Multi-String HV Battery Pack Control for Fault Isolation
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Solution Overview
Problem
High-voltage batteries in electric vehicles are safety-critical components prone to single-point failures that can lead to propulsion loss and hazards, necessitating improved reliability and redundancy in fault conditions.
Innovation Solution
A multi-string high-voltage battery pack with parallel battery strings, a shared pre-charge circuit, and individual positive and negative main contactors, controlled by a battery management unit to ensure redundancy and balanced operation in normal, fault-on, and fault-recovered conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-point high-voltage battery configuration is used, then the device complexity is reduced, but the reliability deteriorates due to single-point failure risk
Solution Approach 1:
The battery system is divided into multiple independent strings (first battery string, second battery string, etc.), each capable of independent operation. This segmentation allows the system to maintain functionality even when one string fails, directly resolving the contradiction by improving reliability through modular architecture without significantly increasing overall system complexity.
Solution Approach 2:
The system dynamically changes operational parameters by selectively activating or deactivating specific battery strings based on their health status. When a fault is detected in one string, the control device switches to using only the healthy strings, adjusting the operational configuration to maintain reliable propulsion while managing system complexity through intelligent parameter adaptation.
2Power
If all battery strings are connected in parallel to increase power output, then the power delivery capability is improved, but the reliability deteriorates due to fault propagation risk
Solution Approach 1:
The parallel battery string architecture is segmented with individual control over each string's connection to the common bus. This allows the system to maintain high power delivery when all strings are healthy by connecting them in parallel, while simultaneously preventing fault propagation by isolating defective strings through contactor disconnection, thus resolving the reliability contradiction.
Solution Approach 2:
The system dynamically adjusts the parallel connection configuration of battery strings based on real-time health monitoring. Healthy strings are connected in parallel to maximize power output, while faulty strings are dynamically disconnected. This dynamic reconfiguration enables the system to maintain both high power delivery capability and fault isolation, resolving the contradiction between these two requirements.
3Object-affected harmful factors
If a pre-charge circuit is added to prevent inrush current, then the safety is improved, but the device complexity increases
Solution Approach 1:
The pre-charge circuit is designed as a universal protection mechanism that serves multiple functions: limiting inrush current during normal operation, providing a discharge path for capacitor energy during fault conditions, and enabling safe reconnection after faults. This multi-functionality justifies the added circuit complexity by delivering comprehensive safety benefits across multiple operational scenarios.
Solution Approach 2:
The pre-charge resistor acts as an intermediary element between the battery strings and the common bus, mediating the energy transfer to prevent harmful inrush currents. During fault recovery, it serves as an intermediary discharge path for capacitor energy. This intermediary function provides comprehensive safety protection while maintaining relatively simple circuit implementation, resolving the contradiction between safety improvement and complexity increase.
4Reliability
If individual main contactors are used for each battery string to improve fault isolation, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The system uses individual main contactors for each battery string to segment the control architecture, enabling independent disconnection of faulty strings. This segmentation provides superior fault isolation capability, allowing the system to maintain reliability by isolating failures to specific strings while keeping the overall system architecture relatively simple through modular contactor design.
Data Source
AI summary
A vehicle includes an electric motor and a multi-string high-voltage battery pack configured to provide a high output voltage for driving the electric motor. The battery pack includes a positive output terminal, a negative output terminal, a plurality of battery strings, a pre-charge circuit connected to the positive output terminal and to each of the plurality of battery strings, a plurality of positive main contactors, each positive main contactor of the plurality of positive main contactors selectively connecting a corresponding battery string to the positive output terminal, and one or more negative main contactors connecting the plurality of battery strings to the negative output terminal.