TJPRC: Journal of Power Systems &
Microelectronics (TJPRC: JPSM)
Vol. 2, Issue 1, Jun 2016, 41-50
© TJPRC Pvt. Ltd.
ANALYSIS OF SHUNT HYBRID POWER FILTER WITH THYRISTOR
CONTROLLED REACTOR FOR POWER QUALITY IMPROVEMENT
M. DHEEBEEHA1, M. SUDHAKARAN2 & P. AJAY-D-VIMAL RAJ3
1
Research Scholar, Department of Electrical and Electronics Engineering
Pondicherry Engineering College, Puducherry, India
2
Professor, Department of Electrical and Electronics Engineering
Pondicherry Engineering College, Puducherry, India
3
Assistant Professor, Department of Electrical and Electronics Engineering
Pondicherry Engineering College, Puducherry, India
ABSTRACT
This paper presents a combination of shunt hybrid power filter and thyristor-controlled reactor (TCR) for
power quality improvement. The shunt hybrid power filter (SHPF) consists of a Active Power Filter (APF) and fifthharmonic LC tuned passive filter. The tuned passive filter and TCR forms a Shunt Passive Filter (SPF) which is used to
compensate reactive power generated by a critical load. Shunt Active Power Filter is used to perform the current
harmonic elimination and Shunt Passive Filter is used for power factor correction. To obtain a better compensation,
proportional-integral controller and triggering pulses are extracted by pulse generation technique. The simulation
results are found to be quite satisfactory to reduce harmonic distortions and to compensate reactive power.
KEYWORDS: Harmonic Suppression, Hybrid Power Filter, Modelling, Reactive Power, Shunt Hybrid Power Filter with
Thyristor-Controlled Reactor (SHPF-TCR)
Original Article
separate control technique has been adapted for both hybrid power filter and TCR. The control part includes
Received: Mar 12, 2016; Accepted: Mar 27, 2016; Published: Apr 11, 2016; Paper Id.: TJPRC:JPSMJUN20166
INTRODUCTION
The power electronic based equipments are used in industrial and domestic purpose. These equipments
have some issues on the quality of supplied voltage and it has current harmonics in the systems. They also have
negative effects on power system equipments and customers. Due to the usage of capacitive and inductive load,
the reactive power is generated; it means the reactive power is produced when the current waveform is out of
phase with the voltage waveform. Passive filter used for reducing the distortion due to harmonic current. But they
have disadvantages of resonance. And it depends on their performance of the system impedance and also it
absorbs the harmonic current of non-linear load. This leads to harmonic propagation through the power system. To
overcome these problem, active power filters is introduced. It has no such disadvantages like passive filter. Active
filter will inject the harmonic voltage or current with some appropriate magnitudes and phase angle into the
system and cancel the harmonics of non-linear loads. But it has also some demerits like high initial cost and high
power losses due to which it limits their wide applications, normally with high power rating system. To minimize
these limitations, Shunt hybrid filter consists of both active power filter and passive filter with a three phase PWM
inverter.
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42
M. Dheebeeha, M. Sudhakaran & P. Ajay-D-Vimal Raj
Figure 1: Block Diagram of SHPF–TCR Compensator
This filter effectively reduces the problem of both active and passive filter. There are different control techniques
are there for improving power quality. Some of them are vector control and unit vector template generation which are used
for extracting harmonic components of the source current from the fundamental components.
Power quality is defined by the parameters which express reactive power, harmonics, and load unbalance. The
harmonics are generally characterized by the total harmonic distortion or THD. In resistive loads the current produces the
heat energy which produces the desired output but in case of inductive loads the current creates the magnetic field which
will produce the desired work. Therefore reactive power is the non – working power caused by the magnetic current to
operate and support magnetism in the device. Reactive power is required to maintain the voltage to deliver active power
through transmission lines.
A
B
C
A
B
C
Three-Phase Source
+
-
Non-Linear Load
TCR
Control
technique
for TCR
Shunt
Passive
filter (SPF)
Control
technique
for APF
g
A
B
C
+
N
Shunt active power
filter (APF)
Shunt hybrid power filter
(SHPF)
Figure 2: Basic Circuit of SHPF–TCR Compensator
The best ideal electrical supply would be a sinusoidal voltage waveform with constant magnitude and frequency.
But in reality due to the non-zero impedance of the supply system, the large variety of loads may be experienced and of
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Analysis of Shunt Hybrid Power Filter with Thyristor
Controlled Reactor for Power Quality Improvement
43
other phenomena such as transients and outages, the reality is often different. If the power quality of the networks is good,
then any load connected to it will run satisfactorily and efficiently. In AC supply, the current is usually phase-shifted from
the supply voltage. This leads to different power definition. The active power P[KW], which is responsible for the useful
work is associated with the portion of the current which is in phase with the voltage. The reactive power Q[KVAR], which
sustains the electromagnetic field used to make a motor operate, is an energy exchange (per unit of time) between reactive
components (capacitors and reactors) and source. It is associated with the portion of the current which is phase shifted by
90 degree with the voltage. The apparent power S[KVA], which is a combination of the active and reactive powers, can be
seen as the total power drawn from the network. The ratio between active and apparent power is known as the power
factor (cosφ) and is a measure of a efficient utilization of the electrical energy. Unity power factor (cosφ that equals to 1)
refers to the most efficient transfer of useful energy. Cosφ equals to 0 refers to the most inefficient way of transferring
energy.
