Research On Dc Converter For Battery Discharge Maintenance

In the development and utilization of renewable energy,the low-voltage energy storage system with battery as the core has a wide output voltage range.The use of a large number of batteries in production life is accompanied by problems such as battery maintenance and energy recycling.In the maintenance process,after the electric energy in the battery is converted,the secondary utilization of energy can be realized,and the effect of energy saving and environmental protection is achieved.The isolated resonant DC converter represented by LLC is widely used in various power supply systems.However,when the input voltage or load range is wide,if the PFM control mode is adopted,a larger frequency adjustment range will inevitably reduce the converter efficiency.For the application of the low voltage level wide input range in the energy storage system,the resonant network of the traditional resonant converter is placed on the high voltage output side,and the voltage doubled capacitor is replaced by the resonant capacitor to form a double voltage resonant rectification structure.The output gain of the converter is adjusted by changing the duty cycle of the secondary bidirectional switch or the effective power transfer duty of the primary full bridge switching network.The advantages of the resonant converter are fully utilized while avoiding the disadvantages of the wide frequency adjustment range,and the overall efficiency is improved.Based on the analysis of the working principle of the circuit topology,the basic characteristics of the converter are obtained by the state plane method and the time domain analysis.Based on the above-mentioned topological structure applied in the low-voltage wide-range energy storage system,a high-gain isolated resonant converter with boosting link is proposed,and its resonant network is divided on both sides of the transformer.The resonant inductor in the conventional converter resonant network is placed on the high voltage side,and the resonant capacitor is placed on the low voltage side.Also a set of bidirectional switching tubes is added in the double-voltage rectifying structure on the secondary side,and constitutes a boosting link with the resonant inductor.The output gain of the converter is adjusted by changing the duty ratio of the secondary bidirectionalswitch and the switching frequency of the primary switch.While taking advantage of the high efficiency of the resonant converter,it also reduces the shortcomings of the wide frequency adjustment range.The combination of PWM and PFM control modes further improves the input range of the converter and optimizes the overall efficiency.Based on the analysis of the working principle of the circuit topology,the equivalent modeling of the converter is carried out by combining the time domain analysis method and the fundamental wave analysis method,and the steady state characteristics of the topology structure are analyzed in detail.After the time domain simulation of the above two topologies by PSIM simulation software,an experimental prototype with a power of500 W was fabricated.The experimental waveform of the prototype verified the feasibility and superiority of the two topologies.