Battery and method for controlling a battery voltage by pulse-width modulated signals

Abstract

A battery comprising a plurality of battery cells (11) configured to be connected to or bridged by a battery string (13) by controlling coupling circuits (12), wherein the battery comprises control means (15) for controlling the coupling circuits (12) by control signals, characterized in that the control means (15) are configured to control the coupling circuits (12) by means of pulse-width-modulated signals (14, PWM1, PWM2) and to process a specification of a pulse-width-modulated signal (PWM1) by means of weighting circuits (21) assigned to the battery cells (11) in order to generate weighted pulse-width-modulated signals (PWM2), so that an average switch-on time of a respective battery cell (11) is determined by the duty cycle of a respective weighted pulse-width-modulated signal (PWM2).wherein the coupling circuits (12) each comprise semiconductor switches, in particular arranged in a half-bridge configuration (19) or full-bridge configuration, as well as a driver circuit (20), and the weighting circuits (21) are each implemented by microcontrollers (16) belonging to the battery cell and connected to the measuring and evaluation electronics and the central control unit, in particular via a communication bus, each comprising a memory with instructions for implementing a weighting function (W(x)).

Description

[0001] The present invention relates to a battery comprising a plurality of battery cells configured to be connected to or bridged by a battery string by controlling coupling circuits. The battery comprises control means for controlling the coupling circuits by control signals. Furthermore, the invention relates to a method for regulating a battery voltage of a battery. State of the art

[0002] It is becoming apparent that battery systems will increasingly be used in the future, both in stationary applications and in vehicles such as hybrid and electric vehicles. To meet the voltage and available power requirements of a specific application, a large number of battery cells are connected in series, forming a battery string that provides a battery voltage. To achieve a high battery current, additional battery cells are often connected in parallel.

[0003] Previous applications by the applicant described batteries comprising a battery string with a variable or adjustable battery voltage. This was achieved by activating a specific number of battery cells or battery modules so that their total voltage corresponds to a desired target value for a battery voltage, with the other, unused battery cells being deactivated or bypassed. According to the prior art, coupling circuits of the battery cells are controlled by microcontrollers, with the microcontrollers typically communicating with a central control unit via galvanic isolation. The coupling circuits can be implemented by semiconductor switches, in particular MOSFET transistors, and a respective associated driver circuit. The semiconductor switches can be arranged in a half-bridge configuration or a full-bridge configuration.Furthermore, each of the coupling circuits can be designed to switch a single battery cell or a battery module with multiple battery cells. A central control unit must communicate to each coupling circuit via a communication interface or a signal transmission connection (communication bus) whether the battery cell or battery module should be connected or bypassed, or which transistor should be switched on and which not.

[0004] Document DE 10 2010 041 036 A1 discloses a method for operating a controllable energy storage device, which is used to control and supply electrical energy to an n-phase electrical machine. The controllable energy storage device has n parallel energy supply branches, each of which has at least two series-connected energy storage modules, each of which comprises at least one electrical energy storage cell with an associated controllable coupling unit. Depending on control signals, the coupling units either bridge the associated energy storage cells or connect the associated energy storage cells to the energy supply branch.

[0005] Document EP 0 907 238 A1 discloses a pulse-width modulation power converter for variable speed control of a three-phase AC motor. The power converter also includes control circuits for controlling the power converters.

[0006] Document DE 10 2010 064 311 A1 discloses a controllable energy storage device with n parallel power supply branches. Depending on control signals, the coupling units bridge the respective energy storage cells or switch the respective energy storage cells into the respective power supply branch.

[0007] A disadvantage, however, is the high communication overhead required, which becomes particularly significant when the number of battery modules or battery cells connected by a coupling unit is reduced in order to achieve fine voltage gradations. The high communication overhead is primarily due to the requirement that, in order to maintain a sufficiently robust and efficient battery system, the battery cells or battery modules generally have to be addressed and switched in real time. Disclosure of the invention

[0008] According to the invention, a battery with a plurality of battery cells is provided, wherein the battery cells are configured to be selectively connected to or bridged within a battery string by controlling coupling circuits. The battery has control means for controlling the coupling circuits by control signals, wherein the control means are configured to control the coupling circuits by means of pulse-width-modulated signals. To generate weighted pulse-width-modulated signals, a preset pulse-width-modulated signal is processed by weighting circuits assigned to the battery cells in such a way that an average switch-on time of a respective battery cell is determined by the duty cycle of a weighted pulse-width-modulated signal.

