Combined Sepic and Luo converter for

Electric vehicle to increase the life of battery

Abstract:

With the ever increasing concern on oil prices and energy conservation have paved the way for different

green power technologies such as 1wind power 2 photo voltaic 3gas turbine 4fuel cell .Today by using this power

plug in hybrid electric vehicle provide the most promising solution for fuel consumption and pollution . In general,

batteries, ultra-capacitors (UCs), and fuel cells are widely being proposed for electric vehicles (EVs) and plug-in

hybrid EVs (PHEVs) as an electric power source or an energy storage unit. Typical power electronics circuits in

hybrid vehicles include electric motor drive circuits and DC/DC converter circuits. Conventional converters such as

buck converters, voltage source inverters, bidirectional boost converters, isolated bidirectional DC/DC converters,

multilevel converters, and Z-source inverters provide challenging effect on cost, efficiency, controllability, thermal

management, voltage and current capability, and packaging issues. For which a new choice of combined sepic and

luo converter offer potential improvement to hybrid vehicle system performance, extended controllability and power

capabilities. By providing the proper voltage to the vehicle according to its speed. This paper gives an overview of

the topologies, design, and thermal management, and control of power electronics circuits in hybrid vehicle

application. Finally, this paper summarizes the benefits of the various techniques and suggests the most viable

solutions for on-board power management, more specific to PHEVs with multiple/hybrid ESSs.

Keywords:

DC/DC converter; electric drives, electric vehicles, fuel cell, Energy storage system (ESS), ultra-capacitors,

Equivalent voltage Consumption Minimization (EFCM)

Bibliography notes:

Mr .k.sathiyaraj was born in Neyvelii in 1987.He received his B.E degree from Anna university in 2009 and

currently doing M.E degree (power electronics and drives) in ANNA University of technology , Coimbatoore .His

areas of interest are in the areas of power electronics and drives and electrical machines.

1.Introduction:

Power electronics circuits play an important role in the success of electric, hybrid and fuel cell vehicles . Typical

power electronic circuits used in hybrid electric vehicles (HEV) include rectifiers, inverters and DC/DC converters.

In this paper, we first provide an overview of the topological evolution of power electronics circuits, including buck

converters, bidirectional boost converters, rectifiers and full bridge inverters. Power electronics for hybrid electric

vehicle applications topologies, such as multilevel converters, Z-source inverters and bidirectional isolated

converters, are discussed. Modelling and simulation of power electronics circuits are investigated, including system

level modelling, physics based device modelling, feedback control and stability analysis.

Plug-in Hybrid Electric Vehicles (PHEVs) are the new generation of automobiles that can run not only on

the energy from gasoline but also that from an electric outlet stored in a battery pack. Hence , these vehicles can

significantly reduce the consumption of gasoline by taking advantage of cheaper renewable and non renewable

sources of energies available at the domestic electric outlet. Thus PHEVs can contribute significantly in reducing the

overall green house gas emissions from automobiles. In this paper a simplified power-train of power split PHEV is

modeled. The main objective of the study is to provide proper voltage to the PHEV

To achieve this goal, a converter, has been implemented using the aforementioned simplified model. An

optimization problem is formulated with Equivalent voltage Consumption Minimization (EFCM) as the main

objective function along with some constraints to be satisfied. A critical factor propelling the shift from conventiona l

gasoline/diesel engine vehicles to electric, hybrid and fuel cell vehicles is the revolutionary improvement in

performance, size, and cost of power electronics circuits over the past decade, with parallel improvements in sensors

and microprocessors.

This paper deals with Power electronics based solutions for plug in hybrid vehicle. A Hybrid vehicle is

advantages over other systems in terms of performance, efficiency, emissions and control. Electric cars have long

been regarded as potentially an ideal solution to the problems of air pollution and noise from road traffic. A word

about hybrid vehicle Electric cars go electric, go green today .Potentials of hybrid vehicle some of them are HEVs

have demonstrated significant potential to reduce fuel consumption and exhaust emissions. Advances in battery,

power electronics technologies have made commercialization possible Performance is generally as good as or better

than Convectional cars.

a. About hybrid vehicle

In simple words, the word hybrid refers to anything that has a combination of two different ideas. When a car uses

two different ideas to move, it is called a hybrid car. Usually our cars run on petrol, diesel or gas. But their

inefficiency, led to the invention of electric cars. But, since electric cars also had disadvantages of frequent battery

charging and inefficient long drives, there evolved a combination of both. When gas and electricity were used in the

combined mode, a better solution was made to the inefficiency and mileage. A user of a car always asks for some

minimum requirements while using a car. They are

For long distances, the car must run for at least 450 kilo-meters before re-fuelling.

