JOURNAL OF RESOURCE MANAGEMENT AND TECHNOLOGY …

JOURNAL OF RESOURCE MANAGEMENT AND TECHNOLOGY ISSN NO: 0745-6999

Vol 10, Issue1, JAN / 2019

www.jrmat.com Page No:44

Identification of Suitable Unified Power Quality Conditioner

topology for Power Quality Enhancement of Industrial Applications

P.Mahes Kumar, A.Senthil Kumar, R.Venkata Krishna

Abstract

The voltage sag, current harmonic distortions and reactive power demand are the most common problems

that affect the industrial performance. Conventionally, the UPQC with voltage source inverter topology is used to

address power quality problems. But, the topology based on conventional voltage source inverter suffers from major

disadvantages such as depends on system parameters, high transient period and limited operating conditions. To

overcome the drawbacks of the conventional inverter topology, a new neutral point clamped based UPQC topology

is proposed in this paper. The performance of the proposed UPQC topology is evaluated for various industrial loads

such as RL load and rectifier RL load. Also the effectiveness of the proposed UPQC topology is investigated for

various operating conditions extensively through SIMPOWERSYSTEM block sets of MATLAB/SIMULINK

simulation and compared with the conventional scheme.

Index Terms—Power Quality, Power Factor Improvement, Total Harmonic Distortion, UPQC strategy,

Series and Shunt Active Power Filter.

1. Introduction

The proliferation of power electronic based loads has brought great awareness on power quality of the

electrical power supply. These power electronics based loads are very sensitive and need a clean power supply for

optimal performance. In recent years, the power electronic devices are incorporated with equipments for power

conversion, measuring purposes, electronic controller has increased power quality distortion in a power transmission

and distribution system. The power electronic devices generate the unwanted current and voltage harmonics in the

power system network [1-3]. These unwanted current and voltage harmonics have caused over heating, reduced life

time, acoustic noise emission, pulsating torque in the electrical machines, malfunction of equipments and radio

interference. These effects are very expensive for the customer, ranging from minor quality variations to production

downtime. All this interest has resulted in a variety of compensation devices have developed by power engineers for

dynamic and adjustable solution to power quality problems encountered in a power distribution system.[4-6].

Traditionally, the passive filters have installed to compensate the current harmonics produced by nonlinear

load and to improve the power factor of the system. But these conventional methods have a lot of disadvantages

such as tunning problem, creates series and parallel resonance [7]&[8]. To overcome these problems, the custom

power devices are proposed. The custom power devices [7-9] provide an appropriate solution to compensate the

power quality problems and also protects the load from voltage sags, swells, outages etc. According to the topology

the custom power device is classified into the shunt active power filter, series active power filter and unified power

quality conditioner strategy. The unified power quality conditioner is the universal power conditioner for

compensating power quality problems. The unified power quality conditioner strategy is the combination of series

and shunt active power line conditioner with a common DC link capacitor.

Conventionally, the series and shunt active power filter of UPQC strategy utilizes back to back connect

three phase three leg voltage source inverter with a common DC link capacitor. The conventional topology required

high DC link capacitor voltage to mitigate the power quality problems. This problem made the control technique

more complicated and increases the rating of the system. To overcome this problem three level neutral point

clamped based voltage inverter is proposed in this paper. A number of control techniques for the UPQC strategy

have presented in the literature [14-17]. The unit vector template generation (UVTG) is a familiar time domain

based control techniques designed and analyzed in this paper. The advantage of the unit vector control technique is




that is simple to implement, easy to analyze and it has high reliability on the compensation of the power quality

problems.

In this paper, the performance of conventional and proposed UPQC topology is investigated for management of

inherent power quality issues. The implementation of sinusoidal pulse width modulation technique for proposed

UPQC strategy is discussed The power quality of a nonlinear load for before and after connecting the proposed

UPQC is investigated. The compensation of voltage sag power quality and power consumed by the load is derived

and analyzed

A general introduction to the problem of power quality is presented the in introduction, to quantify the power

quality problems, conventional distribution system is discussed in section 2, the configuration of conventional and

proposed UPQC topology for the management of inherent power quality issues are represented in section 3, the

control technique deployed in UPQC strategy for the DC link voltage regulation using a PI controller is discussed in

the section 4 and the simulation results for quantifying the benefits of proposed system is brought out in section 6,

finally the conclusions of this paper finds a place in section 7.

2. Conventional Distribution System

In conventional distribution system, the domestic loads and industrial loads are directly connected to the grid. Any

active power line conditioner is not installed between grids and loads. Such that, the three phase source voltage of

the system is given as follows

(1))tωsin(mVtsaV

(2) )ο120tωsin(mVtsbV

(3) )ο120-tωsin(mVtscV

Without any active power line conditioner, the load voltage and current is delivered from the source voltage and

current. The non linear loads created harmonic components at the point of common coupling such that the source

voltage and current contains both the fundamental and the harmonic current component is given as follows.

