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

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

JohnsonAbraham Mundackal 1 Alan C Varghese2 P G Scholar Amal Jyothi College of Engineering Kanjirappally, Kerala

[email protected] [email protected]

Sreekala P.1

Reshmi V2

Assistant Professor Amal Jyothi College of Engineering

Kanjirappally, Kerala [email protected] [email protected]

Abstract The sources such as wind and solar are expected to be promising energy sources when it is connected to the power grid. The power from above energy sources varies due to environmental conditions. Due to the fluctuation nature of the wind wind power injection into an electric grid affects the power quality. The influence of the wind sources in the grid system concerns the power quality such as the active power, reactive power, and variation of voltage, harmonics, and electrical behavior in switching operation. The power quality problems when wind turbine installed to grid side is demonstrated here. A Static Compensator (STATCOM) is connected at a point of common coupling with a battery energy storage system (BESS) to rectify the power quality problems. The battery energy storage used to maintain constant real power from varying wind power. 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. The amount of energy consumed or given to the grid can be view through an online smart meter connected in the circuit. Using the online smart meter the utility can view the energy consumption of each system simultaneously. So the utility can coordinate all the system effectively. Keywords- Battery energy storage system (BESS), Power quality, Smart energy meter, Wind energy generating system (WEGS), Static compensator (STATCOM).

I. INTRODUCTION

To pertain the distributed power system by maintaining sustainable improvement, it is necessary to tap the renewable energy sources. Energy conservation measures, the use of renewable sources are the main factors to meet the sustainable energy in these days. The integration of wind energy into existing power system presents a technical challenges and that requires consideration of voltage regulation, stability, power quality problems [1-2] [9].

The power quality is an essential customer-focused measure and is greatly affected by the operation of a distribution and transmission network. The power quality

problem is of great importance to the wind turbine. There has been an extensive growth and quick development in the exploitation of wind energy now days. Each unit has high capacity up to 2 MW, fed into distribution network, which is very near to the customers [3]. Today, more than 28,000 wind generating turbines are successfully operating all over the world and India stands at position four in utilizing wind energy sources. International Electro-Technical Commission IEC-61400-21 describes the norms for power quality of micro-wind generating system [4]. In the constant-speed wind turbine operation, fluctuation of wind speed variation transmits as variation in mechanical torque. This leads to large variation of electrical power on the grid system. Under normal operating condition wind turbine has fluctuating output power. This fluctuation is caused by the variation of wind due to tower-shadow, turbulence and wind shear etc. Thus, the systems have ability to control such variations. The problems in power quality are viewed with the wind generation, transmission and distribution network due to voltage dip and flickers. The wind generator introduces disturbances in the distribution network. To reduce the disturbances, we use the induction generator connected directly to the grid system. The induction generator is simple and robust having reactive power for excitation. The active power varies due to fluctuating wind. The reactive power and terminal voltage of generator also varies with this.

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. This STATCOM technically manages the power level associated with the commercial wind turbines. This system produce a proper voltage level having powe quality improvements. This system provides energy saving and un-interruptible power [5]. The wind energy system is used to charge the battery as and when the wind power is available. The voltage source inverter is controlled by using the

978-1-4673-5149-2/13/$31.00 2013 IEEE

International Conference on Microelectronics, Communication and Renewable Energy ( ICMiCR-2013)

current control mode. The proposed system with battery storage has the following objectives: Unity power factor and power quality at point of commoncoupling bus. Real and reactive power support only from wind generatorand batteries to load. Self operation in case of grid failure.

The utility companies can view the current, voltage and power of each system simultaneously by using the online smart metes. The utility can measure power generation of each system simultaneously.

Figure 1. Scheme of wind generator with battery storage [6]

II. POWER QUALITY ISSUES

Perfect 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. It is most often described in terms of voltage, frequency and interruptions [3].

1. 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 [3] (a) Voltage Variations: Voltage variation has implications on both real and reactive power associated with wind farms. A decreased voltage condition increases the current through the generator, making line losses to increase. Decreasing voltage also affects the power factor as the capacitive VAR generated out of the installed capacitor decrease as voltage decreases. (b) 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 [4]. These leads to decrease the energy capture and output power of wind turbines.

(c) Voltage transients: Large transients voltage could be created due to switching of capacitors using mechanical switches, which are the integral part of WEG for reactive power compensation [4]. These internally generated transients could result in damage to sensitive electronic devices of the WEG control system. (d) 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.

2. 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 WEGs [3] (a)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. This reactive power consumption leads to increased transmission and distribution losses [4]. (b) 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. (c) 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 [4].

