A method for controlling a battery system, a battery system, and a measuring assembly

Abstract

The invention involves a method for controlling a battery system comprising one or more battery assemblies (40, 41), 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 of a load and / or charging system (30, 15), wherein each battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the respective battery assembly terminals (105, 106), the method comprising - receiving or determining an actual value (V(t)) indicative of an actual current or voltage, - receiving or determining a target value (Vref) indicative of a desired current or voltage, - wherein the actual current or voltage and the target current or voltage are currents or voltages at the load terminals or at the battery assembly terminals (105, 106) of one or more of the battery assemblies, - wherein the method further comprises controlling, in dependence on the actual value and the target value, a respective actuation assembly of one or more of the battery assemblies, which actuation assembly is connected between the respective battery terminals and one or more of the battery cells of the respective battery assembly, so as to direct the actual current or voltage towards the desired current or voltage, - wherein the received or determined actual value is in an analog form, and the received or determined target value is in a digital form, - wherein the target value is converted into an analog form, - wherein an error value (e(t)) in an analog form is determined in dependence on the actual value and the converted target value, - wherein the error value is converted into a digital form, - wherein said control of the actuation assembly comprises controlling the actuation assembly in dependence on the converted error value.

Description

[0001] A METHOD FOR CONTROLLING A BATTERY SYSTEM, A BATTERY SYSTEM, AND A MEASURING ASSEMBLY

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method for controlling a battery system, a battery system, and a measuring assembly for a battery system.

[0004] BACKGROUND

[0005] 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 battery assemblies 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.

[0006] For example, W02021094011 Al discloses a method for maintaining a target voltage of a battery assembly during charging or discharging. The battery assembly comprises a first battery module capable of outputting a range of voltages, and a plurality of second battery modules, each of which may be switched-on or bypassed.

[0007] It is desired to keep both flexibility of signal speed in the control for a current or voltage of a battery system at high levels.

[0008] SUMMARY

[0009] An object of the invention is to provide a flexible and fast control for directing an actual current or voltage of a battery system towards a desired current or voltage. The object is reached by 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 charging system, wherein each battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the respective battery assembly terminals, the method comprises the following steps:

[0010] - Receiving or determining an actual value indicative of an actual current or an actual voltage.

[0011] - Receiving or determining a target value indicative of a desired current or a desired voltage.

[0012] The actual current or the actual voltage and the target current or the target voltage, are currents or voltages at the load terminals or at the battery assembly terminals of one or more of the battery assemblies.

[0013] The method further comprises controlling, in dependence on the actual value and the target value, a respective actuation assembly of one or more of the battery assemblies, which actuation assembly is connected between the respective battery terminals and one or more of the battery cells of the respective battery assembly, so as to direct the actual current towards the desired current, or to direct the actual voltage towards the desired voltage.

[0014] The received or determined actual value is in an analog form, and the received or determined target value is in a digital form.

[0015] The target value is converted into an analog form.

[0016] An error value in an analog form is determined in dependence on the actual value and the converted target value.

[0017] The error value is converted into a digital form.

[0018] Said control of the actuation assembly comprises controlling the actuation assembly in dependence on the converted error value.

[0019] Controlling the actuation assembly in dependence on the error value converted into a digital form allows accurate and flexible control steps in a digital environment. Forming the error value in an analog form contributes to avoiding delays entailed by a digital handling of an error value determination, and to thereby keep a fast response with low signal delay. Thereby, the invention allows for a flexible and fast control for directing an actual current or voltage of a battery system towards a desired current or voltage.

[0020] Steps of the method, including the control, in dependence on the actual value and the target value, of the respective actuation assembly of one or more of the battery assemblies, may form a control algorithm. The control algorithm may work at a frequency of 0.1-10 kHz, e.g. around 1 kHz. Thereby, dynamic requirements, e.g. in vehicles, may be fulfilled. The control, in dependence on the actual value and the target value, of the respective actuation assembly, may involve a proportional, integrating, and derivative (PID) control.