[0009] Furthermore, a method for regulating the battery voltage of a battery with multiple battery cells is provided, in which coupling circuits are controlled by means of pulse-width-modulated signals, each using individually adapted weightings for the duty cycle of a pulse-width-modulated signal. The average on-time of each battery cell is determined by the duty cycle of a weighted pulse-width-modulated signal, and the battery cells are connected to the battery string on average in such a way that the battery voltage is set to a desired target voltage.

[0010] One advantage of the invention is a drastic reduction in communication overhead, since all coupling units can be controlled using a single pulse-width-modulated signal. At the same time, the invention allows for high battery scalability, since the weighting circuits allow for a largely autonomous control function to be implemented for each battery cell. By determining the average on-time of each battery cell by the duty cycle of a pulse-width-modulated signal, simple, centralized control of the battery voltage is initially possible.Furthermore, the two-stage control according to the invention, in which a specification is initially made centrally and then weighting is carried out locally, also allows, for example, balancing control, depending on the arrangement of the weighting circuit, to be carried out directly at or on the battery cells, without having to specify or control the balancing for each battery cell individually via a central control unit. This makes it possible to set an overall battery voltage without all cell voltages having to be transmitted to a central control unit and / or evaluated there to decide which battery cells should be added to the battery string and which should be bypassed.

[0011] Preferably, a weighting circuit is provided for each battery cell of the battery. This allows for particularly high scalability of the battery while simultaneously allowing particularly fine gradations of the adjustable battery voltage. In other embodiments, the weighting circuit is provided for each battery module.

[0012] According to an advantageous embodiment of the invention, the weighting circuits are each configured to adapt the specification for a pulse-width modulated signal based on operating parameters of the battery and / or based on operating parameters of individual battery cells.

[0013] This ensures reliable regulation of a battery voltage that can be adapted to a specific situation.

[0014] Furthermore, the battery preferably has a central control unit which is configured to generate the specification for the pulse-width modulated signal based on a comparison of a battery voltage generated by the battery with a predetermined target voltage.

[0015] This enables functional regulation of the battery voltage regardless of the battery cell charge level. This is achieved in particular by the central control unit generating a different pulse-width-modulated signal with a lower duty cycle to connect the cells, for example, in the case of a higher average cell charge level.

[0016] According to one embodiment of the invention, the battery has a signal transmission connection which is configured to transmit the generated specification directly as a predetermined pulse-width modulated signal to the weighting circuits.

[0017] Alternatively, it is possible for the signal transmission connection to transmit analog or digital information about the predetermined pulse-width modulated signal to the weighting circuits. Thus, according to a preferred embodiment, the signal transmission connection is designed as a communication bus for transmitting a digital signal.

[0018] Furthermore, the battery is preferably equipped with measurement and evaluation electronics for determining current values ​​of the operating parameters used to adjust the pulse-modulated signal by the weighting circuits. The more operating parameters are currently being determined, the more selectively the weighting function can be used.

[0019] Furthermore, it is preferred that the measured values ​​be transferred from the measurement and evaluation electronics to the weighting circuit for processing. This direct method of transmitting measured values ​​further reduces communication overhead, for example, the communication overhead between the battery cells or coupling units and a central control unit.

[0020] In another particular embodiment, at least parts of the measuring and evaluation electronics are arranged directly near or on the battery cells.

[0021] According to a particularly advantageous development of the invention, the measuring and evaluation electronics has means for determining values ​​for a state of charge, a service life, and / or a calculated quality factor, which can be present for individual battery cells, as an average value for all battery cells, and / or as a distribution across all battery cells.

[0022] Furthermore, it is preferred that the instantaneous current direction of a battery current is also determined and reported to the weighting circuit. This allows, when calculating the weighting function, a balancing specification can be adequately taken into account in each battery state, without this specification having to be communicated by a central control unit. Therefore, the weightings are calculated, in particular, from a weighting function that incorporates a charge state, in particular a charge state of a respective battery cell to be switched, a current direction of a battery current, and / or other operating parameters of the battery.

[0023] According to a particularly advantageous procedure of the method according to the invention, it can be provided that it is first determined for each battery cell whether the battery cell is in a low state of charge or a high state of charge. If the battery cell is in a low state of charge, a predetermined duty cycle for the pulse-width modulated signal is reduced if the battery cell is discharging. This is preferably done in such a way that the battery cell is clocked less intensively. In contrast, if the battery cell is charging, the duty cycle is increased accordingly. On the other hand, if the battery cell is in a high state of charge, the duty cycle is increased if the battery cell is discharging, so that the battery cell is clocked more intensively. Conversely, if the battery cell has a high state of charge, the duty cycle is reduced if the battery cell is charging.

