Method and system for battery cell charge balancing

Abstract

Embodiments include methods and systems for charge balancing in a battery system having a string of battery packs, each battery pack including a plurality of battery cells. Aspects include obtaining an electrical parameter for each of a plurality of battery cells, and calculating a battery pack equilibrium point for each of the battery packs in the string. Aspects also include instructing the cell balancing system to execute a cell charge balancing routine to balance each of the plurality of cells in each battery pack to a battery pack balance point corresponding to the battery pack, calculating a string balance point for the string of battery packs based on the battery pack balance points, and instructing the cell balancing system of each battery pack to balance the plurality of cells in the battery pack to the string balance point.

Description

Technical Field

[0001] The present disclosure relates to the charge balancing of battery cells in an electric vehicle. More specifically, the present disclosure relates to performing charge balancing across multiple batteries, each battery including a plurality of battery cells. Background Art

[0002] A battery is an electrochemical device that can include a plurality of battery cells electrically interconnected to provide electrical power to a device (such as an electric motor). In use, the battery cells can exhibit different electrical characteristics that can be quantified in terms of charge capacity, state of charge, discharge rate, impedance, and / or voltage. Additionally, one or more battery cells of a battery can be replaced and / or added during use, resulting in different capacities, states of charge, discharge rates, impedances, and / or voltages between the new battery cells and the existing battery cells. An imbalance in the electrical characteristics between battery cells can affect the performance characteristics and service life of a multi-battery cell battery. Appropriately balancing the battery cells can prevent overcharging and / or undercharging of the individual battery cells and can maximize the available battery energy.

[0003] A vehicle can include one or more batteries for operating the electrical and / or powertrain systems of the vehicle. For example, a vehicle can include a 12V lead-acid automotive battery configured to supply electrical energy to a vehicle starter system (such as a starter motor), a lighting system, and / or an ignition system. Additionally, electric vehicles and hybrid vehicles can include a high-voltage battery to provide electrical power to electric powertrain components (such as an electric drive motor).

[0004] It may be necessary to have a long period of battery rest time (i.e., an operating period at low or no current) to determine the amount of charge to be removed from a battery cell having a high level of state of charge to achieve a balanced state in the battery. A vehicle operating in autonomous mode can operate continuously, making it less likely for a long rest time to occur. It may be necessary to evaluate the battery cell charge balancing calculations in progress to ensure that the most accurate information is used in the balancing of the battery cells in the battery. Summary of the Invention

[0005] In an exemplary embodiment, a method for charge balancing in a battery system is provided. The battery system has a string of battery packs, and each battery pack includes a plurality of battery cells. The method includes obtaining electrical parameters of each of the plurality of battery cells, calculating a battery pack balance point for each of the battery packs in the string, and instructing a cell balancing system to perform a cell charge balancing routine to balance each of the plurality of battery cells in each battery pack to the battery pack balance point corresponding to the battery pack. The method further includes calculating a string balance point for the string of battery packs based on the battery pack balance points, and instructing the cell balancing system of each battery pack to balance the plurality of battery cells in the battery pack to the string balance point.

[0006] In addition to one or more of the features described herein, the battery packs of the string are connected in series with each other.

[0007] In addition to one or more of the features described herein, each battery pack includes a battery pack controller, and the battery pack controller is configured to calculate the battery pack balance point of the battery pack.

[0008] In addition to one or more of the features described herein, the battery pack controller of each battery pack is configured to transmit the battery pack balance point of the battery pack to the battery pack controllers of the other battery packs in the string.

[0009] In addition to one or more of the features described herein, the battery pack controller of each battery pack is configured to transmit the battery pack balance point of the battery pack to a string controller associated with the string.

[0010] In addition to one or more of the features described herein, the string controller is configured to calculate a string balance point for the string of battery packs based on the battery pack balance points, and transmit the string balance point to the battery pack controllers.

[0011] In addition to one or more of the features described herein, the battery pack controller of each battery pack is configured to transmit the battery pack balance point of the battery pack to a central battery system controller, and the central battery system controller is configured to calculate a string balance point for the string of battery packs based on the battery pack balance points.

[0012] In an exemplary embodiment, a battery system is provided. The battery system includes a plurality of strings, and each of the plurality of strings includes a plurality of battery packs connected in series with each other. Each of the plurality of battery packs includes a plurality of battery cells, a sensor configured to monitor electrical parameters of each of the plurality of battery cells, a cell balancing system configured to selectively charge or discharge the plurality of battery cells of the battery pack, and a battery pack controller configured to monitor electrical parameters of each of the plurality of battery cells and correspondingly control the operation of the cell balancing system. The battery pack controller is further configured to calculate a battery pack balance point based on the electrical parameters of each of the plurality of battery cells.

[0013] In addition to one or more features described herein, the battery system further includes a central battery system controller configured to communicate with a battery pack controller of each battery pack of a plurality of strings.

[0014] In addition to one or more features described herein, the central battery system controller is configured to calculate a string balance point for each of the plurality of string battery packs based on a battery pack balance point and transmit the corresponding string balance point to the battery pack controller of each battery pack.

[0015] In addition to one or more features described herein, the battery pack controller of each battery pack is configured to control a battery cell balancing system of each battery pack to balance a plurality of battery cells in the battery pack to the string balance point.

[0016] In addition to one or more features described herein, the battery system further includes a string controller associated with one of the plurality of strings, wherein the string controller is configured to communicate with a battery pack controller of each battery pack of one of the plurality of strings.

[0017] In addition to one or more features described herein, the string controller is further configured to calculate a string balance point of one of the plurality of strings and transmit the string balance point to the battery pack controller of each battery pack of one of the plurality of strings.

[0018] In addition to one or more features described herein, the battery pack controller of each battery pack is configured to control a battery cell balancing system of each battery pack to balance a plurality of battery cells in the battery pack to the string balance point.

