A Fault Clearance and Restoration Approach for MMC-Based MTDC Grid

Abstract

With the growth in continuous energy demand, high-voltage Multi-Terminal DC (MTDC) systems are technically and economically feasible to transmit bulk power and integrate additional energy sources. However, the high vulnerability of the MTDC systems to DC faults, especially pole-to-pole (P2P) faults, is technically challenging. The development of DC fault ride-through techniques such as DC circuit breakers is still challenging due to their high cost and complex operation. This paper presents the DC fault clearance and isolation method for an MMC-based MTDC grid without adopting the high-cost DC circuit breakers. Besides, a restoration sequence is proposed to re-energize the DC grid upon clearing the fault. An MMC-based four-terminal DC grid is implemented in a Control-Hardware-in-Loop (CHIL) environment based on Xilinx Virtex-7 FPGAs and Real-Time Digital Simulator (RTDS). The RTDS results show that the MTDC system satisfactorily rides through DC faults and can safely recover after DC faults.

Multiline Fault Current Limiter for DC Line Fault in Multi‐terminal DC Grids

“…However, due to the low impedance, once a dcside fault occurs, the submodule capacitors in the voltage source converters will discharge rapidly, leading to extremely fast fault current rising speed. Therefore, in order to guarantee the converter continuous operation and fault ride-through of the healthy network, the coordination operation of dc circuit breakers (DCCBs) and fault current-limiting devices is necessary [3][4][5].…”

Implementation of a Modular Distributed Fault-Tolerant Controller for MMC Applications

“…During a steady state, the insertion index for the upper and lower arm is determined in Equation ( 4) and Equation ( 5), respectively, where V x cu, l represents individual capacitor voltage in the arms. Similarly, upper (i u,x ) and lower (i l,x ) arm current can be expressed in terms of differential current and AC side current Equation (6) and Equation (7), respectively. Differential current (i z,x ) Equation ( 8) has AC and DC parts.…”