Battery-electric system with reference electrode and circuit for compensating the measuring impedance

Abstract

A battery electrical system, for example in a vehicle, comprises a battery cell, a reference electrode, a voltage sensing circuit, a compensation circuit, and a battery control unit. The sensing circuit measures the cell voltage of the battery cell as the measured battery voltage and outputs a digital voltage signal indicating the battery voltage. The compensation circuit comprises a capacitor and a first and a second switch. According to one procedure, the first switch closes to connect the voltage source to the capacitor to charge it, with the capacitor connected in parallel to the sensing circuit. The second switch closes out of phase with the first switch to connect the compensation circuit to the sensor circuit.The battery control unit outputs switching control signals to control the respective operating cycles of the switches when the cell voltage is measured, and then uses the digital voltage signal to perform a battery management action.

Description

introduction

[0001] Electrochemical battery cells are used as direct current energy storage devices in a variety of applications, including battery packs to power electric motors in vehicles, consumer goods and other mobile or stationary systems.

[0002] Hybrid electric vehicles and battery electric vehicles use a rechargeable high-energy battery pack to power one or more electric drive motors and other high-voltage power electronic components. The battery pack's cells consist of positive and negative electrodes, each forming a cathode and an anode, as well as an electrolyte material and a separator. A stack of battery cells is electrically connected to a load, such as the electric drive motor(s) mentioned above.

[0003] Lithium-ion batteries, commonly used in battery-electric systems, operate by reversibly transferring lithium ions between the anode and cathode via the electrolyte during charging. When the battery pack is discharged during a drive mode or other discharge mode, the lithium ions flow in the opposite direction, from the anode to the cathode. The state of charge of the battery pack can be determined during operation of the battery-electric system using a battery management system (BMS). The BMS can communicate with a cell sensing circuit to detect a voltage difference between the cathode and anode. However, the measured voltage tends to change dynamically as the battery pack is actively being charged or discharged.For this reason, battery voltages are often determined by measuring the cathode or anode voltages relative to a reference electrode that is otherwise not involved in the energy storage or discharge processes. The reference electrode is therefore used as a reference point against which the measured cathode and anode potentials are compared. Description

[0004] This paper describes battery-electrical systems with one or more battery cells and reference electrodes, for example, in a vehicle traction battery pack, and an associated method for determining and compensating for polarization effects of the reference electrode. Electrode polarization can occur due to shifts in the electrical potential of the reference electrode. Factors such as aging, degradation, electrolyte impurities, and temperature fluctuations tend to exacerbate the detrimental effects of polarization. Among other potential problems, polarization of a reference electrode reduces measurement accuracy when the reference electrode is used to determine cell voltages. The solutions presented here therefore aim to improve the available accuracy of battery voltage measurements.Conversely, the present teachings optimize various battery management processes, such as the estimation or calculation of the state of charge, the state of health, the remaining energy capacity, the control of charging / discharging parameters and other useful quantities, but are not limited to these.

[0005] In particular, according to one aspect of the description, a battery electrical system comprises a battery cell, for example, a cell stack or a series of cells with a lithium-ion or lithium-metal construction, a reference electrode (for example, a porous electrode), and a voltage sensing circuit ("sensing circuit"). The sensing circuit can measure a cell voltage of the battery cell as a test voltage and output a digital voltage signal indicating the measured voltage. The battery electrical system also comprises a compensation circuit and a battery control unit. The compensation circuit comprises a voltage source, an isolation capacitor connected in parallel with the sensing circuit, and a first and a second switch.

[0006] The first switch, located between the voltage source and the sensing circuit, closes in response to an initial switching control signal from the battery control unit. This control connects the voltage source to the isolation capacitor. The second switch is connected between the compensation circuit and the sensing circuit. In this specific configuration, the second switch closes in response to a second switching control signal from the battery control unit, connecting the reference electrode and the compensation circuit to the sensing circuit when a voltage measurement is performed. The battery control unit is connected to both the first and second switches.To measure the cell voltage, the battery control unit outputs the first and second switching control signals and then uses the digital voltage signal (measured voltage) to perform one or more battery management actions.

[0007] In one or more embodiments, the battery control unit is programmed to control a closing and opening sequence of the first and second switches to adjust a reference voltage between the reference electrode and a working electrode of the battery cell in a previous time step during the recharging of the isolation capacitor.

[0008] The sensing circuit can optionally include an analog-to-digital converter. In such an embodiment, the analog-to-digital converter can include a buffer amplifier with a parasitic bias current. The battery control unit is therefore configured to control the operation of the compensation circuit to minimize a voltage drop across the reference electrode due to the parasitic bias current.

