Wireless communication system for a battery management system, battery management system, and method of operating a battery management system

Abstract

Embodiments of the present invention include a battery wireless communication system (10) for a battery management system (20) comprising: at least one wireless communication device (11, 11a, 11b), said RF master, managing a communication protocol; a plurality of battery cells (13); a plurality of monitoring devices (12), said RF slaves, communicating with wireless link (18) with RF master (11, 11a, 11b), each RF slave (12) monitoring one cell (13); characterized in that the system (10) is configured to exchange data via command from RF master (11, 11a, 11b) and / or reply from RF slave (12) with a message comprising a payload less than 10 bytes.

Description

WIRELESS COMMUNICATION SYSTEM FOR A BATTERY MANAGEMENT SYSTEM, BATTERY MANAGEMENT SYSTEM, AND METHOD OF OPERATING A BATTERY MANAGEMENT SYSTEMField of the invention

[0001] The present invention relates to a battery management system and a method of operating this battery management system, more specifically a battery pack implemented for example in an electric or hybrid electric vehicle or in a system for storage energy. Such a system or method improve and optimize the operational performance (e.g. autonomy, lifetime, power, ...), production (e.g. costs, weight, complexity, scarcity of raw materials, ...) or recycling (costs, degree of recycling, complexity, ...) of batteries for various uses such as electric mobility, energy storage, to name only two applications.Background of the invention

[0002] The importance of battery-based power systems within today's markets is well understood by one of skill in the art. These battery systems are replacing traditional power systems in several different markets as products are moving towards more environmentally friendly and cost-effective power solutions. For example, markets such as the electrical vehicle and home energy markets are experiencing rapid growth as battery powered systems are becoming more dynamic in their ability to store and deliver power to corresponding products. This movement away from traditional power sources (e.g., fossil fuels, coal, etc.) to battery-based power sources is placing higher performance demands on the management of battery cells to ensure proper operation within ever-increasing complex products.

[0003] Many battery-based power systems have a centralized management controller that communicates with multiple battery management integrated circuits. Each of these battery management integrated circuits manages a plurality of battery cells and performs various tasks. For example, a battery management integrated circuit may sense voltage and charge levels on battery cells, may manage charge bybleeding charge or re-charging cells, as well as perform other sensing operations and low-level battery management functions.

[0004] In this context, there is a need for a more efficient and dynamic alternative battery management system solution.Summary of the invention

[0005] To this end, the various aspects of the invention relate to a wireless communication system, a battery management system and a method of operating this battery management system disclosed in the set of claims.

[0006] According to another aspect, the invention relates to a wireless communication system for a battery management system comprising:- at least one wireless communication device, said RF master, managing a communication protocol;- a plurality of battery cells;- a plurality of monitoring devices, said RF slaves or RF slaves, communicating with wireless link with RF master, each RF slave monitoring one cell.

[0007] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination:- the wireless communication system can be configured to exchange data via command from RF master and I or reply from RF slave with a message or instruction comprising a payload less than 10 bytes, preferably equal to 9 bytes, preferably less than 9 bytes, preferably equal to 8 bytes, preferably less than 8 bytes, preferably equal to 7 bytes, preferably less than 7 bytes, preferably equal to 6 bytes;- wireless communication or wireless link can implement radio wave, especially 2,4 GHz base band;- the wireless communication system can synchronize the plurality of RF slaves by asking or sending everyone of them with message comprising a payload less than 10 bytes, preferably equal to 9 bytes, preferably less than 9 bytes, preferably equal to 8 bytes, preferably less than 8 bytes, preferably equal to 7 bytes, preferably less than 7 bytes, preferably equal to 6 bytes;- the wireless communication system can be configured, via RF master to send command or request so that RF slaves receive said command or request with a jitter, of max 0.3 microseconds;- the system can be configured in that RF slaves only reply when a command I request from RF master is received;- the system can be configured in that RF slaves reply without acknowledgement;- the system can be configured to define a predetermined fixed time slot so that RF slaves reply one after the other;- the system can be configured in that when a reply from one RF slave is not received by the RF master within a synchronization period, RF master will not repeat the last command I request, implying for that period the data I reply of RF slave is lost and the previous information becomes the current information;- the battery management system comprises an electronic control system comprising: a master electronic control unit, said BMS master, and at least one wireless communication device, said RF master;- the battery management system comprises at least two wireless communication devices, said RF masters, wherein one of the RF masters is active, said active RF master, and the others are passive, said passive RF masters, wherein an active RF master is configured to calculate and send commands to the RF slaves, and a passive RF master is configured to only receive data from the RF slaves;- preferably RF masters and RF slaves being configured to communicate solely using wireless communication link, and BMS master and RF masters being configured to communicate using a wired communication link, in order to exchange data for managing the battery cells;- preferably active RF master is configured to receive commands / requests from BMS master ;- preferably active RF master is configured to forwards commands I requests to RF slaves;- preferably active RF master is configured to receives back information from RF slaves;- preferably active RF master is configured to sends back information to BMS master;- preferably passive RF master is configured to receive commands / requests from BMS master;- preferably passive RF master is configured to not forward commands / requests to RF slaves;- preferably passive RF master is configured to receive back information from RF slaves;- preferably passive RF master is configured to send back information to BMS master;- according to one embodiment, the at least two RF masters are configured to switch roles between active and passive;- according to one embodiment, the master electronic control unit is configured to assign the roles active or passive;- according to one embodiment, the at least two RF masters are configured to assign themselves the roles active or passive;- the system can be configured in that the communication protocol can be based on a “command I request” respectively “data I reply” principle, preferably implying that a RF slave must only reply when a command I request from active RF master is received ; in case of at least one active RF master and at least one passive RF master, command / request is sent by the active RF master and a passive RF master cannot send command I request;- preferably, for the cell information(s), when a reply from RF slave is not received by the RF masters, or active and passive RF masters, within a synchronization period, RF master or active RF master will not repeat the last command I request, implying for that period the data I reply of RF slave is lost and the previous information becomes the current information (e.g. cell voltage, current and temperature, status, error);- preferably, an exception for the preceding principle is for family user frame (setup and diagnostic): active RF master retries n times to send the command I request. In case this is not successful, a communication error is raised for this faulty RF slave;- preferably, when a RF slave is replying, it has a dedicated time to do it, to start and end wireless transmission, herein called the slot time.

