Dynamic Power Quality Compensator with an Adaptive Shunt Hybrid Filter

International Journal of Power Electronics and Drive System (IJPEDS)
Vol. 4, No. 4, December 2014, pp. 508~516
ISSN: 2088-8694  508
Journal homepage: http://iaesjournal.com/online/index.php/IJPEDS
Dynamic Power Quality Compensator with an Adaptive Shunt
Hybrid Filter
Sindhu M R, Manjula G Nair, T N P Nambiar
Department of Electrical and Electronics Engineering, AMRITA VISHWA VIDYAPEETHAM
Article Info ABSTRACT
Article history:
Received May 24, 2014
Revised Oct 7, 2014
Accepted Oct 20, 2014
Major portion of nonlinear loads in industries are contributed by variable
speed drives because of their desirable features such as energy saving,
smooth control, flexible operation and fast response. These electric drives
introduce large amount of current and voltage harmonic distortions at the
point of common coupling. These distortions are propagated throughout the
system and affect all other loads connected in the system. Hence these
distortions are to be mitigated with suitable harmonic filters installed near to
the respective load terminals. This paper presents an effective ANN based
digital controller for shunt hybrid harmonic filter to provide instantaneous
harmonic and reactive compensation. The performance of the adaptive shunt
hybrid filter is verified by simulation and experimental studies under steady
state and dynamic conditions. The results show that it is an effective, flexible
and low rated hybrid filter configuration.
Keyword:
Harmonic Distortion
Harmonic Filter
Power Quality
Reactive power compensation
Active Filter
Copyright © 2014 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Sindhu M R,
Department of Electrical and Electronics Engineering,
Amrita Vishwa Vidya Peetham,
Amrita nagar, Coimbatore – 641112.
Email:
1. INTRODUCTION
Utilities take efforts to maintain good power quality at the point of common coupling (PCC).
Majority of industrial loads are induction motor drives [1, 2]. They are preferred because of saving in energy,
rugged nature, easiness in control and cheapness [1, 2]. Various PWM techniques such as Space Vector pulse
width modulation, sinusoidal PWM etc. are implemented [3]-[5]. These are implemented with digital
controllers and it improved performance of induction motor drives. These equipment resulted in generation
of large amounts of current and voltage harmonics, reduction in source power factor, voltage sag, voltage
swell etc. [6]. The propagation of these power quality issues are prevented by installing harmonic filter of
suitable configuration at point of common coupling. Different power quality improvement schemes such as
passive filters [6] and active filters [7] are developed by various researchers. Passive filters have drawbacks
such as bulky in size, high no load losses, resonance, fixed compensation etc [6]. Active filters provide
effective and dynamic compensation with the help of efficient controllers [7]. But this scheme is expensive.
Hence as an economical solution, hybrid filters were developed. Here, shunt passive filter contributes major
part of reactive power compensation and remaining harmonics are compensated by shunt active filter.
Various research papers on intelligent digital controller based harmonic filters are published [8-12]. This
paper describes an ANN based adaptive shunt hybrid filter for harmonic mitigation and reactive power
compensation of adjustable speed drives.ANN controller helps to provide instantaneous harmonic and
reactive power compensation under steady state and dynamic conditions.

IJPEDS ISSN: 2088-8694 
Dynamic Power Quality Compensator with an Adaptive Shunt Hybrid Filter (Sindhu M R)
509
2. TEST SYSTEM
An industrial system is selected for performance study of the adaptive shunt hybrid filter. A scaled
down laboratory model of industrial drive, three phase 3 HP, 4 pole, induction motor drive is used in this
work. It is operated as an adjustable speed drive using three phase voltage source inverter. The specifications
of the induction motor drive are shown in Table 1.
Table 1. Induction Motor Drive Specifications
Power rating 3 HP
Switching frequency 10kHz
Rotor resistance 1.24
Stator resistance 1.517
Vdc 300V
Base frequency 100Hz
Stator Leakage Reactance 5.12
Rotor Leakage Reactance 120
No. of poles 4
Moment of Inertia 0.2 kgm2
The experimental set up is made as shown in the block diagram in Figure 1.
Figure 1. Schematic Diagram of Three Phase Test System
The VSI is controlled using space vector PWM. The space vector PWM based speed control is
implemented through the following steps:
(a) Measure the motor quantities (speed and phase currents)
(b) Transform them to two phase system (,β) using Clarke transformation
(c) Calculate rotor flux space vector magnitude and angle
(d) The stator current torque and flux components are separately controlled (isd, isq)
(e) The output stator voltage space vector is calculated using decoupling block (vsd, vsq)
(f) The stator voltage space vector is transformed by an inverse park transformation back from d –q
reference frame into two phase system fixed with the stator (vs, vsβ)
(g) Using space vector modulation, output three phase voltages is generated.
The whole process of the speed controller, implemented in the dsPIC30F4011, is explained using
flow chart in Figure 2. Three phase source currents, and source voltages at the point of common coupling are
sensed and harmonic analysis is performed with the help of power quality analyser. The power system
quantities –magnitudes and waveforms of source currents and source voltages for different speed settings are
shown in Figure 3.