[0009] The battery control unit can, in one or more implementations, control the operation of the compensation circuit such that current draw at the reference electrode is characterized by the absence of frequencies below the respective duty cycle frequencies of the first and second switches. The battery control unit can also be configured to estimate the state of charge (SOC) of the battery cell as a battery management action and to set a charging or discharging parameter based on the SOC.

[0010] A vehicle is also disclosed herein. In a non-restrictive embodiment, the vehicle comprises road wheels connected to the vehicle body, an electric drive motor connected to one or more of the road wheels, and a battery pack connected to the electric drive motor. The battery pack is configured to supply energy to the electric drive motor to power one or more of the road wheels and comprises a reference electrode, a voltage sensing circuit called the sensing circuit, a compensation circuit, and a battery control unit. The sensing circuit is operable to measure the cell voltage of a battery cell of the battery pack as the measured battery voltage and to output a digital voltage signal indicating the measured battery voltage. The compensation circuit is connectable to the voltage sensing circuit.

[0011] One possible configuration of the compensation circuit includes a voltage source, an isolation capacitor connected in parallel with the sensing circuit, and a first switch placed between the voltage source and the isolation capacitor. The first switch is configured to close in response to a first switching control signal, thereby connecting the voltage source to the isolation capacitor. The compensation circuit also includes a second switch connected between the compensation circuit and the sensing circuit. The second switch is configured to close in response to a second switching control signal, out of phase with the first switch. Closing the second switch connects the reference electrode and the compensation circuit to the sensing circuit.The aforementioned battery control unit communicates with the first and second switches and can output the first and second switching control signals to manage their respective operating cycles. The battery control unit also measures the cell voltage via the reference electrode and the sensing circuit and subsequently performs a battery management action using the digital voltage signal.

[0012] In addition to the system implementations summarized above, a method for use with a battery-electrical system comprising a single battery cell is also disclosed. The method, according to one or more implementations, includes closing a first switch via a battery control unit to connect a voltage source of a compensation circuit to an isolation capacitor. The isolation capacitor is connected in parallel to the voltage sensing circuit. The method further includes charging the isolation capacitor using the voltage source, opening the first switch via the battery control unit after the isolation capacitor has been charged, and closing a second switch after the first switch has been opened, thereby connecting a reference electrode and the compensation circuit to a voltage sensing circuit, referred to as the sensing circuit.

[0013] The method in this embodiment also includes measuring the cell voltage of the battery cell using the reference electrode via the sensing circuit and subsequently outputting a digital voltage signal to the battery control unit via the sensing circuit. The digital voltage signal is an indicator of the measured cell voltage. The method then includes performing a battery management action of the battery cell via the battery control unit in response to the digital voltage signal.

[0014] The above features and advantages, as well as other features and advantages of the present teaching, are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the present teaching as defined in the attached claims, in conjunction with the attached drawings. Brief description of the drawings

[0015] The accompanying drawings, which are part of this description, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. Fig. Figure 1 shows a representative battery electrical system with a battery pack equipped with a measuring and compensation circuit, constructed according to the description. Fig. Figure 2 is an equivalent circuit diagram of a representative embodiment of a compensation circuit, which is connected to the one in Fig. 1 can be used in the battery-electric system shown. Fig. 2A is an equivalent circuit diagram that represents part of the representative compensation circuit of Fig. Figure 2 shows how parasitic voltages and currents are compensated by the technical solutions described here. Fig. Figure 3 shows exemplary operating cycles of the first and second switches of the in Fig. 2 compensation circuit shown. Fig. Figure 4 is a flowchart that describes an embodiment of a method for compensating for a high impedance in a battery sensing circuit according to one aspect of the description.

[0016] The accompanying drawings are not necessarily to scale and may represent a simplified depiction of various preferred features of the present description as disclosed herein, including, for example, certain dimensions, orientations, positions, and shapes. Details associated with such features are partly determined by the intended application and operating environment. Detailed description

[0017] The components of the disclosed embodiments can be arranged in a multitude of configurations. Therefore, the following detailed description is not intended to limit the scope of the disclosure as claimed, but is merely representative of possible embodiments thereof. Furthermore, while numerous specific details are included in the following description to provide a comprehensive understanding of various representative embodiments, some embodiments can also be implemented without some of the disclosed details. For the sake of clarity, the description of certain technical details known from the prior art has also been omitted. Moreover, the embodiment presented and described herein can also be implemented without any element not specifically described here.

