Spectral excitation

Abstract

An apparatus includes a charge transfer circuit (202), a control circuit, and a processing circuit (110). The charge transfer circuit (202) has a first terminal, a second terminal, a third terminal, and a control input. The control circuit has a control output coupled to the control input. The processing circuit (110) has a first input, a second input, and an output. The processing circuit (110) is configured to receive a first signal at the first input and a second signal at the second input. The first signal is representative of a current through the charge transfer circuit. The second signal represents at least one of a first voltage between the first terminal and the second terminal or a second voltage between the second terminal and the third terminal. The processing circuit (110) is further configured to provide a third signal at the output based on the first signal and the second signal.

Description

Background Technology

[0001] Spectroscopy is commonly used in various fields, including electrical spectroscopy, mechanical spectroscopy, optical spectroscopy, and electrochemical impedance spectroscopy. One way to perform spectral measurements is to provide an excitation stimulus (e.g., voltage or current) to the device under test (DUT), and measure the DUT's response to the stimulus (e.g., voltage response to a current stimulus, current response to a voltage stimulus), repeating the excitation and response measurements at different frequencies. A challenge with spectral measurements is that the energy expended in generating the stimulus (e.g., in the form of charge from a current stimulus) may be lost after the measurement, reducing the overall power efficiency of the system, particularly for battery management systems that draw power from the battery being managed and monitored. Summary of the Invention

[0002] In one example, a device includes a charge transfer circuit, a control circuit, and a processing circuit. The charge transfer circuit has a first terminal, a second terminal, a third terminal, and a control input. The control circuit has a control output coupled to the control input. The processing circuit has a first input, a second input, and an output. The processing circuit is configured to receive a first signal at the first input and a second signal at the second input. The first signal represents a current flowing through the charge transfer circuit. The second signal represents at least one of a first voltage between the first and second terminals or a second voltage between the second and third terminals. The processing circuit is further configured to provide a third signal at the output based on the first and second signals.

[0003] In another example, a system includes a charge transfer circuit, an energy storage device, a control circuit, a first voltage sensor, a second voltage sensor, a current sensor, and a processing circuit. The charge transfer circuit has a first device under test (DUT) terminal, a second DUT terminal, a third DUT terminal, a first current terminal, a second current terminal, and a control input. The energy storage device and the current sensor are coupled between the first and second current terminals. The current sensor has a current sensor output. The control circuit has a control output coupled to the control input. The first voltage sensor is coupled between the first and second DUT terminals. The first voltage sensor has a first voltage sensor output. The second voltage sensor is coupled between the second and third DUT terminals. The second voltage sensor has a second voltage sensor output. The processing circuit has a first sensing input, a second sensing input, a third sensing input, and an output. The first sensing input is coupled to the first voltage sensor output. The second sensing input is coupled to the second voltage sensor output. The third sensing input is coupled to the current sensor output.

[0004] In another example, a method includes transferring charge from a first DUT to a second DUT through a circuit. The method further includes measuring a current flowing through the circuit generated by the charge, and measuring at least one of a first voltage across the first DUT or a second voltage across the second DUT. The method further includes generating at least one of a first impedance spectrum of the first DUT or a second impedance spectrum of the second DUT based on the current and at least one of the first voltage and the second voltage. Attached Figure Description

[0005] Figure 1 This is a block diagram of an example system used to determine the properties of the device under test.

[0006] Figure 2 This is a block diagram of an example system for determining the properties of a device under test using charge transfer between devices under test.

[0007] Figure 3 It is suitable for Figure 2 A schematic diagram of an example charge transfer circuit used in the system.

[0008] Figure 4 yes Figure 2 The graph shows the signal in the charge transfer circuit.

[0009] Figure 5 yes Figure 3 The curve of normalized current versus phase shift in a charge transfer circuit.

[0010] Figure 6 This is a block diagram of an example system for determining the properties of a device under test using charge transfer between devices under test.

[0011] Figure 7A and 7B This is a schematic diagram illustrating an example current flow system for generating an excitation current by transferring charge between two devices under test.

[0012] Figure 8 yes Figure 7A and 7B A graph showing example current flow during the charging and discharging phases of the circuit during the generation of the excitation current.

[0013] Figure 9A and 9B This is a schematic diagram illustrating an example current flow system for generating excitation current by transferring charge between multiple modules.

[0014] Figure 10 This is a schematic diagram of an example circuit used to generate excitation current through charge transfer between two battery cells.

[0015] Figure 11This is a schematic diagram of an example circuit used to generate excitation current through charge transfer between battery cells in a battery module.

[0016] Figure 12 This is a schematic diagram of an example system for generating excitation current by using a half-bridge circuit to transfer charge between battery modules.

[0017] Figure 13 This is a schematic diagram of an example system for generating excitation current by using a transformer to transfer charge between batteries.

[0018] Figure 14 This is a flowchart of an example method for electrochemical impedance spectroscopy, which generates an excitation current by transferring charge between devices under test. Detailed Implementation

[0019] Spectroscopy is commonly used in various fields, such as electrical spectroscopy, mechanical spectroscopy, optical spectroscopy, and electrochemical impedance spectroscopy. One way to perform spectral measurements is to provide an excitation stimulus (e.g., voltage or current) to the device under test (DUT) and measure the DUT's response to the stimulus (e.g., voltage response to a current stimulus, current response to a voltage stimulus), and repeat the excitation and response measurements at different frequencies.

[0020] Spectroscopic measurements, such as electrochemical spectroscopy, are performed on batteries to analyze their behavior, which can indicate various operational conditions. Specifically, battery behavior changes based on battery condition and environmental influences on the supplied current. Predicting battery behavior during operation is crucial for managing and improving the battery power supply of these devices. Battery condition is typically characterized by the level of available charge (e.g., state of charge (SOC)) and the percentage of remaining useful charge / discharge cycles (e.g., state of health (SOH)). Predictions of battery parameters (e.g., SOC, SOH, and temperature) rely on mathematical models of the battery that estimate these parameters based on the chemical reactions within the battery. Some battery models use lumped-parameter circuit representations with resistors and capacitors to simulate battery behavior under different conditions.

[0021] During charging, discharging, and aging, the physical effects occurring inside the battery can be represented by an equivalent circuit model, which includes capacitors, resistors, and series combinations of several parallel resistors and capacitors. The series capacitors represent the charge stored in the battery, the resistors represent the DC resistance of the battery cell, and the RC series represents the time constant of instantaneous battery voltage changes.

[0022] Once the parameter values ​​are determined using a characterization method, the battery impedance can be determined from the equivalent circuit model. A given characterization method can determine appropriate parameter values ​​for the SOC, SOH, and environmental conditions encountered during the battery's lifespan. Most characterization methods apply excitation signals to the battery within a reasonable range of operating conditions and estimate the circuit parameters that best model the measured response.