[0019] In addition to one or more features described herein, the battery pack controller of each battery pack of one of the plurality of strings is configured to transmit a battery pack balance point to the battery pack controller of other battery packs in one of the plurality of strings.

[0020] In one exemplary embodiment, an electric vehicle is provided. The electric vehicle includes a battery system having a plurality of strings, each of the plurality of strings including a plurality of battery packs connected in series with each other. Each of the plurality of battery packs includes a plurality of battery cells, a sensor configured to monitor electrical parameters of each of the plurality of battery cells, a battery cell balancing system configured to selectively charge or discharge the plurality of battery cells of the battery pack, and a battery pack controller configured to monitor electrical parameters of each of the plurality of battery cells and responsively control the operation of the battery cell balancing system. The battery pack controller is further configured to calculate a battery pack balance point based on the electrical parameters of each of the plurality of battery cells.

[0021] In addition to one or more features described herein, the battery system includes a central battery system controller configured to communicate with a battery pack controller of each battery pack of a plurality of strings.

[0022] In addition to one or more features described herein, the central battery system controller is configured to calculate a string balance point for each of the plurality of string battery packs based on a battery pack balance point and transmit the corresponding string balance point to the battery pack controller of each battery pack.

[0023] In addition to one or more features described herein, the battery pack controller of each battery pack is configured to control a battery cell balancing system of each battery pack to balance a plurality of battery cells in the battery pack to the string balance point.

[0024] In addition to one or more features described herein, the battery system further includes a string controller associated with one of the plurality of strings, wherein the string controller is configured to communicate with a battery pack controller of each battery pack of one of the plurality of strings.

[0025] The above features and advantages of the present disclosure, as well as other features and advantages, are apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features, advantages, and details appear only by way of example in the following detailed description, which refers to the accompanying drawings, in which:

[0027] Figure 1A is a schematic diagram of an electric vehicle according to an exemplary embodiment;

[0028] Figure 1B is a schematic diagram of a battery system of an electric vehicle according to an exemplary embodiment;

[0029] Figure 1C is a schematic diagram of a battery system of an electric vehicle according to an exemplary embodiment;

[0030] Figure 1D is a schematic diagram of a battery system of an electric vehicle according to an exemplary embodiment;

[0031] Figure 2 graphically shows data associated with respective battery cell voltages according to an exemplary embodiment;

[0032] Figure 3 schematically shows, in flowchart form, a process for performing a charge balancing routine based on a first quality metric and a second quality metric according to an exemplary embodiment;

[0033] Figures 4-1 to 4-6Graphically illustrates a quality index related to corresponding parameters according to an exemplary embodiment; and

[0034] Figure 5 Schematically shows, in a flowchart form, a method for performing charge balancing across multiple battery packs, each battery pack including a plurality of battery cells, according to an exemplary embodiment. Detailed Description

[0035] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. The various embodiments of the present disclosure are described herein with reference to the related drawings. Alternative embodiments of the present disclosure may be designed without departing from the scope of the claims. The various connections and positional relationships (e.g., above, below, adjacent, etc.) between the elements are set forth in the following description and the drawings.

[0036] Unless otherwise specified, these connections and / or positional relationships may be direct or indirect, and the present disclosure is not intended to be limited in this regard. Thus, the coupling of entities may refer to direct or indirect coupling, and the positional relationship between entities may be direct or indirect positional relationship.

[0037] Now referring to Figures 1A to 1D , a vehicle 10 including a powertrain 20 and a battery system 100 is shown according to an exemplary embodiment. The overall operation of the vehicle 10 is controlled by a vehicle controller 15. In one embodiment, the vehicle 10 further includes an autonomous vehicle control system 40. In another embodiment, the vehicle 10 may be configured as a non-autonomous vehicle manually controlled by an operator. In one embodiment, the vehicle 10 includes a four-wheel passenger vehicle having steerable front wheels and fixed rear wheels. As a non-limiting example, the vehicle 10 may include a passenger vehicle, a light or heavy truck, a multi-purpose vehicle, an agricultural vehicle, an industrial / warehouse vehicle, a recreational off-road vehicle, an aircraft, or a marine vehicle.

[0038] The powertrain 20 of the vehicle 10 may be configured as an electric vehicle (EV), a hybrid vehicle (HV) including an internal combustion engine (“ICE”), or another configuration incorporating the systems and methods disclosed herein. The battery system 100 may be used to supply power to the electrical components of the powertrain 20.

[0039] The autonomous vehicle control system 40 includes an on-vehicle control system capable of providing a certain level of driving automation. The terms "driver" and "operator" describe a person responsible for guiding the operation of the vehicle 10, whether actively participating in controlling one or more vehicle functions or guiding the autonomous vehicle operation. Driving automation can include a series of dynamic driving and vehicle operations. Driving automation can include a certain degree of automatic control or intervention related to individual vehicle functions (such as steering, acceleration, and / or braking), where the driver continuously exercises overall control of the vehicle. Driving automation can include a certain degree of automatic control or intervention related to simultaneously controlling multiple vehicle functions (such as steering, acceleration, and / or braking), where the driver continuously exercises overall control of the vehicle. Driving automation can include simultaneous automatic control of all vehicle driving functions (including steering, acceleration, and braking), where the driver relinquishes control of the vehicle for a period of time during the journey. Driving automation can include simultaneous automatic control of vehicle driving functions (including steering, acceleration, and braking), where the driver relinquishes control of the vehicle throughout the journey. Driving automation includes hardware and controllers configured to monitor the spatial environment in various driving modes to perform various driving tasks during dynamic operation. As a non-limiting example, driving automation can include cruise control, adaptive cruise control, lane change warning, intervention and control, automatic parking, acceleration, braking, etc.

[0040] The vehicle 10 includes a charging system 50 for charging the battery cells 115 of the battery system 100. In one embodiment, the charging system 50 includes a charger 52 that can be electrically connected to an off-vehicle power source (not shown) available at a public or private charging station. The power source can be arranged to supply power to charge the battery system 100 via the charging system 50. The supplied power can be in the form of alternating current (AC) power or direct current (DC) power.