[0018] Fig. Figure 1 shows a battery-electric system 10 with a rechargeable battery pack (B HV ) 12, where identical reference numbers refer to identical features in the different views. The battery pack 12 is equipped with a cell measurement and compensation circuit (MC) 34, which includes a compensation circuit 14 and a voltage sensing circuit (“sense circuit”) 15, the latter being used for periodic or continuous measurement of battery voltage levels as measured battery voltages (V). M ) and to output a digital voltage signal (V DC ) is operational, that the measured battery voltage (V M ) displays. The measured battery voltage(s) (V) M) can (can) include, for example, individual cell voltages of a plurality of electrochemical battery cells 120, e.g., lithium-ion or lithium-metal battery cells 120. In particular, the sensing circuit 15, especially if it is designed to facilitate mass production and integration into a vehicle fleet 11 or other mobile or stationary hosts for the battery-electric system 10, may tend to draw a large input bias current.

[0019] In the Fig. 2 and Fig. Figure 2A briefly shows that the battery pack 12 contains a reference electrode 40R of the type described above. Due to polarization effects, the reference electrode 40R acts as a high-impedance element for the downstream sensing circuit 15. As a result, a large voltage drop can occur across the sensing circuit 15 during voltage measurements, which in turn reduces the overall measurement accuracy. The electrical potential of a working electrode 40E of the battery pack 12, for example, a cathode or an anode of one of the battery cells 120, is Fig. 1, can during the operation of the battery-electric system 10 of Fig. 1 is determined with respect to the reference electrode 40R. The reference voltage (V REF ) is subsequently used as (or to determine the) measured voltage (V) M ) from Fig. 1 used.

[0020] In one or more embodiments, the reference electrode 40R can be designed as a porous electrode, for example made of a porous lithium metal. As those skilled in the art know, the degree of porosity of a porous electrode increases the surface area of ​​the reference electrode 40R compared to non-porous alternatives and thus its energy and power density.

[0021] As in Fig. As shown in Figure 1, the measurement accuracy can be improved by polarizing the reference electrode 40R in Fig. 2 and Fig. 2A may be affected. To address potential problems related to polarization, the battery electrical system 10 is equipped with a compensation circuit 14, a non-restrictive example of which is described below with particular reference to the Fig. 2 and Fig. 2A is described. The operation of the compensation circuit 14 is described with reference to the Fig. 3 and Fig. 4 explained in more detail. The compensation circuit 14 considered here receives and processes the measured voltages (V M ) for one of the battery cells 120 or for the battery pack 12 as a whole. The sensing circuit 15 acts on the measured voltage (V M ) and functions, for example, in some embodiments as an analog-to-digital converter. The detection circuit 15 outputs the digital voltage signal (V DC ) also to a battery control unit (C) 50, for example to a battery management system of the representative vehicle 11 in a non-restrictive embodiment.

[0022] The battery-electric system 10 of Fig. 1 can be used in one or more non-restrictive embodiments as part of a vehicle 11, for example, a motor vehicle, as shown. In such an embodiment, the vehicle 11 can comprise a vehicle body 16, which defines a vehicle interior 18. While the vehicle 11 is described here as a non-restricted host system for implementing the present teaching, those skilled in the art will recognize that the battery-electric system 10 can be used in a wide range of mobile and stationary systems, including, but not limited to, consumer products, electrified propulsion systems of aircraft, ships, rail vehicles, agricultural equipment, transport equipment and other mobile platforms on land, water or in the air, as well as power plants, lifting equipment, conveyor systems and the like. The descriptions contained herein of the implementation on board the vehicle 11 of Fig. The numbers 1 are therefore not restrictive and only illustrate one possible implementation.

[0023] In embodiments where the battery-electric system 10 of Fig. As part of the vehicle 11, the battery pack 12 can optionally be configured as a lithium-ion traction battery pack 12 with a voltage capacity of, for example, approximately 300 volts (V) or more. Such representative voltages are suitable for generating drive torque for vehicle propulsion functions and for supplying various high-voltage accessories on board the vehicle 11. In the exemplary embodiment of Fig. 1. The battery pack 12 is selectively connected to and disconnected from a load via a series of high-voltage contactors 22 arranged on a high-voltage DC bus 23. While current and voltage sensing circuits in the laboratory are designed precisely so that very little current flows into the sensing circuit hardware, mass production of the sensing circuits 15 for integration into a large vehicle fleet can result in the sensing circuit 15 being designed with a relatively high impedance and a resulting high current draw compared to the laboratory versions, as is known in the field. The compensation circuit 14 is therefore designed according to method 100 of Fig. 4 provided and controlled to minimize the undesirable effects of the internal impedance of the sensor circuit 15.

