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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
Recommended