III WIND POWER EXTRACTION WITH BATTERIES

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 [9]. 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 [11]. The current is injected which will cancel out the reactive part and harmonic part of the load and induction generator current, improves both power factor and the power quality [5]. The proposed system is implemented for power quality improvement at point of common coupling (PCC) , as shown in Fig. 1 [11]. The grid connected system in Fig. 1, shows wind energy generation system and battery energy storage system with STATCOM [4].

A. Wind Energy Generating system The wind generating system (WEGS) consists of

turbine, induction generator, interfacing transformer, and rectifier to get dc bus voltage. For constant dc bus voltage, the power flow is represented with constant dc bus current.


In this configuration, wind generationsconstant speed topologies with pitch contThe induction generator is used in thissimplicity, does not need a separate field cuse constant and variable loads, and has nfor short circuit [4]. The available wind epresented as below in (1)

P 1 2 A V

Where (kg/m3) is the air density and A swept out by turbine blade, Vwind is the wi[5]. There is no possibility to extract all kwind, thus it extract a fraction of this powecalled power coefficient Cp of the wind turbin (2).

P CPWhere Cp is the power coefficient, dependand its operating condition of wind turbine.can be expressed as a function its of tip speeangle [4]. The mechanical power produce bgiven in (3) [5].

P C1 2 A V

Where R is the radius of the blade (m).

Figure 2. Dc link battery storage and wind g

B. DC Link for Battery storage and Wind EGenerator The battery energy storage system (BES

energy storage element for the purporegulation. The BESS maintain dc caconstant and is suited for STATCOM sinceor absorbed reactive power to stabilize thealso controls the fast rate of distribution asystem. When a power variation occurs inBESS can be used to control the powcharging and discharging operation. Tconnected in shunt to the dc capacitor of ST

The battery storage and WEGs are conndc link as shown in Fig.2. The dc link conwhich decouples the wind generating system(grid) system [9]. The battery storage will the help of wind generator. The use of dc lmore efficient, less expensive and is repres[4]:

s are based on trol turbine [10]. s because of its circuit and it can natural protection energy system is

1 (m2) is the area

ind speed in m/s kinetic energy of er in wind, this is bine, and is given

(2) ds on which type . This coefficient ed ratio and pitch y wind turbine is

3

generator[4].

Energy

SS) is used as an ose of voltage apacitor voltage it rapidly injects e grid system. It and transmission n the system, the wer variation by The battery is

TATCOM [4]. nected across the sists of capacitor

m and ac source get charged with link capacitors is sented as follows

C V= I I I

Where C is dc link capacitor, Vdc isIdc(rec) is dc-side rectified current, current and Ib is the battery currentis connected to series connected dand resistance Rb. Then its voltage status of the battery. The terminal v

V = E- I*RWhere battery current is represented

C. STATCOM-current controlled dThe STATCOM is also a thr

inverter having the capacitor on itsat the point of common coupSTATCOM injects compensatingvariable magnitude and frequency common coupling. The shunt connbattery energy storage is connectedinduction generator and non-lineargrid system [10].

Figure 3. Shunt connected static com

According to the coSTATCOM compensator output is the power quality standards in the control strategy is included in the cdefines the functional operationcompensator in the power systinsulated gate bipolar transistor reactive power support, to the noinduction generator in the grid sysdiagram of the shunt connected statFig. 3.

IV CONTROL SCHEME OF

The control scheme with bwind generating system utilizes thenergy from the wind. The windthrough a step up interfacing transfobridge so as to obtain the dc voltabattery is used for maintaining the Thus the inverter is implementdistributed system. The control scheinjecting the current into the gridcurrent controller [9]. Using suckeeps the control system variables of hysteresis area and thus gives c

(4) s rectifier output voltage, Idc(inv) is inverter side dc

t [4]. The battery storage dc link voltage source Eb

varies with the charging oltage Vdc is given by

(5) d by Ib .

device ee-phase voltage source s DC link and connected

pling (PCC) [10]. The g controlled current of component at the bus of nected STATCOM with d as the interface of the r load at the PCC in the

mpensator in grid[2].

ontrolled strategy the varied so as to maintain grid system [4]. Current control scheme so that it n of the STATCOM tem. STATCOM using is proposed to provide

onlinear load and to the tem [5]. The operational

tic compensator in grid in

SYSTEM

attery storage and micro-he dc link to extract the d generator is connected former and to the rectifier ge. Also a lead acid cell dc bus voltage constant. ed successfully in the eme approach is based on d using hysteresis band ch techniques controller

between the boundaries correct switching signals


for the inverter operation [4]. Fig. 4shows the control scheme for generating the switching signals to the inverter [9].

Figure 4. Control circuit for switching inverter circuit[6].

