Apparatus for cell balancing in electrical battery system and corresponding method

Abstract

The present disclosure relates to a battery pack of an electrical battery system for balancing individual cells within the battery pack with respect to voltage, charge, and / or state of charge. The electrical battery system includes at least one pack, each pack including a plurality of battery cells, and each battery cell being monitored via a cell monitoring device (CMD) that provides cell-level measurements. The cell balancing is provided in a manner that allows a cell-level balancing current and a cell-level balancing voltage to be measured simultaneously during the balancing. This measurement allows the cell balancing to be controlled without having to continuously interrupt and restart the cell balancing process.

Description

Background Art

[0001] Battery systems comprising a plurality of battery cells are used in a wide range of modern power applications. For example, they are used to power electric vehicles, they are used in industrial power applications, transportation, and commercial applications such as powering modern electronic devices. In view of the relatively high power requirements of such applications, battery systems typically include a plurality of battery cells coupled together to achieve the required power output. Battery cells may be coupled together to form a battery pack, and a battery system may include one or more battery packs.

[0002] Individual cells in a battery pack may include different capacities, and the capacities may also vary over time due to different degradation rates, and therefore over multiple charge and discharge cycles, the cells may include different states of charge. State of charge (SOC) is defined as the ratio of the available capacity of a battery pack cell to the maximum possible charge that the cell can store. Balancing the cells in a multi-cell battery pack can help increase the capacity and life of the battery pack by maintaining equivalent (or balanced) state of charge levels at each cell within the pack. Summary of the invention

[0003] Current cell balancing approaches do not allow for obtaining measurements useful for monitoring and controlling cell balancing during the balancing itself. Therefore, current balancing approaches require that the balancing process be stopped periodically in order to obtain cell-level measurements related to, for example, state of charge, cell-level balancing voltage, and / or cell-level balancing current. Therefore, example embodiments presented herein provide a cell balancing approach in which measurements useful for controlling the balancing process can be obtained without interrupting the balancing process.

[0004] Thus, an example embodiment relates to a battery pack, the battery pack comprising a plurality of cell monitoring devices (CMDs), the battery pack being used to balance the cells within the battery pack with respect to voltage, charge and / or state of charge. The battery pack comprises a plurality of battery cells, wherein each battery cell is monitored via a corresponding cell monitoring device (CMD) providing cell-level measurements. Each CMD comprises a first measurement unit, the first measurement unit comprising at least one sensor, the at least one sensor being configured to obtain a cell-level voltage measurement and / or a cell-level charge measurement of a corresponding cell. Each CMD further comprises a balancing control unit, the balancing control unit being configured to identify a corresponding cell for cell balancing based on a measured cell-level voltage, a measured cell-level charge and / or a determined state of charge of the corresponding cell. The balancing control unit is further configured to passively balance the corresponding cells when the battery pack is discharged or charged. Each CMD further includes: a second measurement unit configured to measure a cell-level balancing current of a corresponding cell during the cell balancing; and a balancing control unit further configured to control the cell balancing of the corresponding cell based on at least one of the measured cell-level balancing current, the measured cell-level voltage, or the measured cell-level charge. In controlling the balancing process, each CMD is further configured to determine the internal resistance value of the battery cell to which the CMD is connected.

[0005] Example embodiments also relate to a method for balancing cells within a battery pack of an electrical battery system with respect to voltage, charge, and / or state of charge. The electrical battery system includes at least one pack, each pack including a plurality of battery cells, wherein each battery cell is monitored via a cell monitoring device (CMD) that provides cell-level measurements. The method includes: continuously measuring at least one of a cell-level voltage or a cell-level charge of a corresponding cell using at least one sensor included in a corresponding CMD. The method also includes: identifying at least one cell of the plurality of battery cells to be subjected to cell balancing based on at least one of the corresponding measured cell-level voltage, the measured cell-level charge, or the determined cell-level state of charge. The method also includes: passively balancing the at least one identified cell of the pack when the battery pack having the at least one identified cell is charged or discharged. The method further includes measuring a cell-level balancing current of the at least one identified cell during the balancing, and controlling the balancing of the at least one identified cell based on at least one of the measured cell-level balancing current, the measured cell-level voltage, or the measured cell-level charge.

[0006] Example embodiments also relate to a method for determining an internal resistance value of a battery cell in a battery pack of an electrical battery system, wherein the electrical battery system comprises at least one pack, each pack comprising a plurality of battery cells, wherein each battery cell is characterized by an internal resistance value and is monitored via a cell monitoring device CMD providing cell-level measurement values. The method comprises: performing one or more measurement cycles on at least one battery cell. The measurement cycle comprises the following steps: starting a balancing process; measuring a cell-level balancing current and a cell-level voltage before and after starting the balancing process; deactivating the balancing process after a first predetermined time period; measuring the cell-level balancing current and the cell-level voltage before and after deactivating the balancing process; and, waiting for a second predetermined time period. The method further comprises: determining the internal resistance value of the at least one battery cell based on the measured cell-level balancing current and the cell-level voltage during the one or more measurement cycles.

[0007] Example embodiments also include a computer-readable medium storing instructions that, when executed by a processor of a corresponding CMD of a battery pack, cause the corresponding CMD to perform the above-described method. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing will be described in greater detail by the following more particular description of example embodiments, as illustrated in the accompanying drawings, wherein reference characters refer to the same parts in the different views. The drawings are not necessarily drawn to scale, emphasis instead being placed upon illustrating example embodiments.

