A battery system and a method for controlling a battery system

Abstract

The invention involves to a battery system comprising one or more battery assemblies (100, 200, 300), wherein each battery assembly comprises two battery assembly terminals (105, 106), wherein the battery assemblies are via the battery assembly terminals connected to two load terminals (101, 102) of a load and / or a battery charger, wherein each battery assembly comprises a plurality of battery cells (163) connected in series and / or in parallel between the respective battery assembly terminals (105, 106), - wherein the battery system comprises a control system configured to provide a voltage control function which controls, for each battery assembly, connections of the respective battery cells to the respective battery assembly terminals, so as to direct an actual current or voltage at the load terminals (101, 102) or a respective actual current or voltage at the respective battery assembly terminals (105, 106) towards a desired current or voltage at the load terminals (101, 102) or a respective desired current or voltage at the respective battery assembly terminals, - characterised in that the control system is configured to provide a cell utilization control function which determines, for each of one or more of the battery assemblies, and for said control of the connections of the respective battery cells to the respective battery assembly terminals, utilization data indicative of a desired distribution of the utilization of the battery cells, - wherein the control system is configured such that the cell utilization control function provides the utilization data for the voltage control function, - wherein the control system is configured such that the voltage control function performs said control of the connections of the respective battery cells to the respective battery assembly terminals in dependence on the utilization data.

Description

[0001] A BATTERY SYSTEM AND A METHOD FOR CONTROLLING A BATTERY

[0002] SYSTEM

[0003] TECHNICAL FIELD

[0004] The present invention relates to a battery system, a vehicle, a method for controlling a battery system, and a control system.

[0005] BACKGROUND

[0006] As the application of battery systems, particularly in electric vehicles and energy storage systems, continues to expand, the need for efficient, reliable, and safe operation of these systems becomes increasingly important. Battery systems often comprise one or more battery assemblies, often referred to as battery packs, each with multiple battery cells connected in series and / or parallel. These cells are typically connected to a load or a charger through battery assembly terminals. The current or voltage at these terminals is monitored and controlled to ensure optimal operation of the battery system.

[0007] W02021094011 Al describes a battery assembly for aiming at outputting a target voltage during charging or discharging of the battery assembly. A specific value to be used as target voltage is delivered to a control unit of the battery assembly from an external device. The battery assembly comprises a plurality of “discrete battery modules”, each of which can be controlled so at to be switched-on or bypassed. Thereby, the control unit can control the output voltage of the battery assembly in a number of discrete steps. The battery assembly further comprises an “analog battery module”, adapted to output a range of voltages. This makes it possible to fine-tune the output voltage of the battery assembly so that it is close to the target voltage.

[0008] Said document further describes a combination of signals sent from the control unit to all the discrete battery modules. For each discrete battery module, the signals determine whether the battery module is switched-on or bypassed. Further, the control unit can, at a fixed frequency, evaluate whether or not there is need for a new configuration of switched- on and bypassed battery modules. Reasons to change the configuration include:

[0009] • To keep the battery assembly output voltage reasonably close to the target value.

[0010] • To balance the utilization of each battery module such that the battery module is used according to the available capacity of the module.

[0011] • To minimize the temperature deviation between the modules and to limit the temperature ripple of each battery module.

[0012] • To avoid that any single battery cell in the battery module have too high or too low state of charge or too high temperature, as this could degrade the battery cell.

[0013] • To keep the analog battery module(s) within the control range with a suitable margin.

[0014] There is nevertheless a desire to further increase the robustness of battery systems, and to decrease the risk of errors and faults. There is also a desire to increase the life of a battery system.

[0015] SUMMARY

[0016] An object of the invention is to increase the robustness of battery systems, and to decrease the risk of errors and faults in battery systems. Another object of the invention is to increase the life of a battery system.

[0017] The objects are achieved by a battery system comprising one or more battery assemblies, wherein each battery assembly comprises two battery assembly terminals, wherein the battery assemblies are via the battery assembly terminals connected to two load terminals of a load and / or a battery charger, wherein each battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the respective battery assembly terminals,

[0018] - wherein the battery system comprises a control system configured to provide a voltage control function which controls, for each battery assembly, connections of the respective battery cells to the respective battery assembly terminals, so as to direct an actual current at the load terminals or a respective actual current at the respective battery assembly terminals towards a desired current at the load terminals or a respective desired current at the respective battery assembly terminals, or so as to direct an actual voltage at the load terminals or a respective actual voltage at the respective battery assembly terminals towards a desired voltage at the load terminals or a respective desired voltage at the respective battery assembly terminals,

[0019] - wherein the control system is configured to provide a cell utilization control function which determines, for each of one or more of the battery assemblies, and for said control of the connections of the respective battery cells to the respective battery assembly terminals, utilization data indicative of a desired distribution of the utilization of the battery cells,

[0020] - wherein the control system is configured such that the cell utilization control function provides the utilization data for the voltage control function,

[0021] - wherein the control system is configured such that the voltage control function performs said control of the connections of the respective battery cells to the respective battery assembly terminals in dependence on the utilization data.

[0022] Thus, the control system is configured such that the voltage control function performs said control of the connections of the respective battery cells to the respective battery assembly terminals in dependence on the utilization data provided by the cell utilization control function. The voltage control function may be configured to control the connections of the respective battery cells to the respective battery assembly terminals. Thus, embodiments of the invention provide a control function, i.e. the cell utilization control function, which is separate from the voltage control function, which provides the utilization data for the voltage control function, which then performs its connection control in dependence on the provided utilization data. The cell utilization control function may be configured to determine the utilization data. The utilization data is preferably indicative of a desired distribution of the utilization of the battery cells in a time domain.

[0023] Each battery assembly may comprise a plurality of battery modules connectable in series between the battery assembly terminals of the battery assembly. As exemplified below, such a battery module may comprise one or more of the battery cells. Where a battery module comprises a plurality of battery cells, these cells may be connected in series and / or parallel to output conduits of the battery module. For a battery module, one or more switches may be arranged to be controlled to selectively connect or disconnect the battery module to or from the battery assembly terminals. The voltage control function may control connections of the respective battery modules to the battery assembly terminals. The utilization data determined by the cell utilization control function may be indicative of a desired distribution of the utilization of the battery modules. Thereby, the voltage control function may control the connections of the respective battery modules to the battery assembly terminals in dependence on the utilization data.

