This relates to a Battery Management System (BMS) and Battery Charger in any application where high energy, and inherently unsafe, batteries cells are used.
High-energy lithium battery cells have complex degradation modes and are inherently unsafe because internal short circuits will statistically occur. Cell short circuits are typically formed when the separator fails, allowing the positive and negative electrodes to come in contact. At that point, heat is generated, which typically leads to a thermal runaway event.
As described in papers, including “Reliable and Early Warning of Lithium Battery Thermal Runaway based on Electrochemical Impedance Spectrum” (Peng Dong et al 2021 J Electrochem. Soc 168 090529, “the Peng Dong article”), Electrochemical Impedance Spectroscopy (EIS) can be used as an analysis tool to detect early warnings and indications of pending safety issues, such as an imminent cell short. EIS lab equipment typically are current-mode controlled devices with very low output capacitance and high sampling rates, features that are cost prohibitive to live in mobility on-board chargers. The challenge is how to bring this EIS lab-based equipment to a vehicle level that is cost effective and reliable.
An Energy Management Unit (EMU) which combines a battery management system (BMS) and On-Board Charger (OBC) and Electric Drive System (EDS) for managing a battery is disclosed. The EMU includes a plurality of communications to Analog Front End (AFE) application-specific integrated circuit (ASICs) and current sensors, and a power-electronics assembly designed to take AC grid power and charge the battery.
Various aspects of the novel systems, apparatuses, and methods are described more fully hereinafter with reference to the accompanying drawings. Aspects of this disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein, one skilled in the art should appreciate that the scope of the disclosure is Intended to cover any aspect of the novel systems, apparatuses, and methods disclosed herein, whether implemented independently of or combined with any other aspect. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope is intended to encompass such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects set forth herein. It should be understood that any aspect disclosed herein may be embodied by one or more elements of a claim.
Although particular aspects are described herein, many variations and permutations of these aspects fall within the scope of the disclosure. Although some benefits and advantages of the preferred aspects are mentioned, the scope of the disclosure is not intended to be limited to particular benefits, uses, or objectives. Rather, aspects of the disclosure are intended to be broadly applicable to e-mobility systems, including automotive, some of which are illustrated by way of example in the figures and in the following description of the preferred aspects. The detailed description and drawings are merely illustrative of the disclosure rather than limiting, the scope of the disclosure being defined by the appended claims and equivalents thereof.
Vehicle On-board chargers typically convert and isolate alternating current (AC) power to direct current (DC) battery power using a combination of capacitance and inductor energy storage devices as part of intermediate and output stages. As described in U.S. Pat. No. 1,458,856 entitled “Combined BMS, Charger, DC-DC in Electric Vehicles,” a charger can be engineered with very little capacitance in every power stage, including the output. Taking advantage of this low capacitance invention, new high-bandwidth charge control schemes, together with new high-voltage system architecture, can be realized to allow a vehicle charger to behave like a lab based Electrochemical Impedance Spectroscopy (EIS) or Frequency Response Analysis (FRA). During vehicle AC charging, the charger outputs current, that sweeps across various frequencies (typically, in the lab at 0.1 Hz to 10 kHz), into the high voltage (HV) battery, and the battery management system (BMS) measures the current and voltage responses from each cell and create the Nyquist Plot (Real Vs Imaginary Impedance) of battery cell parameters. The Peng Dong article describes how to use phase angle for early warning detection of shorted cells (thermal runaway). This is only one example of how to use an EIS for early warning detection of thermal runaway.
According to an embodiment of the present disclosure as illustrated in
According to embodiments of the present disclosure, once parameters are extracted from EIS and combined with battery impedance and open circuit voltage directly measured from the BMS, direct measurements of the State of Charge, State of Health and State of Power of a battery can be inferred. In addition, anomalies of frequency response can indicate a cell may be on the verge of runaway, while the DC response shows a normal behavior.
The Nyquist Theorem tells us that to properly recreate a waveform of a particular frequency, we need to theoretically sample at minimum two times of that frequency. But practically due to higher order noises, the sampling frequency usually needs to be several times (e.g., 10 times) higher. The challenge is that most Battery Management Systems (BMS) cannot sample cell voltages quickly enough as required by the EIS because the Analog Front End (AFE) application-specific integrated circuit ASICs used in BMSs struggle to obtain samples quicker than 10 msec, due to loop rate limit of typical isolated communication between BMS and AFEs, heavy filtering and precise A/D measurements needed for cell voltage inputs to battery algorithms, making it impossible to sample waveforms faster than 50 Hz (½*10 msec). However, due to the real-time digital control capability of modern digital power supplies, the frequency is known and can be communicated between the on-board charger (OBC) and BMS modules. Therefore, we can have a much lower sampling rate.
In one embodiment, as illustrated in
By controlling a BMS and Charger (e.g., OBC) in a combined system, another technique can be used in an addition to EIS.
To minimize data storage, the frequency sweep or pulse test can be periodically within a charge, perhaps at 10% state of charge (SOC) steps. To minimize the BMSs compute requirements, all signal processing and parameter extraction steps can be done on the charger or with the cloud.
Also, in a system, bus-bar/contactor/fuse impedance, and capacitance can be measured. If an anomaly is detected the appropriate action can be taken.
In another embodiment of this disclosure, the low voltage (typically 12V, 24V, or 48V) battery charger, e.g., a DC/DC converter 208 of
Although embodiments of this disclosure have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of embodiments of this disclosure as defined by the appended claims.
Number | Date | Country | |
---|---|---|---|
63294727 | Dec 2021 | US |