Wide Input Dc-dc Converter, High Gain Isolated

The isolated step-up DC-DC converter is a kind of converter which can convert low voltage DC bus into high voltage DC bus and realize electrical isolation. The common topologies are forward converter, flyback converter, isolated Boost converter and their variations. The isolated step-up DC-DC converter has been widely used in fields such as energy storage system and aeronautical power supply system. And according to the developing tendency of power electronics, the isolated step-up DC-DC converter will become one of the key technology in fields like new energy generation and new energy vehicle. In conclusion, the characteristics of the new generation isolated step-up DC-DC converter is wide input, high step-up gain and high efficiency.LLC resonant converter can achieve zero-voltage switching (ZVS) for primary side switches and zero-current switching for secondary side rectifiers without auxiliary circuit, so it features simple structure and high efficiency. And it is widely used in front-end DC-DC converter in recent years. LLC resonant converter has avdantages over other topologies, such as wide input adaption, full load range soft switching and high efficiency power conversion, and it satisfies the requirements of the new generation isolated step-up DC-DC converter. This paper takes objective of LLC resonant converter, firstly proposes a improved design methodology and then presents two kinds of power conversion solutions based on it, which are single stage and cascaded stage power conversion.The design of LLC resonant converter is mainly the design of three resonant components. Traditional design is based on the gain curve, therefore the key point is drawing out the gain curve. There are three methods to realize it, which are fundamental harmonic approximation, simulation analysis and time domain analysis. The disadvantages of traditional design method is that it is excessively depended on experience and has no normal form. According to this, this paper proposes a improved design methodology based on the current angle. The size of the current angle directly determines the charging and discharging precess of MOSFET parasitic capacitor during commutation. The larger the current angle, the easier the realization of soft switching. Howerver, the excess energy makes additional power loss which degrades the converter efficiency. For this reason, the proposed method optimizes the current angle for efficiency optimisation.According to high step-up isolated DC-DC power conversion, this paper presents two practical solutions, which are single stage and cascaded stage. The single stage means that there is only one DC-DC topology between the input and output. And the cascaded stage is a two stage power conversion, that is Boost+DC-DC transformer. The effect of the DC-DC transformer is to boost the DC voltage bus so that the Boost converter can work in satisfactory region. Two prototypes are made to verify the two power solutions respectively.The output voltage doubling technology of isolated DC-DC converter has two kinds, which are the rectified doubling and the resonant doubling. Theoretically, any isolated DC-DC converter with two-way magnetization can adopt output voltage doubling. The topology of current form can adopt rectified doubling and the voltage form can adopt resonant doubling. A prototype is made to verify the feasibility of resonant doubling in the voltage form topology.Finally, this paper makes a conclusion of each part and presents further research direction.