[0024] The voltage control in a battery system may have requirements on fast responses to quickly varying control input, e.g. in cases of transients where the battery system is provided for the propulsion of a vehicle. The cell utilization balancing on the other hand have different requirements, e.g. balancing the utilization of each battery module, minimizing cell temperature ripple or temperature deviation between the cells, and / or avoiding that a state of charge for any cell is too high or too low, or that the temperature of any cell is too high. To burden a single function in the control system with all these requirements in real-time creates a risk of undesired errors and fault modes. Since embodiments of the invention provide a division of functions between voltage control and cell utilization balancing distribution, such a risk is reduced and a more robust system is obtained. For example, the division of functions according to embodiments of the invention allows voltage control to occur without being “slowed down” by considerations of cell utilization balancing.

[0025] The facilitated utilization balancing allowed by embodiments of the invention provides for an improved utilization of capacities of individual battery cells, which in turn increases the life of the battery system.

[0026] Where the battery system comprises a plurality of battery assemblies they may be connected in parallel to the load and / or battery charger. Thereby, the control system may comprise a control assembly for each battery assembly. Thereby, the voltage control function may be distributed in the control assemblies for individual voltage control of the respective battery assemblies. Each battery assembly may comprise an actuation assembly, wherein the respective actuation assembly is configured to control connections of the respective battery cells to the respective battery assembly terminals. Thereby, the voltage control function may be configured to control the actuation assembly for the control of the connections of the respective battery cells to the respective battery assembly terminals.

[0027] The respective actuation assembly may comprise a DCDC converter. Such a DCDC converter may be implemented in an analog battery module, comprising one or more battery cells, e.g. as described in W02021094011 Al, adapted to output a range of voltages. In addition, or alternatively, the respective actuation assembly may comprise a plurality of switches, arranged to be controlled to selectively connect or disconnect one or more of the battery cells to or from the battery assembly terminals. Within the range of output voltages, the DCDC-converter may have two or more possible output voltages that in combination with the configuration of the switched battery modules can fulfil the target output voltage.

[0028] Preferably, the utilization data comprises prioritization data indicative of a prioritization of one or more of the battery cells in the respective battery assembly, over one or more of the remaining battery cells in the respective battery assembly.

[0029] Preferably, the control system comprises one or more control assemblies configured to provide the voltage control function, and a utilization balancing assembly configured to provide the cell utilization control function.

[0030] Preferably, the utilization balancing assembly is physically separated from the one or more control assemblies, wherein the utilization balancing assembly is arranged to send the utilization data to the one or more control assemblies.

[0031] Thus, embodiments of the invention provide a division of voltage control and cells utilization balancing distribution into different physical units, e.g. different computers. However, in some embodiments, the voltage control function and the cell utilization control function are provided in one or more common units. In some embodiments, the voltage control function and the cell utilization control function are provided by one single software code.

[0032] Preferably, the cell utilization control function determines the utilization data in dependence of whether the voltage control function will perform said control of the connections in dependence on the utilization data when the battery cells are discharged or charged.

[0033] In such embodiments, the control system may be configured to provide the cell utilization control function such that the cell utilization control function determines the utilization data in dependence on whether the battery cells are charged or discharged. For example, the cell utilization control function may determine a utilization dataset including the utilization data, which comprises a charging utilization data sub-set in dependence on which the voltage control function performs said control of the connections when the battery cells are charged, and a de-charging utilization data sub-set, differing from the charging utilization data sub-set, in dependence on which the voltage control function performs said control of the connections when the battery cells are discharged. This is beneficial e.g. where the utilization data is provided in dependence on the state of charge of the battery cells. For example, when a battery assembly in the battery system is discharged, battery cells with a low state of charge preferably have a low priority in the battery assembly current production, whereas, when the battery assembly is charged, battery cells with a low state of charge preferably have a high priority in the distribution of charging.

[0034] Preferably, each of the one or more of the battery assemblies, for which the utilization data is provided, comprises a plurality of battery modules connected in series between the respective battery assembly terminals. Thereby, each battery module comprises one or more of the battery cells. Where there are a plurality of battery cells in a battery module, the battery cells may be connected in series and / or in parallel between terminals of the module. Thereby, preferably, the control of the voltage control function of the connections of the respective battery cells to the respective battery assembly terminals comprises determining a number of the battery modules which are to be bypassed. A bypassed battery module does not contribute to the voltage of the respective battery assembly. Thereby, the cell utilization control function is configured to determine the utilization data so as to be independent of the number of the battery modules which are to be bypassed.

[0035] For example, the utilization data may comprise a plurality of utilization data sets forming a group of utilization data sets, Thereby, the control of the voltage control function of the connections of the respective battery cells to the respective battery assembly terminals is made in dependence on one after the other of the utilization data sets in a sequence of the utilization data sets. Thereby, the group of utilization data sets is determined so as to be independent of the control of the connections of the respective battery cells to the respective battery assembly terminals.

[0036] However, in some embodiments, the utilization data is determined in dependence on the number of the battery modules which are to be bypassed. Thereby, the voltage control function may repeatedly send to the cell utilization control function information indicative of number of the battery modules which are to be bypassed.

[0037] The objects are also reached with a vehicle according to claim 7. Thereby, the embodiments are particularly advantageous with their ability to adapt to strong load transient which may be present. Nevertheless, the invention is also useful in other fields, e,g, stationary applications such as charging stations, and / or devices supporting electric grids.

[0038] The objects are also reached with a method for controlling a battery system comprising one or more battery assemblies, wherein each battery assembly comprises two battery assembly terminals, wherein the battery assemblies are via the battery assembly terminals connected to two load terminals of a load and / or a battery charger, wherein each battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the respective battery assembly terminals,

[0039] - wherein the method comprises controlling, for each battery assembly, connections of the respective battery cells to the respective battery assembly terminals, so as to direct an actual current at the load terminals or a respective actual current at the respective battery assembly terminals towards a desired current at the load terminals or a respective desired current at the respective battery assembly terminals, or so as to direct an actual voltage at the load terminals or a respective actual voltage at the respective battery assembly terminals towards a desired voltage at the load terminals or a respective desired voltage at the respective battery assembly terminals, wherein the method comprises determining, for each of one or more of the battery assemblies, and for said control of the connections of the respective battery cells to the respective battery assembly terminals, utilization data indicative of a desired distribution of the utilization of the battery cells, providing the utilization data for said control of the connections of the respective battery cells to the respective battery assembly terminals, and performing said control of the connections of the respective battery cells to the respective battery assembly terminals in dependence on the utilization data.

