| This paper is conducted on the basis of the new energy power generation to study the wide input DC/DC converter.According to previous studies,the reason why LLC resonant converter is highly suitable for the unidirectional DC / DC converter is that they can realize the ZCS of the primary side switch and the ZCS of the secondary side diode in the full load range.However,resonant converter FM control is limited to use in wide input environment due to its inherent characteristics.In this paper,the operating principle of a three-level half-bridge LLC resonant converter is analyzed,the gain formula is deduced,the gain curve is drawn and the phase-shifting control suitable for the half-bridge LLC is proposed.Combined with the frequency modulation control,its input range has been enlarged.This converter has the following advantages: 1)the three-level clamping technology reduce the voltage stress of the primary switch,the converter can be applied to high-voltage input occasions;2)the primary power switch can achieve ZVS,secondary rectifier can achieve ZCS;3)overcomes the shortcoming that the traditional half-bridge LLC converter can not carry out the phase-shift control and the gain range is narrow;4)the switching between the frequency modulation control and the phase-shift control in the hybrid control is smooth,No need to set the voltage hysteresis,to avoid the output voltage of the closed-loop system oscillation in the vicinity of the modulation mode switching point,in order to ensure system stability.Secondly,by analyzing and comparing some advantages of fixed-frequency phase-shift control,variable-mode control and multi-level technology,a T-type three-level LLC resonant converter topology is proposed together with five feasible working mode.Additionally,a hybrid control strategy applied to ultra-wide input is raised in line with the five models.Switching over the switch state,the newly proposed strategy allows the power supply by independently selecting the input source or divider capacitor.Besides,choosing full bridge LLC topology or half-bridge LLC topology are also available.Meanwhile,the design requirement of 6 times gain ratio is achieved by phase shifting and frequency modulation control under the established power supply.The five models are demonstrated in detailed by analyzing the operating modals,deducing gain formula,plotting gain curve and presenting typical resonant tank current waveform and the switch driving waveform under different modes and under different loads respectively.On top of those,this article also introduces controlling and mode switch among different modes to verify the feasibility of closed-loop control in the full input and full load.The converter not only inherits the advantages of traditional LLC soft switching,high efficiency,but also greatly widens the input voltage range,taking into account the requirements of wide input and variable load,to provide a solution for efficient use of new energy sources.Finally,the simulation results of the half-bridge LLC converter are given and the feasibility of the proposed scheme is verified.,and a prototype of 100 W T-type three-level LLC resonant converter is fabricated in this paper,which can meet the wide range of input voltage 50~300V.At the same time,the main circuit and control circuit parameters design steps are given accompanying by the flow chart of the relevant procedures.The feasibility of the theoretical analysis is proved by providing the typical operating wave forms of the main devices of the converter with different modes and different loads and the variation of the frequency and the phase shift angle under different input voltage.Moreover,some suggestions for improving power and increasing power density are put forward. |
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