Power Management Strategy of a Standalone Hybrid Energy ...acadpubl.eu/jsi/2017-114-7-ICPCIT-2017/articles/12/7.pdf · such as fuel cell or ultra -capacitor will be backup source

Power Management Strategy of a Standalone Hybrid

Energy Power System 1A. Ananthi Christy and

2Vara Rushiraj

1Department of EEE,

SAVITHA University, Chennai. 2Department of EEE,

SRM University, Chennai.

Abstract The objective is to analyze control strategy for proposed hybrid power

system for stand-alone applications. The system includes photovoltaic system

and a proton exchange membrane fuel cell (PEM-FC) with battery storage

system. In the proposed system PV will be taken as a primary source to

supply the load and FC will be backup source. During day time when

sunshine is sufficient PV will feed the load and excess power will be stored in

a battery storage system and when the weather conditions unfavorable say

during cloudy day or night time, FC will come into picture to supply the

load.Hence by integrating these sources we can maintain and control demand

power. A Simulation model is designed for the proposed hybrid energy

system under MATLAB/SIMULINK environment. The control strategy used

in this proposed system is fuzzy logic controller (FLC). The proposed system

is most effective one to be used in remote areas or an island where grid

supply is difficult and costly.

Index Terms:Hybrid power system, photovoltaic system, fuzzy logic

controller, maximum power point tracking.

International Journal of Pure and Applied MathematicsVolume 114 No. 12 2017, 59-69ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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1. Introduction

The demand of renewable energy technology has been increasing day by day for

fulfilling the energy deficiency. Present day challenges such as environmental

pollution, energy crises, climate change, global warming etc. can be reduced by

appropriate use of renewable energy sources. Renewable sources like solar,

wind and fuel cells are significant sources to overcome mentioned problems.

Solar system is one of the most remarkable source due to advantages such as no

moving parts, no emission or harmful gases, compact design, minimal

maintenance etc. However there are some disadvantages that makes solar

system inefficient like it is not available during night time or cloudy atmosphere

so the output will vary and it will decrease efficiency and reliability of the

system. Hence single renewable source might be unable to feed the power all

the time due to the intermittent nature of renewable sources. The possible

solution to this problem is that we can integrate two or more RES to meet the

demand. It will improve availability of power all the times therefore system will

become more efficient and reliable. Such system will be known as hybrid power

system in which solar system will be taken as a primary source and other source

such as fuel cell or ultra-capacitor will be backup source whenever solar is not

sufficient. Battery can also be used for storage purpose to store excess power

and feed the power difference. Fuel cell can be taken as a backup source. This

combination is the most effective one. The proton exchange membrane fuel cell

has advantages such as low working temperature, compactness, excellent load

following capability etc. Due to the slow response of FC we will connect battery

so it can improve dynamic characteristics of the hybrid power system. This

hybrid power is controlled by fuzzy logic controller in which membership

function and fuzzy rules are developed. The application of the hybrid power

system is for stand-alone residential purpose such as some remote location or

island where grid power is not available. Hence by integrating these sources we

can feed uninterruptable power supply. The system is developed using Mat-

lab/Simulink environment.

2. System Description

The proposed block diagram of hybrid power system is shown in the figure

1.The system consists of PV system with maximum power point tracking

(MPPT), FC system and battery system for storage purpose at the source side.

Incremental conductance(IC) algorithm is used for maximum power tracking of

PV system. Here fuel cell is used as a backup source and PV system will work

as a primary source. There are some advantages of PEM (Proton exchange

membrane) fuel cell type over others like low working temperature, fast

dynamic response, compactness etc... If PV system fails FC or Battery will

supply the power. Battery is used whenever both the sources are insufficient to

feed the power. Fuzzy logic controller is used to supply uninterruptable power

supply. cuk converter is used for step up the generated

International Journal of Pure and Applied Mathematics Special Issue

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Voltage and the output is given to the load via inverter for -Sinusoidal voltage

waveform. Neutral point clamp inverter is used for generation of multilevel

output voltage waveform. The system is designed for standalone applications

where grid power is not available and costly such as remote area or island.

Fig. 1: Block diagram

3. System Modeling

A. PV System Modeling with MPPT Technique

The figure 1 shows one diode equivalent circuit model of PV cell. The model

contains one current source Iph, one diode, series resistance Rs and parallel

resistance Rsh.

Fig. 2: One diode model of PV cell

Where, Iph is the total current produced by the cell for a given irradiance and

temperature conditions in Amperes, Id is the diode current and V is load

voltage. PV systems have nonlinear characteristics which will vary the power

output. Hence it is necessary to get the maximum power which will be tracked

by MPPT technique. Such a point is highly dependent on temperature and

irradiance of the cell which will be varying throughout the day time. Here PV


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system rating is 1.1 kW with 250 series connected cells and 25°c temperature,

short circuit current, Isc=7.34 A, open circuit voltage, Voc=0.6v.

Table 1: PV system parameters

Parameters Value

Type Series connected Solar cells

Power rating 1.1 kW

Voltage 150 volt

Number of cells 250

The incremental conductance method has been developed to overcome the

drawbacks of previous method P&O. In incremental conductance method the

conductance value is compared with the incremental conductance value and

according to power curve duty ratio is increased when slope of power curve is

positive and duty ratio is decreased when slope of power curve is negative [2].

Hence this method is more complex and advanced version of P&O technique

which has drawbacks such as oscillations in MPP. The method will calculate

conductance value and flowchart is shown in figure 3 below.

