International Conference on Electrical, Electronics, and Optimization Techniques (ICEEOT) - 2016
Performance Evaluation of Sinusoidal Current
Control Strategy Unified Power Quality Conditioner
Rudranarayan Senapati, Rajesh Kumar Sahoo, Rajendra Narayan Senapati, Prafulla Chandra Panda, Senior
Member,IEEE
KIIT UNIVERSITY, Bhubaneswar, Odisha
e-mail: rsenapatifel@kiit.ac.in, rajeshkumarsahoo131@gmail.com, rns11@iitbbs.ac.in, pcpandafel@kiit.ac.in
Abstract- This paper focuses on Constant Sinusoidal
current control strategy based simulation of UPQC
(Unified Power Quality Conditioner). The proposed
methodology guarantees sinusoidal current to be drawn
from the supply system. In addition to this it compensates
the reactive power, for which the compensated current and
the source voltage are in phase. In case of non-linear loads
connected to the system which draw harmonic power
along with constant average power, UPQC is able to
supply the harmonic power, so that harmonic components
are not drawn from the supply system. . The UPQC not
only deals with harmonic power of the load but also deals
with zero sequence power owing to imbalances in the
power system. Simulation studies of UPQC for Three
Phase Four Wire system with neutral point clamped
topology has been performed using MATLAB R2014b for
combination of Linear and non-linear loads. The results of
the simulation study reveal that the current obtained from
the supply system is apparently sinusoidal with a very low
THD (Total Harmonic Distortion) within 0.04 percent.
Keywords- UPQC, Power Quality, Non Linear Load,
Harmonics, Power factor, Reactive power compensation.
I. INTRODUCTION
The present energy scenario puts an immense
challenge for electrical engineers to meet the consumer’s
rising expectations of getting high quality of power. The
advanced load that comprises of microprocessor and
microcontroller based power electronic (PE) devices are
susceptible to Power Quality (PQ) issues than that of
equipments used earlier. The increased demand of power
system efficiency and accurate controllability can be achieved
successfully with the excessive use of electronic controllers
for various load equipment such as adjustable speed motor
drives, power factor correction devices as capacitors, but due
to excessive use of these PE devices the harmonic level on
power systems increases which indirectly affects the system
capabilities in future as it can cause enormous voltage drop
and line losses. The most critical area for the above problems
are mainly continuous process large industry and the
information technology utilities. Due to disruption, an
978-1-4673-9939-5/16/$31.00 ©2016 IEEE
enormous amount of financial disaster may occur, with the
related fall of productivity and competitiveness.
Consumers are becoming informative about the PQ
problems such as sags, cut-off or disruption and switching
transients and imposed the suppliers to deliver enhanced
quality of power. Utilities have taken number of attempts to
achieve consumer demand so far and many measures have
been taken for power quality improvement to obtain the higher
PQ level. In general, low quality of power may arise the
increased power diminutions, unusual and unwanted behavior
of devices, intervention with adjacent communication lines,
and so on. Moreover the wide application of PE operated
devices has brought the charge on power distribution system
by producing power quality problems like harmonics in
currents and voltages in addition to excessive reactive current.
For improving the performance of distribution system and
with increase in the use of improved power semi conductor
technology, the custom power concepts were introduced in
distribution system which elaborates the beneficial power that
electrical suppliers will provide their consumers in near future,
emphasizing on condition of flow of power and dependency.
Due to the high demand and technological advancement in the
field of high power semi-conductor devices, the proposed
custom power solution are implementing now days. The
customer obtains rated power quality from the service
provider or by installing the equipment in co-ordination with
the utility.
The cost effective solution for filtering harmonics
and solving other PQ issues is passive filters, but the
disadvantages are harmonic resonance and amplification that
totally depends upon the source and line impedance and other
load parameters which are uncertain [1]-[2]. To mitigate the
above problems, the Active Filter along with power electronic
devices and application of FACTS concepts all together
results a single compensating device, i.e., Unified Power
Quality Conditioner (UPQC). Then question arises why only
UPQC, why not DSTATCOM, DVR and other FACTS
devices? DSTATCOM is shunt connected device meant for
current compensation whereas DVR is series connected device
meant for voltage compensation only, but UPQC as a single
unit uses both the above concepts [4].
The configuration of UPQC has been described in
section II, whereas the control strategy has been explained in
section III. The results from the simulation and analysis using
MATLAB\SIMULINK are discussed in section IV and section
V draws the conclusion.
Whereas
p0 =
+
p0

