Trolley Interfacing Device Pre-Charging Unit
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Solution Overview
Problem
Conventional trolley interfacing systems experience surge currents when coupling traction loads to trolley lines, leading to voltage fluctuations and potential damage to components, as they rely on heavy and expensive mechanical switches for precharging capacitors to mitigate this issue.
Innovation Solution
A trolley interfacing device with a pre-charging unit that uses electronic switches to pre-charge capacitors across inductors before coupling to the voltage source, preventing surge currents and reducing component stress, employing a parallel configuration with a voltage converting unit to step down voltage for the traction load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If mechanical switches (MV switches) are used to disconnect the resistor from the pantographs after capacitor charging, then the resistor can be bypassed to avoid high electrical losses, but the mechanical switches are heavy in weight, slow in switching, and very expensive
Solution Approach 1:
The patent replaces mechanical switches (MV switches) with electronic switches in the pre-charging unit. This substitution eliminates the drawbacks of mechanical switches (heavy weight, slow switching, high cost) while maintaining the ability to bypass the resistor after capacitor charging to avoid electrical losses. The electronic switches provide faster response, lighter weight, and lower cost while achieving the same functional outcome of disconnecting the resistor from the circuit.
2Reliability
If a resistor is used to precharge the capacitor before coupling to the voltage source, then surge current is prevented, but the resistor causes high electrical losses when connected during normal operation
Solution Approach 1:
The patent employs a pre-charging unit with electronic switches that activates before the main coupling to the voltage source. This preliminary action charges the capacitor through the pre-charging unit, preventing surge current when the main switch closes. After pre-charging is complete, the electronic switches disconnect the pre-charging unit (including the resistor) from the circuit, eliminating ongoing electrical losses while maintaining surge current protection during the critical switching moment.
Solution Approach 2:
The patent makes the pre-charging circuit dynamic by using electronic switches to connect the resistor only when needed for pre-charging, and disconnect it afterward. This dynamic configuration allows the system to have low electrical losses during normal operation while providing surge current protection when required, resolving the contradiction between reliability and energy loss.
3Device complexity
If the capacitor is not precharged before coupling to the voltage source, then the system is simpler, but large surge current flows from the DC grid to the buck converter causing voltage fluctuations and potential damage
Solution Approach 1:
The patent introduces a pre-charging unit with electronic switches as an intermediary between the capacitor and the voltage source. This intermediary component provides a controlled path for charging the capacitor before main coupling, preventing direct surge current flow. The electronic switches act as a mediator that manages the charging process, protecting the buck converter and DC grid from damage while adding minimal complexity compared to the alternative of dealing with surge current damage.
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
The solution effectively minimizes surge currents and reduces component damage, using lightweight and inexpensive electronic switches to enhance the interface between traction loads and voltage sources, thereby improving system reliability and efficiency.
Implementation Method 1
a pre-charging unit coupled in parallel to the second charging unit and configured to pre-charge the first charging unit with a voltage across the at least one inductor
Implementation Method 2
a voltage converting unit disposed between the first charging unit and the second charging unit and configured to step down a voltage provided by the voltage source to the traction load
Data Source
AI summary
A trolley interfacing device for interfacing a traction load to a voltage source is presented. The trolley interfacing device includes a first charging unit coupled in parallel to the voltage source. Further, the trolley interfacing device includes a second charging unit coupled in parallel to the traction load, where the second charging unit includes at least one inductor. Also, the trolley interfacing device includes a pre-charging unit coupled in parallel to the second charging unit and configured to pre-charge the first charging unit with a voltage across the at least one inductor prior to electrically coupling the first charging unit to the voltage source. In addition, the trolley interfacing device includes a voltage converting unit disposed between the first charging unit and the second charging unit and configured to step down a voltage provided by the voltage source to the traction load.