VSC Fault Clearance via DC Circuit Interruption
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Solution Overview
Problem
Voltage source converters (VSCs) interconnecting DC and AC networks face challenges in fault clearance due to high fault currents and the inability to limit current, leading to potential AC undervoltage or overvoltage issues, which can cause cascade tripping and disrupt network stability.
Innovation Solution
A method involving primary and back-up protection sequences, where DC circuit interruption devices are opened to disconnect the VSC from the DC network, allowing fault clearance while maintaining reactive power exchange with the AC network, and automatic re-closing to re-energize the DC network, ensuring continuous operation and preventing AC voltage instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the VSC continues to supply current to the DC network during a fault, then the fault current increases, but the VSC cannot limit the current and AC voltage instability occurs
Solution Approach 1:
The patent extracts the VSC from the DC network by opening the DC circuit interruption device during a fault condition. This isolation removes the VSC from the fault current path, preventing the harmful effect of high fault current while maintaining system reliability through automated protection sequences
Solution Approach 2:
The patent implements preliminary protective actions by detecting faults and automatically executing protection sequences before the fault can cause damage. The system preliminarily opens the DC circuit interruption device and adjusts reactive power exchange to prevent AC voltage instability before it occurs
2Reliability
If the DC circuit interruption device is opened to clear the fault, then the fault is cleared, but the DC network loses power supply
Solution Approach 1:
The patent implements periodic action through automated re-closing sequences. After opening the DC circuit interruption device to clear the fault, the system waits for a predetermined time, then automatically attempts to re-close the device to restore power transmission. This periodic open-close action ensures both fault clearance and productivity recovery
Solution Approach 2:
The system performs self-service through automated protection and re-closing sequences without requiring manual intervention. The VSC controller automatically detects faults, opens the DC circuit interruption device, waits for fault clearance, and re-closes the device to restore power transmission, maintaining both reliability and productivity
3Reliability
If the VSC is disconnected from the AC network during fault clearance, then the fault is cleared, but the VSC cannot exchange reactive power and AC voltage instability occurs
Solution Approach 1:
The patent applies segmentation by separating the DC network isolation from AC network connection. The DC circuit interruption device opens to disconnect the VSC from the DC network for fault clearance, while the AC circuit interruption device remains closed to maintain AC network connection. This segmented approach allows simultaneous fault clearance and reactive power exchange
Solution Approach 2:
The VSC acts as an intermediary between the DC and AC networks. During fault clearance, the VSC remains connected to the AC network to exchange reactive power and maintain voltage stability, while simultaneously being isolated from the DC network through the DC circuit interruption device. This intermediary role resolves the contradiction between fault clearance and voltage stability
Data Source
AI summary
There is a method of fault clearance for a voltage source converter that interconnects a DC network and an AC network. The voltage source converter is connected to the DC network via one or more DC circuit interruption devices. The method comprises the steps of: (a) detecting a fault in the DC network; (b) carrying out a primary protection sequence, wherein the step of carrying out the primary protection sequence involves carrying out a first sub-sequence that includes the steps of: i. opening the or each DC circuit interruption device, ii. setting a DC power order of the voltage source converter to zero, iii. controlling the voltage source converter to exchange re-circuit breaker active power with the AC network.