Journal of Chemical and Pharmaceutical Sciences ISSN: 0974-2115

JCHPS Special Issue 8: December 2016 www.jchps.com Page 5

Charging series hybrid electrical vehicle

Traction battery with design of DC/DC converter P. Alageswari*, S. Kirthika

Dept. of EEE, M. Kumarasamy College of Engineering, Karur, Tamil Nadu, India

*Corresponding author: E-Mail: alageswariabi@gmail.com

ABSTRACT

This paper presents the design of DC to DC converter for charging the traction battery of the series hybrid

electrical vehicle. To design a Dc to DC converter for high power applications size, losses and cost of the components

are very important. Considering this factors, a simple interleaved buck converter with fuzzy logic controller is

implemented. Due to lower inductor ripple current and higher step-down conversion ratio, this converter is applicable

for high power applications with high step down convention ratio. The simulink model of the series hybrid electrical

vehicle traction battery of 48v is charged with the input voltage of 60v using the MATLAB/SIMULINK.

KEY WORDS: Interleaved buck converter, fuzzy logic control, traction battery, series hybrid electrical vehicle.

1. INTRODUCTION

With today’s persistently high oil prices, people are spending more money on gasoline than ever. Decreasing

world oil and gas resource as well as environmental concerns have driven automobile industry to develop more

efficient and cleaner vehicles to reduce the fuel consumption and protect the environment. The proposed model of

hybrid vehicle offers a solution to both the challenges of energy and environment. It helps to reduce global warming

and to slash the oil dependency. Our hybrid vehicle employs both an internal combustion engine (ICE) and a switched

reluctance motor to give an optimum efficiency and reliability using the power from the energy storage system (ESS).

The hybrid electrical vehicle can be operated in four modes of operation. It can be solar alone mode of operation,

wind alone mode of operation, combined solar and wind mode of operation, engine mode of operation.

Most of the research work have been taken so far is to design the battery charger for the hybrid electrical

vehicle which consists of AC-DC converter with PFC followed by an isolated DC/DC converter. These architecture

requires soft switching technology to reduce the switching losses. So many charger configuration with soft switching

technologies were introduced. This will increase the cost and losses of the system further for high power applications.

And all the semiconductor devices are suffered at high input voltage. Various charging techniques has been employed

to charge the battery depends upon the battery type. Among these charging techniques constant voltage charging is

simple and reliable. This paper describes the simple converter design used to charge the traction battery of the series

hybrid electrical vehicle during engine mode of operation using constant voltage charging technique. The output of

the converter is controlled through the fuzzy logic control which is very robust and easily upgraded. Compared to

the conventional interleaved buck converter this converter has higher step down conversion ratio with low ripple

current and voltage.

Figure.1. Schematic diagram of series hybrid electrical vehicle

Circuit Description: An interleaved buck operation consists of number of mini-converter cells (or phases) which

are placed in parallel. The power is distributed equally among the converted cells using active phase shifting and this

method removes the current ripples at the output. The effective ripple frequency will be increased and reduces the

requirement of output filter capacitor.

Figure.2. Circuit diagram of interleaved buck converter

Journal of Chemical and Pharmaceutical Sciences ISSN: 0974-2115

JCHPS Special Issue 8: December 2016 www.jchps.com Page 6

This interleaving approach can also significantly reduces the input inductor and capacitor requirements. In

this configuration three active switches are connected in series and two coupling capacitors are employed in the

power path. The switches S1, S2 and S3 are driven with the phase shift angle of 180◦. Each switching period is divided

into six modes. In order to demonstrate the working principle of the proposed IBC, some considerations are made as

follows: The three inductors L1, L2 and L3 are having the same inductance Z. All power semiconducting devices are

ideal. The coupling capacitors C1 and C2 are considered as the voltage source.

2. DESIGN DETAILS

Battery: The charging of a battery depends on two things charging time and battery discharge rate. A voltage source

should be strong enough to move current through a battery. The more current we can push into a battery, the faster

we can charge it. Charging at too high rate however can overheat the battery.

Therefore the battery should be charged with minimum charging voltage and current. The formula to

calculate the charging voltage for the battery is as follows.

Peak power required = [𝑣𝑜𝑙𝑡𝑎𝑔𝑒𝑏𝑎𝑡𝑡(𝑣) ∗ 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦𝑏𝑎𝑡𝑡(𝐴ℎ)]/𝑝𝑜𝑤𝑒𝑟(𝑘𝑤) (1)

Charging voltage = charging V per cells * No. of cells (2)

= 2.30V * 24

Charging voltage = 55V (3)

The maximum charging voltage of the battery is 48V-55V.The charging current will be the 1/10th of the

battery capacity. Here the capacity of the lead acid battery is 150Ah.Therefore maximum safe charging current will

be 15A.

Figure.3. Simulink model of 48v battery

Engine: When the vehicle is operated in engine mode of operation the traction battery is charged through the

interleaved buck converter. Here the engine is designed to rotate the DC alternator at a speed of 1000rpm.The output

of the DC alternator is a battery, the faster we can change it. Charging at too high rate however can over heat the

battery. Given as input to the interleaved buck converter.

Input voltage to the converter (V) = 60v.

Input current to the converter (I) = 25A.

Speed of the DC alternator = 1000rpm.

Figure.4. Simulink model of engine

Control Technique: The Fuzzy control is a non-linear and adaptive control technique and it is most commonly

preferred alternative for a various control applications. It process the data through membership functions rather than

crisp variables. There are four main elements in the fuzzy logic controller system named as Fuzzifier, Rule base,

Inference engine and defuzzifier. Three main steps are followed in fuzzy logic.i. Fuzzification. ii. Inference. iii.

Defuzzification. In this process, at the first step crisp set used as input data or non-fuzzy data, Table 1 shows the

crisp set used in the simulation. After this it is converted to a fuzzy set using fuzzyfier by the help of linguistic

variables, fuzzy linguistic terms and membership functions. The most important thing regarding fuzzy logic is that a

numerical value does not have to be fuzzified using only one membership function. Membership functions vary such

as Triangular, Gaussian, Trapezoidal, Generalized Bell and Sigmonoidal. Rulebase is the backbone of fuzzy logic

controllers. The membership function of triangular is used to create the fuzzy rules. According to the requirement,

there are nine fuzzy rules updated to generate the triggering pulse for the converter based on the output. The input

pulses to the converter are shown in fig.5.

Journal of Chemical and Pharmaceutical Sciences ISSN: 0974-2115

JCHPS Special Issue 8: December 2016 www.jchps.com Page 7

Table.1. Crisp variables

Input 0.3 0.6 0.9

0.3 low Low medium

0.6 low medium High

0.9 medium High high

Figure.5. Input pulses to the converter

3. SIMULATION RESULTS

The simulink model of converter and series hybrid vehicle is simulated with following values. Speed of the

DC alternator=1000RPM, Input current to the converter=25A Input voltage to the converter=60V.

Figure.6. Simulation output of the converter Figure.7. Simulation output of the battery

This shows the state of charge of the battery. Each of the battery cell is charged with minimum cell voltage

of 8V.Thus we obtained the constant 48v voltage through the converter for charging the battery.

4. CONCLUSION

This paper work detailed about charging the traction battery of series hybrid electrical vehicle with safe

charging current and charging voltage without any ripples through the DC/DC converter. The proposed interleaved

buck converter with fuzzy logic control produces the constant voltage output with less ripples and switching losses.

Therefore the series hybrid electrical vehicle traction battery can be charged safely with constant voltage charging

method through the designed converter.

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