Document

SIMULATION AND EXPERIMENTAL VALIDATION OF SHUNT
ACTIVE POWER FILTER FOR HARMONIC MITIGATION
Hamisu Usman, Ramatu Aliyu Abarshi, Aminu Hamisu Kura
Department of Electrical and Electronic Engineering, College of Engineering, Kaduna Polytechnic
ABSTRACT
The proliferation of power electronics devices used in industrial, commercial and residential
applications, have lead to the deterioration of supply current and voltage wave forms, and this caused
power quality problems within the supply system. These power electronics devices are nonlinear in
nature, which draws reactive power and harmonic distortions from the alternating current source in the
fundamental current. Traditional passive filter was the earliest solution for mitigating harmonics and
reactive power produced by nonlinear loads, but passive filter have the disadvantages of series and
parallel resonances with the supply source impedance and it’s heavy in size. Due to these problems in
passive filter, it applications becomes very limited. With the introduction of shunt active power filter,
harmonics mitigations of current and voltage distortion wave forms can therefore be suppressed. In this
paper, the modeling and simulation of DSP based single phase shunt active power filter controlled with
fuzzy logic controller for power quality improvement in MATLAB/ SIMULINK fuzzy inference system
(FIS), is proposed. Synchronous reference frame for the extraction of harmonics is introduced in this
paper. The simulated results are validated with experimented results of the proto type hardware
implementation via TMS320F28335 digital signal processor (DSP) in order to show the effectiveness
and good performance of the proposed control algorithm. The simulated results of the THD are in
conformity with IEEE 519-1992 harmonics standard limit, while the results of the hardware THD do
not obey the IEEE standard because of the hardware deficiency in sampling rate in real time
development.
Keywords: Shunt active power filter, harmonics, fuzzy logic, current extraction and THD
Introduction
Nowadays with the increase demand of power electronics equipment and devices for the use of
industrial, commercial and residential consumers, have lead to the serious power quality problems
within the supply System network. These equipment and devices are nonlinear in nature that draws
harmonic currents which deteriorates the quality of currents and voltage waveforms. Nonlinear loads
like arc furnaces, adjustable speed drives, rectifiers, Fluorescent lamps, personal computers are the
major responsible for harmonics in power system. These nonlinear loads have adverse effects on the
quality of power and system performances of the supply system, which resulted in overheating of the
supply cables, equipment ageing, interference with nearby communication facilities, frequent tripping
of sensitive devices like circuit breakers and can even result in total blackout of the entire power supply
system. As a result of these power quality problems, classical passive filters are the earliest solution to
mitigate harmonics drawn by the nonlinear loads. But passive filters have some drawbacks such as
heavier in size, tendency of series and parallel resonances with the supply impedance (Dehini, Bassou
&Ferdi, 2010) , fixed harmonic compensation and may cause detuning. With the problems of passive
filters, active power filters have been tested and proven to be a viable and dynamic solution to
overcome the difficulties of passive power filters in suppressing current harmonics drawn by nonlinear
loads within the power system network. Active power filters are therefore controlled with various
control techniques in controlling the gating signal of the semiconductor switching devices for proper
compensation of harmonics drawn by nonlinear loads. Among the control algorithms for shunt active
power filters are hysteresis current control, dead beat control, sliding mode control, pulse width
modulation control, neural network, genetic algorithm and fuzzy logic controllers etc. However, with
the emergence of digital controllers, like digital signal processors (DSPs), field programmable gate
array (FPGAs) and electronics micro-controllers, all in the application of shunt active power filter
control algorithms gives rooms for hardware implementation for validation of the shunt active power
filter simulation results. In this paper, modeling and simulation of single phase shunt active power filter
with harmonic extraction in synchronous reference frame (SRF) for the reference current generation of
the filter together with the fuzzy logic controller for the switching of the gating signal of the
semiconductor switching devices for harmonic mitigation drawn by the nonlinear load is presented. An
experimental validation of the proposed simulation results are also presented via digital signal processor
DSP TMS320F28335 in order to show the feasibility and good performance of the proposed control
algorithm.
Single Phase Shunt Active Power Filter Configuration
The Fig. 1 depicts the general configuration of single phase shunt active power filter topology. This
type of active filter topology is the most popular and frequent type in active filtering for harmonic
mitigations drawn by nonlinear loads (El-Habrouk, Darwish & Mehta 2000) . Shunt active power filter
work on the principle of current harmonic injection, its main principle is to control to draw/supply
current compensation from/to the supply authority main at the point of common coupling (Sahu,
Gadanayak, 2012), in such a way as to cancel harmonic currents and reactive power drawn my
nonlinear loads, with the aim at compensating current harmonics which is to be in phase with the source
voltage. Shunt active power filter configuration could be either voltage source inverter (VSI) or current
source inverter (CSI) types, depending on the applications to be used. But (VSI) type is the most widely
employed in active filtering due to its simplicity and popular in recognition topology (Salam, Chenga
&Jusoh, 2006) . Basically, shunt active power filter consists of two parts, the power circuit and control
circuit. The power circuit consists of IGBT or MOSFET semiconductors switching devices with an
interfacing inductor for taking care of the harmonics ripples after compensation by the active filter, DC
capacitor for maintaining DC voltage by the inverter. While the control circuit is the main brain of the
filter, which control the semiconductor switching gating signal for proper compensating of the current
harmonics.
Fig.1 Basic Principle topology of Single Phase Shunt Active Power Filter
Harmonic Current Extraction Technique
In this section, shunt active power filter requires harmonic current extraction of the reference current to
be compensated by the filter. Different current harmonic extraction techniques are available, in either
frequency domain or time domain approaches. In this paper, a time domain approach with balanced
three phase synchronous reference frame (SRF) was modified to work as single phase. In a normal three
phase synchronous reference frame, the load currents of the three phases, and the three phases source
voltages with the DC link voltage of the shunt active power filter are sensed in order to generate the
reference harmonic current which to be control by fuzzy logic controller. In synchronous reference
generation, the sensed load current due to nonlinear loads of the three phases  ia , ib , ic  are converted in
to the d-q coordinates by the use of Park transformation technique which resulted in obtaining the
components of the d-q load currents as shown by equation 1. The source current from d-q coordinates
2
are further transformed by the inverse Clarks transform in to  abc  coordinates as seen by equation 2.
In this work, phase a were selected out of the three phases (SRF) transformations under balanced
phases condition to work as single phase.

