Differential electrical impedance spectroscopy

Abstract

Such an apparatus, having a structure to measure a battery parameter of a battery of a plurality of batteries, can be implemented in a variety of applications. The apparatus can be configured to measure an alternating current (AC) electrical impedance of a battery cell by processing a difference between the battery cell and another battery cell. The battery cell under measurement experiences an AC excitation, while the other does not, with both battery cells sharing a common load current. This differential approach can reduce sensitivity to noisy battery load currents, which are common to both battery cells. This differential approach can also eliminate or substantially reduce a large direct current (DC) offset, i.e., the battery potential itself, under which AC signal measurements are burdened.

Description

[0001] Claiming priority

[0002] This application claims priority to U.S. Application Serial No. 16 / 872877, filed May 12, 2020, which is incorporated herein by reference in its entirety. Technical Field

[0003] This document relates to circuits, particularly circuits for measuring battery pack parameters. Background Technology

[0004] A battery management system (BMS) is used to track the state of charge (SOC) and state of health (SOH) of battery packs, such as, but not limited to, large battery packs used in electric vehicles. The BMS also balances the cells within the battery pack to maximize their lifespan and total stored energy. The BMS integrated circuit (IC) typically operates by measuring the voltage of each cell in the pack and, if necessary, partially bypassing the current flowing through each cell. The BMS IC also typically uses several temperature sensors mounted externally to the cells to measure their temperature. The data from these measurements is used in algorithms to calculate SOC and SOH (among others) and to assess whether the cells are operating at a safe temperature.

[0005] Several issues relate to inaccuracies in certain measurements. The accuracy of determining SOC by measuring battery voltage depends on a well-defined battery voltage and its reliance on SOC. This is not guaranteed by all battery chemistry, and it requires very precise voltage measurements, which in turn necessitate accurate voltage references and precise measurement circuitry. Secondly, measuring temperature via external sensors may underestimate the internal battery temperature. This affects lifespan estimates. Furthermore, these quantities, which are related to internal and external temperatures, can differ significantly under high-current conditions, such as during acceleration and braking. Better measurement of these quantities will improve battery pack applications, such as the usage of batteries in automobiles. Higher accuracy in SOC, SOH, and temperature will improve a vehicle's range, lifespan, and performance. Summary of the Invention

[0006] Such a device, capable of measuring battery pack parameters of a group of multiple battery packs, can be implemented in various applications. The device can be configured to measure the alternating current (AC) impedance of a battery pack by processing the difference between cells in one battery pack and cells in another. One battery pack experiences AC excitation, while the other does not, with the two battery packs sharing a common load current. This differential method reduces the measurement's sensitivity to noisy battery pack load currents, which is common for both battery packs. This differential method also eliminates or substantially reduces large direct current (DC) offsets, i.e., the battery pack potential itself, at which the AC signal measurement is burdened.

[0007] For example, in certain embodiments, an apparatus having structure to measure a battery parameter can be provided, disclosing: a signal driver connectable to two battery cells, the signal driver arranged to selectively excite a first battery cell of the two battery cells with a time-varying signal while maintaining a second battery cell of the two battery cells in a non-excited state during excitation of the first battery cell, the first battery cell and the second battery cell having a common load current battery cell in operation; a circuit to measure a voltage difference between a voltage on the first battery cell and a voltage on the second battery cell with the first battery cell excited and the second battery cell of the two battery cells in the non-excited state; and a signal processing circuit to process the measured voltage difference to determine an electrical impedance of the first battery cell.

[0008] In certain embodiments, a method of determining a battery parameter can be provided, disclosing: exciting a first battery with a time-varying signal; maintaining a second battery in a non-excited state during excitation of the first battery, wherein the first battery and the second battery have a common load current in operation; measuring a voltage difference between a voltage on the first battery and a voltage on the second battery with the first battery excited and the second battery in the non-excited state; and processing the measured voltage difference to determine an electrical impedance of the first battery.

[0009] In certain embodiments, an apparatus having structure to measure a battery parameter can be provided, disclosing: means for selectively exciting a first battery of a pair of batteries with a time-varying signal and maintaining a second battery of the pair in a non-excited state during excitation of the first battery, wherein the first battery and the second battery have a common load current in operation; means for measuring a voltage difference between a voltage on the first battery and a voltage on the second battery; and means for processing the measured voltage difference to determine an electrical impedance of the first battery. BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings, which are not necessarily drawn to scale, generally illustrate the various embodiments discussed in the disclosure.

[0011] Figure 1A Exemplary dual cell measurement circuits according to various embodiments are shown, which can be arranged in an apparatus as structure to measure a battery parameter of two batteries.

[0012] Figure 1AAn exemplary dual cell measurement circuit is shown according to various embodiments, which can be arranged in a device as a structure to measure battery pack parameters of two battery packs arranged as non-adjacent cells in a battery pack cell stack.

[0013] Figure 2 An exemplary dual cell measurement circuit is shown according to various embodiments, with a switched capacitor circuit to measure battery pack parameters of two battery packs.

[0014] Figure 3 An exemplary dual cell measurement circuit is shown according to various embodiments, with a switched capacitor circuit and a charge integrator to measure battery pack parameters of two battery packs.

[0015] Figure 4 An exemplary dual cell measurement circuit is shown according to various embodiments, with a switched capacitor circuit and a charge integrator with feedback to measure battery pack parameters of two battery packs.

[0016] Figure 5 A flowchart of features of an exemplary method of determining battery pack parameters according to various embodiments.

[0017] Figure 6 A flowchart of features of an exemplary method of determining battery pack parameters according to various embodiments. DETAILED DESCRIPTION

[0018] One method of measuring one or more battery pack parameters of a set of battery pack cells is not by voltage, but by frequency-dependent electrical impedance of each battery pack cell. In the range of, for example, 0.1 Hz to 10 kHz, the complex impedance of a battery pack cell is a function of SOC, SOH, and internal temperature in different ways, so each of these parameters can be determined by measuring impedance over frequency. In various embodiments, an electrical impedance spectroscopy (EIS) can be performed using a dual cell method to measure battery pack parameters. In two battery pack cells, only one battery pack cell is excited at a time, and there is a difference between the battery pack cell voltages of the two battery pack cells being processed. These two battery pack cells can be adjacent battery pack cells in a set of battery pack cells sharing a common load current, or they can be two non-adjacent battery pack cells in a set sharing a common load current. This difference measurement can enable load current and battery pack cell voltage offset compensation, making signal processing simpler. Such methods work particularly well because these methods are commensurate with algorithms that have the goal of balancing all the cells to each other. These methods can be further enhanced by applying the dual cell method to two adjacent cells, which can be well matched throughout the life cycle, resulting in good cancellation of common factors.

[0019] Using differential EIS in a dual-cell method can be implemented without using a high pass filter (HPF) and without measuring individual cell voltages, while providing substantially instantaneous load current compensation. This is in contrast to single-cell EIS, where a discharge switch used during balancing is typically driven by an AC signal that causes current to flow through the cell, resulting in a voltage response. In the single-cell EIS method, the voltage is then post-processed and the amplitude and phase shift are calculated, compared to the excitation current. Disadvantages of the single-cell EIS method include load current that disrupts the output voltage and the separate measurement of load current for compensation. This is especially true for low / mid frequency cases. In the single-cell EIS method, a dedicated IC is used for each battery pack cell to perform EIS, which is expensive, and the small AC signal needs to be separated from the large DC offset from the battery pack voltage itself.

[0020] In various embodiments, as taught herein, using a dual-cell method to measure EIS of battery pack parameters can provide a less expensive direct measurement method than a single-cell EIS method. In other embodiments, a multi-cell method similar to the dual-cell method taught herein can be used to perform EIS to measure battery pack parameters. Like the dual-cell method, the multi-cell method can include exciting one battery pack cell of a group of multiple battery pack cells while keeping the other battery pack cells of the group in a non-excited state, and making a differential measurement.

[0021] Figure 1A An embodiment of an example dual-cell measurement circuit 100A is shown, which can be arranged in a structure in a device to measure battery pack parameters of two battery packs 104-2 and 104-3. The dual-cell measurement circuit 100A is coupled to battery packs 104-2 and 104-3 of a group 102 of multiple battery packs 104-0, 104-1, 104-2, 104-3, 104-4, and 104-5 to determine battery pack parameters of the two battery packs using a dual-cell method. The dual-cell measurement circuit 100A can be coupled to battery pack 104-2 using four wires and can be coupled to battery pack 104-3 using four wires, where the coupling can be within the housing of these battery packs. With the dual-cell measurement circuit 100A, battery pack 104-2 can undergo AC excitation to measure battery pack parameters of battery pack 104-2 without battery pack 104-3 being excited, where the two battery pack cells share a common load current. Operation of the dual-cell measurement circuit 100A can include selecting battery pack 104-3 to undergo AC excitation to measure battery pack parameters of battery pack 104-3 when battery pack 104-2 is not excited. The order of measurement of battery pack parameters of battery packs 104-2 and 104-3 can be randomly selected or selected based on a process of the architecture or system in which battery packs 104-2 and 104-3 are deployed.

[0022] The plurality of battery packs 104-0, 104-1, 104-2, 104-3, 104-4, and 104-5 of the group 102 can be implemented as a battery pack cell stack that shares a common load current ILOAD in operation. The battery packs 104-0, 104-1, 104-2, 104-3, 104-4, and 104-5 can be arranged to operate with a common ILOAD in electrical series coupling battery packs 104-0, 104-1, and 104-2, 104-3, 104-3, and 104-5. Although Figure 1A While six battery packs are shown, the group 102 can be implemented as a group of battery pack cells with more or less than six battery packs. The battery packs 104-2 and 104-3 can be arranged as directly adjacent cells in the group 102, arranged as a battery pack cell stack with the battery packs 104-0, 104-1, 104-2, 104-3, 104-4, and 104-5 in series arrangement, such that ILOAD is common to each battery pack of the stack in operation. Alternatively, the battery packs 104-2 and 104-3 can be arranged in the group 102 separated from each other by one or more battery packs of the group 102.

[0023] The dual cell measurement circuit 100A includes a signal driver 105, a measurement circuit 110, and a signal processing circuit 120. The signal driver 105 can be attached to the battery packs 104-2 and 104-3 and arranged to selectively excite one of the two battery packs 104-2, 104-3 with a time-varying signal while holding the other of the two battery packs 104-2 and 104-3 in a non-excited state. During this AC excitation, the battery packs 104-2 and 104-3 can be in operation with a common load current. The AC excitation can be generated in a range of 1 Hz to 10 kHz depending on the impedance model used to process the input of the signal processing circuit 120. The signal driver 105 can be coupled to the battery pack 104-2 through a switch 112-2 and to the battery pack 104-3 through a switch 112-3.

[0024] Switches 112-2 and 112-3 can be implemented in a variety of different ways to provide a switching mechanism. Switches 112-2 and 112-3 can be implemented using field effect transistors (n-type or p-type), relays, bipolar junction transistors (npn or pnp), or other suitable switches. Switches 112-2 and 112-3 can be implemented in a variety of ways that facilitate integrated circuit construction, such as but not limited to, transistors arranged to be selectable between on or off modes. The internal resistance of switches 112-2 and 112-3 can provide some reasonably defined current levels to energize battery cells 104-2 and 104-3, respectively, during different portions of the dual cell measurement. Optionally, a resistor 113-2 can be added in series with switch 112-2, and a resistor 113-3 can be added in series with switch 112-3. When switch 112-2 is on and switch 112-3 is off, the magnitude of the energizing current is given by the battery voltage of battery pack 104-2 divided by the series resistance 112-2. When switch 112-3 is on and switch 112-2 is off, the magnitude of the energizing current is determined by the sum of the battery voltage of battery pack 104-3 and the voltage of series resistance 112-3, given by the battery voltage of battery pack 104-3 divided by series resistance 112-3. For ease of discussion Figure 1A a control unit that controls the operation of switches 112-2 and 112-3 is not shown in addition to signal driver 105.

