Regulation Of Grid Voltage using an integrated Wind-PV system as STATCOM in Distributed Generation systems.

A Novel Approach to Improving Power Quality in DG systems.


Research Paper (postgraduate), 2014
4 Pages, Grade: B.E EEE First Class

Excerpt

1
Regulation of Grid Voltage using an integrated Wind-PV system Based
STATCOM in Distributed Generation System
Shrey Shrikant Naik
Department of EEE,Goa College of Engineering,Farmagudi,Goa
Varun Pratapsinha Jadhav
Department of EEE,Goa College of Engineering,Farmagudi,Goa
Abstract-- In the proposed paper, it is described how a
Solar PV Farm along with a battery storage system can be
used to regulate grid voltage in a PV-Wind integrated
distributed generation System.
At night time Solar PV system is normally dormant (i.e. it
does not generate power) but the stored power in batteries
can be utilised efficiently to regulate the common coupling
voltage by means of a FACTS based Static Synchronous
Compensator (STATCOM) thereby improving the power
quality.
With advancements in RES and increasing DG systems to
provide for load demand the quality of power has to be
maintained to optimum value and this paper focuses purely
on improving regulation of voltage without using external
regulation devices but the installed RES system.
In order to implement and validate the concept of the
prescribed paper, SIMULINK Tool has been used.
I.
I
NTRODUCTION
Transmission grids worldwide are presently facing
challenges in integrating such large scale renewable
systems (Wind Farms (WF) and Solar Farms (SF)) due to
their limited power transmission capacity. To increase the
available power transfer limits/capacity of existing
transmission line, series compensation and various Flexible
AC Transmission System (FACTS) devices are being
proposed.Utilities are presently facing a major challenge of
grid integrating an increasing number of renewable-energy-
based distributed generators (DGs) while ensuring stability,
voltage regulation, and power quality. During the night
time, feeder loads are usually much lower compared to
daytime, while the wind farms (WFs) produce more power
due to increased wind speeds. This potentially causes
reverse power to flow from the point of common coupling
(PCC) toward the main grid resulting in feeder voltages to
rise above allowable limits. To allow further DG
connections, utilities need to install expensive voltage
regulating devices. Voltage-source inverters are essential
components of PV solar farms (SFs), which provide solar
power conversion during daytime (normal operation).
However, PV SFs are practically inactive during night time
and do not produce any real power output. The proposed
concept is to use the existing SF inverter as a STATCOM
during night time to regulate voltage variations at the PCC
due to increased and intermittent WF power and/or by load
variations. With the development of distributed generation
systems, the renewable electricity from PV sources became
a resource of energy in great demand. The current control
scheme is mainly used in PV inverter applications for real
power and reactive power control schemes. The emergence
of windgeneration is the leading source of renewable
energy in the power industry, Wind farms totalling
hundreds, even thousands, of MW are now being
considered. Double Fed Induction Generator is the main
type ofwind generation currently in use (the other is
conventional induction generators) due to their variable
speed operation, four-quadrant active and reactive power
capability, low-converter cost, and reduced power losses.
II.
DG
S
YSTEM
O
VERVIEW
Fig 1 and 2 shows a single line diagram of the integrated
wind energy and PV system, both with battery storage
scheme. The wind farm is modelled as a fully controlled
converter-inverter based doubly fed induction generator and
PV SF modelled as a Voltage fed Inverter.
Fig 1 WECS with Battery storage
Fig 2Operational Modes of the Solar Farm

