HV DC Intermediate Circuit Precharge for Inrush Current Control
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Solution Overview
Problem
The high inrush current during the coupling of a high-voltage DC voltage intermediate circuit to a charging station poses a risk of exceeding operational limits of components and can lead to reduced lifespan of relays due to sticking contacts, necessitating a safer and more cost-effective precharging method.
Innovation Solution
Utilizing charging current-connecting switching elements, such as contactors, to precharge the intermediate circuit by equalizing electric potentials and voltages, eliminating the need for additional relays like Reed relays, and employing DC-to-DC converters for voltage compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If direct coupling of the high-voltage DC voltage intermediate circuit to the charging station is performed, then the coupling process is simple and fast, but a very large inrush current arises that exceeds operational limits of components and may cause relay contact sticking
Solution Approach 1:
The patent applies preliminary action by precharging the high-voltage DC voltage intermediate circuit before coupling to the charging station. A precharging circuit with a precharging contactor is activated beforehand to charge the intermediate circuit capacitors through a precharging resistor, preventing large inrush currents during the main coupling process and ensuring component operational safety
Solution Approach 2:
The patent uses an intermediary approach by introducing a precharging circuit as a mediator between the high-voltage DC voltage intermediate circuit and the charging station. This precharging circuit includes a precharging contactor and precharging resistor that temporarily bridge the connection, allowing controlled charging before the main coupling occurs, thus protecting components from excessive currents
2Ease of manufacture
If Reed relays are used for galvanic separation of the precharging circuit from the charging station, then the system cost is reduced, but the relay switching contacts may stick together when large currents develop, reducing relay lifespan
Solution Approach 1:
The patent extracts the problematic function of relay switching from the precharging circuit by using the main charging contactor instead. The precharging contactor handles only the precharging current, while the main charging contactor handles the main charging current, separating the functions and preventing relay contact sticking by ensuring relays are not exposed to excessive currents beyond their ratings
Solution Approach 2:
The patent creates a redundant switching path by using both a precharging contactor and a main charging contactor. The precharging contactor provides a temporary switching path for precharging current, while the main charging contactor provides the permanent switching path for main charging current, ensuring that no single relay is exposed to currents exceeding its operational limits
3Reliability
If high-voltage relays are used for galvanic separation of the precharging circuit, then the relay can handle large currents without contact sticking, but the system complexity and cost increase
Solution Approach 1:
The patent segments the switching function into two separate contactors: a precharging contactor for the precharging circuit and a main charging contactor for the main charging circuit. Each contactor is sized appropriately for its specific current load, with the precharging contactor handling only the relatively small precharging current, thus avoiding the need for expensive high-voltage relays while maintaining reliability
Data Source
AI summary
A circuit assembly for precharging a high-voltage DC voltage intermediate circuit for a motor vehicle is provided. The circuit assembly includes a high-voltage battery with battery terminals to which the intermediate circuit is electrically coupled. Intermediate circuit terminals of the intermediate circuit are electrically coupled to corresponding station terminals of a high-voltage charging station for providing a charging current, wherein the intermediate circuit terminals are each selectively, electrically coupled to corresponding feeding points of the intermediate circuit via charging current-connecting switching elements by opening and closing. The switching elements are opened prior to coupling the intermediate circuit terminals to the station terminals. Electric potentials of the feeding points are equalized to each other by a first precharging current. A voltage existing between the intermediate circuit terminals is equalized to a nominal charging voltage by changing the potential of at least one of the feeding points by a second precharging current.