[0024] The load in the non-limiting configuration of Fig. 1 comprises a DC link capacitor (CL) and an inverter circuit (24). The inverter circuit 24 is connected to the battery pack 12 and the electric traction motor 26 and is configured to convert a DC waveform from the battery pack 12 into an AC waveform suitable for exciting the electric traction motor 26. The inverter circuit 24 includes a plurality of semiconductor power switches 25 connected to the phase windings of an electric traction motor (“M”) 26. As is known in the art, inverters such as the one in Fig. 1 The inverter circuit 24 shown uses several semiconductor power switches 25 as fast-acting ON / OFF switching devices, for example insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), thyristors, etc. In a typical three-phase configuration of the electric traction motor, the semiconductor switches are turned on or off at predetermined switching intervals to output the AC waveform to the phase windings of the electric traction motor 26.

[0025] The in Fig. The electric traction motor 26 shown in Figure 1 can be connected to a rotatable output element 28, such as a motor shaft and an attached gearbox (not shown). In a drive mode, the inverter circuit 24 is controlled by pulse width modulation or another application-appropriate switching control technology to excite the phase windings of the electric traction motor 26. In the illustrated embodiment, the electric traction motor 26 is designed as a multi-phase AC drive motor, for example, as a three-phase electric lathe. The rotation of the output element 28 ultimately transmits the drive torque (To) to a coupled load, which in the unrestricted embodiment is Fig. 1 comprises a set of one or more wheels 20 connected to the vehicle body 16.

[0026] The battery-electric system 10 can also include additional components for powering various systems or functions on board the vehicle 11. For example, the battery pack 12 can be connected to an accessory power module (“APM”) 30 in the form of a DC-DC converter. The APM 30 is designed to reduce the DC voltage of the DC bus 23, for example, about 300 V or more (see above), to a nominal auxiliary voltage of 12–15 V. An auxiliary battery (“B”) AUX “) 32, for example a 12 V lead-acid battery, can be electrically connected to the APM 30 on a low-voltage DC bus 230, whereby the internal switching operation of the APM 30 ensures that the auxiliary battery remains charged, that is, that the voltage of the auxiliary battery (V AUX ) approximately 12-15 V.

[0027] As in Fig. As shown in Figure 1, the battery control unit 50 of the battery electrical system 10 is programmed to monitor, charge, and discharge the battery pack 12. Furthermore, the battery control unit 50 is programmed to execute instructions that describe the procedure 100 of Fig. 4 using the compensation circuit 14 to counteract the undesirable effects of the high internal impedance of the reference electrode 40R ( Fig. 2 and Fig. 2A) to minimize the overall measurement accuracy. For this purpose, the battery control unit 50 comprises one or more processors 52 and a non-transient, computer-readable storage medium, that is, a memory 54. Instructions embodying the method 100 can be stored in the memory 54, wherein the memory 54 comprises various memory chips or memory circuits, for example, magnetic or optical media, CD-ROM, solid-state / semiconductor memory (for example, various types of RAM or ROM), etc.

[0028] Each processor 52 can consist of various combinations of application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), electronic circuits, and central processing units, such as microprocessors. Non-volatile memory components 54 can store machine-readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuits, input / output circuits and devices, signal conditioning and buffer circuits, and other components that one or more processors 52 can access to provide the described high-voltage discharge functionality.Input / output circuits and devices for use with the Battery Control Unit 50 may include analog-to-digital converters and related devices that monitor sensor inputs, wherein such inputs are monitored at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, code, algorithms, and similar terms refer to sets of instructions executable by the Battery Control Unit, including calibrations and lookup tables.

[0029] In general, the battery control unit is 50 of Fig. 1 configured to receive input signals (CC) during operation I ) receives, whereby the input signals (CC I ) the above-mentioned measured voltage(s) (V M) and other possible values ​​such as battery temperature. The sensing circuit 15 is configured to detect the cell level, pack level, or other battery voltages besides the measured voltage(s) (V). M The battery control unit 50 measures the battery pack 12 to assist it in performing one or more battery management actions, such as estimating the state of charge (SOC), state of health (SOH), and / or other possible parameters of the battery pack 12 or the battery cells 120 comprising it. The battery control unit 50 can also selectively adjust a charging or discharging parameter of the battery pack 12 based on the derived SOC or other parameters. As part of a discharge control strategy informed by the SOC, the battery control unit 50 can, for example, respond by issuing electronic control signals (CC). 10) sends to components of the battery electrical system 10, for example to the MC circuit 34, the inverter circuit 24 and its various semiconductor power switches 25, as well as heating or cooling commands to a resident battery thermal management system (not shown), etc.

