The research paper published by IJSER journal is about Frequency Control in an Isolated Power System By Using Optimizing a BESS Technology 1

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Frequency Control in an Isolated Power System

By Using Optimizing a BESS Technology

,

1 PG student, GMRIT, RAJAM

rajesh.vanama@gmail.com, 9959926610.

2Associate Professor, GMRIT, RAJAM. hemanth_251007@yahoo.co.in, 9493208047.

Abstract—This paper present optimal sizing of the battery energy storing system(BESS) for controlling the frequency fluctuations in a isolated power system, and it also used as revolving reserve in a small isolated power system. The flow chart is used for controlling the state of limits of battery energy. Statistical simulations are performed on LFC of the isolated system. This BESS technology developed in isolated power system for attains maximum expected effectiveness of the device. The BESS can add to considerably the power system stability, the grid security and the planning flexibility for a small isolated power system with low netwo rk inertia. In the meantime, it fulfills the frequency control requirements with a high predictable economic effectiveness.

Index TermsAncillary services market, battery energy storage system, frequency control, isolated power system, load-frequency control, net present value.

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I. INTRODUCTION

The electricity industry currently experiences historical and significant restructuring of its conventional vertically integrated configuration. Indeed, the electricity market deregulation is responsible for an augmentation in discontinuous distributed power generation (e.g., wind, solar, etc.), and an increase in power transfer quantities and distances. In addition, the perpetual load growth results in a stressed and less secure power system operation. Thus, utilities and transmission system operators (TSOs) are now more interested in energy storage systems (ESS) to provide technical and economic advantages throughout the delivery chain. The ESS can provide a technical solution with increased profitability to the current industry challenges such as grid security, congestions management, generator’s low utilization factor, and

fuel price volatility. Consequently, the storage device can enter the ancillary services market for remuneration in exchange for Market benefits such as hedging risk, providing stability, or loss prevention. In recent years, the capital cost of battery storage technologies has significantly reduced, thus justifying a new study of its applications and economic benefits. Moreover, battery energy storage systems (BESS) can cover a wide spectrum of applications ranging from short- term power quality support to long-term energy management. This is a tremendous advantage of BESS technologies since it allows very different applications to be running on the same device with fast response [e.g., load leveling, peak shaving, spinning reserve, black-start capability, uninterruptible power supply (UPS), flicker compensation, voltage sag correction, area regulation, etc.]. Therefore, the BESS increases the

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power system stability and security, which helps the integration of distributed renewable
energies and postpones grid expansion. Previous work has shown the great potential of BESS for
frequency regulation. In fact, the supply of frequency control reserve has even been identified in that study as the application with the highest value for the owner of BESS. Their value analysis is derived by comparing frequency control reserve prices on the ancillary services market with typical BESS installation and maintenance costs. The BESS can satisfy the technical requirements for primary frequency regulation by absorbing power from the grid for high frequency periods, above a nominal value, and injecting power to the grid during low frequency excursions, below nominal set point. Power quality, additionally, since the BESS is composed only of static elements, it has a very fast dynamic response compared to typical generators or other storage devices.
II. BATTERY ENERGY STORAGE SYSTEM MODELING

BESS Description:

Battery energy storage power block includes control and cooling system, converters, harmonic and dc filter circuits, and the battery strings. Using an appropriate control strategy, the BESS can supply rapid change of active and reactive power in both directions, thus providing control in the four quadrants of the P-Q plane. Therefore, the BESS device is capable of improving the performance of load-frequency control by offering fast active power compensation. Moreover, a BESS device as shown in Fig. 1 is recognized for its technological availability, its high reliability and efficiency, its modularity, and the environmental compatibility.

Fig. 1. BESS structure and interconnection diagram.
III. SYSTEM INVESTIGATED
For the purpose of investigating a small isolated power system, an LFC dynamic simulator is implemented with Mat lab/Simulink environment according to the structure of Fig. 2. Each generating unit is modeled with its speed-governing system and corresponding turbine. Respective shafts are included within the sum of the inertia constants of all rotating machines, namely all generators’ contributions in the power system are added to obtain the single machine Equivalent over the network. The difference with the total load is then used in the basic swing equation. The grid frequency is readily obtained from the rotor dynamic equation given in the Following:

……… (1)


Fig.2. Schematic of the LFC power system structure.

