analysis, design and control of a unified power-quality

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ISSN 2348–2370

Vol.10,Issue.05,

May-2018,

Pages:0584-0589

Copyright @ 2018 IJATIR. All rights reserved.

Analysis, Design and Control of a Unified Power-Quality Conditioner

Based On a Current-Source Topology N. OBULESU

1, K. NAGAVENI

2, T. MANOHAR

3

1Assistant Professor, Dept of EEE, ALITS, Anantapur, AP, India.



Abstract: A three-phase unified power quality conditioner

based on current source converters (CSC-UPQC), including

the design guidelines of the key components, an appropriate

control scheme, and a selection procedure of the dc current

level. Particularly, the ride through capability criterion is

used to define a minimum dc current level so that the CSC-

UPQC achieves the same characteristics as a UPQC based

on voltage-source converters in terms of voltage disturbance

compensation in the point of common coupling (PCC) and

load power factor compensation. A series inverter of UPQC

is controlled to perform simultaneous 1) voltage sag/swell

compensation and 2) load power sharing with the shunt

inverter. The active power control is used to compensate

voltage sag/swell and is integrated with theory of power

angle control of UPQC to coordinate the load reactive

power between the two inverters. Since series inverters

simultaneously deliver active and reactive powers, this

concept is named as UPQC-S (S for complex power). A

detailed mathematical analysis, to extend the PAC approach

for UPQC-S is presented in this project A 1.17 MVA load

fed from a 3.3 kV system is used to show the proposed

design procedure, and a laboratory prototype is

implemented to show the system compensating sags and

swells using low switching frequency in the CSC and

maintaining a unitary displacement power factor in the

PCC.

Keywords: Current Source Converters, Nonlinear Control,

Power Quality (PQ), Unified Power-Quality Conditioner

(UPQC).

I. INTRODUCTION

The present power distribution system is becoming highly

susceptible to the different power quality issues. The wide-

ranging use of nonlinear loads is further causal to greater

than before current and voltage harmonic problems. In

addition, the saturation stage of small/large-scale renewable

energy systems (RES) base on wind energy, solar radiation

energy, chemical fuel cell, etc., installs at distribution and

transmission levels is rising fundamentally. In addition of

renewable energy sources in a power system are further

magnificent new difficult task to the electrical industry to

include these newly rising distributed generation systems.

To continue the controlled power quality regulations, some

kinds of compensation at all the power levels are becoming

a familiar perform. The provision of both DSTATCOM and

DVR can control the power quality of the source current and

the load bus voltage. In addition, if the DVR and

STATCOM are connected on the DC side, the DC bus

voltage can be regulated by the shunt connected

DSTATCOM while the DVR supplies the required energy

to the load in case of the transient disturbances in source

voltage. The configuration of such a device (termed as

Unified Power Quality Conditioner (UPQC)) is shown. This

is a versatile device similar to a UPFC. However, the

control objectives of a UPQC are quite different from that of

a UPFC.

Fig.1. UPQC Operation of D-Statcom.

In view of both voltages sag and swell scenarios are

essential for a detailed investigation on VA loading in

UPQC-VA min as shown in Fig.1. The authors have

proposed in the project a concept of Power Angle Control

(PAC) of UPQC. The Power Angle Control idea suggest

that with good control of the series inverter voltage

successfully supports the part of the load reactive power

demand, and thus the VA rating of the shunt inverter

reduces. Most significantly, this synchronize reactive power

sharing feature is achieved without disturbing the resultant

load voltage magnitude, during normal steady-state

condition. Using particle swarm optimization technique the

optimal angle of series voltage injection in UPQC-VA min

is computed. These iterative like methods mostly on the

online load power factor (PF) angle evaluation, and thus

may result into deadly and slower evaluation of optimal

angle.

N. OBULESU, K. NAGAVENI, T. MANOHAR

International Journal of Advanced Technology and Innovative Research

Volume. 10, IssueNo.05, May-2018, Pages: 0584-0589

II. POWER QUALITY

Conceivably, the best electrical supply would be a steady

greatness and frequency sinusoidal voltage waveform. On

account of the non-zero impedance of the supply

framework, of the expansive assortment of loads that may

be experienced and of other phenomena, for example,

transients and outages, the truth is regularly diverse. The

Power Quality of a system communicates to which degree a

practical supply system looks like the perfect supply system.

Poor Power Quality can be depicted as any occasion

identified with the electrical system network that ultimately

results in a budgetary misfortune. Conceivable results of

poor Power Quality incorporate

Unexpected power supply failures (breakers tripping,

wires blowing).

Equipment failure or failing

Equipment overheating (transformers, engines) are

prompting their lifetime reduction.

Damage to delicate supplies (Pc‘s, production line

control frameworks).