[0030] In Fig. 2 is the MC circuit 34 in accordance with an exemplary embodiment for determining the reference voltage (V REF ) between the reference electrode 40R and the working electrode 40E. The MC circuit 34 ultimately uses the reference voltage (V REF ), to measure the voltage (V M ) as described above. The operation of the compensation circuit 14 is described below, in particular with regard to the control of the first switch (S1) 47 and the second switch (S2) 48. The in Fig. The sensing circuit 15 shown in Figure 2 is representative of a possible hardware implementation suitable for performing the voltage measurements presented here, while other possible embodiments of the sensing circuit 15 may be used within the scope of this description. As shown, the representative sensing circuit 15 may include a differential amplifier / buffer amplifier 41, a non-limiting example of which is shown in Figure 2. Fig. As shown in more detail in Figure 2A, the system comprises a comparator switch (S0) 49, which is connected to the buffer amplifier 41, and a comparator array 150, which is connected via the comparator switch 49 to an output side of the buffer amplifier 41. Thus, the comparator switch 49 can be selectively closed by a corresponding switching command from the battery control unit 50 to connect the buffer amplifier 41 to the comparator array 150. In an implementation based on an analog-to-digital converter, a capacitor (C2) 44 can be connected between the comparator switch 49 and the comparator array 150 to ground, which is used to output the digital voltage signal (V). DC ) can be used on the processor 52 of the battery control unit 50.

[0031] In particular with regard to the compensation circuit 14, the first switch 47 is between a voltage source (V S) 43, e.g., a low-voltage cell battery, and the detection circuit 15. Within the framework of the strategy presented here, the voltage supplied by the voltage source 43, i.e., a source voltage, is converted to a measured voltage (V M ) set in a previous time step so that an isolation capacitor (C1) 42 is charged to a threshold voltage that is as close as possible to the currently measured voltage (V M The first switch 47 is configured to connect and disconnect the voltage source 43 when the isolation capacitor 42 is charged to this threshold voltage. The working electrode 40E, whose voltage level is measured, is connected to the sensing circuit 15, in this case to an input side of the buffer amplifier 41. The voltage source 43 can therefore be switched on and off by operating the first switch 47.

[0032] The second switch 48 of the compensation circuit 14 is connected between the compensation circuit 14 and the detection circuit 15 and is configured to close, which happens with a phase shift relative to the first switch 47 (see Fig. 3) By closing the second switch 48, the reference electrode 40R and the compensation circuit 14 are connected to the sensing circuit 15. This process can occur in response to a second switching control signal for the second switch 48, wherein the aforementioned first and second switching control signals for the first and second switches 47 and 48, respectively, are part of the aforementioned control signals (CC). 10 ).

[0033] The reference electrode 40R considered here has a high characteristic impedance (R). INT ), which in turn is represented as resistor 46 in the equivalent circuit of Fig. Figure 2 shows the following. In addition to the voltage source 43, the compensation circuit 14 also includes the isolation capacitor 42, which in turn is connected in parallel to the detection circuit 15. Another resistor 45 is connected in series with the voltage source 43 and represents an internal resistance (R). S ) dar.

[0034] In Fig. Figure 2A shows the buffer amplifier 41 in more detail to illustrate parasitic voltages and currents that can occur due to the high impedance of the reference electrode 40R. While the setup of the sensing circuit 15 can vary depending on the application, the impedance of the reference electrode 40R can lead to such parasitic elements due to polarization or other factors. Without the present teaching, these parasitic elements can generate a large voltage drop across the sensing circuit 15, thus reducing the measurement accuracy. Fig. 2A are the parasitic elements as an input resistance (R) IN ) 61 and a bias current (I B ) 63 within the buffer amplifier 41. In other embodiments, other detection circuits 15 can also be used, including those without the buffer amplifier 41, and therefore the one shown in Fig. The construction shown in 2A is intended to illustrate, and not limit, the present teaching.

[0035] Regardless of the structure of the detection circuit 15, the reference electrode 40R does not act as an ohmic resistor. Rather, the reference electrode 40R acts like a complex impedance element. Therefore, the reference voltage (V) REF ) between the reference electrode 40R and the working electrode 40E during a specific voltage measurement by the sensing circuit 15 of the measured voltage (V M) deviate. The battery control unit 50, which is connected to the first and second switches 47 and 48, can compensate for the negative effects of such parasitic elements by controlling the first and second switches 47 and 48. This is done by instructing the respective operating cycles via the electronic control signals (CC). 10 ) from Fig. 1, in order to thereby determine the cell voltage as a measured voltage (V) M ) to measure. The battery control unit 50 then uses the digital voltage signal (V) DC ), to perform one or more battery management actions as described above.