[0041] In an exemplary embodiment, the battery system 100 includes one or more strings 102-1, 102-2 (collectively referred to herein as strings 102) of battery modules 101-1, 101-2, 102-N (collectively referred to herein as battery modules 101). In an exemplary embodiment, the strings 102 of the battery system 100 are connected in parallel with each other, and the battery modules 101 of each string 102 are connected in series with each other. Although only two strings 102-1, 102-2 are shown, those of ordinary skill in the art will understand that the number of strings 102 can be more or less than the illustrated embodiment.

[0042] In an exemplary embodiment, as Figure 1B 、 Figure 1C and Figure 1DAs shown, each battery module 101 includes a battery pack 110, a battery pack controller 104, a plurality of sensors 106, and a battery cell balancing system 120. The battery pack 110 may be arranged as a multi-cell high-voltage battery system that includes a plurality of battery cells 115 electrically connected in series or parallel to provide power to an actuator (such as a motor). The battery cells 115 may be arranged in one or more battery sections 114, and the battery sections 114 are sized to provide power to a system of the vehicle 10 (e.g., the powertrain 20) at a desired voltage and a desired current. Each of the battery cells 115 may employ rechargeable electrochemical battery technologies, including, for example, lead-acid, nickel metal hydride (“NiMH”), lithium ion (“Li-ion”), Li-ion polymer, lithium air, nickel cadmium (“NiCad”), valve-regulated lead-acid (“VRLA”) including absorbent glass mat (“AGM”), nickel zinc (“NiZn”), molten salt (e.g., Zebra battery), and / or other battery technologies.

[0043] The sensors 106 are configured to measure electrical parameters associated with the battery cells 115. In one embodiment, each of the sensors 106 is a voltmeter or an ammeter. Each of the individual sensors among the sensors 106 may be associated with each of the battery cells or with each of the battery sections 114. State-of-charge information may be determined based on the measured electrical parameters from the sensors 106. The determined state of charge may be provided to the battery pack controller 104. Using the state-of-charge information, the battery pack controller 104 may operate to coordinate battery balancing operations.

[0044] Each of the battery cells 115 or the battery sections 114 may communicate with the battery cell balancing system 120. The battery cell balancing system 120 may include a network of switches and / or gates configured to facilitate selective electrical energy transfer to, from, and / or between the battery cells 115. The battery cell balancing system 120 is configured to balance the battery cells 115 of the battery pack 110 by charging and / or discharging each of the individual battery cells 115 in the battery cells 115 such that each of the battery cells 115 has the same or a similar amount of energy stored therein, as indicated by state-of-charge measurements or voltage measurements.

[0045] The battery system 100 includes a battery pack controller 104 that is configured to monitor and control certain operations of the battery pack 110. For example, the battery pack controller 104 can be configured to monitor information from a plurality of sensors 106 and control the operations of the charging system 50 and the battery cell balancing system 120 to control the charging, discharging, and / or balancing operations of the battery pack 110. The battery pack controller 104 can also be configured to provide information to and / or receive information from other systems included in the vehicle 10. For example, the battery pack controller 104 can be communicatively coupled to the vehicle controller 15 and / or a remotely located external computer system 60 via a telematics system (not shown). In some embodiments, the battery pack controller 104 can be at least partially configured to provide information about the battery pack 110 to a user of the vehicle 10, the vehicle controller 15, and / or the external computer system 60. Such information can include, for example, battery cell state of charge information, battery operation time information, battery operation temperature information, and / or other information about the battery pack 110.

[0046] In some embodiments, the battery cell balancing operation can be performed when the vehicle 10 is started. In other embodiments, the battery cell balancing operation can be performed when the vehicle 10 and / or the battery system 100 is not in use. In further embodiments, the battery cell balancing operation can be performed when a new battery cell 115 is installed and / or an old battery cell 115 is replaced. The battery cells 115 of the battery pack 110 are said to be balanced or in a balanced state when the estimated state of charge and / or the calculated quanta energy is within an acceptable error range.

[0047] Battery cell balancing can begin by determining the state of charge of each of the battery cells 115 within the battery pack 110. The voltage of each of the battery cells 115 can be used as an indicator of the state of charge. The quanta energy to reach the desired state of charge balance point of the battery system can be calculated for each of a plurality of sections. In some embodiments, the quanta energy can be expressed in ampere-hours (“AHr”) required to reach the desired state of charge balance point. Based on the estimated state of charge and / or the calculated quanta energy, it can be determined whether the battery cells 115 are balanced or unbalanced. For example, if the estimated state of charge and / or the calculated quanta energy are equivalent within an acceptable error range, it can be determined that the battery cells 115 are balanced. If the battery cells 115 within the battery pack 110 are balanced, the battery cell balancing operation may not be required. However, if the battery cells 115 within the battery pack 110 are unbalanced, or if the battery cells 115 of different battery packs within the string 102 are unbalanced, then the balancing operation can be performed.

[0048] For example, one or more battery cells 115 may be identified as having a calculated quantitative energy (e.g., calculated based on ΔHR) required to reach the desired state of charge balance point that is different from (e.g., greater than or less than) other battery cells 115. For example, in a battery pack 110 having three battery cells 115, the first and second battery cells may be associated with the same quantitative energy required to reach the desired balance point (e.g., 20 AHr). The third battery cell may be associated with a smaller quantitative energy required to reach the desired balance point (e.g., 15 AHr). In one embodiment, the third battery cell may be discharged (e.g., discharged by 5 AHr) such that all three battery cells 115 require the same quantitative energy (e.g., 20 AHr) to reach the desired state of charge balance point. In this way, when the battery system 100 is charged to the desired state of charge balance point (e.g., the charge termination level), all battery cells 115 of the battery system 100 will be at or near the balance point and the battery system 100 will be balanced.