[0025] Measurement circuit 110 can be implemented as a circuit that measures the voltage difference between the voltage on battery pack 104-2, which is energized, and the voltage on battery pack 104-3, which is in a non-energized state, of the two battery pack cells. Measurement circuit 110 also measures the voltage difference between the voltage on battery pack 104-2, which is in a non-energized state, and the voltage on battery pack 104-3, which is energized, of the two battery pack cells during monitoring of battery packs 104-2 and 104-3 by the dual cell method. Measurement circuit 110 can include a subtraction node at which the effect of ILOAD (e.g., the AC component of ILOAD) and the battery pack voltages are canceled with respect to battery pack 104-2 and battery pack 104-3 because ILOAD is common to both battery pack 104-2 and battery pack 104-3, where these cells have the same nominal voltage. Because battery pack 104-2 and battery pack 104-3 have the same cell voltage characteristics, the differential approach of the dual cell measurement technique allows for subtraction of errors caused by the voltage levels of the similar battery packs, thereby canceling these caused errors.

[0026] The measurement circuit 110 can be coupled to the battery pack 104-2 opposite the switch 112-2 through resistors 108-21 and 108-22. A capacitor 107-2 is connected across the battery pack 104-2 to the input of the measurement circuit 110 between resistors 108-20 and 108-2, opposite the coupling of these resistors to the battery pack 104-2. The measurement circuit 110 can be coupled to the battery pack 104-3 opposite the switch 112-3 through resistors 108-31 and 108-32. A capacitor 107-3 is connected across the battery pack 104-3 to the input of the measurement circuit 110 between resistors 108-31 and 108-32, opposite the coupling of these resistors to the battery pack 104-3.

[0027] The signal processing circuit 120 can be configured to process the measured voltage difference from the measurement circuit 110 to determine the electrical impedance of the battery pack 104-2 in response to the battery pack 104-2 being energized and the battery pack 104-3 not being energized. The signal processing circuit 120 can also process the measured voltage difference from the measurement circuit 110 to determine the electrical impedance of the battery pack 104-3 in response to the battery pack 104-3 being energized and the battery pack 104-2 not being energized. The electrical impedance of the battery pack can be calculated using the ratio between the drive signal applied in the dual battery measurement circuit 100A and the detection signal responsive to the application of the drive signal in the dual battery measurement circuit 100A.

[0028] The signal processing circuit 120 can be implemented to provide one or more signals via a line 125 to provide feedback or control to the signal driver 105. The signal driver 105 can be structured to produce time-varying signals at different frequencies, the signal processing circuit 120 being arranged to process the frequency-dependent electrical impedance of the battery pack 104-2 at the different frequencies. The signal driver 105 can be operable to selectively energize the battery pack 104-3 with a second time-varying signal at a different frequency while maintaining the battery pack 104-2 in a non-energized state during energization of the battery pack 104-3. The signal processing circuit 120 can be coupled to the clock 115 for processing or providing frequency control to the signal driver 105. The signal processing circuit 120 can have an output to transmit digital data representing the frequency-dependent electrical impedance of the battery pack 104-2 or the battery pack 104-3 to a processor over a bus for use in determining one or more of the state of charge, state of health, and internal temperature of the battery pack 104-3 or the battery pack 104-2, respectively, using the frequency-dependent electrical impedance.

[0029] A dual cell measurement circuit 100A including a signal driver 105, a measurement circuit 110 that measures a voltage difference, a signal processing circuit 120, and other components can be provided in an integrated circuit that can be attached to a battery pack 104-2 and a battery pack 104-3. An apparatus, which can include an integrated circuit including a dual cell measurement circuit, such as dual cell measurement circuit 100A, can include a plurality of integrated circuits that are attached to a plurality of pairs of battery pack cells of a battery pack cell stack, with each integrated circuit coupled to a pair of battery pack cells that is different from the battery pack cells coupled to the other integrated circuits of the plurality of integrated circuits. Such battery pack cells in the stack can be coupled in electrical series such that, in operation, a load current is common to each battery pack cell in the stack. Each integrated circuit so constructed can include, with respect to the pair of battery pack cells to which the integrated circuit is attached, a signal driver that can be attached to the pair of battery pack cells, a measurement circuit that measures a voltage difference between a voltage on one battery pack cell of the pair and a voltage on the other battery pack cell of the pair, and a signal processing circuit that processes the measured voltage difference to determine an electrical impedance of each battery pack cell of the pair. The signal driver can be arranged to selectively excite one battery pack cell of a pair of battery pack cells with a time-varying signal while maintaining the other battery pack cell of the pair in a non-excited state during excitation of the one battery pack cell of the pair. The measurement circuit measures the voltage difference when the one battery pack cell of the pair is excited and the other battery pack cell of the pair is in the non-excited state. The signal processing circuit determines the electrical impedance of the one battery pack cell process from the measured voltage difference. The signal driver can then reverse the application of the time-varying signal by exciting the battery pack cell of the pair of battery pack cells that was previously in the non-excited state while maintaining the previously excited battery pack of the pair in the non-excited state. From the reversed application of the time-varying signal, the electrical impedance of the other battery pack cell of the pair of battery pack cells can be determined.

[0030] In Figure 1A In the example of FIG. 1, the battery pack cells of the set 102 can be coupled to three integrated circuits as described above. An integrated circuit can be attached to the pair of battery packs 104-0 and 104-1 to monitor these battery packs and determine the electrical impedances of the battery pack 104-0 and the battery pack 104-1. As described above, an integrated circuit can be attached to the pair of battery packs 104-2 and 104-3 to monitor the battery packs and determine the electrical impedances of the battery pack 104-2 and the battery pack 104-3. An integrated circuit can be attached to the pair of battery packs 104-4 and 104-5 to monitor these battery packs and determine the electrical impedances of the battery pack 104-4 and the battery pack 104-5. In arrangements in which the set 102 has more than six battery packs, such an arrangement can include more than three independent integrated circuits, for example, N / 2 integrated circuits, where N is the number of battery packs in the set 102, where N is a positive even integer. A shared arrangement can be used for a set 102 having an odd number of battery packs.

[0031] Figure 1B An example dual-cell measurement circuit 100B is shown that can be arranged in a device as a structure to measure battery pack parameters of two battery packs 104-1 and 104-4, where the two battery packs are arranged as non-adjacent battery cells of the battery pack cells of the group 102. The dual-cell measurement circuit 100B can include Figure 1A the components of the dual-cell measurement circuit 100A of FIG. IB, where the components are coupled to two non-adjacent battery packs, in the example of FIG. IB, battery packs 104-1 and 104-4.

[0032] The dual-cell measurement circuit 100B is coupled to the battery packs 104-1 and 104-5 to determine battery pack parameters of the two battery packs using a dual-cell method. The dual-cell measurement circuit 100B can be coupled to the battery pack 104-1 using four wires and can be coupled to the battery pack 104-4 using four wires, where the coupling can be within the housing of the battery packs. With the dual-cell measurement circuit 100B, the battery pack 104-1 can be subjected to AC excitation while the battery pack 104-4 is not excited to measure the battery pack parameters of the battery pack 104-1, where the two battery pack cells share a common load current. The operation of the dual-cell measurement circuit 100B can include selecting the battery pack 104-4 to be subjected to AC excitation to measure the battery pack parameters of the battery pack 104-4 while the battery pack 104-1 is not excited. The order of measurement of the battery pack parameters of the battery packs 104-1 and 104-4 can be randomly selected or selected based on a process of the architecture or system in which the battery pack 104-1 or 104-4 is deployed.

[0033] The group 102 of the plurality of battery packs 104-0, 104-1, 104-2, 104-3, 104-4, and 104-5 can be implemented as a stack of battery pack cells that share a common load current ILOAD in operation. The battery packs 104-0, 104-1, 104-2, 104-3, 104-4, and 104-5 can be arranged to operate with the common ILOAD with the battery packs 104-0, 104-1, and 104-2, 104-3, 104-3, and 104-5 coupled in electrical series. Although FIG. IB shows six battery packs, the group 102 can be implemented as a group of battery pack cells with more or less than six battery packs.

[0034] The dual cell measurement circuit 100B includes a signal driver 105, a measurement circuit 110, and a signal processing circuit 120. The signal driver 105 can be attached to the battery packs 104-1 and 104-4 and arranged to selectively energize one of the two battery packs 104-1 and 104-4 with a time-varying signal while holding the other of the two battery packs 104-1 and 104-4 in a non-energized state. During this AC excitation, the battery packs 104-1 and 104-4 can be in operation with a common load current. The AC excitation can be generated in a range of 1 Hz to 10 kHz depending on the impedance model used to process the input of the signal processing circuit 120. The signal driver 105 can be coupled to the battery pack 104-1 through a switch 112-1 and to the battery pack 104-4 through a switch 112-4.

[0035] The switches 112-1 and 112-4 can be implemented in a variety of different ways to provide the switching mechanism. The switches 112-1 and 112-4 can be implemented using field effect transistors (n-type or p-type), relays, bipolar junction transistors (npn or pnp), or other suitable switches. The switches 112-1 and 112-4 can be implemented in a variety of ways that facilitate integrated circuit construction, such as but not limited to, transistors arranged to be selectable between on or off modes. The internal resistance of the switches 112-1 and 112-4 can provide some reasonably defined current levels to the energized battery pack cells 104-1 and 104-4, respectively, during different parts of the dual cell measurement. Optionally, a resistor 113-1 can be added in series with the switch 112-1 and a resistor 113-4 can be added in series with the switch 112-4. When the switch 112-1 is on and the switch 112-4 is off, the magnitude of the excitation current is derived from the battery voltage of the battery pack 104-1 divided by the series resistance 112-1. When the switch 112-4 is on and the switch 112-1 is off, the magnitude of the excitation current is derived from the battery voltage of the battery pack 104-4 divided by the series resistance 112-4. For ease of discussion of Figure IB, a control unit that controls the operation of the switches 112-1 and 112-4 is not shown instead of the signal driver 105.

[0036] The measurement circuit 110 can be implemented as a circuit that measures the voltage difference between the voltage on the battery pack 104-1 and the voltage on the battery pack 104-4, with the battery pack 104-1 energized and the battery pack 104-4 of the two battery pack cells in a non-energized state. The measurement circuit 110 also measures the voltage difference between the voltage on the battery pack 104-1 and the voltage on the battery pack 104-4 during monitoring of the battery pack 104-1 and 104-4 by the dual cell method, with the battery pack 104-4 energized and the battery pack 104-1 of the two battery pack cells in a non-energized state. The measurement circuit 110 can include a subtraction node at which the effect of ILOAD (e.g., the AC component of ILOAD) and the battery pack voltages relative to the battery pack 104-1 and battery pack 104-4 are cancelled out because ILOAD is common to both battery pack 104-1 and battery pack 104-4, which have the same nominal voltage. With the battery pack 104-1 and battery pack 104-4 having the same cell voltage characteristics, the differential approach of the dual cell measurement technique allows subtraction of errors caused by the voltage levels of the similar battery packs, thereby cancelling out these caused errors.

[0037] The measurement circuit 110 can be coupled to the battery pack 104-1 opposite the switch 112-1 through resistors 108-11 and 108-12. The capacitor 107-1 is coupled across the battery pack 104-1 to the input of the measurement circuit 110 between the resistors 108-11 and 108-12, opposite the coupling of these resistors to the battery pack 104-1. The measurement circuit 110 can be coupled to the battery pack 104-4 opposite the switch 112-4 through resistors 108-41 and 108-42. The capacitor 107-4 is coupled from the battery pack 104-4 to the input of the measurement circuit 110 between the resistors 108-41 and 108-42, opposite the coupling of these resistors to the battery pack 104-4.

[0038] The signal processing circuit 120 can be configured to process the measured voltage difference from the measurement circuit 110 to determine the electrical impedance of the battery pack 104-1 in response to the battery pack 104-1 being energized and the battery pack 104-4 not being energized. The signal processing circuit 120 can also process the measured voltage difference from the measurement circuit 110 to determine the electrical impedance of the battery pack 104-4 in response to the battery pack 104-4 being energized and the battery pack 104-1 not being energized. The electrical impedance of the battery pack can be calculated using the ratio between the drive signal applied in the dual cell measurement circuit 100B and the detection signal responsive to the application of the drive signal in the dual cell measurement circuit 100B.