[0040] Preferably, the utilization data comprises prioritization data indicative of a prioritization of one or more of the battery cells in the respective battery assembly, over one or more of the remaining battery cells in the respective battery assembly.

[0041] Preferably, the method comprises repeating the step of providing the utilization data for said control of the connections of the respective battery cells to the respective battery assembly terminals. The method may comprise repetitively comparing the actual current or voltage and the desired current or voltage, and performing said control of the connections in dependence on the comparisons of the actual current or voltage and the desired current or voltage. Thereby, said comparisons may be repeated more often than said step of providing the utilization data for said control of the connections.

[0042] The comparison of the actual current or voltage and the desired current or voltage may comprise determining a current or voltage error value, e.g. as a difference between the actual current or voltage and the desired current or voltage. In some embodiments, the voltage control function and cell utilization control function are separate software functions running on the same microcontroller. In some embodiments, the functions run in different time tasks. Thereby, the voltage control function may be running more frequently than the cell utilization control function.

[0043] Preferably, said step of providing the utilization data for said control of the connections is repeated with a frequency of 0.1-100 Hz, more preferably 0.5-50 Hz.

[0044] The repetition may be done regularly or irregularly. Thus, the frequency may be constant or varying. In contrast, said control of the connections of the respective battery cells to the respective battery assembly terminals may be comprise adjustments of the connections at a frequency of 0.01-10 kHz. It is understood that the connections between the respective battery cells to the respective battery assembly terminals may be adjusted for reasons of a changed load requirement on the battery system, or updated utilization data.

[0045] In some embodiments, the utilization data comprises a plurality of utilization data sets forming a group of utilization data sets. Thereby, at a first point in time during said control of the connections, the connections are controlled in dependence on a first of the utilization data sets, and, at a second point in time during said control of the connections, the connections are controlled in dependence on a second of the utilization data sets. Thereby, at the first and second points in time, the connections may be controlled in dependence on a respective single utilization data set. The first and second points in time are different.

[0046] The first and second utilization data sets are different.

[0047] Preferably, the connections are controlled in dependence on the first utilization data set during a first time period, and the connections are controlled in dependence on the second utilization data set during a second time period, wherein the second time period is longer or shorter than the first time period.

[0048] As exemplified below, by the groups of utilization data sets, the distribution of the utilization of the battery cells may be further optimized.

[0049] As suggested above, the battery assemblies may comprise a plurality of battery modules, each comprising one or more of the battery cells, connected in series between the respective battery assembly terminals, wherein the utilization data is determined so as to be independent of the number of the battery modules which are to be bypassed

[0050] The objects are also reached with a control system according to claim 15.

[0051] As mentioned, each battery assembly may comprise a plurality of battery modules connectable in series between the battery assembly terminals of the battery assembly. Such a battery module may be what is herein referred to as a discrete power unit (DPU). Such a DPU may comprise a plurality of battery cells connected in series and / or in parallel between a low side and a high side terminal of the DPU.

[0052] Embodiments of the invention provide for a control of the use, i.e. the charging or discharging, of the battery cells such that their states meet a pre-defined criterion. Said states may be the state of charge (SOC), state of power (SOP), state of health (SOH) and / or any other definition of state indicative of the battery cell condition. Thereby, embodiments of the invention may dynamically control the use of the DPUs such that their relative use becomes that of a desired value, which may be computed and given by the cell utilization control function. The cell utilization control function may dynamically estimate the states of the battery modules and cells. Based on the knowledge of said states the (future) use of the DPUs can be controlled such that the control objective is met. For example, the control objective may be to use the DPUs such that the SOC and SOH are optimized according to a predetermined optimization criteria.

[0053] For example, it may be desired to balance the battery assembly such that all DPU’s have the same SOH. Thereby, the lifetime of the battery assembly being limited by a DPU with a significantly worse SOH than the rest may be avoided. For example, a DPU may be mounted in the battery system such that it has higher temperature than other DPUs. This may accelerate the ageing process of the DPU over time. By embodiments of the invention, it may be secured that the DPU is used less such that the SOH of all DPU’s are degrading at the same rate.

[0054] Embodiments of the invention may be described mathematically as follows: Consider a battery assembly consisting of M DPU’s. At a given time instant, the DPU’s can be connected (1) in series or bypassed (0). A specific combination of DPU’s are connected in series during a time interval T(fc), where k = 0,1,2, ... denotes a running index and increments by one for each change of DPU-combination.

[0055] Let a vector of dimension (M| 1) denote which DPU’s are connected and disconnected during a time interval T (fc) :

[0056] Zm(fc) = 1 or 0, m = 1,2, ... , M where the m:th entry in L(fc) corresponds to the m:th DPU and M is the total number of DPUs.

[0057] The relative accumulated use of the DPUs over a time-period, such as a future time-period, [T(k + 1), T(k + IV)] can be written as

[0058] The objective of embodiments of the invention may be to utilize the DPUs such that the relative accumulated use is close to and approaching a preferred utilization denoted by R, herein also referred to as a utilization vector. R may be an (M| 1) vector of target values between zero (DPU never used) and one (DPU always used). As suggested above, the preferred utilization may depend on estimated state values for the DPU states in the battery assembly. Let A(t) denote a vector of estimated DPU states. The preferred utilization of the DPUs over a future time interval may depend on time and the states such that R(t) = Z?(A(t)) . The utilization of the DPUs is determined by which of the DPUs that are connected, L(k), and how long they are connected, T(fc). They need to be controlled such that

[0059] The voltage control function may control the series connection and disconnection of DPUs in the battery assembly. Preferably the cell utilization control function provides the preferred utilization, / ?(t), and the voltage control function chooses L and T such that Q(t) -> R(t). Thereby, a cost and performance efficient approach is provided. Also, thereby, an intense communication with the voltage control function, required if the cell utilization control function would provide L(k), is avoided. Thereby, difficulties of handling sudden transients in the load are avoided.

