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EE5001: Independent Study Module [1] Bidirectional DC-DC Converter Topology for low power application This paper is submitted to IEEE BY Manu Jain, M. Daniele, and Praveen K.Jain. The proposed topology is based on a half bridge on the primary side and a current fed push-pull on the secondary side of a high frequency isolation transformer. Usually, conventional schemes have two transformers for Bi directional power flow for charging and discharging. But their proposed topology uses only one transformer for battery charging and discharging. They have utilized the Bidirectional Power transfer property of MOSFET in this case. The basic power topology proposed in this paper is shown in fig.2 Fig: 1 Proposed Bidirectional DC-DC converter The converter’s Buck and Boost mode of operation were shown below along with the components used in the experimental set up along 1

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EE5001: Independent Study Module

[1] Bidirectional DC-DC Converter Topology for low power application

This paper is submitted to IEEE BY Manu Jain, M. Daniele, and Praveen K.Jain. The proposed

topology is based on a half bridge on the primary side and a current fed push-pull on the

secondary side of a high frequency isolation transformer. Usually, conventional schemes have

two transformers for Bi directional power flow for charging and discharging. But their proposed

topology uses only one transformer for battery charging and discharging. They have utilized the

Bidirectional Power transfer property of MOSFET in this case. The basic power topology

proposed in this paper is shown in fig.2

Fig: 1 Proposed Bidirectional DC-DC converter

The converter’s Buck and Boost mode of operation were shown below along with the

components used in the experimental set up along with their ratings. This proposed topology has

overcome the difficulties of increasing the component rating, circuit complexity, conduction

losses in resonant mode implementation, high output current ripple and loss of soft switching at

light loads for soft switched circuits. The operation and control principle for the converter is

explained in this paper. Steady state analysis and small signal analysis for this proposed topology

is done and the results were found to be satisfactory. The nominal voltage of the battery is 48V.

An efficiency of 86% is achieved during battery charging mode and 90% is achieved when

battery provides load power. The design formula for the proposed converter is also included.

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Fig: 2 Forward Charging Mode where Vs=300-400V, Vbattery =48V.

The components values which are used in the experimental set up and shown in the below

table:

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Fig: 3 Current Fed/Back up Mode where Vbattery =48V and Vs=300-400V,

The operating frequency of the switch is taken as 100Khz. Soft switching technique has been

ignored in this paper for the reason of cost of equipment and number of parts. But for a

frequency of 100 KHz, the switching losses will be high and implementation of soft switching

technique will reduce the switching loss.

[2] Optimization of a Bi-Directional Hybrid Current–Fed-Voltage-Fed Converter Link

This paper is submitted to IEEE by Dipten Maiti, Nikhil Mondal and Sujit K. Biswas. In this

paper, they have presented an optimized design methodology for an isolated bidirectional hybrid

full-bridge converter. The topology used by them operates as a current-fed isolated Converter

when feeding power from the battery and as a voltage-fed isolated converter when feeding power

from the rectified dc bus to the battery with controlled charging. The proposed converter is

shown below:

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Fig: 2 Bi-Directional voltage and current fed converter

The converter is designed with the following specifications:

Voltage range: 600-800V

Battery Charging Voltage, V02, out: 125 V DC

Battery Discharging Voltage Range, V02, in: 95-125 V DC

Output Voltage in current-fed operation: 700 V DC

Maximum output Power, (Charging/voltage-fed mode), Po, v : 8.5 kW

Maximum Output Power, (Discharging or Current-fed mode), Po, c : 8 kW

Switching frequency, fs : 8 kHz

Fig: 3 Voltage fed mode of operation

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Fig: 4 Current fed mode of operation

Voltage spikes are created by the transformer leakage inductance which must be minimized. The

complete design procedure for the optimization of the converter is explained in this paper. The

design values were verified using MATLAB and the results were found to be satisfactory.

