GB2554747A

GB2554747A - Battery balancing component

Info

Publication number: GB2554747A
Application number: GB1617118.3A
Authority: GB
Inventors: Gerber Julian; Franz Fuls Wilhelm
Original assignee: University of the Western Cape
Current assignee: University of the Western Cape
Priority date: 2016-10-07
Filing date: 2016-10-07
Publication date: 2018-04-11
Also published as: GB201617118D0; WO2018065853A1

Abstract

A battery balancing component, suitable for inclusion with a battery pack (see fig 5) has balancing circuitry on a printed circuit board (PCB). The PCB has pairs of terminals 111, 112 spaced longitudinally along its length, each pair connecting to one cell (113) of a battery (see also figs 1, 4a, 4b, 5). The PCB has a sub-circuit for cell, linked to pair of electrical terminals, providing a measuring component 122, 123 for measuring the state (voltage and or temperature) of the cell and a bypass resistor 124. The bypass resistor has a switch 125 configured to allow electric current to flow through the resistor, between the terminals, when closed. The bypass resistor may be formed by a PCB trace defined or etched thereon 124. The resistors for each sub-circuit may comprise different patterns arranged to fit a particular location on the PCB, but the patterns are arranged to provide similar resistances (see figure 4a). The PCB has a multi-connector 109 that is connected to each switch and each measuring component. The connector is linked to a programmable battery management system 302.

Description

(54) Title of the Invention: Battery balancing component

Abstract Title: Battery balance circuits on a common PCB for connection to an array of cells (57) A battery balancing component, suitable for inclusion with a battery pack (see fig 5) has balancing circuitry on a printed circuit board (PCB). The PCB has pairs of terminals 111, 112 spaced longitudinally along its length, each pair connecting to one cell (113) of a battery (see also figs 1,4a, 4b, 5). The PCB has a sub-circuit for cell, linked to pair of electrical terminals, providing a measuring component 122, 123 for measuring the state (voltage and or temperature) of the cell and a bypass resistor 124. The bypass resistor has a switch 125 configured to allow electric current to flow through the resistor, between the terminals, when closed. The bypass resistor may be formed by a PCB trace defined or etched thereon 124. The resistors for each sub-circuit may comprise different patterns arranged to fit a particular location on the PCB, but the patterns are arranged to provide similar resistances (see figure 4a). The PCB has a multi-connector 109 that is connected to each switch and each measuring component. The connector is linked to a programmable battery management system 302.

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BYPASS RESISTOR 124

TEMPERATURE

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OVERCURRENT

PROTECTION

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BYPASS SWITCH 125

VOLTAGE

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BATTERY BALANCING COMPONENT

FIELD OF THE INVENTION

The invention relates to a battery balancing component and, more specifically, to a component that assists in balancing of cells within a battery.

BACKGROUND TO THE INVENTION

A battery management system (BMS) is a device that performs balancing of cells in a battery, charging and temperature monitoring in a way that preserves the performance of the battery and improves safety.

Individual cells in a battery have varying capacities and may be at differing states of charge. Without balancing, discharging of all the cells in the battery will stop when the cell with the lowest capacity is empty or reaches a low-charge threshold, and charging of all the cells will stop when the cell with the lowest capacity is fully charged. Cells of lower capacity therefore represent a weak link in a battery and could be undercharged or overcharged while higher capacity cells undergo only partial charging or discharging cycles. In certain cell types such as lithium ion cells, over-charging and over-discharging of cells must be avoided. Over-charging can result in thermal runaway, and discharging below a low-voltage threshold can damage cells.

Battery balancing refers to techniques by which the state of charge (SOC) of the various cells are aligned with each other so that the cells with the largest capacity can be fully charged and discharged without overcharging or over-discharging cells with lower capacity.

