DC Link Precharge Circuit for Overhead Line Contact Interruptions
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Solution Overview
Problem
Existing precharging circuits for intermediate circuit capacitors in electric drive systems of road-guided motor vehicles fail to quickly respond to short-term interruptions in overhead line contact, leading to overvoltages and high currents due to parasitic inductances, especially on uneven roads.
Innovation Solution
A precharging circuit with at least one resistor, two switching elements, and two voltage measuring devices, where the control unit automatically switches the resistance on or off based on voltage thresholds, allowing for local control and faster reaction times, and optional additional switching elements for galvanic isolation or parallel resistor configuration for accelerated charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a precharging circuit with centralized control is used, then the system can limit current flow during normal operation, but the response time to brief interruptions is too slow due to central control system delays
Solution Approach 1:
The control system is segmented into a centralized control unit for normal operation and a decentralized local control unit for emergency responses. The local control unit is positioned at the switching element and can independently detect voltage drops and activate the precharging resistor without waiting for centralized system commands, thus achieving fast response to brief interruptions while maintaining the overall centralized architecture for normal operations.
Solution Approach 2:
The local control unit is pre-configured with the capability to detect voltage drops and immediately activate the precharging resistor. This preliminary preparation ensures that when a brief interruption occurs, the system can respond instantly without needing to process commands through the slower centralized control system, effectively pre-positioning the response mechanism at the point of need.
2Reliability
If the precharging resistor is always connected, then the circuit is simple and reliable, but energy is continuously consumed and galvanic isolation is lost
Solution Approach 1:
The precharging resistor's connection state is made dynamic rather than static. A switching element controlled by voltage detection mechanisms (both centralized and local control units) automatically connects the resistor when voltage drops indicate a brief interruption, and disconnects it when normal operation is detected. This dynamic control ensures the resistor is only active when needed, preventing continuous energy consumption while maintaining circuit reliability during critical moments.
3Reliability
If a third switching element is added for galvanic isolation, then isolation is achieved, but device complexity increases
Solution Approach 1:
The third switching element is designed to serve multiple functions: it provides galvanic isolation between the current collector and intermediate circuit capacitor, and it can also be used to connect or disconnect the precharging resistor. By making this switching element multi-functional, the patent achieves galvanic isolation without proportionally increasing system complexity, as the same component performs both isolation and precharging control tasks.
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 limits current flow and prevents overvoltages by quickly activating and deactivating the precharging circuit in response to voltage drops, ensuring efficient charging and discharging of the intermediate circuit capacitor, even during short-term contact interruptions.
Implementation Method 1
two voltage measuring devices. The first voltage measuring device is arranged between the switching elements and current collectors for the overhead lines, and the second voltage measuring device is arranged parallel to the intermediate circuit capacitor
Implementation Method 2
at least one resistor, at least two switching elements... the resistor can be connected or bridged by at least one switching element... effectively limits current flow and prevents overvoltages
Implementation Method 3
at least two switching elements... The switching element assigned to the resistor can be one of the two switching elements or a separate switching element
Data Source
Figure 1~3
Figure 4~5
AI summary
The invention relates to a pre-charging circuit (10) for a DC link capacitor (C) of an electric drive system with a voltage supply from overhead lines (11, 12), wherein the pre-charging circuit (10) comprises at least one resistor (R), at least two switching elements (5, 6) and two voltage measuring devices (13, 14), wherein the first voltage measuring device (13) is arranged between the switching elements (5, 6) and current collectors (1, 2) for the overhead lines (11, 12) and the second voltage measuring device (14) is arranged in parallel to the DC link capacitor (C), wherein the resistor (R) can be switched on or bypassed by at least one switching element (5, 7, 21, 22), wherein at least one control unit (15) is assigned to the switching element (5, 7, 21, 22), and wherein the control unit (15) is configured such that the at least one resistor (R) is automatically switched on or bypassed is switched offwhen the voltage (U1) of the first voltage measuring device (13) is below a first threshold value (Ux), as well as a road-guided motor vehicle.