[0060] It should be noted that the time interval in which specific values of L and T are applied in the voltage control function does not need to be synchronized with the time-period for updating the preferred (target) utilization. For example, the values of L and T may be updated with a specific and relatively high frequency in the voltage control function, and the update frequency of the preferred utilization vector R(t) may be slow to reflect the relatively slow changes in the battery assembly states. The updating may be asynchronous, and it may be interruption driven.

[0061] Embodiments of the invention provide a communication between the cell utilization control function and the voltage control function which is sufficiently rich in information to meet the control objective while keeping the communication bandwidth as low as possible to facilitate a robust and cost-efficient implementation of a controllable battery system that meets the high requirements on voltage and current control, while at the same time optimizing the life-time by a balanced utilization of the DPU’s. This is preferably done by sending the desired utilization vector, / ?(t), from the cell utilization control function to the voltage control function, which computes a scheme for the vector L(fc) that determines which DPUs are connected and disconnected during future time interval(s) T(fc), such that the utilization of the DPU’s approach that of the desired, i.e., such that

[0062] The voltage control function may be controlled by a prioritization data set, in the form of a priority list, for decisions on when to connect or disconnect battery modules to obtain the desired voltage of the battery assembly. As an example, in a battery assembly with four battery modules, such a priority list could be written as a vector P = <3, 2, 0, 1>, where each number denotes one of the modules, and where modules to the left in the vector are connected before modules to the right.

[0063] The cell utilization control function may divide the battery modules into three groups. A first of the groups consists of modules that are to be connected as much as possible. These modules have the highest priority. A second of the groups consists of modules that are to be disconnected as much as possible. These modules have the lowest priority.

[0064] A third of the groups consists of modules that are to be connected and disconnected with a frequency f. The connections of the modules in the third group have different durations in time in order to realize a module utilization U, herein also referred to as a desired distribution of the utilization of the modules, or a module utilization vector. The module utilization U is provided by the cell utilization control function. As an example, it can be assumed that the third group of modules includes N prioritized modules n(j), 0<=j< N.

[0065] The module utilization U indicates for each module n(j) how much it is to be used in relation to the use of the rest of the modules. For example U = <0.4, 0.45, 0.55, 0.6> for N=4.

[0066] The cell utilization control function may generate a group of utilization data sets, in the form of a group of priority lists. The group of priority lists may be represented as P(i), 0<=i<N. The priority lists in the group are arranged so that a priority list P(i) is effective during a time interval t(i), whereafter another priority list P(i+ 1 ) is effective during another time interval t(i+ 1 ). The group of priority lists is preferably generated so that the sum of the time intervals for the priority lists is equal to the period 1 / f of said frequency f.

[0067] Let M indicate the number of battery modules connected by the voltage control function, so that 0<=M<=K, where K is the number of modules. The group of priority lists is preferably generated so that when an execution of a first priority list P(i) is replaced by an execution of a second priority list P(i+1), exactly one module should be moved from a position pl < M in the first priority list to a position p2 >= M in the second priority list, and exactly one module should be moved in the opposite direction from a position p3 >= M in the first priority list to a position p4 < M in the second priority list. This has to be effected for every M. Such movements of modules in the priority lists have to be effected for any value of M.

[0068] Thus, the cell utilization control function may generate a group of utilization data set group generation may require information about the number M of connected battery modules. The number M of connected battery modules is preferably provided by the voltage control function to the cell utilization control function.

[0069] Preferably, every module assumes a position in any of the priority lists which is different from its positions in any of the other priority lists.

[0070] Here is an example, in which ’’swap” indicates a one module moving from being connected to not being connected, and another module moving from not being connected to being connected, although these modules do not necessarily take each other’s positions in the order of priority:

[0071] The frequency of the execution of the group of priority lists is selected. In this example, this frequency is 5 Hz, and the period 1 / f = (0.060+0.045+0.040+0.055) = 0.2.

[0072] It should be noted that in some embodiments, the cell utilization control function determines the module utilization U, and the voltage control function determines the group of utilization data sets, in the form of a group of priority lists, in dependence on the module utilization U.

[0073] In other embodiments, the cell utilization control function determines the utilization data in the form of a priority list where a battery module above another module in the list is connected before the other module. I.e. the priority list provides, when the voltage control function determines which of the modules are to be connected to the battery assembly terminals, a prioritization of the modules. Thereby, the cell utilization control function may provide a new priority list when a different prioritization of the modules is desired. For example, the cell utilization control function may continuously or repetitively receive or determine respective states of the battery cells or the battery modules. Such states may be, or include, respective states of charge. Thereby, the priority lists may be determined so as to be independent of the number of the battery modules which are to be bypassed.

[0074] In other embodiments, the cell utilization control function determines the utilization data in the form of a priority list, here referred to as a first priority list, along with a first time interval during which the first priority list is to be effective, i.e. to be used by the voltage control function to determine which of the modules are to be connected to the battery assembly terminals. Thereby, the cell utilization control function may provide a second priority list to replace the first priority list as effective, along with a second time interval during which the second priority list is to be effective. Thereby, the priority lists may be determined so as to be independent of the number of the battery modules which are to be bypassed.

[0075] A further way of determining the priority lists so as to be independent of the number of the battery modules which are to be bypassed, is exemplified as follows:

[0076] For K modules with a desired utilization U = <u(0), u(l), ..., u(K-l)>, K priority lists with K elements each are provided.

[0077] The module utilization vector U provides a module order from first module to last, m = <0, 1, ..., K-l> . An adjusted utilization vector Us = <us(0), us(l), ..., us(k-l)> is provided by sorting the utilization vector U from the largest to the smallest utilisation. A mapping mp from the module positions in Us to the modules in U, so that u(m) = us(mp(p)), is created. Thereafter, the sorted positions p = <0, 1, ..., K-l> in the adjusted utilization vector Us is used to refer to a module. The mapping mp is used to translate module position p to an actual module m.

