Multi-Voltage Battery Switching for 400 V/800 V EV Charging
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Solution Overview
Problem
Existing high-voltage storage systems for electric vehicles face challenges in efficiently switching between 400 V and 800 V charging modes while maintaining optimal state of charge and reducing energy losses.
Innovation Solution
A modular high-voltage storage system with a flexible changeover matrix that allows for interconnection of identical energy storage modules in series for high-voltage charging and in parallel for driving, utilizing a switching unit with controllable contactors and an electronic control unit to manage the switching status and ensure equalization of state of charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If DC charging at increased charging voltage (800 V or more) is used to increase charging power, then charging time is reduced, but changes to high-voltage storage technology are required which increase device complexity
Solution Approach 1:
The high-voltage storage unit is divided into multiple strings of battery cells. Each string can be independently connected to the charging socket, allowing selective charging at different voltages. This segmentation enables the system to handle 800V charging by activating only the necessary strings, rather than requiring complete system redesign.
Solution Approach 2:
The system dynamically configures the connection topology between battery strings and the charging socket using switching elements. During charging, the controller can switch between series connections (for 800V) and parallel connections (for 400V), allowing flexible adaptation to different charging power requirements without permanent structural changes.
2Power
If energy storage units with increased rated voltages are used to support 800 V charging, then charging power is increased, but compatibility with existing 400 V drivetrain components is lost
Solution Approach 1:
The system uses dynamic switching to change the effective voltage output during charging. By reconfiguring battery string connections from series to parallel, the system can output 400V for drivetrain compatibility or 800V for fast charging, maintaining versatility across different operational modes.
Solution Approach 2:
A charging socket with integrated switching elements acts as an intermediary between the high-voltage storage unit and the drivetrain. This intermediary manages the voltage transformation and distribution, allowing the battery system to operate at higher voltages during charging while maintaining compatibility with 400V drivetrain components through controlled connection configurations.
3Power
If multiple energy storage units are connected in series to double the voltage for 800 V charging, then charging voltage is increased, but switching reliability between charging and driving modes is compromised
Solution Approach 1:
The battery system is segmented into identical, independently controllable strings. Each string has its own switching elements, allowing granular control over connection topology. This segmentation simplifies the switching logic compared to managing a single large series-connected unit, improving reliability through modular fault isolation and control.
Solution Approach 2:
The system uses identical battery strings with matching characteristics, ensuring uniform voltage and current distribution during switching operations. This homogeneity reduces the risk of imbalances and faults during mode transitions, enhancing switching reliability between 400V and 800V charging modes.
4Adaptability or versatility
If a changeover matrix is designed to switch between 400 V and 800 V modes, then charging flexibility is improved, but the number of switching elements and system complexity increase
Solution Approach 1:
The changeover matrix is segmented into distributed switching elements within each battery string rather than a single complex central switch. This modular approach reduces the complexity of any individual switching element while maintaining overall system flexibility through coordinated control of multiple simpler switches.
Solution Approach 2:
The switching elements are designed with multi-functionality, serving both as connection switches during charging and as isolation switches during driving modes. Each switching element can operate in multiple configurations (series, parallel, disconnected), reducing the total number of dedicated switches needed and simplifying the overall changeover matrix design.
Data Source
AI summary
A multi-voltage storage system for an at least partially electrically driven vehicle comprising: a first high-voltage energy storage module and a second high-voltage energy storage module; one switching unit of identical design for each energy storage module, each switching unit having two positive inputs and two negative inputs, by means of which at least one load connection and one charging connection can be formed, a controllable contactor being provided downstream of each input, and the negative inputs each being able to be connected to a negative pole of an energy storage module and the positive inputs each being able to be connected to a positive pole of an energy storage module by means of the contactors; and a control unit, which is designed such that all the contactors of each switching unit can be controlled independently of each other in any way by the control unit.