The control algorithm needs the measurement of several variables such as three-phase source current iSabc for each phases, dc bus voltage Vdc, and inverter current iiabc with the help of measurement sensors. The current control unit receives an input of reference current i*Sabc and actual current iSabc is measured from each phases respectively, which are subtracted so as to activate the operation of the inverter in current control mode [3]

A. Grid Synchronisation In the balance three-phase system, source amplitude RMS voltage ( is calculated at the sampling frequency from the source phase voltages and is expressed as sample template Vsm as in

V = V V V (6) The in-phase unit vectors are obtained from ac source-phase voltage and the RMS value of unit vector Usa ,Usb , Usc as shown in

U= VV ; U= VV ; U=

VV (7)

From the in-phase unit voltage template, in-phase generated reference currents are derived using

i I. U ; i I. U ; i I. U 8 Where I is proportional to the magnitude of filtered source voltage for each phases and also the output taken from proportional-integral controller (PI). This ensures that the source current is controlled to obtain sinusoidal signal. For the grid synchronization of inverter, unit vector plays the key role. This method is robust, simple, and favorable as compared with other methods [4]. When the grid voltage source fails the wind generator operates as stand-alone mode. In these cases, the voltage sensors sense the condition and it will transfer the micro-switches for the generation of reference voltage from wind generator system [9]. The generated voltage reference without any supply gets switched to the stand-alone reference generator after voltage sensing at the point of common coupling (PCC) [4]. It is a unit voltage vector

which can be realized by using DSP or microcontroller [7]. Hence, the inverter maintains the continuous power for the critical load.

B. Hysteresis Based Current Controller Current control based hysteresis controller is used in this

particular scheme. The reference current is generated as in and the actual current is detected by current sensors that are subtracted for obtaining current errors for a hysteresis based controller [9]. ON/OFF pulse signals for IGBT switches of inverter are derived from hysteresis current controller. When the measured current is higher than the generated reference current, it is necessary to get negative inverter output voltage so that corresponding switches are commutated [9]. Thus output voltages are decreased so that the output current reaches the reference current [4]. Also, if the measured current is less than the reference current, positive inverter output voltage are obtained by commutating particular switch Thus output current increases to the reference current. Hence, the output current will be within a band around the reference one. The switching function SA for phase a is expressed as follows:

0 1 i i HB then SA 1 and 0

where HB is a hysteresis current-band, similarly the switching function SB ,SC can be derived for phases b and c, respectively [9]. The current control mode of inverter injects the current into the grid in such a way that the source currents are harmonic free and their phase-angles are in-phase with respect to source voltage. The reactive and harmonic part of load side is cancel out by the injected current at shunt part. Thus, overall it reduces harmonic content and improves the source current quality at the PCC [9]. As soon as battery energy system is fully charged with the help of micro-wind generator, the power transfers takes place [4]. The source voltage is sensed and synchronized in generating the desired reference current command for the inverter operation. Hysteresis band based current control technique is simple and its implementation is not expensive. The controller has fast response since it has negligible inertia and delay. The figure 5 shows the simulation result of wind turbine voltage. In figure 6 the controller output is seen. The FFT analysis with and without controller is seen in figure 7.

Figure 5. Wind Turbine Model


Figure 6. Statcom Output

Figure 7.FFT Analysis with and without Controller

V. SMART ENERGY METERS Smart energy meters are capable of measuring

instantaneous voltage and current of the electrical circuit. Digital circuit in the meter can calculate any other parameter like instantaneous power, total energy usage and power factor [8]. The parameters of time information for time of use (TOU) calculations can be stored inside the meter. The utility companies can utilize these data for their use. These data contains much confidential information. 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 [8].

A. Design Parameters The microcontroller is able to generate the control

signals required to drive the HAN according to the data read from the meter. The microprocessor consists of an Enhanced Universal Synchronous and Asynchronous Receiver and Transmitter unit. It is used for communication with the smart meter [8]. A USB peripheral is used in exporting data read from the smart meter to a pc for further processing or

monitoring. Fig 6 illustrates the flow of the communication procedure between the two systems [8].

The Graphical user interface developed has three main functions. Reading from the device real time as well as writing to the device. Configuration of the Zigbee device: Every Zigbee device has several parameters like the channel it operates in, the PANID, and the Destination address. These parameters are used in identifying different Zigbee devices [8]. The Zigbee device is preprogrammed to specific values from the meter manufacturer.

It is also possible to read the accumulated current consumption for the month and the current demand and Grid status through the User interface [8]. The user interface shows the accumulated consumption at each grid demand level separately. The utility can monitor the current electric power consumption real time. The user can monitor the variation of the electric load in a power-time curve [8].

