Renewable Sending-End Grid Backup Support for VSC-HVDC Blocking
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Solution Overview
Problem
The 100%-renewable energy sending-end grid lacks effective backup voltage and frequency support, particularly during bipolar blocking events in the VSC-HVDC station, leading to potential shutdowns and instability due to the absence of synchronous machines for energy balancing.
Innovation Solution
A backup voltage and frequency support method involving the selection of support nodes, mounting energy-storage modular multilevel converters (MMC) with dynamic active power adjustment based on grid-frequency, using power-synchronization control strategies to manage active and reactive power, and employing energy storage devices like batteries or supercapacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If only the VSC-HVDC station at the transmission end adopts grid-following control, then the renewable energy source can be operated in a conventional grid-following control mode, but voltage and frequency of the entire 100%-renewable energy sending-end grid are merely supported by the VSC-HVDC station, and when the DC system is faulty and leads to bipolar blocking of the VSC-HVDC station at the sending end, the 100%-renewable energy sending-end grid will lose the voltage and frequency support, thus fails to operate
Solution Approach 1:
The patent applies preliminary action by pre-configuring energy storage devices at multiple support nodes within the renewable energy grid. These devices are prepared in advance to provide voltage and frequency support when the VSC-HVDC station experiences bipolar blocking. The control system is pre-programmed to detect faults and automatically activate the backup support mechanism, ensuring continuous grid operation without shutdown.
Solution Approach 2:
The patent introduces energy storage devices as intermediary elements between the renewable energy sources and the VSC-HVDC transmission system. These intermediaries provide local voltage and frequency support at multiple nodes, reducing the dependency on the central VSC-HVDC station. The energy storage devices act as buffer mediators that can independently maintain grid stability during transmission faults.
2Reliability
If the VSC-HVDC station at the transmission end experiences bipolar blocking, then the DC transmission system fails, but the 100%-renewable energy sending-end grid has no backup support and will lose voltage and frequency support, leading to shutdown
Solution Approach 1:
The patent segments the voltage and frequency support function across multiple independent nodes within the renewable energy grid, rather than relying on a single central VSC-HVDC station. Each support node is equipped with energy storage devices that can independently provide local support. This segmentation ensures that a fault at one location does not cause complete grid shutdown, as other nodes continue to provide support.
Solution Approach 2:
The patent implements beforehand cushioning by pre-deploying energy storage devices at multiple support nodes to cushion against the impact of VSC-HVDC station failures. These devices are positioned in advance to absorb the shock of bipolar blocking events and maintain voltage and frequency stability during transient faults, preventing grid shutdown.
3Device complexity
If synchronous machines are absent in the 100%-renewable energy sending-end grid, then the grid structure is simplified, but transient energy cannot be balanced by rotating equipment, and once bipolar blocking occurs in the VSC-HVDC station, transient energy leads to significant power increase, affecting electrical equipment safety
Solution Approach 1:
The patent replaces the mechanical energy balancing function of synchronous machines with electrical energy storage devices. Instead of using rotating inertia to absorb transient energy, the system employs battery or supercapacitor-based energy storage devices that can rapidly absorb or release electrical energy. This substitution maintains grid simplicity while effectively managing transient energy during VSC-HVDC station faults.
Solution Approach 2:
The patent changes the physical parameters of the energy storage system by using devices with different response characteristics (batteries for longer-term storage, supercapacitors for rapid response). The control system dynamically adjusts the charge/discharge parameters of these devices based on grid conditions, enabling them to effectively balance transient energy without requiring synchronous machines.
Data Source
AI summary
A backup voltage and frequency support method for a 100%-renewable energy sending-end grid, including: (S1) selecting a plurality of support nodes in the 100%-renewable energy sending-end grid; (S2) mounting a backup voltage and frequency support device at each support node; and (S3) dynamically adjusting an active power output of a renewable energy station of the 100%-renewable energy sending-end grid according to a frequency of a grid-connection point.