Switching Valve Module Selection for Thermal Stress Reduction
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Solution Overview
Problem
Conventional module selection processes in voltage source converters for HVDC transmission lead to switching frequency imbalances, causing increased thermal stress, reduced reliability, and shorter lifetimes due to higher commutation losses in modules with lower numerical addresses.
Innovation Solution
A controller is configured to change the order of selecting voltage contributing modules based on their assigned addresses in the address queue between different sampling events, optimizing the module selection process to balance switching frequencies without additional hardware modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If modules are selected in increasing order of their assigned addresses in the address queue for each sampling event, then the module selection process is simple and deterministic, but switching frequency imbalance occurs causing thermal stress and reduced reliability
Solution Approach 1:
The patent applies dynamics by making the module selection order variable rather than static. The controller dynamically adjusts the selection sequence between sampling events based on the switching frequency history of each module. This allows the system to adaptively balance the switching frequency distribution across modules, preventing any single module from being overused and thereby reducing thermal stress and improving reliability.
2Ease of manufacture
If modules with lower numerical addresses are selected more frequently, then the module selection process is straightforward, but thermal hot spots are created and thermal stress increases
Solution Approach 1:
The patent implements feedback by continuously monitoring the switching frequency of each module and using this information to adjust the selection order in subsequent sampling events. The controller provides feedback to the module selection process, ensuring that modules which have been switched frequently are less likely to be selected again, thereby distributing thermal load more evenly and preventing thermal hot spots.
3Device complexity
If the same increasing order is used for module selection in each sampling event, then the control algorithm is simple, but switching frequency variance between modules increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating or pre-determining a varied selection order for modules before each sampling event, based on their switching frequency history. This preliminary adjustment ensures that the selection process inherently balances switching frequency distribution without requiring complex real-time calculations during each sampling event, thus maintaining algorithm simplicity while improving reliability.
Data Source
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AI summary
There is provided a switching valve for a voltage source converter (20). The switching valve comprises a plurality of modules (44), each module (44) including at least one switching element (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) configured 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 selectively carry out a module (44) selection by: assigning each module (44) with a respective address in an address queue; in a respective one of a plurality of sampling events, selecting one or more voltage contributing modules (44) in order of its assigned address in the address queue; and between different sampling events, changing the order of selecting the or each voltage contributing module (44) based on its assigned address in the address queue.