Device and method for cell balancing in a battery system

Abstract

The present disclosure relates to a battery pack of a battery system for balancing individual cells within the battery pack with respect to voltage, charge, and / or state of charge. The battery system includes at least one pack, each pack including a plurality of battery cells, each battery cell being monitored via a cell monitoring device (CMD) that provides cell level measurements. Cell balancing is provided in a manner that enables simultaneous measurement of cell level balancing current and cell level balancing voltage during balancing. Such measurements enable control of cell balancing without the need to continuously interrupt and resume the cell balancing procedure.

Description

Background Art

[0001] Battery systems including a plurality of battery cells are used in a wide range of modern power applications. For example, they are used to supply power to electric vehicles and for commercial applications such as industrial power applications, transportation, and power supply for state-of-the-art electronic devices. Given the relatively high power demand for such applications, battery systems often include a plurality of battery cells coupled together to achieve the required power output. The battery cells can be coupled together to form a battery pack, and the battery system can include one or more battery packs.

[0002] Individual cells within a battery pack can include different capacities, which can also change over time due to different degradation rates. Thus, during multiple charge and discharge cycles, the cells can include different states of charge. The state of charge (SOC) is defined as the ratio of the available capacity to the maximum possible charge that can be stored in the battery cell. Balancing the cells of a multi-cell battery pack can help improve the capacity and lifespan of the battery pack by maintaining an equal (or balanced) state of charge in each cell within the pack.

Summary of the Invention

[0003] Current means of cell balancing do not allow for obtaining measurements useful for monitoring and controlling cell balancing during the balancing itself. Thus, current balancing means require periodically stopping the balancing procedure, for example, to obtain cell-level measurements related to the state of charge, cell-level balancing voltage, and / or cell-level balancing current. Accordingly, the exemplary embodiments presented herein provide means of cell balancing by which measurements useful for controlling the balancing procedure can be obtained without interrupting the balancing procedure.

[0004] Thus, the exemplary embodiments are directed to a battery pack including a plurality of cell monitoring devices (CMDs) for balancing cells within the battery pack with respect to voltage, charge, and / or state of charge. The battery pack includes a plurality of battery cells, and each battery cell is monitored via each cell monitoring device (CMD) that provides cell-level measurements. Each CMD includes a first measurement unit including at least one sensor configured to acquire a cell-level voltage measurement and / or a cell-level charge measurement of each cell. Each CMD further includes a balance control unit configured to identify each cell for cell balancing based on the measured cell-level voltage, the measured cell-level charge, and / or the determined state of charge of each cell. The balance control unit is further configured to passively balance each cell during discharge or charge of the battery pack. Each CMD further includes a second measurement unit configured to measure the cell-level balancing current of each cell during cell balancing, and a balance control unit further configured to control the cell balancing of each cell based on at least one of the measured cell-level balancing current, the measured cell-level voltage, or the measured cell-level charge. When 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] Exemplary embodiments also relate to a method for balancing cells within a battery pack of a battery battery system with respect to voltage, charge, and / or state of charge. The battery system includes at least one pack, each pack includes a plurality of battery cells, and 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 the cell-level voltage or cell-level charge of each cell using at least one sensor included in each CMD. The method also includes identifying at least one cell of a plurality of battery cells that undergoes cell balancing based on at least one of the respective measured cell-level voltages, measured cell-level charges, or determined cell-level states of charge. The method further includes passively balancing at least one identified cell of the battery pack when charging or discharging the pack of at least one identified cell. The method further includes measuring the cell-level balancing current of at least one identified cell during balancing and controlling the balancing of at least one identified cell based on at least one of the measured cell-level balancing current, measured cell-level voltage, or measured cell-level charge.

[0006] The exemplary embodiments also relate to a method for determining the internal resistance value of battery cells in a battery pack of a battery system, the battery system including at least one pack, each pack comprising a plurality of battery cells. Each battery cell is characterized by an internal resistance value and is monitored via a cell monitoring device (CMD) that provides cell-level measurements. The method includes performing one or more measurement cycles on at least one battery cell. A measurement cycle includes starting a balancing process, measuring the cell-level balancing current and the cell-level voltage before and after starting the balancing process, disabling the balancing process after a first predetermined time, measuring the cell-level balancing current and the cell-level voltage before and after disabling the balancing process, and waiting for a second predetermined time. The method also includes determining the internal resistance value of at least one battery cell based on the cell-level balance current and the cell-level voltage measured during one or more measurement cycles.

[0007] The exemplary embodiments also include a computer-readable medium storing instructions that, when executed by a processor of each CMD of the battery pack, cause each CMD to perform the above method.

[0008] The foregoing will be described in more detail by the following more detailed description of the exemplary embodiments, which is shown in the accompanying drawings that refer to the same parts throughout the figures with different reference characters. The drawings are not necessarily to scale and instead focus on showing the exemplary embodiments.

Brief Description of the Drawings

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MODE FOR CARRYING OUT THE INVENTION

[0010] Next, refer to the exemplary embodiments in detail and show their examples in the accompanying drawings. The following description refers to the accompanying drawings, and the same numerals in different drawings represent the same or similar elements unless otherwise expressed. The embodiments described in the following description of the exemplary embodiments do not represent all embodiments that are consistent with the present invention. Rather, they are merely examples of apparatuses and methods that are consistent with aspects related to the present invention described in the appended claims.

[0011] A battery system typically includes a plurality of cells wired in a configuration that provides a desired battery system voltage and capacity, and additional parts necessary for the safe operation of the cells and the transfer of energy between the cells. A cell is the basic unit of any battery system. The decisive characteristic of a cell is its electrochemical characteristic. For the chemical action of a specific cell, there are a minimum voltage, a normal voltage, and a maximum voltage that are determined by the electrochemical characteristics of the system, rather than the system configuration. These voltages can only be changed by changing the electrochemical state of the cell. Cells can be wired in parallel to increase the total capacity, but since these cells connected in parallel still have the same voltage characteristics determined by the electrochemical characteristics, they can be simply regarded as a larger single cell from the perspective of cell monitoring.