[0009] Figure 1 is a schematic diagram of an electrical battery system;

[0010] Figure 2 is a graph showing the relationship between open circuit voltage and state of charge associated with a battery cell;

[0011] Figure 3 It is characterized by multiplexed input Figure 1 A schematic diagram of an electrical battery system;

[0012] Figure 4 is a schematic diagram of an electrical battery system according to an example embodiment presented herein;

[0013] Figure 5 According to some of the exemplary embodiments presented herein Figure 4 An illustration of an example cell monitoring device (CMD);

[0014] Figure 6 According to some of the exemplary embodiments presented herein, Figure 4 A diagram of another example CMD featuring a Kelvin connection;

[0015] Figure 7 is a depiction of some of the example embodiments presented herein. Figures 4 to 6 A flowchart of the operational steps taken by one or more CMDs;

[0016] Figure 8 and Fig. 9 is a graph depicting the relationship of cell voltage over time during a cell balancing process according to some of the example embodiments presented herein;

[0017] Fig.10 is an illustration of another example CMD characterized by the internal resistance of an attached battery cell according to some of the example embodiments presented herein;

[0018] Fig.11 is a graph depicting the evolution of cell voltage and balancing current over time during measurement of internal resistance of a battery cell according to some of the example embodiments presented herein;

[0019] Fig.12 is a graph showing characteristic changes in the internal resistance of a battery cell according to the state of charge and life of the cell according to some of the example embodiments presented herein; and

[0020] Fig.13 is a graph showing characteristic changes in internal resistance of a battery cell according to cell temperature according to some of the example embodiments presented herein. DETAILED DESCRIPTION

[0021] Reference will now be made in detail to the exemplary embodiments, examples of which are shown in the accompanying drawings. The following description refers to the accompanying drawings, wherein the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations set forth in the following description of the exemplary embodiments do not represent all implementations consistent with the present invention. Instead, they are merely examples of devices and methods consistent with aspects related to the present invention described in the appended claims.

[0022] A battery system typically consists of multiple cells wired in a configuration to provide the desired battery system voltage and capacity, along with additional components necessary for safe cell operation and energy transfer to and from the cells. The cell is the fundamental unit of any battery system. The defining characteristic of a cell is its electrochemistry. For a particular cell chemistry, there is a minimum voltage, a typical voltage, and a maximum voltage that are determined by the electrochemistry of the system rather than the configuration of the system. These voltages cannot be changed other than by changing the electrochemical state of the cell. Cells can be wired in parallel to increase the total capacity, but from a cell monitoring perspective, these parallel cells can simply be treated as larger single cells as they still have the same voltage characteristics determined by their electrochemistry.

[0023] Cells can also be wired in series. A stack of cells in series has a voltage that is primarily determined by the stack configuration. The stack voltage will be the sum of the cell voltages. The stack voltage can be changed by adding or removing cells without changing the electrochemical state of the cells. Typically, a stack of cells will be charged and discharged, where the electrochemical state of the cells changes together. Each cell must be monitored to ensure that the cell is within its safe operating range. This is the job of a cell monitoring device (CMD). The CMD provides cell level measurements so that individual cells are measured individually and the information obtained is about the individual cells.

[0024] A battery pack consists of multiple cells connected in series. A battery pack provides the full battery system voltage. Multiple battery packs can be wired in parallel to increase the battery system capacity, but not in series. Cells can be grouped into modules. The defining characteristic of a module is its physical configuration, e.g. the number of cells and the connectivity between multiple cells. A module can consist of any number of cells. A module consists of two or more cells or an entire pack. If there is only a single pack in a battery system, a module can cover the entire battery system.

[0025] But more often, a pack is configured as multiple modules, where each module is configured from multiple cells connected in series. Multiple modules are then wired in series, or in parallel and in series. Modules that are configured to provide the full battery system voltage and are wired in parallel can be considered a pack. Modules have a defined size, shape, and are usually enclosed in some kind of housing.

[0026] The module configuration is driven by the physical requirements of the battery pack. Typically, modules are configured to have a voltage low enough so that they can be handled without risk of electric shock. Typically, the module is configured for a number of cells that matches the number of voltage sensor inputs on the cell monitoring device. A very common example is a twelve-cell monitoring device. The module then consists of the twelve cells and the connections to the cell monitoring device. In many battery packs, the nature of the CMD defines the configuration of the module, and the battery pack is then built from multiple such modules.

[0027] Figure 1 A known prior art system is shown. Figure 1The battery system includes three battery modules 170, each of which includes eight battery cells (C1-C8) 160. Each battery cell C1-C8 within each battery module 170 is hardwired to a corresponding CMD 180. During assembly of the battery module 170, the position of each battery cell C1-C8 within the battery module 170 can be mapped. In use, the CMD 180 receives measurement data from each of the cells C1-C8, and can determine the source of the received measurement data based on predefined cell mapping information. Figure 1 The CMDs 180 shown are connected in a star topology. Alternatively, each CMD 180 may be connected to a battery management system (BMS) via a serial daisy chain connection. The star topology is advantageous because there is no communication hierarchy imposed on the BMS 150, but instead communication is performed with each CMD 180 through a direct wired connection without the use of any proxy.

[0028] A battery pack consisting of multiple lithium-ion cells will become unbalanced over time. At the time of manufacturing, each cell will be at exactly the same state of charge (SOC) when it is assembled into the pack, as indicated by each cell having exactly the same voltage across the cell terminals (terminal voltage). This can be 100% SOC, or a lower (safer) level, such as 30% SOC. Alternatively, the cells can all be at exactly the same terminal voltage. The state of charge SOC maps directly to the cell terminal open circuit voltage. Figure 2 The SOC and open circuit voltage V ocv The terminal voltage (V term ) is equal to V ocv .

[0029] If all battery cells were ideal, the terminal voltage and SOC of all cells would track each other as the pack charges and discharges. But in reality, each cell will have manufacturing variations (capacity differences, resistance differences) and minor operating condition variations. An example variation is cell temperature, where a 5°C cell operating temperature variation across a pack is not uncommon.

[0030] Each cell has a tiny self-discharge current. When left alone, the cell will slowly discharge without any external load. This process can take months or even years. The self-discharge current is always present, but is usually only measurable when the cell is not otherwise being charged or discharged, and only then for very long periods of time. The self-discharge current can be higher at high temperatures, and lower at low temperatures. The self-discharge current may also depend on manufacturing variations. Over months or years, the pack will become unbalanced due to differences in self-discharge current experienced by each cell. Cells with large self-discharge currents will be at a lower voltage than cells experiencing smaller self-discharge currents.