[0039] The signal processing circuit 120 can be implemented to provide one or more signals via a line 125 to provide feedback or control to the signal driver 105. The signal driver 105 can be structured to generate time-varying signals at different frequencies, with the signal processing circuit 120 arranged to process the measured voltage differences at the different frequencies to determine a frequency-dependent electrical impedance of the battery pack 104-1. The signal driver 105 can be operable to selectively excite the battery pack 104-4 with second time-varying signals at different frequencies while maintaining the battery pack 104-1 in a non-excited state during excitation of the battery pack 104-4. The signal processing circuit 120 can be coupled to a clock 115 for processing or providing frequency control to the signal driver 105. The signal processing circuit 120 can have an output to transmit digital data representing the frequency-dependent electrical impedance of the battery pack 104-1 or the battery pack 104-4 to a processor over a bus for use in determining one or more of a state of charge, a state of health, and an internal temperature of the battery pack 104-1 or the battery pack 104-4, respectively.

[0040] A dual cell measurement circuit 100B, including a signal driver 105, a measurement circuit 110 that measures a voltage difference, a signal processing circuit 120, and other components, can be provided in an integrated circuit that can be attached to a pair of battery packs 104-1 and 104-4. An apparatus, which can include an integrated circuit containing a dual cell measurement circuit, such as dual cell measurement circuit 100B, can include a plurality of integrated circuits that are attached to a plurality of pairs of battery pack cells of a battery pack cell stack, with each integrated circuit coupled to a pair of battery pack cells that is different from the battery pack cells coupled to the other integrated circuits of the plurality of integrated circuits. Such pairs of battery pack cells in the stack can be coupled in electrical series, such that, in operation, a load current is common to each battery pack cell in the stack. Each integrated circuit so constructed can include, with respect to the pair of battery pack cells to which the integrated circuit is attached, a signal driver that can be attached to the pair of battery pack cells, a measurement circuit that measures a voltage difference between a voltage on one battery pack cell of the pair and a voltage on the other battery pack cell of the pair, and a signal processing circuit that processes the measured voltage difference to determine an electrical impedance of each battery pack cell of the pair. The signal driver can be arranged to selectively excite one battery pack cell of a pair of battery pack cells with a time-varying signal while maintaining the other battery pack cell of the pair in a non-excited state during excitation of the one battery pack cell of the pair. The measurement circuit measures the voltage difference when the one battery pack cell of the pair is excited and the other battery pack cell of the pair is in the non-excited state. The signal processing circuit determines the electrical impedance of the one battery pack cell process from the measured voltage difference. The signal driver can then reverse the application of the time-varying signal by exciting the battery pack cell of the pair of battery pack cells that was previously in the non-excited state while maintaining the previously excited battery pack of the pair in the non-excited state. From the reversed application of the time-varying signal, the electrical impedance of the other battery pack cell of the pair of battery pack cells can be determined.

[0041] In the example of FIG. IB, the battery pack cells of the set 102 can be coupled to three integrated circuits as described above. An integrated circuit can be attached to the pair of battery packs 104-0 and 104-2 to monitor these battery packs and determine the electrical impedances of the battery pack 104-0 and the battery pack 104-2. As described above, an integrated circuit can be attached to the pair of battery packs 104-1 and 104-4 to monitor the battery packs and determine the electrical impedances of the battery pack 104-1 and the battery pack 104-4. An integrated circuit can be attached to the pair of battery packs 104-3 and 104-5 to monitor these battery packs and determine the electrical impedances of the battery pack 104-3 and the battery pack 104-5. In arrangements in which the set 102 has more than six battery packs, such an arrangement can include more than three independent integrated circuits, for example, N / 2 integrated circuits, where N is the number of battery packs in the set 102, where N is a positive even integer. A shared arrangement can be used for a set 102 that has an odd number of battery packs.

[0042] Figure 2 An embodiment of an example dual cell measurement circuit 200 is shown, with a switched capacitor circuit for sampling battery pack cells 204-2 and 204-3. The dual cell measurement circuit 200 can be arranged in a device as a structure to measure battery pack parameters of two battery packs 204-2 and 204-3. The switched capacitor circuit providing a sampling network can provide a direct method to calculate the difference of two battery voltages by sampling the batteries at a high frequency. The sampling capacitor of the switched capacitor circuit can be connected to a charge balancing ADC 210 so that essentially only the charge difference AQ is processed. This can also be performed by using a continuous time system of resistors and transconductance (gm) stages. With fast sampling or continuous time compensation, the load current is compensated almost instantaneously with very high timing accuracy. This method is much better than using two separate, slower ADCs, which can be located at different points in the system.

[0043] As shown in Figure 2 The dual cell measurement circuit 200 is coupled to battery pack 204-2 and 204-3 of a plurality of battery packs 204-0, 204-1, 204-2, 204-3, 204-4, and 204-5 of a group 202, as shown in FIG. 2, to determine battery pack parameters of two battery packs 204-2 and 204-3 using a dual cell method. The dual cell measurement circuit 200 can be coupled to battery pack 204-2 using four wires and can be coupled to battery pack 204-3 using four wires, where the coupling can be within the housing of these battery packs. With the dual cell measurement circuit 200 arrangement to measure battery pack parameters of battery pack 204-2, battery pack 204-2 can undergo AC excitation with battery pack 204-3 not being excited, where the two battery pack cells share a common load current. The operation of the dual cell measurement circuit 200 can include selecting battery pack 204-3 to undergo AC excitation when battery pack 204-2 is not excited to measure battery pack parameters of battery pack 204-3. The measurement order of battery pack parameters of battery pack 204-2 and 204-3 can be randomly selected or based on a process of the architecture or system where battery pack 204-2 and 204-3 are deployed. The control to measure battery pack parameters of battery pack 204-2 and 204-3 can be implemented by signal processing circuit 220.

[0044] The plurality of battery packs 204-0, 204-1, 204-2, 204-3, 204-4, and 204-5 of the group 202 can be implemented as a battery pack cell stack that shares a common load current ILOAD in operation. The battery packs 204-0, 204-1, 204-2, 204-3, 204-4, and 204-5 can be arranged to operate with a common ILOAD with the battery packs 204-0, 204-1, 204-2, 204-3, 204-4, and 204-5 coupled in electrical series. Although Figure 2 While six battery packs are shown, the group 202 can be implemented as a group of battery pack cells with more or less than six battery packs. The battery packs 204-2 and 204-3 can be arranged as directly adjacent cells in the group 202, arranged as a battery pack cell stack with the battery packs 204-0, 204-1, 204-2, 204-3, 204-4, and 204-5 arranged in series, such that ILOAD is common to each of the battery packs of the stack in operation. Alternatively, the battery packs 204-2 and 204-3 can be arranged in the group 202 separated from each other by one or more battery packs of the group 202.

[0045] The signal processing circuit 220 can generate one or more signals to selectively energize one of the two battery packs 204-2 and 204-3 with a time-varying signal while maintaining the other of the two battery packs 204-2 and 204-2 in a non-energized state. During this AC energization, the battery packs 204-2 and 204-3 can be operated with a common ILOAD. The signal processing circuit 220 is coupled to a switch 211 that selectively couples the signal processing circuit 210 to either the transistor 212-2 or the transistor 212-3. The switch 211 can be implemented in the form of a field effect transistor (n-type or p-type), a relay, a bipolar junction transistor (npn or pnp), or other suitable switching device. The signal processing circuit 220 can be implemented to provide one or more signals to the switch 211 through a line 225. Although the transistors 212-2 and 212-3 can be implemented in various forms of transistors, such as a field effect transistor (n-type or p-type), a relay, a bipolar junction transistor (npn or pnp), or other suitable switching device, Figure 2The example uses n-channel insulated-gate field-effect transistors. Optionally, a resistor can be added in series with transistor 212-2, and a resistor can be added in series with transistor 212-3. When transistor 212-2 is on and transistor 212-3 is off, the magnitude of the excitation current is derived from the battery voltage of battery pack 204-2 divided by the resistance in series with transistor 212-1. When transistor 212-3 is on and transistor 212-2 is off, the magnitude of the excitation current is derived from the battery voltage of battery pack 204-3 divided by the resistance in series with transistor 212-3. Battery pack 204-2 is coupled to transistor 212-2 of dual-battery measurement circuit 200 with its drain coupled to one end of battery pack 204-2 and its source coupled to the other end of battery pack 204-2. Battery pack 204-3 is coupled to transistor 212-3 of dual-battery measurement circuit 200 with its drain coupled to one end of battery pack 204-3 and its source coupled to the other end of battery pack 204-3.

[0046] Battery pack 204-2 can be coupled to resistors 208-21 and 208-22 of dual-battery measurement circuit 200 opposite transistor 212-2. Capacitor 207-21 is coupled between resistors 208-20 and 208-22 opposite the coupling of these resistors to battery pack 204-2. The two nodes of the connection of capacitor 207-21 to resistors 208-21 and 208-22 are coupled to a portion of the switched-capacitor circuit to measure charge Ql. The portion of the switched-capacitor circuit includes switches 209-21, 209-22, 209-23, 209-24, 209-25, and 209-26, and capacitors 207-22 and 207-23. This portion of the switched-capacitor circuit is coupled to two inputs of charge-balancing ADC 210 through switches 209-25 and 209-26. Capacitor 207-22 is coupled between switches 209-21 and 209-25, and capacitor 207-23 is coupled between switches 209-22 and 209-23. Capacitor 207-22 is coupled to capacitor 209-23 using switches 209-23 and 209-24.

[0047] The battery pack 204-3 can be coupled to the resistors 208-31 and 208-32 of the dual battery measurement circuit 200 opposite the transistor 212-3. The capacitor 207-31 is coupled between the resistors 208-33 and 208-32 opposite the coupling of these resistors to the battery pack 204-3. The two nodes of the connection of the capacitor 207-31 to the resistors 208-31 and 208-32 are coupled to a portion of the switched capacitor circuit to measure the charge Q2. This portion of the switched capacitor circuit includes the switches 209-31, 209-32, 209-33, 209-34, 209-35, and 209-36 and the capacitors 207-22 and 207-33. This portion of the switched capacitor circuit is coupled to two inputs of the charge balancing ADC 210 through the switches 209-35 and 209-36. The capacitor 207-32 is coupled between the switches 209-31 and 209-35 and the capacitor 207-23 is coupled between the switches 309-32 and 209-33. The capacitor 307-32 is coupled to the capacitor 209-33 using the switches 209-33 and 209-34. The switches 209-35 and 209-36 associated with the battery pack 204-3 are coupled to the switches 209-25 and 209-26 and the charge balancing ADC 210 with opposite polarity to the battery pack 204-2 and the battery pack 204-3, respectively, so that substantially only the charge difference AQ is processed. The effects of ILOAD, such as the AC component of the load current and the battery voltage, are cancelled out with respect to the battery pack 204-2 and the battery pack 204-3 because ILOAD is common to both battery packs 204-2 and 204-3, which have the same nominal voltage.

[0048] The switches 211, 209-21...209-26, and 209-31...209-36 can be implemented in a variety of different ways to provide a switching mechanism. These switches can be implemented in a variety of ways that facilitate integrated circuit construction, such as but not limited to transistors arranged to be selectable between an on mode or an off mode. Although not shown, control signals to these switches can be provided by the signal processing circuit 220 or other control unit. The switches 209-21...209-26 and 209-31...209-36 of the switched capacitor circuit can operate at about 1 MHz or other relatively high rate, while the AC excitation can be in the range of 1 Hz to 10 kHz or other range.