[0008] According to another aspect, the invention relates to a battery management system according to one or several features of the preceding aspect.

[0009] According to another aspect, the invention relates to a method of operating a battery management system according to the preceding claim, comprising exchanging data via command from RF master and I or reply from RF slave.

[0010] According to one embodiment, when the battery management system comprises at least one active RF master, and at least one passive RF master, active and passive roles of RF masters are switched when the active RF master is faulty.

[0011] In another aspect, the invention relates also to an electrical vehicle comprising this battery management system.

[0012] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination:- the method comprises the step of synchronizing the plurality of RF slaves by asking or sending everyone of them with a command from RF master comprising a payload less than 10 bytes, preferably equal to 9 bytes, preferably less than 9 bytes, preferably equal to 8 bytes, preferably less than 8 bytes, preferably equal to 7 bytes, preferably less than 7 bytes, preferably equal to 6 bytes;- the method comprises the step: RF slaves only reply when a command / request from RF master is received;- the method comprises the step of predetermining fixed time slot so that RF slaves reply one after the other;- method comprises the step: when a reply from one RF slave is not received by the RF master within a synchronization period, RF master will not repeat the last command I request, implying for that period the data I reply of RF slave is lost and the previous information becomes the current information.

[0013] The proposed invention presents the following advantages:- retrieving all necessary information(s) of battery cells to implement all standard and advanced functions of a BMS of battery cells (e.g. 100 cells) within a synchronization period, in particular less than 100ms, preferably less than 50ms, preferably within 20 ms;- synchronizing cells with a jitter of max 0.3 microseconds, where jitter is the relative time between the first and last RF slave receiving a command / request from BMS control system;- having an availability rate of minimum 99.90% on the reception of commands sent by the BMS control system and on reception of information sent by RF slaves;setting up, with robustness, some parameters for each cell, in particular be 100% sure a command sent by BMS control system is received by RF slaves.Brief description of the drawings

[0014] The present invention will be described subsequently in more detail with reference to the attached drawing, given by way of examples, but in no way limited thereto, in which:- Figure 1 is a schematic representation of a system for RF communication of a BMS master of the battery management system according to embodiments of the present invention;- Figures 2 is a schematic representations of the radio message implemented in the battery management system, according to embodiments of the present invention;- Figure 3 is a datagram illustrating representations of the protocol implemented in the battery management system, according to the embodiments of the present invention;- Figure 4 is a representation of a time sequence of operating a battery management system, according to the embodiments of the present invention;- Figures 5 to 7 are schematic representations of the user frame families of the communication protocol implemented in the battery management system, according to the embodiments of the present invention.Detailed description of the invention

[0015] With reference to figure 1 , a battery management system 20, also known under the acronym “BMS”, comprises a battery pack 19 comprising several modules, including cells 13 in series. Inside a module, the cells 13 are mechanically grouped by ten, this group is called stack. The battery pack 19 can comprise one hundred cells 13 or more. For example, in terms of physical / mechanical view, it is (could be) dividedin modules, for instance in a car, a module of sixty cells 13 (or six stacks) and another of forty cells 13 (or four stacks) which are not physically located at the same place. But from the point of view of the electronic control unit, said BMS master 11 , 11 a, 11 b (logical view), it is a pack of n cells 13 (one hundred in a car). Nevertheless, the mechanical introduces some limitations in terms of energy transfer between cells 13.

[0016] The battery management system 20 comprises an electronic control system 14 and an electronic wireless system 10.

[0017] The electronic control system (said BMS control system) 14 implements:- all algorithms relating to management of the battery pack 19;- the wireless communication with the battery pack 19;- the wired communication 21 with the central unit of a vehicle.

[0018] The electronic wireless system 10, also named wireless communication system, implements:- all algorithms relating to management of a battery cell 13;- the wireless communication between the BMS control system 14 and the battery pack 19.

[0019] The electronic control system 14 comprises a central unit named BMS master 15. BMS master 15 implements all algorithms relating to management and functional safety (e.g. relays state) of the battery pack 19 besides handing the sensors (e.g. battery pack current, voltage), actuators (e.g. open / closing relays) of the battery pack 19 and communication 21 to the central unit vehicle.

[0020] The electronic control system 14 comprises a wireless communication device named a RF master 11 , 11 a, 11 b. A RF master 11 , 11 a, 11 b implements the wireless communication with a monitoring device or a control unit named RF slaves 12 of the battery pack 19, and as it will be described hereafter ensures the redundancy of the wireless communication 18.

[0021] The electronic wireless system 10 comprises a plurality of RF slave 12, wherein each RF slave 12 is associated with one battery cell 13.