( ) ( ) ( ) ( ) tLV=tsV and tLI=tsI

(4) )οnφtωnsin(

∞

3,1n

nI)ο1φtωsin(1ItsI

and )tωnsin(

∞

3,1n

nV)tωsin(1VtsV

∑

∑

component lfundamenta =)ο1φ+tωsin(1I and )tωsin(1V

component harmonics = )οnφ+tωnsin(∑∞

3,1=nnI and )tωnsin(∑

∞

3,1=nnV

These harmonic components created the major power quality problems in the distribution system. A novel UPQC

strategy is introduced to mitigate the power quality problems presented in the distribution system. The compensation

capability of UPQC strategy is determined by the topologies implemented for active power filter, the following

section deals with the configuration of UPQC strategy with conventional and proposed topology.

3. Unified Power Quality Conditioner Strategy

The power quality issues gain a quantify attention in industrial sectors. In recent years for power quality

management, many compensating devices are designed by the various power engineers. Among several devices, a




unified power quality conditioner strategy is novel power device proposed to compensate the power quality

distortions in a distribution system simultaneously. The power circuit for UPQC strategy to solve power quality

problems encountered in industries and distribution system is highlighted in Fig.1. It consists of two voltage source

inverters are connected back to back which shares a common DC link. One voltage source inverter is connected in

parallel between source and load at the point of common coupling point (PCC) which forced to act as a shunt active

power filter. Another voltage source inverter is connected in series between grid and load through series transformer

acting as a series active power filter. Normally, the shunt active power filter is utilized to compensate current

harmonics created by

nonlinear loads, power factor corrections and compensate load reactive power demand. The compensation of voltage

related problems such as sag, swell, flicker, unbalance, interrupt is done by series active power filter. The

performance of shunt and series active power filter of UPQC strategy is mainly depends on its voltage source

inverter topology.

3.1 Conventional voltage source inverter topology for UPQC strategy

The impact of UPQC strategy of mitigating power problems is generally depends on the voltage source

inverter topology. The conventional voltage source inverter topology for UPQC strategy and its pulse generation

technique are shown in the Fig.2. In general, the voltage source inverter is used to generate the AC voltage from a

DC source with controlled magnitude, frequency and phase. It consists of two voltage source inverter connected

back to back with a common DC link capacitor. These inverters are forced to act as series and shunt active filter.

These active filters share a single DC link and no place for providing neutral point at the DC link. And also the

compensation of harmonics is greatly depends on passive filter. These reasons




are limited the compensation capability of the active power filter, its operating conditions and also source current

THD is quite high even after compensation. In order to overcome these problems a new voltage source inverter

topology is proposed for series and shunt active power filter.

3.2 Proposed voltage source inverter topology for UPQC strategy

The three level PWM based neutral clamped voltage source inverter topology is proposed in UPQC

strategy. The construction of the proposed topology is shown in the Fig.3. It consists of two back to back connected

three level PWM based neutral clamped voltage source inverter which sharing a common two DC link capacitor

with a neutral point. One neutral clamped voltage source inverter connected in series between source and load

through a series transformer which forced to act as series active power filter for UPQC strategy. Another neutral

clamped voltage source inverter is connected in parallel between source and load at the point of common coupling

which behave as a shunt active power filter. The advantage of the proposed topology is

two DC link capacitor is equally charged. Hence the voltage across any one of a capacitor is regulated to

compensate the power quality problems. Hence, the proposed topology reduces the power rating of filters and




thereby it helps to reduce cost investment. The sinusoidal pulse generation technique is used to generate the pulse

for proposed UPQC strategy is shown in Fig.4.

4. Modeling of control technique

The control technique deployed in the UPQC strategy is classified into shunt control technique and series control

technique. In order to demonstrate the effective compensation using UPQC strategy, a unit vector template

generation technique is implemented for series and shunt control technique. The block diagram of a unit vector

template generation technique for generating reference signal is shown in the Fig.5.

4.1 Series control technique

The primary objective of series controller of UPQC strategy is to mitigate the voltage disturbances such as

sag, swell, unbalance, flickers encountered either in grid or load side. When UPQC strategy is connected to the

system, the series control technique is computed the reference voltage signal is shown in equations (5-6). The rated

load voltage (Vm) is predetermined and kept it constant for throughout operation. The three phase unit sine signal is

generated with the help of phase lock loop (PLL), while the product of rated load voltage and unit sine signal gives

the reference voltage signal.

