Battery String Sorting and Pre-Charging for DC Bus Inrush Current
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Solution Overview
Problem
The connection of multiple battery strings to a DC bus in vehicle systems poses challenges due to differing output voltages, leading to severe inrush currents that can damage electrical components, necessitating a sophisticated system to manage the connection and limit inrush currents.
Innovation Solution
A method and system that sorts battery strings by output voltage and uses pre-charge circuits to pre-charge the DC bus before connecting them, employing power transistors instead of bulky contactors to manage inrush currents, with a controller orchestrating the process to ensure safe and efficient connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple battery strings with different output voltages are connected to the DC bus, then system reliability and availability are improved, but severe inrush current is generated that may damage electrical components
Solution Approach 1:
The patent applies preliminary action by pre-charging the DC bus before connecting battery strings with different voltages. The controller charges the DC bus to a predetermined voltage level using a pre-charge circuit before closing the contactor, which prevents severe inrush current while enabling reliable parallel connection of unbalanced battery strings.
Solution Approach 2:
The patent uses an intermediary approach by introducing a pre-charge circuit as a mediator between the battery strings and the DC bus. This intermediate charging mechanism allows unbalanced battery strings to be safely connected by first equalizing the voltage through controlled charging, then connecting through the pre-charged bus, thereby eliminating inrush current damage while maintaining system reliability.
2Reliability
If battery strings are connected in parallel to improve reliability, then system availability increases, but system complexity rises due to need for sophisticated connection management
Solution Approach 1:
The patent applies self-service by implementing a controller that automatically monitors the voltages of multiple battery strings and autonomously determines the optimal connection sequence. The controller compares voltages, identifies which battery string to connect first, and executes the pre-charge and connection process without manual intervention, thereby reducing operational complexity while maintaining high reliability.
Solution Approach 2:
The patent uses parameter changes by dynamically adjusting the connection strategy based on voltage parameters. The controller monitors voltage differences between battery strings and modifies the connection sequence accordingly - connecting strings with similar voltages together and using pre-charge for voltage-mismatched connections, thereby simplifying the overall system management while ensuring reliable operation.
3Speed
If battery strings with different output voltages are connected without pre-charging, then connection speed is fast, but electrical components may be damaged by inrush current
Solution Approach 1:
The patent applies preliminary action by pre-charging the DC bus to a predetermined voltage level before connecting battery strings with different voltages. This preliminary charging step, controlled by a controller that monitors battery string voltages, prevents severe inrush current while enabling reliable parallel connection, thus protecting components without significantly delaying the overall connection process.
Data Source
AI summary
A method is disclosed for connecting a plurality of battery strings to a direct-current (DC) bus. The method may include sorting the plurality of battery strings in an order based on respective output voltage values of the battery strings. The sorted plurality of battery strings may include, in the order, at least a first battery string and a second battery string. The method may also include connecting the first battery string to a pre-charge circuit. The method may further include pre-charging the DC bus using the first battery string and the pre-charge circuit. The method may further include connecting the first battery string to the DC bus. The method may further include connecting the second battery string to the DC bus.