[0021] Preferably, converting the error value into a digital form is done by an analog-to-digital converter (ADC) which receives the error value in the analog form, wherein the method comprises establishing an upper limit and a lower limit for the error value in the analog form to be received by the analog-to-digital converter (ADC), and adjusting the upper limit and / or the lower limit. Thereby, the adjustment of the upper limit and / or the lower limit may be done in dependence on a difference between the error value in the analog form and the upper limit or the lower limit.

[0022] The upper limit and the lower limit may form a window for receiving the error value. A relatively small window may reduce noise. However, in some applications, such as in electric or hybrid electric vehicles, time periods of relatively steady control values are alternated with time periods of transients. The adjustable window for receiving the error value allows for an adaption to transient processes.

[0023] In some embodiments the method comprises defining two or more work modes of the battery system, and determining, from the defined work modes, a work mode in which the battery system is operating or is expected to operate, wherein the adjustment of the upper limit and / or the lower limit is done in dependence on the determined work mode.

[0024] Thus, the upper limit and / or the lower limit may be set according to the work mode in which the battery system is operating. For example, one work mode could involve ramping up the voltage of the battery system from zero to a target value, such as when starting the battery system. A further work mode could involve ramping down the voltage to zero. If the battery system is provided in a vehicle, for the propulsion of the vehicle, such as in an electric vehicle, a work mode could be defined as involving loading or charging the battery system under relatively constant conditions. A further work mode could be defined as involving transient conditions, e.g. involving sharp braking or relatively high accelerations. Indications that the battery system is entering such a work mode may be given by a driver of the vehicle demanding a high acceleration or strong braking, or when the vehicle is moving into city traffic. Suitable thresholds could be set to distinguish one work mode from another.

[0025] A central controller, configured to give control instructions to all of the one or more control assemblies, could send to the control assemblies data indicative of a current or expected work mode. Thereby, adjustments of the upper and lower limits for the error value in the analog form to be received by the ADC, may be made upon early indications of a work mode change. Therefore, the adjustments may be made with minimal delays.

[0026] Preferably, the battery system is installed in a vehicle. Thereby, the battery system may be provided in a propulsion system for the vehicle.

[0027] Preferably, the respective actuation assembly comprises a DCDC converter, wherein said control of the actuation assembly comprises controlling the DCDC converter in dependence on the converted error value. In addition, or alternatively, the respective actuation assembly may comprise a plurality of switches, wherein said control of the actuation assembly comprises controlling, in dependence on the converted error value, the switches to selectively connect or disconnect one or more of the battery cells to or from the battery assembly terminals, so as to direct the actual current towards the desired current, or to direct the actual voltage towards the desired voltage.

[0028] The object is also reached with a battery system comprising a battery assembly, wherein the battery assembly comprises two battery assembly terminals, wherein the battery assembly is via the battery assembly terminals connected to two load terminals of a load and / or charging system, wherein the battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the battery assembly terminals.

[0029] The battery system further comprises a control system provided with a configuration to determine an actual value indicative of an actual current or an actual voltage at the load terminals or at the battery assembly terminals. Thereby, the control system is configured to determine the actual value indicative of the actual current or the actual voltage.

[0030] The control system is further provided with a configuration to receive or determine a target value indicative of a desired current or a desired voltage at the load terminals or at the battery assembly terminals. Thereby, the control system is configured to receive or determine the target value indicative of the desired current or the desired voltage.

[0031] The battery assembly comprises an actuation assembly which is connected between the battery terminals and one or more of the battery cells.

[0032] The control system is provided with a configuration to control the actuation assembly, in dependence on the actual value and the target value, so as to direct the actual current towards the desired current, or to direct the actual voltage towards the desired voltage. Thereby, the control system is configured to control the actuation assembly.

[0033] The actual value is, when determined by the control system, in an analog form, and the target value is in a digital form when received or determined by the control system.

[0034] The control system is provided with a configuration to convert the target value into an analog form. Thereby, the control system is configured to convert the target value into an analog form. For this the control system may comprise a digital-to- analog converter (DAC).

[0035] The control system is provided with a configuration to determine an error value in an analog form in dependence on the actual value and the converted target value. Thereby, the control system is configured to determine the error value in an analog form. For this the control system may comprise an error value determination unit. The control system is provided with a configuration to convert the error value into a digital form. Thereby, the control system is configured to convert the error value into a digital form. For this the control system may be provided with an analog-to- digital converter (ADC).

