Current Limiter for HVDC Networks Using Inductive and Bidirectional Switch Blocks
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Solution Overview
Problem
HVDC converters in power transmission networks are vulnerable to DC side faults, leading to high fault currents that exceed their rating, causing damage and requiring costly maintenance, as conventional circuit breakers struggle with interrupting DC currents due to their inherent design limitations, especially in multi-terminal interconnection scenarios.
Innovation Solution
A current limiter comprising a first inductive element and a second electrical block with a bidirectional switch, configured to selectively limit the rate of change of current by blocking fault currents and allowing freewheeling paths, reducing peak fault currents and enabling faster fault clearance without slowing down the subsequent fall of current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC circuit breaker is designed to interrupt high fault currents with high rate of rise, then the fault current interruption capability is improved, but the size, weight, and cost of switching components increase significantly
Solution Approach 1:
A current limiter device is introduced as an intermediary component between the fault and the DC circuit breaker. This device limits the rate of rise of fault current (di/dt) and reduces peak fault current magnitude, thereby protecting the DC circuit breaker from excessive current stress without requiring oversized switching components. The current limiter acts as a protective mediator that prepares the fault current for safe interruption.
Solution Approach 2:
The current limiter performs preliminary action by limiting the fault current characteristics before the DC circuit breaker attempts to interrupt it. By pre-limiting the rate of rise and peak magnitude of fault current, the system avoids the need for the breaker to be designed for worst-case scenarios, thus reducing component size and cost while maintaining reliability.
2Loss of time
If the operating speed of a DC circuit breaker is increased to interrupt fault currents faster, then the fault clearance time is reduced, but the complexity and cost of the breaker increase
Solution Approach 1:
The current limiter serves as a mediator that reduces the stringency of the interruption task for the DC circuit breaker. By limiting the rate of rise of fault current, the current limiter creates more favorable conditions for interruption, allowing the use of simpler, slower-breaking DC circuit breakers while still achieving acceptable fault clearance times.
Solution Approach 2:
The current limiter changes the parameters of the fault current (specifically the rate of rise di/dt and peak magnitude) to more favorable values. This parameter transformation makes the fault current easier to interrupt, enabling the use of less complex circuit breaker designs that operate at lower speeds but still meet system requirements.
3Device complexity
If a conventional AC circuit breaker design is used for DC current interruption, then the design complexity is reduced, but the ability to interrupt DC current effectively is lost due to lack of natural current zeros
Solution Approach 1:
The current limiter acts as an intermediary that modifies the DC fault current characteristics to resemble AC current behavior more closely. By limiting the rate of rise and controlling the peak magnitude, the current limiter creates conditions under which DC current interruption becomes more manageable, bridging the gap between simple AC breaker designs and the requirements for DC current interruption.
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
The current limiter reduces the required current interruption capability of DC circuit breakers, saving on size, weight, and cost, while enabling faster fault clearance and reducing energy dissipation, making it compatible with various DC electrical network configurations.
Implementation Method 1
the inductive element to slow down the rate of rise of current
Implementation Method 2
the bidirectional switch is switchable to a first mode to permit current flow through the second electrical block in a first current direction and at the same time inhibit current flow through the second electrical block in a second current direction
Data Source
Figure 1~2
Figure 3~4a
Figure 4b~5
AI summary
There is a current limiter (10) for selectively limiting a rate of change of current in a DC electrical network. The current limiter (10) comprises: a first electrical block including an inductive element (24); and a second electrical block including a bidirectional switch (26), the first electrical block being connected in parallel with the second electrical block between first and second terminals (12,14), the first and second terminals (12,14) being connectable to the DC electrical network, wherein the bidirectional switch (26) is switchable to a first mode to permit current flow through the second electrical block in a first current direction and at the same time inhibit current flow through the second electrical block in a second current direction, the first and second current directions being opposite to each other, and the bidirectional switch (26) is switchable to a second mode to permit current flow through the second electrical block in the second current direction and at the same time inhibit current flow through the second electrical block in the first current direction.