Cell balancing with local sensing and switching

Abstract

Cell balancing system comprising: a battery module (20) having a plurality of battery cells (22) in a series circuit; wherein each battery cell (22) of the plurality of battery cells (22) has a switched cell terminal (24) and an unswitched cell terminal (26) associated therewith; one or more circuits (30) each configured to switch an associated battery cell (22) of the plurality of battery cells (22) between a first mode in which the associated battery cell (22) is in operation or connected to the battery module (20) and a second mode in which the associated battery cell (22) is functionally separated from the battery module (20); wherein each of the one or more circuits (30) comprises a first switch (32) configured in the first mode as a closed circuit to allow electrical current to flow between the switched cell terminal (24) of the associated battery cell (22) and a module node (34), and configured in the second mode as an open circuit to block electrical current to flow between the switched cell terminal (24) of the associated battery cell (22) and the module node (34); wherein each of the one or more circuits (30) includes a cell bypass conductor (38) in electrical contact with the unswitched cell terminal (26) of the associated battery cell (22); wherein each of the one or more circuits (30) comprises a second switch (36) configured in the first mode as an open circuit (30) to block electrical current flow between the cell bypass conductor (38) and the module node (34), and in the second mode as an open circuit (30) to allow electrical current flow between the cell bypass conductor (38) and the module node (34); a cell controller (42) associated with each of the one or more circuits (30) and configured to monitor a plurality of cell parameters of the associated battery cell (22) associated therewith and to cause the circuit (30) to change from the first mode to the second mode in response to at least one of the plurality of cell parameters exceeding a corresponding parameter threshold, the system further comprising: a threshold input terminal (44) on each of the cell controllers (42) for receiving an input signal corresponding to the parameter threshold; and a common control line (48) in electrical communication with a module controller (40) and with the threshold input terminal (44) of each of the cell controllers (42) to communicate the parameter threshold therebetween, wherein the parameter threshold is one of two or more parameter thresholds; wherein the threshold input terminal (44) of each of the cell controllers (42) is one of two or more threshold input terminals (44) of each of the cell controllers (42); and wherein the common control line (48) is one of two or more common control lines (48) each in electrical communication with the module controller (4) and with a corresponding one of the two or more threshold input terminals (44) of each of the cell controllers (42) to communicate a corresponding one of the two or more parameter thresholds; characterized in that the plurality of cell parameters comprise a cell voltage and a cell temperature, and / or wherein the plurality of cell parameters comprise a cell voltage and a cell heat flux.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US provisional patent application serial number 62 / 585,824, filed November 14, 2017, and US patent application US 2019 / 0 148 952 A1 serial number 16 / 188,551, filed November 13, 2018, the contents of which are incorporated herein by reference in their entirety. BACKGROUND OF THE INVENTION 1. Field of the Invention

[0002] The invention relates to a system for cell balancing with local sensing and switching in a multi-cell battery module. 2. Description of the state of the art

[0003] It is well known that variability in the electrical properties of individual cells can limit the overall performance of a battery. This is especially true for batteries with a high cell count. Typically, the battery's performance is limited to the performance of the weakest cell. The performance of each cell can be measured using parameters such as total voltage under load, temperature under load, charge storage capacity, internal impedance or resistance, dynamic charge mobility, and others.

[0004] For example, the peak current flow in a series-connected group of cells is limited by the internal resistance of the cell with the highest internal resistance due to heat generation. According to another example, the total available charge in a series-connected group of cells is limited by the charge storage of the weakest cell. In this and other cases (similar results apply to cells connected in parallel and for voltage equalization, etc.), the overall battery performance can be improved by balancing the currents and voltages of all cells in the battery or battery module.

[0005] Traditional approaches to balancing battery cells within a battery module include shunt resistors (also known as leakage resistor balancing), charge current modulation responsive to individual cell voltage, and switched current pumping to shift charge from one cell to another. However, each of these traditional approaches has associated disadvantages. Leakage resistor balancing consumes additional charge from high-efficiency cells until low-efficiency cells are charged. With this approach, a significant amount of energy can be dissipated as heat in the shunt resistors. Charge current modulation can be more efficient, but current implementations require many wire connections to each cell.Charge pumping is likely to be very efficient, but cannot be applied to batteries with a high number of cells due to excessive wiring requirements.

[0006] From US 2011 / 0057617 A1 a non-contiguous group of cells in a battery of cells is known, which is selected for charging and discharging the battery.

[0007] US 2014 / 0035532 A1 discloses a cell balancing module, in particular for voltage balancing in a stack of batteries.

[0008] EP 2 911 269 A1 discloses a power supply device with a battery monitoring device and an operating method for a battery monitoring device.

[0009] DE 10 2012 208 454 A1 discloses a conditioning device for conditioning a data channel of a cell of a multi-cell electrical energy storage device, wherein the conditioning device is designed to condition a signal frequency suitable for transmitting data via the data channel and / or an AC resistance of the data channel. SUMMARY OF THE INVENTION

[0010] The invention provides a system and method for cell balancing with local sensing and switching. The system includes a battery module with a plurality of battery cells connected in series, each of the battery cells having a switched cell terminal and a non-switched cell terminal.

[0011] The system of the present invention is defined by the features of claim 1. The system of the present invention comprises one or more switching circuits, each configured to switch an associated battery cell in the battery module. Each of the switching circuits is switchable between a first mode in which the associated battery cell is operative or connected to the battery module, and a second mode in which the associated battery cell is functionally disconnected from the battery module. Each of the switching circuits comprises a first switch configured as a closed circuit in the first mode to permit electrical current flow between the switched cell terminal of the associated battery cell and a module node.The first switch is also configured as an open circuit in the second mode to block the flow of electrical current between the switched cell terminal and the module node. Each of the circuits also includes a cell bypass conductor in electrical contact with the non-switched cell terminal of the associated battery cell. Each of the circuits also includes a second switch, configured as an open circuit in the first mode, to block an electrical current connection between the bypass conductor and the module node. The second switch is also configured as an open circuit in the second mode to allow the flow of electrical current between the cell bypass conductor and the module node.

[0012] The system of the present invention also includes a cell controller associated with each of the circuits. Each of the cell controllers is configured to monitor a cell parameter of the associated battery cell and cause the circuit to transition from the first mode to the second mode in response to the cell parameter exceeding a parameter threshold.