[0078] A column vector C with module positions is constructed. This construction starts with 0 and continues with increasing even numbers up to K-l or K-2 whichever is even. The construction continues with odd numbers in descending order, starting with K-l or K-2 whichever is odd, all the way down to 1. Examples:

[0079] K = 3, C = <0, 2, 1>

[0080] K = 4, C = <0, 2, 3, 1>

[0081] K = 5, C = <0, 2, 4, 3, 1>

[0082] K = 6, C = <0, 2, 4, 5, 3, 1>

[0083] Let P(i, j) designate the position j in the priority list i. 0<=i<K, 0<=j<K.

[0084] P(i, j)={ j is even: C( (i + (j / 2) ) MOD K ) j is odd: C( (i + (K - ((j+l) / 2))) MOD K )}

[0085] Each priority list is active for a time period T = <t(0), t(l), t(K-l)> where l / SUM(t(x)) = f.

[0086] A simple approximation of the adjusted utilization vector Us can be realized by setting t(x) proportional to us(x) while maintaining the constraint l / SUM(t(x)) = f. t(x) = 1 / f * us(x) / SUM(us(x)), 0<=x<K

[0087] For an exact realization of the adjusted utilization vector Us, t(x) depends on the number of connected modules M. This t(M, x) may be computed by solving an equation system. For each module, the ratio of the time connected and the period time shall be equal to us(x). With K=4 and M=2 the following equations are provided: us(0) = (t(2, 0) + t(2, 1)) * f us(l) = (t(2, 3) + t(2, 0)) * f us(2) = (t(2, 1) + t(2, 2)) * f us(3) = (t(2, 2) + t(2, 3)) * f

[0088] Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

[0089] BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Below, embodiments of the invention will be described with reference to the drawings, in which:

[0091] - fig. 1 shows components of a battery system according to an embodiment of the invention,

[0092] - fig. 2 and fig. 3 show components of a battery assembly in the battery system in fig. 1,

[0093] - fig. 4 is a flow diagram depicting steps in a method in the battery system of fig. 1, and

[0094] - fig. 5 shows components of a control system for the battery system of fig. 1.

[0095] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0096] Fig. 1 shows a battery system with a plurality of parallel battery assemblies 100, 200, 300. The battery assemblies 100, 200, 300 each comprise a plurality of battery cells, as exemplified below. The battery system may be provided in an electric or hybrid electric vehicle, or in an electric power system. The battery assemblies 100, 200, 300 are connectable to load terminals 101, 102 of a common load or charging circuit 10. For this, the battery assemblies are connected to a direct current (DC) voltage bus. The DC voltage bus can serve many purposes such as delivering or receiving power to or from AC electric motors or the AC grid via inverters, to or from other battery assemblies, to or from DC electric motors, from solar cells, from a fuel cell or the like. The battery system comprises a control system, comprising, for each battery assembly 100, 200, 300, a control assembly comprising a main controller 120. The battery system further comprises a master control unit 40. The master control unit 40 is arranged to receive information from the main controller 120 of the respective battery assembly 100, 200, 300. The information that is received can for example be an actual voltage of the respective battery assembly as measured inside the battery assembly, an actual current flowing through the battery assembly during charging or discharging, and / or a state of charge of the respective battery assembly.

[0097] A measurement device MD 20 is connected to the DC voltage bus 15. The measurement device 20 is arranged to measure the DC bus voltage 22 and the DC bus current 21. A DC link capacitor 30 is also connected to the load or charger 10. The master control unit 40 is arranged to receive the information from the measurement device MD 20. The master control unit 40 is arranged to determine, based on the information from the measurement device MD 20, and for the battery assemblies 100, 200, 300, target values indicative of currents or voltages at battery assembly terminals of the battery assemblies 100, 200, 300.

[0098] The control system further comprises a utilization balancing assembly 500 described further below.

[0099] Fig. 2 shows one of the battery assemblies in fig. 1. The battery assembly comprises two battery assembly terminals 105, 106, and a plurality of switched battery modules 170, herein also referred to as discrete battery modules.

[0100] The control assembly 120 is configured to provide a voltage control function as exemplified below.

[0101] Fig. 3 shows the battery assembly in fig. 2 in more detail. The set of battery modules also comprises an analog battery module 110, e.g. as described in W02021094011 Al incorporated herein by reference. The analog battery module 110, e.g. a local controller 171 thereof, is configured to receive from the main controller 120 a signal representing a target current to be output through the analog battery module 110. The analog battery module 110 comprises a DCDC converter 177 which forms a part of the actuation assembly of the battery assembly. The local controller 171 is configured to minimize the error between a measured current through the DCDC converter and the target current value. The local controller 171 may be configured to generate one or more pulse width modulated (PWM) signals to be used by the DCDC converter. The DCDC converter may comprise a plurality of switches, and the switches may be controlled by the PWM signal to minimize said error. By controlling the current through the DCDC converter, the PWM signal controls the output voltage over the analog module in relation to the battery assembly’s input voltage to the DCDC converter. The local controller 171 thus functions as a controlled current source. Thereby, the current through the DCDC converter is connected to the output voltage over the analog module. Thereby, the PWM signal makes it possible to fine-tune the output voltage of the battery assembly 100 so it is close to a target voltage.

[0102] In alternative embodiments, the DCDC converter is configured to receive a signal representing a target voltage over the analog battery module. Thereby, the local controller 171 may be integrated into the main controller.

[0103] Each switched battery module 170 comprises sets 163 of two or more battery cells connected in series to output conduits 170C of the respective battery module 170. More specifically, the battery cells of each battery module 170 are connected to a half-bridge comprising at least one switch in the form of a high side (HS) transistor 176 for connecting the battery module in the battery assembly and at least one switch low side (LS) transistor 175 that can bypass the battery module so that the battery cells do not contribute to the total output voltage of the battery assembly. The transistors may be MOSFET transistors. However, instead of transistors some other kind of switches may be used. More generally the HS transistors 176 are referred to as HS switches and the LS transistors 175 are referred to as LS switches.

[0104] As indicated in fig. 3, each switched battery module 170 comprises a local controller 171.

