Current Collector Power Switching for Contact Voltage Protection
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Solution Overview
Problem
Vehicles with non-grounded frames, such as trucks and trolleybuses, face dangerous contact voltages due to galvanic contact with overhead contact lines, posing risks of injury or death from body currents, especially when protection systems fail.
Innovation Solution
A vehicle with a current collector for a two-pole overhead contact line system, incorporating a hybrid-electrical traction drive, an energy storage device, and a galvanically isolating DC converter, along with a switching mechanism to switch between two protection levels: a higher level using a galvanically isolating DC converter for low speeds and a lower level using a non-isolating DC converter for higher speeds, ensuring safe power transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a galvanically isolating DC converter is used to ensure safety at low speeds, then protection against contact voltages is improved, but device complexity and cost increase
Solution Approach 1:
The patent divides the speed range into two segments: low speeds (0-50 km/h) where galvanic isolation is required for safety, and high speeds (>50 km/h) where isolation can be relaxed. This segmentation allows using different converter types in different operating conditions, optimizing both safety and complexity.
Solution Approach 2:
The protection level is made dynamic by switching between two DC converter configurations based on vehicle speed. The control unit automatically selects the appropriate converter type according to the current speed, making the protection system adaptive rather than static.
2Reliability
If a galvanically isolating DC converter is used for all operating conditions, then safety is improved, but weight and cost increase
Solution Approach 1:
The patent segments the operating conditions based on speed thresholds and applies different converter types accordingly. At high speeds where the risk of contact is lower, a lighter non-isolating converter is used, reducing overall vehicle weight while maintaining adequate safety.
Solution Approach 2:
The protection parameter (galvanic isolation) is changed based on the operating speed parameter. By varying the isolation level according to speed, the system achieves weight optimization without compromising safety in critical low-speed conditions.
3Device complexity
If a galvanically non-isolating DC converter is used for high speeds, then device complexity is reduced, but protection against contact voltages deteriorates
Solution Approach 1:
The system dynamically adjusts the protection level based on speed. The control unit monitors vehicle speed and automatically switches between isolating and non-isolating converter modes, ensuring that reduced protection at high speeds is compensated by the lower risk of contact in that operating condition.
Solution Approach 2:
The protection parameter is changed as a function of speed parameter. At high speeds, the system accepts lower galvanic isolation in exchange for reduced complexity, while maintaining high isolation at low speeds where contact risk is higher.
4Ease of operation
If protection level is reduced for high speeds, then ease of operation is improved, but safety deteriorates
Solution Approach 1:
The control system automatically manages the protection level based on speed, providing operational flexibility without requiring manual intervention. The system adapts the protection level dynamically, making operation easier while maintaining appropriate safety margins for each speed condition.
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
Enables improved power transmission while maintaining safety by using smaller, lighter, and cheaper non-isolating DC converters for higher speeds, and isolating components to prevent dangerous contact voltages, enhancing operational safety and efficiency.
Implementation Method 1
a galvanically isolating DC converter that is interposed in the second line branch
Implementation Method 2
an electrical energy storage device for the intermediate storage of traction energy that is fed in
Implementation Method 3
an electric or hybrid-electric traction drive
Data Source
AI summary
A vehicle has a current collector for feeding traction energy from a two-pole overhead contact line system, an electric or hybrid electric traction drive, and an electric energy storage device for temporarily storing fed traction energy. A first line branch can connect the traction drive to the current collector. A second line branch, which can connect the traction drive and the energy storage device to the current collector, includes a switched-in, galvanically isolating DC-to-DC converter. Due to a third line branch which can connect the traction drive and the energy storage device to the current collector, and which includes a switched-in, non-galvanically isolating DC-to-DC converter, enables higher charging rates for charging the energy storage device to be transmitted while maintaining the protection system.