Lithium ion cells have a very low self-discharge rate and typically only minor balancing is required to keep a battery in good working order. Most BMS devices for lithium ion cells perform balancing by passing a small current from the most charged cell to a shunt resistor to discharge that cell until it matches the level of the other cells. This is known as passive balancing as opposed to active balancing where charge in a more highly charged cell can be transferred to a cell of lower charge. Although passive balancing does waste some stored charge, it is less expensive to implement than active balancing and avoiding the losses generally does not justify the increased cost of active balancing.

In BMS devices, the shunt resistor is typically mounted adjacent a heat sink so as to dissipate heat, and individual wires are connected from the BMS device to each cell or cell stack terminal in the battery. Installing all of these wires requires appreciable time during battery assembly. The wires could loosen or experience physical damage through heat or friction. The heat sink increases the size and complexity of the BMS device, and may limit its location within a battery casing.

The invention seeks to address these and other problems.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

In this description the term “cell” will be understood to include both a single sealed cell as well as a stack of individually sealed cells which are packaged together in series with one positive and one negative terminal.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a battery balancing component comprising a printed circuit board (PCB) having several pairs of electrical connectors spaced along a length of the PCB for connection to corresponding pairs of positive and negative terminals of a cell in a battery, wherein the PCB has electronic circuitry thereon that includes one sub-circuit for each corresponding pair of electrical connectors, each sub-circuit having a measuring component for measuring a cell state, a bypass resistor between the pair of electrical connectors, and a switch for allowing current to flow through the bypass resistor when the switch is closed, and wherein the PCB includes a multi-port connector connected to each switch and connected to each measuring component.

Further features provide for the bypass resistor of each sub-circuit to be formed by a PCB trace defined thereon; for the bypass PCB trace of each sub-circuit to be of substantially the same electrical resistance; and for the bypass PCB trace of each sub-circuit to be arranged in tight loops so that the bypass PCB trace substantially fills an available space on the PCB and dissipates heat across the available space.

Further features provide for the switch of each sub-circuit to be a transistor, preferably a field effect transistor (FET) and for a controlling terminal of each transistor to be connected to the multiport connector operable to configure the transistor from a non-conducting state, in which the transistor inhibits the flow of electric current there through, to a conducting state in which the transistor conducts electric current therethrough.

Further features provide for the PCB to have a width which is wider at each corresponding pair of electrical connectors and narrower part-way between each corresponding pair of electrical connectors.

Further features provide for the multi-port connector to be provided at or near one end of the PCB; for the multi-port connector to receive one end of a multi-core conductor, preferably a ribbon cable; and for the other end of the multi-core conductor to be connected to a battery management system (BMS) device that includes a programmable microcontroller.

Further features provide for the measuring component to include a temperature sensor that measures the temperature at each electrical connector so as to approximate the temperature of each cell.

Further features provide for the measuring component to include PCB traces extending between the electrical connectors and the multi-port connector, by means of which the voltage between the positive and negative connectors can be measured.

Further features provide for each cell to be an individually sealed electrochemical cell or a stack of individually sealed electrochemical cells; and for the cells to be lithium ion cells.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Figure 1 is a schematic representation of a battery balancing component according to the invention;

Figure 2 is a block diagram of a bypass circuit for a battery balancing component;

Figure 3 is a schematic representation of the bypass circuit of Figure 2;

Figure 4A is a top plan view of the battery balancing component of Figure 1;

Figure 4B is a bottom plan view of the battery balancing component of Figure 4A; and

Figure 5 is a three dimensional view of a battery having a number of adjacent cell stacks with the battery balancing component of Figure 4 positioned for connection to each cell stack.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

An exemplary embodiment of a battery balancing component and its various circuits, sub-circuits and components are described below. This exemplary embodiment may comprise a printed circuit board (PCB) having several pairs of electrical connectors or electrical connection terminals spaced longitudinally along a length of the PCB. These pairs of connectors or terminals provide for connection to corresponding pairs of positive and negative terminals of a cell in a battery.