(5) )tωsin(*mV)t(a_refV

(6) )ο120tωsin(*mV)t(b_refV

(7) )ο120-tωsin(*mV)t(c_refV

The sinusoidal pulse width modulation (SPWM) is used to generate pulse for UPQC strategy for obtaining robust

compensation voltage and current. The difference of reference voltage and actual load voltage determines the error

for generating the pulses shown in (8). The pulsed generated using error signal is illustrated in Fig. 4.

(8) LV - refV controller seriesfor signal Error

Hence after compensated, the source voltage is found to be sum of load voltage and compensation voltage derived

in equation (9).

(9) tsrVtLVtsV

4.2 Shunt control technique

The shunt active power filter of UPQC strategy plays a vital role on mitigating current and voltage harmonic

distortions, power factor corrections, compensate load reactive power demand and regulating the DC link voltage at




rated value. The shunt control technique is utilized PI controller for decreasing the error between actual and

reference DC link voltage and extract the reference current signal is displayed in equation (10).

(10) )tωsin(*)s

IK+p(K*)dcV-dcref(V)t(srefI

where

)sIK

+p(K is PI Controller

)dcV-dcref(V is error

)tωsin( is unit vector

The three phase reference signal for extracting compensating current is obtained as following equations

(11) )tωsin(*)dcV-dcref(V*)s

IK+p(K)t(a_srefI

(12) )ο120tωsin(*)dcV-dcref(V*)s

IK+p(K)t(b_srefI

(13) )ο120-tωsin(*)dcV-dcref(V*)s

IK+p(K)t(c_srefI

The difference of reference current and the actual source current determines error signal processed for producing the

pulses shunt active inverter shown in (14).

(14) sI - refI controller seriesfor signal Error

Hence after compensated, the source current is found to be difference of compensation current and load derived in

equation (9).

(15) tlItshItsI

5. Simulation Results, Analysis and Discussion

The performance of conventional and proposed UPQC topology is evaluated in SIMPOWERSYSTEM

block sets of MATLAB/SIMULINK of simulation software. The system ratings are taken for investigation are

230*sqrt(3/2) line to line RMS voltage, three phase RL load is 5KW+j0.1KVAR, three phase rectifier load is

20ohms and 20mH, shown in table. This investigation carried two sections: one is a comparative analysis between

conventional and proposed UPQC topology and another one is a performance analysis of the proposed strategy. In

the second section, the power quality of nonlinear loads is tested for before and after connecting proposed UPQC

strategy and also compensation of voltage sag, unbalance also carried out.




5.1 Performance Analysis of conventional and proposed UPQC topology

The regulation of DC link voltage determines the compensation capability of UPQC strategy for mitigating power

quality problems. The DC link voltage profile for conventional and proposed UPQC topology is represented in

Fig.6. the compensation of power quality by using conventional topology is done when its DC link capacitor is

charge and maintained at 550V whereas DC link voltage of proposed topology required only 260V for compensating




power quality problems. Hence, the proposed topology reduces the complexity of control technique, burdern of the

protecting device and improves the compensation capability. The peak overshoot and settling time of DC link

voltage using proposed topology is minimum compared to convention topology explained in the table. Fig. 7 shows

that the relation between DC link voltage and source current harmonic distortions using conventional and proposed

topology. This relation helps to choose the rated DC link voltage. This relation proved that the proposed UPQC

strategy has less DC link voltage. The compensation total harmonic distortion of voltage and current is illustrated in

Fig. 8. From the obtained Fig. 8, the proposed UPQC strategy has a better compensation of voltage and current

harmonic distortion.

5.2 Investigations on power quality of nonlinear load for before and after connecting proposed UPQC

strategy

In this investigation, the proposed UPQC strategy is connected to the system at 500msec shown in Fig.9. Before

500msec, the harmonics generated by the nonlinear load, is still not compensated is clearly visualized in Fig.9-A and

E. After connecting UPQC strategy, DC link voltage is regulated at rated voltage is shown in Fig.9-D. After

500msec the compensation voltage and current is starting to inject by the series and shunt active power filter. Hence

after injecting compensation voltage and current, the harmonics of source voltage and current is mitigated by the

proposed UPQC strategy

5.3 Simulation analysis for compensation of voltage sag in source side using UPQC strategy

The compensation of voltage sags conditions using proposed UPQC strategy is illustrated in the Fig. 10. In this

investigation, 20% of rated voltage is reduced in grid voltage during peak load condition at 400 msec shown in

Fig.10-A. In this state, without power line conditioner means the performance of industrial loads and domestic loads

is greatly affected. With the help of proposed UPQC strategy, the series active power filter has started to inject the

required voltage for maintaining the load voltage at rated level at the instant of 400 msec represented in Fig.10-C.

