Firing thyristors with negative firing angle using multilevel current reinjection concept: an experimental evaluation

Thyristor based multilevel current reinjection (MLCR) current source converter (CSC) provides self-commutation capability to thyristors. It also has high quality line current waveform by accurately shaping the DC bus current using an auxiliary reinjection bridge. However the theoretical and PSCAD/ETDC simulation analysis do not take into account the inevitable stray capacitances and inductances which may influence the thyristor turnon/off and the simulation switching model may not represent the switching characteristics of the main bridge thyristors fully or accurately. Questions have been raised about the ability to achieve self-commutation with thyristors and the possibility of operating thyristors with negative firing angles. Therefore, it is necessary to experimentally verify whether neglecting the realworld artefacts actually impedes the performance of thyristor based MLCR CSC. The experimental results presented in this paper prove that the auxiliary reinjection circuit can force the thyristor to commutate independently from their respective line-to-line voltages and thyristor converter can operate with a negative firing angle