Design and Analysis of Single Switch Transformer less DC-DC Converter with Universal Input Voltage for Fuel Cell based Vehicles

A new single switch solar powered high gain step-up DC-DC converter is proposed for plug-in hybrid battery charger in Electric vehicle (EV). The proposed topology utilizes a L2C3D2network to obtain high voltage gain and reduce the voltage stress on the power switch. Also, the proposed converter has a universal input voltage to suit the soft output attributes of the fuel cell. The fuel cell has a relatively low output voltage and high current, and it has soft output characteristics as its output voltage drops as the output current increases. Accordingly, the fuel cell can't be straightforwardly interfaced to the dc-link bus (400V) of the inverter inside the EV. This dc-dc converter has a universal input voltage feature with wide voltage gain range to suit the soft output characteristics of the fuel cell. Also, this dc-dc converter must have low input current ripple to delay the existence time of the fuel/solar cell, and a shared ground between its input and output ports to keep away from extra EMI and support security issue. This control strategy is modelled and simulated using MATLAB -Simulink. A proto type experimental has been fabricated and tested. The experimental analysis was done and the results are in line with the simulation results.


INTRODUCTION
With the increasing efforts to decrease the dependency on the depleting fossil fuels and the growing acceptance of clean energy sources adoption, a lot of research has been focused on the electrification of transportation means Fuel cell / solarpowered electric vehicles (EVs) are an important player in the clean energy vehicles segment and they have the following advantages: [9,10] clean electrical energy generation with zero emissions, high energy conversion efficiency, and a higher range compared to battery-powered EVs. [7] On the other hand, the fuel cell has a relatively low output voltage and high current, and it has soft output characteristics as its output voltage drops as the output current increases. In this manner, the fuel cell can't be straightforwardly interfaced to the dc-link bus (400V) of the inverter inside the EV. The fuel cell requires a high step-up DC-DC converter to interface it to dc-link of the inverter.
This DC-DC converter should have a universal input voltage feature with wide voltage gain range to suit the soft output characteristics of the fuel cell. Also, this dc-dc converter must have low input current ripple to delay the existence time of the fuel/solar cell, and a shared ground between its input and output ports to keep away from extra EMI and support security issue.

LITERATURE SURVEY
Y Zhang, et al. [1] a Boost converter with a diode-capacitor multiplier cells are discussed. This converter has a low input current ripple, high conversion ratio, and low voltage stress on the power switch. The main drawback for this converter is that the output voltage and the efficiency will drop as the number of multiplier cells increase due to the increased conduction losses of the diodes.
M. Forouzesh, et al. [2] many high steps up DC-DC converter topologies have been discussed in literature, and can generally be classified into topologies with magnetic coupling and topologies without magnetic coupling. The topologies with magnetic coupling utilize either a high frequency transformer or a coupled inductor to achieve high conversion ratios and reduce the voltage stress on the power switches via turns ratio of the magnetic coupling component [3].
L. S. Yang, et al. [4] to achieve higher voltage conversion ratio and further reduce voltage stress on the switch and diode, the high step-up ratio converter [4] and the Ultra high step up converter [5] have been proposed. These converters can provide large step-up voltage conversion ratios. Sadly, the voltage stress of diodes in those converters remnants rather high.
C. T. Pan, et al. [6] a novel transformerless adjustable voltage quadruplet topology is proposed. It incorporates twophase interleaved boost converter to understand a high voltage gain and keep up with the upside of an automatic current sharing capacity at the same time. [8] Furthermore, the voltage stress of active switches and diodes in the proposed converter can be greatly reduced to enhance overall conversion efficiency.

EXISTING CONVERTER TOPOLOGY Boost Converter
The DC-DC boost converter is used to step-up the low input voltage to a higher output voltage. The circuit of a boost converter consists of an inductor, a capacitor, a switch and a diode are shown in the figure 1.

Modes of Boost Converter
The boost converter has two modes of operation, During the switch ON period the current flows through inductor and switch. The inductor stores energy during ON period. During the switch OFF period the current flows through inductor, diode, capacitor and load resistance. The stored energy in inductor is transferred to load resistance through diode during OFF period.

Considerations of Boost Converter
The voltage gain of boost converter is, The voltage gain of boost converter is given in equation 1. The output voltage of boost converter is, The output voltage of boost converter is given in equation 2.
The duty cycle of the boost converter is, The duty cycle of the boost converter is given in equation 3. The value of inductance is designed by following equation, The value of inductance is designed by the equation is given in equation 4. The value of capacitance is designed by following equation,

Simulation and Output Waveform
The parameters specification of the boost converter is mentioned in the table 1. The Boost converter is simulated in the MATLAB / SIMULINK is shown in the figure 2 and the boosted voltage is obtained at output. The waveform shown in figure 3 indicates that the boost converter gives stepped up voltage of 20.32 V for the input voltage 9.5 V.

Modes of Three Level Boost Converter
The three-level boost converter has two modes of operation, (i) switch ON mode and (ii) switch OFF mode.