[0022] According to an architectural setup, a central unit of a vehicle communicates with the central unit (also called BMS control system) 14 of a battery management system (BMS) 20. BMS control system 14 is being in communication (sending commands I receiving information) with the batteries 19 via a wireless communication link 18. Wireless communication is being facilitated by electronic control units or monitoring devices (also called RF slaves) 12 associated with each battery cell 13. BMS control system 14 comprises an electronic control unit (also called BMS master) 15 that communicates with the central unit of a vehicle via a wired communication link 21.

[0023] In one embodiment of this invention, this battery management system 20 is dedicated to the automotive industry. Each battery cell - basic building unit of an EV battery pack - has its own RF slave 12 for health, current, voltage, temperature, and charge control. These RF slaves 12 communicate with and are driven by a central unit named BMS control system 14 which comprises a master electronic control unit named BMS master 15, a primary or active 11 a, and a secondary or passive 11 b, masters for redundancy.

[0024] According to figure 1 , this battery management system 20 comprises:- a BMS control system 14 comprising: a BMS master 15, and at least two RF master 11 , 11 a, 11 b, wherein one of the RF masters 11 , 11 a, 11 b is active, said active RF master 11a, and the others are passive, said passive RF masters 11 b;- a plurality of RF slaves 12 each RF slave 12 monitoring one battery cell.

[0025] This BMS control system 14 comprises a redundant system for RF communication by comprising the active RF master 11 a and the passive RF masters 11 b as it is visible in figure 1. In fact, this approach implements a redundant system for the RF masters 11 , 11 a, 11 b, wherein the active and the passive RF masters 11 , l l a, 11 b can switch their respective roles. As said before, a BMS unit is logically composed of a BMS master 15, an active RF master 11 a and a passive RF master l l b, and a plurality of RF slaves 12. The approach retained in this application, in order to reduce the cost as well, is a full redundant backup only of the wireless or RFpart. There is only one BMS master 15 which communicates with active 11 a and passive 11 b RF masters that communicate with the RF slaves 12. The two RF masters 11 a, 11 b are communicating with the BMS master 15.

[0026] In the rest of the document, the primary RF master 11 a is replaced by the active RF master 11 a; the secondary RF master 11 b is replaced by the passive RF master 11 b.

[0027] The active RF master 11a calculates and sends commands, the passive one 11 b only receives. Active RF master 11a sends and receives from BMS master 15 to slaves 12 and vice-versa. The passive RF master 11 b receives everything as the active RF master 11 a but sends nothing to the RF slaves 12 or, according to one embodiment to the BMS master 15.

[0028] In this context, the active RF master 11 a is in an active operating mode and the passive master 11 b is in a passive operating mode. For example, the wireless communication module of passive RF master 11 b is able to switch in the active mode when the active RF master 11 a is faulty. In particular, active RF master 11 a and passive RF master 11 b can switch roles or assignment, namely active role or passive role, when the current active RF master 11 a is faulty. Roles can be switched by RF masters 11 , 11 a, 11 b themselves or by BMS master 15.

[0029] Redundancy is the ability to replace the active 11 a role of RF master 11 by one of the passive 11 b RF masters 11 , in case of the malfunction of the active RF master 11. This results in increasing reliability of the system.

[0030] E.g. If active RF master 11 , 11 a, 11 b becomes malfunctioning (e.g. no more sending commands / requests to RF slaves 12), and BMS master 15 recognizes the problem, BMS master 15 would request one of the passive RF masters 11 , 11a, 11 b to take the role of the active RF master 11 , 11a, 11 b.

[0031] In case both active and passive RF masters 11 , 11 a, 11 b are functioning, the redundancy results in increasement the availability of the information sent back by RF slaves 12.

[0032] E.g. While we get back information from all RF slaves 12 by active RF master 11a, we may have missed one (information from) RF slave 12 e.g. address 5. But this RF slave 12 (address 5) could be received by passive RF master 11 b (if RF slave 12 with address 5 is working). All RF masters 11 , 11 a, 11 b then transmit the information to BMS master 15 and it will merge the data received from all RF masters 11 , 11 a, 11 b. In this manner the probability of losing information is reduced.

[0033] Such an architecture is capable of handling (sending commands I request to and receiving information from) at least one hundred cells 13 within synchronization period (20 ms). If more than one hundred cells 13 are required, the time for communication will increase. However, the wireless system 10 can be duplicated to double (or triple and so on) the number of RF slaves 12 (e.g. 800V respectively up to 5200V) battery pack 19) with the same performance, i.e. up one thousand three hundred cells 13 information can be communicated within the synchronization period (20 ms).

[0034] Hereafter, according to one embodiment, functionalities of each main element are described hereafter.

[0035] BMS master 15:- receives and checks commands / requests from central unit of the vehicle VCU via a proprietary protocol on the CAN network (wired communication link 21 );- updates the behaviour of battery related algorithms (e.g. cells balancing via bypass or energy transfer, charging of the battery) and other algorithms (e.g. command I state of actuators, functional safety);- encodes the commands I requests and send these to all RF masters 11 , 11a, 11 b;- receives all data I replies from all RF masters 11 , 11 a, 11 b and all RF slaves 12. Due to redundancy, each RF master 11 , 11 a, 11 b is sending back all the data I replies it receives from all the RF slaves 12. BMS master 15 must merge all data / replies of the RF slaves 12;- checks, and compute statistics (in that order) of data I reply from each RF master 11 , 11 a, 11 b and RF slave 12 (depending on the command);- extended checks of all the data (e.g. if the measurement is within a range, consistency check between a measure or set of measures or data and command);- encodes data (e.g. as previously) for extended monitoring purposes;- send back information required by the vehicle proprietary protocol (CAN);- updates its own device firmware (DFU) and those of RF masters 11 , 11 a, 11 b and, over the air (OTA), RF slaves 12, all received from the vehicle central unit or an external service tool;

[0036] RF master 11 , 11 a, 11 b:- receives and checks commands I requests from BMS master 15, sends back information regarding its own measures and states (e.g. power supply, CPU temperature, errors) to BMS master 15;- processes and I or forwards commands I requests to RF slaves 12;- receives, checks, and compute statistics (in that order) of data I reply from each RF slaves 12 (depending on the command I request);- forwards data I reply from each RF slaves 12 to BMS master 15;- updates its own device firmware (DFU) and those, over the air (OTA) of RF slaves 12, all received from BMS master 15.

