Impedance Phase Based Active Injection Protection for Radial VSC-HVDC Grid

Abstract

Effective DC fault identification is very important for a half-bridge modular multi-level converter (HB-MMC) based high voltage direct current (HVDC) grid. The performance of the traditional protection principles lacks reliability and sensitivity, and there is a further limitation under the current limiting strategies. To address the problem, a scheme coordinating the control and protection is proposed, which actively creates the known feature for fault identification and limits the fault current at the same time. In this paper, the characteristics of the input impedance phase under different faults are analyzed in various frequency bands. Based on the analysis of the input impedance phase, the converter switches the control mode and generates a characteristic signal at a particular frequency after fault detection. Then, the Prony algorithm is employed to acquire the phase information at the injection frequency. Finally, the faulty zone can be identified by the value of the input impedance phase. This active injection protection scheme is applicable to identify different faults, verified in PSCAD/EMTDC, and tested by hardware-in-the-loop simulation in RTDS.