[0023] A battery impedance spectrum is the ratio between voltage and current in a battery cell in the frequency domain, and it is strongly correlated with the battery's state of charge (SOC), state of equilibrium (SOH), and internal temperature. Measuring a battery impedance spectrum to characterize its behavior is commonly referred to as electrochemical impedance spectroscopy (EIS). EIS measurements can be used to determine SOC, SOH, or temperature parameters based on the measured impedance, or to generate battery models when these parameters are measured via alternative methods. A challenge with EIS measurements is that the energy expended in generating the stimulus (e.g., in the form of charge stimulated by a current) may be lost after the measurement, reducing the overall power efficiency of the system, particularly for battery management systems that draw power from the battery being managed and monitored.

[0024] Figure 1 This is a block diagram of an example system 100 for determining the properties of a device under test (DUT). System 100 includes an excitation current source 102, multiple DUTs 104A, 104B, 104N-2, 104N-1, and 104N (collectively referred to as DUT 104), multiple voltage sensors 106A, 106B, 106N-2, 106N-1, and 106N (collectively referred to as voltage sensors 106), a current sensor 108, and processing circuitry 110. The excitation current source 102, DUT 104, and current sensor 108 are coupled in series, with DUT 104 being coupled in series between the excitation current source 102 and the current sensor 108. The current sensor 108 is coupled between DUT 104 and a reference terminal (e.g., ground). DUT 104 may be an electrochemical cell, a battery consisting of multiple cells (e.g., coupled in series), a battery module, or other energy storage device such as a capacitor.

[0025] Excitation current source 102 draws excitation current from DUT 104. The excitation current can be a single sinusoidal current or a combination of several sinusoidal currents. Current sensor 108 measures the current drawn by excitation current source 102. Current sensor 108 may include a sensing resistor and a current-limiting resistor coupled in series. The voltage across the sensing resistor represents the measured excitation current, and the current-limiting resistor limits the maximum current flowing through DUT 104. In system 100, the excitation current can flow to ground, and the power generated by the excitation current can be dissipated in the current-limiting resistor.

[0026] Each of the voltage sensors 106 measures the voltage across one of the DUTs 104 and is coupled to the DUT 104 via a Kelvin connection. The Kelvin connection includes separate conductors for current and voltage sensing to ensure no current flows in the voltage sensing line, as the voltage sensor 106 has a high input impedance and does not allow current to flow into the input of the voltage sensor 106. The Kelvin connection allows the voltage sensor 106 to measure only the voltage across the DUT 104 and avoids any voltage drop across the conductor between the DUT 104 and the voltage sensor 106. For example, DUT 104A is coupled between the first and second terminals of voltage sensor 106A, DUT 104B is coupled between the first and second terminals of voltage sensor 106B, and so on. The voltage measurement output of each of the voltage sensors 106 is coupled to the input of the processing circuit 110.

[0027] Processing circuit 110 receives current and voltage measurements from current sensor 108 and voltage sensor 106, and calculates the impedance value of each DUT 104 based on the measured voltage across the DUT 104 and the measured excitation current. For example, processing circuit 110 can sample and digitize the measured current and voltage signals received from current sensor 108 and voltage sensor 106, and calculate the Discrete Fourier Transform (DFT) of the current and voltage signals. System 100 can calculate the impedance value of each DUT 104 as the ratio of the voltage DFT to the current DFT at each excitation frequency. Processing circuit 110 or the circuitry coupled to processing circuit 110 can determine the properties (temperature, SOC, SOH, etc.) of each DUT 104 based on the impedance value. Processing circuit 110 may include a processor that executes instructions or a hardware circuitry system that performs impedance and other calculations.

[0028] One challenge posed by System 100 relates to the significant charge loss from DUT 104 during each EIS measurement in order to provide a large-amplitude excitation signal. The excitation signal can have a large amplitude to allow for high signal-to-noise ratio voltage and current measurements, which yields accurate impedance values. As the excitation amplitude increases, the charge loss from DUT 104 increases for each EIS measurement. This charge loss is further exacerbated as the frequency of EIS measurements increases, which necessitates improvements in the efficiency and safety of DUT 104.

[0029] Figure 2This is a block diagram of an example system 200 for determining the properties of a device under test (DUT) using charge transfer between DUTs. System 200 reduces power loss during EIS measurements, allowing the DUT to have greater capacity after the EIS measurement. System 200 moves charge through the DUT (or a group of DUTs) to perform DUT EIS measurements. After the charge is removed from the DUT, system 200 can transfer the charge to a charge storage device, and then discharge the charge storage device and provide the charge to another DUT to perform EIS measurements on that DUT, instead of discharging the charge to ground and thereby dissipating the charge energy. Therefore, by transferring charge between DUTs to perform EIS, system 200 can increase the operating lifetime of the DUTs relative to system 100 while reducing power loss caused by EIS measurements.

[0030] System 200 includes DUTs 104A and 104B, voltage sensors 106A and 106B, processing circuitry 110, and charge transfer circuitry 202. DUTs 104A and 104B, voltage sensors 106A and 106B, and processing circuitry 110 can be as described with respect to system 100. Charge transfer circuitry 202 may include current sensor 204. Alternatively, current sensor 204 may be located externally to charge transfer circuitry 202. Voltage sensors 106A and 106B are coupled to DUTs 104A and 104B using Kelvin connections as described with respect to system 100. A first terminal of voltage sensor 106A is coupled to a first terminal of DUT 104A, and a second terminal of voltage sensor 106A is coupled to a second terminal of DUT 104A. A first terminal of voltage sensor 106B is coupled to a first terminal of DUT 104B, and a second terminal of voltage sensor 106B is coupled to a second terminal of DUT 104B. The second terminal of DUT 104A is coupled to the first terminal of DUT 104B.

[0031] The charge transfer circuit 202 has a first terminal coupled to a first terminal of DUT 104A, a second terminal coupled to a second terminal of DUT 104A and a first terminal of DUT 104B, and a third terminal coupled to the second terminal of DUT 104B. To characterize DUT 104A, the charge transfer circuit 202 draws an excitation current from DUT 104A, stores the charge drawn from DUT 104A, and transfers the charge to DUT 104B. A current sensor 204 measures the excitation current drawn from DUT 104A and provides the current measurement signal to processing circuit 110. A voltage sensor 106A measures the voltage across DUT 104A when the excitation current is drawn and provides the voltage measurement signal to processing circuit 110. The charge transfer circuit 202 includes a charge storage component that stores the energy of the excitation current. The charge transfer circuit 202 transfers the stored energy to DUT 104B.

