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International Journal of Research in Computer and

Communication Technology, Vol 2, Issue 9, September -2013

ISSN(Online) 2278-5841

ISSN (Print) 2320-5156

www.ijrcct.org Page 680

Load frequency control in MicrogridAbhas Kumar Singh, Chandrpal singh, Nitish Kumar Yadav,

Electrical Engineering department National Institute of Technology

Hamirpur, [email protected], [email protected], [email protected],

Abstract -- The objective of this paper is to design a

Load Frequency Control (LFC) mechanism using a

Battery Storage System (BSS) and Diesel Generation

(DG) units for an isolated microgrid system. Load

frequency control is important in power sector &

want to be maintain. They were tested under

different scenarios; random loadvariations, and loss of one of the DG units. In this we also explain the objective

and reasons of load frequency control.

Index Terms-- Microgrid, Real time load frequency

control, BSS, Diesel Generation(DG).

I. I NTRODUCTION

A micro-grid can be considered as a small grid basedon distributed generators (DGs). Generally, themicro-grid consists of renewable energy based DGsand combined heat and power plants. It can supply power to small/medium sized urban housing

communities or to large rural areas. It can be aneconomical, environment friendly and reliable way tosupply power at distribution levels. The sources in amicro-grid can be mainly classified as dispatch-ableor non-dispatchable in terms of power flow control[1,2]. The output power of dispatchable sources suchas micro turbines, fuel cells and bio-diesel generatorscan be controlled to maintain the desired systemfrequency and voltage in an isolated micro-grid.However, non dispatchable sources such as wind andPV, in which the output power depends on theenvironmental conditions, are expected to be mainlycontrolled on the basis of maximum power pointtracking (MPPT).

The sources in a micro-grid can also be classified asinertial and non-inertial depending on the way theyare connected to the system. For example, a dieselgenerator and a hydro generator are inertial sourcessince they include synchronous generators with their rotating inertial masses. On the other hand, thesources connected through converters such as PV,fuel cell and batteries are non-inertial since power

output through these DGs can be changedinstantaneously. A micro-grid can operate either ingrid connected or islanded mode. The available power of all DG units should meet the total loaddemand for islanded operation; otherwise loadshedding need to be implemented.

Fig.1.Schematic diagram of a micro-grid

The control of real and reactive power output of the sources is essential to maintain a stableoperation in a micro-grid, especially when it operatesin the islanded mode. The frequency and voltage inan islanded (autonomous) micro-grid should be

maintained within predefined limits. The frequencyvariations are very small in strong grids; however,large variations can occur in autonomous grids [3].Thus power management strategies are vital for anautonomous micro-grid in the presence of few smallDG units, where no single dominant energy source is present to supply the energy requirement [4]. Also,fast and flexible power control strategies arenecessary to damp out transient power oscillations in

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an autonomous micro-grid where no infinite sourceavailable [5].

II. OBJECTIVE OF LOAD FREQUENCY CONTROL

In an interconnected power system, as a power load

demand varies randomly, both area frequency andtie-line power interchange also vary. The objectivesof load frequency control (LFC) are to minimize thetransient deviations in these variables (area frequencyand tie-line power interchange) and to ensure their steady state errors to be zeros.Frequency does not change in an Interconnection aslong as there is a balance between resources andcustomer demand (including various electricallosses). This balance is depicted in Fig.2.[6]

FIG. 2 — GENERATION / DEMAND

BALANCE

III. R EASONS FOR LIMITS ON FREQUENCY

1.The speed of a.c motors are directly related to thefrequency. Even though most of the a.c drives are notmuch affected for a frequency variation of even50±1.5 Hz but there are certain application wherespeed consistency must be of high order.

2. The electric clocks are driven by synchronousmotors and the accuracy of these clocks is not only afunction of frequency error but is actually of theintegral of this error.

3. If the normal frequency is 50 Hz and the turbinesare run at speed corresponding to frequency lessthan 47.5 Hz or more than 52.5Hz the blades of theturbine are likely to get damaged.

4. The under frequency operation of the power transformer is not desirable. For constant systemvoltage if the frequency is below the normal value theflux in the core increases .As a result the magnetisingcurrent even exceeds the normal full load current

.The sustained under frequency operation of the power transformer result not only in low efficiency but it may even damage the transformer winding dueto overheating.

5. The system operation at subnormal frequency andvoltage leads to loss of revenue to the suppliers dueto accompanying reduction in load demand.

6. The most serious effect of subnormal frequency ison the operation of thermal power plants. Withreduced frequency the blast by ID and the FD fansdecrease as a result of which the generation also

decreases and thus it become a cumulative action andmay result in complete shut-down of the plant if corrective measures like load shedding is not resortedto.