[0049] In an exemplary embodiment, each battery pack 110 is configured to execute a balancing algorithm to identify the battery pack balance point and balance the battery cells 115 within the battery pack 110. Further, once each battery pack 110 has determined the battery pack balance point of the battery pack 110, the battery pack controller 104 of the battery pack 110 communicates with one of the central battery system controller 130 (as shown in Figure 1B ), the string controller 125 (as shown in Figure 1C ), or the battery pack controller 104 of other battery packs 110 of the string 102 (as shown in Figure 1D ), and provides the battery pack balance point to one of the central battery system controller 130 (as shown in Figure 1B ), the string controller 125 (as shown in Figure 1C ), or the battery pack controller 104 of other battery packs 110 of the string 102 (as shown in Figure 1D ). As a result, the string balance point of all battery packs 110 in the string 102 can be determined. Once the string balance point is determined and communicated to the battery pack controller 104, the battery pack controller 104 instructs the battery cell balancing system 120 to achieve battery cell charge balance in the battery pack 110 to bring all battery cells 115 to the string balance point.

[0050] In one embodiment, as shown in Figure 1BAs shown, the battery pack controller 104 of each battery pack 110 is configured to communicate with the central battery system controller 130. In an exemplary embodiment, the central battery system controller 130 is configured to receive the battery pack balance points from the battery pack controllers 104 of each battery pack 110 in the battery system 100. The central battery system controller 130 is further configured to calculate the string balance points of each string 102 based on the battery pack balance points of each battery pack 110 in the string 102. Once the string balance points are calculated, the central battery system controller 130 provides the string balance points to each of the battery pack controllers 104. In an exemplary embodiment, the battery pack controller 104 responsively instructs the battery cell balancing system 120 to achieve battery cell charge balance in the battery pack 110 to bring all battery cells 115 to the string balance point.

[0051] In another embodiment, as Figure 1C shown, the battery pack controller 104 of each battery pack 110 of the string 102 is configured to communicate with the string controller 125 associated with the string 102. For example, the string controller 125-1 is configured to communicate with the battery pack controllers of the battery packs 110 in the string 102-1. Similarly, the string controller 125-2 is configured to communicate with the battery pack controllers of the battery packs 110 in the string 102-2. In an exemplary embodiment, each string controller 125 is configured to receive the battery pack balance points from the battery pack controllers 104 of each battery pack 110 in the corresponding string 102. The string controller 125 is configured to calculate the string balance points of the string 102 based on the battery pack balance points of each battery pack 110 in the string 102. Once the string balance points are calculated, the string controller 125 provides the string balance points to each of the battery pack controllers 104. In an exemplary embodiment, the battery pack controller 104 responsively instructs the battery cell balancing system 120 to achieve battery cell charge balance in the battery pack 110 to bring all battery cells 115 to the string balance point.

[0052] In another embodiment, as Figure 1D shown, the battery pack controller 104 of each battery pack 110 of the string 102 is configured to communicate directly with the other battery pack controllers 104 of the battery modules 101 within the string 102. In an exemplary embodiment, each battery pack controller 104 is configured to calculate the battery pack balance points and transmit the battery pack balance points to the other battery pack controllers 104 in the same string. In an exemplary embodiment, when the battery pack controller 104 receives an indication that another battery pack 110 has a lower battery pack balance point, the battery pack controller 104 responsively instructs the battery cell balancing system 120 to achieve battery cell charge balance in the battery pack 110 to bring all battery cells 115 to the newly received balance point.

[0053] Figure 2is a conceptual diagram illustrating a method for balancing a battery pack according to an embodiment disclosed herein and graphically shows voltage data associated with respective battery cells 115 of an embodiment of battery pack 110. A target open circuit voltage (OCV) 212, an actual OCV 210, and a voltage drop 214 are indicated for each battery cell. Voltage data 201 is an example of a battery assessment that can be employed by a battery cell charge balancing routine 320, as referenced Figure 3 as described. Figure 2 The curve graph of shows a state-of-charge window representing the state-of-charge 200 of a plurality of battery cells 202 (e.g., battery cells A, B, and C) under three different state-of-charge conditions. For example, battery cell A may have a first state-of-charge 206, battery cell B may have a second state-of-charge 208, and battery cell C may have a third state-of-charge 212.

[0054] A quantitative energy to reach a desired state-of-charge equilibrium point 204 of the battery system can be calculated for each of the battery cells 202. In certain embodiments, the quantitative energy may be expressed in ampere-hours (“AHr”) required to reach the desired state-of-charge equilibrium point 204, and in certain embodiments, the desired state-of-charge equilibrium point 204 may be a charge termination level of the battery system. By way of example, as shown, battery cell A may be associated with a quantitative energy (ΔA) of 20 AHr, battery cell B may be associated with a quantitative energy (ΔB) of 20 AHr, and battery cell C may be associated with a quantitative energy (ΔC) of 15 AHr. In certain embodiments, two or more of the battery cells may require the same quantitative energy to reach the state-of-charge equilibrium point 204 but have different associated states-of-charge due to different battery cell capacities (e.g., battery cell A and battery cell B). In additional embodiments, battery cells having the same state-of-charge may be associated with the same quantitative energy to reach the state-of-charge equilibrium point 204.

