1. Field of the Invention
This invention relates generally to an electrical device for providing a data communications link between an electronic monitoring unit associated with each cell in a battery module and a battery system manager (BSM) and, more particularly, to an electrical device that provides capacitive coupling through integrated metal foils in each cell in a battery module to provide a data communications link between the integrated electronic monitoring unit in adjacent cells and a BSM.
2. Discussion of the Related Art
Electric vehicles are becoming more and more prevalent. These vehicles include hybrid vehicles, such as the extended range electric vehicles (EREV), that combine a battery and a main power source, such as an internal combustion engine, fuel cell system, etc., and electric only vehicles, such as the battery electric vehicles (BEV). These batteries can be different battery types, such as lithium-ion, nickel metal-hydride, lead-acid, etc. A typical high voltage battery system for an electric vehicle may include several battery cells electrically coupled in series to provide the vehicle power and energy requirements. The battery cells may be grouped into battery modules, where each module may include a certain number of cells, and where the cells in a module are electrically coupled in series and/or parallel. The number of cells in a module and the number of modules in a vehicle depends on battery technology and application. For example, for Li-Ion type battery modules it is common use to have twelve cells in series in a module. Different vehicles may have different battery designs that employ various trade-offs and advantages for a particular application.
As a result of many factors, such as cell self-discharge rate, internal cell resistance, electrical connections, battery aging, etc., the state-of-charge (SOC) of the cells in the battery may drift apart during operation of the battery over time. A battery management system (BSM) may be provided to monitor the voltage thresholds, impedance, state-of-health and state-of-charge of each battery cell and the temperature of the battery, and control how much the battery can be charged and discharged based on the state-of-charge of the maximum charged cell and the minimum charged cell. The battery cannot be used to provide power if the cell with the lowest state-of-charge drops below some minimum state-of-charge because that cell may become damaged, and the battery cannot be over-charged beyond some maximum state-of-charge for the cell with the highest state-of-charge because that cell may become overheated and damaged. Thus, a cell with a low state-of-charge may prevent the battery from being used even though the other cells may have a suitable or significant state-of-charge.
In one known vehicle battery design, each battery module includes a cell sensing board (CSB), where each cell in the module is electrically coupled to the CSB by an analog wire. The CSB receives analog voltage signals from each battery cell in the module and uses filtering circuits, multiplexers, analog-to-digital (ND) converters, etc. to send the voltage signals on a digital wired communications link to the BSM. Because each cell in the battery modules has a voltage potential, such as 3-4 volts, a DC voltage shift occurs from one battery cell to an adjacent battery cell along the communications link as a result of that potential difference. It is known in the art to provide capacitors or transformers between two electrical connections to prevent DC current flow from one side of the capacitor to the other. Typically, an electrical twisted-pair of wires is provided in the communications link between the CSBs that include the capacitors or transformers that provide DC breaking so only the digital signals pass across the capacitor.
A new battery design has been investigated that eliminates the need for the CSBs in each battery module. Particularly, it has been proposed in the art to provide what are sometimes referred to as “smart cells” that include a low cost electronic monitoring unit integrated into the cell that includes electronics for monitoring the voltage and temperature of the cell, and to control the state-of-charge of individual cells by by-passing the cells using a switched resistor, also known as “passive balancing.” Particularly, each battery cell is equipped with an integrated electronic circuit that is part of the cell structure itself. Each electronic monitoring unit in each smart cell is part of the communications link from one cell to the next cell known as a chain topology so that the signals from each cell can be sent to the BSM. However, providing a capacitor, a connector and a twisted wire pair for each monitoring unit in the smart cell along the communications link is somewhat infeasible because of the number of connections that would be required.
In accordance with the teachings of the present invention, a battery module is disclosed that includes a plurality of battery cells having cell elements that are electrically coupled along a power line and an electronic monitoring unit that are electrically coupled along a communications link. Each cell includes a first capacitor plate pair, having a first capacitor plate and a second capacitor plate at a first side of the cell element, where the first capacitor plate pair is electrically coupled to the control unit and is electrically isolated from the cell element. Each cell also includes a second capacitor plate pair, having a first capacitor plate and a second capacitor plate positioned at a second side of the cell element, where the second capacitor plate pair is electrically coupled to the control unit and is electrically isolated from the cell element. The first capacitor plate at the second side of one cell element is capacitively coupled to the first capacitor plate at the first side of the cell element in an adjacent cell and the second capacitor plate at the second side of the one cell element is capacitively coupled to the second capacitor plate at the first side of the cell element in the adjacent cell so as to provide DC breaking along the communications link.
Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
The following discussion of the embodiments of the invention are directed to an electrical circuit that provides capacitive coupling through integrated metal foils to provide a data communications link between an integrated electronic monitoring unit in each cell of a battery module and a BSM is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the electrical circuit described herein has particular application for battery cells in a high voltage vehicle battery. However, as well be appreciated by those skilled in the art, the electrical circuit described herein may have other applications.