[0012] Cells can also be wired in series. A series stack of cells has a voltage mainly determined by the stack configuration. The stack voltage is the sum of the cell voltages. The stack voltage can be changed by adding or removing cells without changing the electrochemical state. Usually, the stack of cells is charged, discharged, and their electrochemical states change in cooperation. In order to ensure that it is within a safe operating range, it is necessary to monitor each cell. This is the role of the cell monitoring device (CMD). The CMD provides cell-level measurements so that separate measurements are made for each individual cell and information about each individual cell is obtained.

[0013] The battery pack is composed of a plurality of cells in series. The battery pack provides the total battery system voltage. A plurality of battery packs can be wired in parallel to increase the capacity of the battery system, but not in series. The cells may be grouped into modules. The defining characteristics of a module are its physical configuration, e.g., the number of cells and the connectivity between the plurality of cells. A module may be composed of any number of cells. A module is composed of two or more cells, or the entire pack. If there is only a single pack within the battery system, the module may encompass the entire battery system.

[0014] However, more often, the pack is configured as a plurality of modules, and each module is composed of a plurality of cells in series. Next, the plurality of modules are wired in series, or in parallel and in series. Modules configured to provide the total battery system voltage and wired in parallel may be regarded as a pack. A module has a defined size and shape and is usually packaged in a certain kind of enclosure.

[0015] The module configuration is determined by the physical requirements of the battery pack. Often, a module is configured to have a sufficiently low voltage so that it can be handled without the risk of electric shock. Often, a module is configured for a number of cells that matches the number of voltage sensor inputs of the cell monitoring device. A very common example is a 12-cell monitoring device. Also, a module is composed of 12 cells and the connections to the cell monitoring device. In many battery packs, the module configuration is defined by the characteristics of the CMD, and the battery pack is constructed from a plurality of such modules.

[0016] FIG. 1 shows a known prior art system. The battery system of FIG. 1 includes three battery modules 170, and each battery module includes eight battery cells (C1 to C8) 160. Each battery cell C1 to C8 within each battery module 170 is hard-wired to each CMD 180. The positions of each cell C1 to C8 within the battery module 170 may be mapped during the assembly of the battery module 170. In use, the CMD 180 can receive measurement data from each of the cells C1 to C8 and determine the source of the received measurement data based on pre-defined cell mapping information. The CMD 180 shown in FIG. 1 is connected in a star topology. Alternatively, each CMD 180 may be connected to a battery management system (BMS) via a serial data-chain connection. The star topology is advantageous because there is no communication layer imposed on the BMS 150 and instead communication with each CMD 180 is by a direct wired connection without using any proxy.

[0017] A battery pack consisting of a plurality of lithium-ion cells tends to become unbalanced over time. At the time of manufacture, all cells are at the same state of charge (SOC) as indicated by all cells having exactly the same voltage (terminal voltage) across the cell terminals when assembled into the pack. This can be at 100% SOC or at a lower (safer) level such as 30% SOC. Alternatively, all cells can be at exactly the same terminal voltage. The state of charge SOC is directly mapped to the open-circuit voltage of the cell terminals. FIG. 2 shows a function associating SOC with the open-circuit voltage V ocv and the function is highly non-linear, and the terminal voltage (V term ) is equal to V ocv only when the current is zero and the cell is at rest.

[0018] If all battery cells were ideal, when the pack is charged and discharged, the terminal voltages and SOCs of all cells would track each other. However, in reality, all cells have manufacturing variations (capacity variations, resistance variations) and slight variations in operating conditions. As an example, the cell temperature varies, and it is not uncommon to see a 5°C variation in the operating temperature of cells across the pack.

[0019] All cells have a small self-discharge current. Individually, the cells discharge slowly without an external load. This process can take months or even years. The self-discharge current is always present but is typically measurable only when the cell is not being charged or discharged, and even then, it is measured only over a very long period. The self-discharge current can be higher at higher temperatures and lower at lower temperatures. The self-discharge current can also depend on manufacturing variations. Over months or years, due to the differences in self-discharge current seen in each cell, the pack becomes unbalanced. Cells with a higher self-discharge current have a lower voltage than cells with a lower self-discharge current.

[0020] When the pack is charged, the charging process must stop as soon as the first cell reaches its maximum allowable voltage V max . Continuing to charge beyond this point can lead to cell damage. However, since all cells are in series, when the charging of one cell stops, the charging of all cells stops. Therefore, any cell at a lower voltage, i.e., SOC, is not fully charged. Similarly, when the pack is discharged, the discharging process must stop as soon as the first cell reaches its allowable minimum voltage V min . Any cell at a higher voltage or SOC is not fully discharged.

[0021] Therefore, the pack capacity ranges from the state where a single cell with the highest voltage accidentally reaches V max to the state where a single cell with the lowest voltage accidentally reaches V minIt is determined by the charge applied to the pack until it reaches the state therein. Since the pack capacity is then determined by the cell with the lowest actual capacity, ideally this should be the same cell. In practice, the power supply is determined by different cells. This is because over time, the cells settle at different voltages due to self-discharge. A pack with an unbalanced state may appear to have a lower usable capacity even if the individual cell capacities are higher.

[0022] Therefore, cell balancing is necessary to assist in maintaining the balance of the cells of a battery pack with respect to charge, voltage, and / or state of charge. During cell balancing, it is useful to know the current values for the voltage, current, and / or state of charge of the cells being balanced in order to properly monitor and control the balancing. General battery systems such as the system shown in FIG. 1 cannot monitor the cells during the balancing process and instead must periodically stop the cell balancing procedure to obtain measurements of voltage, current, and state of charge.