[0049] The signal processing circuit 220 can be configured to process the input from the charge balancing ADC 210 to determine the electrical impedance of the battery pack 204-2 in response to the battery pack 204-2 being energized and the battery pack 204-3 not being energized. The signal processing circuit 220 can also process the input from the charge balancing ADC 210 to determine the electrical impedance of the battery pack 204-3 in response to the battery pack 204-3 being energized and the battery pack 204-2 not being energized. The electrical impedance of a battery pack can be calculated using a ratio between a drive signal applied in the dual battery measurement circuit 200 and a detection signal in the dual battery measurement circuit 200 in response to the application of the drive signal. The signal processing circuit 220 can be structured to generate time-varying signals at different frequencies, where the signal processing circuit 220 is arranged to process the input from the charge balancing ADC 210 to determine the electrical impedance of the battery pack 204-2. The signal processing circuit 220 can be operable to selectively energize the battery pack 204-3 with a second time-varying signal at a different frequency while maintaining the battery pack 204-2 in a non-energized state during the energization of the battery pack 204-3. The signal processing circuit 220 can be arranged to transmit digital data representing the frequency-dependent electrical impedance of the battery pack 204-2 or the battery pack 204-3 over a bus to a processor, where one or more of a state of charge, a state of health, and an internal temperature of the battery pack 204-3 or the battery pack 204-2, respectively, is determined using the frequency-dependent electrical impedance.

[0050] The dual battery measurement circuit 200, including the charge balancing ADC 210, the signal processing circuit 220, and other components, can be provided in an integrated circuit, where the integrated circuit is attachable to the battery pack 204-2 and the battery pack 204-3. An apparatus, which can include an integrated circuit including the dual battery measurement circuit, such as the dual battery measurement circuit 200, can include a plurality of integrated circuits attached to a plurality of pairs of battery pack cells of a battery pack cell stack, where each integrated circuit is coupled to a pair of battery pack cells different from the battery pack cells coupled to the other integrated circuits of the plurality of integrated circuits. Such battery pack cells in the stack can be coupled in electrical series such that, in operation, a load current is common to each battery pack cell in the stack. Each integrated circuit structured can include a charge balancing ADC, a switched capacitor circuit, and a signal processing circuit to determine the electrical impedance of each battery pack cell of the pair relative to the pair of battery pack cells to which the integrated circuit is attached. A signal driver can be arranged to selectively energize one battery pack cell of a pair of battery pack cells with a time-varying signal while maintaining the other battery pack cell of the pair in a non-energized state during the energization of the one battery pack cell of the pair. The charge balancing ADC measures a voltage difference when the one battery pack cell of the pair is energized and the other battery pack cell of the pair is in a non-energized state.

[0051] The signal processing circuit determines the electrical impedance of one battery cell by measuring the voltage difference. The signal driver can then reverse the application of the time-varying signal by exciting the battery cell in the pair of battery cells that was previously in the non-excited state while keeping the previously excited battery cell of the pair in the non-excited state. From the reversed application of the time-varying signal, the electrical impedance of the other battery cell of the pair of battery cells can be determined.

[0052] In Figure 2 In the example of the set 202 of battery cells, the battery cells of the set 202 can be coupled to three integrated circuits as described above. The integrated circuits can be attached to the pair of battery cells 204-0 and 204-1 to monitor the battery cells and determine the electrical impedance of the battery cell 204-0 and the battery cell 204-1. The integrated circuits can be attached to the pair of battery cells 204-2 and 204-3 to monitor the battery cells and determine the electrical impedance of the battery cell 204-2 and the battery cell 204-3 as described above. The integrated circuits can be attached to the pair of battery cells 204-4 and 204-5 to monitor the battery cells and determine the electrical impedance of the battery cell 204-4 and the battery cell 204-5. In arrangements where the set 202 has more than six battery cells, such an arrangement can include more than three independent integrated circuits, for example, N / 2 integrated circuits, where N is the number of battery cells in the set 202, where N is a positive even integer. Shared arrangements can be used for sets 202 having an odd number of battery cells.

[0053] Figure 3 An embodiment of an example dual cell measurement circuit 300 is shown, with a switched capacitor circuit for sampling battery cell 304-2 and battery cell 304-3. The switched capacitor circuit providing the sampling network can provide a direct method to compute the difference of the two battery voltages by sampling the batteries at a high frequency. The sampling capacitor of the switched capacitor circuit can be connected to a charge integrator 310 with opposite polarity, so that essentially only the charge difference AQ is processed. This can also be performed by using resistors and gm stage continuous time systems. With fast sampling or continuous time compensation, the load current is compensated almost instantaneously with very high timing accuracy. This approach is much better than using two separate, slower ADCs, which can be located at different points in the system.

[0054] As Figure 3As shown in the middle, the dual cell measurement circuit 300 is coupled to the battery packs 304-2 and 304-3 of the plurality of battery packs 304-0, 304-1, 304-2, 304-3, 304-4, and 304-5 of the set 302 to determine battery pack parameters of the two battery packs 304-2 and 304-3 using a dual cell method. The dual cell measurement circuit 300 can be coupled to the battery pack 304-2 using four wires and can be coupled to the battery pack 304-3 using four wires, where the coupling can be within the housing of these battery packs. With the dual cell measurement circuit 300 arrangement to measure the battery pack parameters of the battery pack 304-2, the battery pack 304-2 can experience AC excitation with the battery pack 304-3 not being excited, where the two battery pack cells share a common load current. The operation of the dual cell measurement circuit 300 can include selecting the battery pack 304-3 to experience AC excitation while the battery pack 304-2 is not excited to measure the battery pack parameters of the battery pack 304-3. The order of measurement of the battery pack parameters of the battery packs 304-2 and 304-3 can be randomly selected or based on a process of the architecture or system in which the battery packs 304-2 and 304-3 are deployed. The control of measuring the battery pack parameters of the battery packs 304-2 and 304-3 can be implemented by the drive / demodulation circuit 320.

[0055] The plurality of battery packs 304-0, 304-1, 304-2, 304-3, 304-4, and 304-5 of the set 302 can be implemented as a battery pack cell stack that share a common load current ILOAD in operation. The battery packs 304-0, 304-1, 304-2, 304-3, 304-4, and 304-5 can be arranged to operate with the common ILOAD with the battery packs 304-0, 304-1, 304-2, 304-3, 304-4, and 304-5 coupled in electrical series. Although Figure 3 While six battery packs are shown, the set 302 can be implemented as a set of battery pack cells with more or less than six battery packs. The battery packs 304-2 and 304-3 can be arranged as directly adjacent cells in the set 302, arranged as a battery pack cell stack with the battery packs 304-0, 304-1, 304-2, 304-3, 304-4, and 304-5 arranged in series, such that in operation, ILOAD is common to each battery pack of the stack. Alternatively, the battery packs 304-2 and 304-3 can be arranged in the set 302 separated from each other by one or more battery packs of the set 302.

[0056] The drive / demodulation circuit 320 can generate one or more signals to selectively energize one of the two battery packs 304-2 and 304-3 with a time-varying signal while maintaining the other of the two battery packs 304-2 and 304-3 in a non-energized state. During this AC energization, the battery packs 304-2 and 304-3 can be in operation with a common ILOAD. The drive / demodulation circuit 320 is coupled to a switch 311 that selectively couples the drive / demodulation circuit 320 to either the transistor 312-2 or the transistor 312-3. The switch 311 can be implemented in the form of a field effect transistor (n-type or p-type), a relay, a bipolar junction transistor (npn or pnp), or other suitable switching device. The drive / demodulation circuit 320 can be implemented to provide one or more signals to the switch 311 through a line 325. Although the transistors 312-2 and 312-3 can be implemented in various forms of transistors, such as a field effect transistor (n-type or p-type), a relay, a bipolar junction transistor (npn or pnp), or other suitable switching device, Figure 3 The example uses an n-channel insulated-gate field-effect transistor. Optionally, a resistor can be added in series with the transistor 312-2, and a resistor can be added in series with the transistor 312-3. When the transistor 312-2 is on and the transistor 312-3 is off, the magnitude of the energizing current is derived from the battery voltage of the battery pack 304-2 divided by the resistance in series with the transistor 312-1. When the transistor 312-3 is on and the transistor 312-2 is off, the magnitude of the energizing current is derived from the battery voltage of the battery pack 304-3 divided by the resistance in series with the transistor 312-3. The battery pack 304-2 is coupled to the transistor 312-2 of the dual-battery measurement circuit 300 with its drain coupled to one end of the battery pack 304-2 and its source coupled to the other end of the battery pack 304-2. The battery pack 304-3 is coupled to the transistor 312-3 of the dual-battery measurement circuit 300 with its drain coupled to one end of the battery pack 304-3 and its source coupled to the other end of the battery pack 304-3.

[0057] Battery pack 304-2 can be coupled to resistors 308-21 and 308-22 of dual battery measurement circuit 300 opposite transistor 312-2. Capacitor 307-21 is coupled between resistors 308-21 and 308-22 opposite the coupling of these resistors to battery pack 304-2. Two nodes of the connection of capacitor 307-21 to resistors 308-21 and 308-22 are coupled to a portion of switched capacitor circuit to measure charge Ql. The portion of switched capacitor circuit includes switches 309-21, 309-22, 309-23, 309-24, 309-25, and 309-26, and capacitors 307-22 and 307-23. The portion of switched capacitor circuit is coupled to two inputs of charge integrator 310 through switches 309-25 and 309-26. Capacitor 307-22 is coupled between switches 309-21 and 309-25, and capacitor 307-23 is coupled between switches 309-22 and 309-23. Capacitor 307-22 is coupled to capacitor 307-23 using switches 309-23 and 309-24.

[0058] Battery pack 304-3 can be coupled to resistors 308-31 and 308-32 of dual battery measurement circuit 300 opposite transistor 312-3. Capacitor 307-31 is coupled between resistors 308-33 and 308-32 opposite the coupling of these resistors to battery pack 304-3. Two nodes of the connection of capacitor 307-31 to resistors 308-31 and 308-32 are coupled to a portion of switched capacitor circuit to measure charge Q2. The portion of switched capacitor circuit includes switches 309-31, 309-32, 309-33, 309-34, 309-35, and 309-36, and capacitors 307-22 and 307-33. Capacitor 307-32 is coupled between switches 309-31 and 309-35, and capacitor 307-23 is coupled between switches 309-32 and 309-33. Capacitor 307-32 is coupled to capacitor 307-33 using switches 309-33 and 309-34. The portion of switched capacitor circuit is coupled to two inputs of charge integrator 310 through switches 309-35 and 309-36. Switches 309-35 and 309-36 are coupled to switches 309-26 and 309-25, respectively, and charge integrator 310 is opposite in polarity such that substantially only the charge difference AQ is processed. The effects of ILOAD, such as the AC component of load current and battery pack voltage, are cancelled out for battery pack 304-2 and battery pack 304-3 because ILOAD is common to both battery packs, which have the same nominal voltage.

[0059] Switches 311, 309-21...309-26, and 309-31...309-36 can be implemented in a variety of different ways to provide a switching mechanism. These switches can be implemented in a variety of ways that facilitate integrated circuit construction, such as but not limited to transistors arranged to be selectable between an on mode or an off mode. Although not shown, control signals to these switches can be provided by signal processing circuit 320 or other control unit. Switches 309-21...309-26 and 309-31...309-36 of the switched capacitor circuit can operate at about 1 MHz or other relatively high rate, while the AC excitation can be in the 1 Hz to 10 kHz or other range.

[0060] Charge integrator 310 is an integrator circuit that integrates the charge difference from the sampling capacitor of the switched capacitor circuit that is opposite in polarity from the integrating circuit. An input of charge integrator 310 is coupled to one end of capacitor 307-44, and an output of charge integrator 310 is coupled to the other end of capacitor 307-44. The other two inputs of charge integrator 310 are coupled to one end of capacitor 307-45, and the other outputs of charge integrator 310 are coupled to the other end of capacitor 307-45. These two outputs of charge integrator 310 are coupled to ADC 335 at two different inputs of ADC 335. An output of ADC 335 is coupled to an input of drive / demodulation circuit 320. This arrangement of charge integrator 310 and ADC 335 can provide a charge balancing ADC circuit that can operate similarly to charge balancing ADC 210 of Figure 2 Drive / demodulation circuit 320 can be implemented similarly to signal processing circuit 220 of Figure 2 .