[0055] Based on the state-of-charge 206 - 210 and / or the calculated quantitative energy (e.g., ΔA, ΔB, and ΔC), it can be determined whether the battery cells 202 are balanced or unbalanced. For example, if the estimated state-of-charge 206 to 210 and / or the calculated quantitative energy are equivalent within a predefined range, it can be determined that the battery cells 202 are balanced. If the battery cells 202 are balanced, a balancing operation may not be required. However, if the battery cells 202 are unbalanced, as Figure 2As shown, a balancing operation can be performed. One or more battery cells can be identified as having a calculated quantized energy that is different (e.g., greater than or less than other battery cells) from that required to reach the desired state-of-charge equilibrium point 204. For example, as shown, battery cell C can have an associated quantized energy (e.g., ΔC = 15 Ahr), which is different from the quantized energies associated with battery cells A and B (e.g., ΔA and ΔB), which are approximately 20 Ahr. Then, battery cells A, B, and / or C can be charged and / or discharged such that the quantized energies associated with the battery cells are the same or similar (e.g., ΔA and ΔB) approximately equal to ΔC (e.g., 20 Ahr). For example, as shown, battery cell C can be discharged by a quantized energy (ΔC) of 5 AHr to a state-of-charge level 212 such that the quantized energies associated with the battery cells are the same or similar (e.g., ΔA is approximately equal to ΔB is approximately equal to C), which is approximately equal to 20 AHr. In this way, when charging the battery pack to the desired state-of-charge equilibrium point 204, all the battery cells 202 of the battery pack will be at or near the equilibrium point 204, and the battery pack will be balanced.

[0056] Now referring to Figure 3 , and continuing to refer to Figures 1A-1D the battery system 100 described, a battery cell charge balancing control routine 300 is schematically shown. The battery cell charge balancing control routine 300 can be executed by the battery pack controller 104 to monitor the battery pack 110 via a plurality of sensors 106 and control the operation of the battery cell balancing system 120 to achieve battery cell charge balancing in the battery pack 110. The battery cell charge balancing control routine 300 is shown as a collection of blocks in a logic flow diagram, which represents a series of operations that can be implemented in hardware, software, firmware, or a combination thereof that has been configured to perform a specific function. In the context of software, the blocks represent computer instructions that perform the operations when executed by one or more processors. During operation of the vehicle 10, the battery pack controller 104 monitors the sensors 106 associated with each of the battery cells 115 of the battery pack 110 and periodically communicates with the charging system 50 to perform a battery assessment that can be utilized by the battery cell charge balancing routine 320.

[0057] In one embodiment, the battery pack controller 104 can be triggered to perform a battery assessment that can be utilized by the battery cell charge balancing routine 320 when the battery pack 110 has achieved a rested state at block 302. The rested state of the battery pack 110 can be defined as the battery pack 110 being in a zero current state for an extended period of time (e.g., greater than 4 hours). When the battery pack 110 has reached the rested state, a plurality of sensors 106 can be utilized to determine the electrical parameters of each of the battery cells 115.

[0058] In another embodiment, the battery pack controller 104 can be triggered to perform a battery evaluation, and when the battery is operating in a low current state at block 304, the battery cell charge equalization routine 320 can utilize this battery evaluation. The low current state of the battery pack 110 can be defined as the battery pack 110 being at a current level less than 10 amperes for an extended period of time (e.g., greater than 0.5 hours). When the battery pack 110 has achieved the low current state, multiple sensors 106 can be employed to determine the electrical parameters of each of the battery cells 115.

[0059] In another embodiment, at block 306, the battery pack controller 104 can be triggered to perform a battery evaluation, and when the battery pack 110 is in a charge complete state, the battery cell charge equalization routine 320 can utilize this battery evaluation. The charge complete state of the battery pack 110 can be defined as occurring immediately after the interruption or end of a charging event of the battery pack 110, and can include the battery pack 110 being fully charged, or the battery pack 110 being partially charged. When the battery pack 110 has reached the charge complete state, multiple sensors 106 can be employed to determine the electrical parameters of each of the battery cells 115.

[0060] When one of the above conditions at blocks 302, 304, or 306 triggers a battery evaluation for potential use of the battery cell charge equalization routine 320 by the battery pack controller 104, multiple sensors 106 are employed to capture and determine the electrical parameters of each of the battery cells 115. In one embodiment, and as described with reference to Figure 2 the electrical parameters of each of the battery cells 115 can be in the form of the voltage of each of the battery cells 115. Additionally, the temperature of the battery pack 110 can be determined.

[0061] The battery cell charge equalization control routine 300 determines a quality index Q based on the electrical parameters of each of the battery cells 115 and the temperature of the battery pack 110, the electrical parameters and temperature being captured when one of the above conditions triggers the battery pack controller 104 for potential use of a battery evaluation to be performed by the battery cell charge equalization routine 320 at block 308. The new quality index Q can be determined according to the following equation new . Q new = Q cellV * Max(Q oct , Q low curr t , Q cc ), where Q new represents the quality index associated with the new event, Q cellV represents the battery cell voltage quality index, Q octRepresents the open - circuit time quality index, Q low curr t Represents the low - current quality index, and Q cc Represents the charge - complete event quality index.

[0062] In one embodiment, the cell voltage quality index Q cellV is determined relative to the cell voltage and the cell temperature and is an indication of several factors including, but not limited to, the flatness of the OCV / SOC relationship, regions of high voltage hysteresis, and differences from the equilibrium point target, which may cause errors in capacity measurement errors in the balance calculation. Some of the effects on the listed qualities can be predetermined and defined as fixed calibrations, while other effects can be determined empirically in real - time in the battery pack controller 104. Figure 4-1 Graphically shows the cell voltage quality index Q cellV 410 versus the voltage level 412 (including the low voltage V low and the target voltage V tgt ) at a known cell temperature.

[0063] In one embodiment, the open - circuit time quality index Q oct is determined relative to the open - circuit time and the cell temperature and is an indication of the elapsed time period that the battery pack 110 has been maintained in an open - circuit state before capturing the electrical parameters of each of the cells 115 in the battery pack 110 and the temperature of the battery pack 110 (i.e., has been resting). The open - circuit time quality index Q oct increases as the elapsed time period increases because the accuracy of the electrical parameters of each of the cells 115 increases with time. Figure 4-2 Graphically shows the open - circuit time quality index Q oct 420 versus the time under open - circuit conditions 422 at a known cell temperature.

