Optimized algorithm of active injection circuit to calibrate DC circuit breaker

Abstract

The widely acknowledged high-voltage direct current (HVDC) technology has now been accepted as a solution of connecting renewable energy sources. However, this technology is vulnerable when facing DC-side faults; due to the low DC impedance, the fault current can rise to an extremely high value in a short time. In addition, when building a multi-terminal DC (MTDC) system, the fault can make a worse failure or blackout of the system when it is not cleared or isolated in time. The urgent need to ensure reliable mentioned HVDC power system can be realized by making use of DC circuit breaker (DCCB). The vacuum CB, which is one division of active DCCBs, has its own operational limit; it can interrupt fault currents when the di/dt of injected current is lower than a critical value, otherwise the arc may reignite. Therefore, the designing and testing of a DCCB must consider this feature. On the other hand, because of the complex configuration of an MTDC system, one DC-side fault can result in different fault currents at faulty line’s terminals; thus, the DCCB needs to be calibrated based on its local fault information. This paper presents an algorithm to optimize the DCCB according to its critical di/dt and local fault current. Furthermore, the operational delay and chopping current of circuit breaker are also considered and modelled. The simulation results from PSCAD platform verify the effectiveness of the presented algorithm.