[0023] There are two types of balancing architectures. The first architecture, which is the subject of the present disclosure, is passive balancing. In passive balancing, a cell having a high state of charge, or cell voltage, is identified compared to other cells within the battery pack. Next, an electrical load (e.g., a resistor) is switched in place across the entire cell, providing a discharge path for that cell and not for the other cells. The excess charge or energy within the cell is dissipated by the electrical load (e.g., as heat in the resistor) until the cell reaches the same state of charge or voltage state as the other cells and thus reaches an equilibrium state. A typical balance current is less than an ampere and is usually on the order of 100 mA or so. This is a simple and low-cost method, but it wastes energy as the charge dissipates.

[0024] An alternative method 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 high-voltage cell(s) to low-voltage cell(s). There are many active balancing architectures that use switched capacitors, inductors or transformers, but what is common to all is that the excess energy is transferred and not dissipated. Active balancing is relatively complex and costly to implement compared to passive balancing. Active balancing is generally only used in applications that require high balancing currents such as many amperes or tens of amperes. High currents can be achieved by passive balancing, but energy waste becomes a problem, for example, it is necessary to remove the heat generated in the balancing resistor. Active balancing always requires one or more source cells and one or more target cells. Active balancing cannot function with a single isolated cell.

[0025] In either case, the balancing circuit is typically located on a centralized control panel away from the cells. Connections are made from this board to the individual cells, the cell voltages are measured, and balance currents are drawn. As can be seen, measuring the balance current via a voltage sensing wire introduces measurement errors, so balancing is often switched off while the voltage is being measured. This is inefficient and adds complexity. An alternative is to use separate measurement and balance connections, but this operation is costly.

[0026] One reason why the system of FIG. 1 cannot obtain measurement values during cell balancing is the hardware architecture. Specifically, as shown in FIG. 1, each cell C1 - C8 makes two wired connections to CMD180. Therefore, in the case of a battery module characterized by eight cells, 16 wired connections to the CMD are required. To obtain measurement values during balancing with such a configuration, as shown in FIG. 3, a multiplexer (MUX) is required. However, as the number of cells, modules, and battery packs increases within a single system, the hardware configuration of such a solution becomes complex.

[0027] According to an exemplary embodiment, a system for cell balancing that enables the execution of monitoring and measurement during the cell balancing procedure is provided. An example of such a system is shown in FIG. 4. The system of FIG. 4 shows a battery pack characterized by eight battery modules 301, and each module is characterized by 12 battery cells. Each battery cell 305 communicates with each CMD307 that provides various measurement values of the associated cell. All CMD307 communicate with each other and with a central control device via a wireless antenna 311 and a wireless communication bus 313. As described herein, according to other exemplary embodiments, it is understood that each module is characterized by a different number of battery cells, and each battery cell communicates with each CMD. According to yet another exemplary embodiment, some of the modules may be characterized by a different number of battery cells than other modules of the same system.

[0028] FIG. 5 shows an exemplary configuration of a CMD according to some exemplary embodiments. The CMD includes a measurement unit 501. The measurement unit may include any number or type of sensors used for monitoring the battery system. Examples of such sensors may include temperature, voltage, and current-based sensors. In FIG. 5, the measurement unit 501 is configured to measure the cell voltage.

[0029] The CMD may also include a balancing control unit 503 configured to balance the cells associated with each CMD if the aforementioned cells are identified as requiring cell balancing. The field effect transistor (FET) 505 is in communication with the balancing control unit 503. The CMD of FIG. 5 further comprises a balance resistor R bal 509. The cell balancing current I bal and the cell balancing voltage V bal (the voltage across the balance resistor 509) may be measured across the balance resistor R bal via, for example, a measurement unit 507 separate from the balancing control unit 503. Thus, the CMD can independently control cell balancing and simultaneously measure the cell balance current I bal and / or the cell balance voltage V bal . The CMD further includes a parasitic resistor R wire in the connection located between the CMD and each cell, and a cell-level voltage measurement V cell can be obtained.

[0030] According to some of the exemplary embodiments, the CMD of FIG. 5 can be configured to perform passive balancing involving reducing the charging current or increasing the discharging current in individual cells. Thereby, cells with a lower voltage are charged at a lower rate relative to other cells in the pack, or cells with a higher voltage are discharged at a higher rate relative to other cells in the pack. For example, this causes the voltage of the cell to drop faster than other unbalanced cells. By measuring the cell voltage and determining which cell is at a higher potential relative to other cells, the cells that require balancing can be selected. The CMD shown in FIG. 5 arranges a passive balance circuit for each battery cell, reducing the cost of the connection and enabling balancing during cell voltage measurement.

[0031] A decrease in the charging current, or an increase in the discharging current, can be achieved by drawing a current that bypasses the cell. This can be done by switching a resistive load in parallel with the cell, i.e., R bal . Next, a portion of the charging current of the cell bypasses the cell by flowing through the balancing resistor during charging, or the discharging current of the cell is increased by an additional current flowing through the balancing resistor. According to some of the exemplary embodiments, the balancing resistor (R bal ) can be a simple resistor, or a certain type of current source (current source connected MOSFET), or a switch operating as a pulse width modulation load, or some combination thereof.

[0032] Since the cell-level voltage changes during the balancing procedure, the voltage error (V err ) does not remain constant. However, since each cell is monitored individually during cell balancing, the voltage error V err can be continuously calculated and compensated. In FIG. 5, the second measurement unit 507 measures the voltage V bal across the balancing resistor R bal . The value of R bal is known by design. Next, the balancing current can be calculated as I bal = V bal / R bal . For example, the voltage error is equal to the balancing current with respect to the parasitic resistance in the connection with the individual cell (V err = R wire × I bal ). Therefore, by knowing the voltage error V err , the cell-level voltage measurement can be compensated by taking into account the known error, specifically, V cell_compensated = V err + V cell . Note that in prior art systems (e.g., the system of FIG. 1), it is necessary to pause the cell balancing in order to allow the voltage error to return to zero before measuring the cell-level voltage. Such a means of providing cell balancing is not efficient. Also, the value of R wire is the current I under controlled conditionsbal It should also be noted that it can be determined by measuring the change in voltage V while switching it on and off. I cell The value of I bal is not only useful for compensating V err but also for calculating balancing power and energy.

