grid power quality improvement and battery energy storage in wind energy systems

Grid Power Quality Improvement
and Battery Energy Storage in
Wind Energy Systems

CONTENTS:
 ABSTRACT
 INTRODUCTION
 POWER QUALITY ISSUES
 WIND POWER EXTRACTION WITH BATTERIES
 SMART ENERGY METERS
 CONCLUSION
 REFERENCES

ABSTRACT
 In this proposed scheme Static Compensator (STATCOM) is
connected at a point of common coupling with a battery
energy storage system (BESS) to mitigate the power quality
issues.
 The generated power can be stored in the batteries at low
power demand hours.
 The combination of battery storage with wind energy
generation system will synthesize the output waveform by
absorbing or injecting reactive power and enable the real
power flow required by the load.
 Due to the fluctuation nature of the wind power injection into
an electric grid affects the power quality.

INTRODUCTION
 The integration of wind energy into existing power system presents a
technical challenges and that requires consideration of voltage
regulation, stability, power quality problems.
 The power quality is an essential customer-focused measure and is
greatly affected by the operation of a distribution and transmission
network.
 In the constant-speed wind turbine operation, fluctuation of wind speed
variation transmits as variation in mechanical torque.
 This fluctuation is caused by the variation of wind due to tower-shadow,
turbulence and wind shear etc.
 In normal operating system we need a control circuit for the active
power production.
 For reducing the disturbance we use a battery storage system.
 This compensates the disturbance generated by wind turbine.
 A STATCOM has been proposed for improving the power quality.

Scheme of wind generator with battery storage

 The proposed wind energy extraction from wind generator and
battery energy storage with distributed network is configured on its
operating principle and is based on the control strategy for switching
the inverter.
 The STATCOM based current control voltage source inverter injects
the current into the grid in such a way that the source current are
harmonic free and there is phase difference with respect to source
voltage has some desired value .
 The proposed system is implemented for power quality improvement at
point of common coupling (PCC) , as shown in above Fig.
 The grid connected system in above Fig. shows wind energy
generation system and battery energy storage system with STATCOM.

POWER QUALITY ISSUES
 power quality means that the voltage is
continuous and sinusoidal having constant figures
of amplitude and frequency.
 Power quality can be expressed in terms of physical
characteristics and properties of electricity.

Grid side power quality issues
 The power quality problems in the grid side that
affect the WEG (Wind Electric Generator) are mainly
concerned with the quality of voltage that is being
supplied by the utility.
Voltage Variations:
 Voltage variation has implications on both real and
reactive power associated with wind farms.
 Decreasing voltage also affects the power factor as the
capacitive VAR generated out of the installed capacitor
decrease as voltage decreases.

 Frequency Variations:
 The variation in frequency affects the power generation
in WEG to a large extent changing the aerodynamic
efficiency.
 Frequency changes lead to imperfect tip speed ratios
and reduced aerodynamic efficiencies.
 These leads to decrease the energy capture and output
power of wind turbines.

Voltage transients
 Large transient’s voltage could be created due to
switching of capacitors using mechanical switches,
which are the integral part of WEG for reactive
power compensation.
 These internally generated transients could result in
damage to sensitive electronic devices of the WEG
control system.
 Voltage unbalance:
 Voltage unbalance is caused due to large unbalanced
loads.
 The unbalance in voltage causes negative sequence
currents to flow in induction machines, causing
overheating.

WEG side power quality issues
 Power quality issues that affect the WEG are
mainly concerned with the quality of current that is
being drawn or generated by the WEG’s.
 Reactive power consumption:
 Reactive power consumption in a wind farm is
mainly due to the use of induction generators for
energy saving.
 The basic principle of Induction generators is that
they consume reactive power to set up the excitation
or magnetic field in order to generate real power.

 Generation of current harmonics:
 Current harmonics are generated due to soft starting of
induction generators during motoring mode.
 This distorts the voltage on the line and affects all
the consumers connected to the line.
 injection of fluctuating power:
 Power in wind by nature is varied and is checked by
annual, monthly, daily and hourly variations.
 This results in generation and supply of a power that is
fluctuating and leading to operational problems.

Wind Energy Generating system
 The wind generating system (WEGS) consists of
turbine, induction generator, interfacing transformer,
and rectifier to get dc bus voltage.
 In this configuration , wind generation are based on
constant speed topologies with pitch control turbine.
 The available wind energy system is presented as below
in
 Where ρ(kg/m2) is the air density and A(m2)I is the area
swept out by turbine blade, Vwind is the wind speed in
m/s.

DC Link for Battery storage and Wind Energy
Generator

 The battery energy storage system (BESS) is used as an
energy storage element for the purpose of voltage
regulation.
 The BESS maintain dc capacitor voltage
 constant and is suited for STATCOM since it rapidly
injects or absorbed reactive power to stabilize the
grid system.
 The battery is connected in shunt to the dc capacitor of
STATCOM.
 The battery storage and WEG’s are connected across
the dc link as shown above in Fig.
 The battery storage will get charged with the help of
wind generator.

STATCOM-current controlled
device

 The STATCOM is also a three-phase voltage
source inverter having the capacitor on its DC link
and connected at the point of common
coupling(pcc).
 The shunt connected STATCOM with battery
energy storage is connected as the interface of the
induction generator and non-linear at the PCC in
the grid system.
 The operational diagram of the shunt connected
static compensator in grid in above fig.

SMART ENERGY METERS
 Smart energy meters are capable of measuring
instantaneous voltage and current of the
electrical circuit.
 The parameters of time information for time of
use (TOU) calculations can be stored inside the
meter.
 Data are transmitted to the utility company using
wireless medium.
 Protecting the privacy of the customer and
confidentiality of data is the responsibility of a
utility.

CONCLUSION
 Proposed study on wind energy conversion scheme using
battery energy storage for nonlinear load includes interface of
inverter incurrent controlled mode for exchange of real and
reactive power.
 The hysteresis current controller is used to generate the
switching signal for inverter in such a way that it will cancel
the harmonic current in the system.
 This scheme improves power factor and also make harmonic
free source current in the distributed network at the point of
common connection.
 Battery energy storage provides rapid response and enhances
the performance under the fluctuation of wind turbine output
and improves the voltage stability of the system.

REFERENCES
 C. Han, A. Q. Huang, M. Baran, S. Bhattacharya, and W. Lichtenberger,
“STATCOM impact study on the integration of a large wind farm into a
weak loop power system” IEEE Transactions on Energy Conversion, vol. 23, no.
1, pp. 226232, March 2008.
 J. Manel, “Power electronic system for grid integration of renewable energy
source: A survey” IEEE Transactions on Industrial Electronics, vol. 53, no. 4, pp.
10021014, 2006, Carrasco.
 R. Billinton and Y. Gao, “Energy conversion system models for adequacy
assessment of generating systems incorporating wind energy”, IEEE
Transaction on Energy Conversion, volume. 23, no. 1, pp. 163169, December
2008
 S. W. Mohod and M. V. Aware, “Micro wind power generator with battery
energy storage for critical load”, in IEEE Systems Journal, Volume6,no.1,
September 2012.
 S. W. Mohod and M. V. Aware, “A STATCOM-Control scheme for Grid connected
Wind Energy System for Power Quality Improvement”, in IEEE Systems
Journal, Volume 4,no.3, September 2010.

grid power quality improvement and battery energy storage in wind energy systems

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