[0064] In one embodiment, the low - current quality index Q low curr t is determined in relation to the low - current time and the cell temperature and is an indication of the elapsed time period that the battery pack 110 has been maintained in a low - current state before capturing the electrical parameters of each of the cells 115 in the battery pack 110 and the temperature of the battery pack 110. The low - current quality index Q low curr t increases as the elapsed time period increases because the accuracy of the electrical parameters of each cell in the cells 115 increases with time. Figure 4-3 Graphically shows the low - current quality index Q low currt The relationship between 430 and time.

[0065] In one embodiment, the charge completion event quality index Q cc is determined relative to the occurrence of the charge completion event and is an indication of the long period of unidirectional current entering the battery pack 110. The charge completion event quality index Q cc increases as the charging current or power provided via the charger 52 decreases, because the accuracy of the electrical parameters of each of the battery cells 115 decreases accordingly. Figure 4-4 Graphically shows the relationship between the charge completion event index Q cc 440 and the charging power 442 provided via the charger 52 at a known battery temperature.

[0066] The existing quality index Q old represents the quality index determined at a previous time point when one of the foregoing conditions triggers the charging system 50 to perform a battery assessment for use in the battery cell charge balancing routine at block 310. The existing quality index Q old is initially set to zero and is reset to zero when the battery cell balancing operation is complete. By subjecting the previously determined quality index Q new (t - 1) to an attenuation factor Q decay to determine the existing quality index Q old . The attenuation factor Q decay has a value range between 1 and 0 and decreases with respect to the time elapsed since the previously determined quality index Q new was determined. Figure 4-5 Graphically shows the relationship between the attenuation factor Q decay 450 and the time 452. The attenuation factor Q decay is an indication of the occurrence of self - discharge and other factors in individual battery cells. The existing quality index Q is determined according to the following equation old : Q old = Q new (t - 1) * Q decay , where Q new (t - 1) represents the previously determined quality index.

[0067] Referring again to Figure 3, each determined electrical parameter in the battery cell 115 can be evaluated to determine a battery cell spread based on data captured during the battery evaluation at block 309. The battery cell spread is a measure of the variation in state of charge between multiple battery cells 115. In one embodiment, the battery cell spread is associated with the state of charge of the multiple battery cells 115 and can be determined as the difference between the maximum state of charge associated with the state of charge of the multiple battery cells 115 and the minimum state of charge associated with the state of charge of the multiple battery cells 115.

[0068] Figure 4-6 Graphically illustrates the relationship between the battery cell spread threshold 460 and the new quality index Q new 462. The battery cell spread threshold 460 increases as the new quality index Q new 462 decreases, where the relationship between the new quality index Q new 462 and the battery cell spread threshold 460 is a quadratic relationship. In operation, the new quality index Q new 462 can be determined dynamically according to Equation 1 above, and the battery cell spread is also determined based on the same data. The new quality index Q new 462 is used to determine the battery cell spread threshold 460 based on the relationship described in Figure 4-6 . Thus, the battery cell spread threshold 460 is determined dynamically.

[0069] Referring again to Figure 3 , at decision block 312, the new quality index Q new is compared with the previously determined quality index Q old , and the battery cell spread is compared with the dynamically determined battery cell spread threshold 460. When the new quality index Q new is less than or equal to the previously determined quality index Q old , or when the battery cell spread is less than the battery cell spread threshold (0), it indicates that the most recently performed battery evaluation lacks sufficient quality index to warrant re-evaluating the state of charge of the battery cells 115 of the battery system 100. When the new quality index Q new is greater than the previously determined quality index Q old and when the battery cell spread is greater than the battery cell spread threshold (1), an action is taken to re-evaluate the state of charge of the battery cells 115 of the battery system 100 based on the most recently performed battery evaluation. This includes determining, at block 314, the amount of electrical energy (in ampere-hours) that needs to be depleted from or added to each of the battery cells 115 of the battery system 100 such that the battery section 114 is balanced with respect to the state of charge.

[0070] In other words, the battery cell spread threshold 460 is based on the referenceFigure 4-6 determined by the relationship shown. When the cell expansion is greater than the cell expansion threshold and the new quality index Q new is greater than the old quality index Q old , or when there is no ongoing update (i.e., no old quality index Q old ), the data used to determine the new quality index Q new is used to achieve cell balancing. When the cell expansion is less than the cell expansion threshold and / or the new quality index Q new is less than the old quality index Q old , the data used to determine the new quality index Q new is discarded, and the data associated with the old quality index Q old is used to achieve cell balancing, or the cell charge balancing is delayed until new data is obtained. At block 320, the cell charge balancing routine is performed using the state of charge of the cell 115 of the battery system 100 determined when the previously determined quality index Q old was determined at block 316.

[0071] In an exemplary embodiment, a dynamic balance threshold is determined based on the quality of the SOC expansion, as indicated by the cell expansion threshold 460 determined according to the relationship shown in the reference Figure 4-6 . The concept is to prevent an operation that causes cell balancing that may result in an increase in cell expansion, which otherwise may occur when the new SOC expansion is lower than the existing or old SOC expansion. For example, when there is a poor quality update under conditions including a small SOC expansion, the cell balancing will not change in a way that may increase the cell SOC imbalance. However, when the battery SOC expansion is relatively high, a lower quality update may be allowed because the error will be less than the magnitude of the SOC expansion calculated during the calculation of Q new .

[0072] The execution of the cell charge balancing routine 320 includes controlling the cell balancing system 120 to balance the cells 115 of the battery pack 110 by charging and / or discharging each of the cells 115 such that each of the cells 115 has the same or similar quantity of energy stored therein, as indicated by the state of charge measurement or the voltage measurement.

[0073] The cell charge balancing routine 320 may continue in the current state until the cells 115 are fully balanced at block 322, or until the battery assessment is updated and the cell charge balancing routine 320 restarts at block 324 with the updated battery assessment.

[0074] Generally, the battery cell state-of-charge balance control routine 300 monitors inputs from sensors 106 associated with each of the battery cells 115 at a first time point to measure their electrical parameters, such as voltage, determines a state-of-charge parameter for each of the battery cells 115 based on the electrical parameters, and determines a quality index of the state-of-charge parameter at the first time point.