[0037] RF slave 12:- receives, checks, compute statistics (in that order) commands I request from active RF master 11 , 11a, 11 b;- processes commands (e.g. cell management (we will describe these in the protocol);- collects information regarding its own state (e.g. cell voltage I current I temperature, errors (such as overcurrent, undercurrent, overvoltage, undervoltage, RF wireless communication) CPU temperature);- sends back above information (see previously) to all RF masters 11 , 11 a, 11 b;- update its own device firmware (DFU) received from BMS master 15 via all RF masters 11 , 11 a, 11 b wirelessly. Due to limitations of standard and robust wireless protocol used for the over the air (OTA) device firmware update (DFU), even active RF master 11a and passive RF masters 11 b are exchanging data with RF slaves 12. Each RF master 11 , 11 a, 11 b is communicating with fifty RF slaves 12 (e.g. active RF master 11 , 11 a, 11 b is responsible to update RF slaves 12 with addresses 1 to 50 and passive RF master 11 b is responsible to update RF slaves 12 with addresses 51 to 100). In that case, all RF masters 11 , 11a, 11 b and their associated RF slaves 12 are communicating over different radio channels. These specifications concern only the over the air (OTA) device firmware update (DFU)) as another protocol (wireless standard) than which is described in this document is used.

[0038] In reference to figure 1 , the primary RF master 11a or the secondary RF master 11 b comprises a main system that will be connected to:- a central control system like for example an EMU (acronym for “Electronic Monitoring Unit”) and / or ECUs (acronym for “Electronic Control Units”) in a vehicle via a communication system like a CAN (acronym for Controller Area Network);- a RF slave 12 via RF communication (acronym for Radio frequency communication).

[0039] The active RF master 11a and the passive RF master 11 b act as RF transceiver of BMS master 15. The RF masters 11 , 11a, 11 b (active and passive) are able to manage the protocol and wireless communication with the RF slaves 12.

[0040] In this configuration, these active 11 a and passive RF masters 11 b both receive, via RF communication, the messages from the RF slaves 12. These active and passive RF masters 11 , 11 a, 11 b have the same technical characteristics. In this context they execute the same algorithms based on the same instructions and data from their environment, and therefore produce the same results.

[0041] However, at any given time, only one of them is the active RF master 11 a in sending, via RF communication, instructions to the RF slaves 12. In other words, at any given time, the active RF master 11 a, is able to receive and / or transmit data from / to at least one of the RF slaves 12. When the passive RF master 11 b, is only able to receive the same data as the active RF master 11 a from at least one RF slave 12. According to one embodiment, an interface, other than CAN and RF, exists between the active RF master 11 a and passive RF master 11 b to identify which of the two is in the active operating mode and to allow, if necessary, switching from passive to active operating mode, respectively from active to passive operating mode.

[0042] In reference to figure 3, the primary 11 a and secondary 11 b RF masters are able to communicate periodically, via RF communication (acronym for Radio frequency communication), with each RF slave 12, every 20 ms thanks to a proprietary communication protocol. This implies that every 20 ms, the RF master 11 which is in an active operating mode, here the primary master 11 a, gives its (common) instructions to the RF slaves 12 and receives, from each RF slave 12, a set of cellspecific information(s).

[0043] The communication channel between RF masters 11 a, 11 b and all RF slaves 12 is wireless. The active RF master 11 a or the passive RF master 11 b is able to use a radio transceiver, generate the radio signals and manage the protocol. Preferably, this communication channel operates in the 2.4 GHz base band (2400 - 2420 MHz), for example is based on the basic RF stack of Bluetooth® I ZigBee® (IEEE 802.15) and Wi-Fi® (IEEE 802.11 ) communications with the following configuration: 2-GFSK modulation, 1 MHz bandwidth, 20 channels, 2 Mbps data rate and fixed user frame of 6 bytes (see Figure 2 (4)). The developed protocol does not follow the IEEE 802.15. xx or IEEE 802.11.xx standards. Standard protocol wassuggested to increase to increase reliability, we prefer to be fast over robustness for periodic data collection from the cells in a synchronization of 20 ms.

[0044] In reference to figure 2, a message or instruction like command or reply comprises a plurality of fields wherein first and sixth (1 & 6) are 2.4 GHz radio transmissions initiating and closing the transmission, respectively. Field number 2 is a preamble related to the 2.4 GHz radio transmission that advice, for example, the RF slaves 12 that data are on the way. Field number 3 is synchronization, which is a known sequence of data used to identify the start of the user frame, or payload, field number 4. Field number 4 is the user frame, which is managed by the firmware running on the RF masters 11 , 11 a, 11 b or RF slaves 12 such as command / request and data / reply. Field number 5 is a field to detect error in the user frame.