[0033] FIG. 6 shows another exemplary configuration of the CMD according to some of the exemplary embodiments. The CMD configuration of FIG. 6 includes a Kelvin connection between the CMD and each battery cell, providing four connections. In such a configuration, the cell balancing current I bal is not affected by the parasitic resistance R wire . Thus, this eliminates voltage and current fluctuations and can eliminate the voltage error (V err = 0) at a cost where the balancing resistor cannot share the connection with 501.

[0034] FIG. 7 is a flowchart showing exemplary operations that can be performed by the CMDs of FIGS. 5 and 6 as described herein when providing cell balancing to each cell within the battery pack. It will be understood that FIG. 7 includes some operations indicated by solid edges and some operations indicated by dashed edges. The operations included within the solid edges are those included in the broadest exemplary embodiments. The operations included within the dashed edges are exemplary embodiments that may be taken in addition to, may be included in, may be part of, or may be further operations of the operations of the broader exemplary embodiments. It should also be understood that the operations may be performed in any order and in any combination.

[0035] Operation 701

[0036] According to the exemplary embodiments presented herein, the measurement unit 501 uses at least one sensor included in (or connected to) the CMD or within the measurement unit itself to perform cell voltage measurement (V cell ) or cell-level charge measurement values (I cellconfigured to successively measure at least one of them. As shown in FIGS. 5 and 6, such measurement values can be obtained through the parasitic connection resistance in the direct communication with each cell R wire and can be obtained through the connection with each cell common to the balanced current path. As shown in FIG. 5, such measurement values can be obtained through the connection with each cell through a path different from that used by the balanced current. The parasitic connection resistance R wire causes a measurement error Verr due to the balanced current I bal flowing through it. As shown in FIG. 6, such measurements may be obtained by connecting to each cell through a path different from that used by the balanced current. In this case, the voltage error in the measurement is reduced to almost zero.

[0037] Operation 703

[0038] According to an exemplary embodiment, the balancing control unit 503 is configured to identify at least one cell of a plurality of battery cells that undergoes cell balancing based on at least one of the measured values of each cell level voltage (V cell ), the measured value of the cell level charge (I cell ), or the determined state of charge of the cell level. The state of charge of the cell level can be calculated based on the measured value of the cell level voltage and / or the measured value of the cell level charge.

[0039] Exemplary operation 705

[0040] According to some of the exemplary embodiments, the balancing control unit 503 may be configured to identify at least one cell of a plurality of battery cells based on self-identification. Specifically, the CMD may be able to determine the need for cell balancing of the associated cell without receiving an explicit command to do so.

[0041] According to some of the exemplary embodiments, the balancing control unit 503 may self-identify the need for cell balancing based on the cell-level voltage, charge, or state of charge of each cell that exceeds an intended voltage or a charge target threshold. The intended voltage threshold may be used in top balancing to start a balancing process by charging the cell intentionally to exceed the intended voltage threshold. The charge target threshold may be used to determine whether the charge level of each cell has drifted above a charge level that is considered acceptable for the cells of the battery pack. In that case, top balancing may be used.

[0042] According to some of the exemplary embodiments, the balancing control unit 503 may self-identify the need for cell balancing based on a cell-level voltage, cell-level charge, or cell-level state of charge that does not fall within a predetermined bottom balancing threshold or bottom balancing voltage or bottom balancing charge range. In this case, the measured parameter of each cell is below an acceptable level associated with the cells of the battery pack. In this case, balancing is provided by bottom balancing.

[0043] According to some of the exemplary embodiments, the balancing control unit 503 may self-identify based on the difference in cell-level voltage, cell-level charge, or cell-level state of charge of each cell with respect to at least one other cell within the battery pack. In such exemplary embodiments, the CMD may have knowledge of the measurements made by one or more other CMDs within the battery pack. According to some of the exemplary embodiments, the CMDs may communicate with each other via a wireless communication bus and / or each CMD may report its respective measurement and access a centrally managed location for storing the acquired measurements. Thus, when it is detected that the measurement of each cell acquired by the CMD is different from the measurement of another cell acquired by a different CMD, cell balancing may be initiated within the battery pack, for example, based on the magnitude of the measurement difference. An example of the tolerance level of the measurement difference between different cells may be 50 mV, and the lower the value, the more frequently balancing will occur, and the higher the value, the more the effective capacity of the battery pack may decrease.

[0044] Exemplary operation 707

[0045] According to some of the exemplary embodiments, the balancing control unit 503 may be configured to identify at least one cell for cell balancing via a central control unit. According to such embodiments, the CMD may transmit cell-level voltage, cell-level state of charge, and / or cell-level charge measurements to the central control unit via the wireless communication bus through their respective wireless antennas. The CMD may also receive from the central control unit an instruction to balance its associated cell based on each cell-level voltage, cell-level state of charge, and / or cell-level charge measurement.

[0046] Operation 708

[0047] The exemplary embodiments further include passively balancing at least one identified cell during charging or discharging of the battery pack. Passive balancing of at least one cell can be achieved by using a passive balancing architecture (where charge is dissipated through an electrical load) as described above. For example, in the case of top balancing, balancing is brought about by a decrease in the effective charge rate of the cell being balanced. In the case of bottom balancing, balancing is provided by an increase in the effective charge rate of the identified cell of the cell being balanced.