[0032] To characterize DUT 104B, charge transfer circuit 202 draws excitation current from DUT 104B, stores the charge drawn from DUT 104B, and transfers the charge to DUT 104A. Current sensor 204 measures the excitation current drawn from DUT 104B and provides the current measurement signal to processing circuit 110. Voltage sensor 106B measures the voltage across DUT 104B when drawing excitation current and provides the voltage measurement signal to processing circuit 110. Charge transfer circuit 202 stores the energy of the excitation current. Charge transfer circuit 202 transfers the stored energy to DUT 104A. By transferring the energy of the excitation current between DUTs, system 200 can provide a high excitation current to EIS while reducing energy loss in EIS measurements.

[0033] Figure 3 This is a schematic diagram of a charge transfer circuit 202 (or a portion thereof) suitable for use in system 200. Figure 3 Adjacent DUTs 104A and 104B coupled to charge transfer circuit 202 are also shown. Charge transfer circuit 202 includes half-bridge circuit 302, half-bridge circuit 304, inductor-capacitor (LC) circuit 306, and control circuit 308. Half-bridge circuit 302 is coupled in parallel with DUT 104B and includes a first terminal coupled to a first terminal of DUT 104B and a second terminal coupled to a second terminal of DUT 104B. Similarly, half-bridge circuit 304 is coupled in parallel with DUT 104A and includes a first terminal coupled to a first terminal of DUT 104A and a second terminal coupled to a second terminal of DUT 104A.

[0034] Each half-bridge circuit includes a pair of transistors. The transistors may be n-channel field-effect transistors (NFETs). Half-bridge circuit 302 includes transistors 310 and 312. A first terminal (e.g., source) of transistor 310 is coupled to a second battery terminal, and a second terminal (e.g., drain) of transistor 310 is coupled to a switching node 332. Capacitor 322 represents the drain-to-source capacitance of transistor 310. A first terminal (e.g., source) of transistor 312 is coupled to the switching node 332, and a second terminal (e.g., drain) of transistor 312 is coupled to a first terminal of half-bridge circuit 302. Capacitor 324 represents the drain-to-source capacitance of transistor 312.

[0035] The half-bridge circuit 304 includes transistors 314 and 316 and a switching node 334. A first terminal (e.g., source) of transistor 314 is coupled to a first terminal of DUT 104A, and a second terminal (e.g., drain) of transistor 314 is coupled to switching node 334. Capacitor 326 represents the drain-to-source capacitance of transistor 314. A first terminal (e.g., source) of transistor 316 is coupled to switching node 334, and a second terminal (e.g., drain) of transistor 316 is coupled to a second terminal of DUT 104A. Capacitor 328 represents the drain-to-source capacitance of transistor 316.

[0036] An LC circuit 306 is coupled between switching nodes 332 and 334. The LC circuit 306 includes an inductor 318 and a capacitor 320 coupled in series. The capacitor 320 capacitively couples half-bridge circuits 302 and 304. The capacitance of the capacitor 320 and the inductance of the inductor 318 can be relatively small. For example, in some embodiments of the LC circuit 306, the inductance of the inductor 318 can be 50 nanohenries (nH), and the capacitance of the capacitor 320 can be 3 microfarads (μF). The voltage across transistors 310, 312, 314, 316, inductor 318, or capacitor 320 can be limited to approximately the voltage of a single battery cell. Therefore, the rated voltage of these components can be relatively low.

[0037] Control circuit 308 generates a driver signal that controls transistors 310, 312, 314, and 316 to manage the extraction of excitation current and charge transfer between DUTs 104A and 104B. Control circuit 308 operates at a switching frequency f... sw The rate of the switching cycle is generated, which includes two phases—phase 1 and phase 2. One phase is used to discharge one of the DUTs into the LC circuit 306 storing the transferred charge, and the other phase is used to charge another DUT using the charge stored in the LC circuit 306.

[0038] Figure 3An example of charge transfer from DUT 104B to DUT 104A using charge transfer circuit 202 is shown. During phase 1, by turning on transistor 310 in half-bridge circuit 302 and turning off transistor 312, and then at time delay t... delay Then transistor 314 is turned on and transistor 316 is turned off, transferring charge from DUT 104B to LC circuit 306 (as shown in path 336). During phase 2, transistor 310 in half-bridge circuit 302 is turned off and transistor 312 is turned on, then by the same time delay t... delay Then, transistor 314 is turned off and transistor 316 is turned on, transferring charge from LC circuit 306 to DUT104A (as shown in path 338).

[0039] During phase 1, current flows through DUT 104B, while no current flows in DUT 104A. Then, in phase 2, current flows through the cells of DUT 104A in the opposite direction to phase 1, while no current flows in DUT 104B. The current amplitude for each switching cycle is determined by the phase, according to the desired sinusoidal excitation. Control. This is achieved by using a control signal that lags behind or leads the half-bridge circuit 304 relative to the half-bridge circuit 302. It can be positive or negative. Therefore, the excitation signal can be centered at zero even without direct current, to reduce power loss. The polarity of the excitation signal amplitude determines... The polarity of the circuit controls the charging and discharging phases of DUTs 104A and 104B. The average current in each DUT, determined by removing high-frequency switching components using a low-pass filter, can be equal to the desired sinusoidal excitation waveform through the DUT. Using this method, charge exchange between DUTs during a single EIS measurement allows the DUTs to retain their initial charge capacity with only minimal losses. This is because the power loss through the circuit resistance is less than that of standard EIS measurement architectures (such as...). Figure 1 As shown in the figure, the DUT retains more charge after EIS measurement.

[0040] Figure 4 This is a graph of the signals in charge transfer circuit 202, showing the charge transfer from DUT 104B to DUT 104A during the switching cycles of half-bridge circuits 302 and 304. In interval 402, control circuit 308 provides [the following information] in the first state. and Transistors 310 and 314 are turned on, and in the second state, C1 and C2 are provided to turn off transistors 312 and 316. The voltage across transistors 310 and 314 is zero or close to zero. Current i B,AC1 It is negative.

[0041] In interval 404, control circuit 308 provides in the first state To turn on transistor 314, and provide in the second state C1 and C2 ( (The transition from the second state to the first state) turns off transistors 310, 312, and 316. Transistor 312 can be turned off using a zero-voltage switch. The voltage across transistor 310 ( )Increase.

[0042] In interval 406, after the voltage across transistor 310 has risen to a selected value, control circuit 308 can provide C1 in the first state to turn on transistor 312. Due to the DUT voltage across inductor 318, current i B,AC1 The current flows through transistor 312. In this configuration, transistors 310 and 316 are off, and transistors 312 and 314 are on to provide a path for current flow. As mentioned above, capacitor 320 can provide capacitive isolation between adjacent DUTs and can have a relatively low voltage tolerance (e.g., 5 volts). The voltage across capacitor 320 can be the average of the voltage v1 across DUT 104B and the voltage v2 across DUT 104A. The voltage across inductor 318 has the opposite polarity to the voltage across capacitor 320 (such that the total voltage is zero when switching nodes 334 and 332 are shorted together by transistors 314 and 312), resulting in a current (i) flowing through inductor 318. B,AC1 The current increases (ramp-up), and the ramp rate can be determined by the inductance of inductor 318. The duration of interval 406 can determine the amount of current increase and the amount of charge transferred before the current stops increasing.

