COMPARATIVE ANALYSIS OF DYNAMIC VOLTAGE RESTORER …€¦ · Dynamic Voltage Restorer (DVR) plays key role in resolving power quality issues like voltage sag, swell, harmonics, interruption

http://www.iaeme.com/IJMETT/index.asp 1268 [email protected]

International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 10, October 2018, pp. 1268–1276, Article ID: IJMET_09_10_130

Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=10

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

COMPARATIVE ANALYSIS OF DYNAMIC

VOLTAGE RESTORER SUPPORTED WITH

BESS AND SUPER CAPACITOR

V. Srikanth Babu and M. Ram Babu

Department of Electrical & Electronics Engineering,

GMR Institute of Technology, Rajam, Srikakulam, Andhra Pradesh. India.

Dr. T. Suresh Kumar

Department of Electrical & Electronics Engineering,

Gokaraju Rangaraju Institute of Engineering & Technology, Bachupally, Hyderabad,

Telangana. India.

ABSTRACT

Dynamic Voltage Restorer (DVR) plays key role in resolving power quality issues

like voltage sag, swell, harmonics, interruption etc., which are detrimental in the power

system if uncompensated. Further, they improve power transfer capacity of the

transmission line. In this research article, the performance of the DVR is analysed under

two different scenarios: Battery Energy Storage supported and Super-Capacitor

supported dc link. A three phase PLL is used for generating reference signals for the

Synchronous Reference Frame based PWM signals. The proposed system is tested

through simulation using MATLAB/SIMULINK and the results are compared.

Key words: Power quality, Series compensation, Dynamic voltage restorer, in-phase

injection, BESS, Super capacitor.

Cite this Article V. Srikanth Babu, M. Ram Babu and Dr. T. Suresh Kumar,

Comparative Analysis of Dynamic Voltage Restorer Supported With Bess and Super

Capacitor, International Journal of Mechanical Engineering and Technology, 9(10),

2018, pp. (1268)-(1276).

http://www.iaeme.com/IJMET/issues.asp?JTypeIJMETT&VType=9&IType=10

1. INTRODUCTION

With technological advancements and globalisation, prices of electric appliances have come

down drastically. Though this also resulted in increased energy demand, which boosts

development index, it also resulted in heavy utilization of power electronic based appliances.

These appliances produce harmonics, demand higher reactive power and hence leads to large

currents in the distribution lines. If the transfer capability of the lines are not improved, it will

result in power quality issues as well. The secondary effect of it is supply interruptions. To

Comparative Analysis of Dynamic Voltage Restorer Supported With Bess and Super Capacitor

http://www.iaeme.com/IJMET/index.asp 1269 [email protected]

avoid black outs, governments are encouraging distributed energy sources [1], [2]. This resulted

in large-scale injection of renewable energy sources into the power system. However, this

results in more power quality issues at the distribution side due to intermittent nature of

renewable energy sources [3]. Hence, power quality issues arise from both transmission and

distribution sides and appropriate measures are to be taken from either sides to mitigate those

issues. Critical loads such as hospital loads, chemical industries, military applications etc., are

greatly affected by these power quality issues. Especially, chemical processes result in loss of

entire batch of the process resulting in loss of time, energy and money [4].

In general, passive filters, capacitors, are installed to smooth out harmonics, reactive power

and to improve voltage profile. However, they result in more losses and the compensation is

based on average control rather than instantaneous control. In addition, each device offer only

one solution, resulting in infrastructure burden on the consumer as well as grid operator.

Further, controlling of passive filters is difficult as it involves mechanical switches that are not

fast acting in nature [5]. With advanced in control techniques for controlling power electronic

converters, active devices offer multiple solutions with a single device. They also provide

redundancy advantage in the system and hence reduces financial burden on both grid operators

and consumers.

FACTS devices offer transmission-side solution while custom power devices (CPD) offer

from consumer side. In general, power electronic devices controlled by the utility are termed as

FACTS devices, whereas those controlled by consumers are termed as CPD. They offer

instantaneous compensation unlike passive filters that offer average control. The commonly

used CPDs are Uninterruptible Power Supplies Dynamic Voltage Restorers and Active Power

Filters. While Active power filters are used to mitigate harmonics and reactive power

compensation, UPS and DVR are used to compensate other power quality issues like Sag, swell,

and unbalanced loads. In this article, the control of DVR for voltage deviations due to step

disturbances has been presented. DVR offers a better solution in reducing industrials processes

susceptibility to supply voltage sags [6], [7], [8]. The power electronic converter of DVR can

be either VSI converter or Modular Multilevel Converter (MMC) [9].