[0036] Said configuration of the control system to control the actuation assembly comprises a configuration to control the actuation assembly in dependence on the converted error value. Thereby, the control system is configured to control the actuation assembly in dependence on the error value which has been converted into a digital form.

[0037] Advantages with the battery system is understood from the description above of the method according to the invention.

[0038] The load and / or charging system may comprise a load and / or a battery charger, which may be variable. The load and / or charging system may comprise an electric motor generator, e.g. of an electric or electric hybrid vehicle. The load and / or charging system may comprise an inverter and / or a rectifier, e.g. for converting DC of the battery system to AC of the electric motor generator, or vice versa. The control system may be configured to determine the actual value indicative of the actual current or the actual voltage at a Delink capacitor at the load terminals.

[0039] Preferably, the control system comprises a measuring assembly provided with said configuration to determine the actual value, and a control assembly provided with said configuration to receive or determine the target value. Thereby, the measuring assembly is configured to determine the actual value, and the control assembly is configured to receive or determine the target value. Thereby, the measuring assembly may be located at a distance from the control assembly. Further, in such embodiments, the measuring assembly is provided with said configuration to convert the target value into an analog form. Thereby, the measuring assembly is configured to convert the target value into an analog form. Further, in such embodiments, the measuring assembly is provided with said configuration to determine the error value in an analog form, Thereby, the measuring assembly is configured to determine the error value in an analog form. Further, in such embodiments, the measuring assembly is provided with a configuration to send the determined the error value in an analog form to the control assembly. Thereby, the measuring assembly is configured to send the determined the error value in an analog form to the control assembly.

[0040] Thus, the measuring assembly is located at a distance from the control assembly. For example, the measuring assembly may be located at a DC-link capacitor at the load terminals. The measuring assembly may comprise a voltage meter with an analog output, for measuring the voltage across the DC-link capacitor. The control assembly may be located at or in the battery assembly.

[0041] Preferably, the control assembly is provided with said configuration to convert the error value into a digital form, and the control assembly is provided with said configuration to control the actuation assembly in dependence on the converted error value. Thereby, the control assembly is configured to convert the error value into a digital form, and the control assembly is configured to control the actuation assembly in dependence on the converted error value.

[0042] In such embodiments, the measuring assembly is provided with said configuration to convert the target value into an analog form. Thereby, the measuring assembly is configured to convert the target value into an analog form. For this, the measuring assembly may be configured to receive the target value in the digital form. The target value in the digital form may be transferred to the measuring assembly via a data bus. Such a transfer of a signal in a digital form is usually more robust than a transfer in an analog form. The measuring assembly may comprise a digital-to-analog (DA) converter for the conversion of the target value into the analog form. Further, the measuring assembly may be configured to make an analog calculation of the error voltage. Where the measuring assembly is located at a distance from the control assembly, signals between the assemblies could be affected by interference, such as electromagnetic interference, which may be present e.g. in a vehicle. There may also be disturbances caused by voltage ripple, such as those caused by an inverter that controls the electric motor in a vehicle, or induced by a DC-DC converter in an electric vehicle charging station. The error voltage can be amplified to an appropriate signal level before being sent to the control assembly. If the analog measurement value sent from the measuring assembly to the control assembly contains the error voltage only, rather than the measured voltage, the noise in relation to the error value will be reduced. The reason is that the noise level is proportional to the amplitude of the analog signal. If the signal represents the measured voltage, the noise will be relatively large in relation to the error value. Thus, if the error value, rather than the measured voltage, is sent, the influence of signal interference on the error value, on the way to the control assembly, can be reduced. Thereby, the signal -to-noise ratio is increased.

[0043] The control assembly may comprise an AD converter configured to receive the error value in the analog form. The AD converter may be provided with the configuration to convert the error value into a digital form. Thereby, the AD converter is configured to convert the error value into a digital form. The control assembly may be configured with an upper limit and a lower limit for the error value in the analog form. The control assembly may be configured to adjust the upper limit and / or the lower limit in dependence on a difference between the error value in the analog form and the upper limit or the lower limit.

