Segmented DC Bus Fuses for Power Conversion Overcurrent Protection
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Solution Overview
Problem
The existing power conversion apparatuses in uninterruptible power supply systems require large, costly fuses with high rated current values to prevent overcurrent and overvoltage, which can lead to damage during short-circuit events and reduce efficiency due to continuous current flow and power losses.
Innovation Solution
A power conversion apparatus is designed to convert three-phase AC voltages into four-phase to six-phase AC voltages, using multiple power converters and inverters with strategically placed fuses between DC buses to isolate phases during failures, allowing for a simpler configuration and lower rated fuses that prevent overcurrent and overvoltage effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fuse with a high rated current value is used to prevent inadvertent melting during normal operation, then the fuse will not melt during normal operation, but a large short-circuit current will flow through the current path during a failure before the fuse melts, damaging other semiconductor switching devices and diodes
Solution Approach 1:
The current path is segmented into multiple sections with fuses placed at strategic locations (between DC positive buses and between DC negative buses). This segmentation allows the fuse to interrupt only the affected phase's current path during a short-circuit, rather than allowing large currents to flow through all components. The segmentation creates isolated protection zones that limit the spread of overcurrent damage.
Solution Approach 2:
The fuse acts as an intermediary protective element inserted into the current path between the semiconductor switching device and the DC bus. During normal operation, the fuse conducts current with minimal impedance. During a short-circuit, the fuse melts to interrupt the current path, serving as a mediator that protects other components from direct exposure to destructive overcurrents.
2Reliability
If a fuse with a great rated current value is used for each of the nine fuses in the three-level converter and three-level inverter, then the fuse will not melt until a short-circuit current exceeding the rated current value flows, but the size and cost of the apparatus will increase
Solution Approach 1:
The protection system is segmented into multiple fuse locations rather than requiring one oversized fuse for the entire system. Each fuse is rated for a lower current value appropriate to its specific location, allowing the use of smaller, less expensive fuses while maintaining comprehensive protection coverage across all phases and components.
Solution Approach 2:
Each fuse is assigned a local quality characteristic (rated current value) appropriate to the specific requirements of its location in the circuit. Rather than uniform high-rated fuses throughout, the segmentation allows optimization of fuse ratings for local conditions, reducing overall system cost and size while maintaining protection effectiveness.
3Reliability
If a fuse with a high rated current value is used, then the fuse will not melt during normal operation, but power loss generated in each fuse during operation will increase, reducing the efficiency of the power conversion apparatus
Solution Approach 1:
The current path is divided into segmented sections with individually rated fuses. This segmentation allows each fuse to have a lower rated current value matched to its local requirements, reducing the I²R power losses in each fuse during normal operation compared to using high-rated fuses throughout the system.
Solution Approach 2:
The rated current parameter of the fuses is changed from high values to lower values appropriate for each segmented location. This parameter change reduces the power loss (P=I²R) in each fuse during normal operation while the segmented configuration ensures that the lower-rated fuses still provide adequate protection by isolating failures to specific phases.
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 reduces the size and cost of the apparatus, minimizes power losses, and enhances efficiency by using lower rated fuses that melt only during failures, effectively preventing overcurrent and overvoltage without affecting normal operations.
Implementation Method 1
a fuse is connected between one terminal of each semiconductor switching device and a DC bus (DC positive bus, DC negative bus, or DC neutral bus). This configuration melts the fuse to interrupt a path through which current flows if any of the semiconductor switching devices shorts out, thus preventing an occurrence of overcurrent or overvoltage.
Data Source
AI summary
A power conversion apparatus in which wiring lines are provided between DC buses of a first converter unit and DC buses of a second converter unit. The wiring lines are provided between the DC buses of the second converter unit and DC buses of a third converter unit. Fuses are interposed in the wiring lines, respectively.