[3] High-efficiency Bidirectional Soft Switching DC-DC Converter

This paper is proposed by Jun-Gu Kim*, Seung-Won Park*, Young-Ho Kim*, Yong-Chae

Jung**, and Chung-Yuen Won*. The size of the bidirectional converter can be reduced by

increasing the switching frequency. As the switching frequency increases, the size reduces. But

the switching losses increases. In this paper, an auxiliary circuit is implemented by using soft

switching method in order to overcome this drawback. The switch of the auxiliary circuit,

however, is operated as hard switching. With the help of resonant circuit, the proposed converter

can achieve zero voltage switching condition. All theoretical analysis were discussed in detail.

The circuit configuration of the proposed converter and its design specifications are shown

below

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Fig:5 Circuit of proposed converter

Compared to the half-bridge topology, it has a resonant inductor, two resonant capacitors and

two parallel capacitors additionally to avoid current ripple. In addition, a resonant technique is

used to avoid the current ripple. Both buck and boost modes of operation along with design

equations are explained in this paper. The circuit is experimented by a hardware set up. It can be

found that the proposed converter efficiency in boost mode is 97.6% and 97.48% for buck mode

of operation. The only disadvantage is the resonant technique and the auxiliary circuit to assist

switches for soft switching are complex.

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[4] Intelligent Technique for Improved transient and dynamic response of Bidirectional Dc-Dc converter

This paper is proposed by Narasimharaju B. L, , Satya Prakash Dubey, and S. P. Singh. In this

paper, they have designed an intelligent technique (Fuzzy Logic Control) to improve the

transient and dynamic response of the system. They have also incorporated the PI control

technique to the converter. Comparison of results between the two techniques is made and it has

been proved by simulation results that the intelligent technique followed gives satisfactory

results and can be applied to any Bi-Directional DC-DC converter.

Fig: 6 Bi-directional dc-dc converters proposed in this paper.

Fig: 7 Fuzzy Logic Control system for Bi-Directional Converter System

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The design equations of the Conventional PI controller and the Fuzzy Logic membership

function tables are explained in this paper. All the circuits are simulated using MATLAB and it

is found that the Fuzzy logic controller shows improved dynamic and transient performances for

wide range of load variation.

[5] Analysis and design of a high efficiency Bidirectional DC-DC Converter for a battery and ultra capacitor applications

This paper is proposed by A. Mirzaei*, A. Jusoh*, Z. Salam*, E. Adib**, H. Farzanehfard. In this paper,

they have proposed a converter topology which handles the charging and discharging of ultra capacitor

and battery. All semiconductor devices in the proposed converter are almost soft switched while

the control circuit remains PWM. The converters contain an auxiliary circuit and an auxiliary

switch which provides the instance for soft switching. The control circuit has fast dynamic

response. So, the energy conversion through the converter is highly efficient. Both buck and

boost modes of operation are explained with design equations. They have simulated the circuit

using PSPICE and found the efficiency of converter to be 95%.

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Fig 8 Proposed Bi-Directional Converter Design

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All the modes of operation of the converter is described. But the efficiency of the converter is

found to be decreasing for light loads due to the fact that the circulating current energy involved

in the resonant process is constant and independent of the load.

[6] A carrier Modulation Method for Minimizing the DC Link Capacitor Current Ripple of The HEV DC- DC Converter and Inverter Systems

This paper is proposed by Xi Lu, Wei Qian, Dong Cao , Fang Zheng Peng and Jianfeng Liu. In

this Paper, they have proposed a new carrier modulation method to reduce the current ripple

going through the DC link capacitor. In this paper, a carrier modulation method for the dc-dc

converter, which connects the battery or any energy storage system to the dc link is proposed, in

order to match the converter output current with the inverter input current so as to minimize the

current ripple going through the dc link capacitor. Compared with the conventional triangle

carrier, the proposed carrier is able to shift the converter output current pulses left and right, so

they match with the inverter input current, and finally minimize the current ripple flowing

through the dc link capacitor at unity power factor by a simple and easy implementation without

complex closed loop control. The new proposed model not only reduces the ripple current but

also easy to implement. Actually two new carrier modulation methods has been proposed and

conclusion has been made with a method which is easy to implement. All the design equations

has been mentioned for reference purpose. The design values are given below:

DC Link voltage =300V.