In this paper, a new combination of shunt hybrid power filter (SHPF) and a thyristor – controlled reactor (TCR) is
proposed to suppress current harmonics and to compensate the reactive power which is generated from the load. The
hybrid power filters is the combination of active and passive power filters. The active power filters are better solution for
power quality improvement but they require high converter rating. So the hybrid power filters are designed. The hybrid
power filters have the advantage of both active and passive filters. In the proposed topology, the compensation part is the
passive filter and the TCR while the active power filter (APF) is to improve the filtering characteristics and reduce the
resonance which can occur between the passive filter, the TCR, and the source impedance. The shunt APF when used,
suffers from the high kilovolt ampere rating of the inverter. Hence, the proposed combination of SHPF and TCR
compensates the reactive power and harmonic currents. In addition, it reduces the volt-ampere rating of the APF part. The
control method for the combined compensator is presented. The Simulation results show that the proposed compensator is
suitable for harmonic suppression and reactive power compensation.
SYSTEM CONFIGURATION OF SHPF-TCR COMPENSATOR
Figure 2 shows the topology of the proposed combined SHPF- TCR compensator. The Shunt Hybrid Power Filter
(SHPF) consists of APF connected in series with a fifth-tuned LC passive filter. The Active Power Filter (APF) consists of
a three-phase pulse width modulation (PWM) inverter and a dc bus capacitor (Cdc). It sustains very low fundamental
voltages and currents of the power grid, and thus, its rated capacity is greatly reduced. Because of these merits, the
proposed system is suitable for compensating reactive power and eliminating harmonic currents in power system. The fifth
harmonic tuned LC passive filter in parallel with TCR forms a shunt passive filter (SPF). This SPF is mainly for fifthharmonic compensation and PF correction. The APF is used to filter harmonics generated by the load and the TCR is to
enhance the compensating characteristics of the SPF to eliminate the risk of resonance between the grid and the SPF. The
TCR goal is to obtain a regulation of reactive power. The load is a combination of three-phase diode rectifier and a three
phase star connected resistive inductive linear load.
CONTROL STRATEGY
•
Control Technique
The most commonly used control technique is the Unit Vector Template Generation(UVTG). The required
compensation current is generated by multiplying unit sine vector with reference current and given to Hysteresis Current
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M. Dheebeeha, M. Sudhakaran & P. Ajay-D-Vimal Raj
Control (HCC). It does not require any complicated algorithm or mathematical equation. It is very easy to implement and it
gives a very fast response and good accuracy compared to conventional technique. It does not require any complicated
matrix transformation for its operation.
•
Pulse Generation Technique
The pulse generation technique used here is the Hysteresis Current Control (Hcc).
Figure 3: Pulse Generation Technique (a) Hysteresis Current Control (HCC),
(b) Conversion of Pulse from Sine Wave
•
P-I Control Scheme
The output of PI controller is considered as a peak value of the reference current. It is then multiplied by the unit
sine vectors (Vsa, Vsb and Vsc) in phase with the source voltages to obtain those reference currents (isa, isb and isc). These
reference currents and actual currents are given to a hysteresis controller. The difference of reference circuit template and
actual current decides the operation of switches.
Figure 4: P-I Controller
MODELING OF SAPF
•
Role of DC Side Capacitor
The DC side capacitor is for two main purposes: (i) it maintains a DC voltage with ripples in steady state, and (ii)
as an energy storage element to supply real power difference between load and source during the transient period. In the
steady state, the real power supplied by the source should be equal to the real power of the load plus a small power to
compensate the losses in the active filter. Thus, the voltage of DC capacitor can be maintained at a reference value.
However, when the load condition changes the real power balance the mains and the load will be disturbed. This real
power difference is to be compensated by the DC capacitor. This will changes the DC capacitor voltage away from the
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Analysis of Shunt Hybrid Power Filter with Thyristor
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45
reference voltage. In order to keep satisfactory operation or the active filter, the peak value o the reference current must be
adjusted to proportionally change the real power drawn from the source. This real power charged/discharged by the
capacitor compensates the real power consumed by the load. If the DC capacitor voltage is recovered and attains the
reference voltage, the real power supplied by the source is supposed to be equal to that consumed by the load again.
The peak value of the reference current Isp can be estimated by controlling the DC side capacitor voltage. Ideal
compensation requires the main current to be sinusoidal and in phase with the source voltage, irrespective of the load
current nature. The desired source currents, after compensation, can be given as
isa* = Isp sin ωt
isb* = Isp sin (ωt - 120○)
isc* = Isp sin(ωt + 120○)
where, Isp = (I1 cosΦ1 + Is1) is the amplitude of desired source current where the phase angle can be obtained from
the source voltages. So the waveform and phases of the source currents are known. This peak value of the reference current
has been estimated.