The PCB has electronic circuitry thereon that includes one sub-circuit for each corresponding pair of electrical connectors. Each such sub-circuit may have a measuring component for measuring a state of its associated cell. Each sub-circuit may furthermore include a bypass resistor in electrical communication between the pair of electrical connectors with a switch configured to allow electric current to flow, when the switch is in a conducting (closed) state, from the positive terminal of the cell, through the bypass resistor to the negative terminal. The PCB may include a multi-port connector that is in electrical communication with each switch and each measuring component.

The bypass resistor of each sub-circuit may be formed by a PCB trace defined or etched thereon. These PCB trace bypass resistors may be configured to all have approximately the same resistance. This configured resistance may be preselected so as to effect a predetermined maximum bypass current when the switch is configured in its closed or conducting state. This preselected maximum bypass current may be selected to ensure the integrity of the PCB trace bypass resistor under maximum bypass current conditions.

The resistance of the bypass trace may be determined by the length and width of the trace, the nominal thickness of the conductor layer on the PCB and the unit resistivity of the conducting material. For a PCB manufactured using FR4 substrate, the conductor material is copper which has a resistivity of about 1.68x1 O'⁸ p (Ohm-meter). The conductor thickness for the FR4 substrate is known to be either 18 micrometre (pm), 35pm (most common), 70pm, 105pm or 140pm depending on the particular FR4 subtype. All the relevant quantities may therefore be known to design a PCB trace bypass resistor having a desired predetermined resistance. The PCB trace bypass trace may be designed in the form of tight loops in order to fit to the available space on the PCB and to dissipate heat across the available space. The PCB may be manufactured without through-hole plating (THP) as THP may introduce uncertainties in terms of the electrical characteristics of the conductors on the PCB, including the PCB trace bypass resistor.

The switch of each sub-circuit may be a transistor, such as a bipolar junction transistor (BJT) or a field effect transistor (FET). The controlling terminal of each transistor (base for a BJT and gate for a FET) may be connected to the multi-port connector and may be operable to configure the transistor from a non-conducting (open) state in which the transistor inhibits the flow of electric current there through and the conducting state in which the transistor conducts electric current there through.

The PCB may have a width which is wider at or near each pair of electrical connectors and narrower part-way between each corresponding pair of electrical connectors.

Figure 1 is a schematic representation of an exemplary battery balancing component (100) according to the invention comprising a printed circuit board (PCB) (101) having four pairs of electrical connection terminals (111, 112) spaced longitudinally along a length of the PCB (101). These pairs of terminals (111, 112) provide for connection to corresponding pairs of positive and negative terminals of a cell (113) in a battery.

The PCB (101) has a wider width (102, 104,106, 108) at or near each pair of electrical connectors (111, 112) and a narrower width (103, 105, 107) part-way between each corresponding pair of electrical connectors (111, 112).

The PCB (101) has electronic circuitry thereon that includes one bypass circuit (120) for each corresponding pair of electrical connectors (111, 112). Electrical inputs and outputs to and from each bypass circuit (120) on the PCB (101) are in electrical communication with a board-to-board connector (109) that provides electrical connection between these input and output signals and a battery management circuit (not shown).

A block diagram of such a bypass circuit (120) is shown in Figure 2. Each bypass circuit (120) is inclusive of an above-mentioned pair of electrical connection terminals consisting of a positive terminal (111) and a negative terminal (112). The positive and electrical terminal (111, 112) provides electrical connection to the corresponding positive and negative terminal of an associated cell (113). The bypass circuit (120) includes a measuring component (121) that is in electrical communication with the positive and negative terminals (111, 112) for measuring the state of the associated cell (113).

The measuring component (121) includes a voltmeter (122) for measuring an output voltage of the associated cell (113) and a temperature sensor (123) for measuring or approximating a temperature of the cell (113). The voltmeter (122) and temperature sensor (123) are in electrical connection with the board-to-board connector (109) of the PCB (101).

Each bypass circuit furthermore includes a bypass resistor (124) in electrical communication with the positive and negative terminal (111, 112) through a bypass switch (125). The bypass switch (125) is configured to allow electric current to flow, when the bypass switch (125) is in a conducting state or is closed, from the positive terminal (111) of the cell, through the bypass resistor (124) and to the negative terminal (112), thereby intentionally draining the cell (113) of a portion of its electrical charge. This charge is dissipated through the bypass resistor (124) in the form of heat. Therefore, the bypass resistor is provided by means of a bypass PCB trace that is arranged in tight loops so as to fill an available space on the PCB and dissipate heat across the available space. A bypass indicator (127) is included to indicate when the bypass switch (125) is in the conducting state.

The bypass circuit (120) also includes protection circuitry (128) to protect the bypass circuit (120) from voltages and currents that may damage the circuitry thereon. This includes one or more overcurrent protection component (129) to protect the bypass circuit (120) from currents that exceed a predetermined maximum current threshold as well as one or more voltage clamping component (130) to keep certain voltage levels on the bypass circuit (120) within a preconfigured allowed voltage range.

The voltmeter (122), the temperature sensor (123) and a controlling terminal of the bypass switch (125) is in electrical communication with the board-to-board connector (109) of the PCB (101). This allows a remote battery management circuit (not shown) to interpret output signals from the voltmeter (122) and the temperature sensor (123) and to control the state of the bypass switch (125).

The battery management circuit may be configured to compare the output signal of the voltmeter (122) to a preconfigured upper and lower threshold to detect an over-voltage and/or under-voltage state of the cell (113). The battery management circuit may furthermore be configured to compare the temperature measured by the temperature sensor (123) with a predetermined upper temperature threshold to determine whether the cell (113) is within safe operating temperature conditions.

Figure 3 is a schematic representation of the bypass circuit (120) of Figure 2. The positive terminal (111) and negative terminal (112) provides electrical connection to the corresponding positive and negative terminal of an associated cell (113) shown in Figure 1. The voltmeter (122) is configured to measure the output voltage of the cell (113) and to provide its output signal to the board-toboard connector (109) of the PCB (101). It should be appreciated that the voltmeter (122) is a symbolic representation of any electrical connection that provides the output voltage of the cell (113) at the connector (109). The voltmeter (122) could even simply be PCB traces extending between the electrical connectors and the multi-port connector. The temperature sensor (123) is positioned near the cell (113) and is configured to provide an output signal representative of a temperature of the cell (113) to the connector (109). Different kinds of temperature sensors could be provided as are discussed below.

The bypass resistor (124) is provided by a trace defined or etched on the PCB (101). The bypass resistor (124) is configured to have a predetermined resistance and is determined by the length and width of the 35pm thick copper conductor on the PCB (101). This preconfigured resistance is selected such that a predetermined maximum bypass current of about 1 Ampere (A) will be conductor therethrough when the bypass switch (125) is configured in a conducting state.

The bypass switch (125) is provided by a field effect transistor (FET). Its gate is in electrical communication with the connector (109) through a resistor (301) and is configurable between a conducting and a non-conducting state through the application of an appropriate positive voltage to its gate with reference to the negative terminal (112). The bypass resistor (124) is in the form of a bypass PCB trace (126) that has tight loops so as to fill an available space on the PCB and dissipate heat across the available space. The bypass indicator (127) is provided by a light emitting diode (LED) that is also in electrical communication with the bypass switch (125) such that the bypass switch (125) also controls the flow of electrical current through the LED. Thus, when the bypass switch is in the conducting state, the LED will be lit.

The protection circuitry (128) consists of a number of overcurrent protection components (129) provided by fuses. A dual package of transient voltage surge suppressor (TVS) diodes for the voltage clamping component (130) protects the gate and drain of the FET (125) from voltage surges outside a safe voltage range. A pull-down resistor (303) is provided at the gate of the FET (125) to assist in discharging the capacitive gate as well as a decoupling capacitor (304).

The output signals provided by the voltmeter (122) and the temperature sensor (123) as well as the gate terminal of the FET are in electrical communication with the board-to-board connector (109) of the PCB (101). This allows a remote battery management circuit (302) to interpret the output signals from the voltmeter (122) and the temperature sensor (123) and to control the state of the FET or bypass switch (125).

Figure 4A and Figure 4B respectively show a top plan view and a bottom plan view of a battery balancing component (100) according to the invention. The battery balancing component (100) is a PCB (101) with a 1.6mm thickness FR4 substrate having a 35pm copper thickness with a green solder mask and an immersion tin finish on exposed pads. The positive terminals (111) and negative terminals (112) are provided by circular pads exposed from the solder mask of the PCB (101) having a diameter of about 19mm with a central aperture of about 5mm in diameter. The PCB (101) is not subjected to a through-hole plating processes during manufacture as throughhole plating of the pads would introduce uncertainties into designing the PCB trace bypass resistor (124) for a specific predetermined resistance.

The mechanical outline of the PCB (101) has been routed to machine a profile having a wider width (102, 104, 106, 108) at or near each pair of terminals (111, 112) and a narrower width (103, 105, 107) part-way between each corresponding pair of terminals (111, 112). This is important so as to provide space for mechanical mounting bolts (not shown) as will be discussed below.

Each instance of the PCB trace bypass resistor (124) need not be identically formed. Various design considerations may have an effect on the available space on the PCB (101) into which the bypass resistor (124) must fit. The placement of the board-to-board connector (109) on the area of a first wide section (102) reduces the available space in which the bypass resistor (124) must fit. The available space is further reduced by the space required to route measurement and control signal traces (401) between the board-to-board connector (109) and various components on the PCB (101). Therefore, in order to obtain the desired resistance, the space at a first narrower section (103) adjacent the first wider section (102) is utilised in that some of the loops that form the bypass resistor (124) extend (402) into the first narrower section (103).

Similarly, a fourth wider section (108) is considerably shorter than its counterparts due to design considerations regarding limited space within an enclosure. Therefore, in order to obtain the desired resistance, the space at a third narrower section (107) adjacent the fourth wider section (108) is utilised in that some of the loops that form the bypass resistor (124) extend (403) into the third narrower section (107).

In each of these instances, the extensions (402, 403) of some of the loops that form the relevant bypass resistor (124) allow the relevant trace to have substantially the same length, and therefore, substantially the same resistance, as its counterparts.

The fuses (129) are provided by 0805 size surface mount in-line fuses, resistors (301, 303) by 0603 size surface mount resistive film resistors, and TVS’s (130) are dual diode SOT-23 packages. The bypass indicator LEDs (127) are provided by 0805 size red surface mount LEDs, capacitors (304) by 0603 size ceramic surface mount capacitors, and the bypass switch FETs (125) by SOT-23 N-channel metal oxide semiconductor field effect transistors (MOSFETs).

The temperature sensor (123) is located near the terminals (111, 112) and is provided by a negative temperature coefficient thermistor in a 0603 case size. The thermistor (123) has a nominal resistance of 10 kilo Ohm (kQ) at 25°C and is externally biased on the battery management circuitry (302) in a voltage divider configuration. The placement of the temperature sensor (123) near the terminals (111, 112) allows the temperature sensor (123) to approximate the temperature of the cell (113).

The board-to-board connector (109) is provided by a dual-row straight angled male 2mm spacing pin strip extending away from the bottom of the PCB (101). The PCB trace bypass resistor (124) is designed in tight loops to fit the available space on the PCB (101).

Figure 5 shows a three-dimensional elevation of a battery (500) in which the battery balancing component (100) of Figure 4 is in an assembly with a number of cells (113). Each cell (113) comprises a number of individual lithium ion (Li-Ion) cells (501) in a frame assembly (502). The frame assembly (502) has two metallic plates, a top plate (504) and a bottom plate (505) with punched tabs (506) that are tack welded to the electrical connections of the individual cells (501). This creates a parallel connection between the individual cells (501) of each cell (113).

