Gong-kuang zidonghua (Feb 2021)
Design of high-power intrinsically safe power supply based on fault current change rate
Abstract
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 65 μJ, which meets the design requirements.
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