[0105] The local controllers 171 are arranged to communicate with each other, and with the main controller 120. Further, each local controller 171 is configured to control the HS and LS switches 176, 175 of the respective switched battery module 170. The main controller 120 is configured to receive, e.g. from the master controller 40 (fig. 1), a target value indicative of a desired current or voltage at the battery assembly terminals 105, 106. The main controller 120 is further configured to send, based on the target value, control signals to the local controllers 171, based on which the local controllers control the switches 175, 176 of the respective battery module. Thereby, the switches 175, 176 may be controlled so that none, one, or more, of the battery modules are by-passed. For each battery module 170, if the LS switch 175 is turned on and the HS switch 176 is turned off, the battery cells 163 on the battery module will be bypassed. If the LS switch 175 is turned off and the HS switch 176 is turned on, the battery cells 163 on the current will pass the set 163 of battery cells. Thereby, by selecting a number of battery cells to be bypassed, an actual current or voltage at the battery assembly terminals 105, 106 can be directed towards the desired current or voltage.

[0106] The utilization balancing assembly 500 (fig. 1) is arranged to receive from the control assemblies, e.g. from the main controllers 120 thereof, status data indicative of values of parameters of the battery modules 110, 170 or the battery cells 163. These parameters may include one or more of a state of charge of the battery modules or the battery cells, temperatures of the battery cells 163, and information on whether any of battery cells is close to be overcharged or undercharged.

[0107] The utilization balancing assembly 500 (fig. 1) is configured to provide a cell utilization control function which determines, based on the status data, and for each of the battery assemblies, and for the control of the connections of the respective battery cells to the respective battery assembly terminals, utilization data indicative of a desired distribution of the utilization of the battery cells. The utilization balancing assembly 500 is arranged to send the utilization data to the control assemblies, e.g. to the main controllers 120 thereof. The utilization data comprises, for each battery assembly 100, 200, 300, prioritization data indicative of a prioritization of one or more of the battery modules 110, 170 in the respective battery assembly, over one or more of the remaining battery modules in the respective battery assembly. The respective control assembly 120, 171 is configured so that the respective voltage control function performs said control of the connections of the respective battery modules to the respective battery assembly terminals in dependence on the utilization data.

[0108] The utilization balancing assembly 500 repeats the steps of determining the utilization data, and providing the utilization data for said control of the connections, regularly or irregularly.

[0109] Fig. 4 depicts steps in a method according to an embodiment of the invention, of controlling the battery system described with reference to fig. 1 - fig. 3.

[0110] The method comprises determining SI, for each of the battery assemblies, utilization data indicative of a desired distribution of the utilization of the battery cells, or battery modules. The utilization data comprises prioritization data indicative of a prioritization of one or more of the battery cells, or battery modules, in the respective battery assembly, over one or more of the remaining battery cells, or battery modules, in the respective battery assembly.

[0111] The method further comprises providing S2 the utilization data for a control of the connections of the respective battery cells or battery modules to the respective battery assembly terminals.

[0112] The steps of determining SI and providing S2 utilization data are repeated.

[0113] The method further comprises the measuring assembly 20 determining S3 an actual value indicative of an actual current or voltage at the load terminals 101, 102.

[0114] The method further comprises one of the control assemblies 100, 171, e.g. a main controller 120 thereof, determining S4 a target value indicative of a desired current or voltage at the load terminals. The method further comprises determining S5 an error value, in dependence on the actual value and the target value.

[0115] The method further comprises reviewing S6 the provided utilization data.

[0116] The method further comprises controlling S7 the connections of the respective battery cells, or battery modules, to the respective battery assembly terminals, in dependence on the error value, and in dependence on the utilization data, so as to direct the actual current or voltage at the load terminals 101, 102 towards a desired current or voltage at the load terminals or a respective desired current or voltage at the respective battery assembly terminals.

[0117] The steps of determining S3 the actual value, determining S4 the target value, determining S5 the error value, reviewing S6 the utilization data, and controlling S7 the connections, are repeated more often than the steps of determining SI and providing S2 utilization data. Thereby, if updated utilization data has not been provided after reviewing S6 the utilization data in a cycle for controlling the connections, the previously reviewed utilization data is reviewed again in a following cycle for controlling the connections.

[0118] Preferably, in any given cycle of the battery cell connection control, a single set of utilization data is reviewed. The utilization data set may be replaced by another utilization data set, to be used in one or more further cycles of the battery cell connection control. The utilization data sets may be referred to as prioritization data sets, which may be in the form of priority lists, each indicating priorities of the battery cells, or battery modules, in relation to each other. It should be noted that such priority lists may be adapted to whether the battery assembly is being charged or discharged.

[0119] In some embodiments, the cell utilization control function generates groups of utilization data sets, to be used in a sequence. Thereby, each utilization data set may be valid for a certain time period. Thereby, there could be one specific time period for each utilization data set. A group of utilization data sets to be operated in a sequence can be delivered from the cell utilization control function with a certain repetition rate. The group of utilization data sets may control the utilization of the discrete and analog battery modules during the period of time in which this group of utilization data sets is valid.

[0120] The group of utilization data sets may be updated at a suitable frequency, such as 0.01 - 10 Hz, e.g. depending on how fast the battery modules should switch from bypass state to switch-on state and vice versa.

[0121] As an example, a battery assembly may have a plurality of, e.g. ten, discrete battery modules. The battery assembly may also have an analog battery module. During a time period in which the group of utilization data sets is valid, on average a first subset, e.g. seven, of the discrete battery modules are switched on, Thereby, a second subset, i.e. the remaining, e.g. three, of the discrete battery modules are bypassed. Thereby, the analog battery module may be within its normal operating range. Thereby, the analog battery module is preferably in a higher range of its possible output voltages during the whole time period. For each utilization data set provided for the connection control, the discrete battery modules in the second subset, e.g. three of them, will be bypassed.

[0122] The next utilization data set in the group can be set up to make one discrete battery module to be switched on and another discrete battery module to be bypassed. Thereby, more than two of the battery modules changing state at the same time is preferably avoided.

[0123] In this group of utilization data sets, modules to be used less than average may be sorted together. There might also be a desire to let one discrete battery module rest during the full time period that group of utilization data sets is valid, and let another one be used all the time during the time period.