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Furthermore, the isolated power system shall consider the power rating of an island of small to medium scale power generation (100–500 MW). Consequently, the installed power generation Available is chosen to be about 450 MW. Moreover, isolated power systems often use renewable energy from the wind, and Therefore
90MWof wind power (20% wind penetration) will
be included in the power system under study. The remaining 360 MWcome from both hydraulic units and fossil-fired steam units in equal proportions. References give the different dynamic models necessary for the speed-governing systems and turbines. The steam unit models a fossil-fuelled single reheat tandem compound turbine along with its electro hydraulic control (EHC) speed-governing system. The hydro turbine and speed-governing system are also obtained, and the variable-speed wind turbine units with its speed-governing Systems are given. The speed-governing system is composed of a pitch controller and a tracking characteristic controller. The corresponding different sets of parameters are shown in the Appendix. The resulting LFC isolated power system simulator is shown in Fig. 3. Additionally, to obtain the wind input profile, auto correlated distributed time series are derived from awe bull distribution having a mean wind speed of 7 m/s with scale (n) and shape (β) parameters of 8 and 2, respectively. The load profile prevision is obtained from a typical load profile scaled to the size of the current power system considered, namely 360 MW peak power (total installed power is 450 MW). A random generator output is added on top of the load profile with a variance of to integrate stochastic part of the demand. The reader should be aware that other techniques or models are readily available for wind and load profile definition, such as taking historical measurements for instance. Nevertheless, the methodology developed and presented in this paper is not dependent upon the input profile chosen and is seen as a general method independent of the inputs. Next, an evaluation of the effect of the BESS on the dynamic stability of the power system is performed by comparing simulations with and without the BESS device.
IV. EFFECT OF BESS ON FREQUENCY REGULATION

The BESS device is very effective in reducing the peak frequency deviations by providing fast active power compensation. Fig. 5 shows the simulation for a single month and compares the frequency deviations with and without the BESS. The frequency deviation without the BESS reaches a maximum peak of 490 MHz (49.51 Hz) on the 24th of the month. The BESS effect is to reduce the deviation to only 130 MHz (49.87 Hz) for the same time period. It represents an improvement of nearly a factor 4 in frequency damping. Thus, it is clearly seen that there is a significant improvement of the dynamic performances of the power system in terms of peak deviations and settling time. Also illustrates a noncritical frequency window centered at the nominal frequency of 50 Hz (from
49.95 to 50.05 Hz). The noncritical frequency
window defines a frequency deviation dead band where no primary frequency regulation is applied. Outside of this dead band, primary frequency control is applied linearly as given by the power- frequency (p-f) characteristic shown in [3]. Also, in small isolated power systems, the frequency deviations reach higher values than interconnected networks because of low grid inertia. Indeed, due to renewable devices using inverter interfaced energy sources, small isolated power systems cannot rely on generator inertia as much as in interconnected grids. Thus, greater frequency deviations are allowed and noncritical frequency windows are voluntarily set higher than interconnected power systems requirements (e.g., in comparison, UCTE noncritical window is ). Ultimately, when the measured frequency reaches the window limitation, primary controllers activate the calling up of primary reserve to nullify the power mismatch between production and consumption. If the frequency deviation reaches, full primary power available must be activated within seconds to preserve the power system stability. Between both frequency deviations, namely 50MHz, primary power is linearly activated. For the BESS device, it represents power pulse exchanges, as the BESS alternatively supplies and absorbs power to and

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from the grid. The transfer from frequency deviations to power pulses is done accordingly to the primary control p-f characteristic [3]. Indeed, if an over-frequency occurs, the BESS must absorb power, and conversely it must deliver power to the grid for under-frequency periods. Hence, when the frequency deviation is within, the power supplied or absorbed is zero. For 50 MHz, the BESS primary power is linearly dependent on the deviation and depends on the sign of the deviation (positive deviation means power must be absorbed by the BESS). At and beyond, the BESS is supplying or absorbing full device rated power. Finally, the BESS energy level varies by adding small energy elements, which are obtained by simply taking the product of the time duration of primary power pulses and their related BESS power for power pulse.
V. BESS OPTIMAL SIZING

1) Case 1. BESS with No Additional Charging: The first operating strategy considered no particular action as the BESS charged and discharged in function of frequency variations only (according to p-f characteristic). Due to the limited efficiency of the device, the BESS progressively discharges itself throughout the time period studied. Hence, it requires over-dimensioning the BESS capacity to allow deep state of charge excursions and diminishes consequently the system profitability. An improved control algorithm was then proposed to solve that problem.


2) Case 2. BESS with Additional Charging: The solution led to the second operating strategy using a small recharge power within the noncritical frequency window. Thus, the BESS device recharges itself when the measured frequency falls within . The downside is an over- excessive discharge in the emergency resistors (system inefficiency) as the BESS is constantly fully recharged. Therefore, when an over-frequency occurs, the BESS dissipates the absorbed energy into the emergency resistors.

Fig. 3 . Simulink functional block diagram of LFC power system simulator.