[0013] According to one aspect of the invention, each of the battery cells in the battery module may be an associated battery cell to which a circuit is associated.

[0014] According to the invention, each of the cell controllers has a threshold input terminal for receiving an input signal corresponding to the parameter threshold. Each of the cell controllers also has a common control line in electrical communication with a module controller and with the threshold input terminal of each of the cell controllers for communicating the parameter threshold between them.

[0015] According to another aspect of the invention, the parameter threshold is one of two or more parameter thresholds. The threshold input terminal of each of the cell controllers is one of two or more threshold input terminals of each of the cell controllers. Further, the common control line is one of two or more common control lines, each of the common control lines being in electrical communication with the module controller and with a corresponding one of the threshold input terminals of each of the cell controllers and with each of the common control lines to communicate a corresponding one of the parameter thresholds.

[0016] According to another aspect of the invention, the system may include a parameter output terminal on each of the cell controllers for providing an output signal corresponding to at least one of the cell parameters. The system may also include a common monitoring line in electrical communication with each of the cell controllers for communicating the cell parameter or parameters from each of the cell controllers to a common destination.

[0017] According to one aspect of the invention, the common monitoring line may be one of two or more common monitoring lines, each of the common monitoring lines being in electrical communication with each of the cell controllers and the common target.

[0018] According to a further aspect of the invention, the common monitoring line may be configured to communicate a plurality of cell parameters. In one embodiment, the plurality of cell parameters may be transmitted over the common monitoring line at different times. In some embodiments, the plurality of cell parameters may be communicated simultaneously over the common monitoring line. In one embodiment, each of the plurality of cell parameters may be assigned a different carrier frequency.

[0019] According to a further aspect of the invention, the cell parameter may be selected from a group comprising: a cell heat flux, a cell current, a cell state of charge, a cell temperature, and a cell voltage.

[0020] According to a further aspect of the invention, a cell balancing system is provided, the system comprising a battery module having a plurality of battery cells in a series connection and one or more circuits each configured to switch an associated battery cell of the plurality of battery cells between a first mode in which the associated battery cell is in operation or connected to the battery module and a second mode in which the associated battery cell is functionally disconnected from the battery module.The system also includes a cell controller associated with each of the one of the plurality of circuits and configured to monitor a cell parameter of the associated battery cell associated therewith and to cause the circuit to transition from the first mode to the second mode in response to the cell parameter exceeding a corresponding parameter threshold. The system further includes a threshold input terminal on each of the cell controllers for receiving an input signal corresponding to at least one of the parameter thresholds. The system also includes a common control line in electrical communication with a module controller and with the threshold input terminal of each of the cell controllers for communicating the parameter thresholds therebetween.

[0021] According to one aspect of the invention, the cell balancing system may also include a parameter output terminal on each of the cell controllers for providing an output signal corresponding to at least one of the cell parameters. The system may also include a common monitoring line in electrical communication with each of the cell controllers for communicating the one of the cell parameters from each of the cell controllers to a common destination.

[0022] The method of the present invention is defined by the features of claim 10.A method for cell balancing comprises the steps of: measuring values ​​of one or more cell parameters of each of a plurality of battery cells connected in series by a cell controller operatively associated with each of the battery cells; comparing the measured values ​​of each of the one or more cell parameters by each of the cell controllers to a parameter threshold associated with each of the one or more cell parameters; and signaling a command signal by one of the cell controllers to a corresponding circuit to deactivate an associated one of the battery cells within the battery module in response to the measured value of any one of the one or more cell parameters exceeding the parameter threshold associated with a corresponding one of the one or more cell parameters.

[0023] The cell balancing method further comprises the steps of: blocking an electrical current path between the associated one of the battery cells and a module node by a first switch in response to the command signal from the associated cell controller to cause the associated one of the battery cells to be functionally isolated from operation in the battery module; and establishing an electrical current path through a bypass conductor around the associated one of the battery cells by a second switch in response to the command signal from the associated cell controller to cause the battery module with the associated one of the battery cells to be functionally isolated from operation in the battery module.

[0024] According to one aspect of the invention, one or more of the cell parameters may be selected from the group comprising: a cell heat flux, a cell current, a cell state of charge, a cell temperature, and a cell voltage.

[0025] The cell balancing method may further comprise: receiving an input signal corresponding to the parameter threshold at a threshold input terminal on each of the cell controllers; and communicating the parameter threshold from a module controller to each of the cell controllers via a common control line.

[0026] The cell balancing method further comprises: providing an output signal corresponding to the measured value of one of the one or more cell parameters at an output terminal on each of the cell controllers; and transmitting the measured value of one or more cell parameters from each of the cell controllers to a common destination via a common monitoring line.

[0027] The cell balancing method may further comprise: transmitting the measured values ​​of one of the one or more cell parameters from each of the cell controllers to a summing module via a common monitoring line; and determining an average value of the one of the one or more cell parameters for the plurality of battery cells.

[0028] According to one aspect of the invention, the cell balancing method may further comprise a first testing method for determining the condition of one or more of the battery cells within the battery module. The first testing method may comprise: setting the parameter threshold to a relatively high value to cause most or all of the battery cells to be functionally connected to the battery module; monitoring a module voltage to determine a number of battery cells functionally connected to the battery module at a given time; and gradually lowering the parameter threshold while monitoring the number of battery cells functionally connected to the battery module to determine the impact of the parameter threshold on the battery cells.

[0029] According to another aspect of the invention, the cell balancing method may further comprise a second testing method for determining the condition of one or more of the battery cells within the battery module. The second testing method may comprise: setting the parameter threshold to a predetermined value; monitoring a module voltage to determine a number of battery cells operatively connected to the battery module, wherein the parameter threshold is set to the predetermined value; and assessing the relative health of the battery module based on the number of battery cells operatively connected to the battery module, wherein the parameter threshold is set to the predetermined value.

[0030] Objectives of the system and method of the present invention include achieving accurate cell balancing, minimizing connections to individual cells, and minimizing cost per cell by distributing the functions of sensing, data distribution, computing, and decision making in an optimal manner across the batteries at high cell counts.

[0031] In other words, the system and method of the present invention provide cell balancing using local sensing, setting thresholds based on averaged or calculated parameters, using local decision making, and local cell switching. In this approach, cells are dynamically engaged or disengaged depending on one or more parameters that indicate the cell's state. For example, during recharging, a cell may be functionally disconnected or "off" if its voltage, temperature, or heat flux indicates that the cell is fully charged. During discharging, a cell may be disabled if its voltage, temperature, or heat flux indicates that the cell is overloaded or overcurrent or discharged.

