Technical and Performance Aspects of a Dynamic Voltage Restorer
Author:
K. Chan, ABB High Voltage Technologies Ltd., System Engineering Division,
Switzerland
Keywords: Voltage sags mitigation, DVR, IGCT, Real-time simulator, Computer simulation
Abstract
One of the major issues in improving power quality in distribution networks is the mitigation of
voltage sags. Voltage sags in distribution networks caused by system faults can adversely
affect sensitive electrical equipment in industrial production processes, such as in
semiconductor fabrication, resulting in substantial financial losses. A safe, reliable and clean
power supply to these industries is therefore a prerequisite to their profitable operation.
A Dynamic Voltage Restorer (DVR), with its excellent dynamic capabilities, when installed
between the supply and a critical load feeder, can compensate for voltage sags, restoring line
voltage to its nominal value within a few milliseconds and hence avoiding any power
disruption to that load.
This paper presents the technical aspects of
designing an Integrated Gate Commutated Thyristor
(IGCT) based DVR shown in Figure 1 , a new
device capable of meeting the stringent
requirements of
voltage
sags
mitigation.
Furthermore, performance assessments of the DVR
using a real-time hardware simulator model and
computer simulations are discussed.
The first section of the paper provides a functional description of the DVR. In order to provide
for the capabilities demanded by voltage sag mitigation, the DVR requires functions such as
rapid control response, an energy source and a mechanism for coupling the boosting
voltages compensating the sag. The major components, their related functions and operating
characteristics are presented.
Customer’s requirements dictate the design and performance of the DVR. This section details
the considerations that must be taken into account for the design of the DVR in order to fulfil
the required specifications. Design considerations that influence the rating and performance
of the DVR such as protected load MVA and power factor, magnitudes of single and three
phase voltage sags and fault duration, three phase fault level at the incoming bus, etc. are
discussed. To ensure that the designed DVR is capable of meeting the specified
requirements, its dynamic performance and the control system functions must be verified.
Verification procedures using a real-time analogue simulator and computer simulations are
discussed. The control system functions are described and results from the verification
procedures are then presented.
Newly developed Integrated Gate Commutated Thyristors have been selected for the
converter used in DVR installations. The IGCT merges the attractive features of Gate TurnOff (GTO) thyristors with the strengths of Insulated Bipolar Gate Transistors (IGBT) for
converters with a wide power range and providing the DVR with high converter reliability,
high converter efficiency at steady state operation and inherent safety even under worst
case conditions.
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