[0048] Operation 711

[0049] The exemplary embodiments further include measuring the cell balancing current (I bal ) of at least one identified cell during balancing, and controlling 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, in contrast to prior art systems where the balancing process has to be interrupted to properly monitor the balancing, the exemplary embodiments provided herein offer the possibility of continuously monitoring the balancing process without interrupting the cell balancing. For example, the cell balancing current (I bal ) is measured through a resistor R bal . According to the exemplary embodiments, as shown in FIG. 5 or FIG. 6, the measurement of cell-level characteristics (voltage, current or both), balancing control, and balancing current measurement can be performed simultaneously by three separate units included in the CMD (a measurement unit 501, a balance control 503, and a V bal measurement unit 507, respectively). In particular, the cell-level characteristics can be continuously measured at any stage of the balancing process without interruption and independently of the control of the balancing process. The three units can operate in cooperation by communicating with each other.

[0050] Exemplary operation 713

[0051] According to some of the exemplary 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 discharge rate and / or the charge rate may be evaluated to ensure that the balancing is performed such that the balanced cell reaches a desired charge level.

[0052] Exemplary operation 715

[0053] According to some of the exemplary embodiments, the balancing control unit 503 may be configured to control cell balancing by detecting a fault within the cell balancing current I bal Specifically, the balancing control unit 503 may detect when the cell balancing current exceeds a maximum allowable level to ensure proper operation of the battery cell. Alternatively, there may be a maximum power that can be safely dissipated by the battery cell, or a maximum temperature that the battery cell can reach. In either case, the balancing current I bal may be decreased to avoid a fault, or may be switched off.

[0054] Exemplary operation 717

[0055] According to some of the exemplary embodiments, the balancing control unit 503 may also be configured to adjust the cell balancing current I bal As described above, passive balancing decreases the charge current or increases the discharge current to increase the rate at which the voltage of the cell is adjusted during balancing. Adjustment of the cell balancing current assists in maintaining a desired average current level to achieve the desired cell balancing.

[0056] Exemplary operation 719

[0057] According to some of the exemplary embodiments, the balancing control unit 503 is configured to control balancing based on the cell-level voltage (V cell ) measured by the measurement unit 501 during balancing of at least one identified cell, and the value of the cell-level voltage is known. In such embodiments, the balancing control unit 503 may also be configured to detect when the measured cell-level voltage falls below the minimum cell-level voltage for maintaining safe cell operation or exceeds the maximum safe voltage. However, the true V cell voltage may be higher than that measured during balancing due to the error voltage across R wire (as described with respect to FIG. 5). Operation 719 can compensate for the error voltage by knowing the balance current I bal , and can more appropriately determine when it crosses the threshold.

[0058] Exemplary operation 721

[0059] According to some of the exemplary embodiments, the balancing control unit 503 is further configured to adjust the voltage limit of cell balancing while recognizing the cell-level voltage measured during balancing of at least one identified cell. All cells have an effective internal series resistance R internal . When the balance current I bal is switched on, it may cause a voltage drop at the cell terminals of I bal × R internal . The cell may be determined to require balancing, for example, in operation 711. However, when the balancing current is switched on, the cell voltage may drop, which may cause the balancing to turn off again.

[0060] Exemplary operation 721 is CMD, and the balance current I balIt is grasped and the necessity of balancing with a first threshold value is determined, but the voltage threshold value is adjusted so as to determine the necessity of continuing to balance with a second voltage threshold limit. This second voltage threshold limit may be adjusted during the process in response to the balance current as the balance current changes.

[0061] Exemplary operation 723

[0062] According to some of the exemplary embodiments, the balancing control unit 503 is configured to calculate the state of charge during cell balancing while acquiring measured values of the cell-level balancing current and the cell-level voltage. In contrast to prior art systems that require interruption of the balancing procedure to determine the state of charge, the exemplary embodiments provide means for determining and monitoring the state of charge throughout the balancing process. Thereby, it becomes possible to control the balancing process (e.g., adjusting the charging rate or the discharging rate) more efficiently and accurately using, for example, the state of charge determined or monitored in real time.

[0063] Exemplary operation 725

[0064] According to some of the exemplary embodiments, the balancing control unit 503 may be further configured to calculate the change in energy of each cell undergoing cell balancing by integrating the balancing power over time. The balancing power may be obtained from the measured cell-level balancing current (I bal ) and the measured cell-level balancing voltage (V cell ). An example of the 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 helps ensure that the balance of the cells is at an appropriate level.

[0065] FIG. 8 shows an example of the operation of monitoring and controlling a cell top balancing process, where balancing occurs when each individual cell approaches full charge (or full capacity) and the balance of the individual cells is maintained. Assume that four cells C1, C2, C3, and C4 are connected in series. The nominal capacity of each cell is 1 Amp-hr (1 Ah). Each cell has measured voltages V1, V2, V3, and V4. In an example of the present invention, the maximum allowable voltage of any cell is 4.2V. The minimum allowable voltage is 3.0V. Using the exemplary embodiments presented herein, the voltage of each cell can be continuously measured.

[0066] The cells are placed in a charger circuit, and a current of 1000 mA is supplied through the cells. After a certain period of time, at t1, V1, V2, and V3 all become 4.00V. This voltage corresponds to 95% SOC. However, V4 remains at 3.95V. This is because C4 is undergoing excessive self-discharge, for example, due to a higher temperature than the other cells or the pack not being balanced. This voltage corresponds to 93% SOC. Thus, cell C4 has a charge that is 20 mAh less, which is 2% of 1 Ah, than the other cells. Each cell has a 40Ω balancing resistor that can be switched on and off by a MOSFET.

[0067] When the cell voltage reaches 4.00V and the balancing resistor (R bal ) is switched on, a current of 100 mA flows. This 100 mA current bypasses the cell and reduces the charging current to the cell from 1000 mA to 900 mA. To maintain the balance of the four cells, the balancing resistors of C1, C2, and C3 are switched on. Cells C1, C2, and C3 are now charging at 900 mA. Cell C4 continues to charge at 1000 mA. All four cells continue to charge towards the maximum allowable voltage of 4.20V.

