ABSTRACT :

In this paper, a novel dual active clamp converter with high voltage gain is proposed for DC-DC applications. The active clamps’ switches turn on and off under zero-current switching (ZCS). In addition, the main switch turns on under ZCS condition, as well. Therefore, switching losses are significantly reduced. The converter is also capable of operating under quasiresonance (QR) mode. In this mode, switching losses are reduced further by lowering the voltage and current, at which the main switch turns off. The number of switches and switching loss are reduced and The switching frequency of the active clamps’ switches is half of the main switching frequency. The operation principles of the proposed converter are studied in both PWM and QR modes, and the advantages are investigated. The proposed system is simulated in MATLAB/Simulink software.

INTRODUCTION:

Renewable energy sources (RES) will have a significant role in supplying the required power in the near future. Therefore, improving the ways these sources are utilized is of high importance. Despite the variety in the characteristics of different types of RESs, some common problems exist in most of them. One can consider photovoltaic (PV) and fuel cell (FC) systems as two prominent candidates. Due to the intrinsic features, the output voltage of these systems is much lower than the desired value, suitable for being connected to the utility grid. Using power electronics converters is necessary to connect a RES to the grid or a load. Hence, it seems reasonable to retrofit the converters to overcome the low voltage problem of RESs. There are many methods, and topologies proposed to increase the voltage level. A simple boost convert is a basic solution which functions acceptably in low voltage gains. However, in most of the cases, a high voltage gain converter is needed. Increasing the duty cycle in a boost converter results in low efficiency, diode reverse recovery problem, and electromagnetic interference (EMI). Cascaded/multilevel boost converters are proposed to overcome such limitations. These converters benefit from modularity feature that makes it possible to reach higher voltage gains. But using the increased number of elements causes higher costs, more complex control, and low power density. DC-DC step-up converters based on a transformer or a coupled inductor are suggested as an alternative idea. These converters provide galvanic isolation, and voltage gain can be obtained by adjusting the turn ratio of the magnetic elements. The application of the converters with high turn ratio transformers/coupled-inductors is limited due to some drawbacks. The design of transformers/inductors for high voltage/power applications is difficult and costly. Also, the large size of these elements decreases the power density. The main defect is related to the leakage inductance, which limits the voltage gain. Moreover, in the converters with hard switching condition, it causes high voltage spikes across the switches that increases power loss, and decreases the lifespan of the switches. In order to overcome these problems, interleaved DC-DC converters have been introduced. They are claimed to be a suitable solution to reach higher voltage/power levels. In this type, two or more converters contribute to the voltage boosting process. These converters are connected in parallel at the input and series at the output side. Using magnetic elements provides electrical isolation as it brings softswitching possibilities. Since in the interleaved structure, some partial scale transformers are utilized, the disadvantages related to high turn ratio transformers are relieved. Connecting many converters in parallel at the input side raises the capability to operate at higher power ranges. However, using an increased number of elements, especially semiconductors, is the most crucial challenge associated with interleaved DC-DC converters. It can result in more weight, large size, and more importantly, increases the cost. Hence, any effort to reduce the number of the components while preserving/improving the performance of the converter is significantly important.

PROBLEM STATEMENT:

In this paper, a dual active clamp (DAC) converter with a reduced number of elements is proposed. This converter copes with most of the above-mentioned demands. By reduced number of elements, in comparison with the interleaved converters, the cost is lowered as higher power density is achieved. The proposed converter is highly efficient because of full soft-switching operation (at both turn-on and -off moments) of two auxiliary switches, and turn-on ZCS operation of the main switch.