Design of low-voltage switch phase-sensitive protector based on STM32

To distinguish the short circuit fault overcurrent and the asynchronous motor starting overcurrent in power supply system protection, this paper described a phase-sensitive detection protector based on signal-input-capture function of the timer in STM32 chip. Through many theories, experiments and analyses, the range of the power factor used for discriminant of asynchronous motor starting was set to 0.4 similar to 0.5 in protector. The protector used the power factor as a discrimination criterion. The voltage and current sinusoidal signals were transformed to recognizable signals by the hardware, which were input to the timer and then the relevant data were gotten. At last, the data were dealt by the system task in software, gotten was the power factor of system voltage and current, which was afterwards compared with the set value to distinguish the two kinds of overcurrent. By testing, the protector measured the power factors of system accurately, which met the protection requirements.