fuzzy logic control and coordination of battery energy ... · connected to ac/dc converter. the...

Fuzzy Logic Control and Coordination of Battery

Energy Storage System with Standalone Wind Powered DC

Micro Grid

M.Suresh1, B.Viswanath2, Ajit Kumar

Mohanty3.

1,2,3Vignan’s Institute of Information

Technology, Duvvada [email protected]

[email protected] [email protected]

May17,2017

Abstract

This paper proposes a Fuzzy Logic Controlled Battery

Energy Storage System (BESS) for standalone wind

powered DC Microgrid and coordination between them

to meet the load. Due to the depletion of conventional

energy resources and increased environmental

pollution, there is a need for harnessing green energy

to meet the ever increasing load demand. Some of them

are wind, solar, geothermal, biomass, tidal, etc. The

standalone wind powered DC microgrid consists ofa

wind turbine generator with battery back-up connected

to the load.As the wind speed is not constant.Wind

generator outputpower and voltage are always varying.

To get regulated voltage, wind energy system is

connected to AC/DC converter. The voltage available

from AC/DC converter is low and unregulated. Hence a

DC/DC boost converter is used to boost and regulate

the voltage at point of common coupling. A Fuzzy Logic

Controller is used to make comparison between

International Journal of Pure and Applied MathematicsVolume 114 No. 8 2017, 167-177ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

167

varying load of DC Microgrid system and available

energy from wind systemSimulation study is carried

out by using MATLAB/SIMULINK software. Results

show that Fuzzy Logic Controller effectively controls

the charging and discharging of BESS output power in

co-ordination with wind energy system as per load

demand.

Key Words: DC Microgrid, Fuzzy Logic Controller,

Battery Energy Storage System, BESS DC/DC Bi-

Directional Converter, AC/DC Converter, Interior

Permanent Magnet Synchronous(IPMS) Generator,

Wind Energy System (WES).

1 Introduction

Renewable energy is non- polluting clean energy from natural

resources like wind, tides, geo thermal heat and sun light etc. As

such, it has no limit. The renewability of these energies can be

replenished by natural actions. The current situation of globe

demands the increasing use of renewable energy to meet the energy

demand. To reduce pollution and to meet ever increasing demand it

is the only way. The combustion of fossil fuel based non renewable

energy sources fossil fuel is polluting environment which contributes

to global warming. The increasing usage of renewable energy

sources controls global warming as well as global energy crisis In

renewable energy sources solar is dominating one, but it more

expensive than wind energy system of same size [1]. DC Micro grid

systems are more popular and they have shown advantages in terms

of cost and efficiency compared to AC Micro grids by eliminating

power conversion stages for grid integration [2]. Wind energy system

and energy storage systems offer environmental friendly solution,

but having challenges of appropriate control and coordination

between different components of the system [1]-[3]. Due to the

variable nature of wind, it is difficult to match instantaneous load

demand with instantaneous power extracted from wind. To

overcome this difficulty energy storage systems are important for

continuous operation and reliability of the system[5]-[11]. Energy

storage systems offer good transient stability for sudden load

variation ns [5]-[7]. The Fuzzy Logic Control controller has more

advantages than conventional controllers i.e. cost effective robust

control, and offers good transient stability by reducing oscillations

[3].

International Journal of Pure and Applied Mathematics Special Issue

168

2 Proposed Microgrid System

The proposed standalone DC Microgrid system consists of wind

energy system in conjunction with fuzzy controlled battery

energy storage system and DC load, as shown in Fig.1. The

principle of operation of a wind energy system is characterized

by two key transfer steps. In the first step, the wind turbine

extracts kinetic energy from the wind and it is converted to

mechanical torque in the shaft which is connected to

generator. In the second step, i.e. involves the generation

system which converts mechanical torque into electrical

energy. The generation system, which gives an AC output

power and voltage which depend on the available base wind

speed. The AC power output from wind energy system is

converted to DC power by using AC/DC converter. The output

voltage from AC/DC converter is not at required level for load

3 Modeling of Proposed Microgrid System

LA. Modeling of Wind Energy System (Wes)

The Wind Energy System is having two major parts: 1.Wind

Turbine coupled with 2. Interior Permanent Synchronous

Generator(IPSG). The modeling of both parts is discussed

below[1].

1. Modeling of Wind Turbine

The total power extracted by wind turbine from the available

2. Modeling of IPMS Generator

The Fig.2 represents d- and q-axes circuits of IPMS generator.

The following equations are used for modeling the IPMS

generator.

)1(),(35.0 P

CAvPw


169

The output power of the IPMS Generator can be expressed as

follows

corecuWout PPPP )11(

c

qdfdd

qdsgoutR

iLiLiiRTP

222

22 )(

)12(

The power output from the IPMS Generator is given to the

AC/DC converter which steps up output voltage as per load

ratings. The power from wind energy system is constant at

constant voltage.

B. Modeling of Battery Energy Storage System (Bess)

In this proposed system, BESS has lead acid type battery

which is used as back up to the wind energy system. The BESS

has to supply load on DC Microgrid whenever the load becomes

more than wind power output. The controlling of BESS power

is achieved by Fuzzy Logic Controller. Output of BESS is given

to the Bi-Directional DC/DC converter to regulate voltage on

either side of Microgrid system to make power to flow from

BESS to DC-link and vice versa.

C. Modeling of Bi-Directional DC/DC Converter

Fig.3. represents Bi-Directional DC/DC converter, which

allows power in both ways from BESS to DC link and vice

versa. MOSFET has been used in this converter and the firing

pulses come from Fuzzy Logic Controller to achieve desired

control action [2].