Fig. 3: Flowchart of IC MPPT technique

B. Fuel Cell System Modeling

Fuel cells are electrochemical devices in which chemical energy is converted

into electrical energy. Proton Exchange membrane fuel-cell (PEMFC) is reliable

when supply is intermittent and is commercially available at large industrial

scale capacities [2]. Dynamic response of PEMFC is fast with 1-3s time of

power release.


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Operating regions of fuel cell are activation polarization, ohmic polarization,

and concentration polarization. The activation polarization can be considered as

the no load region where there is a large voltage drop for a small increase in the

output current [2].

Generally single fuel cell output voltage is low therefore group of fuel cells are

connected in series to get the high DC voltage.

Table 2: Fuel cell system parameters

Parameters Value

Type PEMFC(Proton exchange membrane fuel cell)

Power rating 1.26 kW

Voltage 24v DC

Number of cells 42

C. Battery System Modeling

Battery is a device which is used as a storage purpose and it will store energy in

electrochemical form.it has wide range of applications such as hybrid electric

vehicle and hybrid power system.in this paper the battery is integrated to PV

and FC system to develop hybrid power system.

Nickel metal hydride battery is used with a nominal voltage of 18v and initial

SOC (state of charge) 100%.

4. Power Management Strategy Using FLC

Fuzzy logic incorporates a rule-base structure in attempting to make decisions.

Fuzzy logic is an aggregation of rules, based on the input state variables

condition with a corresponding desired output. [4] In this paper the controller is

implemented in such a way that it will control the three sources to feed

uninterruptable power supply.

The controller has one reference input and one output. This fuzzy logic

controller is implemented using membership functions and 18 if…then fuzzy

rules. Error signal generated from the difference of load power and source

power is taken as input.

PV will work for first 0 to 0.04s with irradiance as 1000 w/m2 after that FC will

switch on for 0.04 to 0.07 when irradiance is 600 w/m2.lastly battery will supply

power of difference for 0.0.7 to 1s when PV and FC both are insufficient to feed

the load.

Table 3: Switching of sources

Time 0 to 0.04s 0.04 to 0.07s 0.07 to 0.1s

PV 1000 w/m2 600 w/m

2 zero

FC Off Off On

BATTERY Charge Discharge Discharge

LOAD 1405 w (1405+100)=1505w


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5. Simulation Results and Analysis

Fig. 4: Simulation diagram of PV system with IC MPPT technique

Fig. 5: Output waveforms of Irradiance, current, voltage and power respectively of PV

system

Fig. 6: Simulation diagram of hybrid PV/FC/Battery power system


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Fig. 7: Cuk converter input power

Fig. 8: Cuk converter output voltage and current

Fig. 9: Multilevel inverter three phase output voltage waveform without filter


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Fig. 10: multilevel inverter three phase output voltage waveform with filter

Figure 4 shows simulation diagram of PV system MPPT applied. Dynamic

response of the system is analyzed by step changes in irradiance and to check

how controller is worked. Irradiance changes at 1000 w/m2 to 800 w/m2 for T=

0.4 to 0.7s and it becomes zero for T= 0.7 to 1s.output waveforms of current

voltage and power are changes according to irradiance changes as shown in

figure 5.

Figure 6 shows complete simulation diagram of hybrid power system in which

PV, FC and battery are integrated. Here Incremental conductance MPPT

technique is used for maximum power generation. Outputs of these three

sources are given to cuk converter for step up the voltage. Neutral point clamp

inverter is used for sine wave generation. This system is suitable for stand-alone

applications so here load is taken is RL load and one additional load is taken for

specific period of time testing how system will work.

Figure 7 shows cuk converter input power which is being almost constant

around 1000w throughout with respect to time. There is a spike in the waveform

which shows switching of the sources at time T= 0.04s and T= 0.07s. Hence we

can say that uninterruptable power supply is maintained at the source side by

using controller.

Multilevel inverter output waveform without filter and with filter are shown in

figure 9 and figure 10.Here three phase voltages are shown with proper sine

wave voltage coming around 450volts which is appropriate for residential

applications.


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6. Conclusion

A hybrid power system consisting of PV system and FC system with battery as

a storage purpose is used. The proposed system is most effective for stand-alone

applications such as island or some remote areas where grid power is not

available. MPPT technique is used to track the maximum power from PV.

Fuzzy logic controller is implemented for management of power. The system

draws maximum power when sun-light is available and FC will supply power

during night time or when PV is switched off. Battery will be used to store the

excess power and feed power when both PV and FC are insufficient to supply

demand. It is seen that by integration of different sources uninterruptable power

supply can be feed.

References

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[4] Muhammad H. Rashid, The Fuzzy Logic Concept, Power electronics handbook.

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[8] Varuna S.K., Review of Augmentation of Energy Needs Using Renewable Energy Sources in India, Renewable and Sustainable Energy Reviews 11 (2007), 1607–1615.

[9] Pawan Kumar, Ankit Gupta, Rupendra Kumar Pachauri, Yogesh K. Chauhan, Utilization of Energy Sources in Hybrid PV/FC Power Assisted Water Pumping System, IEEE International Conference on Computational Intelligence & Communication Technology (2015).

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Power Management Strategy of a Standalone Hybrid Energy ...acadpubl.eu/jsi/2017-114-7-ICPCIT-2017/articles/12/7.pdf · such as fuel cell or ultra -capacitor will be backup source