cos t
id  2 

i  
 q  3   sin t


2 

cos  t 

3 

2 

 sin  t 

3 

2  

cos  t 
ia 

3   

  ib
2    

 sin  t 
i 

3    c 



cos t

ia* 
2
 * 2 

ib   3  cos  t  3

ic* 
 

2

cos  t  3


 sin t






2

 sin  t 
3

2

 sin  t 
3

1


 *
  id 
  i* 
  q 



2
Fuzzy Logic Controller
Fuzzy logic controller was first introduced by Professor Zadeh Lotfi of University California Berkeley
in early 1960s. He proposed a technique of how to process an imprecise data with complex input. The
idea of Zadeh’s was fully utilized after the introduction and availability of modern computers and
controllers applications. Fuzzy logic controllers gain interest by many researchers and system engineers
in the application of control system analyst, as well as in the control algorithm for shunt active power
filter applications. Fuzzy logic controller has advantages of simplicity in design procedures that does
not require any accurate mathematical modeling, can work with an imprecise input of the system and it
can also work with non-linearity. Fuzzy controller is very robust than classical controllers such as PI
and PID controllers (Kerrouche, Karim, 2009). In our study, a Mamdani fuzzy controller was chosen
and designed with linguistic term “if then” rules. The linguistic variables for the rule base was selected
as, positive large (PL), positive medium (PM), positive small (PS), negative large (NL), negative
medium (NM), negative small (NS) and zero (Z). However, Fig. 2 depicts the general structure of fuzzy
logic controller.
The design of the proposed fuzzy logic controller is characterize as follows.
1. Five memberships function for each two inputs error (e) and its derivative (Δe) are used.
2. Seven memberships function for the output.
3. Mamdani implication in the design was also used.
4. Centre of area (COA) was used for the Deffuzzification process.
5. Implication using “min-max” approach
6. twenty five rules for both error and change of error are used.
Triangular membership functions are used due to its simplicity, completeness and easy to implement.
3
Fig. 2 Structure of fuzzy logic controller
As it was defined for the linguistic rule variables, table 1 below shows the “if then” rules for the five
membership functions selected for each of the input error (e) and the change of error (Δe). For the two
inputs, only twenty five possible rules are possible based on (5*5) =25 “if then” combinations rules.
Table 1. Linguistic variables rules for the Fuzzy logic Controller
Simulation Model And Analysis
As shown in Fig. 3, the modeling of the single phase shunt active power filter in MATLAB/SIMULINK
environment. The parameters of the simulation model are as follow: VS= 25V peak amplitude, F=
50HZ, RS= 40Ω, CL= 500µF, RL= 150Ω, RF= 40Ω, LF= 1mH. In the simulation, RC parallel load were
fed from the diode rectifier as a nonlinear load. In the same vein, the simulation results are also
presented in this section. AS shown in Fig. 4, the result of the nonlinear load due the harmonic
produced by the rectifier shows a waveform which is opposite to the source voltage (i.e out of phase to
each other). Fig. 5 depicts the filter current which also distorted due to the same nonlinear load, while
Figure 6 and Figure 7 are the corresponding source voltage and source current respectively and they
seems to be purely sinusoidal and in phase to each other. In the same analysis, Figure 8 and Figure 9
indicate the FFT analysis of the THD which are also found to be 39.82% and 3.91% respectively. These
THD have drastically reduced and is within the recommended IEEE 519-1992 harmonic limits.
4
Discrete,
Ts = 1e-006 s.
i
i
+
-
+
-
powergui
+
IL
Rs
Is
A
