L-LLC谐振型双向DC-DC变换器轻载优化控制策略研究

The Optimal Control Strategy for L-LLC Bi-Directional Resonant DC-DC Converter under Light Load

新型L-LLC谐振型双向DC-DC变换器具有隔离、高效等特点,采用轻载下的间歇工作模式是当前提升变换器轻载效率的一种有效手段。该文提出一种在定间歇开通时间内,通过优化该时段内的脉冲宽度来提高轻载效率的三脉冲间歇控制策略。基于时域分析,精确预测出间歇开通阶段第一个脉冲宽度,使变换器在最短时间内达到稳态最高效率点,其后两个脉冲均工作在谐振频率点上,并通过改变间歇闭锁时间以适应间歇阶段负载的变化。该间歇控制策略无需测量谐振电容电压,简化了电路,在提高变换器轻载效率的同时可使输出电压纹波最小。搭建了一台760V/380V/6kW实验样机,实验结果验证了所提三脉冲间歇控制策略的正确性和有效性。

A novel L-LLC resonant bidirectional DC-DC converter(L-LLC-BDC)has characteristics of isolation and high efficiency.The burst mode under light load is an effective way to increase the light load efficiency.In this paper,a three pulses burst mode control strategy is proposed to improve the light load efficiency by optimizing the pulse width in a fixed burst on time.Based on the precise time domain analysis,the first pulse width in the burst on time stage is accurately predicted to make the converter reach the steady-state maximum efficiency point in the shortest time.Then,the next two pulses work at the resonant frequency point.The burst off time is changed to adopt to the load change in the burst mode.This three pulses burst mode control strategy does not need to measure the resonant capacitor voltage,simplifies the circuit,improves the efficiency of light load and minimizes the output voltage ripple.A 760V/380V/6kW experimental prototype is built,the experimental results verify the correctness and effectiveness of the proposed three pulses burst mode control strategy.