[0061] The drive / demodulation circuit 320 can be configured to process the input from the ADC 335 to determine the electrical impedance of the battery pack 304-2 in response to the battery pack 304-2 being energized and the battery pack 304-3 not being energized. The drive / demodulation circuit 320 can also process the input from the ADC 335 to determine the electrical impedance of the battery pack 304-3 in response to the battery pack 304-3 being energized and the battery pack 304-2 not being energized. The electrical impedance of the battery pack can be calculated using a ratio between a drive signal applied in the dual battery measurement circuit 300 and a detection signal in the dual battery measurement circuit 300 in response to the application of the drive signal. The drive / demodulation circuit 320 can be structured to generate time-varying signals of different frequencies, where the drive / demodulation circuit 320 is arranged to process the input from the ADC 335 to determine the electrical impedance of the battery pack 304-2. The drive / demodulation circuit 320 can be operable to selectively energize the battery pack 304-3 with a second time-varying signal of a different frequency while maintaining the battery pack 304-2 in a non-energized state during energization of the battery pack 304-3. The drive / demodulation circuit 320 can have an output to transmit digital data representative of the frequency-dependent electrical impedance of the battery pack 304-2 or the battery pack 304-3 to a processor over a bus for use in determining one or more of a state of charge, a state of health, and an internal temperature of the battery pack 304-3 or the battery pack 304-2, respectively.

[0062] The dual-cell measurement circuit 300, including the charge-balancing charge integrator 310, the ADC 335, the drive / demodulation circuit 320, and other components, can be provided in an integrated circuit that is attachable to the battery pack 304-2 and the battery pack 304-3. A device, which can include an integrated circuit containing a dual-cell measurement circuit, such as the dual-cell measurement circuit 300, can include multiple integrated circuits that are attached to multiple pairs of battery pack cells of a battery pack cell stack, with each integrated circuit coupled to a pair of battery pack cells that are different from the battery pack cells coupled to the other integrated circuits of the multiple integrated circuits. Such battery pack cells in the stack can be coupled in electrical series such that, in operation, a load current is common to each battery pack cell in the stack. Each integrated circuit so constructed can include a charge integrator, an ADC, a switched-capacitor circuit, and a drive / demodulation circuit to determine the electrical impedance of each battery pack cell of the pair relative to the pair of battery pack cells to which the integrated circuit is attached. The drive / demodulation circuit can be arranged to selectively excite one battery pack cell of a pair with a time-varying signal while maintaining the other battery pack cell of the pair in a non-excited state during excitation of the one battery pack cell of the pair. The charge integrator can measure a voltage difference when the one battery pack cell of the pair is excited and the other battery pack cell of the pair is in the non-excited state. The drive / demodulation circuit can determine the electrical impedance of the one battery pack cell by measuring the voltage difference. The drive / demodulation circuit can then reverse the application of the time-varying signal by exciting the battery pack cell of the pair that was previously in the non-excited state while maintaining the previously excited battery pack cell of the pair in the non-excited state. The electrical impedance of the other battery pack cell of the pair can be determined from the reversed application of the time-varying signal.

[0063] In Figure 3 In the example of FIG. 3, the battery pack cells of the group 302 can be coupled to three integrated circuits as described above. An integrated circuit can be attached to the pair of battery packs 304-0 and 304-1 to monitor these battery packs and determine the electrical impedance of the battery pack 304-0 and the battery pack 304-1. As described above, an integrated circuit can be attached to the pair of battery packs 304-2 and 304-3 to monitor the battery packs and determine the electrical impedance of the battery pack 304-2 and the battery pack 304-3. An integrated circuit can be attached to the pair of battery packs 304-4 and 304-5 to monitor these battery packs and determine the electrical impedance of the battery pack 304-4 and the battery pack 304-5. In arrangements in which the group 302 has more than six battery packs, such an arrangement can include more than three independent integrated circuits, for example, N / 2 integrated circuits, where N is the number of battery packs in the group 302, where N is a positive even integer. A shared arrangement can be used for a group 302 having an odd number of battery packs.

[0064] Figure 4An embodiment of an exemplary dual-cell measurement circuit 400 is shown, featuring a switched capacitor circuit and a charge integrator with feedback for measuring parameters of battery pack cells 404-2 and 404-3. The switched capacitor circuit, providing a sampling network, offers a direct method to calculate the voltage difference between the two cells by sampling them at a high frequency. The sampling capacitors of the switched capacitor circuit can be connected to a charge integrator 410 with opposite polarities, so that essentially only the charge difference AQ is processed. This can also be performed using resistors and a continuous-time system in the gm range. With rapid sampling or continuous-time compensation, the load current is compensated almost instantaneously with very high timing accuracy. This approach is far superior to using two separate, slower ADCs located at different points in the system. The feedback loop back to the charge integrator 410 can adjust the feedback charge QFB to approximate the reciprocal of the charge difference between the battery pack cells. The charge integrator 410 can drive the feedback to adjust its average input to essentially zero.

[0065] like Figure 4 As shown, a dual-cell measurement circuit 400 is coupled to battery packs 404-2 and 404-3 of a plurality of battery packs 404-0, 404-1, 404-2, 404-3, 404-4, and 404-5 in a set 402 to determine the battery pack parameters of the two battery packs 404-2 and 404-3 using a dual-cell method. The dual-cell measurement circuit 400 can be coupled to battery pack 404-2 using four wires and to battery pack 404-3 using four wires, wherein the coupling can be within the housing of these battery packs. The dual-cell measurement circuit 400 is used to measure the battery pack parameters of battery pack 404-2, which can undergo AC excitation without excitation of battery pack 404-3, wherein the two battery packs share a common load current. The operation of the dual-battery measurement circuit 400 may include selecting battery pack 404-3 to undergo AC excitation when battery pack 404-2 is not energized, in order to measure the battery pack parameters of battery pack 404-3. The measurement order of the battery pack parameters of battery packs 404-2 and 404-3 may be randomly selected or selected based on the architecture or system process in which battery packs 404-2 and 404-3 are deployed. Control of the measurement of the battery pack parameters of battery packs 404-2 and 404-3 may be implemented by signal processing circuit 420.

[0066] The plurality of battery packs 404-0, 404-1, 404-2, 404-3, 404-4, and 404-5 of the group 402 can be implemented as a battery pack cell stack that shares a common load current ILOAD in operation. The battery packs 404-0, 404-1, 404-2, 404-3, 404-4, and 404-5 can be arranged to operate with a common ILOAD with the battery packs 404-0, 404-1, 404-2, 404-3, 404-4, and 404-5 coupled in electrical series. Although Figure 4 While six battery packs are shown, the group 402 can be implemented as a group of battery pack cells with more or less than six battery packs. The battery packs 404-2 and 404-3 can be arranged as directly adjacent battery packs in the group 402, arranged as a battery pack cell stack with the battery packs 404-0, 404-1, 404-2, 404-3, 404-4, and 404-5 arranged in series, such that ILOAD is common to each of the battery packs of the stack in operation. Alternatively, the battery packs 404-2 and 404-3 can be arranged in the group 402 separated from each other by one or more battery packs of the group 402.

[0067] The signal processing circuit 420 can generate one or more signals to selectively energize one of the two battery packs 404-2 and 404-3 with a time-varying signal while maintaining the other of the two battery packs 404-2 and 404-2 in a non-energized state. During this AC energization, the battery packs 404-2 and 404-3 can be operated with a common load current. The signal processing circuit 420 is coupled to a switch 411 that selectively couples the signal processing circuit 420 to either the transistor 412-2 or the transistor 412-3. The switch 411 can be implemented in the form of a field effect transistor (n-type or p-type), a relay, a bipolar junction transistor (npn or pnp), or other suitable switching device. The signal processing circuit 420 can be implemented to provide one or more signals to the switch 411 through a line 425. Although the transistors 412-2 and 412-3 can be implemented in various forms of transistors, such as a field effect transistor (n-type or p-type), a relay, a bipolar junction transistor (npn or pnp), or other suitable switching device, Figure 4The example uses an n-channel insulated-gate field-effect transistor. Optionally, a resistor can be added in series with transistor 412-2, and a resistor can be added in series with transistor 412-3. When transistor 412-2 is on and transistor 412-3 is off, the magnitude of the excitation current is given by the battery voltage of battery pack 404-2 divided by the resistance in series with transistor 412-2. When transistor 412-3 is on and transistor 412-2 is off, the magnitude of the excitation current is given by the battery voltage of battery pack 404-3 divided by the resistance in series with transistor 412-3. Battery pack 404-2 is coupled to transistor 412-2 of dual-battery measurement circuit 400 with its drain coupled to one end of battery pack 404-2 and its source coupled to the other end of battery pack 404-2. Battery pack 404-3 is coupled to transistor 412-3 of dual-battery measurement circuit 400 with its drain coupled to one end of battery pack 404-3 and its source coupled to the other end of battery pack 404-3.

[0068] Battery pack 404-2 can be coupled to resistors 408-21 and 408-22 of dual-battery measurement circuit 400 opposite transistor 412-2. Capacitor 407-21 is coupled between resistors 408-21 and 408-22 opposite the coupling of these resistors to battery pack 404-2. The two nodes of the connection of capacitor 407-21 to resistors 408-21 and 408-22 are coupled to a portion of the switched-capacitor circuit to measure charge Ql. The portion of the switched-capacitor circuit includes switches 409-21, 409-22, 409-23, 409-24, 409-25, and 409-26, and capacitors 407-22 and 407-23. This portion of the switched-capacitor circuit is coupled to the two inputs of charge integrator 410 through switches 409-25 and 409-26. Capacitor 407-22 is coupled between switches 409-21 and 409-25, and capacitor 407-23 is coupled between switches 409-22 and 409-23. Capacitor 407-22 is coupled to capacitor 407-23 using switches 409-23 and 409-24.

[0069] The battery pack 404-3 can be coupled to the resistors 408-31 and 408-32 of the dual battery measurement circuit 400 opposite the transistor 412-3. The capacitor 407-31 is coupled between the resistors 408-33 and 408-32 opposite the coupling of these resistors to the battery pack 404-3. The two nodes of the connection of the capacitor 407-31 to the resistors 408-31 and 408-32 are coupled to a portion of the switched capacitor circuit to measure the charge Q2. This portion of the switched capacitor circuit includes the switches 409-31, 409-32, 409-33, 409-34, 409-35, and 409-36, and the capacitors 407-22 and 407-33. This portion of the switched capacitor circuit is coupled to the two inputs of the charge integrator 410 through the switches 409-35 and 409-36. The capacitor 407-32 is coupled between the switches 409-31 and 409-35, and the capacitor 407-23 is coupled between the switches 409-32 and 409-33. The capacitor 407-32 is coupled to the capacitor 407-33 using the switches 409-33 and 409-34. The switches 409-35 and 409-36 are coupled to the switches 409-26 and 409-25, respectively, and the charge integrator 410 is opposite in polarity so that substantially only the charge difference AQ of the switched capacitor circuit is processed. The effects of ILOAD, such as the AC component of the load current and the battery voltage, are cancelled out with respect to the battery pack 404-2 and the battery pack 404-3 because ILOAD is common to both battery packs 404-2 and 404-3, which have the same nominal voltage.

[0070] The switches 411, 409-41...409-26, and 409-31...409-36 can be implemented in a variety of different ways to provide a switching mechanism. These switches can be implemented in a variety of ways that facilitate integrated circuit construction, such as but not limited to transistors arranged to be selectable between an on mode or an off mode. Although not shown, control signals to these switches can be provided by the signal processing circuit 420 or other control unit. The switches 409-41...409-26 and 409-31...409-36 of the switched capacitor circuit can operate at about 1 MHz or other relatively high rate, while the AC excitation can be in the 1 Hz to 10 kHz or other range.

[0071] The charge integrator 410 is an integrator circuit that integrates the charge difference from the sampling capacitors of the switched capacitor circuit of opposite polarity to the integrating circuit. The input of the charge integrator 410 is coupled to one end of the capacitor 407-44, and the output of the charge integrator 410 is coupled to the other end of the capacitor 407-44. The other input of the charge integrator 410 is coupled to one end of the capacitor 407-45, and the other output of the charge integrator 410 is coupled to the other end of the capacitor 407-45. The two outputs of the charge integrator 410 are coupled to the ADC 435 at two different inputs of the ADC 435. The output of the ADC 435 is coupled to an input of the signal processing circuit 420. This arrangement of the charge integrator 410 and the ADC 435 can provide a charge balancing ADC circuit that can operate similarly to the charge balancing ADC 210 of Figure 2 The signal processing circuit 420 can be implemented similarly to the signal processing circuit 220 of Figure 2 or similarly to the drive / demodulation circuit 320 of Figure 3 The ADC 435 can be coupled to provide feedback to the charge integrator 410 so that the charge integrator 410 is operable to drive feedback in order to adjust the average input of the charge integrator 410 to substantially zero.