7.The overall operation of power system can be better controlled if a strict limit on frequency deviation ismaintained.[7]

IV. LOAD FREQUENCY CONTROL (SINGLE-AREA CASE)

To understand the load frequency control problem,

let us consider a single turbo-generator systemsupplying an isolated load.[8]

Fig.3.functional diagram of real power controlmechanism of Generator.

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1. Fly ball speed governor: This is the heart of thesystem which senses the change in speed (frequency).As the speed increases the fly balls move out wardsand the point B on linkage mechanism movesdownwards. The reverse happens when the speed

decreases.

2. Hydraulic amplifier: It comprises a pilot valveand main piston arrangement. Low power level pilotvalve movement is converted into high power level piston valve movement. This is necessary in order toopen or close the steam valve against high pressuresteam.

3.Linkage mechanism: ABC is a rigid link pivotedat B and CDE is another rigid link pivoted at D. Thislink mechanism provides a movement to the controlvalve in proportion to change in speed. It also

provides a feedback from the steam valve movement.

4.Speed changer: It provides steady state power output setting for the turbine Its downwardmovement opens the upper pilot valve so that moresteam is admitted to the turbine under steadyconditions.

V. R EAL TIME LOAD FREQUENCY CONTROL

MICRO-GRID SYSTEM (UNDER STUDY)Micro-grids are small power grids. They can operateeither independently or connected to larger grids.They can be, for example, a university campusconnected to the main grid, an island in the middle of the ocean or a military base in a desert where thereare no means of connecting to primary grid power .Such concept provides a platform for incorporation of several Distributed Energy Resources (DERs), suchas solar and wind power generations, and energystorage technologies. However, micro-grids are notwithout flaws.

In order to ensure a stable operation for a micro-gridsystem it is crucial to have a real-time matching between generation and demand so that the system’s

frequency is maintained at its nominal value. Suchrequirement is attained by implementing a LoadFrequency Control (LFC) mechanism. Attaining such balance between generation and demand in a smalland isolated system, however, is an issue of muchgreater significance as generations might be limitedand/or intermittent .

Furthermore the micro-grid system, in normaloperation conditions experiences random demandfluctuations and possibly emergency conditions if one of the system’s primary generation units issuddenly lost. Hence it is crucial to have anautomated and robust LFC mechanism implemented

to ensure a stable system operation under allconditions.

Load Frequency Control (LFC) mechanism using aBattery Storage System (BSS) and Diesel Generation(DG) units for an isolated micro-grid system. Themicro-grid system under consideration is comprisedfrom two DG units, a BSS unit, and two solar panels.They were tested under different scenarios; randomload variations, and loss of one of the DG units.[9]

VI. SYSTEM DESCRIPTION AND CONTROL

DESIGN

System Description : The micro-grid system under consideration is comprised from two DieselGeneration (DG) units, two PV systems, and aBattery Storage System (BSS). The two DG units are100 and 20 KVA. The two PV systems are 14.8 KWeach, and the BSS is 30 Kwh . The micro-grid systemhas no means of connecting to any other power gridi.e. isolated system.

Fig.4. Micro-grid system under study

Control Design: The control objective is tominimize a performance index (J) associated with thefrequency error Δf (Δf = f - fs), and

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defined by (1).

Minimize J = ∫ |Δf|2 dt(1)

Where fs, and f are the scheduled frequency of 60 Hz

and the system’s measured frequency respectively.The objective is to minimize (J) under both normaloperation conditions, where the power demandfluctuates, and contingency situations , where one of the system’s generation units is suddenly lost.

1) Diesel Engine Control System: The dieselengine model gives a description of the fuelconsumption rate as a function of speed andmechanical power at the output of theengine, and is usually modelled by a simplefirst order model relating the fuelconsumption (fuel rack position) to theengine mechanical power. As a prime mover

it is crucial that the diesel engine equippedwith a robust control system to ensure stableoperation and foster disturbance rejection.The objective of the control system is tomaintain the system’s frequency at thedesired reference value i.e. drives thefrequency error (fm – fr) to zero where fr isthe reference frequency (60 Hz or 1 p.u.)and fm is the measured frequency.

Fig. 5. Diesel engine model with control system

2) 2) Battery Storage Control System: Fig.6.shows a block diagram of a battery storagesystem hooked up to a micro-grid. The

control system developed for LFC is theDC/AC inverter control system. In order toutilize the BSS in LFC it is crucial that theinverter control system track the system’sfrequency error signal and control the active power injected or absorbed by the BSS. Thenecessity to save on the amount of energystored in the BSS to secure the maximumamount of reserve. Hence the BSS should

not contribute much in LFC when thesystem’s DG units are available.