[0043] In interval 408, after the current flowing to inductor 318 has increased to a selected value, and control circuit 308 can provide in the second state... Transistor 314 is turned off. In this configuration, transistors 310, 314, and 316 are turned off, and transistor 312 is turned on. The voltage across transistor 314 is... )Increase.

[0044] In interval 410, after the voltage across transistor 314 has increased to a selected value, control circuit 308 can provide C2 in a first state to turn on transistor 316 using a zero-voltage switch. In this configuration, transistors 310 and 314 are off, and transistors 312 and 316 are on. The voltage across inductor 318 is zero, and the current through the inductor (i...) B,AC1The charge remains at (or near) the selected value. In interval 410 (power transfer interval), charge is transferred from LC circuit 306 to DUT 104A. Therefore, the charge transferred from DUT 104B to LC circuit 306 is transferred to DUT 104A.

[0045] In interval 412, control circuit 308 can provide C1 in the second state to turn off transistor 312. The voltage across transistor 310 ( )decline.

[0046] In interval 414, after the voltage across transistor 310 has dropped to a selected value, control circuit 308 can provide in the first state. Transistor 310 is switched on using a zero-voltage switch. Current i B,AC1 Decrease and become negative.

[0047] In interval 416, when the current flowing in inductor 318 has decreased to a selected value, control circuit 308 can provide C2 in the second state to turn off transistor 316. The voltage across transistor 314 ( )decline.

[0048] In interval 418, when the voltage across transistor 314 has dropped to a selected value, control circuit 308 can provide in the first state... Transistor 314 is turned on using a zero-voltage switch. In interval 418, charge transfer circuit 202 is in the same state as interval 402 used to perform continuous charge transfer cycles.

[0049] exist Figure 4 In this circuit, inductor 318 and capacitor 320 can form a resonant circuit and support soft switching, and the switching nodes (332 and 334) can commutate without discharging capacitors 322, 324, 326, and 328. This arrangement accelerates switching and allows half-bridge circuits 302 and 304 to operate at higher switching frequencies, which in turn allows for smaller fabrication of the half-bridge circuits 302 and 304. The increased switching frequency also reduces the time capacitor 320 blocks DC voltage, which can further reduce the size of capacitor 320.

[0050] Although Figure 4 The charge transfer from DUT 104B to DUT 104A is shown, but it can be achieved through exchange. Figure 4 Signal C1 and Timing and Figure 4 Signal C2 and The timing is used to provide charge transfer from DUT 104A to DUT 104B.

[0051] Phase shift between control signals C1 and C2 (in radians) based on switching frequency And the time delay between the edges of C1 and C2 ( ) is defined as:

[0052]

[0053] Average current I during the switching cycle, voltage V of the DUT, and switching frequency Series inductance of inductor 318 and phase shift The relationship between them is given by the following equation:

[0054]

[0055] When in a relatively small During operation, the equation can be simplified to:

[0056]

[0057] Considering maximum phase shift (in radians) and maximum time delay Switching frequency It can be written as:

[0058]

[0059] Considering the maximum current The voltage V of the DUT and the switching frequency and maximum phase shift (in radians) Series inductor It can be written as:

[0060]

[0061] A capacitor of 320 can be selected to set the resonant frequency much smaller than the switching frequency. This ensures the inductor operation of the LC circuit 306. To reduce the size of the capacitor 320, the resonant frequency and switching frequency can be adjusted. The maximum resonant frequency is selected by choosing a coefficient of 5, as shown below:

[0062]

[0063] Figure 5 This is a graph showing the normalized current versus phase shift in charge transfer circuit 202. Figure 5 This shows the normalized maximum current. current Phase shift shown in degrees .for At lower values, the relationship between phase shift and current is fairly linear. For larger values ​​of phase shift, this linear approximation leads to significant errors. Figure 5 For example, the maximum phase shift can be chosen as (i.e., 30°).

[0064] Figure 6 This is a block diagram of an example system 600 for determining the properties of a device under test (DUT) using charge transfer between DUTs. System 600 includes a charge transfer circuit 602, DUTs 104A-104N (DUTs 104A, 104M, 104M+1, and 104N are shown), and voltage sensors 106A-106N (voltage sensors 106A, 106M, 106M+1, and 106N are shown). One of the voltage sensors 106 is coupled across each DUT 104 to measure its voltage.

[0065] The charge transfer circuit 602 is similar to Figure 3 The charge transfer circuit 202 shown includes a half-bridge circuit 302, a half-bridge circuit 304, an LC circuit 306, and a control circuit 308. The charge transfer circuit 302 also includes a current sensing resistor 603 coupled in series with the LC circuit 306, and a voltage sensor 604 coupled across the current sensing resistor 603. The current sensing resistor 603 and the voltage sensor 604 form... Figure 2 The current sensor 204 is shown.

[0066] Half-bridge circuit 302 is coupled across a first group of DUTs 104, including DUTs 104M+1 to 104N. Half-bridge circuit 304 is coupled across a second group of DUTs 104, including DUTs 104A to 104M. Charge transfer circuit 602 can draw excitation current from the first group of DUTs and transfer charge to the second group of DUTs. Charge transfer circuit 602 can also draw excitation current from the second group of DUTs and transfer charge to the first group of DUTs.

[0067] Current sensing resistor 603 and voltage sensor 604 measure the excitation current drawn from the DUT, and voltage sensors 106A-106N measure the voltage across the DUT from 104A to 104N. The voltage and current measurement signals can be provided to processing circuit 110 and used by processing circuit 110 to calculate the impedance values ​​of the DUT from 104A to 104N.

[0068] Figure 7A and 7B This is a schematic diagram of system 600, showing the transfer of charge from the first set of DUTs to the second set of DUTs. Figure 7AIn this configuration, transistors 310 and 314 are turned on, while transistors 312 and 316 are turned off, allowing current to flow from DUT 104M+1 to 104N in path 702. The charge drawn from DUT 104M+1 to 104N is stored in LC circuit 306. No current flows through this circuit. Figure 7A The DUTs are 104A to 104M. A current sensing resistor 603 and a voltage sensor 604 measure the current drawn from the DUTs 104M+1 to 104N. Voltage sensors 106M+1 to 106N measure the voltage across the DUTs 104M+1 to 104N.

[0069] exist Figure 7B In this configuration, transistors 310 and 314 are turned off, and transistors 312 and 316 are turned on, causing the charge stored in LC circuit 306 to be transferred from LC circuit 306 to DUT 104A-104M via path 704. No current flows. Figure 7B The DUTs in the range are 104M+1 to 104N.

