DE-102024003727-A1 - Method for operating an electrically powered vehicle when the high-voltage battery is discharged below a voltage threshold

DE102024003727A1DE 102024003727 A1DE102024003727 A1DE 102024003727A1DE-102024003727-A1

Abstract

The invention relates to a method for operating an electrically powered vehicle with at least one high-voltage battery, a battery management system, a low-voltage battery and a DC/DC converter, wherein the high-voltage battery is electrically coupled or can be coupled to the low-voltage battery via the DC/DC converter, wherein when the high-voltage battery is discharged below a predetermined voltage threshold, in particular below a discharge cut-off voltage of a cell of the high-voltage battery, active deep discharge protection of the high-voltage battery is requested by the battery management system, and/or a jump-start procedure is carried out by a second vehicle.

Inventors

Tobias Clemens Bach
Jochen Siehr
Johannes Sieg

Assignees

Mercedes-Benz Group AG

Dates

Publication Date: 20260513
Application Date: 20241113

Claims (10)

Method for operating an electrically powered vehicle with at least one high-voltage battery, a battery management system, a low-voltage battery, and a DC/DC converter, wherein the high-voltage battery is electrically coupled or can be coupled to the low-voltage battery via the DC/DC converter, whereby, when the high-voltage battery is discharged below a predetermined voltage threshold, in particular below a discharge cut-off voltage of a cell of the high-voltage battery, active deep discharge protection of the high-voltage battery is requested by the battery management system, and/or whereby a jump-start procedure is carried out by a second vehicle.
Procedure according to Claim 1 , wherein, when active deep discharge protection is requested by the battery management system, the high-voltage battery is charged from the low-voltage battery via the DC/DC converter until the low-voltage battery is completely discharged, whereby when the low-voltage battery is completely discharged, all control units of the vehicle are put into a sleep state.
Procedure according to Claim 1 or 2 , whereby during the jump-start process the high-voltage battery is charged via the DC/DC converter from the low-voltage battery of the second vehicle with a charge sufficient to drive to a charging station.
Method according to one of the preceding claims, wherein, when all control units of the vehicle are put into a sleep state, as soon as the second vehicle is ready for the jump-start procedure, the control units of the vehicle are put from the sleep state into an active state, wherein energy is fed in from the low-voltage battery of the second vehicle and the high-voltage battery is charged via the DC/DC converter with a charge amount sufficient to drive to the charging station.
Method according to one of the preceding claims, wherein a user of the vehicle is shown a message indicating whether a sufficient amount of charge can be supplied via the jump-start process to reach a nearby charging station with the vehicle, taking into account system limits and the distance to the nearest charging station.
Method according to one of the preceding claims, wherein an estimate of the time required for the jump-start procedure is given.
Method according to one of the preceding claims, wherein during the duration of the jump-start process an estimate of the distance to be covered is displayed at example speeds of the vehicle.
Method according to one of the preceding claims, wherein a range assistant indicates when the next charging station is reachable.
Procedure according to Claim 8 , whereby the range assistant displays a "ready" message when the next charging station can be reached, and navigation is started.
Method according to one of the preceding claims, wherein a maximum charge quantity and/or a power limitation to reach the next charging station is implemented.

Description

The invention relates to a method for operating an electrically powered vehicle when the high-voltage battery is discharged below a voltage threshold. Batteries are used to power electric vehicles. They consist of battery cells, housing, cooling system, and electrical/electronic components with measuring technology for current, voltage, and temperature of the cells, as well as a battery management system (BMS) for, among other things, determining the battery's state of charge. Important cell states are the capacity, i.e., the amount of charge, typically between a defined full state and a discharge state, and the state of charge (SOC), i.e., the amount of charge stored, so that 100% SOC corresponds to a full state and 0% SOC to a discharge state. Furthermore, the BMS determines operating limits for the battery, such as current and voltage limits, e.g., as fixed parameterized values or depending on the battery's state. These operating limits serve to prevent excessive aging or safety-critical cell conditions. The BMS of a high-voltage battery is usually powered in the vehicle by one or more low-voltage batteries with a voltage of 12V. Battery cells based on lithium-containing electrode materials, which in a partially charged state exhibit a phase equilibrium between lithium-poor and lithium-rich crystal phases, show a very steep cell voltage curve in the discharged state. This means that at a low state of charge (SOC), the cell voltage (both the open-circuit voltage and the dynamic voltage during operation) drops very sharply. Therefore, after the discharge cutoff, very little charge can be drawn before the cell, at its lowest state of charge, is deeply discharged, i.e., falls below a lower voltage limit. This is the case, for example, for batteries with cells using lithium iron phosphate (LFP) cathodes. The electrical/electronic components of the BMS, which provide the measurement technology for cell voltage and cell temperature, are often located near the battery cells and draw their power directly from the cells. This means that the battery cells discharge due to self-consumption as soon as the BMS is active. Reasons for this can include requests from other control units to switch to active mode, or reactivation cycles of the BMS itself. When a battery is empty or nearly empty, the problem arises that cells continue to discharge as soon as the BMS (Battery Management System) switches to active mode. In the worst-case scenario, this can lead to deep discharge of the battery, resulting in deactivation due to safety concerns, as recharging deeply discharged cells poses a safety risk. In this case, the battery must be replaced, resulting in significant financial loss. An electric vehicle with a discharged high-voltage battery cannot continue driving electrically because the cells can no longer deliver sufficient power and/or because the operating limits for cell protection have been reached. Unlike vehicles with combustion engines, it's not possible to simply get gasoline from a can and continue driving. Due to the lack of a large number of other vehicles with a so-called vehicle-to-vehicle charging capability, the vehicle must be towed or a mobile charging solution must be requested. The situation of a discharged high-voltage battery is usually counteracted by applying the discharge limit, avoiding excessive activation of the battery management system, and issuing a warning in a vehicle display and/or in the operating instructions. In the CN 213461126 U This document describes an undervoltage protection device for a high-voltage battery in an electric vehicle. The device can interrupt the battery's power supply when the available energy level is low. Simultaneously, an alarm signal is sent. This prevents permanent damage from excessive deep discharge of the battery and extends its operating time. The DE 102012214358 A1 This describes a deep discharge protection method for safeguarding the battery of a parked vehicle. The battery's state of charge is regularly monitored by a battery control unit and transmitted to an evaluation unit. When the battery reaches a predefined state of charge, a communication unit sends a message via mobile network to a stored address and/or uses sensor data to determine whether the vehicle's condition is suitable for autonomous battery recharging. One object of the invention is to provide an improved method for operating an electrically powered vehicle when the high-voltage battery is discharged below a voltage threshold. The aforementioned problem is solved using the features of an independent claim. Favorable embodiments and advantages of the invention will become apparent from the further claims, the description and the drawing. According to one aspect of the invention, a method is proposed for operating an electrically powered vehicle with at least one high-voltage battery, a battery management system, a low-voltage battery and a DC/DC converter, wherein the high-voltage batter