The drive should be smooth and easy.

The car should maintain a good speed so as to cope up with other cars in traffic.

Easy and fast re-fuelling of cars.

A good mileage.

Less pollution.

Though most of the conventional cars can provide the first four requirements correctly, they are very much

backwards in the case of mileage and pollution. Electric cars, on the other hand can provide a very good mileage and

very less pollution. But, the first four requirements will be let down. A combined use of both electric and gas energy

will clearly find all these requirements satisfactory.

b. Types of hybrid vehicle

i. Mild hybrid vehicle:

In mild hybrid cars, the electrical motor is used only when additional power is needed. The conventional

engine is used to provide most of the power. The electrical motor alone cannot operate the vehicle. Whenever

power is needed the electric motor acts as a side-kick to the conventional engine.

ii. Full hybrid vehicle:

In a full hybrid car, the electrical energy is used while the car needs less power. The gasoline energy is used

when the car needs less power. Thus at lower speeds the battery drives the vehicle and at higher speed the

gasoline drives the vehicle. This technology has been used in cars like Toyota Prius and Ford Escape.

iii. Plug in hybrid vehicle

Most of the hybrid vehicles have rechargeable batteries which can restored to full charge by connecting to

external power source. Those vehicles are said to be plug in hybrid vehicle. Battery charging stations are available to

charge the battery. This is the most used in day to day life to improve efficiency to reduce pollution.

c. Need for converters

• Battery voltage varies with state of charge in it, which would cause motor to vary performance with state of

charge. This would affect motor vehicle performance to vary the speed of vehicle.

• The battery is charged during regenerative braking, Charging of battery during regenerative braking mainly

depends upon speed affects the life of battery due to variable charging.

• To overcome these difficulties to maintain constant voltage converters are employed. Different converters

are employed to at maximum efficiency and to use maximum utilization of battery .

2. Parallel Energy Storage Topologies:

Three configurations of hybrid drive trains exist, namely, series, parallel, and series–parallel configurations. Due to

the varying sizes of the drive trains and the availability of space on the vehicle, parallel and series–parallel hybrid

drive trains are used in smaller passenger vehicles, while the series configuration is deemed suitable for larger

vehicles. A combination of UC and battery results in a hybrid ESS (HESS) .This configuration can be either

passively or actively connected. An actively connected configuration requires power electronic components, which

drive their costs upward. The actively connected HESS regulates the transfer of energy from each component of the

system through a controllable power electronics buffer between the batteries and the UC.

Figure1 Three Way parallel PHEs

The advantage of HESS is that the overall mass of the system can be potentially smaller than that of a

passive configuration for the same load. A parallel connection of battery and UC results in a simple configuration, as

shown in Fig. 1.Control overcharging and discharging of the components is limited in the parallel configuration.

Parallel connected UC and battery have equal voltages across them. A dc/dc converter supplies the power demand of

motor from the HESS, thus maintaining a constant voltage on the bus .

2.1 Thermal management of power electronics

At power levels of 100kW, even with efficiency of 96 to 98%, the power losses of each power electronic unit are 2

to 4kW. With two or three powertrain motors and associated power electronics circuits, as well as a high power

bidirectional DC/DC converter.. Significant advancements in the thermal management of both the power electronics

and motors for the HEV propulsion system must be achieved to meet the automotive industry's goals of reduced

weight, volume and cost The main areas of concern in the thermal management of power electronics are:

operating temperature of converters (which should be less than 125_C)

contact resistance between various layers of a power module

low thermal conductivity thermal paste

heat flux limitations (ideally, faster converters would have to reject heat at a rate of 250 W/cm2)

limitations on the inlet cooling fluid temperature (it is desirable to use the engine coolant at 105_C)

the cost of the cooling system; weight and volume.