[0032] The system and method of the present invention provide several advantages over current systems. They allow for a reduction in the cost and packaging size of cell balancing. With this reduced cost and size, cell balancing is feasible for batteries with high cell counts. The concept is adaptable to batteries with a hierarchy of connections, including series, parallel, and series / parallel connection schemes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Further advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic diagram illustrating a battery module with local sensing for switching circuitry; Fig. Figure 2 is a schematic diagram illustrating a circuit for a battery module; Fig. 3A is a flowchart illustrating method steps of an embodiment for cell balancing with local sensing and switching according to one aspect of the invention; Fig. 3B a continuation of the flowchart of Fig. 3A is; Fig. 3C a further continuation of the flow chart of Fig. 3A is; Fig. 4 is a flowchart illustrating method steps for a testing method according to one aspect of the invention; and Fig. 5 is a flowchart illustrating method steps for an alternative testing method according to one aspect of the invention. DESCRIPTION OF THE EMBODIMENTS

[0034] With reference to the figures, in which like reference numerals indicate corresponding parts throughout the several views, a system for cell balancing with local sensing and switching is provided. As shown in Fig. 1, the system includes a battery module 20 having a plurality of battery cells 22 arranged in a series circuit, with a module terminal 28 provided at each end of the series of battery cells 22 for charging or discharging the battery module 20. Each of the battery cells 22 may, as indicated in this specification, refer to a single electrochemical cell or to a group of two or more electrochemical cells connected and monitored together as a group.

[0035] Each of the battery cells 22 has a switched cell terminal 24 and a non-switched cell terminal 26. In the Fig. 1 and Fig. In the exemplary embodiment illustrated in Figure 2, the switched cell terminal 24 is the positive terminal of the battery cell 22, and the non-switched cell terminal 26 is the negative terminal of the battery cell 22. However, it should be noted that the switched and non-switched cell terminals 24, 26 may also be connected to terminals of the battery cell 22 that have opposite polarity. In other words, the switched cell terminal 24 may be the negative terminal of the battery cell 22, and the non-switched cell terminal 26 may be the positive terminal of the battery cell 22.

[0036] A switching circuit 30 is in communication with each of the battery cells 22 and is switchable between a first mode in which the associated battery cell 22 is in operation or in communication with the battery module 20, and a second mode in which the associated battery cell 22 is functionally isolated from the operation of the battery module 20. In other words, in the first state, the associated battery cell 22 is connected in the series circuit of the battery module 20 and is capable of being charged and discharged with the battery module 20. In the second mode, the associated battery cell 22 is functionally isolated from the series circuit of the battery module 20 and is not charged or discharged with the battery module 20.

[0037] As in Fig. 1 and detailed in Fig. 2, the switching circuit 30 includes a first switch 32 in electrical communication with the switched cell terminal 24. The first switch 32 is configured as a closed circuit in the first mode to permit electrical current flow between the switched cell terminals 24 and a module node 34 that is in electrical contact with one of the module terminals 28 or one of the cell terminals 24, 26 of another of the battery cells 22. The first switch 32 is also configured as an open circuit in the second mode to block electrical current flow between the switched cell terminal 24 and the module node 34. Therefore, the first switch 32 operates to selectively connect or disconnect the associated battery cell 22 to the battery module 20.

[0038] The switching circuit 30 also includes a cell bypass conductor 38 in electrical contact with the unswitched cell terminal 26, and a second switch 36 configured as an open circuit in the first mode to block electrical current flow between the cell bypass conductor 38 and the module node 34. The second switch 36 is configured as a closed circuit in the second mode to allow electrical current flow between the cell bypass conductor 38 and the module node 34. Therefore, the second switch 36 operates to selectively enable the cell bypass conductor to conduct electrical current bypassing the associated battery cell 22 in the second mode, thereby allowing the battery module 20 to continue to function and be charged and / or discharged even when the associated battery cell 22 is functionally disconnected therefrom.

[0039] The switches 32, 36 may take the form of P-channel and N-channel enhancement-mode metal-oxide-semiconductor field-effect transistors (MOSFETS), as shown in Fig. 2; however, other types of switching devices with different types of transistors may also be used, such as field-effect transistors (FETs), bipolar transistors (BJTs), including insulated-gate bipolar transistors (IGBTs), or contacts such as those in an electromechanical relay. Preferably, to avoid a short-circuit condition of the battery cell 22, the switches 32, 36 should comprise an interrupting switching arrangement, as shown in Fig. 1, may be embodied as Form C contacts. The combination of the two switches 32, 36 with a common control input to place an output in one of two differently defined states, each based on an electrical connection to a corresponding switching node, can be referred to as a "totem pole configuration."

[0040] As in Fig. 1, the system also comprises a module control 40, which is available for the battery module 20 as a whole and is intended to set one or more parameter threshold values ​​Φ qTH , I TH , SoC TH , T TH , V TH including a heat flow threshold Φ qTH , a current threshold I TH , a state of charge threshold SoC TH , a temperature threshold T TH and a voltage threshold V TH, as maximum operating values ​​for operating the battery cells 22 within the battery module 20. The module controller 40 may include circuitry for measuring the electrical current in the module, the module voltage, which is the voltage between the module terminals 28, and / or other parameters.

[0041] According to one aspect, the module controller 40 may also provide management or control of the battery module 20 as a whole by monitoring changes in the module voltage and / or current that indicate that one or more of the battery cells 22 have been turned off. During charging or during off states, the entirety of the battery cells 22 may be controlled by slowly modulating one of the common parameter thresholds Φ qTH , I TH , SOC TH , T TH , V THand monitoring cell switching activity. This creates a plot of the total cells versus the parameter of interest.

[0042] In one aspect, the system may provide an initial calibration of the battery module 20. For example, after initial assembly, the calculation block 41 may calculate and store, or be provided with, a graph of the individual cell performance for comparison with results when the battery is in operation. This is useful for monitoring changes in use or degradation of the battery cells 22.

[0043] According to a further aspect, the system may also perform subsystem diagnostics. For example, measurements of individual cell parameters Φ qTH , I TH , SOC TH , T TH , V THWhen combined appropriately, they can be used to monitor, predict, and diagnose problems in subordinate systems such as the thermal management system, the module voltage measurement system, and the module current measurement system.

[0044] The system also includes a cell controller 42 in communication with each of the battery cells 22 to control one or more of a plurality of cell parameters Φ q , I, SoC, T, V including a cell heat flow Φ q , a cell current I, a cell state of charge SoC, a cell temperature T and a cell voltage V and to cause the circuit 30 in response to one of the cell parameters Φ q , I, SoC, T, V a corresponding parameter threshold Φ qTH , I TH , SOC TH , T TH , V THexceeds, switches from the first mode to the second mode. The cell controller 42 may have a time delay before causing the circuit 30 to switch from the first mode to the second mode in order to accommodate things such as erroneous measurements or temporary excursions in the value of one of the cell parameters Φ q , I, SoC, T, V, such as a current spike due to switching a non-linear load into operation. In other words, the cell controller 42 monitors at least one of the cell parameters Φ q , I, SoC, T, V and leads the circuit 30 to functionally separate the associated battery cell 22 from the battery module 20 if a monitored cell parameter Φ q , I, SoC, T, V exceeds the value of the associated parameter threshold. For example, if the temperature threshold T TH90 °C, the cell controller 42 allows the corresponding cell to be electrically connected in the series circuit of the battery module 20 until and unless the cell temperature T exceeds the temperature threshold T TH of 90 °C. If the cell temperature T exceeds the temperature threshold T TH of 90°C, the cell controller 42 would cause the switching circuit 30 to disconnect the cell from the series connection of the battery module 20 and would direct the electrical current through the cell bypass conductor 38, thereby allowing the battery module 20 to continue to function (but with a reduced capacity as a result of the battery cell 22 being functionally disconnected).

[0045] In cases where the battery cell 22 is part of a series circuit, a functionally separated and bypassed battery cell 22 would result in a reduced voltage of the entire series circuit. In other words, for a battery module 20 arranged as a series circuit, switching one of the individual battery cells 22 to a functionally separated and bypassed state would result in the battery module 20 having a reduced module voltage, which would be reduced by the voltage that would have been provided by that battery cell 22. According to one aspect, the cell controller 42 may cause the circuit 30, in response to the cell parameters Φ q , I, SoC, T, V all below the corresponding parameter threshold Φ qTH , I TH , SoC TH , T TH , V THare switched back from the second mode to the first mode. This may involve using some isolation, such as a deadband and / or a delay circuit, to prevent rapid switching in the event that one of the cell parameters Φ q , I, SoC, T, V equal to their corresponding parameter threshold Φ qTH , I TH , SoC TH , T TH , V TH or oscillate around it. Alternatively, the cell controller 42 may cause the circuit 30 to remain in the second mode until a predetermined condition is met, such as the receipt of a reset signal or the occurrence of an event such as a charge cycle or the passage of a predetermined period of time. The cell controller 42 may also use deadband values ​​or delay circuits to prevent the circuit 30 from rapidly switching between modes.

[0046] Each of the cell controllers 42 can be equipped with analog discrete components, an analog IC, a digital IC, or a combination thereof. Because the system requires a plurality of cell controllers 42, they are most advantageously implemented at low cost. In other words, it is economically advantageous to minimize the complexity and cost of the cell controllers 42.

[0047] The cell heat flow Φ q can be, for example, the differential temperature across parts of the battery cell 22, the differential temperature of cooling water across a cooling plate thermally connected to the battery cell 22, or a product of current and voltage in the thermoelectric thermal management device. The cell heat flow Φ qcan be measured in one or more of many different ways, including, for example, with a thin thermopile-type heat flux sensor (such as a Hukseflux FHF01) between the battery cell 22 and a cold plate; as the difference between the surface temperature of the battery cell 22 at the cold plate and a core temperature of the battery cell 22 (at equilibrium); as the difference between an inlet coolant temperature versus an outlet coolant temperature to or from a cold plate (at equilibrium); or using voltage and / or current from a thermoelectric thermal management device to establish temperature equilibrium. For heat flux measurements, if significant thermal mass is involved (“at equilibrium” above), a bulk temperature measurement ora measurement of the calorific mean temperature and a mathematical model of the thermal mass between the temperature measurements calculate the heat flow during non-equilibrium conditions.

[0048] Since the battery module 20 is a series combination of battery cells 22, the cell current I for each of the battery cells 22 operatively connected to the battery module 20 is equal to the module current. For this reason, only a single current sensor 43 is required for the entire battery module. For battery modules 20 having two or more branches connected in parallel, a corresponding number of current sensors 43 would be required to determine the electrical current through the battery cells 22 in each of the branches.

[0049] The cell state of charge (SoC), also referred to as accumulated charge, can be determined by integrating the charge into or out of the cell to generate an accumulated charge indicator. This can be achieved using an analog or digital circuit. A reset of the integrator can be triggered by global or local conditions to recalibrate the cell state of charge (SoC).

[0050] The cell temperature T may be measured by the cell controller 42 using a shift in device characteristics, such as diode forward or diode leakage or dark current. Other temperature measuring devices and circuits may also be used, such as a thermocouple or resistance temperature detector (RTD) mounted on or near the battery cell. The cell voltage V is preferably measured by the cell controller 42 using insulated gate or reverse bias devices that have very low current draw to cause a measurable change in the device's characteristics.

[0051] As in Fig. 1, each of the cell controllers 42 has a threshold input terminal 44 for receiving an input signal corresponding to at least one of the parameter threshold values ​​Φ qTH , I TH , SoCTH , T TH , V TH Each of the cell controllers 42 also has a parameter output terminal 46 for providing an output signal corresponding to at least one of the cell parameters Φ q , I, SoC, T, V corresponds.

[0052] The system also includes a common control line 48 that is in electrical communication with the module controller 40 and with the threshold input terminal 44 of each of the cell controllers 42 to control the parameter thresholds Φ qTH , I TH , SoC TH , T TH , V TH and communicate or transmit an AC clocking signal from the module controller 40 to each of the cell controllers 42. A first blocking capacitor 50 is disposed between the common control line 48 and each of the threshold input terminals 44 to prevent DC current from flowing therebetween while allowing AC signals to pass.

