HVDC Converter Station Fault Control via Transient Power Modulation
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Solution Overview
Problem
High voltage direct current (HVDC) networks face challenges in maintaining transient stability and feasibility due to rapid propagation of short-circuits, which can exceed the breaking capacity of circuit breakers and damage power electronics, especially in multipoint transmission systems where traditional sectioning methods are ineffective.
Innovation Solution
A control method for HVDC networks involving converter stations with MMC converters, where each station can modulate power and maintain nominal voltage, allowing for increased transient power exchange on healthy poles to compensate for faults, thereby minimizing the impact on AC system stability and preventing fault propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If ultra-fast hybrid direct current circuit breakers are positioned at each end of the lines to isolate faulty lines quickly, then fault isolation time is reduced, but device complexity and cost increase significantly
Solution Approach 1:
The patent introduces a current limiting coil as an intermediary device placed in series with the HVDC line. This coil acts as a mediator that limits the rate of current increase during faults, allowing conventional circuit breakers to operate effectively without requiring ultra-fast hybrid breakers. The coil enables fault isolation while maintaining compatibility with simpler, more cost-effective switching devices.
2Reliability
If current limiting coils are placed at each end of HVDC lines to limit current increase rate, then IGBT blocking is prevented, but significant energy losses and increased device size occur
Solution Approach 1:
The patent applies current limiting coils only at specific locations (ends of HVDC lines) rather than throughout the entire network. This partial application provides sufficient protection for converter stations while minimizing total energy losses and device quantity. The coils are positioned strategically to protect the most vulnerable components without over-engineering the entire system.
3Reliability
If the number of operational lines is reduced from N to N-k during fault isolation, then faulty line isolation is achieved, but transient stability of AC systems deteriorates
Solution Approach 1:
The patent implements preliminary control actions on AC/DC converters before and during fault isolation. These pre-coordinated control actions prepare the system to maintain power balance and voltage levels when lines are taken offline, preventing transient stability deterioration. The control strategy is pre-configured to activate automatically during fault conditions.
4Ease of operation
If sectioning is performed using converters at line ends in point-to-point transmission, then simple breaking is achieved, but sectioning capability is lost in multipoint transmission networks
Solution Approach 1:
The patent divides the HVDC network into multiple independently controllable segments by implementing fast control capabilities at each converter station and node. This segmentation allows any line or section to be isolated independently in multipoint networks, providing sectioning capability comparable to point-to-point systems while maintaining adaptability to various network topologies and configurations.
Data Source
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AI summary
The invention relates to a method for controlling a high-voltage direct-current network (1) comprising: - high-voltage power lines (121, 123, 131, 133, 231, 233); - first to third conversion stations (11, 12, 13) each comprising: - a direct-current network interface comprising first and second poles (141, 142, 143); - at least two AC/DC converters (101, 102) connected between the alternating-current network interface and the direct-current network interface; - a control device (15) accessing a database storing a maximum intensity value at the nominal voltage and the corresponding growth time for each of the converters; - the control device determines an increased power to be exchanged for compensation on the second pole of the stations in the event of a fault on one of the high-voltage lines connected to the first pole based on the defective pole and based on the values stored in the database.