The PCB (101) is located at the side otthe cells (113) in a plane substantially perpendicular to the top and bottom plates (504, 505) such that the positive terminals (111) and negative terminals (112) otthe PCB (101) align with mounting holes on the top plate (504) and bottom plate (505) respectively, depending on the desired polarity of the battery. In this exemplary embodiment, the cells (113) have been placed in alternating polarities to facilitate series connection of the cells (113) to obtain an overall nominal output voltage of about 12V from the battery (500).

The narrower sections (103, 105, 107) provide a clearing for the mechanical mounting bolts of the frames (502) to conductor buss bars (not shown).

The battery balancing component (100) therefore provides an interconnection between cells (113) without requiring individual loose wires. This may therefore provide an improvement in the overall ease of assembly and may furthermore reduce the risk of damage to individual conductors, which could otherwise pose a safety risk. The battery balancing component (100) also provides an integrated bypass shunt resistor (124) in the form of a PCB trace (126) which also provides an inherent heat dissipation mechanism or heat sink.

Throughout the specification and claims unless the contents requires otherwise the word 5 ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:

1. A battery balancing component comprising a printed circuit board (PCB) having several pairs of electrical connectors spaced along a length of the PCB for connection to corresponding pairs of positive and negative terminals of a cell in a battery, wherein the PCB has electronic circuitry thereon that includes one sub-circuit for each corresponding pair of electrical connectors, each sub-circuit having a measuring component for measuring a cell state, a bypass resistor between the pair of electrical connectors, and a switch for allowing current to flow through the bypass resistor when the switch is closed, and wherein the PCB includes a multi-port connector connected to each switch and connected to each measuring component.

2. A battery balancing component as claimed in claim 1 wherein the bypass resistor of each sub-circuit is formed by a PCB trace defined thereon.

3. A battery balancing component as claimed in claim 2 wherein the bypass PCB trace of each sub-circuit has substantially the same electrical resistance.

4. A battery balancing component as claimed in claim 2 or claim 3 wherein the bypass PCB trace of each sub-circuit is arranged in tight loops so that the bypass PCB trace substantially fills an available space on the PCB and dissipates heat across the available space.

5. A battery balancing component as claimed in any one of claims 1 to 4 wherein the switch of each sub-circuit is a transistor and wherein a controlling terminal of each transistor is connected to the multi-port connector operable to configure the transistor from a nonconducting state in which the transistor inhibits the flow of electric current therethrough, to a conducting state in which the transistor conducts electric current there through.

6. A battery balancing component as claimed in claim 5 wherein the transistor is a field effect transistor (FET) and wherein the controlling terminal of the transistor is a gate of the transistor.

7. A battery balancing component as claimed in any one of claims 1 to 6 wherein the PCB has a width which is wider at each corresponding pair of electrical connectors and narrower part-way between each corresponding pair of electrical connectors.

8. A battery balancing component as claimed in any one of claims 1 to 7 wherein the multiport connector is provided at or near one end of the PCB.

9. A battery balancing component as claimed in any one of claims 1 to 8 wherein the multi5 port connector receives one end of a multi-core conductor and the other end of the multicore conductor is connected to a battery management system (BMS) device that includes a programmable microcontroller.

10. A battery balancing component as claimed in claim 9 wherein the multi-core conductor is

10 a ribbon cable.

11. A battery balancing component as claimed in any one of claims 1 to 10 wherein the measuring component includes a temperature sensor that measures the temperature at each electrical connector so as to approximate the temperature of each cell.

12. A battery balancing component as claimed in any one of claims 1 to 11 wherein the measuring component includes PCB traces extending between the electrical connectors and the multi-port connector, by means of which the voltage between the positive and negative connectors can be measured.

13. A battery balancing component as claimed in any one of claims 1 to 12 wherein each cell is an individually sealed electrochemical cell.

14. A battery balancing component as claimed in any one of claims 1 to 12 wherein each cell

25 includes a stack of individually sealed electrochemical cells.

15. A battery balancing component as claimed in any one of claims 1 to 14 wherein the cells are lithium ion cells.

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