Analysis of Traveling Wavefront Information and Wavefront Protection for Power Electronic Device-Interfaced AC System

The power electronic device-interfaced ac system becomes an important scene of renewable energy power system. The response of the power-electronic devices confronting faults is restricted by their overcurrent withstand capability, showing weak-feed characteristic. Therefore, the sensitivity of protection can be ensured only when the fault can be located before fault ride through of power-electronic device. In this article, the expression of fault traveling wavefront is derived first and it is pointed out that the expression contains two terms, which are power frequency sine term and exponential decay term. The index of the exponential decay term is only determined by fault distance, whereas the fault occurrence time, fault type, and fault impedance only influence amplitudes of the two terms. In this way, the fault distance and fault severity can be characterized by index and amplitude coefficients respectively and thereby be decoupled. On this basis, an algorithm is proposed to extract fault distance and fault severity information from wavefront, then a novel protection principle is proposed using fault distance information contained in wavefront. The proposed wavefront protection can fast locate faults and have higher sensitivity and reliability compared with the existing non-unit protections, which is verified by numerous simulations and experimental tests.