A Switch Partial Turned OFF Cycle by Cycle Current Limiting Method for 3L-NPC Half-Bridge Inverters

Instantaneous hardware protection is a very important method to protect inverters at the moment of over current or short circuit fault. For standalone inverters, the hardware protection can also be modified to achieve current limiting during the over current or short-circuit period. In conventional cycle by cycle (CBC) current protection, all switches of the inverter are turned OFF immediately when current is higher than the over current threshold. However, it may lead to protection being triggered frequently and high di/dt in switches and diodes, which will do harm to the reliability of the inverter. To solve this issue, a new CBC current limiting method is proposed, which turns off partial switches of the inverter. The operation principle of the conventional method and the presented method are detailed analyzed with switching states and implementation circuits given. In addition, the presented method is verified by an engineering prototype, and experimental results verified the effectiveness of the proposed method.