[0072] A feedback loop is coupled to the output of the ADC 435 and the input of the signal processing circuit 420, with a coupling at the input of a digital to analog converter (DAC) 445. Two output nodes of the DAC 445 are coupled back to the two input nodes of the charge integrator 410, the capacitors 407-44 and 407-45 and the switched capacitor circuit to this point, providing AQ, as shown in Figure 4 This feedback coupling is provided by another switched capacitor circuit, including switches 409-51...409-56 and capacitors 407-46 and 407-47 to capture the feedback charge QFB. The feedback loop can adjust the feedback charge QFB to approximate the inverse of the battery cell charge difference. The charge integrator 410 can drive feedback in order to adjust its average input to substantially zero. The switches 409-51...409-56 can operate at approximately 1 MHz or other relatively high rate, along with the switches 409-21...409-26 and 409-31...409-36.

[0073] The signal processing circuit 420 can be configured to process the input from the ADC 435 to determine the electrical impedance of the battery pack 404-2 in response to the battery pack 404-2 being energized and the battery pack 404-3 not being energized. The signal processing circuit 420 can also process the input from the ADC 335 to determine the electrical impedance of the battery pack 404-3 in response to the battery pack 404-3 being energized and the battery pack 404-2 not being energized. The electrical impedance of the battery pack can be calculated using the ratio between the drive signal applied in the dual battery measurement circuit 400 and the detection signal in the dual battery measurement circuit 400 in response to the application of the drive signal. The signal processing circuit 420 can be structured to produce time-varying signals of different frequencies, where the signal processing circuit 420 is arranged to process the input from the ADC 435 to determine the electrical impedance of the battery pack 404-2. The signal processing circuit 420 can be operable to selectively energize the battery pack 404-3 with a second time-varying signal of a different frequency while maintaining the battery pack 404-2 in a non-energized state during energization of the battery pack 404-3. The signal processing circuit 420 can have an output to transmit digital data representing the frequency-dependent electrical impedance of the battery pack 404-2 or the battery pack 404-3 to a processor over a bus, where one or more of the state of charge, state of health, and internal temperature of the battery pack 404-3 or the battery pack 404-2, respectively, is determined using the frequency-dependent electrical impedance.

[0074] The dual cell measurement circuit 400, including the charge integrator 410, the ADC 435, the signal processing circuit 420, the DAC 445, and other components, can be provided in an integrated circuit that is attachable to the battery pack 404-2 and the battery pack 404-3. A device, which can include an integrated circuit containing a dual cell measurement circuit, such as the dual cell measurement circuit 400, can include multiple integrated circuits that are attached to multiple pairs of battery pack cells of a battery pack cell stack, with each integrated circuit coupled to a pair of battery pack cells that are different from the battery pack cells coupled to the other integrated circuits of the multiple integrated circuits. Such battery pack cells in the stack can be coupled in electrical series such that, in operation, a load current is common to each battery pack cell in the stack. Each integrated circuit so constructed can include a charge integrator, an ADC, a plurality of switched capacitor circuits, a DAC, and a signal processing circuit to determine the electrical impedance of each battery pack cell of the pair with respect to the pair of battery pack cells to which the integrated circuit is attached. The signal processing circuit can be arranged to selectively excite one battery pack cell of a pair of battery pack cells with a time-varying signal while maintaining the other battery pack cell of the pair in a non-excited state during the excitation of the one battery pack cell of the pair. The charge integrator can measure a voltage difference when the one battery pack cell of the pair is excited and the other battery pack cell of the pair is in the non-excited state. The signal processing circuit can determine the electrical impedance of the one battery pack cell by measuring the voltage difference. The signal processing circuit can then reverse the application of the time-varying signal by exciting the battery pack cell of the pair that was previously in the non-excited state while maintaining the previously excited battery pack cell of the pair in the non-excited state. The electrical impedance of the other battery pack cell of the pair can be determined from the reversed application of the time-varying signal.

[0075] In Figure 4 In the example of the set 402, the battery pack cells of the set 402 can be coupled to three integrated circuits as described above. An integrated circuit can be attached to the pair of battery packs 404-0 and 404-1 to monitor these battery packs and determine the electrical impedance of the battery pack 404-0 and the battery pack 404-1. As described above, an integrated circuit can be attached to the pair of battery packs 404-2 and 404-3 to monitor the battery packs and determine the electrical impedance of the battery pack 404-2 and the battery pack 404-3. An integrated circuit can be attached to the pair of battery packs 404-4 and 404-5 to monitor these battery packs and determine the electrical impedance of the battery pack 404-4 and the battery pack 404-5. In arrangements where the set 402 has more than six battery packs, such an arrangement can include more than three independent integrated circuits, for example, N / 2 integrated circuits, where N is the number of battery packs in the set 402, where N is a positive even integer. A shared arrangement can be used for a set 402 that has an odd number of battery packs.

[0076] Figure 5is a flowchart featuring aspects of an embodiment of an example method 500 of determining parameters of a battery pack. The method 500 can be applied to a plurality of battery packs. At 510, a first battery pack is excited with a time-varying signal. At 520, during the excitation of the first battery pack, a second battery pack is held in a non-excited state, wherein the first battery pack and the second battery pack have a common load current in operation. The common load current can be obtained by the first battery pack and the second battery pack being arranged electrically in series, with the common load current flowing. The first battery pack and the second battery pack can be arranged in a plurality of battery packs, wherein the arrangement has more than two battery packs. The arrangement of the plurality of battery packs can be a battery pack stack. The first battery pack and the second battery pack can be directly adjacent battery pack cells in a battery pack stack, wherein the battery pack cells are arranged in series such that, in operation, the load current is common for each battery pack cell in the stack. The first battery pack and the second battery pack can be arranged as battery pack cells in a battery pack stack, wherein other battery pack cells separate the first battery pack from the second battery pack, wherein the first battery pack and the second battery pack share the common load current.

[0077] At 530, for the excited first battery pack and the second battery pack in the non-excited state, a voltage difference between a voltage on the first battery pack and a voltage on the second battery pack is measured. At 540, the measured voltage difference is processed to determine an electrical impedance of the first battery pack.

[0078] Variations of the method 500 or methods similar to the method 500 can include a number of different embodiments, which can be combined depending on the application of these methods and / or the architecture of the system implementing these methods. Such methods can include determining a frequency-dependent electrical impedance of each battery pack cell in a battery pack stack comprising a first battery pack and a second battery pack, wherein each battery pack cell is arranged in a pair with one other battery pack cell in the stack. The determination of the frequency-dependent electrical impedance of each battery pack cell can include selectively exciting a respective battery pack cell in the pair while the other battery pack cell in the pair is held in a non-excited state; and determining a voltage difference between a voltage on the respective battery pack cell of the pair and a voltage on the other battery pack cell of the pair held in the non-excited state.

[0079] Variations of the method 500 or methods similar to the method 500 can include varying the frequency of the time-varying signal and using the time-varying signal with the varying frequency to determine a frequency-dependent electrical impedance of the first battery pack. By processing the frequency-dependent electrical impedance of the first battery pack, one or more of a SOC, a SOH, and an internal temperature of the first battery pack can be determined. The determination of one or more of the SOC, the SOH, and the internal temperature can be made by a processor that receives digital data representative of the frequency-dependent electrical impedance from a bus sent by signal processing circuitry that processes the measured voltage difference to determine the electrical impedance of the first battery pack.

[0080] Variations of the method 500 or methods similar to the method 500 can include measuring the voltage difference by sampling the first battery pack and the second battery pack with a switched capacitor circuit. Such variations can include integrating the charge difference with a sampling capacitor of the switched capacitor circuit that is opposite in polarity to a charge integrator circuit.

[0081] In various embodiments, an apparatus having structure to measure a battery pack parameter can include a signal driver connectable to two battery cells, a circuit to measure a voltage difference between a voltage on a first battery cell of the two battery cells and a voltage on a second battery cell of the two battery cells, and signal processing circuitry to process the measured voltage difference to determine an electrical impedance of the first battery cell or the second battery cell. The signal driver can be arranged to selectively excite the first battery cell of the two battery cells with a time-varying signal while maintaining the second battery cell of the two battery cells in a non-excited state during excitation of the first battery cell. The first battery cell and the second battery cell can be arranged relative to one another such that the first battery cell and the second battery cell have a common load current in operation. The circuit to measure the voltage difference between the voltage on the first battery cell and the voltage on the second battery cell can be operable to measure the voltage when the first battery cell is excited and the second battery cell of the two battery cells is in the non-excited state. The difference measurement can be made with the first battery cell and the second battery cell having the common load current. The first battery cell and the second battery cell can be configured in a variety of arrangements. The first battery cell and the second battery cell can be arranged in series in a battery cell stack. The first battery cell and the second battery cell can be directly adjacent cells in a battery cell stack, where the battery cells are arranged in series such that, in operation, the load current is common to each battery cell in the stack.

[0082] Variations of such an apparatus or similar apparatuses can include many different embodiments that can be combined depending on the application of such an apparatus or the architecture of a system in which such an apparatus is implemented. The signal driver can be arranged to generate time-varying signals having different frequencies, and the signal processing circuitry can be arranged to process the voltage differences measured at different frequencies to determine a frequency-dependent electrical impedance of the first battery cell. The signal driver can be operable to selectively excite the second battery cell with a second time-varying signal while maintaining the first battery cell in a non-excited state during excitation of the second battery cell, wherein the first battery cell and the second battery cell have a common load current in operation. The signal processing circuitry can be arranged to transmit digital data representing the frequency-dependent electrical impedance over a bus to a processor, where one or more of a SOC, a SOH, and an internal temperature of the first battery cell are determined based on the frequency-dependent electrical impedance.

[0083] Variations of such an apparatus or similar apparatuses can include a charge balancing analog-to-digital converter coupling the signal processing circuitry to the circuit to measure the voltage difference. Other variations can include a switched capacitor circuit to sample the first battery cell and the second battery cell. Such an apparatus or similar apparatuses can include an integrator circuit to integrate a charge difference of a sampling capacitor of the switched capacitor circuit opposite in polarity to the integrator. Such an apparatus or similar apparatuses can include an analog-to-digital converter coupled to an output of the integrator circuit, wherein the analog-to-digital converter is coupled to provide feedback to the integrator such that the integrator circuit is operable to drive the feedback to regulate an average input to the integrator circuit to be substantially zero.

[0084] Variations of such a device or similar devices can include a signal driver, a circuit to measure a voltage difference, and a signal processing circuit, disposed in a first integrated circuit, where the first integrated circuit is attachable to a first battery pack cell and a second battery pack cell. Variations can include a plurality of integrated circuits attached to a plurality of pairs of battery pack cells of a stack of battery pack cells, where each integrated circuit is coupled to a pair of battery pack cells different from the battery pack cells coupled to other integrated circuits of the plurality of integrated circuits, the first integrated circuit being one of the plurality of integrated circuits, where such battery pack cells of the stack are coupled in electrical series such that, in operation, a load current is common to each battery pack cell of the stack. Each integrated circuit so constructed can have, with respect to the pair of battery pack cells to which the integrated circuit is attached: a signal driver attachable to the pair of battery pack cells, the signal driver arranged to selectively energize one of the pair of battery pack cells with a time-varying signal while maintaining the other of the pair of battery pack cells in a non-energized state during energization of the one of the pair; a circuit to measure a voltage difference between a voltage on the one of the pair of battery pack cells energized and a voltage on the other of the pair of battery pack cells in the non-energized state; and a signal processing circuit to process the measured voltage difference to determine an electrical impedance of the one of the pair of battery pack cells.

[0085] In various embodiments, a device having structure for measuring a battery parameter can include means for selectively energizing a first battery of a pair of batteries with a time-varying signal and for maintaining a second battery of the pair in a non-energized state during energization of the first battery, where the first battery and the second battery have a common load current in operation; means for measuring a voltage difference between a voltage on the first battery and a voltage on the second battery; and means for processing the measured voltage difference to determine an electrical impedance of the first battery.

