An improved area-minimum control using zero-sequence components and current deviation term

In the synchronous firing control system of the line commutated converter (LCC) HVDC project, the Area-Minimum (AMIN) control is responsible for real-time calculation of the commutation margin of each converter valve. If AMIN control detects that the commutation margin of a converter valve falls below the minimum threshold during AC faults, the converter valve will be fired immediately to prevent commutation failure. However, the existing AMIN control faces several issues such as slow response time, inaccurate calculations, and a negative impedance characteristic that can negatively impact the steady operation of the HVDC project. Therefore, this paper proposes an improved AMIN control using zero-sequence components and a current deviation term that provides quick and accurate calculations of the commutation margin by utilizing the zero-sequence component of three-phase voltages and considering the DC current changes during commutation. Additionally, employing the current deviation term helps to enhance the performance of the LCC-HVDC's control system. Our simulations show that the proposed improved AMIN control significantly enhances the first commutation failure immunity and lowers the probability of subsequent commutation failures, which would ultimately benefit the restoration of the LCC-HVDC project.