[0044] However, in some embodiments, the measuring assembly is located close to, or is integrated with, the control assembly. Thereby, the measuring assembly may be configured to determine the actual current or the actual voltage at the battery assembly terminals.

[0045] In specific embodiments, the DA converter for the target value may be a 12-bit DA converter. Thereby, the target value of the DC-link voltage can be set with a resolution of about IV or better. For a battery with a system voltage of about 800-1200V, this is fully sufficient. The analog error value may be sampled by, for example, + / -10V. For AD converting the error value, a 16-bit AD converter may be used. Thereby, a resolution of the error value in the range of about 0.3 mV may be obtained. Even if the measurement range is extended to + / - 30V, the resolution of the error value may be better than 1 mV. The AD converter for the error value may be a so-called Sigma Delta ADC. Sigma Delta ADCs may have a relatively large quantization noise. However, preferably the Sigma Delta ADC is configured to filter out a large part of this quantization noise through oversampling. Thereby, the ADC may have low noise and an effective resolution For example, the digital representsion of the error value may be 10-12 bits or similar after filtering. Thereby, an effective resolution of approximately 15-60 mV with an error range of + / -30V may be obtained. A high voltage battery system for vehicle usage, can have a low internal impedance, typical in the range of 50 mohm to 100 mohm. Thereby, a PID controller can be implemented with a low noise output for the battery reference current.

[0046] The object is also reached with a measuring assembly for a battery system comprising a battery assembly, wherein the battery assembly comprises two battery assembly terminals, wherein the battery assembly is via the battery assembly terminals connected to two load terminals of a load and / or charging system, wherein the battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the battery assembly terminals, wherein the battery assembly comprises an actuation assembly which is connected between the battery terminals and one or more of the battery cells,

[0047] - wherein the measuring assembly is provided with a configuration to determine an actual value in an analog form, indicative of an actual current or an actual voltage at the load terminals or at the battery assembly terminals,

[0048] - wherein the measuring assembly is further provided with a configuration to receive a target value in a digital form, indicative of a desired current or a desired voltage at the load terminals or at the battery assembly terminals,

[0049] - wherein the measuring assembly is provided with a configuration to convert the target value into an analog form,

[0050] - wherein the measuring assembly is provided with a configuration to determine an error value in an analog form in dependence on the actual value and the converted target value,

[0051] - wherein the measuring assembly is provided with a configuration to send the determined the error value in an analog form to a control assembly for converting the error value into a digital form and controlling the actuation assembly in dependence on the converted error value, so as to direct the actual current towards the desired current, or to direct the actual voltage towards the desired voltage.

[0052] Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Below, embodiments of the invention will be described with reference to the drawings, in which:

[0054] - fig. 1 shows components of a battery system,

[0055] - fig. 2 and fig. 3 show components of a battery assembly in the battery system in fig. 1,

[0056] - fig. 4 shows control loops for currents and voltages in the battery system in fig. 1,

[0057] - fig. 5 is a flow diagram depicting steps in a method according to an embodiment of the invention,

[0058] - fig. 6 is a diagram showing a control error value as a function of time, and

[0059] - fig. 7 shows control loops for currents and voltages in a battery system according to an alternative embodiment of the invention.

[0060] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0061] Fig. 1 shows a battery system with a plurality of parallel battery assemblies 40, 41. The battery assemblies 40, 41 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 40, 41 are connectable to a load and / or charging system which comprises a common load or charging circuit 30. More specifically, the load and / or charging system comprises direct current (DC) voltage bus 15, and the battery assemblies are connected to load terminals 301, 302 of the 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.

[0062] A measuring assembly 20 is connected to the DC voltage bus 15. The measuring assembly 20 is arranged to measure the DC bus voltage or the DC bus current. A DC link capacitor 50 is also connected to the load or charger 30. Each battery assembly 40, 41 comprises a control assembly comprising a main controller 10, 11. As exemplified further below, each control assembly is arranged to determine for the battery assemblies 40, 41 target values indicative of currents or voltages at battery assembly terminals of the battery assemblies 40, 41, and each control assembly is arranged to receive the information from the measuring assembly 20.