A verag e V alu e
II. UPQC
In low or medium distribution system, the problems related
to PQ (e.g., voltage disturbances/fluctuations, injection of
harmonic load current, etc.) that affects the performance of
critical load is mitigated by a multi tasking standalone custom
power device, named UPQC-Unified Power Quality
Conditioner[3]. To justify its name the device works for the
common objective synchronically to mitigate the three basic
issues of PQ (Voltage Sags, Voltage Swells, harmonics, etc.),
Power factor Improvement and Phase Unbalancing [7].
o f th e Z ero S eq u en ce
P o w er aid s th e

p0

O scillatin g C o m p o n en t
o f Z ero S eq u en ce P o w er
to tal en erg y tran sfer
(3)
(
1
v i + v ia + vca i
and q = v β iα − vα iβ =
bc
b
3 ab c
)
(4)
Configuration of UPQC
UPQC consists of two interconnected inverters (Series
and Shunt) realized either by Capacitor (Voltage Source
Inverter-VSI) or by Inductor (Current Source Inverter-CSI) as
a common DC-link voltage bus as shown in
Fig.1.
Fig.2. Physical significance of instantaneous power in αβ 0 frame.
p + p0 → Total Instantaneous power flow in unit-time.
q → Power exchange between three phases without any
transfer of energy
[Where ia , ib , ic and va , vb , vc are the Instantaneous Current
and Voltage in
VSI-embedded UPQC is mostly used due to its
compact nature and more cost effective as compared to CSIembedded UPQC having bulky DC-side filter and improper
switching devices [5].The shunt part that contributes the
required reactive power and harmonic currents is in opposite
to the load whereas the series part that provides the required
voltage is connected along the source voltage [6]. Apart from
the above parts UPQC also have shunt coupling inductor (a
link between the shunt inverter and the network), an LC filter
(for elimination of high-frequency switching ripples) and a
coupling transformer.
III. CONTROL STARTEGY
The 3-φ 4-wire system allows all line currents to be
independent unlike 3-φ 3-wire system where two of them are
independent[8].Hence for correct representation, additionally
instantaneously p0 (zero sequence power) is introduced in
αβ0-reference frame as the third instantaneous power along
with p (instantaneous active power) and q (instantaneous
reactive power) [9].
Mathematically that can be expressed as:
0
vα
v
β

0 i 
0
 
v   iα 
β  
i 
−vα   β 
(1)

The 3-φ instantaneous active power is:
P
= vaia + v i + vcic = vα iα + v i + v i = p + p
3−φ
β β 00
0
bb
frame. iα , iβ , i0 and vα , vβ , v0 are the
Instantaneous Current and Voltage in αβ 0 -frame].
The active, reactive current components are derived from the
instantaneous abc voltages and currents and represented as:
Fig.1. Block diagram of UPQC

 p  v
0
   0
 p = 0
  
 q  
0
 

abc
(2)
v 
v 
 vα
 vα
 iα 
β   p
β  0
1
1


 =
+





 
2
2
iβ  v 2 + v 2 v
v
v
v
−
−
0
α    vα + vβ  β
α   q 
 
α β  β


 


ReactivePart
ActivePart
By the use of Inverse Clarke Transformation
imaginary current can be obtained as follows:

 ia ( p )

i
 b( p )

i
 c ( p )