Fig.6.Schematic diagram of a micro-grid connected batterysystem.

V. CONCLUSION

This paper is presented the detail about the neccecityof load fresquency control and different type of control with its importance.This paper presented adecentralized LFC mechanism to control a BSS andDGs incorporated in an isolated microgrid system toregulate the system’s frequency. The mechanism wastested under three different scenarios; fluctuatingdemand which represents the normal operationconditions of a power system, and two emergencyscenarios where one of the DG units was lost in each

scenario.

VI. R EFERENCES

[1] C. Hua and C. Shen, "Study of maximum power trackingtechniques and control of DC/DC converters for photovoltaic

power system," 29th Annual IEEE Power Electronics Specialists

Conference, pp. 86 - 93, 1998.

[2] Y. Chuanan and Y. Yongchang, "An Improved Hill-ClimbingMethod for the Maximum Power Point Tracking in PhotovoltaicSystem," IEEE International Conference on Machine Vision and

Human-Machine Interface, pp. 530 - 533 2010.[3] S.-K. Kim, J.-H. Jeon, C.-H. Cho, E.-S. Kim, and J.-B. Ahn,"Modeling and simulation of a grid-connected PV generationsystem for electromagnetic transient analysis," Solar Energy, vol.

83, pp. 664-678, 2009.[4] J. Xue, Z. Yin, B. Wu, and J. Peng, "Design of PV ArrayModel Based On EMTDC/PSCAD," Power and Energy

Engineering Conference, pp. pp.1-5, 2009.[5] I. H. Altas and A. M. Sharaf, "A Novel Photovoltaic On-LineSearch Algorithm For Maximum Energy Utilization," The

International Conference on Communication, Computer and

Power 2007.[6] F. Katiraei, R. Iravani, N. Hatziargyriou, and A. Dimeas,"Microgridsmanagement," Power and Energy Magazine, IEEE, vol. 6, pp. 54-65,

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2008.[7] L. D. Watson and J. W. Kimball, "Frequency regulation of amicrogrid using solar power," in Applied Power Electronics

Conference and Exposition (APEC), Twenty-Sixth Annual IEEE ,2011, pp. 321-326.[8] Oudalov, A.; Chartouni, D.; Ohler, C.; "Optimizing a BatteryEnergy Storage System for Primary Frequency Control," Power

Systems, IEEE Transactions on , vol.22, no.3, pp.1259-1266, Aug.2007.[9] A. Madureira, C. Moreira and J. P. Lopes, "Secondar Load-Frequency Control for MicroGrids in Islanded Operation."Engenharia da UP and Power Systems Unit of INESC Rua Dr.Roberto Frias, 378, 4200- 465 Porto, Portugal. Available athttp://www.icrepq.com/full-papericrep/ 335- madureira.pdf [10] K. M. Brokish, "Adaptive load control of microgrids withnondispatchable generation," Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 2009.[11] F. A. Mohamed, "Microgrid Modelling and OnlineManagement," Doctor of Science in Technology, Department of Automation and Systems Technology, Helsinki University of Technology, Finland, 2008.Available:http://lib.tkk.fi/Diss/2008/isbn9789512292356/isbn97895122 92356.pdf

[12] Moataz Elbaz and Ali Feliachi, “Real Time Load FrequencyControl for an Isolated Microgrid System”, North American Power Symposium (NAPS), 2012, Page(s): 1 - 6

VIII. BIOGRAPHIES

Abhas Kumar Singh was born in Ambikapur (Surguja) C.G., India. He received the 3 year Diploma inElectrical Engg. from Govt. Polytechnic College Ambikapur India,in 2007 and the B.Tech. degree in Electrical and Electronics

Engineering from Shri Shankaracharya College of Engg. & Tech.Bhilai, India, in 2010.He is currently pursuing the M.Tech. degreein Power System from National Institute of Technology, Hamirpur.

Chandrpal Singh was born in Agra(U.P), India.He received the 3 year Diploma in Electrical Engg. from Govt.College P.M.V Polytechnic Mathura(U.P) India, in 2009 and theB.Tech. degree in Electrical and Electronics Engineering fromHindustan College of Science & Tech.,Mathura (U.P), India, in2012.He is currently pursuing the M.Tech. degree in Power Systemfrom National Institute of Technology(NIT), Hamirpur(H.P).

Nitish kumar yadav was born in jaunpur uttar Pradesh, India.He received B.tech degree in Electricl & Electronicsfrom Inderprastha Engineering college, Ghaziabad , uttar Pradesh,India,in 2010. He is currently pursuing the M.Tech. degree

in Power System from National Institute of Technology, Hamirpur,Himachal Pradesh ,India.

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