DC Voltage Control for Multi-Terminal Flexible DC Transmission Systems
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Solution Overview
Problem
In multi-terminal flexible DC transmission systems, the instability of DC voltage control leads to poor reliability and availability, as existing coordinated control schemes either result in system instability when the primary control station stops or suffer from poor DC voltage control quality and potential oscillations when secondary stations take over.
Innovation Solution
A method and apparatus that enable a DC voltage secondary control station to take over and adjust active power when the primary control station loses functionality, using auxiliary control functions to maintain voltage stability, and setting thresholds for enabling these functions to ensure seamless transition and minimize oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a single-point DC voltage control scheme is used, then DC voltage stability is improved, but system reliability deteriorates when the primary control station stops running
Solution Approach 1:
The patent applies preliminary action by pre-configuring multiple potential secondary control stations and establishing their control priorities before any failure occurs. When the primary control station fails, the pre-designated secondary station can immediately take over without delay, ensuring both voltage stability and system reliability. This is implemented through priority flags and control mode settings that are prepared in advance.
Solution Approach 2:
The patent implements dynamics by making the control station roles dynamic rather than fixed. A control station can transition between primary and secondary roles based on operational status. The system dynamically adjusts control responsibilities through mode switching mechanisms that allow any station to become the primary control station if needed, thereby maintaining both voltage stability and reliability.
2Adaptability or versatility
If a multi-point DC voltage coordinated control scheme based on DC voltage droop is used, then power adjustment capability is improved, but DC voltage control quality deteriorates
Solution Approach 1:
The patent applies local quality by assigning different control functions to different stations based on their operational status and capabilities. The primary control station maintains constant DC voltage control for high precision, while secondary stations operate in constant active power control mode. This differentiated functional assignment allows the system to achieve both high voltage control quality and flexible power adjustment capability simultaneously.
Solution Approach 2:
The patent implements universality by designing control stations that can perform multiple functions. Each station is capable of both constant DC voltage control and constant active power control, switching between these modes based on whether it is the primary or secondary control station. This multi-functionality enables the system to maintain high voltage control quality while achieving versatile power adjustment capability.
3Stability of the object's composition
If a multi-point DC voltage coordinated control scheme based on DC voltage margin is used, then system stability is improved, but severe oscillation occurs when secondary station takes over
Solution Approach 1:
The patent applies preliminary action by pre-establishing the control priority relationships and operational modes of secondary stations before any failure occurs. The secondary stations are pre-configured with their priority levels and control parameters, allowing them to take over smoothly without causing severe oscillations. This pre-preparation eliminates the instability issues that occur with traditional DC voltage margin methods during takeover.
Data Source
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AI summary
The present invention discloses a direct current (DC) voltage control method, including: determining, when it is determined that a DC voltage primary control station loses a DC voltage control function, whether the DC voltage primary control station can communicate with the DC voltage secondary control station, and if yes, sending, by the DC voltage primary control station, information about the DC voltage primary control station losing the DC voltage control function to the at least one DC voltage secondary control station and enabling a DC voltage control function of one DC voltage secondary control station, so as to adjust a DC voltage; before the DC voltage control function of the DC voltage secondary control station is enabled, if the DC voltage exceeds an operation range, enabling, by the at least one DC voltage secondary control station, a DC voltage auxiliary control function, so as to adjust emitted or absorbed active power; and when the DC voltage primary control station cannot communicate with all of or some of the at least one DC voltage secondary control station, and if the DC voltage exceeds the operation range, enabling, by at least one DC voltage secondary control station, a DC voltage auxiliary control function, so as to adjust current emitted or absorbed active power, and determining, according to a policy, one DC voltage secondary control station to enable a DC voltage control function, so as to adjust the DC voltage. The present invention further discloses an apparatus for implementing the method. With the present invention, DC voltage oscillation of a system, which is caused when a DC voltage primary control station stops running, may be reduced: