[0001] Embodiments of the invention relate to batteries and management of batteries.

[0002] Battery management systems are used to control the operation of multi-cell power sources by monitoring various associated parameters such as, for example, the State of Charge, Depth of Discharge, overall battery voltage, individual cell voltages cells, and battery and cell temperature. Battery management systems are also arranged to protect the battery as a whole and, in particular, the cells constituting the battery, by ensuring operation within safe parameters. To achieve a desired level of performance, and prevent over-charging or to address under-charging, a battery management system strives to ensure that all cells exhibit the same state of charge via one or more balancing currents. Thermal management is also desirable given the electrochemical processes associated with charging and discharging cells, which are temperature dependent.

[0003] Therefore, embodiments of the present invention provide a battery comprising a. a cell having first and second terminals,

b. a cell balancing device associated with cell; the cell balancing device being operable, in response to a control signal, to form a resistive shunt across the first and second terminals; and

c. a cell management module arranged to provide the control signal to the cell balancing device in response to detecting a predetermined condition associated with the cell.

[0004] Advantageously, embodiments of the present invention eliminate the need for a separate resistor to dissipate power associated with balancing currents. The advantage is realised by using, for example, FETs as such dissipative elements by operating them in the Ohmic region.

[0005] Embodiments of the present invention will now be described with reference to the following drawings in which:

[0006] Figure 1 shows schematically a known battery;

[0007] Figure 2 depicts a battery and a cell management module according to an embodiment;

[0008] Figure 3 illustrates control electronics for current balancing according to an embodiment;

[0009] Figure 4 shows thermally managed substrates according to an embodiment; [0010] Figure 5 depicts a temperature measurement system according to an embodiment;

[001 1] Figure 6 illustrates various connectors according to an embodiment;

[0012] Figure 7 shows a flowchart according to an embodiment.

[0013] Figure 1 shows schematically a known battery 100 having a housing 102 containing a battery management system 104 that uses charge shunting to achieve active balancing of a number of cells 106 to 112 of the battery 100. Active shunting or current balancing is achieved via a number of switches 1 14 to 120, which are under the control of the battery management system 104 via a bus 121 , to provide balancing currents to U via resistors 122 to 128 shunted across respective cells 106 to 112 to maintain the cells at a predetermined voltage during charging. The resistors 122 to 128 are arranged to dissipate heat associated with the respective balancing currents to U. The resistors 122 to 128 are closely coupled to a heat sink 130 that assists in dissipating the heat.

[0014] The battery 100 comprises four cells 106 to 1 12 that are arranged in series to provide an overall voltage and current at the output terminals 132 and 134.

[0015] It can be appreciated that the battery management system 104, switches 1 14 to 120 and resistors 122 to 128 are mounted on a common substrate 136. The common substrate 136 also conducts heat from the resistors 122 to 128 in a manner that adversely affects the other electronics such as, in particular, the battery management system 104 and any control electronics associated with driving the switches 114 to 120.

[0016] Typically, prior art battery management systems offer a balancing current of the order of 900mA due to, for example, the need to dissipate power associated with the balancing currents. The resulting heat, in turn, can cause operational issues that lead to a need to shut-down completely a battery, notwithstanding using heat sinks in an effort to thermally manage the heat; all of which is clearly undesirable. Still further, manufacturing processes are relatively complex in that they require the resistors to be mounted to heat sinks. Yet further, resistors mounted to prior art substrates are prone to failure due to vibrations.

[0017] Referring to figure 2, there is shown an embodiment of a battery 200 having a housing 202 containing a cell management module 204 that uses charge shunting to achieve active balancing of a number of cells 206 to 212 of the battery 200. Active shunting or current balancing is achieved via a number of switches 214 to 220 that are under the control of the cell management module 204 via a bus 221 to provide balancing currents to U across respective cells 206 to 212 to maintain the cells at a predetermined voltage during charging. In preferred embodiments, the switches are realised using FETs that are arranged to dissipate heat associated with respective balancing currents to U by operating the FETS in their Ohmic regions as opposed to their saturation regions as would be conventional for FETs used as switches.

[0018] In the embodiment illustrated, the battery 200 comprises four cells 206 to 212 that are arranged in series to provide an overall voltage and current at the output terminals 222 and 224 during operation. However, embodiments are neither limited to using four cells nor to a series arrangement of cells. Embodiments can be realised that use some other number of cells such as one cell or more than one cell. Preferred embodiments use eight cells. Furthermore, embodiments are not limited to series arrangements of cells. Parallel arrangements could be used, subject to at least one of individual charging and balancing.

[0019] It can be appreciated that the switches 214 to 220 are coupled to a respective substrate, preferably a heat sink 226. Preferably, the thermal coupling between the switches 214 to 220 and the respective heat sink substrate is improved via a thermally conductive layer, in the form of, for example, a paste or sheet material. In a preferred embodiment, the switches 214 to 220 are coupled to an insulated metal substrate that acts as a heat sink. The FETS 214 to 220 are bonded directly to the IMS, which is preferably realised using aluminium. In such embodiments, the heat sink 130 described above with reference to figure 1 is no longer needed, or at least is optional. Also shown in figure 2 is such an optional further heat sink 130 onto which the IMS can be mounted. The cell management module 204 is mounted on a respective substrate 228. Preferred embodiments can be realised in which the cell management module substrate 228 is different to the switch substrate 226.

[0020] Referring to figure 3, there is shown a view 300 of a control circuit or control electronics associated with one or more of the cells for achieving current balancing. Preferably, each cell has a respective control circuit 300. The control circuit 300 is arranged to ensure that a predetermined balancing current IB flows in response to a FET drive signal on a FET drive terminal 302 of an isolator 304. The isolator 304 is preferably an opto-isolator. In the embodiment illustrated the opto-isolator is a 4n25 series opto- isolator comprising an infrared LED and a NPN phototransistor in a 6 pin dual in-line package. Alternatively, dual opto-isolators are used in the form of ELD206 opto-isolators. In the embodiment shown the opto-isolator is operable in response to the FET drive terminal 302 being driven with a predetermined waveform. The other end of the LED of the opto-isolator is connected high via a respective resistor 306. In the embodiment illustrated the respective resistor is a 470Ω resistor.

[0021] The opto-isolator 304 operates, in essence, as a switch for the control circuit 300 such that when the FET drive signal is "on", that is, LED is forward biased, the control circuit 300 is powered and conversely when the FET drive signal is "off", that is, since the LED is reverse biased, the control circuit 300 is unpowered. This has the advantage that, since the switch is between the cell and the FET(s), leakage currents associated with the FETs are minimised and consequently unintentional leakage balancing currents are at least minimised and preferably eliminated. In preferred embodiments, power for the control circuits can be supplied by one or more, preferably respective, cells. It will be appreciated that the opto-isolator therefore influences powering of the control circuits.

[0022] The collector of the phototransistor is coupled to the positive terminal 308 of a respective cell (not shown). The emitter of the phototransistor is coupled to the negative terminal 310 of the respective cell (not shown) via a respective capacitor 312. In the illustrated embodiment, the capacitor 312 is a 100nF capacitor. The emitter is also coupled to the VCC 314 of an op-amp 316. In the embodiment illustrated the op-amp 316 is a TSV621 ILT op-amp available from ST Microelectronics. A potential divider 318 is used in conjunction with a constant voltage source 320 to establish a predetermined reference voltage at the positive input 322 of the op-amp 316. In the embodiment shown, the potential divider comprises a pair of resistors arranged in series, that is, a first resistor 318' in series with a second resistor 318". The first resistor 318' has a resistance of 8k2 Ohms. The second resistor 318" has a resistance of 1 k0 Ohms. The predetermined voltage reference 320 is preferably realised using a diode 320' and a resistor 320". The predetermined reference voltage is arranged to ensure that the op-amp output drives the gate of a respective FET 324 to allow the predetermined balancing current IB to flow via a respective resistor 326. In the embodiment illustrated the predetermined balancing current IB is 3.5A. In the embodiment illustrated the respective resistor 326 carrying the predetermined balancing current is a 0.005Ω resistor. The respective FET 324 corresponds to the FETs 214 to 220 described above with reference to figure 2. The FET 324 is driven to operate in a resistive mode, that is, in its Ohmic region, so that it operates to dissipate power in the form of heat when the balancing current flows.

[0023] The output of the op-amp 316 is coupled to the gate of the FET 324 via a stability circuit 328 that is arranged to prevent oscillations arising from the feedback. In the embodiment shown, the stability circuit 328 comprises a resistor 330, having a first end that is coupled to the output of the op-amp, in series with an RC circuit comprising a parallel arrangement of a capacitor 332 and a respective resistor 334. The other end of the resistor 330 is also coupled, preferably via an optional gate resistor 336, to the gate of the FET 324. The gate resistor 336 is used to influence the rise and fall times of the gate voltage using the gate capacitance. In the embodiment illustrated, the gate resistor is a 100 Ohm resistor. The capacitor 332 and resistor 334 of the RC circuit have values of 100nF and lOkQ

[0024] In response to sensing that a cell has reached a predetermined level of charge, the CMM 204 drives the FET drive terminal 302 with a predetermined waveform. In preferred embodiments, the predetermined level of charge is 3.65V. Preferably, the predetermined waveform is a pulse waveform having a respective frequency. Preferred embodiments of the waveform have a frequency of 10Hz, but embodiments are not limited thereto. Preferably, the waveform has a duty cycle of 50%, but embodiments are not limited thereto. Embodiments can be realised in which different frequencies and/or duty cycles are used such as, for example, a frequency of between 0.5 Hz and 100 Hz and/or a duty cycle of between 0% and 100%, that is, always off or always drawing 3.5A.