[0053] As in Fig. 1, a summing module 52 is in electrical communication with the module controller 40 and with a plurality of the cell controllers 42 to provide the module controller 40 with an average value of one of the cell parameters Φ q , I, SoC, T, V based on a plurality of values ​​of one of the cell parameters Φ q , I, SoC, T, V from the connected plurality of cell controllers 42. The system may include two or more summing modules 52, each having an average value of one of the cell parameters Φ q , I, SoC, T, V. The summing modules 52 may take the form of hardware, software, or a combination of hardware and software, which may be arranged within the module controller 40. Alternatively, a single summing module 52 may average values ​​of two or more of the cell parameters Φ q, I, SoC, T, V, such as when two or more of the cell parameters Φ q , I, SoC, T, V are communicated or transmitted at different times. In other words, the module controller 40 can perform the task of summing and / or averaging the values ​​of one or more of the cell parameters.

[0054] The module control 40 has a calculation block 41 for calculating the one or more parameter threshold values ​​Φ qTH , I TH , SoC TH , T TH , V TH The calculation block 41 may calculate one or more of the average values ​​of the cell parameters Φ q, I, SoC, T, V, as provided by the summing modules 52, as inputs. The calculation block 41 may also use other values ​​as inputs, such as the module voltage or the module current. The calculation block 41 may be implemented using a microcontroller having adequate I / O, processing power, and ambient operating range. Alternatively or additionally, the calculation block 41 may be implemented using an application-specific device, such as an application-specific integrated circuit (ASIC). The calculation block 41 may be a component or a module of another device, such as a combined controller for multiple battery modules 20 in a multi-module battery pack.

[0055] The calculation block 41 and the summing module 52 can be functionally combined and each implemented in software. Such software implementations of the calculation block 41 and the summing module 52 can run on the same processor or controller, such as the module controller 40. Alternatively, the software implementations of the calculation block 41 and the summing module 52 can run on different processors or controllers. The module controller 40 can include one of the different processors or controllers that implement one or both of the calculation block 41 and the summing module 52. Additionally or alternatively, one or more of the calculation block 41 and / or the summing module 52 can communicate with the module controller 40.

[0056] The system also includes a common monitoring line 54 that is in electrical communication with each of the cell controllers 42 to monitor one of the cell parameters Φ q, I, SoC, T, V from each of the cell controllers 42 to a common destination. In the Fig. 1, the common target is the summing module 52, which calculates one of the cell parameters Φ q , I, SoC, T, V from each of the cell controllers 42. A second blocking capacitor 56 is arranged between the common monitor line 54 and each of the cell controllers 42 to prevent direct current from flowing therebetween while allowing alternating current signals to pass. A signal resistor R s is arranged between each of the cell controllers 42 and the common monitoring line 54 to limit the electrical current flow between them. The use of the summing module 52 to receive two or more of the cell parameters Φ q, I, SoC, T, V together on the same common monitoring line 54 can be used as a “common line summer” method for determining the average value of one of the cell parameters Φ q , I, SoC, T, V. The blocking capacitors 50, 56 together provide DC isolation of the cell module and cell controller 42, respectively, to prevent high-voltage DC from being transferred to the respective common lines 48, 54. The value and rating of the blocking capacitors 50, 56 must be selected to provide this isolation while allowing the AC signals to pass with minimal attenuation.

[0057] In a Fig. 1, the summing module 52 includes an operational amplifier 58, which is designed as an inverting operational amplifier, with a non-inverting input 60 connected to a ground reference voltage, and with an inverting input 62 in electrical contact with the common monitoring line 54, and with a summing resistor R G , which is connected between the inverting input 62 and an output terminal 64 thereof to provide an output voltage V out which is proportional to the sum of the voltages from each of the parameter output terminals 46 in connection with the common monitoring line 54. In this manner, the summing module 52 also functions to average the values ​​of the associated cell parameter from each of the cell controllers 42.

[0058] According to one aspect, the module controller 40 may set one or more of the parameter threshold values ​​ΦqTH , I TH , SoC TH , T TH , V TH in response to the mean value of the corresponding cell parameter Φq, I, SoC, T, V. For example, the module controller 40 can be configured to generate a temperature threshold T TH which is 10% above the average cell temperature T, so that an average cell temperature T of 60° Celsius is the temperature threshold T TH to 60° Celsius. These average-based parameter thresholds Φ qTH , I TH , SoC TH , T TH , V TH can be limited to predefined absolute maximum or minimum thresholds. For example, the temperature threshold T TH to the lower value of 10% above the average of the measured cell temperatures T or 90° Celsius, where 90° Celsius is an example of the maximum threshold temperature.

[0059] According to one aspect, one or more of the parameter thresholds Φ qTH , I TH , SoC TH , T TH , V TH be set based on average values ​​of the measured parameters of neighboring battery cells 22 that are subject to the same current load and the same thermal management. For the voltage threshold V TH This can be determined by dividing the total stack or module voltage by the number of battery cells 22 that are functionally connected to this stack at a given time. For the temperature threshold T TH This can be a group temperature indicator, such as a coolant outlet flow or the mass heat sink temperature. For the heat flow threshold Φ qTHThis can be calculated from the coolant flow and temperature rise in a liquid-cooled thermal management system. For the heat flow threshold Φ qTH This can also be calculated from the impedance or from the current and voltage of thermoelectric cooling devices.

[0060] According to one aspect, the cell parameters Φ q , I, SoC, T, V and / or the parameter thresholds Φ qTH , I TH , SoC TH , T TH , V TH communicated using one of several different coding schemes, such as by modulating a carrier frequency with a varying amplitude, phase, or frequency. The cell parameters Φ q , I, SoC, T, V and / or the parameter thresholds Φ qTH , I TH , SoC TH , T TH , V THcan also be communicated by varying the duty cycle of the signal. According to a preferred embodiment, the module controller 40 can set a threshold value Φ qTH , I TH , SoC TH , T TH , V TH as an alternating current waveform with a predetermined frequency and an amplitude corresponding to the value of the signal. For example, a predetermined frequency of 30 MHz can be used together with a 0-10 VAC coding corresponding to a temperature threshold T TH range of 0-100° Celsius. At a temperature threshold T TH of 85° Celsius, the module control 40 would provide an AC signal of 30 MHz and 8.5 V (RMS) on the common control line 48.