Electronic communication interferences

Increase of system power losses

A. Definition Of Power Quality Power quality could be a term which means various things

to completely different individuals. Institute of Electrical

and Electronic Engineers (IEEE) normal IEEE1100 defines

power quality as “the conception of powering and

grounding sensitive instrumentation equipment in an

exceedingly manner appropriate for the equipment. All

electrical devices are prone to malfunction or failure when

exposed to more power quality problems. The electrical

machine be a transformer, an electric motor, a computer a

generator, a printer, a household appliance, or a

communication equipment. Depending on the severity of

problems others and all of these devices react adversely to

power quality issues as shown in Fig.2.

B. Power Quality Progression

Since the invention of power 300 years ago, the

distribution, generation and use of electricity have correctly

evolved. New and innovative suggest to generate and use

electricity the economic revolution, and since then

engineers, scientists, and hobbyists have contributed to its

continued evolution. In the starting stage, electrical devices

and machines were crude at best but nonetheless more

utilitarian. They performed quite well and consumed gaint

amounts of electricity. The machines were designed with

price consideration solely secondary to performance issues

as shown in Fig.3. They were probably liable to however the

consequences were not readily discernible, whatever power

quality problems existed at the time, and due partly to the

robustness of the machines and due to the lack of good ways

to measure parameters of power quality. However, within

the last 50 years or so, the economic years to the need for

products which are to be economically competitive, that

meant that electrical machines were smaller and more

efficient and were designed without performance margins.

At a uniformity time, diverse variables were becoming

possibly the most important factor.

C. Power Quality Nomenclature

Webster’s New World Dictionary defines nomenclature as

the “the terms employed in a specific art science etc.”

Understanding the terms employed in any branch of

humanities or science is basic to developing a way of

familiarity with the topic. The science of power quality is

not any exception. Inter connecting the conductive parts

electrically to ensure common voltage between the

connected parts. Electrical bonding is done for two reasons.

When bonded using low impedance connections, conductive

parts, would be at the same electrical potential, which

means that the difference in voltage between the connected

parts would be negligible or minimal. Electrical Bonding

additionally states current likely imposed on a metal part

should be safely conducted to other grid systems or ground

serving as ground.

Fig.2. Distortion.

Fig.3 notch & noise.

Fig.4 voltage swell.

D. Power Quality Issues

Power quality is an easy term, nevertheless it describes

a different issue which are found in any electrical power

system network and it is a subjective term. The concept of

bad and good power depends on the end user. The consumer

feels that the power is good if a piece of equipment

functions satisfactorily. If the equipment fails prematurely

Analysis, Design and Control of a Unified Power-Quality Conditioner Based On a Current-Source Topology



or does not function as intended there is a feeling that the

power will be bad. Depending on the perspective of the

power user In between these limits, many grades or layers

of power quality might exist as shown in Fig.4. A better

starting point for solving all /power quality problems is,

understanding the power quality issues. Power frequency

disturbances are low-frequency phenomena which results in

voltage swells or sags. They may be load or source

generated due to switching operations or faults in a power

system. The susceptibility of electrical equipment is

concerned the end results are the same as shown in Fig.5.

Fig.5. Voltage sag.

Power system transients are short-duration, fast events

that produce distortions such as ringing, notching and

impulse. Transient energy is propagated in power lines,

eventually dissipated and transferred to other electrical

circuits are different from the factors which effect power

frequency disturbances. Harmonics in Power system are low

frequency phenomena characterized by waveform

distortion. It introduces harmonic frequency components.

Current and Voltage harmonics have undesirable effects on

power system components and power system operation In

some instances, interaction between the power system

parameters (R–L–C) and the harmonics can cause severe

consequences. The concept of bonding and grounding is the

more complex issues in power quality studies. For three

reasons grounding is done as shown in Fig.6. In the U.S.,

the fundamental objective of grounding is safety by the

National Electrical Code (NEC) safety grounding is

mandated.

Fig.6. Power quality issue.

Radio Frequency Interference (RFI) is the interacting

between conducted or radiated radio frequency fields and

communication equipment and sensitive data. Including of

RFI in the category of EMI is convenient, but the two

phenomena are different. Electrostatic discharge (ESD) is a

unpleasant and very common occurrence. In our day to day

lives, ESD is an uncomfortable nuisance we are subjected to

when we open the refrigerated case in the supermarket and

door of a car. But, ESD is harmful to electronic equipment

at high levels, which causes damage and malfunction.

Non Linear Load: Here we are considering nonlinear loads

where current not proportional to voltage. Voltage supplied

to a non linear system, either by generator set or utility, is

sinusoidal. For most inductive loads and resistive, current is

also sinusoidal, but rectifiers charging a battery draw an

almost square wave current pulse. AC line current will flow

only when the rectified instantaneous voltage exceeds

battery voltage. Original sine wave voltage from the source

now becomes distorted due to voltage drop across the

source impedance during the cycle portion when current is

flowing.