[0070] Figure 8 yes Figure 7A and 7B A graph illustrating the current flow in an example circuit. Figure 8 In this context, i1(t) is Figure 7A The current flow in phase 1 shown is i2(t) Figure 7B The current in phase 2 shown, and It is the relative phase of control signals C1 and C2. According to... Figure 8 The desired sinusoidal excitation shown is given in each switching cycle (C1, ...). C2 and The current amplitude of the switch is determined by the phase. Control. This is achieved by using a control signal that lags behind or leads the half-bridge circuit 304 relative to the half-bridge circuit 302. It can be positive or negative. Therefore, the excitation signal can be centered at zero even without direct current, to reduce power loss. The polarity of the excitation signal amplitude determines... The polarity, the polarity control as Figure 7A and 7B The charging and discharging phases of the DUT are shown. The average current in each group of DUTs, determined by removing high-frequency switching components using a low-pass filter, can be equal to the desired sinusoidal excitation waveform through the DUT.

[0071] Figure 9A and 9BThis is a schematic diagram of a system 900 for generating excitation current by transferring charge between multiple modules under test (MUTs). System 900 includes MUTs 901A, 901B, 901C, and 901D, each MUT potentially containing multiple DUTs coupled in series as a battery pack. MUTs 901A, 901B, 901C, and 901D are coupled in series. The DUTs can be battery cells, and the modules under test can be battery modules. System 900 includes voltage sensors 906A, 906B, 906C, and 906D. Voltage sensor 906A contains a voltage sensor coupled across each DUT of MUT 901A. Voltage sensor 906B contains a voltage sensor coupled across each DUT of MUT 901B. Voltage sensor 906C contains a voltage sensor coupled across each DUT of MUT 901C. Voltage sensor 906D contains a voltage sensor coupled across each DUT of MUT 901D. The connection between the voltage sensors and the DUTs can be a Kelvin connection.

[0072] System 900 includes a half-bridge circuit 304 coupled across MUT 901A, a half-bridge circuit 302 coupled across MUT 901B, a half-bridge circuit 904 coupled across MUT 901C, and a half-bridge circuit 902 coupled across MUT 901D. An LC circuit 306 is coupled between half-bridge circuits 302 and 304 to store charge transferred between MUT 901A and MUT 901B. An LC circuit 907A is coupled between half-bridge circuits 904 and 302 to store charge transferred between MUT 901C and MUT 901B. An LC circuit 907B is coupled between half-bridge circuits 902 and 904 to store charge transferred between MUT 901D and MUT 901C.

[0073] Current sensor 204 is coupled between LC circuit 306 and half-bridge circuit 302 to measure the current flowing between MUT 901A and MUT 901B. Current sensor 905A is coupled between LC circuit 907A and half-bridge circuit 904 to measure the current flowing between MUT 901B and MUT 901C. Current sensor 905B is coupled between LC circuit 907B and half-bridge circuit 902 to measure the current flowing between MUT 901C and MUT 901D.

[0074] Control circuits 910A, 910B, 910C, and 910D are coupled to half-bridge circuits 304, 302, 904, and 902, respectively, to control the switching of transistors in the half-bridge circuits. Control circuits 910A, 910B, 910C, and 910D can be provided as a single control circuit or as separate control circuits (e.g., Figure 9A and 9B (As shown).

[0075] exist Figure 9A In this configuration, control circuits 910A, 910B, 910C, and 910D have configured half-bridge circuits 304, 302, 904, and 902 to draw excitation current from MUT 901D and store charge in LC circuit 907B, and to draw excitation current from MUT 901B and store charge in LC circuit 306. Figure 9B In this configuration, control circuits 910A, 910B, 910C, and 910D have configured half-bridge circuits 304, 302, 904, and 902 to transfer charge from LC circuit 306 to MUT 901A and from LC circuit 907B to MUT 901C. (See also: Regarding...) Figure 7A and 7B The transistors in the half-bridge circuit are controlled as described to perform charge transfer. In some instances, the LC circuits 306, 907A, and 907B can be replaced by other LC networks, such as those shown in the relevant U.S. Patent Applications Nos. 18 / 340,399 and 18 / 340,476.

[0076] Figure 10 This is a schematic diagram of an example circuit 1000 for generating an excitation current through charge transfer between two battery cells. Circuit 1000 includes battery cells 1002A and 1002B, a charge transfer circuit 602, and voltage sensors 106A and 106B. Voltage sensor 106A is coupled across battery cell 1002A via a Kelvin connection to measure its voltage. Voltage sensor 106B is coupled across battery cell 1002B via a Kelvin connection to measure its voltage.

[0077] The charge transfer circuit 602 is similar to Figure 3 The charge transfer circuit 202 shown includes a half-bridge circuit 302, a half-bridge circuit 304, an LC circuit 306, and a control circuit 308. The charge transfer circuit 302 also includes a current sensing resistor 603 coupled in series with the LC circuit 306, and a voltage sensor 604 coupled across the current sensing resistor 603. The current sensing resistor 603 and the voltage sensor 604 form... Figure 2 The current sensor 204 is shown. The switches of the half-bridge circuits 302 and 304 are controlled by the control circuit 308 to draw excitation current from one of the battery cells 1002A and 1002B and store the charge in the LC circuit 306, and then transfer the charge stored in the LC circuit 306 to the other of the battery cells 1002A and 1002B.

[0078] Half-bridge circuit 302 is coupled across battery cell 1002B. Half-bridge circuit 304 is coupled across battery cell 1002A. In one example, control circuit 308 causes charge transfer circuit 602 to draw excitation current from battery cell 1002B and store charge in LC circuit 306. Subsequently, control circuit 308 causes charge transfer circuit 602 to transfer the charge stored in LC circuit 306 to battery cell 1002A. In another example, control circuit 308 causes charge transfer circuit 602 to draw excitation current from battery cell 1002A and store charge in LC circuit 306. Subsequently, control circuit 308 causes charge transfer circuit 602 to transfer the charge stored in LC circuit 306 to battery cell 1002B.

[0079] Current sensing resistor 603 and voltage sensor 604 measure the excitation current drawn from battery cells 1002A and 1002B, and voltage sensors 106A and 106B measure the voltages of battery cells 1002A and 1002B. The voltage and current measurement signals can be provided to processing circuit 110 and used by processing circuit 110 to calculate the impedance values ​​of battery cells 1002A and 1002B.

