15-09-2016, 02:53 PM
Analysis, Modeling and Simulation of Dynamic Voltage Restorer (DVR)
for Compensation of Voltage‐Quality Disturbances
1454654509-DVR.pdf (Size: 422.48 KB / Downloads: 10)
Abstract—Dynamic voltage restorer (DVR) can provide the
most commercial solution to mitigate voltage sag by injecting
voltage as well as power into the system. This paper describes the
effectiveness of using dynamic voltage restorers (DVRs) in order
to mitigate voltage sags in power distribution systems at critical
loads. The DVR is a power electronic based device that provides
three-phase controllable voltage source, whose voltage vector
(magnitude and angle) adds to the source voltage during sag
event, to restore the load voltage to pre-sag conditions. The DVR
can restore the load voltage within few milliseconds. A control
technique based on a proportional–integral (PI) controller and a
selective controller is used. The controller is designed in a
synchronously-rotating reference frame. In fact, three
independent controllers (homopolar component, d-axis
component and q-axis component) have been used to tackle
balanced and unbalanced voltage supplies. Simulation results
using Simulink’ SimPowerSystem Toolbox is presented to
illustrate the principle and performance of a DVR operation in
load voltage compensation.
INTRODUCTION
Power quality is a very important issue due to its impact on
electricity suppliers, equipment manufactures and customers.
“Power quality is described as the variation of voltage, current
and frequency in a power system. It refers to a wide variety of
electromagnetic phenomena that characterize the voltage and
current at a given time and at a given location in the power
system” [1], [2]. An important percentage of all power quality
problems are of the voltage-quality type. Voltage Sag (dip) is
a momentary decrease in the root mean square (RMS) voltage
magnitude in the range of 0.1 to 0.9 per unit, with a duration
ranging from half cycle up to 1 min. It is considered as the
most serious problem of power quality. It is often caused by
balanced or unbalanced faults in the distribution system or by
the starting of large induction motors [3].
Though there are many different ways to mitigate voltage
sags in power systems. Among these, the distribution static
compensator and the DVR are the most effective devices; both
of them based on the voltage source converter (VSC) principle
[4]. This paper focus on the DVR, which is one of the most efficient and modern custom power device used in power
distribution networks. A DVR is a series-connected solid-state
device that injects voltage into the system in order to regulate
the load side voltage. It is normally installed in a distribution
system between the supply and a critical load feeder at the socalled
Point of Common Coupling (PCC) which is defined as
the point of the network changes [5], [6]. Its primary function
is to rapidly boost up the load-side voltage in the event of
voltage sag in order to avoid any power disruption to that load.
There are various circuit topologies and control schemes that
can be used to implement a DVR [7], [8]. In addition to
voltage sags and swells compensation, DVR can also have
other features such as harmonic compensation, power factor
correction and reduction of transients in voltage and fault
current limitations [9], [10].
Although, the inverter used in the a DVR can have many
different topologies, this paper uses a traditional 2-level, 3-
phase pulse width modulation (PWM) inverter since this
topology is still the most popular one.
This paper is organized as follows: Section 2 describes
briefly the DVR system. The transfer function between the
controllable voltage (inverter voltage) and the sensitive-load
voltage is investigated. Strong and weak voltage supplies are
considered. Section 3 presents and discusses the control
system employed. To start with, two independent PI
controllers using a synchronously-rotating frame (one for the
d-axis and one for the q-axis) are proposed. Section 4 presents
the simulation set-up and provides extensive simulation results
of various scenarios. Balanced and unbalanced faults in the
distribution systems are considered. Section 5 presents
simulation results of the operation of the DVR when switching
extra loads suddenly close to the sensitive load. Balanced and
unbalanced extra loads are investigated. It will be shown that
an extra controller for the homopolar component is necessary
in the latter case and its structure will be proposed and
justified. Finally, the main conclusions of the work are
presented in Section 6.
II. DYNAMIC VOLTAGE RESTORER (DVR) SYSTEM
Figure 1 depicts a Dynamic Voltage Restorer (DVR) system
with a series insertion transformer connected between the
distribution transformer and the sensitive load. The electrical
system viewed from the Point of Common Coupling (PCC)
has been modeled as a 3-phase voltage source with a shortcircuit
impedance. The DVR can compensate voltage sags by
means of the injection of the inverter voltage through the
series connected transformer