Inverter Switching Frequency =10.8 KHz

Equivalent DC-DC Converter Switching Frequency =21.6 KHz.

Fundamental Frequency = 60 Hz.

Power Factor =0.884

Inductor = 3.5Mh

Resistor = 2.5Ω

Modulation Index of SPWM =0.92

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Fig 9 Proposed DC-DC Converter with inverter

Simulation results were found to be satisfactory. It has been found that almost 17-20% reduction

in current ripple has been achieved compared to their base paper.

[7] A Frequency Controlled Bi-directional Synchronous Rectifier Converter For HEV Using Super-capacitor

In this paper, a control method of a bi-directional zero-voltage-switching (ZVS) DC-DC

converter for HEV power system is presented. By controlling the minimum and maximum values

of the inductor current, the ZVS condition is achieved. Also employing the variable frequency

control with respect to the variation of the DC-link current and the super-capacitor voltage, the

circulating energy loss at the light load condition is minimized. A 1.25kW experimental

hardware prototype module is built to verity the efficiency improvement, especially at the light

load condition. It shows about 34% efficiency improvement compared to the fixed frequency

control at the light load condition.

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Fig 10 HEV System using Super capacitor

Proposed Control design:

The main function of the control is to regulate the DC- link capacitor voltage for both the

charging and discharging mode by controlling the duty cycle of the boost switch. Two modes of

operation were discussed in this paper. Comparing to fixed frequency control, the variable

frequency control has good efficiency.

Fig:11 Proposed Control scheme

The battery has been replaced by a super capacitor since it has longer life cycle and higher power

density. An adaptive control scheme is provided for wide variation of load. The variable

frequency control minimizes the variation in DC Link current, super capacitor voltage and also

the circulating energy loss at light loads.

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[8] A New High Efficiency ZVZCS Bidirectional DC/DC Converter for 42V Power System of HEVs

A new high efficiency zero-voltage and zero- current switching (ZVZCS) bidirectional DC/DC

converter is proposed in this paper. The proposed converter consists of two half-bridge cells as

the input and output stages, symmetrically. MOSFETs of input stage are turned-on in ZVS

condition, and those of output stage are turned-off in ZCS condition. In addition, MOSFETs of

input and output stages have low voltage stresses clamped to input and output voltage,

respectively. Therefore, the proposed converter has high efficiency and high power density. The

operational principles are analyzed and the advantages of the proposed converter are described.

The 300W prototype of the proposed converter is implemented for 42V hybrid electric vehicle

(HEV) application in order to verify the operational principles and advantages.The conventional

DC-DC converter has the disadvantages of current and voltage stresses on the active components

and also increases the count of the passive components. Also the efficiency of the converter is

reduced by hard switching of active components. To overcome the disadvantages in the

conventional DC-DC converter, a new high efficiency Zero voltage zero current switching

Bidirectional DC-DC converter is proposed in this paper and is shown below. The design

specifications are as follows:

Vs=42v; Fs=1KHZ

Lf=Lb=0.39µH; C1=C2=1nF; Cf = Cb=220µF;

Fig: 12 Proposed DC-DC Converter design

The operation modes of the converter are described in this paper. A 300w prototype for 42 V

power system of HEV is implemented and the results are confirmed and same as the simulation

results. The main advantage of the proposed model is the ZVZCS of the MOSFET’’s which

reduces the switching loss and also reduces the number of heat sinks for the MOSFET’s. The

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voltage stresses are reduced in this case. Thus the proposed converter has less switching and

conduction losses.