[0045] Design’s option taken is a very low weight protocol in terms of user frame with only 6 bytes, and protocol layers (only 1 ). When missing information from a cell 13, the probability to receive it at the next synchronization period is very high due to the availability rate achieved (> 99.9%) and definitively better than trying to repeat n times to be sure to receive a missing cell, which introduce some big jitters (many ms, 10 or 100’s of ms) in the synchronization period.

[0046] In reference to figure 3 illustrating communications between RF master 11 , 11 a, 11 b and RF slaves 12, every 20 ms (synchronization period) the BMS master 15 (a) or RF master 11 , 11 a, 11 b (b)) sends a command I request to all RF masters 11 , 11 a, 11 b (a) or RF slaves 12 (b) respectively. Figure 3 illustrates two cases: case 1 : BMS master 15 is communicating with RF masters 11 , 11a, 11 b, and case 2: BMS master 15 is communicating with RF slaves 12 via the active RF master 11 , 11 a, 11 b.

[0047] Case 1 : BMS master 15 sends commands I requests (A) to RF masters 11 , 11 a, 11 b. Commands I requests are only for the RF masters 11 , 11a, 11 b in terms of processing but nevertheless these are forwarded (only on active RF master 11 , 11 a, 11 b ) to the RF slaves 12 to keep the synchronization with RF slaves 12 but RF slaves 12 ignore the request.

[0048] As the communication between BMS master 15 and RF masters 11 uses a wired and synchronous communication link, the RF master 11 is sending its owndata I reply (F) at the same time it receives command I request. It implies that the information RF master 11 sent back to BMS master 15 is a result of the algorithms based on the state of the previous synchronization.

[0049] Case 2: BMS master 15 is sending command I request (A) to RF slaves 12 via the active RF master 11 , 11 a, 11 b. Active RF master 11 , 11 a, 11 b does not add or modify the command I request, but only forwards it. The passive RF master 11 , 11a, 11 b does not send anything.

[0050] All RF slaves 12 are replying within their individual slot times (C) as a confirmation of the command I request. It is a data I reply. Each RF slave 12 indicates its own address. This date / reply comprises measures or parameters depending on the command / request. When receiving command / request from RF master 11 a the RF slaves 12 first perform acquisition of measures, such as cell voltage, cell current, and checks their values which is done in a period of time as indicted by (B). After sending its data / reply (C), the RF slaves 12 are handling and applying the command / request (A), which is done in the indicated time (D). When not performing the operation related to B, C and D, the RF slaves are in the sleep mode (E) in order to reduce energy consumption.

[0051] Slot time applies only for the RF slaves 12: it is a defined and fixed time. It is measured from a reference time which is the receipt of the command I request. At this fixed time (the slot time) the RF slave 12 is allowed to transmit its data I reply. The duration of the wireless transmission is fixed and depends on the radio specifications (and is the same for all RF slaves 12). Slot time is computed with the RF slave 12 address. The next slot time (for the RF slave 12 with the following address) will start at the slot time of the previous RF slave 12 plus the duration of wireless transmission plus a small fixed spare time (and is the same for all RF slaves 12).

[0052] The system is ‘set up’ and ‘tune up’ to permit that 100 RF slaves 12 can transmit their data / reply within the synchronization period (20 ms).

[0053] The accuracy of the synchronization (jitter) received by all RF slaves 12 is less than 0.3 microseconds. This ensures that all RF compute their respective slottime such that no overlap of wireless transmission can happen between two consecutive RF slaves 12. This also ensures that RF slaves 12 are measuring at least the cell voltage and current at the same time. (Although the 1 st RF slave 12 and the 100th RF slave 12 send the cell voltage and cell current taken at a common absolute time but sent at various times). This common absolute time is the Acquisition Time. After sending the data / reply, RF slave 12 processes algorithms according to the measures done during Acquisition Time and the decoding of the command / request it receives. This is the Handle Time. Once this time is over, RF slaves 12 are Idle / Sleeping to reduce their energy consumption. It is to be noted that Idle / Sleep could be between acquisition (Acquisition Time) and wireless transmission and / or handle (Handle Time) and end of synchronization period.

[0054] Furthermore, for setup and services commands to the RF slaves 12, a mechanism is implemented in order to ensure the slaves receive and acknowledge the commands. For the OTA DFU (acronym for “Over-The-Air Device Firmware Upgrade”) mode, another protocol (CONNECT standard) is used to ensure all the slaves receives the new firmware.

[0055] In reference to the figure 4 (Measure), it is illustrated data exchanges between BMS master 15, RF masters 11 , 11 a, 11 b and RF slaves 12. Most of the time, the aim of the exchanges between BMS master 15, RF masters 11 , 11 a, 11 b and RF slaves 12 is to collect cell information (e.g. cell voltage, current, temperature, states, errors). Horizontals lines in Setup and Measure are either Command / Request and / or Data I Reply.

[0056] In reference to figure 4, during the setup or during the measure behaviors of the RF masters 11 , 11a, 11 b and / or RF slaves 12 is adapted using one-time specific commands / requests with family user frame (setup and diagnostic). E.g. during power on, we need to set up RF masters 11 , 11 a, 11 b and RF slaves 12. For that we can send one or more set up identification from BMS master 15 to RF master 11 , 11a, 11 b and / or RF slaves 12.

[0057] In figure 4, during measure, an example is an external monitoring system or service tool which is requesting to get or set calibration parameters for cell voltage,current and temperature or to request every minute some statistics from RF master 11 , 11a, 11 b and / or RF slaves 12. Another example could be, during the charge at a given voltage BMS master 15 is requesting to the RF slaves 12 to measure the internal impedance.

[0058] For the rest of the description, the protocol specifications are presented according to several cases.