[0031] When the pack is charging, once the first cell reaches its maximum allowable voltage V max , the charging process must be stopped. Continuing to charge beyond this point may cause damage to the cells. However, since all cells are connected in series, if charging is stopped for one cell, charging is stopped for all cells. Therefore, any cells at a lower voltage or SOC will not be fully charged. Similarly, when the pack is discharged, once the first cell reaches its minimum allowed voltage V min , the discharge process must stop. Any cells at a higher voltage or SOC will not be able to be fully discharged.

[0032] Therefore, the pack capacity is determined by the single cell that will cause the pack to be at V max The state is reached in which the single cell with the lowest voltage is at V min The state of charge is determined by the cell. Ideally this should be the same cell, as the pack capacity is then determined by the cell with the lowest actual capacity. In practice it will be determined by different cells, as over time the cells will be at different voltages due to self-discharge. Although each individual cell will have a higher capacity, an unbalanced pack will appear to have a lower usable capacity.

[0033] Therefore, cell balancing is needed to assist in keeping the cells of a battery pack balanced with respect to charge, voltage, and / or state of charge. During cell balancing, it is useful to know the current values ​​of the voltage, current, and / or state of charge of the cells to be balanced in order to properly monitor and control the balancing. A typical battery system (such as Figure 1 The system shown in FIG. 1 is unable to monitor the cells during the balancing process, but instead must periodically stop the cell balancing process in order to obtain voltage, current, and state of charge measurements.

[0034] There are two types of balancing architectures. The first is passive balancing, which is the subject of the present disclosure. In passive balancing, cells that have a high state of charge or cell voltage relative to the other cells in the battery pack are identified. An electrical load (e.g., a resistor) is then switched into position across the cell, thereby providing a discharge path for that cell and not for the other cells. Excess charge or energy in the cell is dissipated by the electrical load (e.g., as heat in a resistor) until the cell has the same state of charge or voltage as the other cells and is therefore balanced. Typical balancing currents are less than one ampere, typically 100mA or similar. This is a simple, low-cost approach, but it wastes energy as the charge is dissipated.

[0035] An alternative approach is active balancing. Active balancing identifies cells or groups of cells with a high state of charge and cells or groups of cells with a low state of charge. An active circuit transfers excess energy from one or more high cells to one or more low cells. There are many active balancing architectures, some using switched capacitors and others using inductors or transformers, but what all active balancing architectures have in common is that excess energy is moved rather than dissipated. Active balancing is relatively complex and expensive to implement compared to passive balancing. Active balancing is typically only used for applications that require high balancing currents (such as many amperes or tens of amperes). Although high currents can be achieved using passive balancing, wasted energy becomes a problem, and the heat generated in the balancing resistors, for example, needs to be removed. Active balancing always requires one or more source cells and one or more target cells. Active balancing cannot operate independently on a single cell.

[0036] In both cases, the balancing circuit is typically located on a centralized board at some distance from the cells. Connections are made to the individual cells through this board, through which the cell voltage is measured and the balancing current is drawn. As will be seen, drawing the balancing current through the voltage sense lines leads to measurement errors, and for this reason balancing is typically turned off while the voltage is being measured. This is inefficient and adds complexity. An alternative is to use separate measurement and balancing connections, however, this operation is costly.

[0037] Figure 1 One reason why a system cannot obtain measurements during cell balancing is due to the hardware architecture. Specifically, Figure 1 As shown, each cell C1-C8 establishes two wired connections with CMD 180. Therefore, for a battery module featuring eight cells, sixteen wired connections must be made to the CMD. In order to obtain measurements during balancing in this configuration, a multiplexer (MUX) will be required, such as Figure 3 However, as the number of cells, modules, and packs within a single system increases, the hardware configuration of this solution becomes complex.

[0038] According to an example embodiment, a system for cell balancing is provided that allows monitoring and measurements to occur during the cell balancing process. Figure 4 An example of such a system is shown in . Figure 4 The system of shows a battery pack featuring eight battery modules 301, wherein each module features twelve battery cells. Each battery cell 305 communicates with a corresponding CMD 307 that provides various measurements of the associated cell. All CMDs 307 communicate with each other and with a central controller via a radio antenna 311 and a wireless communication bus 313. It should be understood that, as described herein, according to other example embodiments, each module features another number of battery cells, each battery cell communicating with a corresponding CMD. According to yet another example embodiment, some of the modules may feature a different number of battery cells than other modules of the same system.

[0039] Figure 5 An example configuration of a CMD according to some of the example embodiments is shown. The CMD includes a measurement unit 501. The measurement unit may include any number or type of sensors for monitoring an electrical battery system. Examples of such sensors may include temperature, voltage, and current based sensors. Figure 5 In the embodiment, the measuring unit 501 is configured to measure the battery voltage.

[0040] The CMD may also include a balancing control unit 503, which may be a controller or a processor configured to balance the cells associated with the corresponding CMD when the cells are identified as requiring cell balancing. A field effect transistor (FET) 505 communicates with the balancing control unit 503. Figure 5 The CMD also includes a balancing resistor R bal 509, the balancing resistor is configured to be switched by the balancing control unit 503. bal The cell balancing current I is measured (eg, via a measurement unit 507 separate from the balancing control unit 503) bal And the cell balance voltage V bal (voltage across balancing resistor 509). Therefore, CMD can independently control cell balancing and simultaneously measure the cell balancing current I bal and / or cell balance voltage V bal The CMD also includes a parasitic resistance R located in the connection between the CMD and each corresponding cell. wire , where the cell-level voltage measurement value V cell .

[0041] According to some of the exemplary embodiments, Figure 5The CMD can be configured to perform passive balancing, which involves reducing the charge current or increasing the discharge current on individual cells so that cells that are at a low voltage relative to the other cells in the pack are charged at a lower rate, or cells that are at a high voltage relative to the other cells in the pack are discharged at a higher rate. For example, this causes the voltage of the cell to drop faster than other cells that are not being balanced. By measuring the cell voltages and determining which cells are at a high potential relative to the other cells, cells that need to be balanced can be selected. Figure 5 The CMD shown places passive balancing circuitry on each battery cell, reducing connection costs and allowing balancing to occur during cell voltage measurement.