After compensated, the load voltage is maintained at rated voltage with the support of series active power filter,

Fig.10-B. Corresponding DC link voltage is also represented in the Fig.10-D. In normal operating condition, the DC

link voltage is maintained at rated value. After occurring sag conditions on the source side, the DC link voltage has

begun to reduce. The shunt active power filter has started to inject the compensation current which helps to regulate




the DC link voltage at rated value, Fig.10-G. The load current has not found to be disturbed with the help of

shunt active power filter during voltage sag condition. The fundamental magnitude of voltage is represented in

Fig.10–H for understanding the operation of UPQC strategy. This demonstration

ensured that the UPQC strategy has capable of compensating the voltage sags and maintain the load voltage at rated

value.

5.4 Simulation analysis for power consumption of load using UPQC strategy

In this section, the power consumption of the load for before and after compensation is analysed using

proposed UPQC Normally, the power consumed of the load is measured from the product of voltage and current.

However, without any power line conditioner the source current contains both the fundamental and harmonic

component and the power consumption of the nonlinear load is derived as

(16) ))nφtωnsin(

3,1nnI)1φtωsin(1I(*)tωsin(mVtsP

))nφtωnsin(

3,1nnI*)tωsin(mV

)1φtωsin(1I(*)tωcos(*)1φsin(*)tωsin(1ImV)1φcos(*)tω(2sin1ImVtsP

Power Consumed= Real power + Reactive Power + Harmonic Power

Due to the presence of harmonic and reactive power, the power consumption of the load is found to be high

for before compensation. While after connecting the UPQC strategy, the harmonic current and reactive current are

mitigated from the system such that source current is contained only fundamental component and harmonic

components are brought to zero. The power consumption of the load after compensation is measured from the

following equation.

(17) ))1φtωsin(1I(*)tωsin(mVtP




However after compensation, the voltage and current are found to be in phase with each other. The angle

between voltage and current is observed to be approximately zero, then the power equation became

(18) )1φcos(*)tω(2sin*1I*mVtsP

The power consumed as well as delivered by the UPQC strategy for maintaining the load voltage at rated

value and also compensating power quality problems is given in following equations.

The active and reactive power of series active power filter of UPQC strategy are derived as

(18) )srφcos(*sI*srVtsrP

(19) )srφsin(*sI*srVtsrQ

The active and reactive power of series active power filter of UPQC strategy are derived as

(20) )shφcos(*shI*LVtshP

(21) )shφsin(*shI*LVtshQ

The active and reactive power profile for before and after connecting UPQC strategy is shown in Fig.11. Without

UPQC strategy, the active and reactive power demand of load is delivered by

grid and also due to the presence of harmonics, power consumption is observed to be high, shown in equation (16).

After connecting UPQC strategy, the harmonic distortions are mitigated and power consumption of the load is

minimized . During normal operating conditions, the series and shunt active power filter didn’t consume the active

power. The reactive power demand of the load is supplied by the shunt active filter shown in Fig.11. The simulation

analysis of active and reactive consumption of the load during voltage sag condition using UPQC strategy is shown

in Fig.12. During voltage sag condition, active power consumption of load is maintained constant with the help of

series active power filter and reactive power is supplied by the shunt active power filter. This demonstration ensures

that the load reactive power demand is compensated at grid side.




6. Conclusion

A neutral point clamped voltage source inverter based UPQC strategy for the management of inherent power quality

issues is proposed in this paper. The performance of the proposed UPQC strategy is outperforms the conventional

UPQC strategy for mitigation of current harmonics generated by nonlinear load. The proposed UPQC strategy has

reduced the power consumed by the nonlinear and also it helps to maintain the power factor of the system in unity.

The control strategy deployed for maintaining the load voltage at rated condition with respect to different operating

conditions is addressed. The better computational efficiency of the proposed approach has shown that it can be a

wide range of power quality problems. The dynamic simulation results have brought out the advantage of the

proposed UPQC strategy for power quality enhancement of domestic and industrial applications.

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Appendix

System Parameter

Source

Voltage and frequency 230V and 50Hz

Impedance R=0.1Ω and L=0.1mH

DC Link

Voltage

Conventional Topology 550V

Proposed Topology 260V

Capacitor 30000µF

Shunt Active Power

Filter Impedance R=0.001Ω and L=15mH

Series Active Power

Filter

Transformer 1KVA and 1:1

Impedance R=0.001Ω and L=10mH

Load

Impedance R=0.001Ω and L=15mH

RL Load 5KW and 1KVAR

Rectifier RL Load R=20Ω and L=20mH

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