[0061] According to a further aspect, the cell controller 42 may generate the common threshold signal in response to the measured value of the associated cell parameter Φ q, I, SoC, T, V to modulate or otherwise modify the value of the associated cell parameter Φ q , I, SoC, T, V on the common monitoring line 54. Such an arrangement would have the advantageous result of synchronizing the value signals of the cell parameters Φ q , I, SoC, T, V from each of the cell controllers 42, which are connected to the same common monitoring line 54, so that a relatively simple summing module 52, such as the one in Fig. 1. In other words, the cell controller 42 can adjust the amplitude of the received threshold value Φ qTH , I TH , SoC TH , T TH , V TH according to the measured value of the cell parameter Φ q , I, SoC, T, V. The summing module 52 is used to calculate average values ​​of one or more of the measured cell parameters Φ q, I, SoC, T, V from the battery cells 22 in the battery module 20. These average values ​​are sent to the calculation block 41 for use in generating the threshold values ​​Φ qTH , I TH , SoC TH , T TH , V TH made available.

[0062] Cell switching can be synchronized with other events in the battery module 20, using the AC threshold signal as a clock. For example, switching events by the circuits 30 can be synchronized with the zero crossing of the AC threshold signal.

[0063] The system may include a separate shared monitoring line 54 associated with each of the cell parameters Φ q , I, SoC, T, V, and a separate, shared control line 48 associated with each of the parameter threshold values ​​Φ qTH , I TH , SoC TH , T TH , V THAlternatively, the system may be configured or intended to include two or more of the cell parameters Φ q , I, SoC, T, V on the common monitoring line 54 by determining the cell parameters Φ q , I, SoC, T, V at different times. Alternatively, the system can be configured to simultaneously transmit two or more of the cell parameters Φ q , I, SoC, T, V on the common monitoring line 54, for example, by using different AC carrier frequencies associated with each of the cell parameters. Likewise, the system can monitor two or more of the parameter thresholds Φ qTH , I TH , SoC TH , T TH , V TH communicate on a common control line 48.

[0064] The AC carrier frequency or frequencies used to communicate the cell parameters Φ q, I, SoC, T, V and / or the parameter threshold values ​​Φ qTH , I TH , SoC TH , T TH , V THused can be any suitable frequency or range of frequencies. In general, it is advantageous to work with frequencies that are relatively noise-free for a particular application. The frequency of the AC signaling is chosen to be well outside the band of the primary current circuit in the battery. This is done to minimize interference between the primary current circuit and the cell threshold and cell parameter signals. Variable frequency drives and other power electronic devices of this type, commonly used to drive electric motors in vehicle applications, can generate significant RF interference in the range 30 kHz to 1.0 MHz. In such applications, it would be advantageous to use carrier frequencies outside this range. According to a preferred embodiment, a carrier frequency may be in the range of 30 MHz.

[0065] In summary, the system provides for local decision making at each of the battery cells 22 by a cell controller 42 which controls one or more cell parameters Φ q , I, SoC, T, V with one or more common parameter threshold(s) Φ qTH , I TH , SoC TH , T TH , V TH to determine when a particular battery cell 22 should be switched on (functionally connected) or switched off (bridged or bypassed). In other words, a comparison between a value of one of the cell parameters Φ q , I, SoC, T, V of a battery cell 22 and a corresponding common parameter threshold Φ qTH , I TH , SoC TH , T TH , V THdetermines whether this battery cell 22 should be functionally connected or bridged. This comparison may include one or more of the above-mentioned parameters. The system also provides for local switching at each of the battery cells 22 by a switching circuit 30 to locally isolate each of the battery cells 22 from a series-connected stack, with an arrangement of a changeover switch with interruption that maintains the current flow of the series stack when the cell is switched off. In addition, the system provides for the local isolation of the battery cell 22 from a series-connected stack with a switch 32, 36. This may, for example, as in Fig. 2, can be realized with a totem pole MOSFET configuration.

[0066] A method 100 for balancing battery cells using local sensing and switching is also described. The method 100 begins with the step 102 of measuring one or more cell parameters Φ q , I, SoC, T, V of each of a plurality of battery cells 22 connected in series by a cell controller 42 operatively connected to each of the battery cells 22.

[0067] The method 100 comprises the step 104 of transmitting a measured value of one of the cell parameters Φ q , I, SoC, T, V by the cell controller 42 as an AC signal via a common monitoring line 54 to a summing module 52.

[0068] The method 100 also includes the step 106 of blocking DC current through a second blocking capacitor 56 between the common monitor line 54 and each of the cell controllers 42 while passing AC signals therebetween.

[0069] The method 100 continues with step 108, averaging the measured values ​​corresponding to a predetermined cell parameter Φ q , I, SoC, T, V correspond, by the summing module 52, to an average value of the predetermined cell parameter Φ q , I, SoC, T, V.

[0070] The method 100 also includes the step 110 of providing the mean value of the predetermined cell parameter Φ q , I, SoC, T, V to a module controller 40. The module controller 40 can average values ​​of one or more of the cell parameters Φ q , I, SoC, T, V for all battery cells 22 within the battery module 20. Alternatively, the module controller 40 can record average values ​​of one or more of the cell parameters Φ q, I, SoC, T, V for a subset of fewer than all battery cells 22 within the battery module 20. The average value of the predetermined cell parameter may be transmitted by any suitable means, including, for example, a digital or analog signal. Average values ​​of two or more of the cell parameters Φ q , I, SoC, T, V can be transmitted to the battery module 20. The average values ​​of two or more of the cell parameters Φ q , I, SoC, T, V can be transmitted together or separately.

[0071] The method 100 further comprises the step 112 of determining a parameter threshold value Φ qTH , I TH , SOC TH , T TH , V TH by the module control 40, which corresponds to the specified cell parameter Φ q , I, SoC, T, V. One or more of the parameter thresholds Φ qTH , I TH , SoC TH , T TH , V THcan be static or unchanging. For example, one or more of the parameter thresholds Φ qTH , I TH , SoC TH , T TH , V TH be a predetermined threshold value that must never be exceeded, such as a voltage, current, or state of charge known to be associated with a high probability of damage to the battery cells 22. Alternatively or additionally, one or more of the parameter threshold values ​​Φ qTH , I TH , SOC TH , T TH , V TH be variable. For example, one or more of the parameter thresholds may change depending on one or more states or modes, or to implement a test method for determining the condition of battery cells within a battery module. Two different examples of such test methods 200, 300 are described below.

