Pre-charge System Using Transistors to Limit Inrush Current
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Solution Overview
Problem
High-voltage battery packs in electric vehicles experience severe inrush currents when connected to a DC bus, potentially damaging electrical components, and conventional pre-charge circuits with bulky contactors are costly and difficult to package.
Innovation Solution
A pre-charge system using a first transistor and a controller to manage the connection of a battery string to a DC bus, incorporating a discharge circuit to handle leakage current, replacing bulky contactors with compact silicon-based transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional pre-charge circuit with a pre-charge contactor is used, then inrush current is limited, but the system becomes bulky and expensive
Solution Approach 1:
The patent replaces the mechanical pre-charge contactor with an electronic switching device (transistor or MOSFET) that has no moving parts. This electronic switch is controlled by a control circuit to achieve the same current limiting function during pre-charge, eliminating the need for bulky mechanical contactors while maintaining inrush current protection
Solution Approach 2:
The patent changes the operating parameters of the switching device by controlling its resistance dynamically. During pre-charge, the switching device is configured to have higher resistance to limit inrush current. Once pre-charge is complete, the resistance is reduced to enable full power transfer, thus adapting the electrical parameters to different operational phases
2Reliability
If a high-power pre-charge contactor is used to limit inrush current, then safety is improved, but packaging space increases
Solution Approach 1:
The patent replaces the mechanical pre-charge contactor with an electronic switching device (transistor or MOSFET) that has no moving parts. This electronic switch is controlled by a control circuit to achieve the same current limiting function during pre-charge, eliminating the need for bulky mechanical contactors while maintaining inrush current protection
Solution Approach 2:
The electronic switching device serves multiple functions: it acts as the pre-charge switch, the main power switch, and provides current limiting capability all in one component. This multi-functionality eliminates the need for separate pre-charge contactors and reduces overall system volume
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 inrush currents, reduces component costs, and enhances packaging flexibility by using transistors instead of contactors, ensuring safe and efficient battery connections.
Implementation Method 1
a pre-charge circuit may include a pre-charge resistor and a pre-charge contactor (or relay) connected in series. During operation, the pre-charge contactor may be closed to connect the pre-charge resistor to the high-voltage battery pack, so as to limit the inrush current
Data Source
AI summary
A system is disclosed for connecting a battery string to a direct-current (DC) bus of a vehicle. The system may include a pre-charge circuit coupled between the battery string and the DC bus. The pre-charge circuit may include a first transistor. The system may also include a first contactor connected to the pre-charge circuit in series. The system may further include a controller configured to close the first contactor and switch on the first transistor.