The existing cooling technologies are depicted in Figure 14 shows the impact of the conductivity of the thermal

grease on the overall temperature difference between the junction and the heat sink. For a thermal conductivity of

0.5 W/mK, the temperature difference is about 65_C. If the thermal conductivity of the thermal grease is doubled to

1.0W/mK, the maximum temperature difference can be reduced to 35_C.

3. Conventional Boost Converter:

3.1Step-up converter

The boost converter is also called as step- converter.this converter is used to produce higher voltage at the load than

the supply voltage. The convectional circuit diagram shown in the Fig is the boost converter in which it involves

two modes of operation when switch is turned on and when switch is turned off .in this boost circuit the output

voltage will higher than input voltage depend upon duty cycle. The induced voltage across the inductor is negative

The inductor adds to the source voltage to force the inductor current into the load. the output voltage is given as

(1)

Thus for variations of D in the range 0 < D < 1, THE LOAD VOLTAGE will vary in the range

.the schematic in Fig. shows the basic boost converter T his circuit is used when a higher output voltage than

input is required.

3.2 Circuit diagram operation:

A boost converter (step-up converter) is a power converter with an output DC voltage greater than its input DC

voltage. It is a class of switching-mode power supply (SMPS) containing at least two semiconductor switches (a

diode and a transistor) and at least one energy storage element.

Figure2. Step Up Converter

Filters made of capacitors (sometimes in combination with inductors) are normally added to the output of the

converter to reduce output voltage ripple .While the transistors on .For this analysis it is assumed that

inductor current always remain flowing (continuous conduction) .Thus the average voltage must be zero is given as

(2

This can be arranged as

(3)

And for a lossless circuit the power balance ensures

(4)

Since the duty ratio "D" is between 0 and 1 the output voltage must always be higher than the input voltage in

magnitude

4.Combined sepic and luo converter:

4.1 DESCRIPTION

`The combined sepic and luo converter consists of two inductors as inductors are present this reduce the ripple

content. Sepic stands for “single ended primary inductor converter” This circuit has zero current and voltage ripple

It improves the power factor .The input voltage is higher than output voltage where as luo converter is used for

elevation traction purposes. A combined sepic and luo is similar to a traditional buck-boost converter, but has

advantages of having non-inverted output (the output voltage is of the same polarity as the input voltage), the

isolation between its input and output (provided by a capacitor in series), and true shutdown mode: when the switch

is turned off, its output drops to 0 V.

Figure 3. Combined sepic and luo converter

SEPIC is a kind of important topological structure. It means input voltage adds the value of the output

voltage in one that it controls stress clamping of MOSFET voltage, and dispelled EMI in the reverse converter. The

reduced voltage stress allows to use the part of the low-voltage, thus bring more high-efficiency and more low-cost

power. Can simplify shutting rule test of the end product in reducing of EMI. Finally, if configure to much output

power supply, it cross voltage regulation will be superior to the reverse converter

4.2 Block diagram:

4.2.1 DC/DC converter :

Dc to dc converters are used to convert fixed dc to variable dc .Dc to dc converter are used to control the output

voltage and to maintain constant voltage.In this paper we are using combined sepic and luo converter.This is the

buck boost circuit with not inverter output.This is advantages compared to other type of converter .

4.2.2 MOTOR:

The motor what we are using in this hybrid vehicle is dc motor which is easy to operate and run at constant

speed moreover the output from the converter will be dc.

4.2 3 Micro controller:

Micro controller is used to generate triggering pulse for mosfets. It is used to control the outputs. Micro

controller have more advantage compare then analog circuits and micro processor such as fast response, low cost,

small size and etc.

4.2.4 Driver:

It is also called as power amplifier because it is used to amplify the pulse output from micro controller. It

is also called as opto coupler IC. It provides isolation between microcontroller and power circuits.

4.2.5 Regulated Power supply (RPS):

RPS give 5V supply for micro controller and 12V supply for driver. It is converted from AC supply. AC

supply is step down using step down transformer

4.3Advantages Of Sepic And Luo Converter

The combined sepic and luo converter has the relatively good features that follow:

1) The polarities of the input and output voltage are the same from the same ground reference

2) The input current ripple is low due to the existence of large input inductor.