Figure 5: Proposed Control Scheme of SHPF-TCR Compensator
•
Unit Current Vector
The source currents are sensed and converted into unit sine currents and also the corresponding phase angles are
maintained. The unit current vectors templates are represented as,
ia = sin ωt
ib = sin (ωt - 120○) and
ic = sin (ωt + 120○)
These unit currents are multiplied with peak – amplitude of the estimated reference current (using PI) which is
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M. Dheebeeha, M. Sudhakaran & P. Ajay-D-Vimal Raj
used to generate the desired reference currents.
•
DC Side Capacitor (Cdc)
The design of DC side capacitor is based on the power flow of instantaneous power flow. The selection of Cdc will
reduce the voltage ripple.
SIMULATION RESULTS
Table 1 shows the parameters of the system. Simulations were performed under the MATLAB / Simulink model
in order to verify the SHPF–TCR compensator. Figure 6 shows the waveform of voltage and current which are connected
in the supply side for one phase.
Table 1: Specification Parameters
Supply Voltage Vrms(ph-ph)
Frequency
415 V
50 Hz
R = 15 ohms
L = 0.1e(-3)H
R = 15 ohms
L = 15e(-3)H
R = 0.1 ohms
L = 5e(-3) H
C = 1000e(-6)F
Vdc = 700 V
C = 1000e(-6)F
R = 15 ohms
L = 2e(-3)H
C = 100e(-6)F
Kp = 0.3
Ki = 9
Source impedance
Reactive load impedance
Active power filter parameters
DC bus voltage of APF
Non- linear load
Passive filter parameters
Controller parameters
50
40
30
20
10
0
-10
-20
-30
-40
-50
0.1
0.12
0.14
0.16
0.18
0.2
0.22
0.24
0.26
0.28
Time
400
300
200
V s1 (V )
100
0
-100
-200
-300
-400
0
0.05
0.1
0.15
0.2
0.25
Time
Figure 6: Source Current and Source Voltage Waveform for One Phase of SHPF-TCR
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S O U RC E V O LTA G E
V s (V )
400
200
0
-200
-400
0.65
0.655
0.66
0.665
0.67
0.675
0.68
0.685
0.69
0.695
0.655
0.66
0.665
0.67
0.675
Time
0.68
0.685
0.69
0.695
SOURCE CURRENT
Is (A )
50
0
-50
0.65
Figure 7: Three Phase Source Voltage and Source Current Waveform of SHPF-TCR
And also Figure 7 shows the three phase voltage and current waveform in which we can see that only a small
distortions in the three phase current. There are more distortions in both voltage and current which are reduced after
compensation are shown in those waveforms.
Total Harmonic Distortions
Figure 11 and 12 shows the harmonic spectrum of the source current before and after compensation. THD is the
total harmonic distortion which is brought down from 16.87% to 2.87%. It shows that the SHPF-TCR compensator offers a
very good performance level such that the THD percentage was reduced within the IEEE – 519 standard limit which is 5%.
LO A D V O LTA G E
400
200
0
-200
-400
0.11
0.12
0.13
0.14
0.15
0.16
0.17
0.18
0.19
0.12
0.13
0.14
0.15
Time
0.16
0.17
0.18
0.19
LO A D CUR RE N T
50
0
-50
0.11
Figure 8: Three Phase Load Voltage and Current of SHPF-TCR
Figure 8 shows the three phase load voltage and current in which no much ripples in the current and voltage after
compensation.
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M. Dheebeeha, M. Sudhakaran & P. Ajay-D-Vimal Raj
50
40
30
20
10
0
-10
-20
-30
-40
-50
0.1
0.15
0.2
0.25
Time
Figure 9: Voltage and Current Are In Phase with PI Controller after Compensation
From Figure 9 we came to know that the voltage and current are in phase with PI controller so that the reactive
power is compensated and the power factor was also improved.
1000
900
800
700
V d c (V )
600
500
400
300
200
100
0
0
0.1
0.2
0.3
0.4
0.5
Time
0.6
0.7
0.8
0.9
1
Figure 10: DC Capacitor Voltage with PI Controller
Figure 10 is the dc capacitor voltage drawn from the capacitor which is connected across the inverter. It shows
that the voltage rises to the peak because of tuning the Kp and Ki values and after a certain period it falls down and
maintain constant level at 700V , which is the reference voltage Vdcref and this reference voltage is compared with the DC
voltage Vdc using PI controller.
Figure 11: Harmonic Spectrum of Supply Current before Compensation
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Analysis of Shunt Hybrid Power Filter with Thyristor
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49
Figure 12: Harmonic Spectrum of Supply Current after Compensation
CONCLUSIONS
In this paper, a SHPF-TCR has been proposed for harmonics mitigation and reactive power compensation. The
proposed scheme has been designed and simulated on MATLAB/Simulink environment. It has been found that the SHPFTCR can eliminate current harmonics and compensate reactive power. The power factor of the system was also improved
and is able to reduce the THD of the supply currents well below the limit of 5% of the IEEE-519 standard.
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