[0059] User frame or payload can be: 1 . Command I Request, 2. Data I Reply.

[0060] When command / request is the user frame: a) BMS master 15 is transmitting to one specific or all RF masters 11 , 11 a, 11 b, or b) active RF master 11 , 11 a, 11 b is transmitted-ing to one specific or all RF slaves 12.

[0061] When Data / Reply is the user frame: a) a RF master 11 , 11 a, 11 b is transmitted to the BMS master 15 or b) a RF slave 12 is transmitted to all RF masters 11 , 11a, 11 b.

[0062] Command can be: 1. Broadcast, 2. Unicast.

[0063] Broadcast: address field in the user frame is a specific address which is outside the RF slave 12 addresses range. Broadcast permits send a command I request: a) from BMS master 15 to RF masters 11 , 11 a, 11 b, or b) from active RF master 11 , 11 a, 11 b to all RF slaves 12.

[0064] Broadcast address is never used by RF masters 11 , 11 a, 11 b and RF slaves 12 in their reply.

[0065] Unicast: address field in the user frame is an address which is in the range of RF slave 12 address (1 to 100). It is used by the RF masters 11 , 11 a, 11 b and RF slaves 12. Unicast permits to send command I request: a) to one specific RF master 11 , 11 a, 11 b by the BMS master 15, or b) to one specific RF slave 12 by the active RF master 11 , 11 a, 11 b.

[0066] RF masters 11 , 11 a, 11 b and RF slaves 12 are always replying with their address in the user frame.

[0067] Replies of a) RF masters 11 , 11 a, 11 b to BMS master 15 and / or b) RF slaves 12 to RF masters 11 , 11 a, 11 b are unicast replies.

[0068] Furthermore, there are three families of user frames: 1. Setup, 2. Measure, 3. Diagnostic.

[0069] Measure: according to figure 5, it is presented in fields in the command / request user frame used a) in communication from BMS master 15 to RF masters 11 , 11 a, 11 b or b) from active RF master 11 , 11 a, 11 b to RF slaves 12:- read or write (5.0): field that indicates if the parameter is written or read, address field (5.1 ): always broadcast address is used;- command identification (5.2): a field which indicates that the command I request is a measure user frame;- counter (5.3): incremental counter field. The goal is to check whether a) the RF masters 11 , 11a, 11 b receives all commands I requests from the BMS master 15 or b) the RF slave 12 receives all commands I requests from the active RF master 11 , 11a, 11 b. This serves to compute the quality of the reception on each device (BMS master 15, RF masters 11 , 11a, 11 b, RF slaves 12);- mode (5.4): field that indicates if the vehicle is currently charging, driving, or testing on a test bench;- temperature set point (5.5): a field that indicates which temperature limit to use for heating, respectively, cooling the battery pack 19;- bypass mode (5.6): field that indicates if the balancing is done via bypassing the current (mostly used in charging mode) or via the energy transfer (mostly used during driving mode).

[0070] Energy transfer (5.7): field that indicate whether a set of 10 RF slaves 12 within a given stack can do energy transfer or bypass to their left and / or right neighbour cell (current bypass 0 - 100% using a PWM method) or in general balancing.

[0071] Measure: according to figure 6, it is presented fields in the data / reply user frame used a) in communication from RF masters 11 , 11 a, 11 b to BMS master 15 or b) from RF slaves 12 to RF masters 11 , 11a, 11 b:- read or write (6.0): field that indicates if the parameter is written or read;- unicast address (6.1 ): field with the address of the RF slave 12 from 1 to 100 who is replying;- command identification (6.2): a field which indicates that the data I reply is a measure user frame;- status (6.3): mode field that indicates if the vehicle is currently charging, driving or testing on a test bench. In addition to the mode, there is an error indicator;- cell voltage (6.5) and cell current (6.6): fields are received at each synchronization period;- channel indicator (6.4) and value (6.7): at each synchronization period, successively provide one of eight additional measures or cell status (e.g., incremental counter, status, cell temperature, bypass temperature, wireless transmission, and reception error rates). Once reached the last measure (e.g., wireless reception error rate), at the next synchronization period, it restarts with the first one (e.g., incremental counter), and so on.

[0072] These following items are information one finds in data / reply from RF slaves 12 to BMS master 15 via active RF master 11 , 11 a, 11 b:- mode (e.g., driving, charging, testing) (each 20 ms),- general error indication (each 20 ms),- cell voltage (6.5) (each 20 ms),- cell current (6.6) (each 20 ms),- cell temperature (6.7) (each 160 ms),- bypass temperature (6.7) (each 160 ms),- transmission and reception errors rates view from RF slave 12 (6.7) (each 160 ms),- transmission counter (6.7) (each 160 ms),- errors detail (6.7) (each 160 ms),- internal state (e.g., bypass, energy transfer, heating) (6.7) (each 160 ms).

[0073] These following items are information one finds in data / reply from RF master 11 to BMS master 15:- mode (e.g., driving, charging) (each 20 ms),- errors detail (each 20 ms),- internal state (e.g., testing, debug version) (each 20 ms),- CPU temperature (each 160 ms),- CPU voltage (each 160 ms),- radio frequency signal level I transmission and reception errors rates from each RF slave 12 view from RF master 11 (sends sequentially, each 160 ms),- transmission counter (each 160 ms).

[0074] According to figure 7, a family user frame Set up / Diagnostic case is presented. Both Setup and Diagnostic user frames are using the same user frame description. It is the case for the command I request and for the data / reply user frame. Nevertheless, the nature of the information given by the parameter identification (7.3) is variable.

