Improved software current-limiting protection strategy for starting the high-power motor

The current is limited within a certain range with poor waveforms by fast response of hardware current limiting. The current limiting with software can produce good waveforms. The emphasis is the switch between the voltage loop and the current. In order to switch smoothly without shock waves, the traditional method is used to switch into the current loop, when current exceeds the upper limit point of the threshold. It switches into the voltage loop when the voltage rises to the rated value. However, for starting the high-power motor, it is necessary to set a high threshold of the current entering the current loop. Nevertheless, for the reliable protection of breakdown, such as short circuit, the value of threshold is expected to be small. To solve the contradiction, a method of relying on their own characteristics to enter current loop is presented in this paper. The contrastive experiments are made on the 400 KVA/50 HZ experimental machines. The experimental results show that the method presented in this paper can not only limit reliably current for the instantaneous impact, but also escape going into the current loop at the moment of starting the high-power motor. The desirable effects are achieved.