As will described in detail below, the present invention provides a communications link in a battery module including battery cells. The described communications link topology has a “chain” topology, which means that information is routed through all nodes, as opposed to a “star” topology, where all nodes would have a direct point-to-point connection to the BSM. The difference between a chain topology and a star topology is illustrated in
Each monitoring unit 18 is in communication with the monitoring unit 18 in an adjacent cell 12 along a communications link 22 including communications lines 24 and 26, where the lines 24 and 26 allow digital signal flow for the data being provided to and received from the units 18. Each smart cell 12 includes one plate of a capacitor 28 in the line 24 and one plate of a capacitor 30 in the line 26 that provide the DC breaking necessary because of the difference in voltage potential provided by the cell elements 14 in a manner that is well understood by those skilled in the art. The communications link 22 is coupled to a BSM 32 outside of the battery module 10 that receives, processes and transmits digital signals along the lines 24 and 26 to receive and process voltage signals from the cell elements 14 and to provide commands form the BSM 32 to the monitoring units 18.
As discussed above, providing integrated smart cells in a battery module has been proposed in the art to improve the cost, reliability, performance, etc. of the battery module. The traditional way for electrically coupling the capacitors 28 and 30 within the cell 12 would be to provide a separate electrical capacitor component and connect the capacitors 28 and 30 to the lines 24 and 26 by a wire through connectors. The present invention proposes a more cost effective and reduced complexity approach for integrating the capacitors 28 and 30 into the smart cells 12 that includes using capacitive coupling. The proposed approach provides a number of benefits, such as reduced cabling complexity, eliminated risk of connector failure, minimized risk of electrical hazard, and a minimized EMC exposure.
The smart cell 42 includes a cell element 52 that provides the chemistry and power of the cell 42, and which can be any suitable cell element that provides electricity, such as a lithium-ion pouch cell well known to those skilled in the art. It is stressed, however, that the chemistry of the smart cell 42 does not limit the invention as discussed herein. The cell element 52 includes a positive terminal 54 and a negative terminal 56 that are used to provide the electrical connection (not shown) from one smart cell to the adjacent smart cell in series along the line 16 shown in
The smart cell 42 includes an electronic monitoring unit 60, such as an ASIC, that includes the various circuitry and devices 62 for monitoring the cell voltage would be well understood by those skilled in the art. The monitoring unit 60 also includes electrical terminals 64 and 66 for providing an electrical connection for the communications link 22 as will be discussed in more detail below. The smart cell 42 includes four capacitor plates that are configured as metal films or foils, such as an aluminum foil, having a thickness of about 0.1 mm. Particularly, the smart cell 42 includes a pair of capacitor plates 68 and 70 on one side of the cell element 52 adjacent to the cooling fin 58 and another pair of capacitor plates 72 and 74 adjacent to and at the other side of the cell element 52 from the capacitor plates 68 and 70. The pair of the capacitor plates 68 and 70 provides electrical coupling to the cell 44 at one side of the smart cell 42 and the other pair of the capacitor plates 72 and 74 provides electrical coupling to another adjacent smart cell (not shown) at the other side of the smart cell 42. The capacitor plates 72 and 74 are positioned adjacent to the monitoring unit 60 and are electrically coupled thereto. The capacitor plate 68 includes an extended terminal 78 and the capacitor plate 70 includes an extended terminal 80. The terminal 78 makes electrical contact with the terminal 64 and the terminal 80 makes electrical contact with the terminal 66. These electrical connections are not specifically shown in
The capacitor plates 68-74 need to be electrically isolated from the adjacent conductors. This electrical isolation is not specifically shown in
The capacitive coupling between the capacitor plate 68 in the smart cell 42 and the capacitor plate 72 in the smart cell 44 define a capacitor, such as one of the capacitors 28 in the communications line 24. Likewise, the capacitive coupling between the capacitor plate 70 in the smart cell 42 and the capacitor plate 74 in the smart cell 44 define one of the capacitors 30 in the other communications line 26. The distance between the plates 68 and 72 and the plates 70 and 74 is selected to provide the desired capacitance and DC breaking necessary for the digital signal flow, and is defined by the thickness of the mantels 86 in the smart cells 42 and 44. In one non-limiting example, that distance is typically less than 0.1 mm, resulting in a capacity value typically of 1 nf. The parasitic capacitance created between the capacitor plates 68 and 70 and the cooling fin 58 and the parasitic capacitance created between the capacitor plates 72 and 74 and the cell element 52 needs to be considered in the electrical design of the battery module 40. Thus, it is not necessary to provide wires in the communications lines 20 and 22 for connecting one cell to an adjacent cell.
As mentioned above, the communications link 22 between the smart cells in the battery modules includes both the lines 24 and 26. Different communications schemes are known in the art where both communications directions can be operated in parallel at the same time, known as full-duplex, or where the digital signals can propagate in both directions only one after the other on the lines 24 and 26, known as half-duplex.
As will be well understood by those skilled in the art, the several and various steps and processes discussed herein to describe the invention may be referring to operations performed by a computer, a processor or other electronic calculating device that manipulate and/or transform data using electrical phenomenon. Those computers and electronic devices may employ various volatile and/or non-volatile memories including non-transitory computer-readable medium with an executable program stored thereon including various code or executable instructions able to be performed by the computer or processor, where the memory and/or computer-readable medium may include all forms and types of memory and other computer-readable media.
The foregoing discussion disclosed and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.