Page 1 of 11
European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
Available online: https://ejbss.org/ P a g e | 1936
Enhanced Power Quality Management of Grid
Connected Wind Farm
RAMKUMAR .B
PG Student,
PRIST Deemed to be University, Thanjavur
Abstract- Increasing sensitivity of the loads with respect to power quality has gained the interest of power system analysis and
power quality improvement techniques. The voltage sags or swells which are characterized by rms voltage variations outside
the normal operating range of voltages due to faults may lead to improper disconnection of wind turbines. This paper deals
with the effective voltage sag/swell mitigation using Dynamic Voltage Restorer (DVR), to regulate the terminal voltage of the
wind farm. The DVR utilizes a feed forward vector control based algorithm to generate the PWM based firing signals for
injecting appropriate compensation voltages. The actual wind farm field data of the voltage sag and swell events during fault
conditions are re- created using MATLAB/Simulink and restored by employing the DVR. The simulation results are shown to
verify the operation of DVR during balanced voltage sag and swell conditions.
Keywords Dynamic Voltage Restorer (DVR), Voltage sag, Voltage swell, Feed forward vector control, Fault Ride Through
Capability.
1. Introduction
There is an increasing need for study of power quality
issues in wind farms due to the steady growth of wind power
integration to grid. It mainly affects the reliability and
dynamic stability of power system due to the following
reasons: (a). The difference in behavior of wind plants
compared to the conventional generation system and (b).
Most of the wind farms in India are connected to weak grids
due to rural area installations. Thus, wind farms connected to
weak grids lack the capacity to handle high penetrations.
Therefore, more dynamic analysis and study on power
quality issues are required. The various power quality issues
which can be noted in connection to wind farms are shown in
Figure. 1.
Wind Power Plants (WPP) will stop operating during
abnormal conditions to avoid further voltage collapse [1].
Due to increasing capacities of wind farms and large single
WPPs being connected to the grid, new grid codes have been
laid to ensure the system stability and reliability. Thus, Fault
Ride Through (FRT) capability requirements of wind farms
in India necessitate efficient ride through of voltage
sag/swells. During the occurrence of a grid fault, the grid
codes prescribe that the wind turbines must stay connected to
the grid and support it by generating reactive power to
restore the grid voltage quickly after the fault [2].
Voltage sags and swells are the major power quality
issues, generally associated with system faults. These faults
include Single Line to Ground faults (SLG), Double Line to
Ground faults (DLG) and Short- Circuit faults or tripping [3-
5]. A voltage swell can happen due to switching off a large
load, energizing a large capacitor bank or on unfaulted
phases during a SLG fault. The Low Voltage Ride Through
(LVRT) capability of WPPs requires the wind turbines to
remain connected to the grid for a specific period of time
during grid voltage sag conditions [6]. The High Voltage
Ride Through (HVRT) capability requires the wind turbines
to remain connected during voltage swell as prescribed by
the grid codes [7].
Therefore, the Dynamic Voltage Restorer (DVR) attempts
to ride through voltage sag/swell conditions during faults to
Page 2 of 11
European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
Available online: https://ejbss.org/ P a g e | 1937
prevent WPPs from unwanted tripping and to enhance the
FRT capability. The compensation capability of a DVR
depends on its maximum voltage injection ability and the
amount of stored energy available. The compensating
voltages are measured appropriately by the controller and
injected using injection transformer. The compensating
voltages are drawn from a temporary supply/ storage unit.
The DVR also attributes to lower cost, smaller size, and fast
dynamic response to disturbances [8].
The objective of the paper is to simulate a DVR based
voltage sag/swell mitigation technique with dc-link capacitor
energy storage using feed forward based compensation. This
paper presents a feed-forward vector control based modeling,
analysis and simulation of DVR using MATLAB/Simulink
with performance comparison during fault occurrences as per
field data. The same sag/swell amplitude and duration in the
field data are used for simulation. The field data recorded at
the Chinnaputhur Substation for 40 days at Dharapuram
district in Tamil Nadu of India is used for the study. Totally
22 events have occurred during the study period, of which 6
are sag events, 1 swell event and remaining are interruptions
[9]. By incorporating the same duration,the reliability of the
DVR compensation technique during the corresponding
symmetrical and unsymmetrical fault conditions can be
ensured.
The paper has the following sections: Section 2 describes the
principle of DVR operation; Section 3 includes the circuit and
control strategy description of the DVR and Section 4 includes
the simulated results with field data. Finally, Section 5
concludes the paper with observation and remarks.
2. Principle of Operation of DVR
Dynamic Voltage Restorer (DVR) consists of a voltage
source converter, a LC based line filter, coupling transformer
connected in series with the grid to correct the voltage
disturbances during faulty grid conditions [10]. It protects the
sensitive loads during the voltage sag/swell conditions by
injecting the corresponding compensating voltages through
the transformer. The phasor diagram of a voltage sag event
correction through In-phase voltage injection scheme is
shown in Figure. 2.
The dynamic voltage restorer injects a dynamically
controlled voltage in series based on the widely used In- phase compensation scheme to the bus voltage by means of a
coupling transformer for voltage restoration and regulation
[11]. The amplitude of the injected phase voltage is
controlled to avoid any power quality disturbance of the
loads connected to the same feeder.
Vpresag
Vsag
Vinj
Figure. 2 Phasor diagram of the In-phase voltage
injection scheme in DVR
The DVR injects a voltage Vinj such that the load voltage
Vsag remains at Vpresag both in magnitude and phase angle.
Figure. 3 shows the principle of operation of DVR.
Power Quality Issues in grid connected Wind Power
Plants
Local Impacts System Wide Impacts
Branch Flow and Fault Currents Voltage Quality Reactive Power Dynamics and System Balancing Node Voltages Stability
Slow Voltage Rapid Voltage Transients Voltage Frequency Variations (Sags and Harmonics Islanding variations Unbalance Variations (Flickers) Swells)
Page 3 of 11
European Journal of Business &
Social Sciences
Available at https://ejbss.org/
ISSN: 2235-767X
Volume 07 Issue 04
April 2019
Available online: https://ejbss.org/ P a g e | 1938
Figure. 1 Various Power Quality Issues in Wind Farms.