Switch on mode
During the switch ON mode, inductor L is connected to the source voltage. The inductor voltage during on condition is equal to the input voltage. If the voltage across the capacitor C4 is less than the voltage across capacitor C5, then the capacitor C4 gets charged from capacitor C5 through diode D4 and switch(S). Simultaneously, if the sum of the voltages across capacitors C4 and C2 is less than the sum of the voltages across capacitors C5 and C3, then the capacitors C4 and C2 gets charged from capacitors C5 and C3 through diodes D4 and D2 respectively and switch(S).
The charging system continues until the voltage across the charging-discharging

Design Considerations of Three Level Boost Converter
The voltage gains of the three-level DC-DC boost converter is, Voltage gain, G= The Effectiveness of the converter can be calculated by the following, Vs*Is=Vo*Io Ƞ= = * *

AND DISCUSSION
A battery, which is really an electric cell, is a device that produces electricity from a chemical reaction. Strictly speaking, a battery consists of two or more cells connected in series or parallel, but the term is generally used for a single cell. A cell consists of a negative electrode; an electrolyte, which conducts ions; a separator, also an ion conductor; and a positive electrode. The electrolyte may be aqueous (composed of water) or nonaqueous (not composed of water), in liquid, paste, or solid form. When the cell is connected to an external load, or device to be powered, the negative electrode supplies a current of electrons that flow through the load and are accepted by the positive electrode. When the external load is taken out the reaction ceases. A 13 primary battery is one that can convert its Recent Trends in Control and Converter Volume 4 Issue 2 chemicals into electricity only once and then must be discarded. A secondary battery has electrodes that can be reconstituted by going electricity back through it, also called a storage or rechargeable battery, it very well may be reused commonly.
The specifications of the three-level boost converter are shown in table 2 The simulation circuit of DC to DC converter is shown in the figure 5.

Fig. 5: Simulation Circuit of DC to DC Converter.
The performance of the proposed Transformer less DC -DC Converter for the solar vehicle's outputs are verified Using MATLAB -Simulink. As shown in figure 5, solar panel gets the input from temperature and irradiance, where the panel output voltage and current are given to the converter. The converter used here is three level boost converters, which reduces the voltage stress on the semiconductor devices. The converter uses the PI controller for its PWM pulse generation, where the output of PI is compared with saw tooth pulse is given as signal to the DC-DC converter.
Further, the DC-DC boost converter increases the input voltage from 73 V to Set Voltage of 400 V is shown in figure 6.
This voltage is been used to store or charge the battery, which is further used in electric vehicle.
The proposed converter utilizes a L2C3D2 network and has the following advantages: high step-up gain, low voltage stress on the semiconductor devices, common ground, and low input current ripple. The topology of the proposed converter is shown in Figure 6. It is composed of one power switch (Q), three diodes (D1, D2, and D3), three inductors (L1, L2, and L3), five capacitors (C1, C2, C3, C4, and Co), and R represents a resistive load. A conventional boost switching network is formed by (L1, Q, D1, and C3), and an L2C3D2 network formed by (L2, L3, C1, C2, C4, D2, and D3) is integrated between the conventional boost switching network and the output capacitor Co. The L2C3D2 network enhances the voltage gain of the proposed converter and reduces the voltage stress on the power switch.

EXPERIMENTAL SETUP AND DISCUSSION
In this project work, the hardware implementation of the single switch transformer less DC-DC converter is first the power supply unit of converter is designed with step-down transformer and rectifier circuit. In this design the transformer is used to step-down the voltage and rectifier is used to convert AC into DC. By this setup, DC supply for converter is obtained.
The proposed converter is designed as per the circuit diagram. In this setup the automotive vehicle systems are consisting of solar panel, plug in charger, transformer less DC to DC chopper, battery, three phase voltage source inverters.
The topology of the proposed converter act as a DC to DC High step up voltage boost converter without transformer, its composed of one power switch, three diode, three inductor and five capacitors, it's given high voltage gain and reduce the switch stress. The output of the converter voltage is charge to Battery then battery voltage is applied to three phase voltage source inverters. The one separate microcontroller is used for PWM generation is shown in figure 8.  The assembling of components and fabrication of the hardware setup of project has been completed and shown in figure 9.  The Embedded micro controller DSPIC 4011 is act as a heart of system, it produces the PWM Pulse to drive the converter circuit. The converter output voltage maintained using Proportional Integral controller.
The hardware setup of the proposed converter with solar panel is shown in the figure 11.  The output voltage from three levels of the proposed converter is shown in the figure 12. A Closed-loop system are intended to automatically accomplish and keep up with the ideal output condition by contrasting and the genuine condition.
It is also called as fully automatic control system in which its control action being dependent on the output. In the connection of RPS is connected with the Input side and the battery is connected with the output ,Manually varying the Actual voltage and set voltage is 15v from the closed loop system by using the LCD display of the proposed converter gives the output of 0.13 A, and 12.5 V from the regulated power supply is shown in the figure 12. The input voltage to the converter is depicted by an adjustable DC power supply, and the converter is controlled by a microcontroller DSPIC 4011.
The power circuit is built using power MOSFET and Schottky diodes.

CONCLUSION
The proposed converter has many merits such as high voltage gains without magnetic coupling, low voltage stress on the semiconductor devices, common ground, and universal input voltage. These features make it an excellent candidate for fuel cell-based vehicles. Steady state analyses in Continuous conduction mode and Discontinuous conduction mode operations of the proposed converter was completed. The proposed converter was compared with other step-up converters in literature regarding the voltage gain, the voltage stress on the semiconductor devices, the number of components, and other specifications, and the privilege of the planned topology is justified. The output waveforms obtained from the simulation indicates the performance of the proposed converter. This control strategy is modelled and simulated by using MATLAB -Simulink. A proto type experimental has been fabricated and tested. The experimental analysis was done and the results are in line with the simulation results.

FUTURE SCOPE
The following are the future scope of the proposed DC-DC converter.
• The output from the proposed converter can be given to charge a battery on Electric vehicle (EV), DC loads. • Another essential improvement is to design a boost converter with hybrid inputs sources such as PV-panel, fuel-