Series RLC Branch
AC Source
B
-
+
v
-
Vs
Universal Bridge Full wave Rectifier
R
g
+
Cdc
Vdc
i
Source voltage
Source current
+
-
Load Current
Rf & Lf
A
B
Shunt Active Filter
Iref
Vc
Iref
Pulses
1
z
iF, iL, iref
Iinj
Unit Delay1
Vs
Harmonic Extraction
Current Controller with Fuzzy
Fig. 3 Simulation of Single Phase Shunt Active power Filter
Fig. 4 Load current before applying shunt active power filter
5
v
-
VL1
IL1
-
IL
+
Fig.5 Filter current
Fig.6 Source Voltage
Fig.7 Source Current after compensation
6
Fig. 8 FFT Spectrum of the load current before compensation
Fig. 9 FFT Spectrum of the load current after compensation
Experimental Validation
In this section the experimental validation of the proposed simulation results is presented. A prototype single
phase shunt active power filter was constructed in the laboratory, in order the show the validity of the
proposed fuzzy logic controller algorithm in suppression current harmonics produced by nonlinear loads
within the power system network. Fig. 10 shows the hardware of the complete reference current generated
with the fuzzy logic controller setup of the shunt active power filter. In this paper, four electrical quantities
are sensed for the implementation of the prototype hardware implementation via the DSP (Singh, 2008). Two
current sensors LA25-NP for sensing the load current and the injected current of the active power filter which
are fed to the DSP for conversion from analog to the digitized form are also shown in setup. However, two
voltage sensors were also sensed, one from the source voltage while the other from the DC side capacitor of
the shunt active filter. The digitized output of the TMS320F28335 was fed to the gating signal of the IGBT
semi conductor switching for compensation of the harmonics produced by nonlinear load. Fig. 11 depicts the
experimental load current before compensation, and Fig. 12 shows the source voltage which is purely
sinusoidal in nature, while Fig. 13 is the source current. The THD for the load current before and after
compensation found to be 99.98% and 16.69% respectively. This result indicates a drastic reduction in the
THD, but is not in conformity with the IEEE harmonic standard limit because of the deficiency in hardware
sampling rate in real time application.
7
ADC-PWM Synchronization via ADC Interrupt
10
Gain1
1.21
C280x/C28x3xA0
Constant
IL
A1
A2
ADC
A3
91.8
Vc
Gain2
Vs
ADC2
Iref
Iref
Iinj
Harmonic Extraction1
91.8
Current Controller with Fuzzy
1.21
Gain3
Constant2
10
Copyright 2007-2014 The MathWorks, Inc.
Info
Gain4
1.21
F28335 eZdsp
Constant1
Fig. 10 Control algorithm interfaced with DSPTMS320F28335 processor
Fig 11 Experimented load current before compensation
8
Fig. 12 Experimented source voltage
Fig. 13 Experimented source current
Conclusion
This paper, discussed the simulation of single phase shunt active power filter controlled with fuzzy logic
controller, the simulation results are validated with a prototype hardware constructed in the laboratory via
DSPTMS320F28335 digital processor. The simulation results of the proposed controller indicates that, THD
of the load current and source current obtained to be 39.82% and 3.91% respectively. While THD of the
experimental results shows that, load current to be 99.98% and 16.69% for the corresponding source current
without and with compensation. The simulation result obeyed the IEEE 519-1992 harmonic standard limit,
while that of the hardware shows a drastic reduction in the THD, but does not meet the harmonic standard;
this is because of the limitation of real time hardware implementation and losses in the system.
9
References
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