High Step-Up Integrated Boost-Zeta Converter with Coupled Inductor and Resonant Soft-Switching

The output voltage generated by the photovoltaic array and fuel cell is very low, which needs to be boosted to a high DC-bus voltage for inverting or grid connection. In order to obtain a DC-DC converter with high step-up capability, various boosting techniques, such as switched inductor, switched capacitor, and cascade techniques, have been proposed. However, their related converters have a large number of components and work in a hard-switching model, resulting in increased cost and reduced efficiency. Therefore, a high step-up coupled inductor integrated Boost-Zeta converter with coupled inductor and resonant soft-switching for photovoltaic/fuel cell systems has been proposed. The proposed converter achieves higher voltage gain with fewer components. Meanwhile, the resonant soft switching technique reduces the switching losses. Firstly, the integrated Boost-Zeta converter topology is obtained by integrating the Boost converter and the Zeta converter using the topology combination technique. The voltage gain of the Boost-Zeta converter is the sum of the Boost converter and the Zeta converter. At the same time, continuous input and output currents are obtianed. Then, based on this topology, a novel converter is proposed by replacing the diodes with switches. The proposed converter has a high voltage gain using a resonantly coupled inductor voltage multiplier cell. The zero voltage switching (ZVS) turn-on of all switches is achieved by active clamp branches, which reduces voltage stress and switching losses. Meanwhile, the zero current switching (ZVS) turn-off of all diodes is achieved by resonating the secondary winding with the resonant capacitor, effectively solving the diode reverse recovery problem. Thirdly, the operation principle of the converter is analyzed, and the performance parameters of the converter and the conditions of soft switching are given. Finally, the general topology of the proposed converter is given and compared with other converters proposed in the literature. An experimental prototype with 24 V to 32 V input and 200 V-200 W output was built. It can be seen that the ZVS turn-on of both switches is achieved. The blocking voltages of the switches are around 54 V, much lower than the output voltage. The ZCS turn-off of diodes is realized through resonance between the leakage inductor and resonant capacitor, effectively reducing the reverse recovery loss. The voltage stress of diodes is around 145 V, also lower than the output voltage. The measured efficiency of the prototype at full load is 97.1% (32 V input), demonstrating the better performance of the proposed converter. The conclusions can be drawn as follows. (1) The proposed converter has higher voltage gain and lower switch voltage stress using the combination and coupling multiplier techniques. (2) All switches can achieve ZVS turn-on by the active clamp branch. (3) All diodes achieve ZCS shutdown by the resonance of the secondary winding multiplier branch, which effectively alleviates the reverse recovery problem of the diodes. (4) The control of the proposed converter is simple, and the resonance does not affect the voltage gain. (5) Adding multiple voltage cells can further expand the proposed converter. The proposed converter is suitable for high step-up applications such as PV power generation and fuel cell systems. © 2024 China Machine Press. All rights reserved.