[0063] Fig. 2 shows one of the battery assemblies in fig. 1. The battery assembly 40 comprises two battery assembly terminals 105, 106, and a plurality of switched battery modules 170. The battery assembly comprises an actuation assembly exemplified below.

[0064] 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 10 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 40 so it is close to a target voltage.

[0065] 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. Each of the switched battery modules 170 may comprise sets 163 of two or more battery cells connected in series to output conduits 170C of the respective battery module 170. The battery cells of each battery module 170 may be 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.

[0066] The switches of the switched battery modules 170 are arranged to be controlled by the control assembly, in dependence on the target value indicative of the desired current or voltage at the battery assembly terminals 105, 106. Thereby, the switches 175, 176 may be controlled so that none, one, or more, of the switched battery modules 170 are by-passed. Thereby, by selecting a number of battery cells to the bypassed, an actual current or voltage at the battery assembly terminals 105, 106 can be directed towards the desired current or voltage. For this , each control assembly may comprise a local controller 171. The local controllers 171 are arranged to communicate with each other, and with the main controller 10. Further, each local controller 171 is configured to control the HS and LS switches 176, 175 of the respective battery module 170. Thereby, the switches 175, 176 may be controlled so that none, one, or more, of the battery modules are by-passed.

[0067] Reference is made to fig. 4 showing control loops for currents and voltages in the battery system in fig. 1. Reference is made also to fig. 5 depicting steps in a method according to an embodiment of the invention.

[0068] The method comprises the measuring assembly 20 determining SI an actual value V(t) indicative of an actual current or voltage at the load terminals 301, 302. The determined actual value is in an analog form.

[0069] The method further comprises one of the control assemblies 10, 171, e.g. a main controller 10 thereof, determining S2 a target value Vref indicative of a desired current or voltage at the load terminals. The determined target value is in a digital form. The target value Vref may be determined by a digital portion 101 of the control assembly 10, 171. The digital portion may be a computer with a processor.

[0070] The target value Vref is sent to respective digital-to-analog converters (DAC) of the control assemblies 10, 171, 11, 172, e.g. of main controllers 10, 11 thereof. The target value Vref is converted S3 to an analog form by the digital-to-analog converters (DAC). In alternative embodiments the target value Vref is converted to an analog form by a single DAC. The DAC could thereby be provided in one of the control assemblies 10, 171, 11, 172. Thereby, the converted target value in analog form may be sent to the other control assembly(ies). Alternatively, the DAC could be provided in in a central control unit configured to perform control actions for all battery assembles. Thereby, the converted target value may be sent to the control assemblies 10, 171, 11, 172.

[0071] The method further comprises determining S4 an error value e(t) in an analog form, in dependence on the actual value V(t) and the converted target value Vref. In the example in fig. 4, each control assembly 10, 171, 11, 172, e.g. a main controller 10, 11 thereof, performs their respective determinations of error values e(t). In alternative embodiments the error value is determined by one of the control assemblies. Thereby, the error value may be sent to the other control assembly(ies). Alternatively, the error value is determined by a central control unit configured to perform control actions for all battery assembles. Thereby, the error value may be sent to the control assemblies 10, 171,11, 172.

[0072] The method further comprises converting S5 the error value e(t) into a digital form, by means of an analog-to-digital converter (ADC). As detailed below with reference to fig. 6, limits for the signals received by the ADC can be adjusted.

[0073] The method further comprises controlling S6 the respective actuation assemblies in the battery assemblies 40, 41 in dependence on the converted error value e(t), so as to direct the actual current or voltage towards the desired current or voltage. For this, each control assembly 10, 171,11, 172, e.g. a main controller 10, 11 thereof, has a proportional, integral, and derivative (PID) control unit. The PID control unit determines, in dependence on the error value e(t) a value of a total control current to be produced by the battery assemblies 40, 41 to direct the actual current or voltage towards the desired current or voltage. Each control assembly 10, 171, 11, 172, e.g. a main controller 10, 11 thereof, comprises a distribution factor unit which determines a respective local control current value Imref, Isref in dependence on the total control current value and a respective distribution factor K2, K3. The local control current value is converted to an analog form by a digital-to-analog converter (DAC). A respective current measuring unit determines a respective actual current Im(t), Is(t) at the terminals of the respective battery assembly 40, 41. A respective current error is determined in dependence on the respective local control current value Imref, Isref and the respective actual current Im(t), Is(t). A respective control unit, e.g. in a respective local controller 171, 172 as exemplified above with reference to fig. 3, determines a respective current adjustment control value in dependence on the respective current error. The control unit could be proportional (P) control unit, a proportional and integral (PI) control unit (as indicated in fig. 4), or a proportional, integral, and derivative (PID) control unit. The current at the terminals of the respective battery assembly 40, 41 is adjusted in dependence on the respective current adjustment control value, e.g. by means of a DCDC converter 177 as exemplified above with reference to fig. 3.

