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) isconnected at a point of common coupling with a batteryenergy storage system (BESS) to mitigate the power qualityissues.

The generated power can be stored in the batteries at lowpower demand hours.

The combination of battery storage with wind energygeneration system will synthesize the output waveform byabsorbing or injecting reactive power and enable the realpower flow required by the load.

Due to the fluctuation nature of the wind power injection intoan electric grid affects the power quality.

INTRODUCTION

The integration of wind energy into existing power system presents atechnical challenges and that requires consideration of voltageregulation, stability, power quality problems.

The power quality is an essential customer-focused measure and isgreatly affected by the operation of a distribution and transmissionnetwork.

In the constant-speed wind turbine operation, fluctuation of wind speedvariation 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 activepower 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 andbattery energy storage with distributed network is configured on itsoperating principle and is based on the control strategy for switchingthe inverter.

The STATCOM based current control voltage source inverter injectsthe current into the grid in such a way that the source current areharmonic free and there is phase difference with respect to sourcevoltage has some desired value .

The proposed system is implemented for power quality improvement atpoint of common coupling (PCC) , as shown in above Fig.

The grid connected system in above Fig. shows wind energygeneration 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 toswitching of capacitors using mechanical switches,which are the integral part of WEG for reactivepower compensation.

These internally generated transients could result indamage to sensitive electronic devices of the WEGcontrol 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, causingoverheating.

WEG side power quality issues

Power quality issues that affect the WEG aremainly concerned with the quality of current that isbeing drawn or generated by the WEG’s.

Reactive power consumption:

Reactive power consumption in a wind farm ismainly due to the use of induction generators forenergy saving.

The basic principle of Induction generators is thatthey consume reactive power to set up the excitationor magnetic field in order to generate real power.

Generation of current harmonics:

Current harmonics are generated due to soft starting ofinduction generators during motoring mode.

This distorts the voltage on the line and affects allthe consumers connected to the line.

injection of fluctuating power:

Power in wind by nature is varied and is checked byannual, monthly, daily and hourly variations.

This results in generation and supply of a power that isfluctuating and leading to operational problems.

Wind Energy Generating system

The wind generating system (WEGS) consists ofturbine, induction generator, interfacing transformer,and rectifier to get dc bus voltage.

In this configuration , wind generation are based onconstant speed topologies with pitch control turbine.

The available wind energy system is presented as belowin

Where ρ(kg/m2) is the air density and A(m2)I is the areaswept out by turbine blade, Vwind is the wind speed inm/s.

DC Link for Battery storage and Wind Energy Generator

The battery energy storage system (BESS) is used as anenergy storage element for the purpose of voltageregulation.

The BESS maintain dc capacitor voltage constant and is suited for STATCOM since it rapidly

injects or absorbed reactive power to stabilize thegrid system.

The battery is connected in shunt to the dc capacitor ofSTATCOM.

The battery storage and WEG’s are connected acrossthe dc link as shown above in Fig.

The battery storage will get charged with the help ofwind generator.

STATCOM-current controlleddevice

The STATCOM is also a three-phase voltagesource inverter having the capacitor on its DC linkand connected at the point of commoncoupling(pcc).

The shunt connected STATCOM with batteryenergy storage is connected as the interface of theinduction generator and non-linear at the PCC inthe grid system.

The operational diagram of the shunt connectedstatic compensator in grid in above fig.

SMART ENERGY METERS

Smart energy meters are capable of measuringinstantaneous voltage and current of theelectrical circuit.

The parameters of time information for time ofuse (TOU) calculations can be stored inside themeter.

Data are transmitted to the utility company usingwireless medium.

Protecting the privacy of the customer andconfidentiality of data is the responsibility of autility.

Smart Energy Meters

CONCLUSION

Proposed study on wind energy conversion scheme usingbattery energy storage for nonlinear load includes interface ofinverter incurrent controlled mode for exchange of real andreactive power.

The hysteresis current controller is used to generate theswitching signal for inverter in such a way that it will cancelthe harmonic current in the system.

This scheme improves power factor and also make harmonicfree source current in the distributed network at the point ofcommon connection.

Battery energy storage provides rapid response and enhancesthe performance under the fluctuation of wind turbine outputand 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 aweak 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 energysource: 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 adequacyassessment of generating systems incorporating wind energy”, IEEETransaction on Energy Conversion, volume. 23, no. 1, pp. 163169, December2008

S. W. Mohod and M. V. Aware, “Micro wind power generator with batteryenergy 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 connectedWind Energy System for Power Quality Improvement”, in IEEE SystemsJournal, Volume 4,no.3, September 2010.