[0025] Still further, embodiments are preferably realised in which the dissipative elements, that is, at least the FETs, and optionally associated control circuits, are arranged on a separate substrate, that is, the above IMS, from the cell management module 204 and other components that are heat sensitive as can be appreciated from figure 4, which is a view 400 schematically illustrating the foregoing thermal management or thermal separation. Referring to figure 4, it can be appreciated that the FETs 214 to 220 are mounted onto the insulated metal substrate 226. Also, optionally, included on the dissipative substrate 226 are respective instances 402 to 408 of the above described control circuits 300 for operating the FETs in a resistive mode to dissipate heat arising from the balancing currents, as and when needed.

[0026] The insulated metal substrate 226 comprises a connector 410 that having a plurality of lines 412 that couple to the terminals of the cells. Lines 308 and 310 described above are examples of the plurality of lines 412. Each line of the plurality of lines 412 is actually two lines; one for each of the cell terminals, but shown as a single line for purposes of clarity. Preferably the plurality of lines is realised using wires having stripped ends bearing respective crimped connectors that are inserted into a corresponding plastic connector.

[0027] Similarly, the substrate 414 carrying the cell management module 204 has a connector 416 for coupling the FET drive signals to the control electronics 402 to 408 associated with the FETs 214 to 220 via a respective connector 418 on the insulated metal substrate 226 and an associated plurality of lines using wires having stripped ends bearing respective crimped connectors that are inserted into a corresponding plastic connector 420. [0028] A further connector 422 is provided for receiving signals associated with the temperature of the cells. The CMM 204 responds to the temperature by at least one of controlling, reducing, the balancing currents or controlling the charging of the cells via a further connector 424 that is coupled to a charging controller (not shown).

[0029] A still further connector 426 is used for providing cell voltages to the CMM 204 via a respective connector 428. It can be appreciated that connector 426 is coupled to connector 418 to provide the cell voltages to the CMM 204 respective via wires having stripped ends bearing respective crimped connectors that are inserted into a corresponding plastic connector .

[0030] An external communications bus 430 is provided for exchanging data and control signals with a further controller such as, for example, a master control unit (not shown). Preferably, the external communications bus complies with a relevant standard such as, for example, J 1939 or CAN2.0B standards.

[0031] Figure 5 shows a view 500 of the connectors 410, 416/418, and 426/428 in greater detail. The FET drive connector 418 is shown in greater detail. Although the embodiment described above with reference to figure 4 uses four FETs for respective cells, the connector 418 depicted in figure 5A is adapted for eight cells. Therefore, the connector 418 receives eight FET drive signals. Preferably, the connector 418 also has three contacts for the thermistors 502 and 504. It will be appreciated that connector 416 is complementary to connector 418. The connector 410 is shown as presenting a coupling for nine lines arranged to span the terminals of the eight cells.

[0032] Figure 6 depicts a view 600 of an arrangement for measuring the temperature of one or more cells of the battery or the temperature of the battery as a whole, or any part thereof. Given that the performance of cells is temperature dependent, one or more temperature dependent devices such as, for example, thermistors, like first and second thermistors 602 and 604, are used by the CMM 204 to monitor, via connector 422, the temperature of the cells and to take appropriate action accordingly.

[0033] Embodiments of the present invention allow very high electrical isolation of the order of 3-4 kV to be realised, which is a significant improvement on known battery management systems that have an isolation of 1 kV. Furthermore, embodiments of the present invention support balancing currents of at least 3.5A and 15A. Still further, embodiments of the present invention can dissipate 400W of power substantially continuously. However, embodiments of the present invention can arbitrarily establish a required balancing current by appropriate component selection and FET drive waveform selection. [0034] Electric vehicles use multi-cell batteries. The vehicles can include cars, boats, bikes etc. During construction of such vehicles, the batteries need to be installed and carefully managed to ensure that they do not suffer damage due to, for example, an inadvertent deep discharge. This can be particularly challenging depending upon the vehicle concerned. For example, larger, more expensive yachts and cruisers need to have batteries installed long before the boat is finished, put into service and able to provide power for charging and otherwise managing the batteries. Therefore, embodiments provide for installing a battery as described herein with reference to figure 2 et seq. and for managing the state of charge of the cells of the battery including using balancing currents to maintain the cells at a predetermined voltage during vehicle construction.

[0035] Figure 7 shows a flowchart 700 of processing steps according to an embodiment. The cell management module 204 receives, at step 702, via connector 428, an indication of the current voltage of a cell. A determination is made at step 704 regarding whether or not cell balancing is needed. The determination can take the form of noting whether or not the current, that is, present, cell voltage is at or beyond a predetermined threshold. Preferably, the predetermined threshold is 3.65V. If the determination at step 704 is positive, cell balancing is initiated at step 706. Processing the returns to step 702. The step of initiating cell balancing 704 can take many forms. Preferred embodiments are arranged to output the above-described predetermined waveform for driving the opto- isolator 304 and, in turn, driving the FETs or selectable appropriate ones of the FETs.

[0036] Embodiments of the present invention facilitate providing a constant current system, which facilitates simpler Coulomb counting.

[0037] It will be appreciated that embodiments of the present invention can be realised in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement embodiments of the present invention. Accordingly, embodiments provide machine executable code for implementing a cell management module, assembly, battery, system, device or method as described herein or as claimed herein and machine readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and embodiments suitably encompass the same.