[0086] Variations of such an apparatus or similar apparatuses can include many different embodiments that can be combined depending on the application of such an apparatus or the architecture of a system implementing such an apparatus. For example, the means for selectively exciting the first battery pack can include means for varying the frequency of the time-varying signal. The means for processing the measured voltage difference can include means for determining a frequency-dependent electrical impedance of the first battery pack using the time-varying signal having the varying frequency, and means for determining the state of charge, state of health, and internal temperature of the first battery pack by processing the frequency-dependent electrical impedance of the first battery pack. The means for determining the SOC, SOH, and internal temperature of the first battery pack by processing the frequency-dependent electrical impedance of the first battery pack can be remote from and coupled to the means for determining a frequency-dependent electrical impedance of the first battery pack using the time-varying signal having the varying frequency by a bus. Variations of such an apparatus or similar apparatuses can include means for capacitively sampling the first battery pack voltage and the second battery pack voltage, and means for integrating the charge difference with the sampling capacitor in a polarity opposite that of the charge difference integration means.

[0087] Figure 6 is a feature block diagram of an embodiment of an example system 600 having a set of battery packs and a set of dual-cell measurement circuits 670-1...670-N. The set of battery packs is arranged in pairs of battery packs 674-1...674-N, where each pair of battery packs is coupled to a single dual-cell measurement circuit that is separate from other dual-cell measurement circuits of the set of battery packs. Dual-cell measurement circuit 670-1 is coupled to battery pair 674-1, and dual-cell measurement circuit 670-N is coupled to battery pair 674-N, with other dual-cell measurement circuits coupled to corresponding pairs of battery packs. The battery packs in a pair of battery packs can be immediate neighbors, such as adjacent battery pack cells in a stack of battery pack cells. Alternatively, the battery packs in a pair of battery packs can be different from immediate neighbors, such as battery pack cells separated by one or more other battery pack cells in a stack of battery pack cells. Dual-cell measurement circuits 670-1...670-N can be implemented in N integrated circuits that are separately connected to respective pairs of battery packs 674-1...674-N. The set of battery packs and the set of dual-cell measurement circuits can be implemented in a plurality of devices that use battery packs and use a BMS to track the SOC, SOH, temperature, or a combination thereof of the battery. The battery packs and dual-cell measurement circuits can be implemented in a stack of battery pack cells, such as but not limited to a large stack of battery pack cells used in an electric vehicle.

[0088] The system 600 can be a networked system in which the battery packs and the dual-cell measurement circuitry are arranged in one device having the dual-cell measurement circuitry 670-1...670-N attached to the respective battery pack pairs 674-1...674-N and coupled to the bus 637 to provide outputs from the dual-cell measurement circuitry 670-1...670-N to determine the SOC and SOH of the battery packs away from the dual-cell measurement circuitry 670-1...670-N. The dual-cell measurement circuitry 670-1...670-N can be implemented similarly to the dual-cell measurement circuitry 100A of Figure 1A the dual-cell measurement circuitry 200 of Figure 2 the dual-cell measurement circuitry 300 of Figure 3 the dual-cell measurement circuitry 400 of Figure 4 a similar dual-cell measurement circuitry or a combination thereof.

[0089] The system 600 can also include a number of components, such as one or more processors 630, a memory 635, a communication unit 640, a data processing unit 645, an electronic device 650, a peripheral device 655, a display unit 660, a user interface 662, and a selection device 664. The one or more processors 630 can operate as a single processor or a group of processors. The processors of the processor group can operate independently according to the assigned functions. The one or more processors 630 can be implemented in one or more application-specific integrated circuits (ASICs). The one or more processors 630 can be implemented in one or more digital signal processors (DSPs). The one or more processors 630 can direct data access to and from a database when operating the components of the system 600 to perform a protocol associated with the function for which the system 600 is designed.

[0090] The system 600 can include one or more processors 630, a memory 635, and a communication unit 640 arranged to operate as a processing unit to control the management of the battery packs and the group of dual-cell measurement circuitry 670-1...670-N. Such control management can include scheduling the operation of the dual-cell measurement circuitry 670-1...670-N to monitor the battery packs to measure the frequency-dependent electrical impedance of each of the battery packs to determine one or more of the SOC, SOH, and internal temperature of each of the battery packs. In addition, for example, the one or more processors 630, the memory 635, and the communication unit 640 can be arranged to adjust the operating parameters of the battery packs. The management of the battery packs can include a master algorithm to balance all the cells with each other. The communication unit 640 can use a combination of wired communication techniques and wireless techniques depending on the application.

[0091] Memory 635 can include a database with information, algorithms, and other data such that system 600 can operate on data from dual cell measurement circuits 670-1...670-N. Algorithms stored in memory 635 can be used for computational and modeling algorithms for extracting the SOC, SOH, and temperature of the cells in battery pairs 674-1...674-N from frequency dependent electrical impedance measured by dual cell measurement circuits 670-1...670-N. These computational and modeling algorithms can include a number of different known algorithms. Such impedance measured from dual cell measurement lines can be calculated using the ratio between the drive signal applied in the dual cell measurement circuit and the detection signal responsive to the application of the drive signal in the dual cell measurement loop. Data processing unit 645 can be implemented as a standalone unit to determine the SOC, SOH, and temperature of the cells from the frequency dependent electrical impedance or data processing unit 635 can be distributed among the components of system 600 including memory 635 and / or electronic device 650.

[0092] Bus 637 provides electrical conductivity between the components of system 600. Bus 637 can include an address bus, a data bus, and a control bus, each of which can be independently configured. Bus 637 can be implemented using a variety of different communication media that allow for distribution of components of system 600. The use of bus 637 can be regulated by one or more processors 630. Bus 637 can operate as part of a communication network to send and receive signals including data signals, commands, and control signals.

[0093] In various embodiments, peripherals 655 can include drivers to provide voltage and / or current inputs to dual cell measurement circuits 670-1...670-N, additional storage memory, and / or other control devices that can operate in conjunction with one or more processors 630 and / or memory 635. Display unit 660 can be disposed with a screen display that can be used with instructions stored in memory 635 to implement user interface 662 to manage the operation of dual cell measurement circuits 670-1...670-N and / or components distributed within system 600. Such a user interface can operate with communication unit 640 and bus 637. Display unit 660 can include a video screen or other structure to visually project data / information and images. System 600 can include a plurality of selection devices 664 operable with user interface 662 to provide user input to operate data processing unit 645 or its equivalent. Selection devices 664 can include a touch screen or selection devices operable with user interface 662 to provide user input to operate data processing unit 645 or other components of system 600.

[0094] The following are example embodiments of devices and methods of operation in accordance with the teachings herein.

[0095] An example apparatus 1 having structure for measuring battery parameters can include a signal driver connectable to two battery cells, the signal driver arranged to selectively excite a first battery cell of the two battery cells with a time-varying signal while maintaining a second battery cell of the two battery cells in a non-excited state during excitation of the first battery cell, the first battery cell and the second battery cell having a common load current battery cell in operation; a circuit for measuring a voltage difference between a voltage on the first battery cell and a voltage on the second battery cell with the first battery cell excited and the second battery cell of the two battery cells in the non-excited state; and a signal processing circuit for processing the measured voltage difference to determine an electrical impedance of the first battery cell.

[0096] An example apparatus 2 having structure for measuring battery parameters can include features of example apparatus 1 and can include that the first battery cell and the second battery cell are directly adjacent cells in a stack of battery cells, wherein the battery cells are arranged in series such that, in operation, the load current is common to each battery cell in the stack.

[0097] An example apparatus 3 having structure for measuring battery parameters can include features of any of the preceding example apparatuses and can include that the signal driver is arranged to generate time-varying signals having different frequencies, and the signal processing circuit is arranged to process the measured voltage differences at different frequencies to determine a frequency-dependent electrical impedance of the first battery cell.

[0098] An example apparatus 4 having structure for measuring battery parameters can include features of example apparatus 3 or any of the preceding example apparatuses and can include that the signal processing circuit is arranged to send digital data representative of the frequency-dependent electrical impedance to a processor over a bus, at which processor one or more of a state of charge, a state of health, and an internal temperature of the first battery cell are determined based on the frequency-dependent electrical impedance.

[0099] An example apparatus 5 having structure for measuring battery parameters can include features of example apparatus 3 or any of the preceding example apparatuses and can include that the signal driver is operable to selectively excite the second battery cell with a second time-varying signal while maintaining the first battery cell in a non-excited state during excitation of the first battery cell, wherein the first battery cell and the second battery cell have a common load current in operation, to determine a frequency-dependent electrical impedance of the second battery cell.

[0100] An example apparatus 6 having structure for measuring battery parameters can include features of any of the preceding example apparatuses and can include: a switched capacitor circuit to sample the first battery cell and the second battery cell.

[0101] An example apparatus 7 having structure for measuring battery parameters can include features of example apparatus 6 or any of the preceding example apparatuses and can include: an integrator circuit to integrate a charge difference of a sampling capacitor of the switched capacitor circuit connected opposite in polarity to the integrator circuit.

[0102] An example apparatus 8 having structure for measuring battery parameters can include features of example apparatus 7 or any of the preceding example apparatuses and can include: an analog-to-digital converter coupled to an output of the integrator circuit, wherein the analog-to-digital converter is coupled to provide feedback to the integrator circuit such that the integrator circuit is operable to drive the feedback to adjust an average input to the integrator circuit to be substantially zero.

[0103] An example apparatus 9 having structure for measuring battery parameters can include features of any of the preceding example apparatuses and can include: a charge balancing analog-to-digital converter coupling the signal processing circuit to the circuit to measure the voltage difference.

[0104] An example apparatus 10 having structure for measuring battery parameters can include features of any of the preceding example apparatuses and can include: a signal driver, a voltage difference measurement circuit, and a signal processing circuit arranged in a first integrated circuit, wherein the first integrated circuit is attachable to the first battery cell and the second battery cell.

[0105] An example apparatus 11 having structure for measuring battery parameters can include features of example apparatus 10 or features of any of the preceding example apparatuses and can include: a plurality of integrated circuits attached to a plurality of pairs of battery cells of a battery cell stack, wherein each integrated circuit is coupled to a pair of battery cells that is different from the battery cells coupled to other integrated circuits of the plurality of integrated circuits, the first integrated circuit being one of the plurality of integrated circuits, wherein the battery cells in the stack are coupled in series such that, in operation, the load current is common to each battery cell in the stack, and wherein each integrated circuit is structured, with respect to the pair of battery cells to which the integrated circuit is attached, to have: a signal driver attachable to the pair of battery cells, the signal driver arranged to selectively excite one of the pair of battery cells using a time-varying signal while maintaining the other battery cell of the pair in a non-excited state during excitation of the one battery cell of the pair; a circuit to measure a voltage difference between a voltage on the one battery cell of the pair and a voltage on the other battery cell of the pair, wherein the one battery cell of the pair is in an excited state and the other battery cell of the pair is in a non-excited state; and a signal processing circuit to process the measured voltage difference to determine an electrical impedance of the one battery cell.

[0106] An example apparatus 12 having structure for measuring battery parameters can include: means for selectively exciting a first battery cell of a stack of battery cells with a time-varying signal while maintaining a second battery cell of the pair in a non-excited state during excitation of the first battery cell, wherein the first battery cell and the second battery cell have a common load current in operation; means for measuring a voltage difference between a voltage on the first battery cell and a voltage on the second battery cell; and means for processing the measured voltage difference to determine an electrical impedance of the first battery cell.

[0107] An example apparatus 13 having structure for measuring battery parameters can include features of example apparatus 12 and can include: the means for selectively exciting the first battery cell includes means for varying a frequency of the time-varying signal; and the means for processing the measured voltage difference includes: means for determining a frequency-dependent electrical impedance of the first battery cell using the time-varying signal having the varying frequency; and means for determining a state of charge, a state of health, and an internal temperature of the first battery cell by processing the frequency-dependent electrical impedance of the first battery cell.