[0042] A reduction in charging current or an increase in discharge current can be achieved by drawing current around the cell. This can be done by switching a resistive load (i.e., R bal ) is completed. Then, a portion of the cell charging current bypasses the cell by flowing through the balancing resistor when charging, or the cell discharging current is increased by additional current flowing through the balancing resistor. According to some of the example embodiments, the balancing resistor (R bal ) can be a simple resistor, or some type of current source (a MOSFET connected to a current source), or a switch operating as a pulse width modulated load, or some combination of these.

[0043] Since the cell level voltage changes during the balancing process, the voltage error (V err ) will not be constant. However, since each cell is monitored individually during cell balancing, the voltage error V can be continuously calculated and compensated err .exist Figure 5 In the embodiment, the second measuring unit 507 is connected across the balancing resistor R bal Measure voltage V bal . R bal The value of will be known by design. Then the balancing current I bal =V bal / R bal For example, the voltage error is equal to the balancing current (V err =R wire ×I bal ). Therefore, by knowing the voltage error V err , the cell-level voltage measurements can be compensated by taking into account known errors, specifically, V cell_compensated =V err +V cell It should be noted that in prior art systems (e.g. Figure 1In a system with a cell level voltage measurement, cell balancing will need to be paused before measuring the cell level voltage to allow the voltage error to return to zero. This means of providing cell balancing is not efficient. It should also be noted that R wire The value of the current I can be determined by bal The voltage V is measured while turning on and off cell I bal The value used to compensate for V err , and is also used to calculate balanced power and energy.

[0044] Figure 6 Another example configuration of a CMD according to some of the example embodiments is shown. Figure 6 The CMD configuration of comprises a Kelvin connection between the CMD and the corresponding battery cells, where four connections are provided. In this configuration, the cell balancing current I bal Not affected by parasitic resistor R wire This removes the voltage and current fluctuations and thus eliminates the voltage error (V err =0), at the expense of the balancing resistor not being able to share a connection with 501.

[0045] Figure 7 is a description of what can be done as described herein Figure 5 and Figure 6 Flowchart of example operations taken by a CMD when providing cell balancing for corresponding cells in a battery pack. It should be understood that Figure 7 Some operations are shown with solid borders and some operations are shown with dashed borders. The operations included in the solid borders are operations included in the broadest example embodiment. The operations included in the dashed borders are example embodiments that may be included in or are part of the operations of the broader example embodiment, or are further operations that may be taken in addition to the operations of the broader example embodiment. It should also be understood that the actions may be performed in any order and in any combination.

[0046] Operation 701

[0047] According to the example embodiments proposed herein, the measuring unit 501 is configured to continuously measure the cell voltage measurement value (V cell ) or cell-level charge measurement (I cell ). Figure 5 and Figure 6 As shown, such measurements can be made via the parasitic connection resistance R wire Obtain. Figure 5As shown, such measurements can be obtained via the connection to the corresponding cell that is shared by the balanced current path. wire Since the balancing current I flowing through it bal This will generate a measurement error Verr. Figure 6 As shown, such measurements can be obtained by connection to the corresponding cell (via a separate path to the path used by the balancing current). In this case, the voltage error on the measurement is reduced to nearly zero.

[0048] Operation 703

[0049] According to an example embodiment, the balancing control unit 503 is configured to measure the voltage of the battery cell level based on the corresponding battery cell level voltage measurement value (V cell ), cell-level charge measurement value (I cell ) or at least one of a determined cell-level state of charge to identify at least one of the plurality of battery cells to undergo cell balancing. The cell-level state of charge may be calculated based on the cell-level voltage measurements and / or the cell-level charge measurements.

[0050] Example Operation 705

[0051] According to some of the example embodiments, the balancing control unit 503 may be configured to identify at least one of the plurality of battery cells based on self-identification. Specifically, the CMD may be able to determine the need to cell balance the associated cell without receiving an explicit instruction to do so.

[0052] According to some of the example embodiments, the balancing control unit 503 can self-identify the need for cell balancing based on the cell level voltage, charge, or state of charge of the corresponding cell exceeding a specific voltage or charge target threshold. The specific voltage threshold can be used in top balancing, where the cell is intentionally charged so as to exceed the specific voltage threshold to initiate the balancing process. The charge target threshold can be used to determine whether the charge amount of the corresponding cell has drifted above the charge level that is considered acceptable for the cell of the battery pack. If so, top balancing can be employed.

[0053] According to some of the example embodiments, the balancing control unit 503 can self-identify the need for cell balancing based on the cell level voltage, charge or state of charge not falling within a predefined bottom balancing threshold or voltage or charge. In this case, the measured parameter of the corresponding cell falls below an acceptable level associated with the cells of the battery pack. In this case, balancing is provided via bottom balancing.

[0054] According to some of the example embodiments, the balancing control unit 503 may self-identify based on the difference in cell level voltage, charge, or state of charge of the corresponding cell relative to at least one other cell in the battery pack. In such example embodiments, the CMD may be aware of measurements taken by one or more other CMDs in the battery pack. According to some of the example embodiments, the CMDs may communicate with each other via a wireless communication bus and / or each CMD may report its corresponding measurements and access a centralized location for storing the obtained measurements. Therefore, once the CMD detects that the obtained measurement of its corresponding cell is different from the measurement associated with another cell in the battery pack obtained by a different CMD, cell balancing may be initiated, for example, based on the size of the measurement difference. An example of an acceptable level of measurement difference between different cells may be 50mV, where lower values ​​will cause balancing to occur more frequently and higher values ​​may reduce the effective capacity of the battery pack.