[0072] The method 100 proceeds with the step 114 of generating an AC signal that determines the parameter threshold Φ qTH , I TH , SoC TH , T TH , V TH which corresponds to the given cell parameter Φ q , I, SoC, T, V, by the module controller 40.

[0073] The method 100 also includes the step 116 of transmitting the parameter threshold value Φ qTH , I TH , SOC TH , T TH , V TH according to the specified cell parameter Φ q , I, SoC, T, V from the module controller 40 by the AC signal via a common control line 48 to each of the cell controllers 42.

[0074] The method 100 further includes step 118 of blocking the DC current through a first blocking capacitor 50 between the common control line 48 and each of the cell controllers 42, while allowing the AC signal to pass therebetween. Blocking the DC current may prevent damage to one or more of the cell controllers 42 and / or the circuits 30 by isolating these devices from high DC voltages that may be present in the battery module 20.

[0075] The method 100 continues with step 120, comparing the value of the predetermined cell parameter Φq, I, SoC, T, V measured by each of the cell controllers with the parameter threshold value Φ qTH , I TH , SoC TH , T TH , V TH , which corresponds to the given cell parameter Φ q , I, SoC, T, V.

[0076] The method 100 includes the step 122 of signaling a command signal to a corresponding circuit 30 by one of the cell controllers 42 to remove an associated one of the battery cells 22 from operation within the battery module 20 in response to the measured value of the predetermined cell parameter Φq, I, SoC, T, V exceeding the parameter threshold Φ qTH , I TH , SoC TH , T TH , V TH exceeds the specified cell parameter Φ q , I, SoC, T, V.

[0077] The method 100 includes the step 124 of designating one of the cell terminals 24, 26 as a switched cell terminal, which is selectively connected to a module node 34 of the battery module by a first switch 32, and designating the other of the cell terminals 24, 26 as a non-switched cell terminal. The switched cell terminal can be either the positive cell terminal 24 or the negative cell terminal 26. Likewise, the non-switched cell terminal can be either the positive cell terminal 24 or the negative cell terminal 26, but the non-switched cell terminal must be the one of the cell terminals 24, 26 with the opposite polarity as the switched cell terminal.

[0078] The method 100 also includes the step 126 of blocking an electrical current path between the associated one of the battery cells 22 and the module node 34 by a first switch 32 in response to the command signal from the associated cell controller 42 to cause the associated one of the battery cells 22 to be functionally isolated from operation in the battery module 20. More specifically, the step 126 includes placing the first switch 32 in an open state to prevent current flow between the switched cell terminal of the associated one of the battery cells 22 and the module node 34.

[0079] The method 100 further includes the step 128 of establishing an electrical current path through a cell bypass conductor 38 around the associated one of the battery cells 22 in response to the command signal from the associated cell controller 42 to cause the associated one of the battery cells 22 to be bypassed and to enable the battery module 20 to operate with the associated one of the battery cells 22 functionally isolated from operation within the battery module 20. More specifically, this step 128 includes closing a second switch 36 to enable electrical current flow between the module node 34 and the cell bypass conductor 38 in electrical contact with the unswitched cell terminal.In other words, this step 128 provides for establishing an alternative current path through the cell bypass conductor 38 to allow current to flow through the battery module 20 even though the associated battery cell 22 is functionally disconnected therefrom.

[0080] A first test method 200 for determining the condition of one or more battery cells 22 within a battery module 20 is also provided. This test method 200 includes causing one or more of the battery cells to be disconnected from the battery module 20, thereby assessing the condition of the battery cells 22 within the battery module 20. It should therefore preferably only be performed when the battery module 20 is not actively in use.

[0081] The first test method 200 includes the step 202, setting each of the parameter threshold values ​​Φ qTH , I TH , SOC TH , T TH , V THto relatively high values, so that most or all of the battery cells 22 are functionally connected to the battery module 20 and thereby contribute to the module voltage, which is the voltage between the module terminals 28.

[0082] The first test method 200 also includes the step 204 of monitoring the module voltage by the module controller 40 to determine the number of battery cells 22 that are operatively connected to the battery module 20 at a particular time.

[0083] The first test method 200 proceeds to step 206, namely the stepwise lowering of at least one of the parameter threshold values ​​Φ qTH , I TH , SoC TH , T TH , V THand simultaneously monitoring the number of battery cells 22 that are functionally connected to the battery module 20 to determine the condition or health of the battery cells 22 within the battery module 20. This step 206 of gradually lowering at least one of the parameter threshold values ​​Φ qTH , I TH , SOC TH , T TH , V TH For example, the recording of the parameter threshold value Φ qTH , I TH , SoC TH , T TH , V TH corresponding to a predetermined number of battery cells 22 in operation, which may, for example, be a minimum number of battery cells 22 required for a particular predetermined purpose. It may comprise the sequential lowering of each of two or more of the parameter threshold values ​​Φ qTH , I TH , SOC TH , T TH , V THto determine the different reactions.

[0084] A second test method 300 for determining the state of the battery cells 22 within a battery module 20 is also provided. The second test method 300 can be used as an alternative to the first test method 200 or as an additional verification thereof. The second test method 300 includes the step 302 of setting one or more of the parameter threshold values ​​Φ qTH , I TH , SoC TH , T TH , V TH to predetermined values ​​and the step 304 of determining the number of battery cells 22 that are functionally connected to the battery module 20, wherein the one or more of the parameter threshold values ​​Φ qTH , I TH , SoC TH , T TH , V THbe set to the predetermined value. The alternative test method 300 continues with step 306, namely assessing the relative health of the battery module 20 based on the number of functionally connected battery cells 22, wherein the one or more of the parameter threshold values ​​Φ qTH , I TH , SOC TH , T TH , V TH be set to the predetermined value.

[0085] The relative health or condition of the battery module 20 can be useful for various operational purposes, such as limiting the use of a relatively weak battery module 20 or throttling its capacity to prevent further deterioration. The relative condition can also be used to signal maintenance actions, such as replacing or rebuilding the battery module 20. The relative health of the battery module 20 can also be useful as an indicator of the expected service life of the battery module 20.

[0086] The above description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or limiting of the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but are, where appropriate, interchangeable and may be used in a selected embodiment even if not specifically shown or described. They may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.