[0068] C1, C2, and C3 are currently being charged at only 900 mA. 100 mA bypasses around each of the cells C1 - C3. Since they are at 95% SOC, 50 mAh which is 5% of 1 Ah is required to reach full charge. This takes 50 mAh × 60 × 60 / 900 mA = 200 seconds. Since C4 is being charged at 100 mA faster than C1, C2, and C3, it reaches full charge in 50 mAh × 60 × 60 / 1000 mA = 180 seconds. At time t2 before 180 seconds have elapsed, the cell voltages may be the same at 4.15 V. At this point, since the balance of all cells is maintained, balancing stops. Charging continues at 1000 mA until t3 when all cells reach the maximum allowable voltage of 4.2 V. Charging needs to be stopped at this point. If any cell reaches the maximum allowable voltage of 4.2 V before balancing is complete, charging and balancing end.

[0069] Figure 9 shows a working example of the monitoring and control of the cell bottom balancing process. At t1, since it is determined that C1 has a higher cell voltage than the others, balancing is turned on. Here, C1 is discharging at 1100 mA until t2 when the voltages become equal. Discharging continues until t3 where it must stop by reaching the minimum allowable voltage. If any cell reaches the maximum allowable voltage of 3.5 V before balancing is complete, charging and balancing end.

[0070] When balancing is on, the balancing current causes a shift in the cell voltage. For example, in the case of the top balancing example in FIG. 8, when the charging currents at C1, C2, and C3 decrease from 1000 mA to 900 mA, the cell voltage increases slightly. Assume that V1 (or V2, V3) reaches the maximum allowable value, C1, C2, and C3 are still balanced, and the charging ends with C4 still charging at a higher rate. Then, at the end of charging, C4 will increase as a voltage in an amount greater than that of C1, C2, and C3. In reality, the charger circuit goes into constant voltage - constant current charging mode, whereby the charging current gradually decreases and the cell voltage is maintained approximately constant. However, since the charging current interferes with this, when balancing is stopped, C4 changes by a different amount than C1, C2, and C3. This reduces the accuracy of the charge and balance process.

[0071] Another aspect results from the ability of an exemplary embodiment to simultaneously measure cell - level characteristics and balance current, i.e., from the determination of the internal resistance of cell R internal FIG. 10 shows the CMD of FIG. 6. FIG. 6 further includes the internal resistance R internal 901 of the connected battery cells according to some of the exemplary embodiments. When balancing is initiated, due to the internal resistance R internal of the cell, the cell voltage V cell drops slightly. The value of R internal is only 1 mΩ or less, and the balancing current I bal is only 100 mA. According to Ohm's law, the voltage drop is 100 μV, so this voltage change is small. The cell voltage V cell and the balancing current I bal are measured by the measurement unit 501 and V balSince it is measured simultaneously by the measurement unit 507 or measured at a time close enough for the noise to be correlated, it is removed by processing. In the context of this description, the start / invalidation of balancing refers to connecting / disconnecting a load such as the balancing resistor 509 to the battery cell terminals. For example, by controlling the gate voltage of the transistor 505, the transistor 505 can function as a switch, and thus can connect or disconnect the balancing resistor to the battery cell terminals.

[0072] Thus, unlike the prior art systems, the embodiments presented herein enable measuring the internal resistance 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 thereto. This is an option that requires a large excitation current. This option significantly changes the state of charge of the battery pack and only enables 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 (the number of battery cells connected in series / parallel).

[0073] FIG. 11 shows the cell voltage V internal over time during the measurement of the internal resistance R cell of the battery cell shown in FIG. 10 and the exemplary gradual changes in the balancing current I bal . The cell voltage V cell and the balancing current I bal are measured at t0. In this state, since balancing is invalidated, the balancing current I bal is expected to be zero, and since no load is connected to the battery cell, V cell is equal to the open circuit voltage. The balance control 503 starts balancing at t1, and a second measurement of the cell voltage V cell and the balancing current I bal is made at t2. Using these measurement values, R internal 901 can be calculated. An example of the calculation is as follows. ΔVcell-1 =V cell-t2 -V cell-t0 (Difference between the cell-level voltages V measured before and after starting balancing), and similarly ΔI cell ), and similarly ΔI bal-1 =I bal-t2 -I bal-t0 (Difference between the cell-level balancing currents I measured before and after starting balancing). The internal resistance value can be calculated from R bal -|ΔV internal / ΔI cell-1 |. ball-1 It can be calculated from.

[0074] After balancing has been disabled, the accuracy of the internal resistance measurement can be improved by performing a second set of measurements. For example, as shown in FIG. 11, another sample is acquired a little later at t3, balancing is disabled at t4, and another sample is acquired at t5. The actual period is not important, but if it is much less than 1 second, many measurement cycles may be required before the balancing current significantly changes the state of the cell. Similarly, the difference between the cell-level voltages V cell measured before and after disabling balancing is defined as ΔV cell-2 =V cell-t5 -V cell-t3 , and the difference between the cell-level balancing currents I bal measured before and after disabling balancing is defined as ΔI bal-2 =I bal-t5 -I bal-t3 . Also, the internal resistance can be calculated according to R internal =(ΔV cell-1 -ΔV cell-2 ) / (ΔI bal-1 -ΔI bal-2 ). Several such measurement cycles (starting / disabling of balancing) can be performed, for example, to improve the accuracy of the determination of the value of R internal by averaging the measurements. The actual frequency of these measurement cycles can be on the order of several Hertz.