[0055] Example Operation 707

[0056] According to some of the example embodiments, the balancing control unit 503 may be configured to identify at least one cell for cell balancing via a centralized control unit. According to such embodiments, the CMD may send the cell level voltage, state of charge, and / or charge measurement values ​​to the centralized control unit via a corresponding radio antenna via a wireless communication bus. The CMD may also receive from the centralized control unit an instruction to perform cell balancing on its associated cell based on the corresponding cell level voltage, state of charge, and / or charge measurement values.

[0057] Operation 708

[0058] Example embodiments also include passively balancing at least one identified cell when charging or discharging the battery pack. Passive balancing of at least one cell can be achieved by using a passive balancing architecture (charge dissipated via an electrical load) as described above. For example, in the case of top balancing, balancing will be provided via a reduction in the effective charge rate on the cell being balanced. In the case of bottom balancing, balancing is provided via an increase in the effective discharge rate of the cell being balanced, the identified cell.

[0059] Operation 711

[0060] Example embodiments also include measuring a cell balancing current (I bal), and controls the balancing based on at least one of the measured cell-level balancing current, the measured cell-level voltage, or the measured cell-level charge. Thus, compared to prior art systems in which the balancing process must be paused in order to properly monitor the balancing, the example embodiments provided herein provide the possibility of continuously monitoring the balancing process without pausing the cell balancing. For example, the cell balancing current (I bal ) through the resistor R bal According to the exemplary embodiment and as Figure 5 or Figure 6 As shown, the cell level property (voltage, current or both) measurements, balance control and balance current measurements are performed by three separate units included in the CMD (measurement unit 501, balance control 503 and V bal The three processes are performed by the measurement unit 507, thereby allowing the three processes to be performed simultaneously. Specifically, the cell-level properties can be continuously measured at any stage of the balancing process without interruption and independently of the balancing process control. The three units can coordinate their work by communicating with each other.

[0061] Sample Operation 713

[0062] According to some of the example embodiments, the balancing control unit 503 may be configured to control the duration of balancing of at least one identified cell. Specifically, by monitoring the cell-level balancing current, the rate of discharge and / or charge may be evaluated to ensure that balancing is performed so that the balanced cells will reach a desired charge level.

[0063] Sample Operation 715

[0064] According to some exemplary embodiments, the balancing control unit 503 may be configured to detect the cell balancing current I bal Specifically, the balancing control unit 503 can detect when the cell balancing current has exceeded the maximum allowed level to ensure normal operation of the battery cells. Alternatively, there may be a maximum power that can be safely dissipated on the battery cells, or a maximum temperature that the battery cells can be allowed to reach. In each case, the balancing current I bal to avoid malfunctions.

[0065] Sample Operation 717

[0066] According to some exemplary embodiments, the balancing control unit 503 may also be configured to modulate the cell balancing current I bal As described above, passive balancing reduces the charge current or increases the discharge current in order to increase the rate at which the voltage of the cell is adjusted during balancing. Modulation of the cell balancing current helps maintain a desired average current level to achieve a desired balance of the cells.

[0067] Sample Operation 719

[0068] According to some of the example embodiments, the balancing control unit 503 is configured to determine the cell level voltage (V cell ) to control the balance and know the value of the cell level voltage. In such embodiments, the balancing control unit 503 can also be configured to detect when the measured cell level voltage is lower than the minimum cell level voltage for maintaining safe cell operation or higher than the maximum safe voltage. However, due to the cross R wire The error voltage (such as Figure 5 As shown), the real V cell The voltage may be higher than the voltage measured at equilibrium. By knowing the equilibrium current I bal , operation 719 may compensate for the error voltage, thereby allowing for a better determination of when the threshold is crossed.

[0069] Sample Operation 721

[0070] According to some of the example embodiments, the balancing control unit 503 is further configured to adjust the cell balancing voltage limit during balancing upon knowledge of the cell level voltage measured during balancing of at least one identified cell. internal . Balancing current I bal The conduction may cause the I bal ×R internal A voltage drop occurs at the cell terminals. For example, at operation 711, it may be determined that one cell requires balancing. However, when the balancing current is turned on, the cell voltage will drop, which may turn off balancing again.

[0071] Example operation 721 is CMD, knowing the balancing current I bal , adjusting the voltage threshold so that it determines the need to balance at a first threshold and also determines the need to continue balancing at a second voltage threshold limit. This second voltage threshold limit can be adjusted during the process in response to the balancing current as the balancing current changes.

[0072] Sample Operation 723

[0073] According to some of the example embodiments, the balancing control unit 503 is configured to calculate the state of charge during cell balancing when obtaining measurements of the cell-level balancing current and the cell-level voltage. Compared to prior art systems that require pausing the balancing process in order to determine the state of charge, the example embodiments provide a means for determining and monitoring the state of charge throughout the balancing process. This then enables the balancing process to be more efficiently and accurately controlled (e.g., adjusting the rate of charging or discharging), for example, using the state of charge determined or monitored in real time.

[0074] Sample Operation 725

[0075] According to some of the example embodiments, the balancing control unit 503 may be further configured to calculate the change in energy of the corresponding battery cell undergoing cell balancing by integrating the balancing power over time. bal ) and the measured cell-level balance voltage (V cell ) to obtain the balanced power. An example of a calculated energy change of a cell is the power of the cell integrated over time, expressed in Watt-hours (Wh) or Joules (J). Monitoring such changes assists in ensuring that the cells are balanced to the correct level.

[0076] Figure 8 A working example of monitoring and control of a cell top balancing process is shown, where balancing occurs when individual cells are balanced as they approach full charge (or full capacity). Take a set of 4 cells C1, C2, C3, and C4, which are connected in series. Each cell has a nominal capacity of 1Amp-hr (1Ah). Each cell has a measured voltage V1, V2, V3, and V4. In this example, the maximum allowed voltage on any cell is 4.2V. The minimum allowed voltage is 3.0V. Using the example implementation scheme presented herein, the voltage on each cell can be measured continuously.

