Converter Cell Third Switch Overcharging Protection
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Solution Overview
Problem
Existing converter cells face challenges in effective failure handling, which can lead to costly and complex issues such as overcharging and increased component ratings, particularly in high voltage applications like HVDC systems.
Innovation Solution
Incorporating a third switch between the energy storage device and the first and second switches, which can be controlled to manage energy transfer and prevent overcharging, using thyristors or a combination of thyristors and mechanical switches to enhance failure handling and reduce component costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If converter cells are used in high voltage applications without additional protection switches, then device complexity is reduced, but reliability deteriorates due to overcharging risks
Solution Approach 1:
The converter cell is segmented into multiple switching elements (first switch, second switch, and third switch) that can be independently controlled. This segmentation allows the third switch to specifically protect the energy storage device while the other switches handle main power conversion, resolving the contradiction by distributing protection functions across separate components.
Solution Approach 2:
The third switch acts as an intermediary protection element between the first/second switches and the energy storage device. It mediates by blocking overcharging currents while allowing normal energy transfer, thus improving reliability without requiring complete redesign of the power conversion path.
2Reliability
If higher rated energy storage devices are used to prevent overcharging, then reliability improves, but cost increases
Solution Approach 1:
The third switch serves as a protective intermediary that prevents overcharging currents from reaching the energy storage device. This allows the use of lower-rated, less expensive energy storage devices while maintaining reliability, as the switch rather than the storage device bears the stress of handling extreme conditions.
Solution Approach 2:
The third switch is designed as a protective element that can be replaced more easily and cheaply than high-rated energy storage devices. By placing this lower-cost protective component in series, the system achieves overcharging protection without requiring expensive high-rated storage devices.
3Reliability
If additional protection switches are added to converter cells, then reliability improves through better failure handling, but device complexity increases
Solution Approach 1:
The protection function is segmented into a dedicated third switch that operates independently from the main first and second switches. This segmentation allows the protection logic to be simplified and assigned to a single component, reducing overall system complexity while maintaining high reliability.
Solution Approach 2:
The third switch is designed to handle multiple protection scenarios (overcharging prevention, failure isolation) within a single component, reducing the need for additional specialized protection circuits and thereby limiting the increase in device complexity.
4Quantity of substance
If energy storage device rating is reduced to lower cost, then component cost decreases, but reliability worsens due to overcharging vulnerability
Solution Approach 1:
The third switch acts as a protective intermediary that shields the lower-rated energy storage device from overcharging conditions. This allows the system to use cost-effective, lower-rated storage devices while the switch absorbs the stress of handling extreme voltage and current conditions.
Solution Approach 2:
By placing a relatively inexpensive third switch in series with the energy storage device, the system protects the storage device from overcharging. The switch serves as a sacrificial protection element that can be replaced more easily than expensive high-rated storage devices, enabling the use of lower-cost storage components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration provides improved failure handling capabilities, reduces the rating requirements of energy storage devices, and results in significant cost savings by preventing overcharging and managing energy transfer effectively, even in the event of switch failures.
Implementation Method 1
The converter cell may be arranged to control energisation of the energy storage device by controlling a phase angle of the thyristor allowing a current to energise the energy storage device
Implementation Method 2
Using a mechanical switch, this reduces any power losses through the third switch when it is closed in a normal operating mode
Data Source
AI summary
It is presented a converter cell comprising: a first terminal and a second terminal; an energy storage device connected on a first end to the second terminal; a first switch connected on a first end to the first terminal; a second switch arranged between the two terminals; and a third switch connected between a second end of the first switch and a second end of the energy storage device. A corresponding converter arm and method are also presented.