Switching Valve Shutdown Control for HVDC Voltage Overshoot
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Solution Overview
Problem
In high voltage direct current (HVDC) transmission networks, existing switching valves face challenges in safely shutting down to prevent transient voltage overshoots that could lead to insulation failures and equipment damage when multiple modules are blocked simultaneously.
Innovation Solution
A switching valve with multiple modules, each containing switching elements and energy storage devices, uses a controller to detect fault conditions and send blocking signals, with each module determining a random or quasi-random delay before switching into a non-conducting state, thereby staggering the shutdown to avoid simultaneous blocking and reduce transient voltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If all modules are blocked simultaneously to achieve rapid shutdown, then shutdown speed is improved, but transient voltage overshoot increases causing insulation failure risk
Solution Approach 1:
The shutdown process is segmented into multiple stages by dividing modules into groups. Each group is blocked sequentially rather than simultaneously, with delay periods between groups. This segmentation reduces the transient voltage overshoot while maintaining adequate shutdown speed by controlling the rate at which modules are blocked.
Solution Approach 2:
The blocking operation is performed periodically across different module groups with specified delay periods between groups. This periodic action allows transient voltages to settle between blocking events, preventing cumulative overshoot effects while achieving complete shutdown within an acceptable time frame.
2Object-affected harmful factors
If modules are blocked sequentially with delays to reduce transient voltage, then transient voltage control is improved, but shutdown time increases
Solution Approach 1:
Not all modules need to be blocked with equal delay periods. The invention applies partial action by blocking critical modules faster while applying larger delays to non-critical modules. This approach achieves adequate transient voltage control while minimizing the overall shutdown time by prioritizing which modules are blocked when.
3Reliability
If larger clearance distances are provided to prevent insulation failure, then insulation reliability is improved, but device compactness deteriorates
Solution Approach 1:
The control system prepares for potential transient voltage overshoots by implementing preemptive control measures through coordinated module blocking sequences. This beforehand cushioning reduces the magnitude of voltage overshoots, thereby reducing the required clearance distances and allowing for more compact device design while maintaining insulation reliability.
Data Source
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AI summary
A switching valve for a voltage source converter (20), the switching valve comprising a plurality of modules (44), each module (44) including one or more switching elements (46) and at least one energy storage device (48), the or each switching element (46) and the or each energy storage device (48) in each module (44) arranged to be combinable to selectively provide a voltage source, the switching valve including a controller (50) programmed to selectively control the switching of the switching elements (46) to select one or more of the modules (44) to contribute a or a respective voltage to a switching valve voltage, wherein the controller (50) is configured to: detect a fault condition; in response to detecting the fault condition, simultaneously provide blocking signals to each module (44); and wherein each respective module (44) of the plurality of modules (44) is configured to: receive a respective one of the blocking signals; in response to receiving the respective blocking signal, determine a respective random or quasi-random delay period; after a time interval equal to the respective random or quasi-random delay period, switch the one or more switching elements of the respective module into a non-conducting state.