[0024] The coupling circuits according to the invention are preferably implemented using an arrangement of semiconductor switches. A half-bridge configuration of semiconductor switches is preferably used. However, the invention is not limited to a specific type of coupling circuit. Thus, a coupling circuit can also be designed as a full-bridge configuration of semiconductor switches.

[0025] According to another advantageous embodiment, the weighting circuits are each implemented by microcontrollers that are internal to the battery cell and connected to the measurement and evaluation electronics and the central control unit. By coupling the measurement and evaluation electronics and the central control unit to a microcontroller, the battery cell can process the pulse-width-modulated signal in a particularly powerful and autonomous manner, and the accuracy and scalability of the battery are further improved. Thus, changes in the boundary conditions for a battery or battery system can be taken into account with correspondingly different programming of the microcontroller. In particular, the microcontroller according to the invention can preferably also comprise a memory with instructions for implementing the weighting function.

[0026] According to one aspect of the invention, a motor vehicle with an electric motor is also provided, which has the battery according to the invention, wherein the battery is connected to a drive train of the electric motor.

[0027] The battery according to the invention is preferably a lithium-ion battery.

[0028] Advantageous further developments of the invention are specified in the subclaims and described in the description. Drawings

[0029] Embodiments of the invention are explained in more detail with reference to the drawings and the following description. They show: Fig. 1 a battery system with a battery string of connectable and bridgeable battery cells, each equipped with a controllable coupling circuit and capable of being controlled by a pulse width modulator, according to a first embodiment of the invention, Fig. 2 a block diagram of the principle of the inventive weighting of a pulse width modulated signal which is used for controlling a coupling circuit, according to a second embodiment of the invention, Fig. 3 a block diagram of a weighting of a pulse width modulated signal according to a third embodiment of the invention, wherein, in contrast to Fig. 2 additional values ​​of an average lifetime state and an average state of charge are included, and Fig. 4 is a block diagram of a weighting of a pulse width modulated signal according to a fourth embodiment of the invention, wherein, in contrast to Fig. 3 Furthermore, distributions of the state of charge and the lifetime state as well as a quality factor are taken into account. Embodiments of the invention

[0030] In the Fig. 1 shows a battery system 10 according to a first embodiment of the invention, comprising a battery string 13 with a series circuit of several battery cells 11, each of which can be selectively connected and bridged by a coupling circuit 12. For the sake of clarity, only one of the battery cells 11 with the associated coupling circuit 12 is explicitly shown in the drawing. The coupling circuit 12 has a semiconductor circuit with semiconductor switches arranged in a half-bridge configuration 19. The semiconductor switches are, for example, MOSFETs, which are operated by a driver circuit 20 associated with the coupling circuit 12.

[0031] As from the Fig. 1, depending on the switching position of the half-bridge configuration, the battery cell 11 can be either in a switched-on state, i.e., connected state, in which the battery cell 11 contributes to a battery voltage of the battery string 13, or in a bridged state, in which at least one side of the battery cell 11 is decoupled from the battery string 13. The coupling circuits 12 of the battery cells 11 can be used to set a desired battery voltage, depending on how many battery cells 11 are simultaneously connected to the battery string. The driver circuit 20 for operating the half-bridge configuration 19 is controlled by the control means 15 according to the invention with pulse-width modulated signals 14. The control means 15 implement a weighting function, which here is essentially in the form of commands in the microcontroller 16, which is connected to the driver circuit 20.The microcontroller is connected via an isolator 17 to a signal transmission link 18, which is implemented here as a communication bus. The signal transmission link 18 transmits a pulse-width modulated signal 14 originating from a central control unit (not shown), which serves as a specification and starting point for a weighting that is individually and situationally tailored to the individual battery cell 11.

[0032] The central control unit (not shown) generates the specification for the pulse-width modulated signal 14 based on a comparison of a battery voltage generated by the battery with a predetermined target voltage, whereby a first control loop is executed which outputs a pulse-width modulated signal 14 which is initially valid for all battery cells 11 but which still has to be weighted.