[0077] The cell is placed on the charger circuit and a current of 1000mA is fed through the cell. After a period of time t1, V1, V2 and V3 are all at 4.00V. This voltage is equivalent to a SOC of 95%. Although V4 is at 3.95V. This is because C4 has suffered from excessive self-discharge because it has been at a higher temperature than the other cells, for example, and the pack has not been balanced. This voltage is equivalent to a SOC of 93%. Therefore, the charge of cell C4 is 2% lower than the other cells, 1Ah = 20mAh. Each cell has a 40Ω balancing resistor that can be turned on and off by a MOSFET.

[0078] Make the balancing resistor (R bal ) is turned on, which causes 100mA of current to flow when the cell voltage is 4.00V. This 100mA current bypasses the cell, reducing the charging current to that cell from 1000mA to 900mA. To balance the four cells, the balancing resistors on C1, C2, and C3 are turned on. Cells C1, C2, and C3 are now charged at 900mA. Cell C4 continues to charge at 1000mA. All four cells continue to charge towards their maximum allowed voltage of 4.20V.

[0079] C1, C2, and C3 are now charging at only 900mA. There is 100mA bypassed around each cell C1-C3. Because they are at 95% SOC, they require 5% of 1Ah = 50mAh to reach full charge. This will take 50mAh × 60 × 60 / 900mA = 200 seconds. Since C4 charges 100mA faster than C1, C2, and C3, it will reach full charge in 50mAh × 60 × 60 / 1000mA = 180 seconds. At time t2, before 180 seconds have passed, the cell voltage can be equal to 4.15V. At this point, balancing stops because all cells are now balanced. All cells continue to charge at 1000mA until t3, when the maximum allowed voltage of 4.2V is reached. Charging must stop at this point. If any cell reaches the maximum allowed voltage of 4.2V before balancing is complete, charging and balancing are terminated.

[0080] Fig. 9 A working example of monitoring and control of the cell bottom balancing process is shown. At t1, it is determined that C1 has a higher cell voltage than the other cells, so balancing is turned on. C1 is now discharged at 1100mA until t2, when the voltages are all equal. Discharging continues until t3, when the discharge must be stopped because the minimum allowed voltage has been reached. If any cell reaches the minimum allowed voltage of 3.5V before balancing is complete, charging and balancing are terminated.

[0081] When balancing is on, the balancing current will cause a shift in the cell voltage. Figure 8 In the top balancing example, a reduction in the charge current on C1, C2, and C3 from 1000mA to 900mA will cause the cell voltage to increase by a small amount. If charging were to terminate when V1 (or V2, V3) reached the maximum allowed, and C1, C2, and C3 were still balanced so that C4 was still charging at a higher rate, then when charging was terminated, the voltage of C4 would increase by a larger amount than C1, C2, and C3. In effect, the charger circuit would enter a constant voltage-constant current charging mode, where the charge current is gradually reduced while keeping the cell voltage nearly constant. But the charge current interferes with this because C4 will change by a different amount than C1, C2, and C3 when the balance is removed. This makes the charging and balancing process less precise.

[0082] Another aspect stems from the fact that the exemplary embodiment can simultaneously measure the cell-level properties and the balancing current, i.e., determine the internal resistance R internal . Fig.10 Some of the exemplary embodiments are shown Figure 6 CMD, which also includes the internal resistance R of the connected battery cell internal 901. When balancing starts, due to the internal resistance R internal , there is a cell voltage Vcell This voltage change is very small because R internal The value of may be only 1mΩ or less, while the balancing current I bal It is only 100mA, so according to the usual Ohm's law, the voltage drop is 100μV. cell and the balancing current I bal By measuring unit 501 and V bal The measurement unit 507 measures simultaneously or close enough in time to correlate the noise, and thus removes the noise through processing. In the context of this specification, balancing activation / deactivation refers to connecting / disconnecting a load such as a balancing resistor 509 to the battery cell terminals. For example, by controlling the gate voltage of the transistor 505, it can act as a switch and thus connect or disconnect the balancing resistor to the battery cell terminals.

[0083] Thus, unlike prior art systems, the embodiments proposed herein allow the internal resistance to be measured for each individual cell without significantly changing the state of charge. In fact, in conventional systems, the internal resistance is usually determined on the scale of the battery pack by measuring the open circuit voltage of the battery pack and then connecting a load to it, an option that requires a large stimulus current. This option significantly changes the state of charge of the battery pack and only allows the determination of the average internal resistance of the battery cells included in the battery pack and requires knowledge of the architecture of the battery pack (how many battery cells are connected in series / parallel).

[0084] Fig.11 Shown in Fig.10 The internal resistance R of the battery cell shown internal The cell voltage V over time during the measurement period cell and the balancing current I bal The cell voltage V is measured at t0. cell and the balancing current I bal In this state, since balancing is disabled, the balancing current I bal is expected to be zero, and since there is no load connected to the battery cell, V cell =Equal to the open circuit voltage. The balancing control 503 starts balancing at t1 and then adjusts the battery voltage V cell and the balancing current I bal Take a second measurement. These measurements can be used to calculate R internal 901. An example of calculation is as follows. ΔV cell-1 =V cell-t2 -V cell-t0 (The cell level voltage V measured before and after starting balancing cell ), and similarly, ΔI bal-1 =Ibal-t2 -I bal-t0 (The cell-level balancing current I measured before and after starting balancing bal The value of the internal resistor can be adjusted according to R internal＝ |ΔV cell-1 / ΔI bal-1 |Calculate.

[0085] The accuracy of the internal resistance measurements can be improved by performing a second set of measurements later when balancing is disabled. Fig.11 As shown, another sample is taken later at t3, balancing is disabled at t4, and another sample is taken at t5. The actual period is not important, but if it is much less than a second, many measurement cycles can be taken before the balancing current significantly changes the cell state. Similarly, ΔV can be defined cell-2 =V cell-t5 -V cell-t3 (Cell level voltage V measured before and after deactivating balancing cell ), and ΔI bal-2 =I bal-t5 -I bal-t3 (The cell-level balancing current I bal The difference of R internal =(ΔV cell-1 -ΔV cell-2 ) / (ΔI bal-1 -ΔI bal-2 ) to calculate the internal resistance. Several such measurement cycles (balance activation / deactivation) can be performed to improve R, for example by averaging the measured values. internal The actual frequency of these measurement cycles may be of the order of a few Hertz.