2. MODELLING OF DVR

The schematic of a DVR-connected system is shown in Fig 1a. When the system voltage, Vs,

is affect due to step loads leading to sags/swells, a compensating voltage, VDVR, is injected by

the DVR such that the voltage magnitude VL across critical load remains constant irrespective

of voltage at the point of common coupling (PCC). The injected voltage of the DVR can be

written as

SLLLdvr VZIVV −+= (1)

Where,

VDVR = Injected voltage

IL = Load current

ZL = Line Impedance

VS = Source Voltage

V. Srikanth Babu, M. Ram Babu and Dr. T. Suresh Kumar


Figure 1 a) Rationale for DVR b) Phasor Diagram depicting DVR operation

Fig. 1b. shows the phasor diagram depicting the operation of DVR. Vpre-sag represents the

voltage across the critical load before the sag condition. Whenever there is a step load, critical

loads undergo a drop in voltage due to that needs to be compensated; otherwise, the

performance of the critical load deteriorates. Hence, the DVR injects voltage through the

injecting transformer. Depending on the phase shift of the injected voltage, the compensation

is named: in-phase injection or quadrature injection. The injected voltage and the sag voltage

Vs u undergo vector addition such that the voltage magnitude always remain constant across

the critical load [10], [11].

The DVR is a combination of a low pass filter, a power electronic converter, an energy

storage device and an injection transformer. The energy storage device can be a battery-energy

storage system, super capacitor or a photovoltaic system. During the normal operation, the DVR

consumes active power required to maintain the DC link voltage [12]. Under abnormal

conditions, the stored energy is used to compensate the reactive power and harmonics produced

by other non-linear loads in the vicinity of the sensitive load under consideration [13].

3. CONTROL AND DESIGN OF DVR

The compensation for voltage sags/swells with DVR can be accomplished by injecting reactive

power or absorbing the active power respectively [14], [15]. A quadrature injection results in

injecting reactive power while the in-phase injection results in active power. The injected active

power from the energy storage device of the DVR is accumulated during normal operation or

through a self-sufficient energy source viz. Photovoltaic system, Fuel Cell system. In case of

super-capacitor or BESS, minimum energy principle has to be employed to reduce the storage

losses. The design of DVR includes ratings of injection transformer, storage device and

converter.

Fig. 2 demonstrates the control diagram of the DVR in which the synchronous reference

frame theory is designed for generating modulating signal. PCC Voltage, VS and critical load

voltage VL are fed back to controller for pulse generation. Direct and quadrature components

of PCC voltage and load voltages are derived using transformation and is passed through low

pass filter for eliminating low frequency components like 100 Hz. The filtered direct voltages

component and quadrature component are then compared with dc link voltage and reference

quadrature component respectively. The resultant voltage components are then transformed

back to a-b-c reference frame for PWM generation [16].

��=

�� (�) ��(�) ��(� − ��

� ) ��(� − �� ) �

�(� + �� ) ��(� + ��

� ) �� (2)



Figure 2 Pulse Generation in DVR with Synchronous Reference Frame Theory

The DC link voltage that is reduced due to switching losses and injection of active

component of current has to be maintain constant. A PI controller is implemented to regulate

the dc link voltage of the super-capacitor. The governing equation is given in eq.(3) as:

][])1[][(]1[][ 11 keKkekeKkVkV vdcivdcvdcpcapcap +−−+−= (3)

Where,

][][ *kVVke dcdcvdc −= is DC voltage deviation at the kth sample. �� and �� are the dc-link

PI controller gains.

capddcd VVV −=*

(4)

As the voltage compensation is done using the quadrature component, a PI controller is

considered to reduce the load terminal voltage’s amplitude, � . Voltage regulation is achieved

using the controller output, !"#. The critical load voltage � is generated from the actual

voltages (! $, ! % , ! &) as in eq.(5). The obtained voltage is fed to the PI controller as in eq. (6).

( )222

3

2LcLbLaL VVVV ++

= (5)

][])1[][(]1[][ 22 keKkekeKkVkV VLiVLVLpqrqr +−−+−= (6)

Where,

][][ *kVVke LLVL −= is the load voltage deviation at the kth sample.

