Buck变换器的输出短路火花放电能量及输出本质安全判据

为得出Buck变换器的输出本质安全判据, 基于安全火花试验装置, 对其输出短路火花放电特性进行了试验研究, 发现其放电过程可分为介质击穿、火花产生、火花维持和火花熄灭四个阶段.基于得出的火花放电特性, 对其输出短路火花放电能量进行了深入分析, 指出对于给定电感的Buck变换器, 当负载电阻 R_L小于给定电感对应的临界电阻R_LC时, 火花放电能量是关于R_L的凹函数; 而在R_L > R_LC时, 是关于R_L的凸函数.考虑到实际的参数取值范围, 进一步指出: R_L < R_LC时的火花放电能量随R_L的增加而增大, 且在R_L=R_LC时达到最大值; 而在R_L > R_LC时, 则随着R_L的增加, 先增大后减小, 在增加到特征电阻R_{L, DCM}时达到最大值. 得出了变换器在全动态范围内的最危险工况: 变换器在输入电压最高及负载电阻等于R_{L, DCM} 时工作于DCM, 此时, 短路火花放电能量达到最大值.基于能量等效, 提出了可模拟变换器输出短路放电特性的等效简单电容电路及输出本质安全判据, 仿真和试验结果验证了理论分析及所提出判据的正确性和可行性. 关键词： Buck变换器 本质安全 短路火花放电能量 输出本质安全判据

Output short-circuit spark discharging energy and output intrinsic safety criterion of Buck converters*

To obtain the output intrinsic safety criterion of Buck converters, the experimental research on its output-short circuit discharge characteristics is conducted by using the safety spark test apparatus. It is found that its spark discharge process can be divided into four stages, i.e., the dielectric-breakdown, spark-generation, spark-keeping and spark-extinguishment. According to the obtained spark discharge characteristics, the output short-circuit spark discharging energy (OSSDE) is deeply analyzed. It is indicated that the OSSDE of the Buck converter with a given inductance is a concave function of load resistance R_L when R_L is less than the critical resistance R_LC corresponding to this inductance, while that is a convex function of R_L in the case of R_L > R_LC. Considering the actual parameter range of the Buck converter, it is further pointed out that when R_L < R_LC, the OSSDE increases with the increase of R_L and reaches its maximum in the case of R_L=R_LC; when R_L > R_LC, the OSSDE first increases and then decreases with the increase of R_L and reaches its maximum in the case of R_{L, DCM}. The most dangerous operating conditions of the converter in whole dynamic range are obtained, i.e., the converter operates in DCM when the input voltage is the highest and R_L=R_{L, DCM}. Meanwhile, the maximum OSSDE is achieved. According to the energy equivalence, an output intrinsic safety criterion for Buck converter is proposed by modeling the output short-circuit discharging behaviour as a simple capacitive circuit. The theoretical analysis and proposed criterion are verified by the simulation and experimental results.
Keywords： Buck converters intrinsic safety short-circuit spark discharging energy output-intrinsic safety criterion