HVDC Interconnection Control for Safe Switch Disconnection
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Solution Overview
Problem
Existing high voltage direct current (HVDC) power transmission networks require converters at each AC-DC interface, necessitating costly current interruption capabilities and inflexible control methodologies, especially in offshore power converters.
Innovation Solution
A multi-terminal power transmission network with supplementary controllers that modify DC voltage references based on local current measurements, allowing for high-fidelity control of DC current and enabling the use of regular interconnector switches without current interruption, accommodating various power converter types and control methodologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If regular interconnector switches are used without current interruption capability, then device complexity and cost are reduced, but the ability to safely disconnect under DC current flow is compromised
Solution Approach 1:
The supplementary controller preemptively modifies the DC voltage reference before the interconnector switch is opened, driving the DC current to zero in advance. This preliminary action ensures that when the switch opens, no harmful DC current flows through it, enabling the use of simple regular switches without current interruption capability while maintaining disconnection safety
Solution Approach 2:
The invention changes the DC voltage reference parameter dynamically based on the switching state. When disconnection is required, the supplementary controller modifies the DC voltage reference to drive DC current to zero, enabling safe operation of regular switches. This parameter change resolves the contradiction by adapting the electrical parameters to match the capabilities of simpler switch equipment
2Reliability
If DC current is driven to zero before switch disconnection, then switch safety is improved, but power transmission continuity is compromised
Solution Approach 1:
The control function is segmented between the converter controller and the supplementary controller. The converter controller maintains overall power transmission, while the supplementary controller handles the specific task of driving DC current to zero during switching events. This segmentation allows safe disconnection without requiring complete system shutdown, maintaining power transmission continuity through coordinated control
Solution Approach 2:
The supplementary controller acts as an intermediary between the converter controller and the power transmission system. It mediates the transition by modifying the DC voltage reference to drive current to zero, enabling safe switch operation while the converter controller maintains overall power flow. This intermediary function resolves the contradiction by providing a controlled transition path
3Device complexity
If AC current reference changes are avoided, then control complexity is reduced, but the ability to manage DC current during switching is limited
Solution Approach 1:
The DC current control function is extracted from the AC current reference control and handled separately by the supplementary controller. The supplementary controller directly modifies the DC voltage reference to drive DC current to zero, independent of AC current reference changes. This extraction simplifies the overall control by separating DC and AC control functions, making switching operations easier while reducing control complexity
Data Source
AI summary
A multi-terminal power transmission network includes first and second DC terminals that are interconnected by a first transmission conduit to permit the transfer of power. The first DC terminal is connected with an interconnection conduit and is separately connected with a first power converter. The first power converter interconnects the first DC terminal with a first AC network element and includes a first converter controller. The second DC terminal is interconnected with a second AC network element by a second power converter which includes a second converter controller. The first power converter further includes a supplementary controller to selectively modify the first DC voltage reference that the first power converter is required to provide so as to drive the DC current flowing in the interconnection conduit below a predetermined threshold and facilitate disconnection of the interconnection conduit from the first DC terminal via opening of the first interconnector switch.