4 Modeling of Fuzzy Logic Controller The Fuzzy Logic Controller has two input parameters and one

output parameter. It compares the output power from wind

energy system and power demanded by the load. The input

parameters to the Fuzzy Logic Controller are change in State-

of-Charge )( SoC and Change in Power )( P . The output

parameter from the Fuzzy Logic Controller is Direction Index

of Current of BESS )(DIC . SoC is the difference between the

state of charge at present (S0CNEW )and state of charge

commanded based on (S0CNEW ) the load power. P is difference

between the power demanded by load PL and power generated

by wind turbine PW. The input parameters of Fuzzy Logic

Controller )( SoC and )( P are given as follows

)13(nowSoCref

SoCSoC

)14(LPwind

PP

)7()(

)6()(

0

0

fddqqsqq

qqddsdd

iLidt

dLRiv

iLidt

dLRiv


170

Input Variable-1 (Change-in. State-of –Charge SoC )

(15)7...2,1 iwhereSoCSoCSoC iii

Fig.6. Membership Function of SoC

Fig. 7. Membership Function of P The above membership functions contain seven grades which

are PL (Positive Large), PM (Positive medium), PS (Positive

Small), EZ (Zero), NS (Negative Small), NM (Negative

Medium) and NL (Negative Large).

Rules inferred in the fuzzy inference

system are given by:

The output triangular membership function can

be defined as follows:

)17(

5.01.0max

5.01.0max

veDICtheveisPifw

SoCP

veDICtheveisPifw

PSoC

DICc

The above Eqn.17 represents membership function of output.

There two conditions are in the above equation

Condition-1

veDIC Means that SOC is positive, i.e. the power flows

from DC-link to BESS the battery is in charging mode. Under

this charging mode of BESS, the Direction of Current is

assumed to be Negative

Condition-2


171

veDIC Means that is SOC negative, that is the power flows

from BESS to Dc-link and its current direction assumed as

positive. The battery is in discharging mode.

5. Matlab/Simulation Results and Analysis:

Fig.9. Regulated Wind Energy System Voltage.

The working voltage of load is at 200V as shown in the fig.7.

Wind energy system backup with battery. The battery is

connected to DC-link through Bi-Directional DC/DC converter

to get regulated output voltage from battery as per load

requirements. Fig.8 shows the output voltage DC/DC converter

across DC-link.

Fig.10. Voltage across Load Terminals

Mode 1: In this mode of operation the power supplied by wind

energy system is more than the load. In Fig.6 & Fig.9 shows

power supplied by wind and variation of load respectively. The

wind supplies 1kW of constant power. In Fig.9 the load

demand below 0.2 sec is less than wind power. During this

time the BESS is in charging mode. The power flows from DC-

link to BESS which is negative assumed as negative direction.

Fig.10 & Fig.11show power output and current supplied by

BESS.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

100

200

300

400

Time

Vola

tge in V

olts

WES Output Voltage

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

100

200

300

400

Time

Vola

tge in V

olts

Load Voltage


172

Fig.12. Load Demand

Fig.13. Power Delivered by BESS

Fig.15. State of Charge of BESS

Mode 2: In this mode the power supplied by the wind energy

system is less than the load demand. The power from Wind

Energy System is only 1kW and the load demands around

2kW. At this time the battery is in discharging mode. The

power flows from BESS to DC-link to meet the load. After 0.2

sec the BESS current and battery power direction was

reversed as shown in Fig.12. The sum of power from Wind

Energy System and power from BESS is exactly equal to load

demand at all instants of time. The state of charge of the

battery is in charging mode before 0.2 sec and discharging

after 0.2 sec as shown in Fig.12

Mode3: In this mode of operation the power from Wind Energy

System is exactly equal to load demand as show in Fig. 13 and

0 0.1 0.2 0.3 0.40

1000

2000

3000

Time

Pow

er

in W

att

s

Load Demand

mode 2mode 1

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

Time

Pow

er in

wat

ts

Power Delivery by BESS

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.439.9999

39.9999

40

40.0001

40.0001

40.0001

40.0002

Time

State of Charge of BESS

Discharging mode

charging mode


173

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4-5000

-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

Time

Pow

er in

Wat

ts

BESS in Floating Condition

Fig.14. During this time the BESS is neither charging nor

discharging i.e. BESS is in floating state as show in Fig. 15.

Fig 16 shows constant State of Charge of BESS in Mode 3

operation.

Fig.17. Load Demand(Mode 3)

Fig.18. BESS is in Floating condition

(Mode 3)

Fig.19. State of Charge of BESS (Mode 3)

Mode 4:In this mode of operation, the load demand is zero. The

Wind Energy System is supplying 1kW power. Since the load

demand is zero, the entire power from Wind Energy System is

used for charging of BESS as shown in Fig. 16, Fig. 17 and Fig.

18. The state of Charge of BESS is in charging as shown in

Fig. 19.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

500

1000

1500

2000

2500

3000

3500

4000

Time

Pow

er

in W

att

s

Load Demand

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.440

40

40

40

40

40

40

40

40

Time

State of Charge of BESS


174

5 Conclusions: This paper proposes an effective control and coordination

of wind energy system and BESS in DC Microgrid

system. The effective control charging/discharging of

BESS through a Bi-Directional converter isachieved by

using Fuzzy Logic Controller under different loading

conditions.The simulation results have shown that

effective performance of Fuzzy Logic Controller during

the wind power zero and load zero conditions. The

advantage of Fuzzy Logic Controller is that; It prevents

system Blackout in the event of low wind conditions

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