Battery String Pre-Charge Circuit for DC Link Inrush Control
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Solution Overview
Problem
Connecting multiple large capacity battery strings in parallel to power large moving work machines can result in high inrush currents when directly connected to a DC link with capacitance, potentially damaging batteries and machine components.
Innovation Solution
A modular battery system with a load bus, pre-charge circuit, multiple battery packs, and a control circuit that selectively pre-charges the DC link using a pre-charge contactor before connecting the battery string to the load bus, thereby preventing high inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple battery strings are directly connected to the DC link, then the battery system can provide sustained energy power, but high inrush currents will damage batteries and components
Solution Approach 1:
The patent applies preliminary action by pre-charging the DC link capacitance before connecting the battery strings. The control circuit first charges the DC link to a predetermined voltage level using a pre-charge circuit, then closes the contactor to connect the battery strings. This preliminary charging action prevents high inrush currents from damaging the batteries and components while still enabling the battery system to provide sustained energy power.
2Reliability
If a pre-charge circuit is added to prevent inrush currents, then battery and component safety is improved, but system complexity increases
Solution Approach 1:
The patent merges the pre-charge circuit and the main battery connection circuit into a single integrated system controlled by a unified control circuit. The pre-charge contactor and main contactor are coordinated through the same control logic, and the pre-charge circuit shares the DC link with the main battery connection. This merging approach provides the necessary safety functions while minimizing additional complexity compared to separate independent circuits.
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 safely brings the battery system online by pre-charging the DC link, preventing damage from inrush currents and ensuring reliable operation of the battery system and the work machine.
Implementation Method 1
it is necessary to avoid connecting battery cells immediately to—a direct current (DC) link and its capacitance
Implementation Method 2
Doing so may result in high inrush currents that can potentially damage the batteries and components of the work machine
Data Source
AI summary
A battery system includes a load bus to connect to a DC link, a single pre-charge circuit connected to the load bus, multiple battery packs, and a control circuit. Each battery pack includes multiple battery strings that include battery cells connected in series, a positive contactor to connect the battery string to the load bus, and a pre-charge contactor to connect the battery string to the pre-charge circuit. The control circuit selects a battery string to pre-charge the DC link, closes the pre-charge contactor of the battery string to connect the selected battery string to the pre-charge circuit, and opens the pre-charge contactor of the selected battery string to disconnect the battery string from the pre-charge circuit and close the positive contactor of the selected battery string to connect the battery string to the load bus when the DC link is pre-charged.