[0033] Furthermore, by coupling the microcontroller 16 with a corresponding measuring and evaluation unit of the battery and with the central control unit, a weighting circuit 21 is formed. A weighting function W(x) is preferably implemented in the microcontroller 16 in the form of, for example, programming or firmware. In the following, Fig. 2 to 4 the principle of the weighting function W(x) according to the invention is explained using block diagrams.

[0034] In Fig. 2 important elements of the weighting function W(x) or of one of the Fig. 1, the program implementing the weighting function W(x) is shown according to a particular embodiment of the invention. According to this embodiment, the microcontroller 16 receives, in addition to the pulse-width modulated signal 14, measured variables and / or calculated variables of current operating parameters 23, 24 of the battery or battery cells, as well as information about the current direction 22 of the instantaneous battery current. For the sake of simplicity, Fig. 2 only the corresponding program flow is indicated, whereby the representation of an exemplary associated hardware connection, for example of the microcontroller 16 with the driver circuit 20, or the driver circuit 20 with the half-bridge configuration 19, in Fig. 2 is omitted, as this is already Fig. 1 was specified. In Fig. 2, PWM1 is used to convert the original, predefined pulse width modulated signal 14 according to Fig. 1 or, as an alternative, information about a corresponding predetermined pulse width modulated signal, and PWM2 denotes a weighted pulse width modulated signal output by the microcontroller 16.

[0035] This enables the driver circuit 20 to switch the semiconductor switches in the half-bridge configuration 19 according to the weighted pulse-width-modulated signal PWM2. Depending on the duty cycle of the pulse-width-modulated signal PWM2, the respective battery cell 11 is clocked more or less strongly.

[0036] According to the invention, an improved voltage regulation of batteries with autonomous battery cells is thus provided, wherein the battery cells can be clocked, for example, with integrated electronics using a control system, in such a way that the desired battery voltage is set for the entire battery. In particular, the invention ensures that not all battery cells 11 are clocked with an identical duty cycle. Rather, an adjustment, i.e. a weighting, takes place in each case, in which relevant operating parameters, which are determined according to the Fig. 2, generally designated by the reference numerals 23, 24.

[0037] The operating parameters include, for example, a state of charge (SOC) or a service life (aging) (SOH) of a battery cell. Thus, the state of charge (SOC) and service life (SOH) of the respective battery cell 11 can be processed by the weighting circuit 21, particularly in comparison with the other battery cells 11.

[0038] According to the second embodiment, a duty cycle can be independently extended or shortened, for example, in such a way that a battery cell 11 with a low state of charge (SOC) reduces the duty cycle value in the event of battery cell discharge (current flow from the battery), thus resulting in less intensive pulsing. For a battery cell 11 with a high SOC, the duty cycle would be extended. Furthermore, if all battery cells have the same state of charge, the control would instead be performed by changing the pulse-width-modulated signal PWM1 from the central control unit to compensate, since all battery cells change the duty cycle in an identical manner.Since battery cells with a low state of charge SOC should only be switched on for a shorter time when discharging the battery, but correspondingly longer when charging the battery, the current direction 22 is either determined by the cell electronics itself or, for example, communicated by a protocol which also transmits the specification for the pulse width modulated signal PWM1.

[0039] In the Fig. 3 shows an extension of the weighting function W(x) according to a third embodiment of the invention, in which the average state of charge SOC, which is known from the overall behavior and the total voltage of the battery, and / or the average lifetime state SOH of each individual battery cell 11 is also communicated via the communication protocol.

[0040] In the Fig. 4 shows a fourth exemplary embodiment of the invention, in which distributions σ SOC , σ SOHthe state of charge and the service life are taken into account. In this case, all cell voltages can be evaluated centrally to determine a scatter, the distributions σ SOC , σ SOH but can also be determined, for example, via the minimum and maximum state of charge SOC or service life SOH or, for example, via a minimum and maximum voltage present in the battery string 13.

[0041] Furthermore, according to the fourth embodiment, further quality factors GF are also used, which flow into the weighting function W(x) and whose mean value GF and their distribution σ\ GF for the individual cells. Such quality factors can be determined, for example, from cell voltage, state of charge (SOC), internal resistance of the battery cell, cell temperature, internal cell pressure, battery current, or other physical measurements.

[0042] In addition to the above written disclosure of the invention, reference is hereby explicitly made to the graphic representation of the invention in the figures to supplement the disclosure.