[0074] In alternative embodiments, the value of a total control current to be produced by the battery packs 40, 41 may be determined by one of the control assemblies 10, 171, 11, 172. Thereby, the total control current value could be sent to the remaining control assembly(ies). Alternatively, the value of a total control current may be determined by a central control unit configured to perform control actions for all battery assembles. Thereby, the total control current value could be sent to the control assemblies 10, 171, 11, 172. Thereby, each control assembly 10, 171, 11, 172 may determine the respective local control current value Imref, Isref in dependence on the total control current value and the respective distribution factor K2, K3.

[0075] Reference is made also to fig. 6. For the conversion of the error value e(t) into a digital form, an upper limit eU and a lower limit eL for the error value to be received by the analog-to-digital converter (ADC) are established. Since the error value may be positive or negative, the upper limit is positive and the lower limit is negative.

[0076] The upper and lower limits eU, eL are adjusted in dependence on a difference between the error value e(t) and the upper limit eU or the lower limit eL. In the example in fig. 6, if the difference between the error value e(t) and the upper limit eU or the lower limit eL is below a first threshold value deTl, the upper and lower limits eU, eL are adjusted. In the example in fig. 6, the upper and lower limits eU, eL are adjusted so as to increase the difference between the upper and lower limits. In some examples, only one of the upper and lower limits eU, eL may be adjusted.

[0077] As exemplified in fig. 6, if, after the increase of the difference between the upper and lower limits, the difference between the error value e(t) and the upper limit eU, and the difference between the error value e(t) and the lower limit eL, are above a second threshold value deT2, the upper and lower limits eU, eL are adjusted so as to decrease the difference between the upper and lower limits.

[0078] In some embodiments, threshold values for the difference between the error value and the upper and lower limits may be combined with time intervals. For example, there may be a condition that the difference between the error value and the upper and lower limits has to be above the second threshold value deT2 for a minimum time period, in order for the difference between the upper and lower limits to be decreased. Thereby, a hysteresis for the control of the upper and lower limits may be provided. Thereby, frequent changes of the upper and lower limits may be avoided.

[0079] The upper and lower limits eU, eL may define a measuring interval for the ADC. The upper and lower limits eU, eL may be set by a control instruction KI (fig. 4) determined by the respective control assembly 10, 171, 11, 172.

[0080] The voltage error determination function may be embodied with a unit having a differential input. Thereby, the target value may go to one of the inputs and the actual value may go to the other input. For controlling the upper and lower limits eU, eL of the error value, the unit may have a variable gain function, and an ADC with a controllable sampling frequency. The unit may also have suitable digital filters which can be controlled by software.

[0081] Reference is made to fig. 7 showing control loops in a battery system according to an alternative embodiment of the invention. In fig. 7, only one battery assembly 40 is shown, although as exemplified in fig. 4 there could be more than one battery assembly in the battery system. A method according to a further embodiment of the invention is similar to the one described above with reference to fig. 4 - fig. 6, but differs as understood in the following description with reference to fig. 7.

[0082] The measuring assembly 20 determines, by use of a voltage meter 201, an actual value V(t) indicative of an actual current or voltage at the load terminals 301, 302. The determined actual value is in an analog form. The control assembly 10, 171 determines a target value Vref indicative of a desired current or voltage at the load terminals. The determined target value is in a digital form. The determined target value is sent to the measuring assembly 20. The measuring assembly 20 receives the digital target value. The measuring assembly 20 converts the target value into an analog form by means of a digital- to-analog converter (DAC). The measuring assembly 20 determines an error value e(t) in an analog form, in dependence on the actual value and the converted target value. The measuring assembly 20 sends the analog error value to the control assembly 10. The control assembly 10, 171 converts the error value into a digital form.