[9] A New Resonant Active Clamping Technique for Bi-directional Converters in HEVs

In this paper a resonant active clamp circuit is presented, addressing the efficient optimization of

a bidirectional DC\DC converter for hybrid electric vehicles applications. The converter structure

is based on a combination of two dc/dc topologies connected through a high frequency

transformer, a full-bridge stage modulated in phase shift for step-down operations and a current-

source push-pull stage used as step-up. The disadvantage in this topology is the voltage spikes

which occur on switched of the push-pull during the turn off making the efficiency of the

converter to go down. In order to overcome this problem, a resonant clamp circuit based on

bipolar transistors and self-commuted driver circuitry with self commutating drivers has been

developed and connected on the low voltage side which reduces the overvoltage across the

device to an acceptable value.

Fig 13 Proposed Bi-Directional DC-DC Converter

The control strategy is based on two separate algorithms and is used to protect the power stages

against overload protection.

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Fig: 14 Proposed control scheme

The design of the converter with appropriate equations have been specified and a 1.5KW lab

prototype has been designed and tested to verify the power flow control schemes and its

performance has been evaluated. The disadvantage in this converter is 3% of the overall

efficiency has been lost on the magnetic which gives way for a better design of the converter.

[10] Advanced Integrated Bidirectional AC/DC and DC/DC Converter for

Plug-In Hybrid Electric Vehicles

In this paper, a novel integrated bidirectional ac/dc charger and dc/dc converter (henceforth, the

integrated converter) for PHEVs and hybrid/plug-in-hybrid conversions is proposed. The

integrated converter is able to function as an ac/dc battery charger and to transfer electrical

energy between the battery pack and the high-voltage bus of the electric traction system. It is

shown that the integrated converter has a reduced number of high-current inductors and current

transducers and has provided fault-current tolerance in PHEV conversion.

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Fig 15 Proposed Integrated converter with controller

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A comparison of the proposed and a conventional converter based on battery voltage range, fault

current tolerance, voltage polarity and number of switches and diodes, current transformers and

high current inductors have been presented and tabulated in this paper. Through simulation and

experimental prototype, the functionalities of the operating modes have been verified.

[11] Isolated Bidirectional DC-DC Converter for Hybrid Electric Vehicle Applications

In this paper, Isolated Bidirectional DC-DC converter for medium power application is

introduced. This power rating is achieved by developing a Dual half bridge topology. A 1kW

prototype of the converter has been built and tested and the experimental results of the

converter’s steady state operation have confirmed the simulation analysis. The proposed

topology differs from the conventional converter by having full isolation between its input and

output circuits. The isolation provides the purpose of high power requirement, bi-directionality

and safety.

Fig 16 Proposed DC-DC Converter

Pulse width Modulation (PWM) controller is implemented for a constant output voltage of 200V

when the input is varying between 36-44V. The design was built and tested and the experimental

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results are matching the simulation results but with small amount of ripple in its output. The

author recommends to use a filter capacitor in order to avoid the ripple in the output. The future

scope of this paper is to scale the converter to 10KW with a focus on optimum power density and

the use of new power diodes such as silicon carbide switches and diodes.

[12] Comparing DC-DC Converters for Power Management in Hybrid

Electric Vehicles

This paper presents an analysis, design, and comparison study of several non-isolated

bidirectional DC-DC converter topologies for an ultra capacitor pack namely, the half-bridge,

Cuk, SEPIC and Luo converters. It follows the philosophy of using the half-bridge as the base

case and extends the analysis to the Cuk,SEPIC and Luo converters. The comparison study is

based on the stresses of the active and passive components using equations expressed in terms of

output/input voltage ratio Vo/Vi, maximum load current lo, duty cycle D, and inductor current

ripple ratio rL. Special emphasis is given to the impact that the wide input voltage requirements

for ultra capacitor-based energy storage systems, have on the stresses of the active and passive

components. The converters are simulated using PSpice in order to verify the derived equations.