Claims

[1] Battery with a plurality of battery cells (11) which are designed to be connected or bridged to a battery string (13) by controlling coupling circuits (12), wherein the battery has control means (15) for controlling the coupling circuits (12) by control signals, characterized bythat the control means (15) are designed to control the coupling circuits (12) by means of pulse-width-modulated signals (14, PWM1, PWM2) and to process a specification of a pulse-width-modulated signal (PWM1) by means of weighting circuits (21) assigned to the battery cells (11) in order to generate weighted pulse-width-modulated signals (PWM2), so that an average switch-on time of a respective battery cell (11) is determined by the duty cycle of a respective weighted pulse-width-modulated signal (PWM2), wherein the coupling circuits (12) each comprise semiconductor switches, in particular semiconductor switches arranged in a half-bridge configuration (19) or full-bridge configuration, as well as a driver circuit (20), and the weighting circuits (21) are each controlled by microcontrollers (16) which are specific to the battery cells and are connected to the measuring and evaluation electronics and the central control unit, in particular via a communication bus,each comprising a memory with instructions for implementing a weighting function (W(x)). [2] Battery according to claim 1, wherein the battery comprises a weighting circuit (21) for each battery cell (11) or each battery module of the battery, and the weighting circuits (21) are each configured to adapt the specification for a pulse-width modulated signal (14, PWM1) based on operating parameters (23, 24) of the battery and / or individual battery cells (11). [3] Battery according to claim 2, wherein the battery further comprises a central control unit configured to generate the specification for the pulse-width modulated signal (14, PWM1) based on a comparison of a battery voltage generated by the battery with a predetermined target voltage, and a signal transmission connection (18) configured to transmit the generated specification directly to the battery cells (11) as a predetermined pulse-width modulated signal (14) or as analog or digital information about the predetermined pulse-width modulated signal (14, PWM1). [4] Battery according to claim 3, wherein the battery is equipped with measuring and evaluation electronics which are designed to determine current values ​​for the operating parameters (23, 24) to be used by the weighting circuits (21) to adapt the pulse-modulated signal (14, PWM1) and to transfer them to the weighting circuits (21). [5] Battery according to claim 4, wherein the measuring and evaluation electronics comprises means for determining the current direction (22) of a battery current and means for determining values ​​for a state of charge (SOC, SOC , σ SOC ), a lifetime state (SOH, SOH , σ SOH ), and / or a calculated quality factor (GF, σ GF ) which are available for individual battery cells (11), as average values ​​for all battery cells (11), or as a distribution over the battery cells (11). [6] Method for regulating a battery voltage of a battery with a plurality of battery cells (11) according to one of claims 1 to 5, wherein the battery cells (11) are designed to be selectively connected to or bridged by a battery string (13) by controlling coupling circuits (12), characterized bythat the coupling circuits (12) are controlled by means of pulse-width modulated signals (PWM1, PWM2) using individually adapted weightings for the duty cycle of a pulse-width modulated signal (PWM1, PWM2), so that an average switch-on time of each battery cell (11) is determined by the duty cycle of a weighted pulse-width modulated signal (PWM2) and the battery cells (11) are on average connected to the battery string (13) in such a way that the battery voltage is set to a desired target voltage, wherein the coupling circuits (12) each comprise semiconductor switches, in particular arranged in a half-bridge configuration (19) or full-bridge configuration, as well as a driver circuit (20), and the weighting circuits (21) are each controlled by microcontrollers (16) specific to the battery cell and connected to the measuring and evaluation electronics and the central control unit, in particular via a communication bus,which each comprise a memory with instructions for implementing a weighting function (W(x)). [7] Method according to claim 6, wherein the weightings are calculated from a weighting function (W(x)) into which a state of charge (SOC), in particular a state of charge (SOC) of a respective battery cell (11) to be switched, and a current direction (22) of a battery current and / or other operating parameters (23, 24) of the battery are included. [8] Method according to claim 7, wherein for each battery cell (11) it is determined whether the battery cell (11) is in a low state of charge (SOC) or a high state of charge (SOC), wherein, if the battery cell (11) is in a low state of charge (SOC), in the case of discharging of the battery cell (11), a predetermined duty cycle for the pulse width modulated signal (PWM2) is reduced so that the battery cell (11) is clocked less intensively, whereas in the case of charging of the battery cell (11), the duty cycle is increased, and wherein, if the battery cell (11) is in a high state of charge (SOC), in the case of discharging of the battery cell (11), the duty cycle is increased, and in the case of charging of the battery cell (11), the duty cycle is reduced. [9] Motor vehicle comprising an electric motor and a battery according to any one of claims 1 to 5 for supplying the electric motor with electrical energy.

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