Neutral Point Clamped Choppers for Low-Loss Rail Battery Conversion
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Solution Overview
Problem
Battery-powered trains face reduced operation distance due to high losses in galvanically separated DC-to-DC converters used to adapt between medium voltage rail propulsion systems and low voltage battery cells.
Innovation Solution
A converter arrangement featuring two neutral point clamped chopper circuits that connect a medium voltage DC link to a low voltage energy storage system, with an overvoltage protection device and efficient duty cycle operation, eliminating the need for galvanic separation and reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a galvanically separated DC-to-DC converter is used to adapt between medium voltage rail propulsion systems and low voltage battery cells, then electrical isolation is achieved, but energy losses increase and operation distance is reduced
Solution Approach 1:
The patent extracts the galvanic isolation requirement from the converter design by using two separate neutral point clamped chopper circuits that operate independently on the medium voltage and low voltage sides. This eliminates the need for a galvanically separated DC-to-DC converter while maintaining electrical isolation through the neutral point clamping topology, thereby reducing energy losses.
Solution Approach 2:
The converter is segmented into two independent chopper circuits (first and second neutral point clamped choppers) that separately handle the medium voltage and low voltage sides. This segmentation allows each circuit to operate optimally without the losses associated with galvanic isolation, while still achieving the required electrical isolation through the neutral point connection.
2Reliability
If a galvanically separated DC-to-DC converter is used, then electrical isolation is achieved, but operation distance of the traction vehicle is reduced
Solution Approach 1:
The patent removes the galvanic isolation component from the converter design, using instead two neutral point clamped chopper circuits that provide the necessary electrical isolation through their topology. This extraction eliminates the energy losses in the galvanic isolation stage, thereby extending the operation distance of battery-powered trains.
Solution Approach 2:
The patent changes the operational parameters of the converter by using neutral point clamped choppers with optimized duty cycles. This allows efficient energy transfer between medium and low voltage without the losses of galvanic isolation, directly impacting and extending the operation distance of the traction vehicle.
3Loss of energy
If neutral point clamped chopper circuits are used, then energy losses are minimized and operation distance is increased, but circuit complexity increases
Solution Approach 1:
The complex converter function is segmented into two manageable neutral point clamped chopper circuits, each handling a specific voltage level. This segmentation makes the overall system more manageable and maintainable while achieving low energy losses through efficient switching in each segment.
4Volume of moving object
If two neutral point clamped chopper circuits are used, then component size is reduced and cost is lowered, but switching control complexity increases
Solution Approach 1:
The patent employs periodic switching action in the neutral point clamped chopper circuits with optimized duty cycles. This periodic switching allows efficient energy transfer and reduces component size while the control complexity is managed through standardized switching patterns in each chopper circuit.
Data Source
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AI summary
A converter arrangement (30) comprises a first chopper circuit (40a) for connecting a positive input (32a) or a neutral point (50) with a positive output (34a), wherein the first chopper circuit (40a) comprises a first switch arrangement (42a), a first inductor (44a) and a first capacity (46a), wherein the first switch arrangement (42a) is adapted for connecting the first inductor (44a) with the positive input (32a) or with the neutral point (50), the first inductor (44a) interconnects the first switch arrangement (42a) with the positive output (34a) and the first capacity (46a) interconnects the positive output (34a) with the neutral point (50). The converter arrangement (30) further comprises a second chopper circuit (40b) for connecting a negative input (32b) or the neutral point (50) with a negative output (34b), wherein the second chopper circuit (40b) comprises a second switch arrangement (42b), a second inductor (44b) and a second capacity (46b), wherein the second switch arrangement (42b) is adapted for connecting the second inductor (44b) with the negative input (32b) or with the neutral point (50), the second inductor (44b) interconnects the second switch arrangement (42b) with the negative output (34b) and the second capacity (46b) interconnects the negative output (34b) with the neutral point (50). The converter arrangement (30) further comprises an overvoltage protection device (52) adapted for short-circuiting the positive output (34a) and the negative output (34b), when an overvoltage is measured between the positive output (34a) and/or the negative output (34b) and the neutral point (50, 54).