[0086] At this frequency, the total time required to determine the value of the internal resistance by averaging the results obtained over several measurement cycles is of the order of tens of seconds. For example, averaging over 40 cycles at a frequency of 2 Hz will take only 20 seconds. This time is negligible compared to the time required for the entire balancing process, which may take several hours. Therefore, in some embodiments, the determination of the internal resistance by repeating the above-mentioned measurement cycles can be performed at different stages of the balancing process without significantly interfering with the balancing process. This makes it possible to track the evolution of the value of the internal resistance at different stages of the balance. Different stages of the balancing process correspond to different values ​​of the cell voltage and / or state of charge, so it is possible to further map the values ​​of the internal resistance of different cells based on these parameters. Alternatively, the values ​​of the internal resistance of different cells at different temperatures can be obtained by correlating the above-mentioned measurements with those of the temperature sensors contained in different CMDs.

[0087] Many different physical and chemical mechanisms affect the value of the internal resistance of a battery cell. Examples of these mechanisms can include the resistivity of electrodes or internal components, contacts between these components, electrode surface area, electrolyte conductivity, or ion mobility. Therefore, the value of the internal resistance can be used to inform or improve estimates of the state of charge, state of health, or available power state of a battery cell. For example, an algorithm may use the value of the internal resistance as part of its calculations and the locally measured value is better than the assumed value. As cells age or degrade, the internal resistance typically increases. Fig.12 This is illustrated in FIG. 1 , which shows the characteristic change in the internal resistance of a battery cell as a function of state of charge and cell age. The evolution of the internal resistance of a newly manufactured cell as a function of state of charge is shown at 1101. As the cell ages, its internal resistance increases, as shown at 1102 and 1103. This increase is a valuable parameter to track. The available power state is closely determined by the internal resistance, and as the resistance increases, the available power decreases. Fig.13 The characteristic change of the internal resistance of the battery cell according to the temperature is shown. The internal resistance of the battery cell is a decreasing function of temperature (1201). Therefore, the available power state that the battery cell can achieve is a decreasing function of temperature. By tracking the internal resistance and temperature, a better estimation of the available power state can be made.

[0088] In some embodiments, each CMD may periodically send a determined value of the internal resistance of its corresponding cell to the central controller. Thus, the central controller may monitor the evolution of the internal resistance of each battery cell included in the battery pack and further infer the state of charge, state of health, or state of available power of the entire battery pack. Additionally, the controller may use the internal resistance information to identify battery cells that may be faulty. For example, by identifying battery cells that have an internal resistance that is much higher than the determined average internal resistance of the battery cells included in the battery pack.

[0089] The description of the example embodiments provided herein has been proposed for the purpose of illustration. The description is not intended to be exhaustive or to limit the example embodiments to the precise form disclosed, and can be modified and varied according to the above teachings, or can be modified and varied by practicing various alternatives or equivalents of the embodiments provided. The examples discussed herein are selected and described to explain the principles and essence of various example embodiments and their practical applications, so that those skilled in the art can utilize the example embodiments in various ways and utilize the example embodiments with various modifications suitable for the specific purposes envisioned. The features of the embodiments described herein can be combined in the form of all possible combinations of methods, devices, modules, systems and computer program products. It should be understood that the example embodiments proposed herein can be practiced in any form combined with each other.

[0090] It should be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed, and the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. It should be further noted that any reference signs do not limit the scope of the claims, that the exemplary embodiments may be implemented at least in part by both hardware and software, and that several "components", "units" or "means" may be represented by identical or functionally equivalent hardware items.

[0091] Various example embodiments described herein are described in the general context of method steps or processes, which in one aspect can be implemented by a computer program product embodied in a computer-readable medium or a non-transitory computer-readable medium, including computer-executable instructions, such as program code, executed by one or more processors in a computer or networked environment. Computer-readable media or non-transitory computer-readable media may include removable and non-removable storage devices, including but not limited to read-only memory (ROM), random access memory (RAM), compact disk (CD), digital versatile disk (DVD), flash memory, etc. In general, program modules may include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. Computer executable instructions, associated data structures, and program modules represent examples of program codes for performing the steps of the methods disclosed herein. A specific sequence of such executable instructions or associated data structures represents an example of corresponding actions for implementing the functions described in such steps or processes.

[0092] In the drawings and description, example embodiments have been disclosed. However, many changes and modifications may be made to these embodiments. Therefore, although specific terms are employed, these terms are used only in a general and descriptive sense and not for the purpose of limitation, and the scope of the embodiments is limited by the appended claims.

Claims

1. A method in a battery pack of an electrical battery system for balancing cells in the battery pack with respect to voltage, charge and / or state of charge, wherein the electrical battery system comprises at least one pack, each pack comprising a plurality of battery cells, wherein each battery cell is monitored via a cell monitoring device CMD providing cell level measurements, the method comprising: continuously measuring at least one of a cell-level voltage or a cell-level charge of a corresponding cell using at least one sensor included in the corresponding CMD; identifying at least one cell of the plurality of battery cells to undergo cell balancing based on at least one of a corresponding measured cell level voltage, a measured cell level charge, or a determined cell level state of charge; passively balancing the at least one identified battery cell in the battery pack during charging or discharging of the battery pack; as well as During the balancing, a cell-level balancing current of the at least one identified cell is measured, and the balancing of the at least one identified cell is controlled based on at least one of the measured cell-level balancing current, the measured cell-level voltage, or the measured cell-level charge.

2. The method of claim 1, wherein the identifying at least one battery cell further comprises self-identifying via the CMD of each corresponding battery cell based on: The voltage, charge or state of charge of the corresponding cell exceeds the intended voltage or charge target threshold; or The voltage, charge, or state of charge does not fall within a predefined bottom balance threshold for voltage or charge; or The voltage, charge or state of charge difference of the corresponding battery cell relative to at least one other battery cell in the battery pack.