[0036] Fig. Figure 3 shows a pulse sequence 65 with exemplary operating cycles for controlling a corresponding opening / closing state of the respective first and second switches 47 and 48 of the compensation circuit 14. Fig. 2. The open / closed state is shown on the vertical axis, where a binary nominal state of "1" corresponds to a closed switch and a binary nominal state of "0" corresponds to an open state. Time in milliseconds (ms) is shown on the horizontal axis. The first switch 47 and the second switch 48 of Fig. 2 have a corresponding closing / conducting duration (SS1, SS2) during which the first and second switches 47 and 48 are both closed. At a calibrated time (t calThe first switch 47 is commanded to close, remaining in a closed state (SS1) until a predetermined time (t1). At t1, the first switch 47 opens, and both the first and second switches 47 and 48 remain open for a predetermined duration. The second switch 48 is then instructed to move to a closed state (SS2). The closed state (SS2) is maintained until time t3.

[0037] As in Fig. As shown in Figure 3, the closed state (SS2) of the second switch 48 is a fraction of the duration of the closed state (SS1) of the first switch 47, that is, SS1 > SS2. The closing of the first switch 47 in Fig. 2 ensures proper charging of the isolation capacitor 42 by the voltage source 43 for this relatively long duration. As already mentioned, the charging of the isolation capacitor 42 by the voltage source 43 continues until a threshold voltage is reached, which is as close as possible to the currently measured voltage (V). M The duration of the closed state (SS2) can be less than half the duration (SS1) in one or more embodiments.

[0038] In some embodiments, the battery control unit 50 can be programmed to respond to the digital signal voltage (V). DC ) the Fig. 1 and Fig. 2 follows at an earlier time, for example at an immediately preceding time step, at which the digital signal voltage (V) DC) was measured. This can help to reduce parasitic current draw subtracted from the reference electrode 40R. For this purpose, the battery control unit 50 can be programmed to control a closing and opening sequence of the first switch 47 and the second switch 48 such that the digital signal voltage (V DC ) with the reference voltage (V REF ) at the reference electrode 40R matches a previous time step when the insulation capacitor 42 is recharged.

[0039] In Fig. Figure 4 shows an embodiment of the method 100, which is combined with the MC circuit 34 of the Fig. 1 and Fig. 2 can be used to compensate for parasitic elements in the battery electrical system 10. For the sake of simplicity, the method 100 is described in the form of discrete logic blocks and can be implemented by the battery control unit 50 of the Fig. 1 during the operation of the vehicle 11. As is known in the field, current and voltage sensing circuits in laboratories are often designed so precisely that very little electrical current is introduced into the sensing circuit 15. In mass production and the integration of host systems, for example in a fleet of vehicles 11 of the Fig. 1. However, designs of the detection circuit 15 may be required that have a relatively high current consumption. In such a case, the compensation circuit 14 of Fig. 2 are controlled according to procedure 100 to minimize undesirable effects of the internal impedance of the reference electrode 40R.

[0040] Procedure 100 begins with block B101 (“Start”). The battery electrical system 10 may be in a specific state when procedure 100 begins; for example, the vehicle 11 may be parked, or it may be in a driving or charging mode. In such a case, block B101 may involve initiating a start-up process of the vehicle 11 or performing another action that results in the measured voltage (V) M ) and the reference voltage (V REF ) the Fig. 2 and Fig. 2A must be recorded. Procedure 100 continues with block B102 as soon as procedure 100 has started.

[0041] Block B102 includes relocating the first and second switches 47 and 48 respectively. Fig. 2 into an open state, that is, S1 = 0 and S2 = 0 in the representative impulse sequence 65 of Fig. 3. This switching control operation can be commanded by the battery control unit 50, for example via a wired or wireless first and second switching control signal for the first and second switches 47 and 48 as part of the electronic control signals (CC). 10 ), which in Fig. 1 are shown, or via a corresponding control circuit. Procedure 100 then proceeds to block B103.

[0042] In block B103, the battery control unit 50 starts a timer and determines, based on the current value of the timer, whether the total elapsed time (t) determined by the counter is equal to a calibrated time (t CAL ) is, for example in Fig. Figure 3 illustrates this. Procedure 100 involves repeating block B103 in a loop until t = t CAL is, whereby the procedure continues with block B104 thereafter.