3) A version with a transformer exists so that the galvanic isolation between the input and output side is

possible

4) improves the power factor

5) The output voltage is higher than output voltage

4.4 Operation:

a)Mode 1

A Combined SEPIC and luo converter is said to be in continuous-conduction mode ("continuous mode") if the

current through the inductor L1 never falls to zero. During a SEPIC's steady-state operation, the average voltage

across capacitor C1 (VC1) is equal to the input voltage (Vin). Because capacitor C1 blocks direct current (DC), the

average current across it (IC1) is zero, making inductor L2 the only source of load current. Therefore, the average

current through inductor L2 (IL2) is the same as the average load current and hence independent of the input voltage

Figure 4. When switch s1 is on and s2 is off

VIN = VL1 + VC1 + VL2 (5)

Because the average voltage of VC1 is equal to VIN, VL1 = −VL2. For this reason, the two inductors can be

wound on the same core. Since the voltages are the same in magnitude, their effects of the mutual inductance will be

zero, assuming the polarity of the windings is correct. Also, since the voltages are the same in magnitude, the ripple

currents from the two inductors will be equal in magnitude.The average currents can be summed as follows:

ID1 = IL1 − IL2 (6)

Where as the values of change in time and current is given by

(7)

(8)

(9)

When switch S1 is turned on, current IL1 increases and the current IL2 increases in the negative direction.

(Mathematically, it decreases due to arrow direction.) The energy to increase the current IL1 comes from the input

source. Since S1 is a short while closed, and the instantaneous voltage VC1 is approximately VIN, the voltage VL2 is

approximately −VIN. Therefore, the capacitor C1 supplies the energy to increase the magnitude of the current in IL2

and thus increase the energy stored in L2. The easiest way to visualize this is to consider the bias voltages of the

circuit in a d.c. state, then close S1

b)Mode 2

When switch S1 is turned off, the current IC1 becomes the same as the current IL1, since inductors do not

allow instantaneous changes in current. The current IL2 will continue in the negative direction, in fact it never

reverses direction. It can be seen from the diagram that a negative IL2 will add to the current IL1 to increase the

current delivered to the load.

Using Kirchoff's Current Law, it can be shown that ID1 = IC1 - IL2. It can then be concluded, that while S1 is

off, power is delivered to the load from both L2 and L1. C1, however is being charged by L1 during this off cycle,

and will in turn recharge L2 during the on cycle.

Figure 5.When switch s1 is off and s2 is on

(10)

(11)

(12)

In the steady-state, the average values of the inductor voltages L1 and L2 are equal to zero

(13)

(14)

The capacitor CIN is required to reduce the effects of the parasitic inductance and internal resistance of the power

supply. The boost/buck capabilities of the SEPIC are possible because of capacitor C1 and inductor L2. Inductor L1

and switch S1 create a standard boost converter, which generate a voltage (VS1) that is higher than VIN, whose

magnitude is determined by the duty cycle of the switch S1. Since the average voltage across C1 is VIN, the output

voltage (VO) is VS1 - VIN. If VS1 is less than double VIN, then the output voltage will be less than the input voltage. If

VS1 is greater than double VIN, then the output voltage will be greater than the.

5. Design &Development Of Embedded Controller Based Sepic Converter:

5.1 Design And Calculation Of Sepic And Luo Converter

The design and calculation of combined sepic and luo converter Figure gives equivalent circuit of combined sepic

and luo converter which is used to provide mathematical analysis. SEPIC (Single Ended Primary Inductance

