Improvement of Power Quality by using Injection Super Capacitor UPQC for BLDC Motor

23 International Journal for Modern Trends in Science and Technology
Improvement of Power Quality by using Injection
Super Capacitor UPQC for BLDC Motor
B. Ramu1
| Afroz Shaik2
1PG Student, Department of Electrical & Electronics Engineering, Guntur Engineering College, Guntur, A.P, India.
2Assistant Professor, Department of Electrical & Electronics Engineering, Guntur Engineering College, Guntur, A.P, India.
To Cite this Article
B. Ramu, Afroz Shaik, “A Improvement of Power Quality by using Injection Super Capacitor UPQC for BLDC Motor”,
International Journal for Modern Trends in Science and Technology, Vol. 02, Issue 12, 2016, pp. 23-29.
This paper presents the operation of unified power quality conditioner (UPQC) as a universal active power
conditioning device to mitigate both current as well as voltage distortions at a distribution end of power
system network. The UPQC is designed by combining a series active power filter and shunt active power filter
which shares a common DC link capacitor and series active filter mitigate the voltage related harmonics in
power supply side and shunt active filters are mitigate the current related harmonics of non linear loads.
UPQC mitigate the harmonics and other harmonic sensitive loads. Among from them unified power quality
conditioner was widely studied by different controllers and we applied to BLDC motor for updating of load
characteristics that improve the power quality in distribution side.
KEYWORDS: Power quality, unified power quality conditioner (UPQC), phase locked loop (PLL), fuzzy logic
controller.
Copyright © 2016 International Journal for Modern Trends in Science and Technology
All rights reserved.
I. INTRODUCTION
In electric power system the power quality mostly
effected by voltage and current variation these are
caused by harmonic content in the supply due to
non-linear loads, such as large thyristor power
converters, rectifiers. These are also affected by
switching of loads and removing of loads in the
form of sags and swells. The above number of
factors are mainly effects the power system quality.
These number of factors issues to maintaining the
fixed voltage at point of common coupling for
various voltage distribution levels and finally to
maintaining the unity power factor drawn from the
electric power supply ,stop unbalance currents and
voltages from different distribution levels , voltage
and current harmonics reduction in the system [1].
In the distribution system using of number of
non-linear loads so want to be maintaining the
quality of power. Hence power quality varies with
the different sources of generations. The
conditioning of power supply by injecting the
specific values of voltage and current by
concentrated the UPQC.
In our power system using single phase loads,
three phase loads it’s all are linear or non-linear
but our final criterion is to eliminate the voltage
and current variations to maintain the system at
exact levels. The receiving of AC supply is
converted into DC by using inverters. The
converted DC supply strictly is clearly stored by
one device is called a battery. The energy is stored
in the form of battery or flywheel etc. These are
artificial type of because of its have slower rate
charge/discharge time by the reason of slower
chemical process. The proposed UPQC presents
super capacitors it require small amount of current
for charging [1]. Power transfer is high and it is very
ABSTRACT
International Journal for Modern Trends in Science and Technology
Volume: 02, Issue No: 12, December 2016
ISSN: 2455-3778
http://www.ijmtst.com

B. Ramu, Afroz Shaik : A Improvement of Power Quality by using Injection Super Capacitor UPQC for BLDC Motor
less weight, efficiency is more when compare to
conventional batteries.
In our electric power system using different types
of loads which are linear and non-linear loads. In
case of linear loads there is no problem from the
harmonics and when there is an using non-linear
loads like 3-phase four were bridge-rectifier and
diode-bridge rectifier with RC load in the DC side. If
using of non linear loads it will presents the
harmonics it may more than 45% is observed. In
paper [6] using bi-directional full bridge DC-DC
converters are used in UPQC. In this paper
concentrated only on voltage variations, current
variations using the series inverter and parallel
inverter. The UPQC is a custom power device and it
contains series and parallel active filters which are
used to compensate voltage and current related
problems. In voltage problems like voltage swell,
sags and flicker, voltage harmonics, in current
related problems like reactive power generation
and poor power factor. The improvement of power
factor and reactive power is neglected so the entire
system is protected to connected the UPQC at the
load end side.