[0043] In block B104, which is reached when the elapsed time (t) equals the calibrated time (t CAL ) is, the battery control unit 50 commands the first switch 47 of Fig. 2 to close, that is, S1 = 1, where "1" in this case corresponds to the binary target state of 1, which is the closed state (SS1) in Fig. 3 is displayed. This process connects the voltage source 43 to the isolation capacitor 42 to begin charging the isolation capacitor 42. The procedure 100 then proceeds to block B105.

[0044] Continuing the discussion from Fig. 4 Block B105 includes the determination by the battery control unit 50, for example using the aforementioned timer, whether the elapsed time (t) is equal to a predetermined first time duration (t1), which in turn is Fig. Figure 3 shows the procedure. Procedure 100 involves repeating blocks B104 and B105 in a loop until t = tCAL is, whereby the procedure continues with block B106 thereafter.

[0045] Block B106 of procedure 100 contains the command to turn off the first switch 47. Fig. 2 to reopen, that is, S1 = 0. As with the switching control actions described above, block B106 can be implemented by the battery control unit 50, e.g. via a voltage signal or a pulse width modulation signal, depending on the design of the first switch 47. The procedure 100 then proceeds to block B107.

[0046] In block B107, the battery control unit 50 determines whether the elapsed time (t) is equal to a predefined second time duration (t2), as for example in Fig. Figure 3 shows that procedure 100 involves repeating blocks B106 and B107 in a loop until t = t2, after which procedure 100 continues with block B108.

[0047] In block B108, the battery control unit 50 commands the second switch (S2) to close, i.e., S2 = 1, in one step analogous to block B104. The second switch thus goes into the closed state (SS2) of Fig. 3, which occurs after the first switch 47 has been opened. After that, procedure 100 proceeds to block B109.

[0048] In block B109, the battery control unit 50 of Fig. 1 determines whether the elapsed time (t) is equal to a given third time duration (t3), where this representative time is also in Fig. Figure 3 shows the procedure 100, which involves repeating blocks B108 and B109 in a loop until t = t3, after which procedure 100 continues with block B110.

[0049] Block B110 of Fig. 3 contains the command to activate the second switch 48 of Fig. To open block 2, that is, S2 = 0. Procedure 100 then proceeds to block B111.

[0050] Block B111 ("End") marks the end of a cycle of impulse sequence 65 of Fig. 3. The procedure 100 can be continued in a loop by restarting in block B102, as long as the battery-electrical system 10 of Fig. 1 remains in operation or as long as the battery control unit requires 50 voltage measurements.

[0051] The procedure 100 of Fig. 4 is therefore connected to the battery-electric system 10 of Fig. 1 or another host system with one or more battery cells 120. In general, embodiments of the method 100 include closing the first switch 47 via the battery control unit 50 to connect the voltage source 43 to the isolation capacitor 42 of Fig. 2 to connect. The procedure 100 comprises charging the isolation capacitor 42 using the voltage source 43 and subsequently opening the first switch 47 via the battery control unit 50. The battery control unit 50 then closes the second switch 48 of Fig. 2 after opening the first switch 47, in order to connect the compensation circuit 14 with the detection circuit 15.

[0052] At this point, the procedure 100 continues by measuring a cell voltage of the battery cell 120 via the detection circuit 15 and then the digital voltage signal (V DC ) outputs to the battery control unit 50. This process takes place via the detection circuit 15, whereby the digital voltage signal (V) DC ) the measured cell voltage, that is V M, as mentioned above. The procedure 100 can also perform a battery management action of the battery cell 120 via the battery control unit 50 in response to the digital voltage signal (V). DC ) include, for example, estimating the SOC of battery cell 120 and subsequently adjusting a charging or discharging parameter based on the estimated SOC.

[0053] The control of the closing and opening sequence of the first and second switches 47 and 48 via the battery control unit 50 can, in one or more embodiments, include the adjustment of the reference voltage (V REF ) at reference electrode 40R of the Fig. 2 and Fig. 2A in a previous time step during the charging of the isolation capacitor 42. As mentioned above, this means that the voltage supplied by the voltage source 43 is equal to the measured voltage (V). M) is set in a previous time step so that the isolation capacitor 42 is charged to a threshold voltage that is as close as possible to the currently measured voltage (V M ) lies.

