International Journal Of Scientific Research And Education
||Volume||2||Issue|| 8||Pages 1483-1491||August-2014|| ISSN (e): 2321-7545
Website: http://ijsae.in
Investigations on Dynamic Performance of Hybrid Shunt Active Power
Filter Strategy for Power Quality Enhancement
Authors
Prabhakar Chaudhari1, Satyam Prakash2
1M. Tech. Scholar, Department of Electrical Engineering, United College of Engineering and Research,
Allahabad, Uttar Pradesh, INDIA.
2Assistance Professor United college of Engineering & Research
Email-pchaudhari007@gmail.com ,satyam.en@gmail.com
ABSTRACT
The present paper describes dynamic Hybrid Active Power Filter (HAPF) designed for harmonic
compensation under variable source/load conditions. A Voltage Regulator & PWM Generator is
employed to give Gate Pulses to the inverter considered in supply system. Hybrid filter utilizing the
merits of both shunt passive filter and shunt active filter for better compensation performance is
applied in this work. Simulation and analysis of three phase hybrid active power filter under
balanced and unbalanced load conditions, unbalanced & distorted source .conditions have been
incorporated using MATLAB/ SIMULINK. The detailed simulation level results have been presented
to validate the proposed methodology.
Keywords: Shunt active power filter, Active power filter; nonlinear loads, Shunt hybrid active filter.
1. INTRODUCTION
Due to proliferation of power electronic equipment and nonlinear loads in power distribution systems,
the problem of harmonic contamination
and treatment take on great significance .These harmonics
interfere with sensitive electronic equipment and cause undesired power losses in electrical equipment. In
order to solve and to regulate
the
permanent power quality problem introduce by this Current
harmonics generated by nonlinear loads such as switching power factor correction converter, for variable
speed AC motor drives and HVDC systems, Since, the use of passive filter has many disadvantages,
such as large size, tuning and risk of resonance problems which decrease more the flexibility and
reliability of the filter devices.
So, we look forward for HSAPF which is not so bulky, risk of resonance is low.
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The functioning of (SAPF) is to sense the load currents and extracts the harmonic component of the
load current to produce a reference current Ir, a block diagram of the system is illustrated in Fig. 1. The
reference current consists of the harmonic components of the load current which the active filter must
supply. This reference current is fed through a controller and then the switching signal is generated to
switch the power switching devices of the active filter such that the active filter will indeed produce
the harmonics required by the load. Finally, the AC supply will only need to provide the fundamental
component for the load, resulting in a low harmonic sinusoidal supply
Fig 1. Basic Principle Block Diagram of SHAPF
TRANSFORMERLESS THREE PHASE HYBRID ACTIVE FILTER
The schematic diagram of the shunt hybrid Active power filter (SHAPF) is presented in Fig 2. This
configuration of hybrid filter ensures the compensation of the source current harmonics by enhancing the
compensation characteristics of the passive filter besides eliminating the risk of resonance. It provides
effective compensation of current harmonics and limited supply voltage distortion. The hybrid filter is
controlled such that the harmonic currents of the nonlinear loads flow through the passive filter and that
only the fundamental frequency component of the load current is to be supplied by the ac mains. The
HAPF topologies in consists many passive components which increases the size and cost of the whole
system which makes the topology non preferable. As a result, a shunt hybrid power filter topology named
transformer less hybrid filter was proposed. The series connection between the passive filter and the
voltage source converter is completed without using any matching transformer.
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Fig 2 Transformerless Shunt Hybrid Power Filter
Fig 3 (a) Single Phase Equivalent Circuit (b) Harmonic Equivalent Circuit
In order to clarify the compensation characteristic of the shunt Hybrid Power Filter, the system can be
simplified by obtaining its single phase equivalent circuit as indicated in (Fig 3) where Zs represents the
source impedance and Zf represents the passive filter impedance. The non linear load is shown as an
ideal current source (I1), and the APF is considered as a voltage source. If the active power filter
terminal voltage is assumed to have no fundamental component, voltage across the PWM inverter can
be represented as K x Ish at harmonic frequencies where ‗h‘ stands for the harmonic components and
K represents the feedback gain. Hence, assuming the source voltage to be pure 50Hz and considering
the current directions as in Fig 2, the following equations can be obtained by applying Kirchhoff‘s
voltage law.
Vsh – Ish.Zsh – Ifh.Zfh – Vaf = 0 (1)
Where, Vsh = 0 and Vaf = K.Ish Ish = Ilh + Ifh (2) Combine (1) and (2),
Ish = Zsh / (Zfh + Zsh + K) (3)
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Equation (3) indicates that as the active power filter is connected to the system, feedback gain K acts as a
damping resistor which suppresses the resonance between the supply and the passive filter.
Theoretically, as K approaches to infinity, the harmonic content of the source current goes towards
zero. However due to stability problems in the control loop, the gain K should be limited to certain
values APF control methods and performance
3.1 APF Topologies
In some industrial and commercial applications, electric power is distributed through three phase fourwire systems. With incorrectly distributed or uncompensated loads such systems may suffer from
excessive neutral currents caused by non-linear or unbalanced loads. In such conditions, a three-phase
four-wire active filter can provide harmonic neutralization, (Aredes et al., 1997, Montero et al., 2007).