 ISSN: 2088-8694
IJPEDS Vol. 4, No. 4, December 2014 : 508 – 516
510
Figure 3. Source voltage and source current at the point of common coupling for variable speed induction
motor drive with speed of (a)135 rad/sec (Case I) (b)320 rad/sec – (Case II)
Figure 2. Flow chart of the speed controller
Table 2 shows large amount of harmonics in currents at the point of common coupling under steady
state conditions. When the load is changed suddenly from 75% rated load to 25% rated load, the source
current, reactive power demand and harmonic components are also changed correspondingly. The
fundamental component of source current, THD in source current, % of current harmonic components,
displacement power factor, distortion power factor, source power factor, real power, reactive power, apparent
power and distortion power in each cycle is shown in Table 3.
Table 2(a). Fundamental component of source current and THD in source current at the point of common
coupling with variable speed induction motor drive – under steady state conditions
Case
Fundamental component of
source current (p.u.)
THD in
Source
Current (%)
% of
5th
harmonic
% of
7th
harmonic
% of
11th
harmonic
% of
13th
harmonic
Phase a Phase b Phase c Phase a
Phase
A
Phase
A
Phase
a
Phase
a
I 0.92 0.92 0.92 34.5 28.2 12.6 4.1 2.1
II 0.51 0.51 0.51 57.13 53.5 19.4 5.2 2.9
Table 2(b). Estimation of Power system parameters for the specified load conditions under steady state
Case
Displacement
power factor
Distortion power
factor
Source power
factor
Real Power
(pu)
Reactive
Power
(pu)
Apparent
Power
(pu)
Distortion
Power (pu)
I 0.98 0.9453 0.9293 0.91 0.16 0.92 0.08
II 0.53 0.87 0.4342 0.46 0.7967 0.92 0.085

511
Table 3(a). Fundamental component of source current and THD in source current in each cycle at the point of
common coupling with variable speed induction motor drive – under dynamic conditions
Cycle
THD in
Source
current (%)
% of
5th
harmonic
% of
7th
harmonic
% of
11th
harmonic
% of
13th
harmonic
Phase
A
Phase
A
Phase
A
Phase
a
I 0.92 0.92 0.92 34.5 28.2 12.6
4.1
2.1
II 0.84 0.84 0.84 39.2
34.6
14.12
4.29
2.25
III 0.78 0.78 0.78 43.8
39.87
15.78
4.47
2.42
IV 0.70 0.70 0.70 47.96
44.3
17.24
4.7
2.63
V 0.62 0.62 0.62 53.2
49.7
18.3
4.95
2.81
VI
0.51 0.51 0.51 57.13
53.5
19.4
5.2
2.9
Table 3(b). Estimation of Power system parameters in each cycle with variable speed induction motor drive -
under dynamic load conditions
Cycle
Displacement
power factor
Distortion power
factor
Source power
factor
Real Power
(pu)
Reactive
Power
(pu)
Apparent Power
(pu)
Distortion
Power (pu)
I 0.98 0.9453 0.9293 0.91 0.16 0.92
0.08
II 0.9397 0.945 0.888 0.7893
0.287
0.84
0.03
III 0.866 0.9289 0.8044 0.6755
0.39
0.78
0.026
IV 0.766 0.9143 0.7004 0.5362
0.45
0.7
0.0036
V 0.6428 0.8955 0.5756 0.3985
0.4749
0.62
0.0082
VI 0.53 0.87 0.4342 0.46
0.7967
0.92
0.085
Results show an effective harmonic filter is necessary to provide variable reactive power and
harmonic compensation to meet IEEE standards of good power quality. Active filters are commonly used for
dynamic power quality compensation. But these active filters are highly expensive. Hence as an economical
solution, hybrid filters were introduced. Here, shunt passive filter contributes major part of reactive
compensation and selected harmonic compensation. Only remaining harmonic compensation is to be met by
the shunt active filter.
3. PROPOSED ADAPTIVE SHUNT HYBRID FILTER FOR POWER QUALITY COMPENSATION
IN INDUCTION MOTOR DRIVES
The adaptive shunt hybrid filter consists of three phase adaptive shunt passive filters and adaptive
shunt active filter. Adaptive shunt passive filters are developed by series combination of thyristor switched
series combination of inductor and capacitor. Their values are designed such as to provide bypass path for
fifth and seventh harmonics. It also provides fundamental frequency reactive power to the system. The
capacitor values are selected as 210F and inductor values are 15mH and 7mH respectively. Remaining
amounts of harmonics and reactive compensation currents are provided by the adaptive shunt active filter.
The shunt active filter is controlled to inject remaining amount of harmonics and reactive compensation
currents such that source need to supply only real part of fundamental component of current. The schematic
diagram of the filtering system is shown in Figure 4. The hybrid filter elements are controlled by ANN based
intelligent digital controller. The responsiveness of filter is improved by hysteresis controller based closed
loop control. PI controller is also used to compensate for inverter losses and regulation of dc link voltage.