[0054] According to the present teaching, the voltage drop across the reference electrode 40R is minimized by controlling the operation of the compensation circuit 14 according to method 100 and its various alternative embodiments. Likewise, the operation of the compensation circuit 14 can be controlled such that the current draw of the reference electrode 40R when the detection circuit 15 is in operation is characterized by the absence of frequencies below the respective operating cycle frequencies of the first and second switches 47 and 48.

[0055] Aspects of the present description have been described in detail with reference to the embodiments shown; however, the person skilled in the art will recognize that many modifications can be made without deviating from the scope of the present description. The present description is not limited to the exact structure and compositions disclosed herein; all modifications, changes, and variations apparent from the foregoing descriptions fall within the scope of the disclosure as defined by the appended claims. Furthermore, the present concepts expressly include all combinations and subcombinations of the preceding elements and features.

Claims

[1] Battery-electric system, comprising: a battery cell; a reference electrode; a voltage sensing circuit, called a sensing circuit, for measuring a cell voltage of the battery cell as the measured battery voltage and for outputting a digital voltage signal that indicates the measured battery voltage; comprising a compensation circuit that can be connected to the detection circuit: a voltage source; an isolation capacitor connected in parallel to the detection circuit; a first switch located between the voltage source and the detection circuit, wherein the first switch is configured to close in response to an initial switching control signal, thereby connecting the voltage source to the isolation capacitor for charging the isolation capacitor; and a second switch connected between the compensation circuit and the sensing circuit and configured to close out of phase with the first switch in response to a second switching control signal, wherein closing the second switch connects the reference electrode and the compensation circuit to the sensing circuit; and a battery control unit connected to the first switch and the second switch, wherein the battery control unit is operable to output the first switching control signal and the second switching control signal to control the respective duty cycles of the first switch and the second switch, thereby measuring the cell voltage via the reference electrode and the sensing circuit and subsequently performing a battery management action using the digital voltage signal. [2] Battery electrical system according to claim 1, wherein the battery control unit is programmed to control a closing and opening sequence of the first switch and the second switch to adjust a reference voltage between the reference electrode and a working electrode of the battery cell in a previous time step during the recharging of the isolation capacitor. [3] Battery-electric system according to claim 1, wherein the detection circuit comprises an analog-to-digital converter. [4] Battery electrical system according to claim 3, wherein the analog-to-digital converter comprises a buffer amplifier with a parasitic bias current and wherein the battery control unit is configured to control operation of the compensation circuit to minimize voltage drop at the reference electrode due to the parasitic bias current. [5] Battery electrical system according to claim 1, wherein the battery control unit is configured to control the operation of the compensation circuit such that a current consumption of the reference electrode is characterized by an absence of frequencies below a respective duty cycle frequency of the first switch and the second switch. [6] Battery electrical system according to claim 1, wherein the reference electrode is a porous electrode. [7] Battery electrical system according to claim 1, wherein the battery control unit is configured to estimate a state of charge, SOC, of ​​the battery cell as a battery management action and to set a charging or discharging parameter based on the SOC of the battery cell. [8] Battery electrical system according to claim 1, wherein the battery cell is a lithium-ion or lithium-metal battery cell. [9] Vehicle, comprising: a vehicle body; a set of wheels that are attached to the vehicle body; an electric drive motor connected to one or more of the wheels; and a battery pack connected to the electric drive motor, wherein the battery pack is configured to supply energy to the electric drive motor in order to power one or more of the road wheels, the battery pack comprising: a reference electrode; a voltage sensing circuit, called a sensing circuit, operable for measuring a cell voltage of a battery cell of the battery pack as measured battery voltage and for outputting a digital voltage signal that indicates the measured battery voltage; a compensation circuit that can be connected to the voltage sensing circuit, comprising: a voltage source; an isolation capacitor connected in parallel to the detection circuit; a first switch arranged between the voltage source and the isolation capacitor, the first switch being configured to close in response to a first switching control signal, thereby connecting the voltage source to the isolation capacitor; and a second switch connected between the compensation circuit and the sensing circuit and configured to close out of phase with the first switch in response to a second switching control signal, wherein closing the second switch connects the reference electrode and the compensation circuit to the measuring circuit; and a battery control unit connected to the first switch and the second switch, wherein the battery control unit is operable to output the first switching control signal and the second switching control signal to control their respective duty cycles, to measure the cell voltage via the reference electrode and the sensing circuit, and thereafter to perform a battery management action using the digital voltage signal. [10] Vehicle according to claim 9, wherein the battery control unit is programmed to control a closing and opening sequence of the first switch and the second switch in order to adjust a reference voltage between the reference electrode and a working electrode of the battery cell in a previous time step during the charging of the isolation capacitor.

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