Techniques for determining the health state of an energy storage device

Abstract

Techniques for determining the health state of an energy storage device utilize a capacitive gain amplifier to provide AC gain and block DC voltage. An input capacitor can be coupled between an input excitation signal generator circuit and the inverting input terminal of the amplifier, and a feedback capacitor can be coupled between the inverting input terminal of the amplifier and the output of the amplifier. A switch can be used to periodically reset the feedback capacitor to prevent leakage current at the inverting input terminal of the amplifier from saturating the output of the amplifier.

Description

[0001] Priority Claim

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 131,047, filed December 28, 2020, by Damien McCartney et al., titled "Techniques for Determining State of Health of a Battery", the entire content of which is incorporated herein by reference. Field of the Invention

[0003] This document is generally applicable to, but not limited to, energy storage device monitoring techniques. Background Art

[0004] Individual battery cells can be connected in series to provide a battery pack with a desired output voltage. A large number of batteries can be connected in series. For example, the total potential difference generated across the battery pack is approximately 150 - 600 volts.

[0005] Generally, it is necessary to monitor the terminal voltage, impedance, state of charge (SOC), and state of health (SOH) of each individual battery in a battery pack. The terminal voltage is a direct measurement of the DC voltage at the battery terminals. The battery impedance can be directly measured by applying an AC excitation current and measuring the small-signal AC voltage generated at the battery terminals. In contrast, the SOC and SOH are typically inferred from one or two direct measurements and sometimes also from the battery's usage history. They are indirect measurements. The internal battery temperature can be directly measured but can also be inferred or measured indirectly, such as through impedance.

[0006] A low terminal voltage may indicate a discharged state. Generally, the terminal voltage (DC) can be monitored periodically. The measurement frequency of the battery impedance (using an AC voltage) is the same (or possibly lower). Changes in SOH are slower than changes in SOC. If the battery internal temperature is inferred from the impedance, then the terminal voltage needs to be measured more frequently. Summary of the Invention

[0007] The present invention describes various techniques for determining the state of health of an energy storage device, such as including one or more batteries or fuel cells, using a capacitive gain amplifier to provide AC gain and block DC voltage. An input capacitor can be coupled between an input excitation signal generator circuit and the inverting input terminal of the amplifier, and a feedback capacitor can be coupled between the inverting input terminal of the amplifier and the output of the amplifier. A switch can be used to periodically reset the feedback capacitor to prevent the output of the amplifier from saturating due to leakage current at the inverting input terminal of the amplifier.

[0008] In some aspects, the present disclosure relates to the following: A system for determining the health state of an energy storage device, the system comprising: a signal generator circuit configured to generate an excitation signal and apply the excitation signal to at least one cell of the energy storage device; a first capacitive gain amplifier circuit coupled to the signal generator circuit and configured to generate a first output signal in response to the excitation signal, the first capacitive gain amplifier circuit including a first inverting input terminal; a control circuit configured to control the operation of a first switching element coupled to the first inverting input terminal to control a DC bias voltage; and a backend circuit configured to use the first output signal of the first capacitive gain amplifier circuit to determine a characteristic of the energy storage device representing the health state of the energy storage device.

[0009] In some aspects, the present disclosure relates to the following: A system for determining the health state of an energy storage device, the system comprising: a signal generator circuit configured to generate an excitation signal and apply the excitation signal to at least one cell of the energy storage device; a first channel including the first capacitive gain amplifier circuit, the first capacitive gain amplifier circuit coupled to the signal generator circuit and configured to generate a first output signal in response to the excitation signal, the first capacitive gain amplifier circuit including a first inverting input terminal; a second channel including the second capacitive gain amplifier circuit, the second capacitive gain amplifier circuit coupled to the signal generator circuit and configured to generate a second output signal in response to the excitation signal, the second capacitive gain amplifier circuit including a second inverting input terminal, a control circuit configured to control the operation of a first switching element coupled to the first inverting input terminal to control a first DC bias voltage; and a second switching element coupled to the second inverting input terminal to control a second DC bias voltage on the second inverting input terminal; and a backend circuit configured to use the first output signal of the first capacitive gain amplifier circuit and the second output signal of the second capacitive gain amplifier circuit to determine a characteristic of the energy storage device representing the health state of the energy storage device.

[0010] In some aspects, the present disclosure relates to the following: A method for determining the health state of an energy storage device, the method comprising: generating and applying an excitation signal to at least one cell of the energy storage device; using a first capacitive gain amplifier circuit to generate a first output signal in response to the excitation signal, the first capacitive gain amplifier circuit including a first inverting input terminal; controlling the operation of a first switching element coupled to the first inverting input terminal to control a first DC bias voltage; and using the first output signal of the first capacitive gain amplifier circuit to determine a characteristic of the energy storage device representing the health state of the energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the accompanying drawings, which are not necessarily to scale, like numerals may describe like components in different views. Like numerals with different letter suffixes may represent different instances of like components. The drawings generally illustrate, by way of example and not limitation, the various embodiments discussed in this document.

[0012] Figure 1 is a schematic diagram of an example of a system for determining the health state of an energy storage device.

[0013] Figure 2 is a schematic diagram of another example of a system for determining the health state of an energy storage device.