II. POWER QUALITY PROBLEMS IN
DISTRIBUTION NETWORK WITH HIGH
PENETRATION OF DGS
In distribution network with high penetration of
DGS output of the power is fluctuated. The power
could be supplied by energy storage technology,
which includes two aspects: one is high efficient
mass storage, and the other is fast and efficient
energy conversion. Energy storage is useful for the
future demand for the critical load. Meanwhile, it
would provide technical support for reducing
network power loss and improving power quality.
Super capacitor storage is normally used for
smoothing the power of short duration, high power
load or used in high peak power situation such as
high power DC motor starting and dynamic voltage
restorer. When it comes to voltage sags or
instantaneous disturbance, Super capacitor
storage technology is able to improve the power
supply and quality. Thus, this technology is
suitable for solving power quality problems in
distribution network with high penetration of DGs
[12]
Custom power technology, based on power
electronic technology, could provide power supply
up to reliability and stability level which users
required in MV/LV distribution network system.
UPQC, with feature of series compensation and
parallel compensation being integrated together,
has been considered as the most full featured and
effective one of all DFACTS technologies so far. To
improve power quality of distribution network with
the high penetration of DGs, developing custom
power technology based on UPQC, which can inject
active power during the voltage regulation and
integrate to reactive compensation, is a feasible
strategy.
Fig.1. Structure scheme of UPQC.
Traditional UPQC used in power distribution
system, integrating series compensation voltage
principle and parallel compensation voltage
principle in one device, can compensate
three-phase asymmetric and harmonicon both
mains supply voltage and nonlinear loads. UPQC is
composed of the main circuit shown in Fig.1,
including series and parallel PWM converter, and
the control circuit. There are two basic control
strategies, i.e. direct control scheme and indirect
control scheme. Direct control scheme means
series converter is controlled as sinusoidal current
source to isolate voltage disturbance comes from
grid and load. And parallel converter is controlled
as sinusoidal voltage source to avoid load reactive
power, load harmonic current and unbalance from
being injected into grid. On the other side indirect
control scheme means series converter works as a
non-sinusoidal voltage source, outputting
compensation voltage which offsets grid voltage
distortion and fundamental deviation, accordingly
it ensures load voltage being rated sinusoidal
voltage.
Meanwhile, parallel converter works as an
non-sinusoidal current source, outputting reactive
power and harmonic current which offset reactive
load power and load harmonic current, accordingly
it could make the injected current be sinusoidal
and running under unit power factor by
compensating reactive power and harmonic
current[13]. Indirect control scheme by researched
more common is mainly discussed in this paper.
With the series and parallel PWM converter
topology, three phase four-leg circuit structure
implements both three-phase and single phase

structure, as a result, it is more flexible and
versatility. And three-phase control systems can
drive unbalanced loads as a result of three phases
being mutually independent [14]. Therefore, it
chooses the three-phase four-leg circuit structure
as the topology of power quality improving device.
In view of the above, this paper presents a kind of
three phase four-wire power quality conditioning
device based on fast energy storage named
Energy-storage UPQC (EUPQC) aiming for power
quality problems in distribution network with high
penetration of DGs.
III. SUPERCAPACITOR BASED UPQC
The block diagram representation for the
proposed system is shown in fig (2). The DC link of
both these active filters is connected to a super
capacitor through a common DC link capacitor.
The source side as well as load side maintain the
stable voltages and currents so using series active
filters and shunt active filters are used, when series
active filters are used to inject the voltage when sag
appears and to consume voltage when swell
appears in the line. The shunt active filter is
reduces the harmonics from source side, load side
and also improve the power factor. These
transformers are also used to filter the ripple
content in the series active filters.
The super capacitor bank consists of number of
series and parallel capacitors. The UPQC is solve
the problem simultaneously, by using UPQC in the
line harmonic reduction and compensation of
voltage and current, but UPQC has the capability of
voltage imbalance compensation and regulation
also harmonic compensation at the consumer end.