Notching Phenomenon: Current is switched on by SCRs

consecutively in a three-phase rectifier circuit. An SCR

conducts only during the time when its particular phase

voltage is more positive than the other two-phase voltages

once switched on. In practice, SCR turn on is delayed to

regulate output and does not occur until the oncoming phase

voltage is significantly higher than preceding conducting

phase voltage. Current cannot build up instantly in the

oncoming phase nor can it decay instantly in preceding

conducting phase Due to inductance in the SCR source

circuit. There is momentary line-to-line shorting action with

Phase 1, which has SCR-1 in the decaying conducting

mode, when the more positive oncoming Phase 2 with SCR-

2 is gated on. The resulting short is of very short duration,

but produces a notch in input voltage waves 1 and 2. Notch

depth and width during this commutation period are

dependent upon SCR firing angle, supply system

impedances and load current.

Ringing Effects: A secondary phenomenon caused by the

rapid switching of SCRs is ringing effect. Ringing is a high

frequency oscillation following sudden "turn on" of an SCR

.Due to inherent inductance and capacitance in the circuit

elements it is the result of high frequency resonance

occurring in the rectifier source circuit. Ringing and

notching effects can result in severe voltage waveform

distortion. The continuous switching affects the power

system severely. This ringing effect causes power

distortions in the system. The inductive effect causes this

ringing effect which causes when turning on the SCR.

Harmonic Current: The rectifier, because it draws non

sinusoidal current from its source, along with ringing and

notching and effects, introduces distortion to the voltage

wave from the source. This is called harmonic distortion.

Cyclical waveform is made up of components consisting of

fundamental sine wave plus other sine waves according to

theories of waveform analysis, called harmonics, which are

multiples of the fundamental frequency. The nonlinear

source, therefore, does not see distorted current waveform

as a single waveform, but as multiple, fundamental plus

harmonic waves. Harmonics may have severe effects upon

the power source connected to the same source or other

loads. It is important to note loads drawing harmonic




currents causes voltage distortion at the source ,the source

does not produce the harmonic distortion.

Power Factor: Generators are rated for 0.8 power factor.

Connected loads may have a lower power factor.

Displacement of current with respect to voltage occurs with

rectifier phase control. Line power factor can vary

depending upon SCR conduction angle. Compounding this

are the high frequency harmonic currents which primarily

result in added KVAR. Consult with the device supplier for

specific input KVA and power factor.

III. PROPOSED SYSTEM

In distribution level, to compensate several major power

quality problems UPQC is a main clarification. In figure the

general block diagram representation of a UPQC-based

system is shown. It normally consists of two voltage source

inverters associated back to back using a general dc bus

capacitor. This project deals with a new concept of most

select utilization of a UPQC. The most important power

quality problems are voltage sag & swell on the system. The

voltage sag/swell will be compensated by the devices of a,

series active power filters, dynamic voltage restorer, UPQC,

etc. as well as with the help of power quality enhancement

devices, the UPQC has higher compensation capability for

voltage problems such as sag/swell. In this project called as

UPQC-VA min. along with the aforementioned the three

approaches, the in-phase voltage injection requires the

minimum voltage magnitude, while the quadrature voltage

injections require a maximum series injected voltage. For

the duration of a minimum VA loading approach, the series

inverter injects the voltage at an certain angle with respect

to the source current. As well the series inverter injection,

the current drawn by the shunt inverter from the network, to

maintain the dc link voltage and the highly power balance in

the network, and plays an vital role in obtaining the overall

UPQC VA loading as shown in Fig.7.

Fig.7. Structure of Unified Power Quality Conditioner

(UPQC) system.

The project on UPQC-VA min is obtained on the optimal

VA loading of the series & shunt inverter of UPQC mainly

during voltage sag/swell condition. while it is necessary an

out of phase module to be injected for compensation of

voltage swell, the recommended VA loading in UPQC-VA

min obtained on the basis of the voltage sag, It could not be

at optimal value. In view of both voltages sag and swell

scenarios are essential for a detailed investigation on VA

loading in UPQC-VA min. The authors have proposed in

the project a concept of Power Angle Control (PAC) of

UPQC. The Power Angle Control idea suggest that with

good control of the series inverter voltage successfully

supports the part of the load reactive power demand, and

thus the VA rating of the shunt inverter reduces. Most

significantly, this synchronize reactive power sharing

feature is achieved without disturbing the resultant load

voltage magnitude, during normal steady-state condition.

