficient 3-phase Shunt
Active power Filter can be implemented in different power
quality problems mitigating techniques. In conjuntion of
transformers using multiple bridges medium to high-level
voltage control can be possible. It can also used to improve the
efficiency of the distribution system.
Figure. 10 Three phase input source voltage with SHUNT
APLC
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ISSN No: 2309-4893
International Journal of Advanced Engineering and Global Technology
Vol-04, Issue-01, January 2016
REFERENCES
[1] S.J.Huang and J.C.Wu “Design and operation of cascaded
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[2] Fang Zheng Peng, John W. McKeever, and Donald J.
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