[0083] The method further comprises controlling the actuation assembly in the battery assembly 40 in dependence on the converted error value e(t), so as to direct the actual current or voltage towards the desired current or voltage. This control may be similar to the one described with reference to fig. 4 and fig. 5.

[0084] Embodiments of the invention comprise measuring the actual value indicative of the actual current or voltage at the load terminals, wherein the error value in an analog form. The error may be sampled with an ADC, at a frequency between 1-20 MHz, preferably 2-10 MHz, for example around 5 MHz. The error value converted into a digital form may be filtered and / or down-sampled, whereupon the ADC provides values of the error with a frequency of 10-200 kHz, preferably 20-100 kHz. After possible further digital filtering the error values may be sent to a digital control portion of the respective control assembly of the respective battery assembly, a frequency of 2-32 kHz, preferably 4-16 kHz, e.g. 8 kHz. Based on the error values, the digital control portion may determine current setpoints, herein also referred to as local control current values Imref, Isref, at a frequency of 250- 4000 Hz, preferably 500-2000 Hz, e.g. around 1 kHz. The current setpoints may be sent to a DAC, and to an analog control portion of the respective control assembly. The analog control portion may be arranged to control a DC-DC converter of the respective actuation assembly.

[0085] Based on the current setpoints and current measurements at the respective battery assembly terminals, the analog control portion controls the DC-DC converter so as to direct the current at the battery assembly terminals towards the current setpoints. Thereby, the control assemblies of the battery assemblies each contribute to directing the actual current or voltage at the load terminals towards the desired current or voltage. Thus, it is understood that the control by the respective control assembly of the respective actuation assembly so as to direct the actual current or voltage at the load terminals 301, 302 towards the desired current or voltage at the load terminals 301, 302 may comprise a control of the respective actuation assembly so as to direct an actual current or voltage at the respective battery assembly terminals 105, 106 towards a desired current or voltage at the respective battery assembly terminals 105, 106.

[0086] Embodiments of the invention provide an efficient reduction of noise in the error signal and filters out unwanted disturbances on the error signal, which noise and disturbances may be caused by other controllers or inverters that act on the load terminals. Thereby, a quick response as well as good stability in the output signal, i.e. the current setpoints, is achieved.

[0087] 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 method for controlling a battery system comprising one or more battery assemblies (40, 41), 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 of a load and / or charging system (30, 15), wherein each battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the respective battery assembly terminals (105, 106), the method comprising receiving or determining an actual value (V(t)) indicative of an actual current or an actual voltage, receiving or determining a target value (Vref) indicative of a desired current or a desired voltage,- wherein the actual current or the actual voltage, and the target current or the target voltage, are currents or voltages at the load terminals or at the battery assembly terminals (105, 106) of one or more of the battery assemblies,- wherein the method further comprises controlling, in dependence on the actual value and the target value, a respective actuation assembly of one or more of the battery assemblies, which actuation assembly is connected between the respective battery terminals and one or more of the battery cells of the respective battery assembly, so as to direct the actual current towards the desired current, or to direct the actual voltage towards the desired voltage, characterized in that- the received or determined actual value is in an analog form, and the received or determined target value is in a digital form,- wherein the target value is converted into an analog form,- wherein an error value (e(t)) in an analog form is determined in dependence on the actual value and the converted target value,- wherein the error value is converted into a digital form,- wherein said control of the actuation assembly comprises controlling the actuation assembly in dependence on the converted error value.

2. A method according to claim 1, wherein converting the error value into a digital form is done by an analog-to-digital converter (ADC) which receives the error value in the analog form, wherein the method comprises establishing an upper limit (eU) and a lower limit (eL) for the error value in the analog form to be received by the ADC, and adjusting the upper limit and / or the lower limit.

3. A method according to claim 2, wherein the adjustment of the upper limit and / or the lower limit is done in dependence on a difference (deTl, deT2) between the error value in the analog form and the upper limit or the lower limit.

