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K.C.Ramya ^{1}, V.Jegathesan ^{2}

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This work deals with reduction of ripple in the bidirectional DCDC converter. This Converter has the ability to transfer the energy in both the directions. This converter is designed, modeled and simulated using MATLAB SIMULINK and the results are presented. The Pifilter is proposed at the output to reduce the peak to peak ripple. The simulation results with Rload and DCMotor load are presented.
Keywords 
Bidirectional DCDC converter, Coupled Inductor, Filter. 
INTRODUCTION 
Bidirectional DC–DC converters (BDC) are used to transfer the power between two DC sources in either direction. These converters are widely used in applications, such as hybrid electric vehicle energy systems [1]–[4], uninterrupted power supplies [5], [6], fuelcell hybrid power systems [7]–[10], photovoltaic hybrid power systems [11], [12], and battery chargers [13]–[15]. Many bidirectional DCDC converters have been researched. The bidirectional DCDC flyback converters are more attractive due to simple structure and easy control [2], [16], [17]. However, these converters suffer from high voltage stresses on the power devices due to the leakage inductor energy of the transformer. In order to recycle the leakage inductor energy and to minimize the voltage stress on the power devices, some literature present the energy regeneration techniques to clamp the voltage stress on the power devices and to recycle the leakage inductor energy [18], [19]. Some literatures research the isolated bidirectional DCDC converters, which include the halfbridge [8], [9], [20], [21] and fullbridge types [13], [22]. These converters can provide high stepup and stepdown voltage gain by adjusting the turns ratio of the transformer. 
For nonisolated applications, the nonisolated bidirectional DCDC converters, which include the conventional boost/buck [1], [5], [12], [14], multilevel [4], threelevel [10], sepic/zeta[23], switched capacitor [24], and coupled inductor types [25], are presented. The multilevel type is a magnetic less converter, but 12 switches are used in this converter. If higher stepup and stepdown voltage gains are required, more switches are needed. This control circuit becomes more complicated. In the threelevel type, the voltage stress across the switches on the threelevel type is only half of the conventional type. However, the stepup and stepdown voltage gains are low. Since the sepic/zeta type is a combination of two power stages, the conversion efficiency will be decreased. The switched capacitor and coupled inductor types can provide high stepup and stepdown voltage gains. However, their circuit configurations are complicated. Fig.1 shows the conventional bidirectional DCDC boost/buck converter which is simple structure and easy control. However, the stepup and stepdown voltage gains are low. A modified DCDC boost converter is presented [26]. The voltage gain of this converter is higher than the conventional DCDC boost converter. Based on this converter, a novel bidirectional DCDC converter is proposed [27], as shown in Fig. 2. The proposed converter employs a coupled inductor with same winding turns in the primary and secondary sides. Compared to the proposed converter and the conventional bidirectional boost/buck converter, the proposed converter has the following advantages:1) Higher stepup and stepdown voltage gains and 2) lower average value of the switch current under same electric specifications. The following sections will describe the operating principles and steadystate analysis for the stepup and stepdown modes. In order to analyze the steadystate characteristics of the proposed converter, some conditions are assumed: The onstate resistance RDS(ON) of the switches and the equivalent series resistances of the coupled inductor and capacitors are ignored; the capacitor is sufficiently large; and the voltages across the capacitor can be treated as constant. 
The above literature does not deal with ripple reduction using Pifilter. This work proposes Pifilter for ripple reduction. 
II. STEPUP MODE 
The proposed converter in stepup mode is shown in Fig.3.The pulse width modulation (PWM) technique is used to control the switches S1 and S2 simultaneously. 
III. SIMULATION RESULTS 
The circuit diagram for boost mode is shown in Fig.4(a).The power output is measured by multiplying the output voltage and the output current. Load voltage and load current are measured using voltage and current blocks respectively.The following are the assumptions made in simulation studies. Ã¯ÂÂ Internal resistance of the source is neglected. Ã¯ÂÂ Resistance of the coupled inductor is neglected. Ã¯ÂÂ ESR of the capacitor is neglected. The simulation parameters for boost mode with Cfilter are as follows: Coupled Inductor = 1 mH ; Cfilter, CO = 400μF and Resistance, RO = 11Ω. 
DC input voltage of 15V is shown in Fig.4(b). The switching voltage and the voltage across the MOSFET are shown in Fig.4(c). 
IV. CONCLUSION 
Bidirectional DCDC converter operating in boost mode and buck mode is simulated successfully with Rload and DC motor load. The ripple in the output voltage is reduced from 0.06Volts to 0.01Volts by using Pifilter. Therefore the performance of DC motor is improved due to the reduced ripple. The scope of this work is to design and simulate the DCDC converter using MATLAB. The hardware will be implemented in future. The drawback of this converter is that it can be used only for low power levels. 
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