基于故障电流变化率的大功率本安电源设计

针对现有本安电源存在的输出功率小、保护效果差、动态响应速度慢等问题,设计了一种基于故障电流变化率的大功率本安电源。将本安电源等效为电势电容(EC)电路,分析了EC电路短路故障特性:短路初始阶段火花放电电流迅速上升,电流变化率会发生突变。通过检测短路故障后电路中故障电流变化率的值,可以提前预知故障状态,在故障电流达到传统电流保护方法所设置的保护阈值之前便触发保护功能,并在短路故障的初始阶段切断输出回路,提高本安电源的输出功率。大功率本安电源包括开关电源和本安保护电路2个部分:开关电源采用反激变换结构,其控制电路以UC3842为核心,反馈电路以光耦与三端稳压器TL431为核心;本安保护电路基于故障电流变化率来限制火花放电的能量,主要包括故障检测电路、比较电路、自恢复电路、软启动电路、驱动电路。本安电源样机性能测试结果表明,交流输入电压在90~265 V波动时,本安电源功率因数不小于0.96,输出直流电压纹波在20 mV以内,电源效率在85%以上。短路实验结果表明,本安电源在发生短路故障后的瞬态输出能量为65μJ,满足设计要求。

Design of high-power intrinsically safe power supply based on fault current change rate

In order to solve the problems of low output power,poor protection effect,and slow dynamic response speed of existing intrinsically safe power supply,a high-power intrinsically safe power supply based on fault current change rate is designed.The intrinsically safe power supply is equivalent to an EC circuit,and the short-circuit fault characteristics of the EC circuit are analyzed as follows:the spark discharge current rises rapidly at the initial stage of the short-circuit,and the current change rate changes suddenly.By detecting the value of change rate of the fault current in the circuit after a short-circuit fault,it is able to predict the fault state in advance,trigger the protection function before the fault current reaching the protection threshold set by the conventional current protection method,and cut off the output circuit at the initial stage of the short-circuit fault so as to increase the output power of the intrinsically safe power supply.The high power intrinsically safe power supply includes 2 parts:the switching power supply and the intrinsically safe protection circuit.The switching power supply adopts flyback converter structure.The core of the control circuit is UC3842,and the core of the feedback circuit is optocoupler and three-terminal regulator TL431.The intrinsically safe protection circuit limits the energy of spark discharge according to the change rate of the fault current,and mainly includes a fault detection circuit,a comparison circuit,a self-recovery circuit,a soft start circuit and a drive circuit.The performance test results of the intrinsically safe power supply prototype show that the power factor of the intrinsically safe power supply is not less than 0.96 when the AC input voltage fluctuating in the range of 90 to 265 V,the output DC voltage ripple is within 20 mV,and the efficiency of the power supply is above 85%.The short-circuit test results show that the transient output energy of the intrinsically safe power supply after a short-circuit fault is 65μJ,which meets the design requirements.