Triple-loop-controlled overload or short circuit current limiter and protection for three phase inverter

It´s required that power electronic equipments for power system can generate reliable and continuous power supply even in overload or short circuit occurs. Conventional dual-loop control strategy for inverter can´t satisfy with all kinds of short circuits. This paper proposes triple-loop control strategy for overload current limiter and short circuit current protection in which a current hysteretic loop is inserted into a conventional dual-loop controller. It determines whether to mask PWM drive pulse or not in order to suppress fast-rising switch current. As long as switch current goes beyond the preset upper limit threshold value of the current hysteretic loop controller which disables the PWM drive pulse immediately until switch current falls down the preset lower limit threshold value. Theoretical analysis and simulation for the triple-loop control strategy is presented. Experiment results validate the proposed control strategy based on digital control.