[0075] Most of the time (except some specific setup user frame e.g., ping), the BMS master 15 will resend the command I request if it does not receive all RF slaves 12 data / replies or upon a time out occurs.

[0076] Then it is presented field in the command I request user frame used a) in communication from BMS master 15 to RF masters 11 , 11a, 11 b or b) from active RF master 11 , 11 a, 11 b to RF slaves 12:- read or write (7.0): field that indicates if the parameter is written or read.

[0077] Parameter identification (7.3) and value (7.4): 64 possible parameters (e.g. cell voltage, current and temperature calibration parameters; voltage value to activate the bypass, set the transmission power for each RF slave 12, reset the statistics). In association with the reading or writing field (7.0), it is possible to set or get parameters.

[0078] Then concerning Set up / Diagnostic: What is present in the Data / Reply user frame used a) in communication from RF masters 11 , 11 a, 11 b to BMS master 15 or b) from RF slaves 12 to RF masters 11 , 11 a, 11 b.

[0079] - Parameter identification (7.3) and value (7.4): 64 possible parameters(e.g. cell voltage, current and temperature calibration parameters; voltage value to activate the bypass, set the transmission power for each RF slave 12, reset the statistics).

[0080] List of Setup identifications:- - Set / Get calibration parameters of each RF slave 12 measures (U / l / T),- - Ping RF slaves 12 (one specific or all),- - Sleep RF slaves 12 (one specific or all, legacy or selective sleep mode),- - Reset RF slaves 12 (one specific or all),- - Wake-up RF slaves 12 (all, legacy or selective wake-up mode),- - Request statistics to be printed out on RF masters 11 debug port (one specific or all),- - Reset statistics on RF masters and / or RF slaves 12 (one specific or all),- - Update RAM parameters in flash on RF masters 11 , 11 a, 11 b and / or RF slaves 12 (one specific or all),- - Get firmware name of RF masters 11 , 11 a, 11 b and / or RF slaves 12 (one specific or all),- - Get hardware and firmware version / revision of RF masters 11 , 11a, 11 b and / or RF slaves 12 (one specific or all),- - Set / Get slot time for RF slave(s) 12 (one specific (Set / Get) or all (Get)),- - Set slave address and its associated RF master 11 , 11 a, 11 b for RF slave 12 (one specific),- - Set / Get RF TX power for RF masters 11 , 11a, 11 b and / or RF slaves 12, (one specific or all),- - Set / Get RF channel for RF masters 11 , 11 a, 11 b and / or RF slaves 12 (one specific (Get) or all (Set / Get)),- - Switch to bootloader mode to be able to upload new device firmware (DFU) for RF masters 11 , 11 a, 11 b and / or all RF slaves 12,- - Set / Get cell voltage bypass limit for RF slaves 12 (one specific or all),- - Set / Get temperature limit 1 and 2 for RF slaves 12 (one specific or all),- - Set / Get battery module identification for RF slaves 12 (one specific),- - Set / Get (synchronization) period for RF masters 11 , 11a, 11 b (all),- - Set / Get RF master 11 , 11 a, 11 b address, RF slaves 12 begin and end addresses range associated for RF master 11 , 11 a, 11 b (one specific (Set) or all (Get)),- - Tune-up: identify the best radio channel and apply it to all RF masters 11 , 11a, 11 b and all RF slaves 12,- - Set / Get role of RF master 11 , 11a, 11 b (Active or Passive).

[0081] List of Diagnostic identifications:- Set / Reset / Get internal resistor of each RF slave(s) 12 (one specific (Set / Reset / Get) or all (Reset / Get)),- Set / Reset / Get min, max and avg cell voltage of RF slave(s) 12 (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12,- Set / Reset / Get min, max and avg temperature voltage of RF slave(s) 12 (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12,- Set / Reset / Get transmission error rate of RF slave(s) 12 and / or RF master(s) 11 , 11a, 11 b (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12 and / or RF master 11 , 11 a, 11 b,- Set / Reset / Get reception error rate of RF slave(s) 12 and / or RF master(s) 11 , 11a, 11 b (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12 and / or RF master 11 , 11 a, 11 b,- Set / Reset / Get min, max and avg RF reception level (RSSI) of RF slave(s) 12 and / or RF master(s) 11 , 11 a, 11 b (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12 and / or RF master 11 , 11 a, 11 b,- Set / Reset / Get min, max and avg RF link quality level (LQI) of RF slave(s) 12 and / or RF master(s) 11 , 11 a, 11 b (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12 and / or RF master 11 , 11 a, 11 b,- Set / Reset / Get number of RF calibration of RF slave(s) 12 and / or RF master(s) 11 , 11a, 11 b (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12 and / or RF master 11 , 11 a, 11 b,- Set / Reset / Get number of RF error of RF slave(s) 12 and / or RF master(s) 11 , 11a, 11 b (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12 and / or RF master 11 , 11 a, 11 b,- Set / Reset / Get number of RF timeout error of RF slave(s) 12 and / or RF master(s) 11 , 11a, 11 b (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12 and / or RF master 11 , 11 a, 11 b,- Set / Reset / Get number of sensor specific communication link (I2C) error of RF slave(s) 12 (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12,- Set / Reset / Get number of driver errors of RF slave(s) 12 (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12,- Set / Reset / Get number of errors on cell voltage of RF slave(s) 12 (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12,- Set / Reset / Get number of errors on cell temperature of RF slave(s) 12 (one specific (Set / Reset / Get) or all (Reset / Get)) of each RF slave 12.