[0124] The cell utilization control function may in this case generate a group of utilization data sets, e.g. eight of them. The discrete battery modules to be used all the time will be in the top of the priorities of all utilization data sets. The analog battery module will be in the second place in all utilization data sets as this module is also preferably used as much as possible. The discrete battery module for which a rest is desired, will be in bottom of the priorities of all utilization data sets. Each of the remaining discrete battery modules, in this example eight of them, which are to be operated On and Off, may have places in the priority lists of the utilization data sets, which are different from one list to another. The cell utilization control function might have identified two additional discrete battery modules that should be used less than the average ones. The cell utilization control function can thereby sort the eight battery modules in the following way: First six ones with normal usage followed by two with less utilization. By placing them in the first priority lists in this order and by generating a set of eight priority lists in which these eight battery modules have position three to ten, shifted one position at the time downwards and shifting up the one with position ten to position three, there will be a set of eight priority lists. By making the first of the eight priority lists to be valid for a longer time than the other seven lists, it is possible to reduce the utilization of these two modules as compared to the average ones.

[0125] The skilled person realizes that a group of utilization data sets may be generated in a variety of ways, and the example above indicates one possible way.

[0126] Below is an example of a group of utilization data sets, in the form of a group of priority lists, generated by the cell utilization control function. The utilization data sets in the group are arranged so that they each are assigned a respective time interval during which the respective utilization data set is to be in effect. The sum of the time intervals for the utilization data sets is equal to a period 1 / f of a frequency f, which may be predetermined. Thereby, the time intervals may form duty cycles of a pulse width modulation (PWM) of the execution of the utilization data sets.

[0127] For example, the cell utilization control function may arrange a plurality of, for example ten, battery modules PU1-PU10 in a battery assembly in an order, according to which a module for which the highest level of utilization is desired is followed by the other modules with positions according to their mutually decreasing levels of desired utilization. As an example, such an order may be:

[0128] ( PU3, PU9, PU1, PU2, PU10, PU9, PU8, PU6, PU7, PU5 ) The cell utilization control function provides a priority list

[0129] Pl = [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9] where each number indicates a respective of the modules, and the order of the numbers correspond to the order of the modules according to their respective levels of desired utilization.

[0130] The cell utilization control function further provides a module utilization vector U=[ 100, 90, 80, 70, 60, 50, 40, 30, 20, 10] in which each position indicates a time interval, e.g. in ms, during which each of a plurality of, e.g. ten, priority lists P1-P10, including said priority list Pl, is to be in effect, i.e. to be used by the voltage control function to control (S7, fig.4) the connections of the battery modules to the battery assembly terminals. Preferably, the number of priority lists is the same as the number of modules which are put in order according to their respective levels of desired utilization. These priority lists may be provided by permutations of the modules, e.g. as follows, with indications of the time intervals of the module utilization vector U:

[0131] [0, 1,2, 3, 4, 5, 6, 7,8,9] 100 ms [2,0,4, 1, 6, 3, 8, 5, 9, 7] 90 ms [4, 2, 6, 0, 8, 1, 9, 3, 7, 5 ] 70 ms [ 6, 4, 8, 2, 9, 0, 7, 1,5,3] 50 ms

[0132] [ 8, 6, 9, 4, 7, 2, 5, 0, 3, 1 ] 30 ms

[0133] [ 9, 8, 7, 6, 5, 4, 3, 2, 1,0] 10 ms

[0134] [ 7, 9, 5, 8, 3, 6, 1,4, 0,2] 20 ms

[0135] [5, 7, 3, 9, 1,8, 0,6, 2, 4] 40 ms [3,5, 1,7, 0,9, 2, 8, 4, 6] 60 ms [ 1, 3, 0, 5, 2, 7, 4, 9, 6, 8 ] 80 ms

[0136] [0, 1,2, 3, 4, 5, 6, 7,8,9] 100 ms

[0137] The cell utilization control function may further set up the priority lists in an order in which they are to the effective, e.g. as follows: Connected Not connected

[0138] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ] 100 ms

[0139] [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ] 100 ms

[0140] As understood from the description above, the voltage control function determines a number M of the modules, which are put in order according to their respective levels of desired utilization, which are connected. In this example, the number M is eight. Thereby, as indicated with the vertical line in the table above, eight of the modules will be connected at each priority list execution.

[0141] Thereby, by the selection of the module utilization vector U, the modules will be connected according to their respective levels of desired utilization, in this example as follows:

[0142] 0: 100+90+70+50+30 / 10+20 / 40+60+80 ==> on: 520 ms, off: 30 ms

[0143] 1 : 100+90+70+50 / 30+10 / 20+40+60+80 ==> on: 510 ms, off: 40 ms

[0144] 2: 100+90+70+50+30+10 / 20+40 / 60+80 ==> on: 490 ms, off: 60 ms

[0145] 3: 100+90+70 / 50+30 / 10+20+40+60+80 ==> on: 470 ms, off: 80 ms

[0146] 4: 100+90+70+50+30+10+20 / 40+60 / 80 ==> on: 450 ms, off: 100 ms

[0147] 5: 100+90 / 70+50 / 30+10+20+40+60+80 ==> on: 430 ms, off: 120 ms

[0148] 6: 100+90+70+50+30+10+20+40 / 60+80 / ==> on: 410 ms, off: 140 ms

[0149] 7: 100 / 90+70 / 50+30+10+20+40+60+80 ==> on: 390 ms, off: 160 ms

[0150] 8: 100 / 90+70+50+30+10+20+40+60 / 80 ==> on: 370 ms, off: 180 ms

[0151] 9: / 100+90 / 70+50+30+10+20+40+60+80 ==> on: 360 ms, off: 190 ms Fig. 5 illustrates parts of a control system for a battery system according to embodiments of the invention. The control system may include a computer equipped with various modules to manage the battery system's operations. The modules include a processing module 501 for handling data and executing commands. The modules include various specialized modules such as a sending module 510, controlling module 520, determining module 530, and others, which handle specific tasks like sending signals, controlling operations of battery cells or battery modules, and determining settings based on the battery system’s requirements. The modules include an Input / Output module 506 to interact with external commands and data. The control system may ensure that the battery system maintains a target voltage during charging or discharging. For this a computer program 503 may be provided on a carrier 505, which could be an electronic, optical, or radio signal, or a computer-readable medium. The control system may control battery cells or modules of the battery system with signals that determine whether each battery cell or module should be active or be bypassed, influencing their combined contribution to the target voltage. The control system continuously assesses and adjusts the configurations of these modules, by controlling switches of the modules, to ensure the combined voltage from all active modules matches the target voltage, and to ensure a balanced utilization of the cells or modules.