Claims

[1] Cell balancing system comprising: a battery module (20) having a plurality of battery cells (22) in a series circuit; wherein each battery cell (22) of the plurality of battery cells (22) has a switched cell terminal (24) and an unswitched cell terminal (26) associated therewith; one or more circuits (30), each provided for switching an associated battery cell (22) of the plurality of battery cells (22) between a first mode in which the associated battery cell (22) is in operation or connected to the battery module (20), and a second mode in which the associated battery cell (22) is functionally separated from the battery module (20); wherein each of the one or more circuits (30) comprises a first switch (32) configured in the first mode as a closed circuit to allow electrical current to flow between the switched cell terminal (24) of the associated battery cell (22) and a module node (34), and configured in the second mode as an open circuit to block electrical current to flow between the switched cell terminal (24) of the associated battery cell (22) and the module node (34); wherein each of the one or more circuits (30) includes a cell bypass conductor (38) in electrical contact with the unswitched cell terminal (26) of the associated battery cell (22); wherein each of the one or more circuits (30) comprises a second switch (36) configured in the first mode as an open circuit (30) to block electrical current flow between the cell bypass conductor (38) and the module node (34), and in the second mode as an open circuit (30) to allow electrical current flow between the cell bypass conductor (38) and the module node (34); a cell controller (42) associated with each of the one or more circuits (30) and configured to monitor a plurality of cell parameters of the associated battery cell (22) associated therewith and to cause the circuit (30) to change from the first mode to the second mode in response to at least one of the plurality of cell parameters exceeding a corresponding parameter threshold, the system further comprising: a threshold input terminal (44) on each of the cell controllers (42) for receiving an input signal corresponding to the parameter threshold; and a common control line (48) in electrical communication with a module controller (40) and with the threshold input terminal (44) of each of the cell controllers (42) to communicate the parameter threshold therebetween, wherein the parameter threshold is one of two or more parameter thresholds; wherein the threshold input terminal (44) of each of the cell controllers (42) is one of two or more threshold input terminals (44) of each of the cell controllers (42); and wherein the common control line (48) is one of two or more common control lines (48) each in electrical communication with the module controller (4) and with a corresponding one of the two or more threshold input terminals (44) of each of the cell controllers (42) to communicate a corresponding one of the two or more parameter thresholds; characterized by that the plurality of cell parameters comprise a cell voltage and a cell temperature, and / or wherein the plurality of cell parameters comprise a cell voltage and a cell heat flux. [2] The system of claim 1, wherein each battery cell (22) of the plurality of battery cells (22) is an associated battery cell (22) to which one of the one or more circuits (30) is associated. [3] The system of claim 1, further comprising: a parameter output terminal (46) on each of the cell controllers (42) for providing an output signal corresponding to at least one of the cell parameters; and a common monitoring line (54) in electrical communication with each of the cell controllers (42) for communicating the at least one of the cell parameters from each of the cell controllers (42) to a common destination. [4] The system of claim 3, wherein the common monitor line (54) is one of two or more common monitor lines (54), each of the two or more common monitor lines (54) being in electrical communication with each of the cell controllers (42) and the common target. [5] The system of claim 3, wherein the common monitoring line (54) is arranged to communicate a plurality of the cell parameters. [6] The system of claim 5, wherein the plurality of cell parameters are communicated at different times over the common monitoring line (54). [7] The system of claim 5, wherein the plurality of cell parameters are communicated simultaneously over the common monitoring line (54). [8] The system of claim 5, wherein each of the plurality of cell parameters is associated with a different carrier frequency. [9] The system of claim 1, wherein the cell parameter is selected from a group comprising: a cell heat flux, a cell current, a cell state of charge, a cell temperature, and a cell voltage. [10] A method (100) for cell balancing, comprising: Measuring values ​​of a plurality of cell parameters of each of a plurality of battery cells (22) connected in series by a cell controller (42) operatively associated with each of the battery cells (22); Comparing the measured values ​​of each of the plurality of cell parameters by each of the cell controllers (42) with a corresponding parameter threshold associated with each of the plurality of cell parameters; Signaling a command signal by one of the cell controllers (42) to a corresponding circuit (30) to deactivate an associated one of the battery cells (22) within the battery module (20) in response to the measured value of any one of the plurality of cell parameters exceeding the corresponding parameter threshold associated with a corresponding one of the plurality of cell parameters; Blocking an electrical current path between the associated one of the battery cells (22) and a module node (34) by a first switch (32) in response to the command signal from the associated cell controller (42) to cause the associated one of the battery cells (22) to be functionally isolated from operation in the battery module (20); Establishing an electrical current path through a bypass conductor around the associated one of the battery cells (22) by a second switch (36) in response to the command signal from the associated cell controller (42) to cause the battery module (20) with the associated one of the battery cells (22) to be functionally isolated from operation in the battery module (20); Providing an output signal corresponding to the measured value of one of the plurality of cell parameters at an output terminal (46) on each of the cell controllers (42); and Transmitting the measured value of several cell parameters from each of the cell controllers (42) to a common destination via a common monitoring line (54) characterized by that the plurality of cell parameters comprise a cell voltage and a cell temperature, and / or wherein the plurality of cell parameters comprise a cell voltage and a cell heat flux. [11] The method (100) of claim 10, wherein one or more cell parameters are selected from the group comprising: a cell heat flux, a cell current, a cell state of charge, a cell temperature, and a cell voltage. [12] The method (100) of claim 10, further comprising: Transmitting the measured values ​​of one of the one or more cell parameters from each of the cell controllers (42) via a common monitoring line (54) to a summing module (52); and Determining an average value of the one or more cell parameters for the plurality of battery cells (22). [13] The method (100) of claim 10, further comprising: Setting the parameter threshold to a relatively high value to cause most or all of the battery cells (22) to be functionally connected to the battery module (20); Monitoring a module voltage to determine a number of battery cells (22) that are functionally connected to the battery module (20) at a given time; and gradually lowering the parameter threshold while simultaneously monitoring the number of battery cells (22) functionally connected to the battery module (20) to determine the influence of the parameter threshold on the battery cells (22). [14] The method (100) of claim 10, further comprising: Setting the parameter threshold to a predetermined value; Monitoring a module voltage to determine a number of battery cells (22) operatively connected to the battery module (20), wherein the parameter threshold is set to the predetermined value; and Assessing the relative health of the battery module (20) based on the number of battery cells (22) operatively connected to the battery module (20), wherein the parameter threshold is set to the predetermined value.

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