[0080] Figure 11 This is a schematic diagram of an example circuit 1100 for generating excitation current through charge transfer between battery cells of a battery module. Circuit 1100 includes a battery module 1101. Battery module 1101 includes multiple battery cells B1-B1. N The battery cells of battery module 1101 are subdivided into sub-modules 1102A and 1102B. Sub-module 1102A may contain the first half of the battery cells of battery module 1101, and sub-module 1102B may contain the second half of the battery cells of battery module 1101. Circuit 1100 also includes charge transfer circuit 602 and voltage sensors 1061-106. N (like Figure 11 The voltage sensors 1061 and 106 shown are shown. N / 2 106 N / 2+1 and 106 N One of the voltage sensors is coupled to each of the batteries in the battery module 1101 via a Kelvin connection to measure its voltage.

[0081] The charge transfer circuit 602 is similar to Figure 3 The charge transfer circuit 202 shown includes a half-bridge circuit 302, a half-bridge circuit 304, an LC circuit 306, and a control circuit 308. The charge transfer circuit 302 also includes a current sensing resistor 603 coupled in series with the LC circuit 306, and a voltage sensor 604 coupled across the current sensing resistor 603. The current sensing resistor 603 and the voltage sensor 604 form... Figure 2 The current sensor 204 is shown. The switches of the half-bridge circuits 302 and 304 are controlled by the control circuit 308 to draw excitation current from one of the sub-modules 1102A and 1102B and store the charge in the LC circuit 306, and then transfer the charge stored in the LC circuit 306 to the other of the sub-modules 1102A and 1102B.

[0082] Half-bridge circuit 302 is coupled across submodule 1102B. Half-bridge circuit 304 is coupled across submodule 1102A. In one example, control circuit 308 causes charge transfer circuit 602 to draw excitation current from submodule 1102B and store charge in LC circuit 306. Subsequently, control circuit 308 causes charge transfer circuit 602 to transfer the charge stored in LC circuit 306 to submodule 1102A. In another example, control circuit 308 causes charge transfer circuit 602 to draw excitation current from submodule 1102A and store charge in LC circuit 306. Subsequently, control circuit 308 causes charge transfer circuit 602 to transfer the charge stored in LC circuit 306 to submodule 1102B.

[0083] Current sensing resistor 603 and voltage sensor 604 measure the excitation current drawn from submodules 1102A and 1102B, and voltage sensors 1061-106... N Measuring battery B1-B N The voltage and current measurement signals can be provided to the processing circuit 110 and used by the processing circuit 110 to calculate the impedance value of the battery cell of the battery module 1101.

[0084] Figure 12 This is a schematic diagram of a system 1200 for generating excitation current by transferring charge between battery modules using a half-bridge circuit. System 1200 includes a battery pack 1201 comprising battery modules 1203A, 1203B, 1203C, and 1203D coupled in series. Each of the battery modules may contain multiple cells (B1-B2) coupled in series. N System 1200 includes voltage sensors 906A, 906B, 906C, and 906D. Voltage sensor 906A includes a voltage sensor coupled across each cell of battery module 1203A. Voltage sensor 906B includes a voltage sensor coupled across each cell of battery module 1203B. Voltage sensor 906C includes a voltage sensor coupled across each cell of battery module 1203C. Voltage sensor 906D includes a voltage sensor coupled across each cell of battery module 1203D. The connection between the voltage sensors and the batteries can be a Kelvin connection.

[0085] System 1200 includes a half-bridge circuit 304 coupled across battery module 1203A, a half-bridge circuit 302 coupled across battery module 1203B, a half-bridge circuit 904 coupled across battery module 1203C, and a half-bridge circuit 902 coupled across battery module 1203D. An LC circuit 306 is coupled between half-bridge circuits 302 and 304 to store charge transferred between battery modules 1203A and 1203B. An LC circuit 907A is coupled between half-bridge circuits 904 and 302 to store charge transferred between battery modules 1203C and 1203B. An LC circuit 907B is coupled between half-bridge circuits 902 and 904 to store charge transferred between battery modules 1203D and 1203C.

[0086] Current sensor 204 is coupled between LC circuit 306 and half-bridge circuit 302 to measure the current flowing between battery module 1203A and battery module 1203B. Current sensor 905A is coupled between LC circuit 907A and half-bridge circuit 904 to measure the current flowing between battery module 1203B and battery module 1203C. Current sensor 905B is coupled between LC circuit 907B and half-bridge circuit 902 to measure the current flowing between battery module 1203C and battery module 1203D.

[0087] Control circuits 910A, 910B, 910C, and 910D are coupled to half-bridge circuits 304, 302, 904, and 902, respectively, to control the switching of transistors in the half-bridge circuits. Control circuits 910A, 910B, 910C, and 910D can be provided as a single control circuit or as separate control circuits (e.g., Figure 12 (As shown).

[0088] In various instances of system 1200, charge can be transferred between adjacent battery modules (e.g., between battery module 1203A and battery module 1203B, between battery module 1203B and battery module 1203C, and between battery module 1203C and battery module 1203D) or between non-adjacent battery modules to provide the excitation current for EIS determination. Current and voltage measurement signals provided by the current and voltage sensors of system 1200 can be provided to processing circuitry 110 for EIS calculations.

[0089] Figure 13This is a schematic diagram of a system 1300 for generating excitation current by transferring charge between batteries using transformers. System 1300 includes batteries 1302A-1302N (batteries 1302A, 1302B, and 1302N are shown), a charge transfer circuit 1301, voltage sensors 1308A-1308N (voltage sensors 1308A, 1308B, and 1308N are shown), and processing circuitry 110. Charge transfer circuitry 1301 includes transformers 1304A-1304N (transformers 1304A, 1304B, and 1304N are shown), inverter circuits 1305A-1305N (inverter circuits 1305A, 1305B, and 1305N are shown), current sensors 1310A-1310N (current sensors 1310A, 1310B, and 1310N are shown), and inverter control circuitry 1312.

[0090] Voltage sensors 1308A, 1308B, and 1308N are coupled across batteries 1302A, 1302B, and 1302N, respectively, to measure their voltages. The batteries are also coupled between the first and second terminals of each inverter circuit. Battery 1302A is coupled between the first and second terminals of inverter circuit 1305A. Battery 1302B is coupled between the first and second terminals of inverter circuit 1305B. Battery 1302N is coupled between the first and second terminals of inverter circuit 1305N. Each inverter circuit includes switches coupled as a full bridge. These switches may be implemented using transistors. Inverter circuit 1305A includes switches 1306A1, 1306A2, 1306A3, and 1306A4 connected as a full bridge. Inverter circuit 1305B includes switches 1306B1, 1306B2, 1306B3, and 1306B4 connected in a full-bridge configuration. Inverter circuit 1305N includes switches 1306N1, 1306N2, 1306N3, and 1306N4 connected in a full-bridge configuration.