 ISSN: 2088-8694
512
Figure 4. Three phase system feeding variable speed induction motor drive with Adaptive Shunt Hybrid
Filter
3.1. Methodology
The load current in induction motor drive is represented by:
)sin()sin()(
,5,3
1 1 



h
LhLhLL thititi L
 = Real part of fundamental component
of load current +Reactive part of fundamental component of load current +
Harmonic components of load current
(1)
Adaptive shunt passive filter compensates for major part of fundamental frequency reactive power
and harmonics. Adaptive shunt active filter injects remaining small amount of harmonics and helps to obtain
unity power factor sinusoidal current at the point of common coupling.
Three phase instantaneous source voltages, fundamental load currents and filter compensation
currents are selected as input quantities for training adaptive ANN. The reference compensation currents are
developed by analog controller circuit. The actual compensation currents are compared with reference
compensation currents to generate switching pulses to IGBTs of three phase voltage source inverter. The
current transducers and voltage transducers sample instantaneous load currents, compensation currents and
source voltages. Sampled value of instantaneous load current is expressed as:
i.e. iL[k] = )]cos()sin([ 2
,.....3,2,1
1 tnkWtnkW n
N
n
n 

= )]cos()sin([)]sin()cos([ 2
,.....3,2
12111 tnkWtnkWtnkWtnkW n
N
n
n  

= iL1, re[k] + iL1, im[k] + h
[k]ih (2)
where W1n and W2n are amplitudes of sine and cosine components of the measured load current.
The equation is represented in vectorial form as:
iL[k] = [W11 W21 ---------W1N W2N]
































)cos(
)sin(
)2cos(
)2sin(
)cos(
)sin(
tNk
tNk
tk
tk
tk
tk






The adaptive ANN network is implemented using Widrow-Hoff weights updating algorithm [6], [7].
The weights of the connection links are updated using error in the estimated fundamental component and

513
actual real part of fundamental component of load current. The back propagation neural network was trained
with MATLAB using 1500 training patterns for 2500 epochs with goal of 0.001.Training method used is
Levenberg – Marquardt algorithm. Trained artificial neural network consists of two layers: input layer (6
neurons), output layer (7 neurons) and hidden layer (6 neurons). The ANN network is shown in Figure 5. The
performance characteristics of neural network training is shown in Figure 6. The ANN is programmed and
implemented using dsPIC30F4011 microcontroller. Two bipolar ADCs are used for conversion of analog
quantities to digital quantities. Sampling frequency of 3kHz is selected considering time for sensing input
samples, digital conversion, program execution and generation of switching signals. The switching pulses are
amplified and given to IGBTs in shunt active filter. The isolation between power circuit and controller circuit
is done using an optocoupler 6N136. The shunt active power filter circuit includes power inverter
(SKM50GB12B) with three phase IGBT bridge and two capacitors of 2200F. The compensating currents
injected by three phase inverter through coupling inductors to the point of common coupling. For
sA
dt
diF
/10
max






, 400V 5A 10mH coupling inductor is used. The experimental results with the
insertion of ANN Controller based shunt hybrid filter are discussed in following section.
Figure 5. Artificial Neural Network for controlling adaptive shunt hybrid filter
Figure 6. Performance plot of training neural network for controlling the adaptive shunt hybrid filter
4. PERFORMANCE OF ANN CONTROLLED SHUNT ACTIVE FILTER UNDER DYNAMIC
CONDITIONS–RESULTS AND DISCUSSION
The operating performance of the adaptive shunt hybrid filter is studied under dynamic conditions –
with the application of 25% load and 75% load at t = 0.5s. Fundamental component of source current, THD
in source current and power system parameters at the point of common coupling with the installation of
adaptive shunt hybrid filter is shown in Table 4 and 5. Figure 7, and 8 show waveforms of source voltage,
load current, filter current and source current with the installation of adaptive shunt hybrid filter under