The UPQC is one of the best solutions for the large
capacity loads sensitive to supply voltage
imbalance. The UPQC system with DC/DC
converter is to control the voltage at capacitor end
and also performance of the system is improved.
Fig 2. Proposed Block Diagram of UPQC with Super
capacitor.
The super capacitor bank consists of number of
series and parallel capacitors. The UPQC is solve
the problem simultaneously, by using UPQC in the
line harmonic reduction and compensation of
voltage and current, but UPQC has the capability of
voltage imbalance compensation and regulation
also harmonic compensation at the consumer end.
The UPQC is one of the best solutions for the large
capacity loads sensitive to supply voltage
imbalance. The UPQC system with DC/DC
converter is to control the voltage at capacitor end
and also performance of the system is improved. In
the proposed control method, load voltage, source
voltage, and source current are measured,
evaluated, and tested under unbalanced and
distorted load conditions using MATLAB/Simulink
software.
IV. STRUCTURE OF EUPQC
As shown in Fig.3, the main circuit system
structure of EUPQC includes series converter,
parallel converter, booster and discharge unit
which consisting of super capacitor energy storage
and DC/DC converter, outputting power
transformer TsA~TsC of series converter, output
filters Ls and Cs of series converter and
inductance 𝐿 𝑃 , of parallel converter [5]. The electric
interfaces A1, B1, C1, and N1 connect distribution
network source and the A2, B2, C2, and N2
connect various loads. Two sets of three-phase
four-leg converter respectively compose the series
and parallel converters of the EUPQC. The series
converter output enters into distribution network
via LC filter and transformer in series, while the
parallel device output enters into distribution
network with filter inductance in parallel.
When EUPQC accesses to distribution network
and sets to work, the DC bus voltage equals to that
of the super capacitor bank. Then close contactors
KMp2, 380V AC power supply charges to the dc
side via pre-charge resistance R1 and parallel
converter. When charging completes, close KMp1,
and break KMp2 and DC/DC converter starts to
work. Adjust the DC side voltage to nominal
reference level 690V. Detect unbalanced degree
and harmonic content of mains supply voltage and
load current in load side, in order that parallel
converter could be put into operation when over
ranging problem happens when voltage problems
like voltage sag and swell happen to mains supply,
series converter will be put into operation and
output compensation voltage until the problems
are solved. Then series converter quits working
and the SCRA, SCRB and SCRC bypass.

Fig.3. Main circuit system structure of EUPQC.
The single phase structure schematic diagram of
EUPQC is illustrated in Fig. 4. Series converter
output voltage vector to compensate voltage
unbalance and harmonic of power supply side.
Parallel converter is used to solve power quality
problems in load side, such as unbalance and
harmonic of nonlinear load including reactive
compensating and current harmonic. Super
capacitor energy storage and DC /DC converter
buffer reactive power, exchange and provide energy
for voltage compensation. As a result, decoupling
series converter and parallel converter is
implemented. Moreover, voltage quality problems
of power interruption, which beyond the reach of
traditional UPQC, can be resolved successfully.
Fig. 4.The single phase structure schematic of EUPQC
Fig.5.Control schematic of EUPQC
The ultimate purpose of EUPQC control is to
keep load voltage on a constant level and be
sinusoidal feature, compensate load reactive power
and harmonic and ensure power supply has unity
power factor characteristic in all circumstances. In
this control schematic of EUPQC shown in Fig.5,
series converter works as a non-sinusoidal voltage
source, outputting compensation voltage 𝑢 𝑐 , which
offsets grid voltage distortion and fundamental
deviation, accordingly it ensures load voltage 𝑢 𝐿 ,
being rated sinusoidal voltage.
