Over-voltage protection of single phase grid connected current source inverters using a simplified passive network

Current source inverters (CSIs) feature additional attention, compared to voltage source inverters (VSIs), because of their advantages, like inherent current short-circuit proof and low output voltage THD. The major constrain for CSIs is the necessity of the DC-link current continuity. Transient over-voltage occurs in case of DC-link current interruption due to failure of IGBT/series diode/gate driver. The non-robust behaviour of IGBT at breakdown voltage makes fast over-voltage protection a must. Utilization of Varistors for CSI over-voltage protection is limited because of their flat v-i characteristics. Although active clamping techniques achieve steeper characteristics, several disadvantages are remarked like the need to install a protection circuit per each IGBT and the inability to proper operation if the IGBT is defective. Breakover diodes are also good candidate but their poor dynamic behaviour limits their application to slow rate Thyristor-based CSIs. In this paper, a simplified two-stage fast-acting passive over-voltage protection network is proposed for IGBT based CSIs. In addition to simulation, an experimental setup is implemented to validate the proposed circuit effective performance.