[0152] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

CLAIMS1. A battery system comprising one or more battery assemblies (100, 200, 300), wherein each battery assembly comprises two battery assembly terminals (105, 106), wherein the battery assemblies are via the battery assembly terminals connected to two load terminals (101, 102) of a load and / or a battery charger, wherein each battery assembly comprises a plurality of battery cells (163) connected in series and / or in parallel between the respective battery assembly terminals (105, 106),- wherein the battery system comprises a control system configured to provide a voltage control function which controls, for each battery assembly, connections of the respective battery cells to the respective battery assembly terminals, so as to direct an actual current at the load terminals (101, 102) or a respective actual current at the respective battery assembly terminals (105, 106) towards a desired current at the load terminals (101, 102) or a respective desired current at the respective battery assembly terminals, or so as to direct an actual voltage at the load terminals (101, 102) or a respective actual voltage at the respective battery assembly terminals (105, 106) towards a desired voltage at the load terminals (101, 102) or a respective desired voltage at the respective battery assembly terminals, characterised in that the control system is configured to provide a cell utilization control function which determines, for each of one or more of the battery assemblies, and for said control of the connections of the respective battery cells to the respective battery assembly terminals, utilization data indicative of a desired distribution of the utilization of the battery cells,- wherein the control system is configured such that the cell utilization control function provides the utilization data for the voltage control function,- wherein the control system is configured such that the voltage control function performs said control of the connections of the respective battery cells to the respective battery assembly terminals in dependence on the utilization data.

2. A battery system according to claim 1, wherein the utilization data comprises prioritization data indicative of a prioritization of one or more of the battery cells inthe respective battery assembly, over one or more of the remaining battery cells in the respective battery assembly.

3. A battery system according to any one of the preceding claims, wherein the control system comprises one or more control assemblies (120) configured to provide the voltage control function, and a utilization balancing assembly (500) configured to provide the cell utilization control function.

4. A battery system according to claim 3, wherein the utilization balancing assembly is physically separated from the one or more control assemblies, wherein the utilization balancing assembly is arranged to send the utilization data to the one or more control assemblies.

5. A battery system according to any one of the preceding claims, wherein the cell utilization control function determines the utilization data in dependence of whether the voltage control function will perform said control of the connections in dependence on the utilization data when the battery cells are discharged or charged.

6. A battery system according to any one of the preceding claims, wherein each of the one or more of the battery assemblies, for which the utilization data is provided, comprises a plurality of battery modules connected in series between the respective battery assembly terminals, wherein each battery module comprises one or more of the battery cells, wherein said control of the connections of the respective battery cells to the respective battery assembly terminals comprises determining a number of the battery modules which are to be bypassed, wherein a bypassed battery module does not contribute to the voltage of the respective battery assembly, wherein the cell utilization control function is configured to determine the utilization data so as to be independent of the number of the battery modules which are to be bypassed.

7. A vehicle comprising a battery system according to any one of the preceding claims for the propulsion of the vehicle.

8. A method for controlling a battery system comprising one or more battery assemblies (100, 200, 300), wherein each battery assembly comprises two battery assembly terminals (105, 106), wherein the battery assemblies are via the battery assembly terminals connected to two load terminals (101, 102) of a load and / or a battery charger, wherein each battery assembly comprises a plurality of battery cells (163) connected in series and / or in parallel between the respective battery assembly terminals (105, 106),- wherein the method comprises controlling, for each battery assembly, connections of the respective battery cells to the respective battery assembly terminals, so as to direct an actual current at the load terminals (101, 102) or a respective actual current at the respective battery assembly terminals (105, 106) towards a desired current at the load terminals (101, 102) or a respective desired current at the respective battery assembly terminals, or so as to direct an actual voltage at the load terminals (101, 102) or a respective actual voltage at the respective battery assembly terminals (105, 106) towards a desired voltage at the load terminals (101, 102) or a respective desired voltage at the respective battery assembly terminals, characterised by determining, for each of one or more of the battery assemblies, and for said control of the connections of the respective battery cells to the respective battery assembly terminals, utilization data indicative of a desired distribution of the utilization of the battery cells, providing the utilization data for said control of the connections of the respective battery cells to the respective battery assembly terminals, and performing said control of the connections of the respective battery cells to the respective battery assembly terminals in dependence on the utilization data.

9. A method according to claim 8, wherein the utilization data comprises prioritization data indicative of a prioritization of one or more of the battery cells in the respective battery assembly, over one or more of the remaining battery cells in the respective battery assembly.

10. A method according to any one of claims 8-9, comprising repeating the step of providing the utilization data for said control of the connections of the respective battery cells to the respective battery assembly terminals, wherein the method comprises repetitively comparing the actual current or voltage and the desired current or voltage, and performing said control of the connections in dependence on the comparisons of the actual current or voltage and the desired current or voltage, wherein said comparisons are repeated more often than said step of providing the utilization data for said control of the connections .

11. A method according to claim 10, wherein said repetition of the step of providing the utilization data for said control of the connections is done with a frequency of 0.1-100 Hz, preferably 0.5-50 Hz.

12. A method according to any one of claims 8-11,- wherein the utilization data comprises a plurality of utilization data sets forming a group of utilization data sets,- wherein, at a first point in time during said control of the connections, the connections are controlled in dependence on a first of the utilization data sets,- wherein, at a second point in time during said control of the connections, the connections are controlled in dependence on a second of the utilization data sets.

13. A method according to claim 12, wherein the connections are controlled in dependence on the first utilization data set during a first time period, and the connections are controlled in dependence on the second utilization data set during a second time period, wherein the second time period is longer or shorter than the first time period.

14. A method according to any one of claims 8-13, wherein each of the one or more of the battery assemblies, for which the utilization data is provided, comprises a plurality of battery modules connected in series between the respective battery assembly terminals, wherein each battery module comprises one or more of the battery cells, wherein said control of the connections of the respective battery cellsto the respective battery assembly terminals comprises determining a number of the battery modules which are to be bypassed, wherein a bypassed battery module does not contribute to the voltage of the respective battery assembly, wherein the utilization data is determined so as to be independent of the number of the battery modules which are to be bypassed.

15. A control system configured to perform the steps of any one of claims 7-14.

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