 =



 1

2  1
− 2
3 
 1
− 2

(5)


 vα iα + v β i β  vα
3

2 
vβ
vα2 + v 2

β

− 3 2 
0


 ia ( q ) 
v
ic + v i a + v c a i


bc
b
i
 = ab
 b (q ) 
v 2 + v 2 + v c2a
ab
bc


 i c ( q ) 
v
 bc
 vc a

v
 ab






abc




real and
(6)
(7)
A.Shunt inverter control
To compensate the VAR, the current harmonics and
to control the voltage across DC-link capacitor, it is observed
that the universal expressions for the p − q theory are not
sufficient for compensation of load current. Therefore to
satisfy the compensation characteristics, the following three
control strategies were introduced [10].
Constant instantaneous power control strategy: This is the
strategy used in which the Shunt active filter must compensate
a constant portion of power that is oscillating real-power.
Sinusoidal current control strategy: This strategy may be
used where sinusoidal current is drawn from the source.
Generalized Fryze current control strategy: This is the
strategy normally used to minimize the rms value of current
with which same volume of energy can transfer as that of the
distorted current.
IV. SIMULATION RESULT
The analysis of operation of UPQC for a 3-φ 4-wire
system can be observed by using MATLAB\SIMULINK. The
power circuit and its control circuit for 3-phase 4-wire system
with unbalanced source voltage and distorted load current are
modelled. Various simulation studies were carried for the
system with circuit parameter as shown in Table I given
below.
TABLE I
Simulation Parameter
Load Parameter
Value
Non Linear Load
Resistance
100Ω
Inductance
0.15mH
Linear Load
1000V
Nominal phase-to-phase voltage ( Q )
Active Power ( P
Fig.3. Block diagram of Shunt Inverter control
Out of the above three methods, we use the second
control strategy for our consideration. The Sinusoidal current
control strategy is enforced, iff the Shunt APF is accounted for
the harmonic power to guarantee balanced, fundamental
frequency current to be obtained from the supply.
Additionally, APF compensates the Reactive Power in such
way that, the compensated current and the fundamental
positive sequence component of the voltage are in phase. But,
it does not generate the Real Power (constant) till the system
voltage is non-sinusoidal and unbalanced. Again due to high
rms value, Ohmic Losses are there in the Power Distribution
System.
10kW
)
100Var
Reactive Power (Q )
DC Link Capacitance
1000µF
Fig.5 shows the utility side parameters where Fig.
5(a) shows the nature of supplied voltage in phase and Fig.
5(b) shows the behavior of line current of 3-φ 4-wire system.
These waveforms reveal how UPQC compensate the
disturbances in source side. The source current THD value
was found to be 0.3% due to the compensation process of
UPQC and the FFT analysis result of the system is shown in
Fig.6.
B.Series inverter control
Voltage disturbances like voltage harmonics, voltage
sag or swell due to the overloaded distribution line can be
compensated by the help of series inverter. The comparison of
the components of positive sequence voltage Vabc and the
distorted source voltage VR _ abc , series inverter injects a
reference voltage in phase with the voltage (supply). For the
compensation of voltage sag or swell, there is real power
balancing among the inverters and the real power either
supplied or absorbed from the supply line. To manage the
capacitor voltage to a fixed value, series inverter must absorb
or deliver instantaneous real power equivalent as that of shunt
inverter deliver or absorb.
(a)
(b)
Fig.5. Utility side parameter
(a) Source voltage (b) Source current
Fig.4. Block diagram for series inverter control
loading condition. The sinusoidal current control strategy
drives the UPQC in such a way that the supply system draws
constant sinusoidal current under steady state condition. In
addition to this shunt converter also delivers the reactive
VARs required by the load, so that the input power factor
improves. The THD in source current becomes as low as 0.03
percent which is another achievement of the above study.
VI. REFERENCES
[1]
Fig.6.Total harmonic distortion level
Before compensation due to the nonlinear load (rectifier
circuit using RL) voltage across load and load current was
found to be distorted and unbalanced,but with the use of
sinusoidal current control strategy based unified power quality
conditioner both load voltage and load current is found to be
balanced and smooth as shown in Fig.7(a) and (b). The
potential across the DC-link capacitor common between the
two converters is found to be constant through out the process
and as shown in Fig.7(c).
[2]
[3]
[4]
[5]
[6]
[7]
(a)
[8]
[9]
(b)
(c)
Fig.7.Simulation results
(a) Load voltage (b) Load current (c) Capacitor voltage
V. CONCLUSION
A conceptual study of UPQC has been performed for
3-φ 4-wire system under simultaneous linear and non-linear
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