Meanwhile, shunt converter works as a
non-sinusoidal current source, outputting reactive
power and harmonic current 𝐼𝑐 , which offset
reactive load power and load harmonic current,
accordingly it could make the injected current
𝐼 𝑠 , be sinusoidal by compensating reactive power
and harmonic current. And the angle between the
injected voltage us and the injected current 𝐼𝑠 is
zero at the moment, namely the power factor in grid
side is unity.
V.THE CONTROL STRATEGY OF EUPQC
The control of EUPQC mainly includes three
aspects: the control of series converter, the control
of parallel converter and the control of DC bus
voltage. In control strategy diagram of series
converter shown in Fig.5 𝑢 𝑠𝑎 , 𝑢 𝑠𝑏 , 𝑢 𝑠𝑐 are
distribution network three-phase voltage
respectively. Through software phase-locked loop,
we could get t ω sin and t ω cos, which is essential
to d-q rotary transformation. After that then we
perform d-q transform and d-q inverse transform
on three phase standard voltage to make it
in-phase with mains supply voltage. Then subtract
the distribution network unbalance voltage from
this standard voltage to get three phase reference
compensation voltage Compare reference voltages
with three phase actual compensation voltage 𝑢 𝑐𝑎 ,
𝑢 𝑐𝑏 , 𝑢 𝑐𝑐 , and constitute closed loop control by
using a PI regulator. Specifically, in SPWM mode
three phase driving signal of series converter is
generated, consequently series converter is
controlled to output corresponding voltage vector
to compensate. The control of the forth leg of series
converter is aiming to keep load zero sequence
voltage to zero, which function is implemented
through closed loop control with feed-forward
control for voltage constituted by a PI regulator,
symbols 𝑢 𝐿𝑎 , 𝑢 𝐿𝑏 , 𝑢 𝐿𝑐 , in Fig.6. Represent
three-phase load voltage respectively.

Fig. 6. Series converter control strategy diagram
As parallel converter control strategy diagram
shown In Fig.6, perform d-q transform on three
phase load current 𝑖 𝐿𝑎 , 𝑖 𝐿𝑏 , 𝑖 𝐿𝑐 .
Then let the transformed current pass low-pass
filter to generate active component 𝑖 𝑑 and reactive
component 𝑖 𝑞 . Perform d-q inverse transform on
these two components to get fundamental
component of three phase load current. Subtract
load current from this standard current to get three
phase reference compensation current. Compare
the reference currents with three phase actual
compensation current 𝑖 𝑐𝑎 , 𝑖 𝑐𝑏 , 𝑖 𝑐𝑐 , and constitute
closed loop control by using a PI regulator. The
same as the series converter control mode, in
SPWM mode three phase driving pulse signal of
parallel converter is generated, consequently
parallel converter is controlled to output
corresponding current vector to compensate. The
control of the forth leg of shunt converter is aiming
to keep load zero sequence current to zero, which
function is implemented through closed loop
control constituted by a PI regulators symbols 𝑖 𝑠𝑎 ,
𝑖 𝑠𝑏 , 𝑖 𝑠𝑐 , in Fig.7. Represent three-phase power
supply current respectively.
Parallel converter can realize reactive
compensation by controlling reactive component iq
. If 𝑖 𝑞 =0, then all reactive power of the load is
provided by parallel converter.
Fig.7.Parallel Converter Control Strategy Diagram.
DC side of EUPQC, consisting of bi-directional
DC-DC converter based on super capacitor fast
energy storage, is able to solve problems of deeper
voltage sag and voltage instantaneous
interruption. Fig.8. Illustrates control strategy of
DC/DC converter. After comparing reference
voltage 𝑢 𝑑𝑒𝑓 , with DC bus voltage 𝑢 𝑑 the two
voltages pass through closed loop PI control and
then compared by limited driver to generate PWM
signal. They could drive IGBT3 and IGBT4
respectively to implement the control of DC/DC
converter and then use the output to maintain 𝑢 𝑑
at a desired level. The function of discharge circuit
comprising IGBT1 and IGBT2 could avoid over
tension happens to DC bus voltage 𝑢 𝑑.
Fig.8. DC/DC converter control strategy diagram.