[0082] Then other examples are presented below. Bypass - Setup frame: Bypass is a mechanism wherein during charging when the cell reaches its limiting voltage (e.g. 4.22 V), charging current will be bypassed from 0% to 100% to protect the cell from overcharging and permit the other cells, which are below the limiting voltage, to continue to be charged.

[0083] BMS master 15 sends a setup user frame command (Fig 7, 7.2) to all RF slaves 12 via active RF master 11 , 11 a, 11 b. This command comprises cell voltage limit (7.4 - this is the parameter value e.g. 4.22 V) and the parameter (i.e. Bypass) identification is given in 7.3. As the parameter is the same for all RF slaves 12, a broadcast Address (5.1 ) is used in the user frame. Active RF master 11 , 11a, 11 b does not add or modify the command from BMS master 15 but only forwards the command to the RF slaves 12.

[0084] All RF slaves 12 are replying, at their individual slot times, with confirmation of the applied parameter. It is a setup user frame reply (Fig 7, 7.2). Each slave 12 indicates its address on 7.1 (unicast). This reply comprises applied cell voltage limit (7.4 e.g., 4.22 V) and the parameter (i.e., Bypass) identification is given in 7.3. Applied parameter must be within the voltage limit known by the RF slaves 12otherwise the RF slave 12 indicates its internal limit. When the cell voltage reaches the Bypass limit (e.g., 4.22 V), a regulation is applied, and the charging current is bypassed over a variable resistor.

[0085] If not all RF slaves 12 are replying, the BMS master 15 is trying n times to resend the bypass Setup user frame up all RF slaves 12 confirm or a time out occurs.

[0086] Then BMS master 15 sends again and periodically the measure user frame command.

[0087] According to another example of measure: BMS master 15 sends every 20 ms (synchronization period) a command I request to all RF slaves 12 via active RF master 11 , 11a, 11 b while in charging or driving mode. Active RF master 11 , 11a, 11 b does not add or modify the command but only forwards the command. This command will include driving or charging mode (5.4), the temperature set point (5.5) and a balancing method of use (bypass mode or energy transfer mode) in 5.6. If we are in energy transfer mode, we indicate for a given stack (group of 10 RF slaves 12) e.g. module 1 (RF slaves 12 addresses 1 to 10) for each RF slave 12 of this module, which RF slave 12 needs to activate their left and or right energy transfer coil. All RF slaves 12 are replying at their individual slot times with information described above (e.g., status (6.3), cell voltage (6.5), current (6.6), one of eight measures (6.4 I 6.7) including the mode, which is charging or charging.

[0088] On the next synchronization period (20 ms), it will be the same except we have to select the next module e.g. module 2 (RF slaves 12 addresses 11 to 20) and so on up to module 10 (RF slaves 12 addresses 91 to 100). Restart with module 1.

Claims

C LAIMS1. A wireless communication system (10) for a battery management system (20) comprising:- at least one wireless communication device (11 , 11 a, 11 b), said RF master, managing a communication protocol;- a plurality of battery cells (13);- a plurality of monitoring devices (12), said RF slaves, communicating with wireless link (18) with RF master (11 , 11a, 11 b), each RF slave (12) monitoring one cell (13); characterized in that the system (10) is configured to exchange data via command from RF master (11 , 11 a, 11 b) and / or reply from RF slave (12) with a message comprising a payload less than 10 bytes.

2. The system (10) according to the preceding claim, wherein the system (10) is configured to synchronize the plurality of RF slaves (12) by asking or sending everyone of them with a command comprising a payload less than 10 bytes.

3. The system (10) according to one of the preceding claims, wherein the system (10) is configured in that RF slaves (12) only reply when a command I request from RF master (11 ) is received.

4. The system (10) according to one of the preceding claims, wherein the system (10) is configured to define a predetermined fixed time slot so that RF slaves (12) reply one after the other.

5. The system (10) according to one of the preceding claims, wherein the system (10) is configured in that when a reply from one RF slave (12) is not received by the RF master (11 ) within a synchronization period, RF master (11 ) will not repeat the last command / request, implying for that period the data / reply of RF slave (12) is lost and the previous information becomes the current information.

6. The system (10) according to one of the preceding claims, wherein it comprises at least two wireless communication devices (11 , 11a, 11 b), said RF masters, wherein one of the RF masters (1111 a, 11 b) is active , said active RF master(l l a), and the others are passive, said passive RF masters (11 b), wherein an active RF master (11a) is configured to calculate, send commands to the RF slaves (12) and receive data from the RF slaves (12), and a passive RF master(l l b) is configured to only receive data from the RF slaves (12).

7. A battery management system (20) comprising a wireless communication system (10) according to one of the preceding claims.

8. Electrical vehicle comprising the battery management system (20) according to the preceding claim.

9. A method of operating a battery management system (20) according to claim 7, comprising exchanging data via command from RF master (11 , 11 a, 11 b) and / or reply from RF slave (12) with a message comprising a payload less than 10 bytes.

10. The method according to the preceding claim, further comprising synchronizing the plurality of RF slaves (12) by asking or sending everyone of them with a command from RF master (11 ) comprising a payload less than 10 bytes.11 . The method according to one of the preceding claims 9 or 10, further comprising the step: RF slaves only reply when a command I request from RF master (11 ) is received.

12. The method according to one of the preceding claims 9 to 11 , further comprising the step: predetermined fixed time slot so that RF slaves reply one after the other.1 3. The method according to one of the preceding claims 9 to 12, further comprising the step: when a reply from one RF slave is not received by the RF master within a synchronization period, RF master (11 ) will not repeat the last command / request, implying for that period the data I reply of RF slave (12) is lost and the previous information becomes the current information.

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