A Study On Active Clamp Coupled-inductorbased High Step-up DC/DC Converter With Low Voltage Stresses

DC-DC conversion applications such as uninterruptible power supplies(UPS), high-intensity-discharge(HID) lamps for automobile headlamps, electric vehicles(EV), photovoltaic(PV) grid-connected power systems, and many other fields, call for high efficiency and high step-up converters. The conventional boost converter can not achieve a very high voltage gain due to the equivalent series resistance(ESR) associated with boost inductor, output capacitor and switch. The optimized voltage gain of it is limited to approximately four times with a relative high efficiency. Therefore, it is valueable to study the high efficiency and high voltage gain DC/DC converter.The coupled-inductor-based converter has the advantages of simple topology, low cost, high reliability, etc. What’s more, by designing the turn ratio of coupled-inductor reasonably, it is easy to realize high-gain transformation. In addition, the active clamp circuit can realize zero voltage switching, so as to reduce the switching loss and improve the efficiency of it. Therefore, this paper mainly studies on the active clamp coupled-inductor-based high step DC-DC converter, the main contents and results achieved are as follows:Firstly, to reduce the voltage stress of the active clamp coupled-inductor-based high step-up DC/DC converter, the rectifier circuit is added to the second winding of the coupled-inductor. Thus, an active clamp coupled-inductor-based high step-up Boost-Flyback converter is proposed. Its working principle and performance characteristics are analyzed and verified by simulation and experiment results. Ultimately, the optimal active clamp circuit is obtained by comparing the characteristics of the three common active clamp circuits; they are Boost type, Buck-Boost type and series type.Secondly, in order to improve the utilization of coupled inductor, an active clamp coupled-inductor-based high step-up Boost-Flyback converter is proposed. When the switch is in the ON state, the energy can be transferred to the secondary windings of the coupled-inductor. Its operation principle is analyzed in detail. Moreover, the gain ratio and soft switching condition of the proposed converter are deduced. Ultimately, a 250 W experimental prototype is built to verify the theoretical analysis.Then, to improve the utilization of coupled inductor further, it is expected that the energy can be transferred to the secondary winding no matter the switch in the ON state or OFF state, an active clamp coupled-inductor-based high step-up Boost-Forward-Flyback converter is proposed. The proposed converter not only inherits the merits of the above two high step-up and soft switching converters, but also has a higher voltage gain.Meanwhile, the voltage stresses of the diodes are reduced greatly. An experimental prototype is built to verify the correction of the theory analysis.Finally, using the proposed high step-up Boost-Forward-Flyback converter as a control object, the digital voltage type control based on FPGA is studied, and the related hardware circuit and software system are designed.