[0091] Transformers 1304A-1304N are coupled to the third and fourth terminals of the inverter circuit. The primary coil of transformer 1304A is coupled between the third and fourth terminals of inverter circuit 1305A. The primary coil of transformer 1304B is coupled between the third and fourth terminals of inverter circuit 1305B. The primary coil of transformer 1304N is coupled between the third and fourth terminals of inverter circuit 1305N. The secondary coil of each transformer is coupled to the secondary coil of each of the other transformers. By changing the voltage across the primary coil, the transformer can move charge from one of the batteries 1302A-1302N during EIS measurement, and induce voltage and current in the secondary coil via electromagnetic induction. The induced voltage and current in the secondary coil depend on the winding ratio of the transformer, providing induced charge to the other of the batteries 1302A-1302N, thus minimizing the power loss measured by EIS.

[0092] Inverter control circuit 1312 controls the switching of switches in each inverter circuit. For example, the output of inverter control circuit 1312 is coupled to the control terminal of each switch in each inverter circuit. Inverter control circuit 1312 can control the switch of a selected inverter circuit to draw excitation current from a battery coupled to said inverter circuit. For example, inverter control circuit 1312 can control the switch of (pulse width modulation) inverter circuit 1305A to draw sinusoidal current of one or more frequencies from battery 1302A. Inverter control circuit 1312 can control the switch of inverter circuit 1305B or inverter circuit 1305N to transfer charge drawn from battery 1302A to battery 1302B or battery 1302N. Current sensors 1310A, 1310B, and / or 1310C measure the excitation current, and voltage sensors 1308A, 1308B, and / or 1308N measure the voltage across the battery from which current is drawn, and provide current and voltage measurement signals to processing circuit 110. Processing circuit 110 can calculate the battery impedance based on the current and voltage measurement signals.

[0093] Figure 14 This is a flowchart of an example method 1400 of EIS, in which electrochemical impedance spectroscopy generates an excitation current by transferring charge between devices under test. Although depicted sequentially for convenience, at least some of the actions shown can be performed in a different order and / or in parallel. Furthermore, some embodiments may perform only some of the actions shown. The operation of method 1400 can be performed by system 200, system 600, system 900, circuit 1000, circuit 1100, system 1200, system 1300, etc.

[0094] In block 1402, charge is transferred from a first DUT to a second DUT via a circuit. The DUT can be an electrochemical cell, a battery composed of multiple cells, or other energy storage devices such as a supercapacitor. The circuit can be charge transfer circuit 202, charge transfer circuit 602, or other charge transfer circuits based on a half-bridge switch, or the circuit can be 1301 or a similar transformer-based charge transfer circuit. The charge transfer may include transferring charge from the first DUT to an energy storage device (e.g., LC circuit 306), and subsequently transferring the charge stored in the energy storage device to the second DUT.

[0095] In box 1404, the current flowing during the charge transfer in box 1402 is measured. For example, current sensor 204 or current sensor 1310A can measure the current flowing during the charge transfer.

[0096] In block 1406, the voltage across the first DUT and / or the voltage across the second DUT is measured. For example, voltage sensors 106A, 106M, 106M+1, 106N, 1308A, or 1308B can measure the voltage across the DUT coupled between the terminals of the voltage sensor.

[0097] In block 1408, processing circuit 110 generates the impedance spectrum of the first DUT or the second DUT based on the current measured in block 1404 and the voltage measured in block 1406.

[0098] In this description, the term "coupled" may encompass a connection, communication, or signaling path that achieves a functional relationship consistent with this description. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first instance, device A is coupled to device B via a direct connection; or (b) in a second instance, device A is coupled to device B via an intermediate component C, provided that the intermediate component C does not alter the functional relationship between device A and device B such that device B is controlled by device A via the control signal generated by device A.

[0099] Furthermore, in this specification, the statement "based on" means "at least partially based on". Therefore, if X is based on Y, then X can depend on Y and any number of other factors.

[0100] A device “configured” to perform a task or function may be configured (e.g., programmed and / or hardwired) to perform the function during manufacturing by the manufacturer, and / or may be configured (or reconfigurable) by the user after manufacturing to perform the function and / or other additional or alternative functions. Such configuration may be performed through firmware and / or software programming of the device, through the construction and / or layout of the device’s hardware components and interconnects, or through a combination thereof.

[0101] As used herein, the terms “terminal,” “node,” “interconnect,” “pin,” and “lead” are used interchangeably. Unless otherwise specified, these terms are generally used to refer to interconnections or ends between device elements, circuit elements, integrated circuits, devices, or other electronic devices or semiconductor components.

[0102] The circuits or devices described herein as containing certain components may be practically adapted to be coupled to those components to form the described circuit system or device. For example, a structure described as containing one or more semiconductor elements (e.g., transistors), one or more passive elements (e.g., resistors, capacitors, and / or inductors), and / or one or more sources (e.g., voltage sources and / or current sources) may alternatively contain only semiconductor elements within a single physical device (e.g., a semiconductor die and / or integrated circuit (IC) package) and may be adapted to be coupled to at least some of the passive elements and / or sources during or after manufacturing, for example by a terminal user and / or a third party, to form the described structure.

[0103] While the use of specific transistors is described herein, other transistors (or equivalent devices) may be used alternatively with little or no change to the rest of the circuit system. For example, field-effect transistors (“FETs”) (e.g., n-channel FETs (NFETs) or p-channel FETs (PFETs)), n-type metal-oxide-semiconductor field-effect transistors (nMOSFETs or simply “nMOS”), bipolar junction transistors (BJTs—e.g., NPN or PNP transistors), insulated-gate bipolar transistors (IGBTs), and / or junction field-effect transistors (JFETs) may be used in place of or in combination with the devices described herein. Transistors may be depletion-mode devices, drain-extended devices, enhancement-mode devices, natural transistors, or other types of device structure transistors. Furthermore, the devices may be implemented on / above a silicon substrate (Si), a silicon carbide substrate (SiC), a gallium nitride substrate (GaN), or a gallium arsenide substrate (GaAs).

[0104] Reference may be made to the control input and current terminals of the transistor in the claims. In the context of a FET, the control input is the gate, and the current terminals are the drain and source. In the context of a BJT, the control input is the base, and the current terminals are the collector and emitter.

[0105] In this document, the reference to "FET on" implies the presence of a conductive channel in the FET and that drain current can flow through it. The reference to "FET off" implies the absence of a conductive channel and that no drain current flows through the FET. However, a "off" FET can have current flowing through the body diode of a transistor.

[0106] The circuits described herein can be reconfigured to include additional or different components to provide functionality at least partially similar to that available before the component replacement. Unless otherwise stated, a component shown as a resistor generally represents one or more elements coupled in series and / or parallel to provide the amount of impedance represented by the resistor shown. For example, a resistor or capacitor shown and described herein as a single component may alternatively be multiple resistors or capacitors coupled in parallel between the same nodes. For example, a resistor or capacitor shown and described herein as a single component may actually be multiple resistors or capacitors coupled in series between the same two nodes as the single resistor or capacitor.