4. A method according to any one of claims 2-3, comprising defining two or more work modes of the battery system, and determining, from the defined work modes, a work mode in which the battery system is operating or is expected to operate, wherein the adjustment of the upper limit and / or the lower limit is done in dependence on the determined work mode.

5. A method according to any one of the preceding claims, wherein the battery system is installed in a vehicle.

6. A method according to any one of the preceding claims, wherein the respective actuation assembly comprises a DCDC converter, wherein said control of the actuation assembly comprises controlling the DCDC converter in dependence on the converted error value.

7. A method according to any one of the preceding claims, wherein the respective actuation assembly comprises a plurality of switches, wherein said control of the actuation assembly comprises controlling, in dependence on the converted error value, the switches to selectively connect or disconnect one or more of the battery cells to or from the battery assembly terminals (105, 106).

8. A battery system comprising a battery assembly (40, 41), wherein the battery assembly comprises two battery assembly terminals (105, 106), wherein the batteryassembly is via the battery assembly terminals connected to two load terminals of a load and / or charging system, wherein the battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the battery assembly terminals (105, 106), the battery system further comprising a control system provided with a configuration to determine an actual value indicative of an actual current or an actual voltage at the load terminals or at the battery assembly terminals (105, 106),- wherein the control system is further provided with a configuration to receive or determine a target value indicative of a desired current or a desired voltage at the load terminals or at the battery assembly terminals (105, 106),- wherein the battery assembly comprises an actuation assembly which is connected between the battery terminals and one or more of the battery cells,- wherein the control system is provided with a configuration to control the actuation assembly, in dependence on the actual value and the target value, so as to direct the actual current towards the desired current, or to direct the actual voltage towards the desired voltage, characterized in that- the actual value is, when determined by the control system, in an analog form, and the target value is in a digital form when received or determined by the control system,- wherein the control system is provided with a configuration to convert the target value into an analog form,- wherein the control system is provided with a configuration to determine an error value in an analog form in dependence on the actual value and the converted target value,- wherein the control system is provided with a configuration to convert the error value into a digital form,- wherein said configuration of the control system to control the actuation assembly comprises a configuration to control the actuation assembly in dependence on the converted error value.

9. A battery system according to claim 7, wherein the control system comprises a measuring assembly (20) provided with said configuration to determine the actual value, and a control assembly (10, 171, 11, 172) provided with said configuration to receive or determine the target value,- wherein the measuring assembly is located at a distance from the control assembly,- wherein the measuring assembly is provided with said configuration to convert the target value into an analog form,- wherein the measuring assembly is provided with said configuration to determine the error value in an analog form,- wherein the measuring assembly is provided with a configuration to send the determined the error value in an analog form to the control assembly.

10. A battery system according to claim 8, wherein the control assembly is provided with said configuration to convert the error value into a digital form, and wherein the control assembly is provided with said configuration to control the actuation assembly in dependence on the converted error value.

11. A measuring assembly for a battery system comprising a battery assembly (40, 41), wherein the battery assembly comprises two battery assembly terminals (105, 106), wherein the battery assembly is via the battery assembly terminals connected to two load terminals of a load and / or charging system, wherein the battery assembly comprises a plurality of battery cells connected in series and / or in parallel between the battery assembly terminals (105, 106), wherein the battery assembly comprises an actuation assembly which is connected between the battery terminals and one or more of the battery cells,- wherein the measuring assembly is provided with a configuration to determine an actual value in an analog form, indicative of an actual current or an actual voltage at the load terminals or at the battery assembly terminals (105, 106), characterized in that- the measuring assembly is further provided with a configuration to receive a target value in a digital form, indicative of a desired current or a desired voltage at the load terminals or at the battery assembly terminals (105, 106),- wherein the measuring assembly is provided with a configuration to convert the target value into an analog form,- wherein the measuring assembly is provided with a configuration to determine an error value in an analog form in dependence on the actual value and the converted target value,- wherein the measuring assembly is provided with a configuration to send the determined the error value in an analog form to a control assembly for converting the error value into a digital form and controlling the actuation assembly in dependence on the converted error value, so as to direct the actual current towards the desired current, or to direct the actual voltage towards the desired voltage.

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