Fig:17 (a)Cascaded Buck-Boost (b) Half Bridge (c) Cuk (d) SEPIC/Luo Converters

The converters are designed to operate in Continuous Conduction Mode. The comparison study

is achieved by means of graph where the variables of interest are plotted as function of voltage

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ratio Vo/Vi. From the analysis result, it can be found that each converter has specific advantages

and disadvantages and the usage of the converter depends on which parameter needs to be

compromised. The main drawbacks are the fact that it requires two large inductors, the output

current is discontinuous and the output capacitor is large.

[13] New Fully Soft Switched Bi-directional Converter for Hybrid Electric

Vehicles: Analysis and Control

A novel fully soft switched bidirectional PWM dc-to-dc is presented in this paper to provide soft

switching for all elements. It also aims to minimize the semi conductor elements in the Hybrid

Electric Vehicle. The proposed bi-directional converter is inserted as an interface circuit between

DC bus and battery in a Hybrid Electric Vehicle to control the charge and discharge current.

Zero Current Switching (ZCS) is provided for all the switches to employ soft switching which

has been missing in other reference papers mentioned. The components specification of the

converter is given below:

V0 (Battery Voltage) =200V

Vin (DC-BUS Voltage) =500V

Switching Frequency =100 KHz.

Output Power =1KW.

Lr1 =10 µH, Lr2 =1 µH, Cr=10nF

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Fig : 18 Proposed soft switched Bi-Directional Converter

Fig 19 Converter Control Diagram

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The design equations are notified in this paper. To verify the theoretical analysis, PSPICE

software has been used. Finally, the converter control is implemented in MATLAB based on the

state of charge of the battery for both buck and boost modes. The strategy used is that when the

state of charge is below 80%, the bi-directional converter acts as buck converter and charges the

battery. If the state of charge is above 80%, then the bidirectional converter acts as Boost

converter and discharges the battery.

[14] A Novel ZVS Bidirectional Converter for Fuel Cell Electric Vehicle

Driving System

A novel ZVS bidirectional dc-dc converter is proposed for fuel cell electric vehicle, where an

approach of dynamic model of the fuel cell model and a hybrid electric vehicle is developed with

PMDC. The model is generic model and combines the features of chemical and electrical models

which is suitable for electrical simulation programs and can also represent the effect of operating

parameters on the fuel cell.

Fig 20 Isolated Bidirectional DC-DC Converter system

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The design specifications are as follows:

Output power =1KW.

Switching frequency =20 KHz.

Low voltage side =12V (Fluctuation from 10-15V)

High Voltage Side =150V (Fluctaution from 140-160V)

Coupled Inductor =15µH

Blocking Capacitor =10µF ; L =17 µH

DC voltage bus capacitor =3300 µF

This is the proposed model and its operation in both charging and discharging mode has been

discussed. In section 2, a dynamic model of Proton Exchange Membrane Fuel cell (PEMFC) has

been proposed with certain assumptions and equations.

Fig 21 Dynamic Model of PEMFC

To verify the feasilibility of the proposed scheme, a 1kW Simulink model is developed in

MATLAB operating at 20 kHz and the results are found to be satisfactory. The detailed design

and operation considerations were analyzed and described. The proposed new converter has the

advantages of high efficiency, simple circuit and low cost.

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[15] The Impact of Bidirectional DC-DC Converter on the Inverter Operation

and Battery Current in Hybrid Electric Vehicles

In this paper, a high power Bi-directional dc-dc converter is equipped in HEV. The converter

which is placed in between the inverter and the battery pack improves the drive capability,

reduce current ripple also extends the battery life due its controlled charged and discharged

behavior.

Fig 22 Bidirectional DC-DC Converter used in HEV

Both the buck and boost modes of operation along with their design equations have been

explained. This paper mainly concentrates how to maintain constant torque range and enhanced

regenerative braking during converter operation.

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