[0107] While some elements of the described examples are contained within the integrated circuit and others are external to the integrated circuit, in other examples, additional or fewer features may be incorporated into the integrated circuit. Additionally, some or all features shown as external to the integrated circuit may be contained within the integrated circuit, and / or some features shown as internal to the integrated circuit may be incorporated externally. As used herein, the term "integrated circuit" means one or more circuits that are: (i) incorporated in / above a semiconductor substrate; (ii) incorporated in a single semiconductor package; (iii) incorporated into the same module; and / or (iv) incorporated in / on the same printed circuit board.

[0108] Within the scope of the claims, modifications may be made to the described embodiments, and other embodiments are also possible.

Claims

1. An apparatus comprising: a charge transfer circuit having a first terminal, a second terminal, a third terminal, and a control input; a control circuit having a control output coupled to the control input; and a processing circuit having a first input, a second input, and an output, the processing circuit configured to: receive a first signal at the first input, the first signal representing a current through the charge transfer circuit; receive a second signal at the second input, the second signal representing at least one of a first voltage between the first terminal and the second terminal or a second voltage between the second terminal and the third terminal; and provide a third signal at the output based on the first signal and the second signal.

2. The apparatus of claim 1, wherein the charge transfer circuit is configured to: in response to the control input having a first state, transfer a first charge from the second terminal through the charge transfer circuit to the third terminal; and in response to the control input having a second state, transfer a second charge from the second terminal through the charge transfer circuit to the first terminal.

3. The apparatus of claim 2, further comprising an energy storage device coupled to the charge transfer circuit, wherein the charge transfer circuit is configured to charge the energy storage device using the first charge and provide the second charge by discharging the energy storage device.

4. The apparatus of claim 3, wherein the energy storage device includes an inductor and a capacitor.

5. The apparatus of claim 4, further comprising a current sensor coupled to the energy storage device, the current sensor having an output coupled to the first input of the processing circuit.

6. The apparatus of claim 1, wherein the charge transfer circuit includes a transformer.

7. The apparatus of claim 3, wherein the charge transfer circuit, the control circuit, and the processing circuit are part of an integrated circuit (IC), and the energy storage device is external to the IC.

8. The apparatus of claim 1, wherein the charge transfer circuit includes a first half-bridge circuit coupled between the first terminal and the second terminal and a second half-bridge circuit coupled between the second terminal and the third terminal.

9. The apparatus of claim 1, wherein the control circuit is configured to provide a control signal at the control output to: cause a first periodic current to flow from the second terminal through the charge transfer circuit to the third terminal; and cause a second periodic current to flow from the third terminal through the charge transfer circuit to the first terminal.

10. The apparatus of claim 1, wherein the processing circuit is configured to provide the third signal representing an impedance spectrum of a DUT.

11. A system comprising: a charge transfer circuit having a first device under test (DUT) terminal, a second DUT terminal, a third DUT terminal, a first current terminal, a second current terminal, and a control input; a control circuit having a control output coupled to the control input; and a processing circuit having a first input, a second input, and an output, the processing circuit configured to: receive a first signal at the first input, the first signal representing a current through the charge transfer circuit; receive a second signal at the second input, the second signal representing at least one of a first voltage between the first terminal and the second terminal or a second voltage between the second terminal and the third terminal; and provide a third signal at the output based on the first signal and the second signal. an energy storage device and a current sensor coupled between the first current terminal and the second current terminal, the current sensor having a current sensor output; a control circuit having a control output coupled to the control input; a first voltage sensor coupled between the first DUT terminal and the second DUT terminal, the first voltage sensor having a first voltage sensor output; a second voltage sensor coupled between the second DUT terminal and the third DUT terminal, the second voltage sensor having a second voltage sensor output; and a processing circuit having a first sense input, a second sense input, and a third sense input coupled to the first voltage sensor output, the second voltage sensor output, and the current sensor output, respectively, and an output.

12. The system of claim 11, wherein the charge transfer circuit is a first charge transfer circuit, the control input is a first control input, the control output is a first control output, the energy storage device is a first energy storage device, the current sensor is a first current sensor, the current sensor output is a first current sensor output, and the system further comprises: a second charge transfer circuit having a fourth DUT terminal, a fifth DUT terminal, a sixth DUT terminal, a third current terminal, a fourth current terminal, and a second control input, the fourth DUT terminal coupled to the third DUT terminal; a second energy storage device and a second current sensor coupled between the second current terminal and the third current terminal, the second current sensor having a second current sensor output; a third energy storage device and a third current sensor coupled between the third current terminal and the fourth current terminal, the third current sensor having a third current sensor output; a third voltage sensor coupled between the fourth DUT terminal and the fifth DUT terminal, the third voltage sensor having a third voltage sensor output; a fourth voltage sensor coupled between the fifth DUT terminal and the sixth DUT terminal, the fourth voltage sensor having a fourth voltage sensor output; and wherein the control circuit has a second control output coupled to the second control input, and the sense inputs are coupled to the second current sensor output and the third voltage sensor output and the fourth voltage sensor output.

13. The system of claim 11, further comprising a first DUT coupled between the first DUT terminal and the second DUT terminal, a second DUT coupled between the third DUT terminal and the fourth DUT terminal.

14. The system of claim 13, wherein: the first DUT includes one or more battery cells coupled between the first DUT terminal and the second DUT terminal; and the second DUT includes one or more battery cells coupled between the third DUT terminal and the fourth DUT terminal. The second DUT includes one or more battery cells coupled between the third DUT terminal and the fourth DUT terminal.

15. The system of claim 11, wherein the energy storage device includes: an inductor and a capacitor.

16. The system of claim 11, wherein the charge transfer circuit includes a first half-bridge circuit coupled between the first DUT terminal and the second DUT terminal and a second half-bridge circuit coupled between the second DUT terminal and the third DUT terminal.

17. The system of claim 11, wherein the control circuit is configured to provide control signals at the control output to: cause a first periodic current to flow from the second DUT terminal through the charge transfer circuit to the third DUT terminal; and cause a second periodic current to flow from the third DUT terminal through the charge transfer circuit to the first DUT terminal.

18. A method comprising: transferring charge through a circuit from a first DUT to a second DUT; measuring a current through the circuit resulting from the charge; measuring at least one of a first voltage across the first DUT or a second voltage across the second DUT; and generating at least one of a first impedance spectrum of the first DUT or a second impedance spectrum of the second DUT based on the current and the at least one of the first voltage or the second voltage.

19. The method of claim 18, wherein transferring the charge through a circuit from the first DUT to the second DUT includes: receiving the charge by discharging the first DUT; charging an energy storage device with the charge; discharging the energy storage device to recover the charge; and moving the recovered charge to the second DUT.

20. The method of claim 19, wherein the energy storage device includes at least one of: a circuit including an inductor and a capacitor. ​

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