Battery Switch Pre-Charging for Load Access Surge Prevention
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Solution Overview
Problem
The existing technologies for battery packs in electric vehicles face a safety hazard due to ignition and ablation issues when connected to a load circuit, primarily because the charging and discharging field-effect transistor is in a normally closed state, leading to potential safety risks and reduced service life.
Innovation Solution
A load access detection method and a battery management system that detect voltage differences between specific detection points to control a switch circuit, entering a pre-charging mode with a reduced charging current to prevent ablation, by using a bridging resistor and a switch circuit with multiple switches to manage the charging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the charging and discharging field-effect transistor is kept in a normally closed state to ensure continuous charging capability, then the charging convenience is improved, but the risk of ignition and ablation at the interface increases
Solution Approach 1:
The patent introduces a pre-charging mode that activates before normal charging operations. When the battery pack is first connected to the load circuit, the system detects the connection state and automatically enters pre-charging mode, where the field-effect transistor operates with limited current capability. This preliminary action prevents the harmful surge current and ignition risk before normal charging begins.
Solution Approach 2:
The patent makes the field-effect transistor's current capability dynamic rather than static. The transistor can operate in two modes: pre-charging mode with limited current capability and normal charging mode with full current capability. The system dynamically switches between these modes based on the connection state detection, allowing the transistor to adapt its characteristics to different operational phases and eliminate the harmful factors during connection.
2Productivity
If a high charging current is used to improve charging speed, then the productivity is improved, but the ablation problem at the interface worsens
Solution Approach 1:
The system performs a preliminary pre-charging phase before entering high-speed normal charging. During this pre-charging phase, the charging current is intentionally limited to a lower level that prevents ablation. Only after the connection is established and stabilized does the system transition to high-current normal charging mode, thus protecting the interface from ablation while still achieving high charging speeds for the majority of the charging process.
Solution Approach 2:
The charging process is divided into distinct periodic phases: pre-charging mode with limited current and normal charging mode with high current. The system periodically switches between these phases based on operational conditions, allowing high productivity during normal charging while preventing ablation during the pre-charging phase at the beginning of each charging cycle.
3Device complexity
If the field-effect transistor operates without pre-charging protection to maintain simple circuit design, then the device complexity is reduced, but the service life of the switch circuit decreases
Solution Approach 1:
The field-effect transistor serves multiple functions: it acts as both a normal charging switch and a pre-charging protection device. The same transistor component is used in both pre-charging mode (with protection) and normal charging mode (full capability), eliminating the need for separate protection circuits or additional components. This multi-functionality maintains circuit simplicity while extending service life through pre-charging protection.
Solution Approach 2:
The battery management system automatically detects the connection state and autonomously controls the field-effect transistor's operating mode without requiring external intervention or complex additional circuits. The system self-regulates by entering pre-charging mode when connection is detected and transitioning to normal charging mode when appropriate, providing built-in protection that extends service life while maintaining design simplicity.
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
This solution effectively prevents ablation and ensures safety by reducing the charging current during connection, thereby extending the service life of the switch circuit and avoiding surge currents, while stabilizing voltage detection.
Implementation Method 1
a first resistor, a second resistor, a third resistor that are respectively connected in series between the positive electrode and the negative electrode of the battery pack; where the first resistor is connected in parallel with the second resistor
Implementation Method 2
detecting, by a battery management system, a voltage at a first detection point, where the first detection point is electrically connected to a positive electrode of a battery group in a battery pack through a bridging resistor
Data Source
AI summary
A load access detection method, a switch circuit, and a battery management system, relating to the field of circuit technology. The load access detection method includes: detecting a voltage at a first detection point; detecting a voltage at a second detection point; if a voltage difference between the voltage at the first detection point and the voltage at the second detection point is less than or equal to a preset voltage threshold, controlling a switch circuit to enter a pre-charging mode, and pre-charging a load capacitor in the load circuit through the battery pack, where a charging current of the switch circuit in the pre-charging mode is less than a charging current of the switch circuit in a charging mode.