SIMULATION RESULTS:

In the numerical simulations, for the first iteration, an initial BESS nominal power of 30MWis used. Again, Figs. 6 and 7 show that the importance of recharge power and sell power is Negligible as long as they are greater than 0.5% of . Fig.
8gives the sensitivity analysis results So


for using . Optimal so is at a depth of discharge of -0.0018 .h (99.5% state of charge) and so at -0.0018 .h (88.9%) for an NPV over 20 years of 17.877 Mauro. The reader should note that a depth of discharge (DOD) of 0 represents a SoC of 100%. After the first iteration, a sensitivity analysis is performed on the BESS rated power to find a new optimum, which raises the NVP of the system over 20 years from



17.877with to 18.163 Mauro; with

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The research paper published by IJSER journal is about Frequency Control in an Isolated Power System By Using Optimizing a BESS Technology 5

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(grey curve of Fig. 10). Next, a new sensitivity analysis on the other input variables, namely So and So with NPV of 31.97
Mauro: over 20 years. Thus, after two iterations, the
algorithm converges and the final optimal solution

MODEL 1: WITHOUT BESS:

2.5e6

wref

Pref Pm

for sizing is given with the input variables shown
recharge and sell powers, with the BESS rated

314

Wref2

w

314

Wref1

Constant

1

-C- we

Constant2 Pe0

-C- dw

gate

Terminator


power locked at converges to a new maximum

314

Constant1 Hydraulic Turbine

R1 and Governor

wref dw_5-2 Terminator1

1

The 'Model pre-load function' defined in the

Model Properties automatically sets the sample time Ts to 1/512/60 ~ 32.5e-6 s

in Table I. Furthermore, that increasing the nominal

Wref3

Pref Tr5-2

R2

Terminator2

G1 change in p

-C- wm

1 Constant3

gate

Terminator3

2.5

2.5

20 w

1 -K-

-C-

d_theta Pm

s Gain1 Scope

power of the BESS device lowers the required
minimum BESS capacity significantly. This is so
because the amount of energy required from the device to bring back frequency deviations within the noncritical frequency window is less important Moreover, having a higher nominal power means that the device can recharge faster as the recharge

R3 Constant4 Steam Turbine G2

and Governor

Out1

SOLAR SYSTEM

In1Out1

WIND FARM

Freq

Gain6

10

Constant5

Gain7 Integrator Gain8

Scope1

Sine Wave

Scope2

power is a percentage of the nominal power, which
results in an optimal sizing of 55 MW, 21.3 MWh
BESS device.

Simulation Results:

Applying these dynamic hourly modulations to the
SoC limits gives the BESS response.

TABLE I

SYSTEM PARAMETERS

SIMULINK FUNCTIONAL BLOCK DIAGRAM OF LFC POWER SYSTEM SIMULATOR

SIMULATED GRAPH OF WITHOUT BESS

MODEL 2: WITH BESS:

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314

Wref2

w

314

Wref1

2.5e6

Constant

1

wref

Pref

-C- we

Constant2 Pe0

-C- dw

Pm

gate

Terminator

resistors, and the energy level of the BESS was kept within a narrow bandwidth of a few percents. Thus,

Constant1 Hydraulic Turbine

R1 and Governor

wref dw_5-2

Terminator1

The 'Model pre-load function' defined in the Model Properties automatically sets the sample time Ts to 1/512/60 ~ 32.5e-6 s

the BESS can extend its lifetime (low DoD means

314

Wref3

1

R2

-C-

1 Constant3

Pref Tr5-2 wm gate

Terminator2

G1 change in p

Terminator3

G2

2.5

2.5

w

-K-

-K- Gain1

more cycle life), while being available for other
ancillary services (e.g., multitasking). In fact, the

-C- d_theta Pm

R3 Constant4 Steam Turbine and Governor

Out1

SOLAR SYSTEM

In1Out1

WIND FARM

-C- PL

Gain6

PBESS

BESS

-K-

Gain7

RESS

-K-

Gain8

Chnage in w

-C- PL1

t

Sine Wave

Function

Scope


future of the BESS certainly lies into multitasking, where a single modular and flexible unit can do peak shaving, load leveling, frequency control, load management, and so on. Even if frequency control is not the primary task of a device, it is still economically attractive to assign a certain battery

SIMULINK FUNCTIONAL BLOCK DIAGRAM OF LFC POWER SYSTEM SIMULATOR

Freq


reserve to perform this particular task. Finally, the

SIMULATED GRAPH OF WITH BESS

Scope2

profitability of the system was measured using the NPV over 20 years and a great economic performance was encountered for the owner of the BESS device.
REFERENCES
VI. CONCLUSION
The BESS offers rapid active power compensation, which improves significantly the dynamic stability of an isolated power system with low grid inertia (i.e., great damping effect and recovery potential). This paper showed a general procedure for optimal dimensioning of a BESS device used for frequency regulation in an isolated power system. The optimal solution was found both in optimal sizing of the device and optimal operation using dynamically adjustable state of charge limits. This study also showed how to define dynamically the SoC limits variations and tested them on an isolated power system test bench in Mat lab. Simulation of the final solution did not dissipate energy into the emergency

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AUTHOR BIOGRAPH

V.Rajesh received his B.Tech

(Electrical and electronics engineering) Degree in the year 2007, from VITAM Institute of Technology and management, vizag,

- Affiliated to JNTUH. Currently he is pursuing M.Tech

Degree in GMRIT Engineering College, Rajam, JNTUK.

His Area of interest include power electronics.

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