Converter

The combined sepic and luo converter consists of two inductors as inductors are present this reduce the

ripple content. Sepic stands for “single ended primary inductor converter” This circuit has zero current and voltage

ripple It improves the power factor .The input voltage is higher than output voltage where as luo converter is used

for elevation traction purposes. A combined sepic and luo is similar to a traditional buck-boost converter, but has

advantages of having non-inverted output (the output voltage is of the same polarity as the input voltage), the

isolation between its input and output (provided by a capacitor in series), and true shutdown mode: when the switch

is turned off, its output drops to 0 V. SEPIC is a kind of important topological structure. It means input voltage adds

the value of the output voltage in one that it controls stress clamping of MOSFET voltage, and dispelled EMI in the

reverse converter. The reduced voltage stress allows to use the part of the low-voltage, thus bring more high-

efficiency and more low-cost power. Can simplify shutting rule test of the end product in reducing of EMI. Finally,

if configure to much output power supply, it cross voltage regulation will be superior to the reverse converter

5.2 INDUCTOR DESIGN

A good rule for determining the inductance is to allow the peak-to-peak ripple current to be approximately 25% of

the maximum input current at the minimum input voltage

(15)

(16)

(17)

5.3 CAPACITOR DESIGN

When the switch S1 is on the capacitor supplies the load current for and capacitor current during this period .The

peak-to-peak voltage value VC1 to within 25% of the input voltage.

(18)

(19)

In the steady-state power balance is satisfied as:

(20)

(21)

(22)

To limit the peak-to-peak value VO to within 0.25% of the predetermined output voltage is the suitable condition to

get the desired output.

(23)

(24)

(25)

(26)

5.4 Assumptions Made:

The input value and various other parameters of the circuit are given below

Input voltage =24v

Output voltage=58v

Input current =1A

Switching frequency=13khz

6. Modeling and simulation of power electronics circuits:

Modeling and simulation plays an important role in the design and development of power electronics circuits. The

simulation of power electronics circuits in hybrid vehicle applications can be divided into two categories: device

level simulations and system level simulations (Amrhein and Krein, 2005; Filippa et al., 2005; Hak-Geunet al.,

2000; Mi et al., 2005; Onoda and Emadi, 2004.

Figure 6.Simulation Model

7.Simulation Result:

Figure 7 shows the resultant output voltages of the boost converter with each feedback control connected to each

output. The values of output voltage and current are close to that in the specification as seen. The regulation analysis

is done by load variation. Here the voltage is taken along y-axis and time in x-axis.

Figure 7. output voltage of boost converter

Figure 8. Output voltage waveform of sepic in boost mode

The graph above shows the output voltage of combined sepic and luo converter when used in luo mode it acts as

boost circuit. The voltage is taken along y-axis and time in x-axis.

Figure 9. Output voltage waveform of luo in buck mode

This is the output of combined sepic and luo converter when it acts like sepic converter the output voltage will be

less the input voltage it acts like a buck circuit.

The current waveform of combined sepic and luo converter in boost mode of operation .This boost current will be

less than that of the buck mode, since voltage is high in this operation.

The graph below shows the waveform for power of the combined sepic and luo converter .The output power will

be greater than that compared with convectional boost circuit and efficiency will be more in combined sepic and luo

converter .The output of this combined sepic and luo converter will be ripple less due to presence of inductor.

Figure.10 Ouput power of sepic converter

8.Conclusion:

Power elecronics based converter is designed for hybrid vehicle with less space ,cost and weight .which is well

suited for hybrid vehicles because of buck boost operation. The combined sepic and luo converter has the relatively

good features that follow: The polarities of the input and output voltage are the same from the same ground

reference and also supports the battery by sensing even small change in voltage fed in. The input current ripple is

also low due to the existence of large input inductor. A version with a transformer exists so that the galvanic

isolation between the input and output side is possible This combined sepic and luo converter is used to overcome

the problems in the traditional. boost converter. This combined sepic and luo can boost and buck the input voltage

.As buck is also possible it easy to control the hybrid vehicle. The efficiency of this converter is shown by using the

simulated results. The proposed system has the potential to improve the overall performance of hybrid vehicle So

the best suited converter for hybrid vehicles are implemented.

Future scope:

Nowadays hybrid vehicles are changed to pure electric vehicles in that case plug in hybrid vehicle they are battery

can be charged to full charge by connecting to an external s ource.Fuel cell ,usage of ultra capacitor reduces the size

of conveter and also increase the life of battery

Reference:

[1] J. Moreno, M. E. Ortuzar, and J. W. Dixon, “Energy-management system for a hybrid electric vehicle, using

ultracapacitors and neural networks,”IEEE Trans. Ind. Electron., vol. 53, no. 2, pp. 614–623, Apr. 2006.