[0075] In an exemplary embodiment, the battery cell state-of-charge balance control routine 300 is used to individually balance each battery pack of a battery system to a determined battery pack balance point. In an exemplary embodiment, once each battery pack has identified its battery pack balance point, a string balance point for all the battery packs in the string is determined. The string balance point is determined in a manner similar to determining the battery pack balance point, as Figure 2 described. In one embodiment, the lowest battery pack balance point is set as the string balance point for all the battery packs in the string.

[0076] Now referring Figure 5 to, a flowchart of a method 500 for performing state-of-charge balance across multiple battery packs, each battery pack including a plurality of battery cells, in accordance with an exemplary embodiment is shown. At block 502, the method 500 includes determining that a battery evaluation of a battery system having a string of battery packs, each battery pack including a plurality of battery cells, should be performed. In an exemplary embodiment, this determination can be made by one of a battery controller, a vehicle controller, a central battery system controller, or a string controller, such as Figures 1A-1D those shown in. In one example, the determination that a battery evaluation of the battery system should be performed is based on an analysis of electrical parameters associated with each of the plurality of battery cells of the battery packs in the battery system. At block 504, the method 500 includes obtaining electrical parameters associated with the plurality of battery cells.

[0077] At block 506, the method 500 includes calculating a battery pack balance point for each battery pack in the string. In an exemplary embodiment, the battery pack balance point of a battery pack is calculated based on electrical parameters associated with the plurality of battery cells of the battery pack. In an exemplary embodiment, the battery pack controller of each battery pack is configured to calculate the battery pack balance point of each battery pack. Next, at block 508, the method 500 includes instructing the battery cell balance system of each battery pack to balance the plurality of battery cells in the battery pack to the battery pack balance point. In an exemplary embodiment, each battery pack in a string of connected battery packs includes a battery cell balance system, such as the battery cell balance system 120 shown in FIG. 1, which is configured to bring the battery cells of the battery pack to the battery pack balance point.

[0078] At block 510, method 500 includes calculating a string balance point of the string of battery packs based on the battery pack balance points. In an exemplary embodiment, the battery pack controller of each battery pack is configured to transmit the battery pack balance point of the battery pack to the battery pack controllers of the other battery packs in the string. In an embodiment where the battery pack controllers of the battery packs within the string transmit the group balance points to each other, the battery pack controllers are further configured to calculate the string balance point based on a plurality of battery pack balance points respectively.

[0079] In an exemplary embodiment, the battery pack controller of each battery pack is configured to transmit the battery pack balance point of the battery pack to a string controller associated with the string. In an exemplary embodiment, the string controller is configured to calculate the string balance point of the string of battery packs based on the battery pack balance points and transmit the string balance point to the battery pack controllers. In an exemplary embodiment, the battery pack controller of each battery pack is configured to transmit the battery pack balance point of the battery pack to a central battery system controller. In an exemplary embodiment, the central battery system controller is configured to calculate the string balance point of the string of battery packs based on the battery pack balance points.

[0080] At block 512, method 500 includes instructing the cell balancing system of each battery pack to balance a plurality of cells in the battery pack to the string balance point. In an exemplary embodiment, each battery pack in a string of connected battery packs includes a cell balancing system, such as cell balancing system 120 shown in FIG. 1, which is configured to bring the cells of the battery pack to the string balance point.

[0081] In an exemplary embodiment, before receiving an instruction to balance to a different balance point (as shown at block 512), the battery pack may be unbalanced to its own calculated balance point (as shown at block 508). In one embodiment, once the battery pack has calculated its balance point, the battery pack continuously checks whether one of the other battery packs in the same string has a lower balance point. If this is the case, the current group will start balancing to the balance point of that other group, even if the current group has not yet balanced to its own balance point or if it is currently balancing to its own balance point. For example, battery pack A calculates its own balance point, and before battery pack A starts balancing its cells, battery pack A determines that the balance point of group B is lower (higher AHr difference to balance), and thus battery pack A balances its cells directly to the balance point of group B. In this example, group A never balances its batteries to its own calculated balance point, only to the balance point of group B. In another example, battery pack A calculates its own balance point and starts discharging its cells to reach that balance point. Then, battery pack A detects that group B has a lower balance point. Then, battery pack A reduces its balance point and continues discharging its cells, but now to the balance point of group B. In this case, battery pack A starts balancing its cells to its own calculated balance point, but never finishes and ends up balancing its cells to the balance point of group B.

[0082] In an exemplary embodiment, a battery controller communicates with a plurality of sensors and a battery cell balancing system, wherein the battery controller includes an instruction set that is executable to determine, at a first time point, a first plurality of electrical parameters associated with the plurality of battery cells, determine, based on the corresponding first plurality of electrical parameters, a plurality of first charge parameters associated with the plurality of battery cells, and determine a first quality index based on the plurality of first charge parameters. The instruction set is further executable to determine, at a second time point after the first time point, a plurality of second electrical parameters associated with the plurality of battery cells, determine, based on the corresponding plurality of second electrical parameters, a plurality of second charge parameters associated with the plurality of battery cells, and determine a second quality index based on the plurality of second charge parameters. Compare the first and second quality indexes. Execute a battery cell balancing routine to control the balancing system based on the first quality index when the first quality metric is greater than the second quality index, and to control the battery cell balancing system based on the second quality index when the first quality index is less than the second quality index.

[0083] Although the battery system 100 disclosed herein has been primarily discussed as part of an electric vehicle, those of ordinary skill in the art will understand that the battery system 100 can be disposed in a variety of other environments. In one example, the battery system 100 can be disposed in a train or locomotive. In another example, the battery system 100 can be disposed in a building such as a home or office and can be configured to provide power to the building.