VI. BLDC MOTOR
Permanent magnet motor is one of the load in
electrical power system. The motor consists of
stator and rotor. These are used in mid power
applications such as robotics, adjustable speed
drives and electric vehicle. In light of the rotor
position, the force gadgets are commutated
consecutively every 60 degrees. The electronic
compensation takes out the issues connected
with the brush and the commutator plan, in
particular starting and destroying of the
commutator brush course of action, along these
lines, making a BLDC engine more rough
contrasted with a dc engine. Fig.9 demonstrates
the stator of the BLDC engine and fig.10 shows
rotor magnet plans.
Fig.9. BLDC motor stator construction
Fig.10. BLDC motor Rotor construction.

The brush less dc engine comprise of four
fundamental parts Power converter, changeless
magnet brushless DC Motor (BLDCM), sensors
and control calculation. The force converter
changes power from the source to the BLDCM
which thus changes over electrical vitality to
mechanical vitality. One of the remarkable
highlights of the brush less dc engine is the
rotor position sensors, in view of the rotor
position and order signals which may be a
torque charge, voltage summon, rate order etc;
the control calculation s focus the entryway sign
to every semiconductor in the force electronic
converter.
The structure of the control calculations
decides the sort of the brush less dc engine of
which there are two principle classes voltage
source based drives and current source based
drives. Both voltage source and current source
based commute utilized for perpetual magnet
brushless DC machine. The back emf waveform of
the engine is demonstrated in the fig. 11. Be that as
it may, machine with a non sinusoidal back emf
brings about diminishment in the inverter size and
lessens misfortunes for the same influence level.
Fig.11 Hall signals & Stator voltages.
VII. MATLAB/SIMULINK RESULTS
Case 1: Proposed UPQC Converter
Voltage Waveforms:
Fig.12.Shows load Voltage, DVR Voltage and Source
Voltage.
Fig : 12 Illustrates the output Load voltage, DVR
Voltage and Source Voltage after introducing
proposed technique. Here the UPQC module with
super Capacitor is used for power quality
improvement instead of the conventional injecting
transformer and Injection Capacitor Methods. The
voltage and current waveforms are as shown in Fig
12 and Fig: 13 respectively. The system minimized
the power quality issues to further level. Here the
sag elimination was more effective and
instantaneously than the transformer.
Currents Waveforms:
Fig.13. Source Current, Load Current and Compensating
Current.
Case 2: Proposed UPQC Converter with BLDC
Motor
Fig.14.Total harmonic distortion of BLDC motor drive
Fig: 14 illustrates that the total harmonic
distortion is improved by using the UPQC with
super capacitor to minimize the power quality
issues generated by the different types of faults.
The proposed system concludes the total harmonic
distortion (THD) as 1.78%which is more
improvement as the conventional methods, in
which the THD is 18.82%.
Fig.15.Simulation results for Stator Current, Speed, and
Torque.

Fig: 15 Illustrates the speed torque
characteristics along with stator current which
shows the variation of all the parameters with
respect to time. At the time of starting of a BLDC
motor, it requires a high starting torque so that the
speed of the motor attains a constant speed with
respect to time.
VIII. CONCLUSION
This paper proposes a new configuration of
UPQC that consists of the DC/DC converter and
the super capacitor. The proposed UPQC
compensated the reactive power, harmonic
currents, voltage sag and swell, voltage unbalance,
and the voltage interruption. This paper
demonstrated for compensation of reactive power,
voltage sag & swell, neutral currents, unbalanced
for voltage and currents, and elimination of current
harmonics and voltage regulation & correction of
power factor, as per IEEE standard the total
harmonic distortion will be equal to 5% and less
than 5%. In our proposed UPQC converter with
BLDC having THD only 1.78%, so that the
harmonics are eliminated and also power factor is
improved. Rotor movement regulated by speed
controller & by varying frequency of the pulse
based on feedback from the hall sensors. The
application of this paper is used in the distribution
side, so the consumer gets reliable and accurate
power without any losses.
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