A Novel Commutation Failure Mitigation Method Based on Transformer-Side Magnetic Coupling Injection

To mitigate the commutation failure (CF), the topology of the line-commutated converter high-voltage direct current (LCC-HVDC) needs to be modified. However, the power loss and capital cost of the modification schemes proposed in the existing literature are relatively high. A novel commutation failure mitigation method based on transformer-side magnetic coupling injection (TMCI) module is proposed in this paper. The topology and working principle of the TMCI module are presented. Considering the CF prediction and turn-off time of the thyristor, the control strategy of the TMCI module is designed. For the TMCI module, the voltage of the capacitor and voltage-current stress of thyristors are analysed, and the method to select parameters is designed. Then, a test system with the TMCI module is developed based on the CIGRE HVDC benchmark model. The simulation results show that the TMCI module can effectively mitigate CFs under AC fault conditions. Furthermore, compared with the enhanced capacitor commutated converter (ECCC) and the evolutional line-commutated converter (ELCC) proposed in the existing literature, the TMCI module can not only offer the best CF immunity with the least capital cost, but also has lower steady-state active power losses and less impact on the system reliability.