Abstract:The commonly used short circuit protection strategy is to combine the constant voltage mode (CVM) in normal situation and the constant current control mode (CCM) in abnormal situation. However, the output characteristics discrepancy and different control parameters cause the time variance retreating from CCM to CVM for the parallel inverters, which results in differences in voltage and large circulating currents. It easily causes power flooding inversely, pumping of DC voltage, and over-voltage protection in light load, which can not satisfy the non-stop requirements during short circuit. The proposed strategy of retreating from CCM in terms of the average voltage and instantaneous current is introduced in this paper. It states that several parallel inverters retreat simultaneously from CCM and enter CVM at the rising edge(or failing edge) of synchronous signal. The initial voltage is increased to reduce the recovery time from CCM, when the short circuit is disappeared. The compensation of the experimental results on two 400kVA/50HZ inverters verifies the effectiveness of the proposed strategy.
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