Multi-terminal VSC-HVDC Control via Segmented Droop and Master-Slave Strategies
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Solution Overview
Problem
Multi-terminal VSC-HVDC networks face challenges in controlling DC voltage distribution across multiple terminals, particularly due to limited nominal power and potential AC network faults, which complicate power balance and require advanced control strategies to ensure safe and efficient operation.
Innovation Solution
A method comprising a primary control strategy that adjusts power transit and activates 'droop' voltage control, followed by a secondary control strategy using a master/slave DC voltage approach to maintain voltage balance and reduce variations, allowing for distributed DC voltage control across multiple nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single terminal controls the DC voltage in a VSC-HVDC network, then the control strategy is simple, but the nominal power of the controlling terminal is limited and AC network faults can trigger protective equipment quickly
Solution Approach 1:
The patent divides DC voltage control into two independent layers: primary control (droop control) distributed across multiple terminals, and secondary control (master/slave) centralized at one terminal. This segmentation allows each layer to perform its specific function without overloading a single terminal, improving reliability while maintaining manageable complexity.
Solution Approach 2:
The patent introduces a communication link as an intermediary between terminals to coordinate the master/slave control strategy. This intermediary enables information exchange about voltage deviations and power flow, allowing distributed terminals to work together toward common control objectives without requiring complex direct coordination between all terminals.
2Reliability
If DC voltage control is distributed to multiple VSC terminals, then system reliability and power handling capacity improve, but control complexity increases
Solution Approach 1:
The patent segments control functions into primary (droop) and secondary (master/slave) layers, with each terminal implementing only the primary control locally and receiving secondary control adjustments through communication. This segmentation distributes control responsibilities appropriately, improving reliability without overwhelming any single terminal with excessive control complexity.
Solution Approach 2:
The patent implements dynamic control where terminals can switch between different control modes (droop control, master control, slave control) based on system conditions and disturbances. This dynamic adaptability allows the system to optimize performance and manage complexity by activating appropriate control strategies only when needed.
3Productivity
If droop control is used for primary control, then power balance is restored quickly, but voltage variations increase
Solution Approach 1:
The patent segments voltage control into two functional layers: droop control handles rapid power balance restoration (primary function), while master/slave control handles voltage regulation (secondary function). This segmentation allows each control strategy to excel at its specific task without compromising the other, achieving both fast response and voltage stability.
Solution Approach 2:
The patent ensures continuous voltage regulation by having the secondary master/slave control continuously adjust reference voltages for all terminals based on actual voltage deviations. This continuous adjustment compensates for the voltage variations introduced by droop control, maintaining overall voltage stability while preserving the fast power balance response.
4Stability of the object's composition
If master/slave control is used for secondary control, then voltage variations are reduced, but control complexity and communication requirements increase
Solution Approach 1:
The patent uses a communication link as an intermediary to simplify master/slave control implementation. The communication channel transmits essential information (voltage deviations, power flow data) between terminals, enabling coordinated voltage regulation without requiring complex direct coordination protocols between all terminals. This intermediary approach reduces control complexity while maintaining voltage stability.
Solution Approach 2:
The patent implements a universal master/slave control framework where any terminal can potentially become the master controller based on system conditions. This multi-functionality allows the system to adapt to different operating scenarios and terminal failures, reducing overall control complexity by using a standardized control architecture across all terminals rather than terminal-specific control logic.
Data Source
AI summary
The invention relates to a method for controlling a multi-terminal HVDC network, including a primary control strategy aiming to re-establish a power generation/power consumption balance, and a secondary control strategy for reducing any fluctuation in voltage resulting from the first strategy.