Using particle swarm optimization technique the optimal

angle of series voltage injection in UPQC-VA min is

computed. These iterative like methods mostly on the online

load power factor (PF) angle evaluation, and thus may result

into deadly and slower evaluation of optimal angle. On the

other hand, by estimating the power angle δ, the PAC of

UPQC concept determines the series injection angle. The

angle δ is compute in adaptive way by computing the instant

load active/reactive power and thus, it ensures fast and exact

estimation. With similar to PAC of UPQC, In a unified

power flow controller (UPFC) the reactive power flow

control utilizes by shunt and series inverters as shown in

Fig.8. A UPQC is used in a power distribution system to

carry out the shunt and series compensation at the same

time, while a UPFC is used in a power transmission system.

In balanced and distortion-free environment, the power

transmission systems are generally operated, unlike to

power distribution systems that may contain dc component,

distortion, and unbalance. The main purpose of a UPFC is to

control the flow of power at fundamental frequency.

Fig.8. Concept of PAC of UPQC.

In this project, a total mathematical formulation of PAC

for UPQC-S is carried out. The prospect and efficiency of

the proposed UPQC-S approach are validates by simulation

as well as experimental results. Also, this power flow

control in UPFC the transmission network voltage may not

be maintained at the rated value while at the stage.

However, the load side voltage is strictly regulated at rated

value in PAC of UPQC, while performing load reactive

power sharing by shunt and series inverters. In this project,

the model of PAC of UPQC is further extended for voltage

sag and swells conditions. This modified model come

within reach of is utilized to compensate voltage sag/swell

while sharing the load reactive power between both shunt &

series inverters. Since in this case the series inverter of

UPQC delivers both active and reactive powers, it is

particular the name UPQCS (S for complex power). The key

in assistance of this project are outline as follows.

Analysis, Design and Control of a Unified Power-Quality Conditioner Based On a Current-Source Topology



For simultaneous voltage sag/swell and load reactive

power compensation in network with shunt inverter, the

series inverter of UPQC-S is utilized.

In UPQC-S, the available VA loading is utilized to its

maximum capacity during the entire running situation

opposing to UPQC-VA min where prime focus is to

reduce the VA loading of UPQC during voltage sag

condition.

The voltage sags as well as swells situation covers by

the concept of UPQC-S.

IV. SIMULATION RESULTS

Simulation results of this paper is as shown in bellow

Figs.9 to 19.

Fig.9. Supply voltage.

Fig.10. Load voltage.

Fig.11. Series inverter injected voltage.

Fig.12. Series inverter current.

Fig.13. Self-supporting dc bus voltage.

Fig.14. Enlarged power angle δ relation between supply

and load voltages during steady-state condition.

Fig.15. Supply current.

Fig.16 Load current.

Fig.17 Shunt inverter injected current.




Fig.18 Enlarged power angle δ during voltage swell

condition.

Fig.19 active and reactive power flow through source,

load, shunt, and series inverter utilizing proposed

UPQC-S approach under voltage sag and swell

conditions.

V. CONCLUSION

In this project, a new concept of controlling complex

power (simultaneous active and reactive powers) through

series inverter of UPQC is introduced and named as UPQC-

S. The proposed concept of the UPQC-S approach is

mathematically formulated and analyzed for voltage sag and

swell conditions. The developed comprehensive equations

for UPQC-S can be utilized to estimate the required series

injection voltage and the shunt compensating current

profiles (magnitude and phase angle), and the overall VA

loading both under voltage sag and swell conditions. The

simulation and experimental studies demonstrate the

effectiveness of the proposed concept of simultaneous

voltage sag/swell and load reactive power sharing feature of

series part of UPQC-S. The significant advantages of

UPQC-S over general UPQC applications are: 1) the

multifunction ability of series inverter to compensate

voltage variation (sag, swell, etc.) while lagging power

factor; DC bus: dc bus capacitor = 1100 μF/220 V,

reference dc bus voltage = 150 V; UPQC: shunt inverter

coupling inductance = 5 mH, shunt inverter switching type

= analog hysteresis current controller with average

switching frequency between 5 and 7 kHz, series inverter

coupling inductance = 2 mH, series inverter ripple filter

capacitance = 40 μF, series inverter switching type = analog

triangular carrier pulse width modulation with a fixed

frequency of 5 kHz, series voltage injection transformer turn

ratio = 1:3, DSP sampling time = 0 μs.

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[3] H.Akagi, “Trends in active filters line conditioner,”

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[8] L. Landaeta, C. Sepúlveda, J. Espinoza, and C. Baier, “A

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Author’s Profile:

N.Obulesu has 7 years of experience in

teaching in Graduate and Post Graduate level

and He Presently working as Assistant

Professor in department of EEE in ALITS,

Anantapur, AP, India.

K.Nagaveni has 1 year of experience in


and She Presently working as Assistant



T.Manohar has 2 years of experience in


and He Presently working as Assistant



analysis, design and control of a unified power-quality

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