[0075] At such frequencies, by averaging the results obtained over multiple measurement cycles, the total time required to determine the internal resistance value is on the order of several tens of seconds. For example, averaging over 40 cycles at a frequency of 2 Hz takes only 20 seconds. This time can be negligible compared to the time required for the entire balancing process, which can take up to several hours. Thus, in some embodiments, the determination of the internal resistance by repeating the above measurement cycles can be performed at different stages of the balancing process without significantly interfering with the balancing process. This makes it possible to follow the course of changes in the internal resistance value at different stages of balancing. Since the different stages of the balancing process correspond to different values of the cell voltage and / or state of charge, it is further possible to map the internal resistance values of different cells as a function of these parameters. Alternatively, by correlating the above measurements with the values of the temperature sensors included in different CMDS, it is possible to obtain the internal resistance values of different cells at different temperatures.

[0076] Many different physical and chemical mechanisms affect the internal resistance value of a battery cell. Examples of these mechanisms can include the resistivity of the electrodes or internal components, the contact between these components, the surface area of the electrodes, the conductivity of the electrolyte, or the ion mobility. As a result, the internal resistance value can be used to inform or improve estimates of the state of charge, state of health, or state of available power of the battery cell. For example, an algorithm can use the internal resistance value as part of its calculations, and the locally measured value is better than the assumed value. As the cell ages or degrades, the internal resistance typically increases. This is shown in FIG. 12. FIG. 12 shows the characteristic change in the internal resistance of a battery cell as a function of the state of charge and cell life. The change in internal resistance is shown at 1101 as a function of the state of charge of a newly manufactured cell. As shown at 1102 and 1103, as the cell ages, its internal resistance increases. This increase is a useful parameter to track. Since the available power decreases as the resistance increases, the state of available power is strictly determined by the internal resistance. FIG. 13 shows the characteristic change in the internal resistance of a battery cell as a function of temperature. The internal resistance of the battery cell decreases as the temperature increases (1201). Therefore, the state of available power that the cell can supply decreases as the temperature increases. By tracking the internal resistance with temperature, the state of available power can be better estimated.

[0077] In some embodiments, each CMD may periodically transmit the determined value of the internal resistance of each cell to a central control device. Accordingly, the central control device can monitor the changes in the internal resistance of all the battery cells 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 can use the internal resistance information to identify battery cells that may be prone to failure. This can be done, for example, by identifying a battery cell that has an internal resistance much higher than the determined average internal resistance of the battery cells included in the battery pack.

[0078] The description of the exemplary embodiments provided herein is presented for purposes of illustration. This description is not intended to be exhaustive or to limit the exemplary embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives or equivalents to the provided embodiments. The examples described herein are chosen and described in order to explain the principles and the nature of the various exemplary embodiments, so that those skilled in the art may utilize the exemplary embodiments and the various modifications in various ways as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products. It should be understood that the exemplary embodiments presented herein may be implemented in any arbitrary combination with each other.

[0079] Note that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed, and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. Further, any reference signs do not limit the scope of the claims, and the exemplary embodiments may be implemented at least in part by both hardware and software, and note that some "means", "units" or "devices" may be represented by the same or functionally equivalent items of hardware.

[0080] The various illustrative embodiments described herein are described in the general context of method steps or processes, which in one aspect may be implemented by a computer program product implemented on a computer-readable medium or a non-transitory computer-readable medium including computer-executable instructions such as program code executed by a computer or one or more processors in a network environment. The computer-readable medium or non-transitory computer-readable medium may include removable and non-removable storage devices. These storage devices may include, but are not limited to, read only memory (ROM), random access memory (RAM), compact discs (CDs), digital versatile discs (DVDs), flash memory, etc. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The computer-executable instructions, associated data structures, and program modules represent examples of program code for executing the method steps disclosed herein. A particular sequence of such executable instructions or associated data structures represents an example of corresponding acts for implementing the functions described in such steps or processes.

[0081] In the drawings and the specification, illustrative embodiments are disclosed. However, many changes and modifications can be made to these embodiments. Therefore, although specific terms are used, they are used only in a general and descriptive sense and not for purposes of limitation. The scope of the embodiments is defined by the following claims.

Claims

1. A method for balancing cells within a battery pack of a battery system with respect to voltage, charge, and / or charge state, wherein the battery system comprises at least one pack, each pack comprises a plurality of battery cells, and each battery cell is monitored via a cell monitoring device (CMD) that provides cell-level measurements. Using at least one sensor included in each CMD, at least one of the cell-level voltage measurement value or cell-level charge measurement value of each battery cell is obtained, Identifying at least one of the plurality of battery cells to be subjected to cell balancing, based on at least one of the cell-level voltage measurement value, the cell-level charge measurement value, or the determined cell-level charge state, The battery pack is charged or discharged, and the at least one identified cell of the battery pack is passively balanced. A method comprising: measuring a cell-level balancing current during the balancing by measuring a cell-level voltage across a balancing resistor (509) contained within the CMD of the at least one identified cell, and the cell-level voltage of the at least one identified cell; and controlling the balancing of the at least one identified cell based on the measured cell-level balancing current and at least one of the measured cell-level voltage of the at least one identified cell, the measured cell-level charge of the at least one identified cell, or the charge state calculated for the at least one identified cell during the balancing.

2. Identifying at least one of the cells is done via the CMD for each cell, The voltage, charge, or charge state of each cell exceeds the intended voltage or charge target threshold. Voltage, charge, or charge state that does not fall within a predetermined bottom balancing threshold, or The method according to claim 1, further comprising self-identifying each cell based on the difference in voltage, charge, or charge state of each cell relative to at least one other cell in the battery pack.

3. Identifying at least one of the aforementioned cells means Transmitting at least one of the cell-level voltage, charge state, or charge measurement value to a central control unit via a wireless communication bus through a wireless antenna for each CMD, wherein the central control unit is configured to control the operation of the battery system. The method according to claim 1, further comprising receiving a command from the centralized control unit via the wireless antenna for each CMD to perform cell balancing on at least one cell based on at least one of the respective cell level voltage, charge state, or charge measurement value.