[0084] The terms "controller" and related terms (such as microcontroller, control module, module, control, control unit, processor, and like terms) refer to one or various combinations of the following: application specific integrated circuit (ASIC), field programmable gate array (FPGA), electronic circuit, central processing cell unit (e.g., microprocessor), and related non-transitory memory components in the form of memory and storage devices (read only, programmable read only, random access, hard disk drive, etc.). The non-transitory memory component is capable of storing machine-readable instructions in the form of: one or more software or firmware programs or routines, combinational logic circuits, input / output circuits and devices, signal conditioning and buffering circuits, and other components that can be accessed by one or more processors to provide the described functionality. The (one or more) input / output circuits and devices include analog / digital converters and related devices that monitor inputs from sensors, where such inputs are monitored at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, code, algorithms, and like terms mean a set of controller-executable instructions that includes calibration and look-up tables. Each controller executes control routines to provide the desired functionality. The routines can be executed at regular intervals, such as every 100 microseconds during an ongoing operation. Alternatively, the routines can be executed in response to the occurrence of a triggering event. Communication between controllers and communication between a controller, an actuator, and / or a sensor can be achieved using a direct wired point-to-point link, a networked communication bus link, a wireless link, or another suitable communication link. Communication includes exchanging data signals in a suitable form, including, for example, electrical signals via a conductive medium, electromagnetic signals via air, optical signals via an optical waveguide, etc. The data signals can include discrete, analog, or digitized analog signals representing inputs from sensors, actuator commands, and communication between controllers.

[0085] The term "signal" refers to a physically distinguishable indicator that conveys information and can be a suitable waveform (e.g., electrical, optical, magnetic, mechanical, or electromagnetic) capable of traveling through a medium, such as DC, AC, sine wave, triangular wave, square wave, vibration, etc.

[0086] The terms "calibration", "calibrated", and related terms refer to the result or process of comparing the actual or standard measurement results associated with a device or system with the perceived or observed measurement results or commanded positions of the device or system. Calibration as described herein can be reduced to a storable parameter table, multiple executable equations, or another suitable form that can be used as part of a measurement or control routine.

[0087] A parameter is defined as a measurable quantity that represents a physical property of a device or other element that can be discerned using one or more sensors and / or physical models. A parameter can have discrete values, such as "1" or "0", or can be infinitely variable in value.

[0088] The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Unless the context clearly dictates otherwise, the term "or" means "and / or". References to "aspect" throughout the specification mean that a particular element (e.g., feature, structure, step, or property) described in connection with that aspect is included in at least one aspect described herein, and may or may not be present in other aspects. Additionally, it should be understood that the described elements can be combined in any suitable manner in the various aspects.

[0089] When an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, no intervening elements are present.

[0090] Unless otherwise indicated herein, all test standards are the latest standards in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standards appear.

[0091] Unless otherwise defined, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0092] Although the foregoing disclosure has been described with reference to exemplary embodiments, those of ordinary skill in the art will understand that various changes may be made and equivalents may be substituted for its elements without departing from its scope. Additionally, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from its basic scope. Accordingly, it is intended that the disclosure not be limited to the particular embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A method for balancing power in a battery system, wherein the battery system has a series of battery packs, each battery pack including a plurality of battery cells, the method comprising: obtaining an electrical parameter of each of the plurality of battery cells; calculating a battery pack balancing point for each of the battery packs in the string; instructing a battery cell balancing system to execute a battery cell charge balancing routine to balance each of a plurality of battery cells of each battery pack to a battery pack balancing point corresponding to the battery pack; Calculating a string balancing point of the string of batteries based on the battery balancing point; and A battery cell balancing system of each battery pack is instructed to balance a plurality of battery cells of the battery pack to the string balancing point.

2. The method of claim 1, wherein the battery packs of the string are connected in series with each other. 3 . The method of claim 1 , wherein each battery pack comprises a battery pack controller, and wherein the battery pack controller is configured to calculate a battery pack balancing point for the battery pack. 4 . The method of claim 3 , wherein the battery pack controller of each battery pack is configured to transmit the battery pack balancing point of the battery pack to the battery pack controllers of other battery packs in the string. 5 . The method of claim 3 , wherein the pack controller of each battery pack is configured to transmit the pack balancing point of the battery pack to a string controller associated with the string. 6 . The method according to claim 5 , wherein the string controller is configured to calculate a string balancing point of the string battery pack based on the battery pack balancing point, and transmit the string balancing point to the battery pack controller.

7. The method according to claim 3, wherein the battery pack controller of each battery pack is configured to transmit the battery pack balancing point of the battery pack to the central battery system controller, wherein the central battery system controller is configured to calculate the string balancing point of the string battery pack based on the battery pack balancing point.

8. A battery system, comprising: A plurality of strings, each of the plurality of strings comprising a plurality of battery packs connected in series with each other, wherein each of the plurality of battery packs comprises: a plurality of battery cells; a sensor configured to monitor an electrical parameter of each of the plurality of battery cells; a battery cell balancing system configured to selectively charge or discharge a plurality of battery cells of the battery pack; and a battery pack controller configured to monitor an electrical parameter of each of a plurality of battery cells and responsively control operation of the battery cell balancing system, The battery pack controller is further configured to calculate a battery pack balancing point based on an electrical parameter of each of the plurality of battery cells. 9 . The battery system of claim 8 , further comprising a central battery system controller configured to communicate with the battery pack controller of each of the battery packs of the plurality of strings.

10. An electric vehicle comprising: A battery system having a plurality of strings, each of the plurality of strings comprising a plurality of battery packs connected in series with each other, wherein each of the plurality of battery packs comprises: a plurality of battery cells; a sensor configured to monitor an electrical parameter of each of the plurality of battery cells; a battery cell balancing system configured to selectively charge or discharge a plurality of battery cells of the battery pack; and a battery pack controller configured to monitor an electrical parameter of each of a plurality of battery cells and responsively control operation of the battery cell balancing system, The battery pack controller is further configured to calculate a battery pack balancing point based on an electrical parameter of each of the plurality of battery cells.

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