2
III.
S
OLAR
PV
F
ARM
A
S
A
B
ATTERY
C
HARGER
A typical PV solar farm is basically inactive during night
time and the bidirectional inverter used to deliver the PV
DC power as three-phase AC power to the grid remains
unutilized as well. Fig. 2 shows thepossible operational
modes of the solar farm. The point at which the solar farm
is connected to the grid is called the point of common
coupling (PCC). In Fig.2, V
S
and I
S
represents the
voltage and current at the secondary of the distribution
transformer; V
PCC
and V
L
denote voltages at PCC and
load terminal respectively; and I
PV
is the current delivered
by the PV solar panels ac current drawn/delivered by the
solar farm inverter and the DC current flowing through the
storage battery are represented by I
SF
and I
Batt
,
respectively. Here a storage battery is connected on DC
side of the solar farm inverter. Switch S
1
inFig.2is utilized
to disconnect the PV solar panels especially during night-
time and to charge the storage batteries from the main grid.
[2]
IV.
D
OUBLE
F
ED
I
NDUCTION
G
ENERATOR
The Double Fed Induction Generator (DFIG) is a
generating principle widely used in wind turbines. It is
based on an induction generator with a multiphase wound
rotor and a multiphase slip ring assembly with brushes for
access tothe rotor windings. It is possible to avoid the
multiphase slip ring assembly but there are problems with
efficiency, cost and size. A better alternative is a brushless
wound-rotor doubly-fed electric machine.The principle of
the DFIG is that the rotor windings are connected to the
grid via slip rings and the back-to-back voltage source
converter that controls both the rotor and the grid currents.
Thus rotor frequency can freely differ from the grid
frequency (50 or 60 Hz). By using the converter to control
the rotor currents, it is possible to adjust the active and
reactive power fed to the grid from the stator independently
of the generator's turning speed. The control principle used
is either the two-axis current vector control or direct torque
control (DTC). DTC has turned out to have better stability
than current vector control, especially when high reactive
currents are required from the generator.The doubly-fed
generator rotors are typically wound with 2 to 3 times the
number of turns of the stator. This means that the rotor
voltages will be higher and currents respectively lower.
Thus in the typical ± 30 % operational speed range around
the synchronous speed, the rated current of the converter is
accordingly lower which leads to a lower cost of the
converter. The drawback is that controlled operation
outside the operational speed range is impossible because
of the higher than rated rotor voltage. Further, the voltage
transients due to the grid disturbances (three-phase and
two-phase voltage dips, especially) will also be magnified.
In order to prevent high rotor voltages and high currents
resulting from these voltages from destroying the IGBTs
and diodes of the converter, a protection circuit (called
crowbar) is used. The crowbar will short-circuit the rotor
windings through a small resistance when excessive
currents or voltages are detected. In order to be able to
continue the operation as quickly as possible an active
crowbar has to be used. The active crowbar can remove the
rotor short in a controlled way and thus the rotor side
converter can be started only after 20-60 ms from the start
of the grid disturbance. Thus it is possible to generate
reactive current to the grid during the rest of the voltage dip
and in this way help the grid to recover from the fault. The
AC/DC/AC converter is divided into two components: the
rotor-side converter and the grid-side converter. The
Voltage-Sourced Converters that use forced-commutated
power electronic devices (IGBTs) to synthesize an AC
voltage from a DC voltage source. A capacitor connected
on the DC side acts as the DC voltage source. A coupling
inductor L
F
is used to connect grid side converter tothe grid.
The three-phase rotor winding is connected to rotor side
converter by slip rings and brushes and the three-phase
stator winding isdirectly connected to the grid. The power
captured by the wind turbine is converted into electrical
power by the induction generator and it is transmitted to the
grid by the stator and the rotor windings.
V.
STATCOM
Fig 3 STATCOM connected to Bus
Fig 3 shows a STATCOM connected to a bus as an
advanced static VAR compensator. A STATCOM basically
consists of a Switching Converter which can both deliver as
well as absorb power from the bus, STATCOMs are
preferred over other SVCs because they provide a wide
range of Reactive Power compensation.It behaves like a
capacitor when bus needs power and like an inductor when
power is needed to be absorbed from the bus.It eradicates
use of bulky passive components and is a very flexible
device for improving the voltage profile of the line.
VI.
C
ONTROL
S
CHEME FOR
PV
I
NVERTER
Fig 4shows the block diagram of the control scheme used to
achieve the proposed concept. The controller is composed
of two proportional
­integral (PI) based voltage-regulation
loops. One loop regulates the PCC voltage, while the other
maintains the dc-bus voltage across SF inverter capacitor at
a constant level. The PCC voltage is regulated by providing
leading or lagging reactive power during bus voltage drop
and rise, respectively. A phase-locked loop (PLL) based
control approach is used to maintain synchronization [5]
with PCC voltage. A hysteresis current controller is utilized
to perform switching of inverter switches.
Excerpt out of 4 pages

Details

Title
Regulation Of Grid Voltage using an integrated Wind-PV system as STATCOM in Distributed Generation systems.
Subtitle
A Novel Approach to Improving Power Quality in DG systems.
Course
M.E Power & Energy Systems Engineering
Grade
B.E EEE First Class
Authors
Year
2014
Pages
4
Catalog Number
V283560
ISBN (eBook)
9783656834755
ISBN (Book)
9783656834762
File size
824 KB
Language
English
Notes
Kindly also Publish the name of Co-author of the paper.This Paper was written to enlighten the Energy Engineers about the recent trends and development of Renewable Energy and improvement of power quality using the same with an energy efficient solution as proposed in the paper. This paper also highlights the flexibility of a FACTS based Compensator compared to conventional compensating methods.
Tags
regulation, grid, voltage, wind-pv, statcom, distributed, generation, novel, approach, improving, power, quality
Quote paper
Shrey Naik (Author)Varun Pratapsinha Jadhav (Author), 2014, Regulation Of Grid Voltage using an integrated Wind-PV system as STATCOM in Distributed Generation systems., Munich, GRIN Verlag, https://www.grin.com/document/283560

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