[2] W. Kempton and S. Letendre, “Electric vehicles as a new power sourcefor electric utilities,” Transportation

Research, Part D (Transport and Environment), vol. 2D, no. 3, pp. 157 – 75, Sept. 1997.

[3] S. Judd and J. Overbye, “An evaluation of PHEV contributions to power system disturbances and economics,”

North American Power Symposium (NAPS), IEEE PES, Sep. 2008.

[4] W. Kempton and J. Tomic, “Vehicle-to-grid power fundamentals calculating capacity and net revenue,” Journal

of Power Sources,vol. 144, no. 1, pp. 268 – 79, Sep. 2005.

[5] S. De Breucker, P. Jacqmaer, K. De Brabandere, J. Driesen, and R. Belmans, “Grid power quality improvements

using grid-coupled hybrid electric vehicles,” 3rd IET International Conference on Power Electronics, Machines and

Drives (PEMD 2006), pp. 505 – 9, Mar.2006.

[6] W. Kempton and J. Tomic, “Vehicle-to-grid power implementation from stabilizing the grid to supporting large-

scale renewable energy,” Journal of Power Sources, vol. 144, no. 1, pp. 280 – 94, Jun. 2005.

[7] E. Hirst and J. Hild, “Integrating large amounts of wind energy with a small electric-power system,” Bellingham,

WA and Xcel Energy, Denver, CO, Tech. Rep., Apr. 2004.

[8] J. Short and P. Denholm, “A preliminary assessment of plug -in hybrid electric vehicles on wind energy

markets,” National Renewable Energy Labratory (NREL), U.S. Department of Energy, washington, DC, Tech.

Rep., Apr. 2006.

[9] N. Jayaram and D. Maksimovic, “Power Factor Correctors Based on Coupled-Inductor SEPIC and CUK

Converters with Nonlinear-Carrier Control”, IEEE APEC98.

[10] S. M. Lukic, S. G. Wirasingha, F. Rodriguez, J. Cao, and A. Emadi,“Power management of an ultra -

capacitor/battery hybrid energy storage system in an HEV,” in Proc. IEEE Vehicle Power Propuls. Conf.,

Sep. 2006.

[11] L. Sanna, “Driving the solution: the plug-in hybrid vehicle,” Electric Power Research Institute (EPRI), 2005.

[12] M. E. Ortuzar, J. Moreno, and J. W. Dixon, “Ultracapacitor-based auxiliary energy system for an electric

vehicle: Implementation and evaluation,” IEEE Trans. Ind. Electron., vol. 54, no. 4, pp. 2147–2156,Aug. 2007.

[13] C. A. Ramos-Paja, C. Bordons, A. Romero, R. Giral, and L. Martinez- Salamero, “Minimum fuel consumption

strategy for PEM fuel cells,” IEEE Trans. Ind. Electron., vol. 56, no. 3, pp. 685–696, Mar. 2009.

[14] A. Lidozzi and L. Solero, “Power balance control of multiple-input DC–DC power converter for hybrid

vehicles,” in Proc. IEEE Int. Symp. Ind. Electron., May 2004, pp. 1467–1472.

[15] H. Matsuo, W. Lin, F. Kurokawa, T. Shigemizu, and N. Watanabe, “Characteristics of the multiple -input DC–

DC converter,” IEEE Trans. Ind. Electron., vol. 51, no. 3, pp. 625–631, Jun. 2004.

[16] A. Di Napoli, F. Crescimbini, S. Rodo, and L. Solero, “Mu ltiple input DC–DC power converter for fuel-cell

powered hybrid vehicles,” in Proc. IEEE Power Electron. Spec. Conf., Jun. 2002, vol. 4, pp. 1685–1690.

[17] M. H. Todorovic, L. Palma, and P. N. Enjeti, “Design of a wide input range DC–DC converter with a robust

power control scheme suitable for fuel cell power conversion,” IEEE Trans. Ind. Electron., vol. 55, no. 3,

pp. 1247–1255, Mar. 2008.