 ISSN: 2088-8694
514
dynamic conditions. The performance of adaptive shunt hybrid filter is verified with reduction in source
current harmonics and sinusoidal source currents in phase with source voltages. Waveforms also confirm the
performance of the filter under dynamic conditions.
coupling with variable speed induction motor drive with Adaptive Shunt Hybrid Filter – Steady state
conditions
Case
THD in Source
Current (%)
% of
5th
harmonic
% of
7th
harmonic
% of
11th
harmonic
% of
13th
harmonic
Phase
A
Phase
A
Phase
a
Phase
a
I 0.84 0.84 0.84 3.15 2.2 1.6 0.7 0.4
II 0.23 0.23 0.23 3.19 2.5 1.4 1.2 0.9
Table 4(b). Estimate of Power system parameters for the specified load conditions – with Adaptive Shunt
Hybrid Filter – Steady state conditions
Case
Displacement
power factor
Distortion power
factor
Source power
factor
Power Delivered by Source
Real Power
(pu)
Reactive
Power
(pu)
Apparent
Power
(pu)
Distortion
Power (pu)
I 1 0.9991 0.9991 0.84 0 0.84 0
II 1 0.9995 0.9995 0.23 0 0.23 0
.
Figure 7. Source voltage, Load current, Filter current, Source current waveforms for induction motor drive
load at 25% rated load under balanced system with adaptive shunt hybrid filter –dynamic conditions
Figure 8 Experimental results - Source current waveforms for the induction motor drive load under balanced
system with adaptive shunt hybrid filter – dynamic conditions; (a) Without filter, (b) With adaptive shunt
hybrid filter

515
coupling with variable speed induction motor drive after the installation of Adaptive Shunt Hybrid Filter –
Dynamic conditions
Cycle
THD in
Source
Current (%)
% of
5th
harmonic
% of
7th
harmonic
% of
11th
harmonic
% of
13th
harmonic
Phase
A
Phase
A
Phase
a
Phase
A
I 0.84 0.84 0.84 3.15 2.2 1.6
0.7
0.4
II 0.72 0.72 0.72 3.24
2.31
1.59
0.6
0.31
III 0.60 0.60 0.60 3.56
2.43
1.87
0.78
0.35
IV 0.48 0.48 0.48 3.32
2.36
1.63
0.63
0.32
V 0.36 0.36 0.36 3.26
2.34
1.60
0.58
0.29
VI 0.23 0.23 0.23 3.19
2.5
1.4
1.2
0.9
Table 5(b). Estimate of Power system parameters in each cycle under dynamic load conditions with the
installation of Adaptive Shunt Hybrid Filter
Cycle
Displacement
power factor
Distortion power
factor
Source power
factor
Power Delivered by Source
Real Power
(pu)
Reactive
Power
(pu)
Apparent
Power
(pu)
Distortion
Power (pu)
I 1 0.9991 0.9991 0.84 0 0.84 0
II 1 0.998 0.998 0.72 0 0.72 0
III 1 0.997 0.997 0.60 0 0.60 0
IV 1 0.997 0.997 0.48 0 0.48 0
V 1 0.998 0.998 0.36 0 0.36 0
VI 1 0.999 0.999 0.23 0 0.23 0
The simulation and experimental results related to the adaptive shunt hybrid filter illustrated:
a) A single controller is used for controlling both adaptive shunt passive filter and adaptive shunt
active filter
b) The digital ANN based controller is flexible and easy to implement in large quantities.
c) In the case of adaptive shunt hybrid filter, the kVA delivered by source for the load is much less
compared with shunt adaptive passive filter or ANN controller based shunt active filter.
d) The fundamental reactive power drawn from source is much reduced and hence source power
factor is improved.
e) The performance of the ANN controller is satisfactory with balanced/ unbalanced source and
balanced/unbalanced nonlinear load under steady state and dynamic conditions.
5. CONCLUSION
Adjustable speed induction motor drives cause large amounts of current and voltage harmonic
distortions and reactive power absorption at the point of common coupling. The propagation of distortions
throughout the power system affects lifetime of all other power system equipment. Various power quality
improvement schemes were suggested by different authors. This paper shows an ANN based adaptive shunt
hybrid filter for power quality enhancement in a variable speed drive system. The simulation and
experimental results show effective performance of adaptive shunt hybrid filter under steady state and
transient conditions.
ACKNOWLEDGEMENT
The authors wish to thank Amrita Vishwa Vidyapeetham, Coimbatore and Department of Science
and Technology, New Delhi for their financial support for carrying out this work.

 ISSN: 2088-8694
516
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