Kp2 and Ki2 are the PI controller gains.



Figure 3 Block Diagram of DVR with Super Capacitor-support

4. RESULTS AND DISCUSSIONS

The proposed DVR as shown in Fig. 3 is implemented in MATLAB/Simulink environment.

The system is tested for various power quality issues like Sag and Swell with Super-Capacitor

support and BESS support and the efficacy of both the systems are evaluated. The design values

of the DVR are taken from [17]. The PI controller gains are tuned using optimization Toolbox

in MATLAB.

4.1. Capacitor Supported DVR

4.1.1 Sag Condition

Whenever a step load is suddenly turned on, it draws huge inrush currents resulting in sag at

the PCC. In the system under consideration, a sag is introduced at 0.35 sec with 5 cycle duration

till 0.45 sec as shown in fig. 4. The DVR draws current from the utility during normal period

for charging the Super-capacitor. Once, the sag is genearted, the proposed DVR injects an in-

phase voltage at the PCC so that voltage profile of the criticla load point is improved as shown

in fig.4. The results show the performance of the DVR under sag condition.



Figure 4 Performance of Super Capacitor-connected DVR with in-phase injection under Sag condition

Figure 5 Performance of Super Capacitor-connected DVR with in-phase injection under Swell

condition

4.1.2 Swell Condition

Whenever a step load is suddenly removed or when a distributed sources starts injecting power

into the system, it a swell is developed at the PCC. In the system under consideration, a swell

is introduced at 0.35 sec with 5 cycle duration till 0.45 sec as shown in fig. 5. The DVR draws

current from the utility during normal period for charging the Super-capacitor. Whenever, the

sag is genearted, the DVR injects an in-phase voltage at the PCC so that voltage profile of the

criticla load point is improved as shown in fig.5. The results show the performance of the DVR

under swell condition.



4.2 BESS supported DVR

4.2.1 Sag Condition

In this scenario, the energy storage device is taken to a battery and the sag conditions are

imposed on the system as in the SC supported DVR. A sag is introduced at 0.25 sec with 5

cycle duration till 0.35 sec as shown in fig. 6. The DVR draws current from the utility during

normal period for charging the battery. Once, the sag is genearted, the proposed DVR injects

an in-phase voltage at the PCC so that voltage profile of the criticla load point is improved as

shown in fig.6. The results show the performance of the DVR under sag condition. From the

results, it can be seen that the battery is drawing limited current from the utility as the voltage

across the battery is maintained almost onstant.

Figure 6 Performance of BESS-connected DVR with in-phase injection under Sag condition

4.2.2 Swell Condition

Similarly, a swell condition is introduced at 0.25 sec with 5 cycle duration till 0.35 sec as shown

in fig. 7. The DVR draws current from the utility during normal period for charging the Super-

capacitor. Whenever, the sag is genearted, the DVR injects an in-phase voltage at the PCC so

that voltage profile of the criticla load point is improved as shown in fig.7. The results show the

performance of the DVR under swell condition.



Figure 7 Performance of BESS-connected DVR with in-phase injection under Swell condition

5. CONCLUSION

With change in the load nature to electronic equipment like computers, adapters and LED bulbs

etc., harmonic content in the power supply has drastically increased. This results in increased

reactive component of current drawn from the utilities. This phenomenon is further escalated

with distributed energy sources in the system that are mostly operated with power electronic

converters. In this paper, a DVR is placed at the sensitive loads to compensate the voltage

fluctuations like sag, swell and harmonics. The dc link voltage of the DVR is maintained using

two scenarios: Super-Capacitor and BESS. The proposed system is validated using

MATLAB/Simulink environment. In-phase injection method is used for generating the PWM

signals to the converter to reduce the rating of DVR. The results showed that BESS supported

system is proven better than Super-capacitor supported system as the dc link voltage with BESS

is maintained smoothly. The proposed system can be improved by using Photovoltaic/PEM

Fuel Cell based dc link to reduce the dependency on the utility and hence can reduce the VAR

utilization from the grid resulting in energy and cost savings to the consumer.

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COMPARATIVE ANALYSIS OF DYNAMIC VOLTAGE RESTORER …€¦ · Dynamic Voltage Restorer (DVR) plays key role in resolving power quality issues like voltage sag, swell, harmonics, interruption