4. Controlling the balancing based on the measured cell-level balancing current and at least one of the measured cell-level voltage of the at least one identified cell, the cell-level charge of the at least one identified cell, or the calculated charge state is: Controlling the duration of the balancing of the at least one identified cell, To detect a fault in the cell-level balancing current, or The method according to claim 1, further comprising adjusting the duty cycle of the cell-level balancing current to obtain an average current.

5. Controlling the balancing of the at least one identified cell based on the measured cell-level balancing current and at least one of the measured cell-level voltage of the at least one identified cell, the cell-level charge of the at least one identified cell, or the calculated charge state is: Detecting when the measured cell level voltage falls below the minimum or maximum cell level voltage required to maintain cell operation, or The method according to claim 1, further comprising adjusting the cell balancing voltage limit during the balancing of the at least one identified cell.

6. Controlling the balancing of the at least one identified cell based on the measured cell-level balance current and at least one of the measured cell-level voltage of the at least one identified cell, the cell-level charge of the at least one identified cell, or the calculated charge state, The method according to claim 4, further comprising calculating a balancing power from the measured cell-level balancing current and the measured cell-level balancing voltage, and calculating the change in energy of each cell undergoing cell balancing by integrating the balancing power with respect to time.

7. Controlling the balancing of the at least one identified cell based on the measured cell-level balancing current and at least one of the measured cell-level voltage of the at least one identified cell, the cell-level charge of the at least one identified cell, or the calculated charge state is: The process further includes determining the internal resistance value of the at least one identified cell, wherein the internal resistance value is Disabling the balancing process, The balancing process is to be started after a predetermined time, Measuring the cell-level balancing current and cell-level voltage before and after disabling the balancing process, measuring the cell-level balancing current and cell-level voltage before and after starting the balancing process, or measuring the cell-level balancing current and cell-level voltage before and after disabling the balancing process and before and after starting the balancing process, and The method according to claim 4, wherein the internal resistance value of at least one battery cell is determined by: calculating the measured cell-level balancing current and cell-level voltage before and after disabling the balancing process, or based on at least one of the measured cell-level balancing current and cell-level voltage before and after initiating the balancing process.

8. A method for determining the internal resistance of a battery cell in a battery pack of a battery system, wherein the battery system comprises at least one pack, each pack comprising a plurality of battery cells, each battery cell characterized by its internal resistance and monitored via a cell monitoring device (CMD) that provides cell level measurement. A step of performing one or more measurement cycles on at least one battery cell, wherein the measurement cycle is: Steps to initiate the balancing process, A step of disabling the balancing process after a first predetermined time, A second step involves waiting for a predetermined time, A step comprising: measuring the cell-level balancing current and cell-level voltage before and after starting the balancing process, measuring the cell-level balancing current and cell-level voltage before and after disabling the balancing process, or measuring the cell-level balancing current and cell-level voltage before and after starting the balancing process and before and after disabling the balancing process; A method comprising the step of determining the internal resistance (901) value of the at least one battery cell based on the measured cell-level balancing current and cell-level voltage before and after initiating the balancing process, or the measured cell-level balancing current and cell-level voltage before and after disabling the balancing process, during one or more measurement cycles.

9. The step of determining the internal resistance value of at least one cell is: The method according to claim 8, further comprising the step of averaging the determined internal resistance of the at least one cell based on at least one of the measured cell-level balancing current and cell-level voltage before and after initiating the balancing process, or the measured cell-level balancing current and cell-level voltage before and after deactivating the balancing process, for each measurement cycle.

10. The steps of performing one or more measurement cycles and determining the internal resistance value of at least one cell are performed at different time intervals or for different values ​​of the voltage, charge state, or temperature of the at least one cell, and the method is The method according to claim 8, further comprising the step of mapping the internal resistance value as a function of time, cell voltage, charge state, or temperature.

11. The method according to claim 10, further comprising the step of estimating the temperature, charge state, health state, or active power state of the at least one cell using at least one map of internal resistance values.

12. A battery pack comprising a plurality of cell monitoring devices (CMDs) for balancing cells within the battery pack with respect to voltage, charge and / or charge state, wherein the battery pack comprises a plurality of battery cells, each battery cell is monitored via each cell monitoring device (CMD) that provides cell level measurement, and each CMD, A first measurement unit including at least one sensor configured to acquire at least one cell-level voltage measurement and / or cell-level charge measurement of each cell, A balance control unit configured to identify each cell for cell balancing based on the cell-level voltage measurement, the cell-level charge measurement, and / or at least one of the determined charge state of each cell, and to passively balance each cell during discharge or charging of the battery pack, The system includes a second measuring unit configured to measure the cell-level balancing current of each cell during cell balancing by measuring the cell-level voltage across the balancing resistor (509) contained within the CMD, A battery pack further configured to control the cell balancing of each cell based on the measured cell-level balancing current and at least one of the measured cell-level voltage of each cell, the measured cell-level charge of each cell, or the calculated charge state of each cell.

13. The battery pack according to claim 12, wherein each CMD is further configured to perform the method according to any one of claims 1 to 11.

14. The battery pack according to claim 12, wherein the balance control unit of each CMD is further configured to calculate a cell voltage error based on the cell level balancing current over the resistance of a common connection for the power supply of each CMD and the measurement unit of each CMD, from each cell to each CMD.

15. The battery pack according to claim 12, wherein each of the at least one CMDs has a separate connection for a power supply and a measurement unit via a Kelvin connection between each of the at least one CMDs and each of the cells.

16. The battery pack according to claim 12, wherein each CMD further comprises an FET switch connected to the balance control unit.

17. A computer-readable medium that stores instructions, when executed by the processor of each cell monitoring device (CMD) of a battery pack, causing each CMD to perform the method according to any one of claims 1 to 11.

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