Modified Bi-directional DC-DC converter For EVs

. This paper introduces a modified bidirectional DC-DC converter with equal current sharing capacity with 4 times the input voltage. This propose circuit has an excellent conversion ratio for use with electric car applications. The proposed system's capacitive voltage-divider stage provides minimal stress across the switches, allowing the designer to use small resistance. The alternative arrangement of switches increases power density while significantly reducing current ripple and filter sizing. Two phases are described here, interleaved to construct the equal current sharing phenomena. This connection of converter is thoroughly examined, and its characteristics are studied and compared to those of other state-of-the-art bidirectional converters.


Introduction
Alternate usage of fossil fuel is Electric vehicles.In electric vehicles (EVs) with hybrid energy storage systems, the energy storage unit (ESU) is essential.The battery in the ESU is for powering the vehicle and capacitor units for absorbs reactive power during frequent starting and stopping [1].Wide band-gap semiconductors are used to built converter, which specifically used for EVS [2].The hybrid EV system is shown in Fig. 1.

Fig.1.Hybrid Electric vehicle
In this diagram, the battery and UC have lower voltage levels than the dc-bus [3].The ESU will attain the desired voltage.To accomplish these goals, a variety of topologies have been proposed [4].The high voltage conversion ratios of converter may be isolated and those that are not [5].In isolated BDCs the gain of voltage raised by either a coupled-inductor or a transformer [6].Yet, a resonant circuit formed by the parasitic capacitance and leakage inductance causes a significant voltage and current spike on the semiconductors.In addition, the converter's bulkiest parts are the coupled-inductor and transformer [7].The most basic non-isolated topology suitable for an EV system is the traditional bidirectional buck-boost converter [8].The effective usage of above method is always accompanied with switching losses [9].The traditional technique for reducing voltage stress is multilevel converters [10].However, more hardware circuits and power switches are required [11].The switchedcapacitor BDC (SCBDC) expands into additional applications, such as the E-transportation but it is costlier [12].For improving voltage gain hybrid BDC are implemented which consists of a switched-capacitor and a Z-source [13].However the hybrid BDC are affected by voltage stress which slow down the converter's efficiency [14].For improving efficiency SEPIC converters are used [15].In this topology range of its applicability is constrained [16].In this paper voltage-multiplied alternate switch arrangement based on bidirectional dc-dc converter is implemented which has high voltage gain and low switching stress which is achieved by proper operation of converter.This proposed results are compared with two and three level BDC.This is easily obtained by controlling the charges in capacitors during forward and reverse mode.The suggested converter may also doing equal current sharing without the use of any more additional circuitry.In this mode, converter attains approximately 800 V for EV operation.Fig. 3 shows the analogous converter circuits at various intervals along with the accompanying current routes.Fig. 4 displays the converter's primary waveforms in clockwise mode (a).Switches S1, S2 ON of the same duty-cycle Tf and 180° phase shift.The switches S3 and S6 ON with complementary of S1,likely switches S4 and S5 ON with complement of S2.The suggested topology's high step-up gain is advantageous for EV applications with ESU and is achievable when it is operating in continuous manner.The value of duty-cycle is taken just higher than 0.5.

Anti-clockwise movement mode:
In this mode, energy is transferred is reversed as that of above mode for to run in opposite direction with appropriate reduced voltage.Switches S3 and S6's are ON which is complement to those of switch S1.In the same manner the gate signals is applied to S4 and S5.The analysis and operation periods are only shown in Fig. 4.The duty cycle TB is less than 0.5for that of above mode.

Steady-State Analysis
This is made simpler by using capacitors operate as a voltage source .The switches are also thought to be perfect.

Clockwise Movement Mode:
The voltage balance concept can be used to determine the exact behavior of the converter between inductors L1 and L2.The equations are shown in Fig. 3(a)-(c): Where   is the duty cycle of S1 and S2.The voltage conversion ratio is described in below equation -----------------(3)

Equal current sharing capability
The proposed converter includes an inherent equal current sharing feature that divides the input current evenly between the two phases without the need for additional circuitry.This is a crucial step in the development of a completely interleaved converter, in which the input current can be distributed equally across the two phases, resulting in symmetrical performance in the two phases.Let equate the average state variables into zero, the following relation can be derived from literature.---------------------(

4.1.Inductors
By decreasing the current ripple, the inductors are crucial to the suggested converter.So, they ought to be carefully chosen.

Switches
For Switches to account for the impact of the parasitic elements, a safety margin of 21% is recommended.

Performance Comparison Using Simulation
In this part, a comparison is done with other converter.As shown in Fig. 4, the voltage multiplied stage of the converter compared with other circuits in terms of the voltage conversion ratio.According to Fig. 4 (a), which compares the voltage gain of various converters from that it is noticeably higher than that of the other converters.The suggested converter has more passive and semiconductor components than its BDC equivalents, which lower the power density and efficiency.The suggested converter offers the lowest voltage conversion ratio in anticlockwise mode, as illustrated in Fig. 4(b).When compared to other BDCs, the proposed converter offers significantly less voltage stress, because of the minimal on-resistance RDS(ON).Different parameters like Cost, voltage stress is compared.The proposed system shows good efficiency.It is proven that the inductance of the suggested converter is 1/2 that of other converter in terms of size and weight.The

Conclusion
A bidirectional voltage-multiplied alternative arrangement DC-DC converter with significant modification has been implemented in this paper.The working idea of this converter in clockwise direction is to charge the capacitors in parallel and discharge that in various pathways, resulting in a high voltage conversion ratio.For other direction the switched capacitors are working in reverse manner as that of in above.The voltage stress across the switches, is reduced by allowing that at lower voltage ratings.This system also reduce switching and conduction losses.Moreover, the suggested converter has equal current sharing built-in without using additional circuitry.This is the best method which applied to large voltage range such as electric vehicle systems.

Fig. 2 .
Fig.2.Proposed Converter Figs.2,3, shows the proposed converter and its flow diagram.The circuit consists of two stage with inductance, capacitances and switches.The circuit designed clock or anti clockwise direction which enables easy power transfer between the ESU and dc-bus.As it is assumed that every component is perfect throughout the analysis, it is possible to ignore the equivalent series resistance and passive component of resistance of switches therefore Energy flow from low to high voltage side.

Fig. 3 Flow diagram of proposed system 3 ITM
Fig.3 Flow diagram of proposed system