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Abstract —The objective of this design is to implement an efficient and economical dynamic voltage restorer (DVR) to compensate for voltage sag conditions in oil and gas industry. In a

power distribution system or plant facility, faults occurring can cause voltage sag that can affect critical loads connected in the power network. Due to the complexity and sensitivity of loads, a

short voltage sag duration can still cause severe power quality problems to the entire system. The proposed DVR scheme is an inverter-based voltage controlled scheme, operating for low power

application, which has excellent dynamic capabilities when connected in power distribution networks to mitigate voltage sag conditions. Installing the DVR between the supply and critical load

will restore the voltage to its nominal value within few milliseconds, hence, delivering the compensated voltage to the load avoiding any power disruption. Modeling and simulation of the DVR

has been conducted using Matlab/Simulink platform with the RMS detection technique and the Energy optimization DVR compensation methods for single-phase applications of low voltage for

oil and gas industry. The presented concept has been validated through practical implementation of DVR using SiC MOSFET-based inverter.

Dynamic Voltage Restorer for Voltage Sag Mitigation

in Oil and Gas IndustryChresteen Baraket*, Marina Messiha*, Ahmed Massoud*, Atif Iqbal* and Ramadan Soliman**

*Qatar University

**Qatar Petroleum

8. Conclusions

Acknowledgment: We would like to express our deep gratitude to Qatar University and the Department of Electrical Engineering for their support to their students and their endless

encouragement.

Introduction

The main concern of customers-as oil and gas industries- is the reliability and quality of the

power supplied. It is very crucial to companies and industries to avoid being affected by any

undesired power disturbances that reduces their profitability, which is the critical driving force

in a highly competitive business environment. Although power generation in well-developed

countries have reached reliable levels, the disturbances and reduction in power quality could not

be totally avoided. Moreover, due to the complexity of many power networks, increases the

sensitivity of loads and electronic devices to power quality problems.

Customers require a constant and well-regulated voltage level to continue their production,

therefore any disturbances for the supplied voltage waveform can cause problems to the critical

loads connected to the system. The major power disturbance event is voltage sag. The decrease

of root mean square value (RMS) of the voltage for a short duration that last for 0.5 cycles to 1

minute, usually caused by a remote fault somewhere on the power distribution network (IEEE

Standard 1159-1995).

The DVR when inserted between the supply and the load will be able to detect and recognize

voltage sag event in milliseconds and compensate the voltage drop by boosting the point of

common coupling at the critical load. Sic MOSFET-based DVR has been prototyped to validate

the concept presented.

Simulation Results

Conclusion

The DVR system to be implemented for Qatar Petroleum is to overcome voltage sag events,

hence secure the power supply to the facility.

The RMS detection method has been chosen for voltage sag detection due to its simplicity and

fast response. An inverter has been employed to introduce voltage sag in order to have a full

controllability on voltage sag event with fast dynamic performance.

The presented DVR system is considered as an appropriate techno-economical solution,

particularly using Energy optimization technique. This technique will lead to minimize energy

storage component, compared to other compensation methods for DVR, thus, having

economical, efficient and reliable system.

The results of the system were presented and the operation principles were addressed to validate

the proposed voltage control scheme – DVR.

Practical implementation of detection techniques of voltage sag with minimum energy

optimization is accomplished with open-loop control scheme. As further improvements is to

have a closed-loop control scheme that will minimize the steady-state error. Moreover, the

system can be enhanced to compensate voltage sags for dynamic loads.

Energy storage

Y

Y

Load

DVR

Critical Load

Grid

DVR overall power circuit

Problem Definition

Most of the voltage dips happens in the range of 90% to 80% for duration less than 1 second,

although the under voltage relays shall be adjusted to avoid such small dips which the motors

can withstand, but some of motors contactor may be released depending on the dip value.

Energy Optimization Compensation Method (cont.)

Its function is to detect the voltage sag, and injecting the voltage difference between the pre-sag

and sag voltage. Unlike UPS, DVR supplies only part of waveform that has been reduced due

to voltage sag and not the whole waveform.

Dynamic Voltage Restorer

0.1 0.102 0.104 0.106 0.108 0.11-0.5

0

0.5

1

1.5

Time (sec)

Tri

gg

er

sig

na

l

Voltage sagdetection

Voltage sagoccurrence

-200

-150

-100

-50

0

50

100

150

200

Lo

ad

cu

rre

nt

[A]

0 0.03 0.06 0.09 0.12 0.15 0.18 0.2-400

-300

-200

-100

0

100

200

300

400

Time [sec]

Mo

difie

d v

olta

ge

acro

ss t

he

lo

ad

[V

]

0 0.03 0.06 0.09 0.12 0.15 0.18 0.2-200

-150

-100

-50

0

50

100

150

200

Time [sec]

Lo

ad

cu

rre

nt

[A]

-100

-75

-50

-25

0

25

50

75

100

DV

R in

jecte

d v

olta

ge

[V

]

Simulation Parameters

Load impedanceSag magnitude Sap phase Sag time

Resistance Inductance

10 Ω 55.133 mH 80% of 𝑉𝑛𝑜𝑚𝑖𝑛𝑎𝑙 30° 100 ms

CoilContactor

Bus Section 230V

Outgoing feeder

Start

Stop

Supply Voltage

Load

Voltage injection transformer

Low pass filterInverter

DC energy storage device

By-pass switch

Energy Optimization Compensation Method

The basic idea of this method is to draw as much as possible active power from the grid in order

to minimize the amount of active power drawn from the DC-link of the DVR. Hence, the DVR

will compensate only the reactive power. For zero active power, the PCC voltage is allowed to

restore until 90% of nominal voltage, according to IEC 60038-1983 standard with the DVR

rating taken into consideration. For minimum active power, the PCC voltage is restored back to

1 p.u, with the sacrifice of minimum amount of energy. The relationship shown below between

displacement factor and p.u level of restored and sagged voltage is maintained to operate with

zero active power method.

𝑉𝑝𝑜𝑠𝑡−𝑠𝑎𝑔 𝑖𝑛 𝑝.𝑢> 𝑉𝑚𝑜𝑑𝑖𝑓𝑖𝑒𝑑 𝑖𝑛 𝑝.𝑢

cos𝜑

0.5 0.6 0.7 0.8 0.9 10.9

0.95

1

0.4

0.5

0.6

0.7

0.8

0.9

1

Restored voltage

level in per unitDisplacement factor

Dro

p v

olta

ge leve

l in

per

un

it

Characteristic curve of

Energy-optimization strategyZero Active

Power Strategy

A

B

Experimental Results

VSG inverter

DVR inverter

RL load

Control unit DSP F28335

PWM2PWM1

Sensing Unit

Hosting PC

Isolated DC Biasing supply Digital

oscilloscope

VSG inverter

DVR inverter

VSG LPF

DVR LPFVoltage

transducer

RL load

System Prototype

Test with connected load of displacement factor 0.79

Block diagram of

Overall Experimental

Setup

Restored voltage to 1 p.u

and sag of 80%

Zero active power strategyRestored voltage to 0.9 p.u

and sag of 75%

Minimum active power strategyRestored voltage to 1 p.u

and sag of 75%

Minimum Active

Power Strategy