| China has a long coastline,vast sea area and many islands.The construction of islands and coastal bases is related to the national economic lifeline and national defense security.In the construction of islands and coastal infrastructure,the traditional energy supply schemes with important loads such as national defense facilities and ports have some defects,such as high energy consumption,high emissions,high pressure on the ecological environment,poor power quality and high security costs.Island/shore-based high-power special power supply equipment is an important means to solve these backward power supply technology,and also the cornerstone and important guarantee of island development and coastal engineering.High-power DC special power supply,using high-efficiency LLC resonant converter topology,requires efficiently and stably operation in the harsh island environment of high temperature,high humidity and high salt fog.In the research and development of high-power DC special power supply,there are many problems to be solved,such as the optimization of resonant tank parameters under wide voltage gain,the transformer design and optimize of efficiency,and the deviation of maximum efficiency point caused by wide frequency range.In this paper,a systematic and in-depth study on the above issues is carried out.The main research contents include:(1)Aiming at the problem that the loss of traditional magnetically integrated LLC transformer accounts for a large proportion of the total loss of resonant converter,a design scheme based on impedance reflection principle to optimize the efficiency of LLC resonant transformer is proposed: using the impedance reflection of transformer,a linear inductance is connected in parallel at both ends of secondary winding or auxiliary winding of transformer to obtain the required resonant inductance.The proposed transformer design scheme does not need to insert air gap into the core magnetic circuit of the main power transformer to obtain resonant magnetizing inductance anymore,the adverse effects caused by edge effect have been basically eliminated.It reduces the loss caused by edge effect and the problem of relatively high local temperature rise of transformer.At the same time,the area utilization ratio of magnetic core window is increased,and reduce the loss caused by proximity effect.Since the magnetizing inductance can be adjusted by the linear inductance outside the transformer,the flexibility of parameter modification is greatly enhanced.The experimental results show that the new LLC resonant transformer design method effectively improves the efficiency of the transformer and reduces the temperature rise of the transformer.(2)Aiming at the contradiction between DC voltage gain range and light load efficiency in LLC resonant converter design,a dynamic regulation method of magnetizing inductance is proposed:the “switching control inductor” is connected in parallel between the secondary winding or the auxiliary winding of the transformer.By controlling the phase difference between the driving signal of the switch in the "switch control inductance" branch and the voltage waveform of the secondary winding or the auxiliary winding terminal,the resonant tank magnetizing inductance is continuously,dynamically and programmable adjusted,so it is a novel LLC resonant converter design method.The proposed design creatively improves the flexibility of the LLC resonant converter design,and can adjust the magnitude of the magnetizing inductance according to the output voltage and load conditions,which can satisfy the output voltage adjustment range of the LLC resonant converter under heavy load,and can also ensure higher efficiency under light load conditions and achieve an increase in overall efficiency.(3)Aiming at the high turn-off loss of semiconductor power devices in LLC resonant converters for high voltage,high current and high power applications,a resonant capacitor minimization resonant tank parameter design method for optimizing the turn-off loss of semiconductor power devices is proposed.The switching loss of semiconductor power devices is closely related to the current flowing through the devices before switching off.The proposed resonant capacitor minimization resonant tank parameter design method effectively reduces the switching-off current of power devices,thereby reducing the switching-off loss.At the same time,it also reduces the frequency regulation range of LLC resonant converters,reduces electromagnetic interference and improves the overall efficiency of the LLC resonant converters at full load range.(4)Aiming at high power applications with high output voltage and wide output voltage regulation range,a new design scheme of high efficiency IPOS power supply witch tracking the maximum efficiency point is proposed.The proposed IPOS power supply consists of a phase-shifted full-bridge converter and a interleaved LLC(iLLC)resonant converter with input parallel and output in series.Phase-shifted full-bridge converter adjusts output voltage to meet the demand of load-side voltage variation and the iLLC resonant converter undertakes most of the power output and always worksnear the resonant frequency,so always keeping at the maximum efficiency point.The proposed phase-shifted full-bridge converter in the power supply system of IPOS adopts a hybrid topology of phase-shifted full-bridge and half-bridge LLC,using the lagging arm of PSFB as the driving switching network of half-bridge LLC resonant converter.It effectively solves the problem that the lagging arm of traditional phase-shifted full-bridge converter is difficult to realize soft-switching under light load.At the same time,it improves the power transmission rate,reduces the volume of the output filter inductors,reduces the circulating current loss during the freewheeling period,and effectively improves the efficiency of the converter.The iLLC converter in the IPOS power supply system uses 2-phase full-bridge LLC resonant converter in interleaved parallel connection,which effectively reduces the input and output current ripple,thus reduces the input and output filter capacitance.The DC voltage gain of the interleaved parallel resonant tank is fine-tuned by using the technology of "switching control inductance" to dynamically adjust the magnetizing inductance of the resonant tank,thus realizing the current sharing between the parallel resonant tank of the iLLC.Experiments show that the unbalanced degree of inter-phase current is less than 4%.Aiming at the technical problems in high efficiency conversion of island high power DC special power supply,this paper presents a high efficiency resonant transformer based on the principle of impedance reflection,a realization method of dynamic regulation of magnetizing inductance,a resonant capacitor minimization resonant tank parameter design method for optimizing switching-off loss and a new multi-stage power supply scheme with maximum efficiency point tracking technique for IPOS.The theoretical analysis and experimental verification show the effectiveness of the proposed method and solution.The research results in this paper can also provide important reference for the development of other industrial or commercial high-power resonant DC-DC converter equipment. |
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