The main converter topologies for three-phase four-wire active power filters are the conventional threeleg converter with neutral point connection in the DC bus and the four-leg converter; the fundamental
difference between them is the number of power semiconductor devices. In some conditions, even in
three phase installations, single-phase compensation can be advantageous. In such cases, the single-phase
shunt active filter is often used, (Komurcugil & Kruker, 2006). However, three-phase systems without
neutral conductor are more general and will be the object of the present work.
3.2 Control Methods And Strategies
Different approaches such as notch filter, (Newman et al., 2002), scalar control, (Chandra et al.,
2000), instantaneous reactive power theory, (Furuhashi et al., 1990, Akagi et al., 2007), synchronous
detection method, (Chen et al., 1993), synchronous d–q frame method, (Mendalek et al., 2003), fluxbased control, (Bhattacharya et al., 1996), and closed loop PI, (Bhattacharya et al., 1996), internal
model control, (Marconi et al., 2007), and sliding mode control, (Saetieo et al., 1995), can be used to
improve the active filter performance. Also, the direct power control method has found application in
active filters, (Chen & Joós, 2008). Specific harmonics can be cancelled out in the grid using the
selective harmonic elimination method (Lascu et al., 2007). In all cases, the goal is to design a simple
but robust control system for the filter. Usually, the voltage-source is preferred over the current-source to
implement the parallel active power filter since it has some advantages, (Routimo et al., 2007).Using
higher voltages in the DC bus is desirable and can be achieved with a multilevel inverter (Lin & Yang,
2004). In this Chapter it is used the voltage source parallel topology, schematically shown in Fig. 1.
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Fig 3. Connection diagram of a voltage source active power filter.
The filter generates currents in the connection point in order to: 1- cancel/minimize the harmonic
content in the AC system, 2- correct the power factor at fundamental frequency, 3- regulate the voltage
magnitude, and 4- balance loads. So, the AC distribution system only carries the active fundamental
component of the load current.
Very different current control algorithms can be applied to the active filter, (Akagi, 2005).
The current reference for the active filter connection node usually satisfies one of the two following
strategies: 1- power factor correction, harmonic elimination, and load unbalance compensation or, 2voltage regulation, harmonic elimination, and load unbalance compensation.
The voltage regulation strategy is a concurrent objective faced to the power factor compensation because
the two depend on the reactive current. However, any control algorithm has enough flexibility to be
configured, in real-time, to either objectives or for the two, in a weighted form. Even under the same
compensation strategy, the filter can be controlled with different control algorithms. Two main
approaches are common: voltage control, and current control. Both methods have advantages and
weaknesses. In Fig. 4 it is represented a block diagram, with the variables shown in Fig. 3, of a voltagebased control algorithm of an active power filter implementing vector control.Fig.4
Fig 4.Voltage control of the active power filter.
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In the presence of the power quality concern the mains current is the most important variable to be
controlled. This method indirectly controls the mains current through the filter output voltage. In Fig. 3 it
is shown a block diagram of a current-based control algorithm of an active power filter also capable of
implementing different compensation strategies. This control method directly controls the mains current
through the isRef signals. However, it has slower dynamics than the voltage-based method.
A static power converter, like the one shown in Fig. 3, capable of doing (almost) all the above referred
functions is necessarily very complex. This complexity arises from the following considerations:
the converter dynamic behavior must be very fast in order to be capable of compensate currents in a
large spectra, the control algorithm must deal with a large number of variables such as mains voltages
and currents, load currents, DC voltage and current, and high dynamic performance and better active and
reactive power decoupling can demand direct and inverse coordinate transformation and a large amount
of signal processing.
So, fast power electronics semiconductors, with high switching frequencies, and
powerful
control
platforms are needed to build this type of power electronics systems.
Fig 5. Current control of the active power filter
3.3 Performance Evaluation of APFs
In order to analyze and evaluate the performance of an active power filter, different aspects must be
considered. Two different performance types can be considered: the qualitative ones and the
quantitative measures.
Qualitative evaluation
The qualitative value of an active power filter is a consequence of different technical merits.
The most important ones are briefly described: power semiconductor characteristics, namely of diodes,
GTOs and IGBTs, and converter topology, type of control system, scalar or vector control, and operating
modes, converter supervision, diagnostics and remote control.
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The active filter must accomplish one, or more than one, specific objective. So, its working conditions
must be in agreement with the established purposes: reactive power compensation; voltage regulation;
load balancing or harmonic compensation. These operating modes should be programmable, remotely
or on a local basis.
SIMULATION RESULTS
Inverter output: Inverter output of system can be shown as follows:
Fig:6- Inverter output
First Filter Output: Here we can see the harmonic content is so much but it going to be sinusoidal
Fig 7: First Filter Output
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Second Filter Output:
We can get more improved sinusoidal result that will be more closer to sine wave, hence we can say
here that power quality is improved here.
Fig 8: Second Filter Output
REFERENCES:
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