Figure 8. Smart Energy Meters

VI. CONCLUSIONProposed 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. The wind power exchange is regulated across the dc bus having energy storage and is made available under the steady state condition. This also makes real power flow at instantaneous demand of the load. Rapid injection or absorption of reactive/real power flow in the power system can be made possible through battery energy storage and static compensator. 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. The utility can view each power plant simultaneously and accurately by using online smart meter. This scheme thus provides the system to operate both in power quality mode as well as in stand-alone.


REFERENCES [1]C. Han, A. Q. Huang, M. Baran, S. Bhattacharya, and W. Litzenberger, 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.[2] 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. [3] 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 [4] 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. [5] 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. [6] K. S. Hook, Y. Liu, and S. Atcitty, Mitigation of the wind generation integration related power quality issues by energy storage, Energy power quality journal., volume XII, no. 2, September 2006. [7] S. W. Mohod and M. V. Aware, Grid power quality with variable speed wind energy conversion, in IEEE International Conference Power Electronic Drives and Energy System(PEDES), Delhi, Dec. 2006. [8] Kulatunga N A, Navaratna S, Dole J, Liyanagendra C, Martin A T, Hardware Development for Smart Meter Based Innovations, in Innovative Smart Grid Technologies in IEEE Conference, page 1 to 5 , September 2012. [9] Jalilzadeh, Saeid; Kazemi, Ahad and Farhang, Peyman. "Analysis and Assessment of Power System Including Wind Farm by Using SVC and STATCOM", International Review of Electrical Engineering, 2012. [10] Saravana Murthy, P., P. Devaki, and J. Devishree. "A Static Compensation Method Based Scheme for Improvement of Power Quality in Wind Generation", 2011 International Conference on Process Automation Control and Computing, 2011. [11] Yuvaraj, V., S.N. Deepa, A.P. Roger Rozario, and Madhusudan Kumar. "Improving Grid Power Quality with FACTS Device on Integration of Wind Energy System", 2011 Fifth Asia Modelling Symposium, 2011. [12] Sharad W. Mohod. "Energy Storage to Stabilize the Weak Wind Generating Grid", 2008 Joint International Conference on Power System Technology and IEEE Power India Conference.

Johnson Abraham Mundackal. Received B Tech in Electrical and Electronics Engineering from College of Engineering, Kidangoor, Kottayam and pursuing M Tech in Power Electronics and Power System from Amaljyothi College of Engineering Kanjirappally, Kerala. He has worked

as Assistant Professor in Electrical and Electronics Engineering Department at College of Engineering Poonjar, Kottayam. His research interests include Renewable Energy Resources, Smart Grid Technology, Soft Computing Techniques, Power Electronics, and Control System.

Alan C Varghese. Received B Tech in Electrical and Electronics Engineering from Amaljyothi College of Engineering Kanjirappally, Kottayam, Kerala and pursuing M Tech in Power Electronics and Power System from Amaljyothi

College of Engineering Kanjirappally, Kerala. His research interests include Power Quality, Power System, Renewable Energy Resources and Power Electronics.

Sreekala.P. Received B Tech in Electrical and Electronics Engineering from Rajiv Gandhi Institute of Government Engineering College Kottayam and M Tech in Power Electronics and Power System from Amaljyothi College of Engineering Kanjirappally, Kerala. She is

now working as Assistant Professor in Electrical and Electronics Engineering Department of Amaljyothi College of Engineering. Her research interests include Renewable Energy Resources, Artificial Intelligence, Smart Grid Technology, Biomedical Engineering and Power Electronics.

Reshmi V .Received B Tech in Electrical and Electronics Engineering from University College of Engineering, Thodupuzha and M Tech in Power System from College of Engineering Trivandrum, Kerala. She is now working as Assistant Professor in Electrical and

Electronics Engineering Department of Amaljyothi College of Engineering. Her research interests include Power System, Power Quality, Renewable Energy Resources, Artificial Intelligence and Smart Grid Technologies.


/ColorImageDict > /JPEG2000ColorACSImageDict > /JPEG2000ColorImageDict > /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 200 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 2.00333 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict > /GrayImageDict > /JPEG2000GrayACSImageDict > /JPEG2000GrayImageDict > /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 400 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 600 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.00167 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict > /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile (None) /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False

/CreateJDFFile false /Description > /Namespace [ (Adobe) (Common) (1.0) ] /OtherNamespaces [ > /FormElements false /GenerateStructure false /IncludeBookmarks false /IncludeHyperlinks false /IncludeInteractive false /IncludeLayers false /IncludeProfiles true /MultimediaHandling /UseObjectSettings /Namespace [ (Adobe) (CreativeSuite) (2.0) ] /PDFXOutputIntentProfileSelector /NA /PreserveEditing false /UntaggedCMYKHandling /UseDocumentProfile /UntaggedRGBHandling /UseDocumentProfile /UseDocumentBleed false >> ]>> setdistillerparams> setpagedevice

Documents

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