3. The method of claim 1, wherein the identifying at least one battery cell further comprises: transmitting the cell level voltage, the state of charge and / or the charge measurement via a wireless communication bus to a centralized control unit via a radio antenna of each respective CMD, wherein the centralized control unit is configured to control the operation of the electrical battery system; as well as Instructions to cell balance at least one cell based on respective cell level voltage, state of charge and / or charge measurements are received from the centralized control unit via the radio antenna of each respective CMD.

4. The method of any one of claims 1 to 3, wherein controlling the balancing based on at least one of a measured cell level balancing current, a measured cell level voltage, or a measured cell level charge further comprises: controlling a duration of the balancing of the at least one identified cell; and / or detecting a fault in the cell level balancing current; and / or The duty cycle of the cell balancing current is modulated to obtain an average current.

5. The method of any one of claims 1 to 4, wherein controlling the balancing based on at least one of a measured cell level balancing current, a measured cell level voltage, or a measured cell level charge further comprises: Detecting when the measured cell level voltage is below a minimum or maximum cell level voltage for maintaining cell operation; and / or A cell balancing voltage limit is adjusted during the balancing of the at least one identified cell.

6. The method of claim 4 or 5, wherein performing the controlling based on at least one of a measured cell-level balancing current, a measured cell-level voltage, or a measured cell-level charge further comprises: calculating a state of charge during the cell balancing of the identified cell; and / or The change of energy of the corresponding cell undergoing cell balancing is calculated by calculating the balancing power according to the measured cell-level balancing current and the measured cell-level balancing voltage and by integrating the balancing power over time.

7. The method of any one of claims 4 to 6, wherein controlling based on at least one of a measured cell-level balancing current, a measured cell-level voltage, or a measured cell-level charge further comprises: The internal resistance value of the at least one identified battery cell is determined by: Deactivate the balancing process; measuring the cell level balancing current and the cell level voltage before and after deactivating the balancing process; initiating the balancing process after a predetermined period of time; measuring the cell level balancing current and the cell level voltage before and after initiating the balancing process; and, The internal resistance value of the at least one identified cell is calculated based on the measured cell-level balancing current and the measured cell-level voltage.

8. A method for determining an internal resistance value of a battery cell in a battery pack of an electrical battery system, wherein the electrical battery system comprises at least one pack, each pack comprising a plurality of battery cells, wherein each battery cell is characterized by an internal resistance value and is monitored via a cell monitoring device CMD providing cell-level measurement values, the method comprising: One or more measurement cycles are performed on at least one battery cell, the measurement cycles comprising the following steps: Initiate the balancing process; measuring a cell-level balancing current and a cell-level voltage before and after initiating the balancing process; deactivating the balancing process after a first predetermined period of time; measuring the cell level balancing current and the cell level voltage before and after deactivating the balancing process; and, waiting a second predetermined period of time; and, The internal resistance value of the at least one battery cell is determined based on the measured cell level balancing current and the measured cell level voltage during the one or more measurement cycles.

9. The method of claim 8, wherein determining the internal resistance value of the at least one battery cell further comprises: The determined internal resistance value of the at least one battery cell is averaged based on the measured cell level balancing current and the cell level balancing voltage for each measurement cycle.

10. The method according to any one of claims 8 or 9, wherein performing one or more measurement cycles and determining the value of the internal resistance of the at least one battery cell is performed at different time intervals or for different values ​​of the cell level voltage, state of charge or temperature of the at least one battery cell, and the method further comprises: The value of the internal resistance is mapped based on time, cell voltage, state of charge, or temperature.

11. The method of claim 10, further comprising: The state of charge, state of health, or state of available power of the at least one battery cell is estimated using at least one map of the values ​​of the internal resistance.

12. A battery pack comprising a plurality of cell monitoring devices CMD, the battery pack being used to balance the cells within the battery pack with respect to voltage, charge and / or state of charge, wherein the battery pack comprises a plurality of battery cells, wherein each battery cell is monitored via a respective cell monitoring device CMD providing cell level measurements, wherein each CMD comprises: A first measurement unit, the first measurement unit comprising at least one sensor, wherein the at least one sensor is configured to obtain a cell-level voltage measurement value and / or a cell-level charge measurement value of a corresponding cell; a balancing control unit configured to identify corresponding cells for cell balancing based on measured cell level voltages, measured cell level charges, and / or determined states of charge of the corresponding cells, and passively balance the corresponding cells when discharging or charging the battery pack; as well as a second measuring unit, the second measuring unit being configured to measure a cell-level balancing current of a corresponding cell during the cell balancing, The balancing control unit is further configured to control the cell balancing of the corresponding cell based on at least one of the measured cell-level balancing current, the measured cell-level voltage or the measured cell-level charge. 13 . The battery pack as claimed in claim 12 , wherein each CMD is further configured to perform the method as claimed in any one of claims 1 to 11 .

14. The battery pack of any one of claims 12 and 13, wherein the second measurement unit of each CMD is further configured to measure a cell-level balancing current by measuring a cell-level voltage across a balancing resistor included in the CMD during the cell balancing.

15. A battery pack as described in claim 14, wherein the balancing control unit of each CMD is further configured to calculate the cell voltage error based on the cell-level balancing current on the resistance of the common connection from the corresponding cell to the corresponding CMD, the power supply for the corresponding CMD and the measuring unit of the corresponding CMD. 16 . The battery pack of claim 14 , wherein at least one respective CMD comprises separate connections for a power source and the measuring unit, the separate connections being via Kelvin connections between the at least one respective CMD and the respective battery cell. 17 . The battery pack according to claim 14 , wherein each CMD further comprises a FET switch connected to the balancing control unit. 18 . A computer-readable medium storing instructions, which, when executed by a processor of a corresponding cell monitoring device CMD of a battery pack, causes the corresponding CMD to execute the method according to claim 1 .

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