DC Line Current Interruption via Zero Setpoint Control
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Solution Overview
Problem
Existing methods for interrupting current in a DC voltage line during faults, such as thermal breakdown or flashover, require expensive switching devices with high breaking currents and struggle with accurately regulating mesh currents in meshed DC voltage networks, leading to costly operations and potential re-ignition of arcs.
Innovation Solution
The method involves temporarily setting the current and voltage setpoints to zero with time-varying periodic signals to dampen oscillations, allowing the use of less expensive switching devices and effectively de-energizing the faulty DC voltage line, thereby reducing operational costs and minimizing arc re-ignition risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the converter current is regulated to a small non-zero setpoint (0.1 or 0.2 of normal operation) during fault, then the current is limited to approximately 4 kA, but switching devices with such high breaking current capability are expensive to manufacture and operate
Solution Approach 1:
The converter proactively regulates current to zero setpoint before the fault current can build up to dangerous levels, preventing the need for expensive high-breaking-current switching devices. This preliminary action of setting current to zero eliminates the requirement for costly 4kA switching equipment.
Solution Approach 2:
The invention changes the current setpoint parameter from a small non-zero value (0.1-0.2 of normal) to exactly zero during fault conditions. This parameter change fundamentally alters the fault current profile, reducing it from approximately 4kA to near-zero levels, thereby enabling the use of inexpensive switching devices.
2Reliability
If the converter acts as an open end to limit current during fault, then current is restricted, but this causes undamped current and voltage oscillations with high amplitudes (voltages up to twice nominal voltage) in the DC voltage line
Solution Approach 1:
The invention converts the harmful oscillations caused by the open-end configuration into a beneficial damping effect. By regulating current to zero setpoint, the converter transforms the oscillation problem into a controlled energy dissipation process, where the oscillations naturally decay without reaching dangerous amplitudes.
Solution Approach 2:
The converter acts as an intermediary element between the fault location and the rest of the DC network. By maintaining zero current setpoint, it mediates the oscillation energy, preventing it from propagating with high amplitude through the DC voltage line while still providing current limiting protection.
3Ease of operation
If switching devices are used to disconnect the DC voltage line during fault, then the line can be isolated, but the decay time of oscillations can be up to one second causing potential re-ignition of arcs
Solution Approach 1:
The converter performs preliminary current suppression by maintaining zero setpoint before disconnection occurs. This preliminary action reduces oscillation amplitudes to minimal levels, ensuring that when switching devices disconnect the line, arc re-ignition risk is eliminated even if disconnection takes up to one second.
Solution Approach 2:
The zero current setpoint regulation provides beforehand cushioning against the potential harm of arc re-ignition. By proactively suppressing oscillations to minimal amplitudes before disconnection, the system cushions against the risk that would otherwise exist during the up-to-one-second decay period.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively dampens current oscillations, allows the use of cost-effective switching devices, and shortens the time to reconnection, reducing adverse effects on AC voltage networks and lowering overall operating costs.
Implementation Method 1
a counter-voltage generated by the converter Current in the DC voltage line is limited
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The invention relates to a method for interrupting an electric current in a DC line (2) connected to a DC connection of an inverter (6), in which, in the event of a DC line fault, an inverter current on the DC side is controlled to a current set point which is lower than a current set point in normal operation, and/or an inverter voltage on the DC side is controlled to a voltage set point which is lower than a voltage set point in normal operation. The invention is characterized in that the predefined current set point is at least temporarily set equal to zero and/or the voltage set point is temporarily is set to zero. The invention further relates to an application of the method in a DC network.