HVDC Frequency Coordination Using VSC Sync and LCC Limit Control
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Solution Overview
Problem
The asynchronous interconnection of the Yunnan power grid with the China Southern Power Grid faces challenges in frequency stability due to high-capacity units, low load levels, and DC faults, leading to significant frequency excursions and instability.
Innovation Solution
A dynamic frequency coordination control method integrating frequency synchronous control in VSC-HVDC with bilateral frequency limit control in LCC-HVDC, utilizing VSC-HVDC to stabilize grid frequency initially, activating LCC-HVDC for power adjustment when limits are exceeded, and providing additional reactive power to regulate voltage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If asynchronous interconnection is implemented between Yunnan power grid and main grid, then DC fault isolation is achieved, but frequency stability deteriorates due to high-capacity units and low load levels
Solution Approach 1:
The patent combines VSC-HVDC frequency synchronous control with LCC-HVDC bilateral frequency limit control into a unified coordination control system. This merging allows the two different control mechanisms to work together synergistically, where VSC provides fast frequency response and LCC provides bilateral frequency support, thereby maintaining frequency stability while preserving DC fault isolation capability.
Solution Approach 2:
The patent dynamically adjusts control parameters based on system conditions. The frequency synchronous control in VSC-HVDC continuously monitors frequency deviations and adjusts power transmission in real-time. Additionally, the bilateral frequency limit control in LCC-HVDC adapts its activation thresholds and control gains according to system frequency states, enabling flexible response to varying load conditions and frequency disturbances.
2Stability of the object's composition
If VSC-HVDC frequency synchronous control is activated to stabilize grid frequency, then frequency stability improves, but device complexity increases due to coordination control requirements
Solution Approach 1:
The patent segments the frequency control function into two distinct but coordinated parts: VSC-HVDC frequency synchronous control and LCC-HVDC bilateral frequency limit control. Each segment has its own control algorithm and activation criteria. This segmentation allows independent optimization of each control mechanism while reducing the overall complexity through modular design, where each module can be implemented and tuned separately.
Solution Approach 2:
The patent introduces a coordination control mechanism that acts as an intermediary between VSC-HVDC and LCC-HVDC control systems. This intermediary layer receives frequency deviation signals, determines the appropriate control action, and coordinates the power adjustments between the two HVDC systems. By centralizing the coordination logic, the system manages complexity while achieving synergistic frequency stabilization.
3Stability of the object's composition
If LCC-HVDC bilateral frequency limit control is activated when power adjustment exceeds limits, then frequency support is enhanced, but reactive power requirements increase affecting voltage stability
Solution Approach 1:
The patent implements feedback control by continuously monitoring system frequency, power adjustments, and voltage levels. The bilateral frequency limit control in LCC-HVDC uses frequency deviation feedback to activate or deactivate based on whether power adjustments exceed predefined limits. Additionally, voltage feedback is used to monitor the impact of reactive power consumption, allowing the system to adjust reactive power compensation dynamically to maintain voltage stability while providing frequency support.
Data Source
AI summary
A dynamic frequency coordination control method combining frequency synchronous control in VSC-HVDC and bilateral FLC in LCC-HVDC includes: when a disturbance occurs in a system, the frequency synchronous control in VSC-HVDC is preferentially used to stabilize a grid frequency, and a power adjustment output by the frequency synchronous control in VSC-HVDC is taken as an activation criterion for the bilateral FLC control in LCC-HVDC; when the power adjustment exceeds a preset limiting range and a system frequency deviation exceeds a control dead zone of the bilateral FLC control in LCC-HVDC, the bilateral FLC control in LCC-HVDC is used to determine and output the power adjustment for LCC-HVDC; based on the power adjustment for LCC-HVDC, an additional reactive power control of VSC-HVDC is utilized to provide additional reactive power to LCC-HVDC to regulate a voltage stability of a grid.