[0108] An example apparatus 14 having structure for measuring battery parameters can include features of example apparatuses 12 and 13 and can include: means for capacitively sampling the first battery cell voltage and the second battery cell voltage; and means for integrating a charge difference of the sampling capacitor connected with a polarity opposite to a polarity of the charge difference integrating means.

[0109] An example method 1 of determining battery pack parameters can include: exciting a first battery pack with a time-varying signal; maintaining a second battery pack in a non-excited state during the excitation of the first battery pack, wherein the first battery pack and the second battery pack have a common load current in operation; measuring a voltage difference between a voltage on the first battery pack and a voltage on the second battery pack with the first battery pack excited and the second battery pack in the non-excited state; and processing the measured voltage difference to determine an electrical impedance of the first battery pack.

[0110] An example method 2 of determining battery pack parameters can include the features of example method 1 and can include: the first battery pack and the second battery pack are directly adjacent battery pack cells in a battery pack cell stack, wherein the battery pack cells are arranged in series such that, in operation, the load current is common to each battery pack cell in the stack.

[0111] An example method 3 of determining battery pack parameters can include the features of any of the preceding example methods and can include: determining a frequency-dependent electrical impedance of each battery pack cell of the battery pack cell stack, including the first battery pack and the second battery pack, wherein each battery pack cell is arranged on a pairwise basis with another battery pack cell of the stack by, for each battery pack cell: selectively exciting the respective battery pack cell of the stack, wherein the other battery pack cells of the stack are maintained in a non-excited state; and determining a voltage difference between a voltage on the respective battery pack cell of the stack and a voltage on the other battery pack cells of the stack that are maintained in the non-excited state.

[0112] An example method 4 of determining battery pack parameters can include the features of any of the preceding example methods and can include: varying a frequency of the time-varying signal; determining a frequency-dependent electrical impedance of the first battery pack using the time-varying signal with the varied frequency; and determining a state of charge, a state of health, and an internal temperature of the first battery pack by processing the frequency-dependent electrical impedance of the first battery pack.

[0113] An example method 5 of determining battery pack parameters can include the features of any of the preceding example methods and can include: measuring the voltage difference includes sampling the first battery pack and the second battery pack using a switched capacitor circuit.

[0114] An example method 6 of determining battery pack parameters can include the features of example method 5 or any of the preceding example methods and can include: integrating a charge difference of a sampling capacitor of the switched capacitor circuit connected in an opposite polarity to a polarity of a charge integrator circuit.

[0115] Example method 7 of determining a battery pack parameter can include features of any of the preceding example methods of determining a battery pack parameter and can include performing functions associated with any of the features of example devices 1-14 having a structure to measure a battery pack parameter and any features of example devices associated with the figures herein.

[0116] In various embodiments, a dual cell measurement method can be applied to a set of battery packs in pairs. In this method, one battery pack of a pair of battery packs is subjected to an alternating current excitation while the other battery pack of the pair is non-alternating current excited, both battery packs of the pair of batteries being under a common direct current load current. Differential measurements can be made on both battery packs of the pair of batteries to measure the AC electrical impedance of the exiting battery pack cell. This impedance measurement can be used to determine one or more of the SOC, SOH, and temperature of the excited battery pack of the pair. The excitation and non-excitation of both battery packs of the pair of battery packs can be reversed to determine one or more of the SOC, SOH, and temperature of the other battery pack of the pair from measurements of the AC electrical impedance of the other battery pack of the pair. The dual cell measurement method can be extended to a multiple cell measurement method, selecting one battery pack for alternating current excitation while the other battery packs are non-alternating current excited, all of the cells being under a common direct current load current. Differential measurements can be made on the AC electrical impedance of the excited cell of the multiple battery packs, from which one or more of the SOC, SOH, and temperature of the excited battery pack can be determined. The other battery packs of the multiple battery packs can be measured in the same manner, one at a time.

[0117] Differential measurements in the multiple cell approach can provide enhancements associated with determining one or more of AC electrical impedance and SOC, SOH, and temperature of the battery. In the dual cell approach, one IC can be used for every two cells of a set of battery pack cells. This can provide a two-fold cost reduction compared to a system where one measurement IC is used per battery pack. This can provide better recommendations for the car user. Furthermore, the load current effect can be eliminated directly at the source, so processing of the load current signal can be avoided. The individual battery pack cell voltage measurements can be deleted. Since the BMS IC can be implemented as a balancing battery pack, the dual cell approach with differential measurements can be applied to two adjacent cells of a set of battery pack cells, where the adjacent cells can have the same voltage, so that the cancellation element of the approach works well. It is convenient to use adjacent battery pack cells, but the dual cell approach can be implemented with two non-adjacent battery pack cells of the same stack. All battery pack cells in the same stack can be at the same voltage, since a balancing algorithm is typically run in the background, whose task is to keep the battery cells at the same relative charge level. Since the dual cell approach with differential measurements can be implemented without a high pass filter, the approach can save the number of components used. Furthermore, this dual cell approach or similar approaches can be implemented without explicit measurement of the current. The specific implementations, such as switched capacitor structures, fast sampling structures with near-instantaneous cancellation, and other implementations, can be done with little overhead and are easier to do with smaller signal swings for analog-to-digital conversion. In other embodiments, the differential driving of the two cells in the dual cell approach can result in an improved EIS method.

[0118] The above detailed description refers to the accompanying drawings, which show various embodiments that can be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice these and other embodiments. Other embodiments can be utilized and structural, logical, mechanical, and electrical changes can be made without departing from the scope of the various embodiments. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The foregoing detailed description is not intended to be limiting in scope, and the foregoing detailed description is not intended to be limiting in scope.

[0119] While specific embodiments have been shown and described in detail to illustrate the principles of various embodiments, it will be understood by one of ordinary skill in the art that any arrangement which is calculated to achieve the same ends can be substituted for the specific embodiments shown. Various embodiments use arrangements and / or combinations of the embodiments described herein. It is understood that the above description is intended to be illustrative and not restrictive, and that the wording or terminology used herein is for the purpose of description.

Claims

1. An apparatus having structure to measure battery parameters, the apparatus comprising: a signal driver attachable to two battery cells, the signal driver arranged to selectively excite a first of the two battery cells with a time-varying signal while maintaining a second of the two battery cells in a non-excited state during excitation of the first battery cell, wherein the first and second battery cells have a common load current in operation, and to selectively excite the second battery cell with a second time-varying signal while maintaining the first battery cell in a non-excited state during excitation of the second battery cell, wherein the first and second battery cells have a common load current in operation, to determine a frequency-dependent electrical impedance of the second battery cell; circuitry to measure a voltage difference between a voltage across the first battery cell and a voltage across the second battery cell with the first battery cell excited and the second of the two battery cells in a non-excited state; and signal processing circuitry to process the measured voltage difference to determine an electrical impedance of the first battery cell.

2. The apparatus of claim 1, wherein the first and second battery cells are directly adjacent cells in a stack of battery cells, wherein the battery cells are arranged in series such that, in operation, the load current is common to each battery cell in the stack.

3. The apparatus of claim 1 or 2, wherein the signal driver is arranged to generate time-varying signals having different frequencies, and the signal processing circuitry is arranged to process the measured voltage differences at the different frequencies to determine frequency-dependent electrical impedances of the first and second battery cells.

4. The apparatus of claim 3, wherein the signal processing circuitry is arranged to send digital data representative of the frequency-dependent electrical impedances over a bus to a processor at which one or more of a state of charge, a state of health, and an internal temperature of the first battery cell are determined based on the frequency-dependent electrical impedances.

5. The apparatus of any preceding claim, wherein the apparatus comprises a switched capacitor circuit to sample the first and second battery cells.

6. The apparatus of claim 5, wherein the apparatus comprises an integrator circuit to integrate a charge difference from a sampling capacitor of the switched capacitor circuit connected to the integrator circuit in a manner opposite in polarity.

7. The apparatus of claim 6, wherein the apparatus comprises an analog-to-digital converter coupled to an output of the integrator circuit, wherein the analog-to-digital converter is coupled to provide feedback to the integrator circuit such that the integrator circuit is operable to drive the feedback to adjust an average input to the integrator circuit to be substantially zero. ​ 8. The apparatus of any preceding claim, wherein the apparatus comprises a charge balancing analog-to-digital converter that couples the signal processing circuitry to the circuitry for measuring the voltage difference.

9. The apparatus of any preceding claim, wherein the signal driver, the circuitry for measuring the voltage difference, and the signal processing circuitry are disposed in a first integrated circuit, wherein the first integrated circuit is attachable to the first battery cell and the second battery cell.

10. The apparatus of claim 9, wherein the apparatus comprises a plurality of integrated circuits that are attached to a plurality of pairs of battery cells in a stack of battery cells, wherein each integrated circuit is coupled to a pair of battery cells that is different from the battery cells coupled to the other integrated circuits in the plurality of integrated circuits, the first integrated circuit being one of the plurality of integrated circuits, wherein the battery cells in the stack are coupled in series such that, in operation, the load current is common to each battery cell in the stack, and wherein each integrated circuit is configured with respect to the pair of battery cells to which that integrated circuit is attached, having: a signal driver attachable to the pair of battery cells, the signal driver arranged to selectively energize one of the pair of battery cells using a time-varying signal while maintaining the other of the pair of battery cells in a non-energized state during energization of the one of the pair of battery cells; circuitry for, with the one of the pair of battery cells in an energized state and the other of the pair of battery cells in a non-energized state, measuring a voltage difference between a voltage across the one of the pair of battery cells and a voltage across the other of the pair of battery cells; and signal processing circuitry for processing the measured voltage difference to determine an electrical impedance of the one of the battery cells.

11. A method of determining battery parameters, the method comprising: determining a frequency-dependent electrical impedance of each battery cell in a stack of battery cells, wherein each battery cell is arranged with another battery cell of the stack in a pairwise manner, the stack comprising a first battery cell and a second battery cell, and for each battery cell: selectively energizing a respective battery cell of a pair using a time-varying signal, wherein the other battery cell of the pair is maintained in a non-energized state, the battery cells of the pair having a common load current in operation; determining a voltage difference between a voltage across the respective battery cell of the pair and a voltage across the other battery cell of the pair that is maintained in a non-energized state; and processing the measured voltage difference to determine an electrical impedance of the respective battery cell.

12. The method of claim 11, wherein the first battery cell and the second battery cell are directly adjacent battery cells in a stack of battery cells, wherein the battery cells are arranged in series such that, in operation, the load current is common to each battery cell in the stack. ​ ​ ​ ​ ​ ​ ​ ​ 13. The method of claim 11 or 12, wherein the method comprises: varying a frequency of the time-varying signal; determining a frequency-dependent electrical impedance of the respective battery cell using the time-varying signal having the varying frequency; and determining a state of charge, a state of health, and an internal temperature of the respective battery cell by processing the frequency-dependent electrical impedance of the respective battery cell.

14. The method of any one of claims 11 to 13, wherein measuring the voltage difference comprises sampling the first battery cell and the second battery cell using a switched capacitor circuit.

15. The method of claim 14, wherein the method comprises integrating a charge difference of a sampling capacitor of the switched capacitor circuit connected to the charge integrator circuit in an opposite polarity.

16. An apparatus having structure to measure battery parameters, the apparatus comprising: means for selectively exciting a first battery cell of a pair of battery cells with a time-varying signal, and maintaining a second battery cell of the pair in a non-excited state during excitation of the first battery cell, wherein the first battery cell and the second battery cell have a common load current in operation; means for measuring a voltage difference between a voltage across the first battery cell and a voltage across the second battery cell; means for processing the measured voltage difference to determine an electrical impedance of the first battery cell; means for capacitively sampling a voltage of the first battery cell and a voltage of the second battery cell; and means for integrating a charge difference of a sampling capacitor connected to the means for integrating a charge difference in an opposite polarity.

17. The apparatus of claim 16, wherein the means for selectively exciting a first battery cell comprises means for varying a frequency of the time-varying signal; and the means for processing the measured voltage difference comprises means for determining a frequency-dependent electrical impedance of the first battery cell using the time-varying signal having the varying frequency, and means for determining a state of charge, a state of health, and an internal temperature of the first battery cell by processing the frequency-dependent electrical impedance of the first battery cell. ​ ​

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