基于输入并联输出串联的高效高升压比DC-DC变换器

High-Efficiency High Voltage Gain DC-DC Converter Based on Input Parallel and Output Series Connection

随着新型可再生能源的快速发展,对高效、高升压比DC-DC变换器的需求日益增加。传统两级级联式结构中,前后两级均需传递全部功率,不利于系统效率的提升。为此,该文提出一种基于输入并联输出串联(IPOS)连接的上下堆叠式高升压比直流变换器,系统的上部分变换器工作在直流变压器(DCX)状态,实现恒电压比传输,处理大部分功率,通过对谐振点处的参数优化实现效率提升;下部分变换器则起到系统闭环动态调压的作用,传输小部分功率。该文详细介绍所提出结构的工作原理、参数设计以及平面变压器的优化设计,并搭建24~32 V/400 V、额定功率200 W、开关频率1 MHz的实验样机验证了理论分析的正确性,所搭建样机峰值测试效率高达96.3%。

Nowadays,with the rapid depletion of traditional fossil fuels,the harm to the environment is becoming more prominent.The proliferation of renewable energy resources has solved the energy shortage problem and realized sustainable development.The high step-up DC-DC converters have received widespread attention in renewable energy systems,such as photovoltaic module-integrated converters,fuel cells,and hybrid electric vehicles.In general,the high step-up DC-DC converters can be divided into non-insolated and isolated types.The non-isolated DC-DC converters usually adopt coupled inductors and voltage multiplier cells to realize the boost capability.In contrast,the isolated structures can realize the galvanic isolation and the expected voltage gain by changing the transformer turns ratio,which is more suitable for high step-up applications with high safety performance.The LLC resonant converter has gained popularity due to the soft switching properties of power devices,constant conversion ratio,and high working efficiency near the resonant working point.However,it will generate large current stress on the primary side of the transformer when a high boost ratio is achieved,causing additional ESR losses of the resonant components and efficiency sacrifice.Thus,the resonant tank is usually located at the secondary side in high step-up applications,and the system voltage gain of LLC is regulated by pulse frequency modulation.The switching frequency change will make the resonant point deviate from the ideal state and generate additional reactive power,which brings difficulties to the design of EMI filters and magnetic components.Besides,the soft switching range of power devices is affected as the switching frequency changes.Although LLC is preferable to operate in the unregulated state,it will lose the voltage regulation capacity.Therefore,the two-stage architecture is a popular solution,where LLC can perform as a DC transformer(DCX),and the system dynamic regulation is achieved by the front or latter DC-DC stage.However,a potential disadvantage is that both stages need to transmit all the system power,which is not conducive to efficiency improvement.A high step-up DC-DC converter based on input-parallel and output-series(IPOS)connection is proposed in this paper.The upper part of the system is an LLC converter with the secondary resonant tank,which operates as a DCX and realizes a constant voltage conversion ratio.A secondary series resonant active clamp DC-DC converter is adopted in the lower part to perform as a system voltage regulator,and the dynamic voltage regulation of the system can be achieved by pulse width modulation.The soft switching properties of all the power devices can be realized in the proposed converter.DXC processes an amount of the system power,and the DC-DC voltage regulator only handles a small part of the total power,thereby reducing device stress and power losses.Compared with the two-stage solution,the IPOS structure can reduce the power level and component ratings of each part more effectively.The transformer’s leakage inductor can replace the resonant inductor in the proposed converter,and the optimization of the windings arrangement reduces the parasitic capacitance.The working efficiency is further improved through the optimal design of the parameters and the magnetic components for DCX at the rated point.The working principle,parameter design criterion,and planar transformer optimization are introduced in detail.An experimental prototype with an input voltage range of 24 V to 32 V,an output voltage of 400 V,a rated power of 200 W,and a switching frequency of 1 MHz is built to verify the theoretical analysis.The peak test efficiency is up to 96.3%.