[0014] Figure 3 is a diagram illustrating an example of a timing diagram showing the relationship between the timing of switches and channels and the corresponding output signals.

[0015] Figure 4 is an example of a waveform reconstruction circuit that can be used to reconstruct the AC battery response signal of an energy storage device.

[0016] Figure 5 is a schematic diagram of another example of a system for determining the health state of an energy storage device.

[0017] Figure 6 is a diagram illustrating an example of using a channel selection signal that changes phase relative to an excitation signal to determine a characteristic of an energy storage device representing the health state of the energy storage device.

[0018] Figure 7 is a diagram showing an example of an excitation signal that changes phase to determine a characteristic of an energy storage device representing the health state of the energy storage device.

[0019] Figure 8 is a schematic diagram of another example of a system for determining the health state of an energy storage device.

[0020] Figure 9 is a schematic diagram of another example of a system for determining the health state of an energy storage device.

[0021] Figure 10 is a block diagram of an example of a system that can implement various techniques of the present disclosure.

[0022] Figure 11 is a schematic diagram of another example of a system for determining the health state of one or more batteries of an energy storage battery stack.

[0023] Figure 12Schematic diagram of another example of a system for determining the health state of one or more batteries of an energy storage battery stack.

[0024] Figure 13 Schematic diagram of another example of a system for determining the health state of one or more batteries of an energy storage battery stack.

[0025] Figure 14 Schematic diagram of another example of a system for determining the health state of one or more batteries of an energy storage battery stack. Detailed implementation

[0026] It is very important to measure the state of charge (SOC) of the battery cells in a battery pack. The SOC is defined as the available capacity (in Ah) and expressed as a percentage of its rated capacity. The SOC parameter can be regarded as a thermodynamic quantity that enables people to evaluate the potential energy of the battery. As energy is drawn from the battery, the SOC parameter of the battery decreases over time.

[0027] In addition or alternatively, it may be desirable to estimate the state of health (SOH) of the battery, which represents a measure of the battery's ability to store and deliver electrical energy compared to a new battery. A decrease in the battery SOH causes the battery to discharge faster. The internal impedance of the battery is an example of a battery characteristic that corresponds well to its SOH and can be measured regularly to monitor the battery.

[0028] In some examples, a low-frequency AC excitation signal can be applied to the battery cells of the battery to measure its complex impedance. The test system can attempt to measure a small AC battery response signal on top of the large DC voltage of the battery.

[0029] In some embodiments, the test system can use a passive RC high-pass filter to block the DC voltage. Then, the low-frequency AC excitation signal can be amplified and converted into a digital code by an analog-to-digital converter (ADC) circuit. Unfortunately, the passive RC high-pass filter may include a large, bulky, external DC-blocking capacitor. When there are many battery cells, the area of the external DC-blocking capacitor may be large. In addition, the high-pass filter causes additional phase shift.

[0030] To address one or more of the above problems, the present disclosure describes various techniques for determining the health state of a battery that utilize a capacitor gain amplifier to provide AC gain and block DC voltage. An input capacitance can be coupled between the input excitation signal generator circuit and the inverting input terminal of the amplifier, and a feedback capacitance can be coupled between the inverting input terminal of the amplifier and the amplifier output terminal. A switch can be used to periodically reset the feedback capacitor to prevent the output of the amplifier from saturating due to the leakage current at the inverting input terminal of the amplifier.

[0031] The techniques of the present disclosure can offer several advantages. For example, no external DC-blocking capacitor is required. Instead, these techniques can provide AC coupling inside the chip, thus forming an embedded solution. In addition, since there is no high-pass RC filter, there is no phase shift when using the techniques of the present invention.

[0032] Figure 1 FIG. 4 is a schematic diagram of an example of a system 100 for determining the health state of an energy storage device. In some examples, the energy storage device may include one or more electrochemical fuel cells. In other examples, the energy storage device may be a battery 102 including one or more battery cells 104. Although the present disclosure specifically refers to the energy storage device as a "battery 102" having "battery cells 104" hereinafter, it should be understood that the battery 102 can generally be an energy storage device that may include one or more battery cells, one or more fuel cells, or one or more devices available for electrolysis.

[0033] The battery 102 may include one or more battery cells 104, such as lithium-ion (Li) battery cells, and in a non-limiting example has an internal impedance Z such as 30 milliohms. The battery 102 may be coupled to a load 106. The excitation signal generator circuit 108 can generate an excitation signal, such as an AC current, and apply it to the battery cells 104 of the battery 102. In one non-limiting example, the excitation signal may be 100 mA and have a frequency between approximately 0.1 hertz (Hz) and approximately 1 kHz.

[0034] The system 100 may include a capacitive gain amplifier circuit coupled to the excitation signal generator circuit 108, generally shown as 110. In some examples, the excitation signal generator circuit 108 can generate a sine tone as a form of excitation. The capacitive gain amplifier circuit may include an amplifier circuit 112, an input capacitor 114 coupled between the excitation signal generator circuit 108 and the inverting input terminal of the amplifier circuit 112, and a feedback capacitor 116 coupled between the inverting input terminal of the amplifier circuit 112 and the output terminal of the amplifier circuit 112. The system 100 is a single-ended configuration and the non-inverting terminal of the amplifier circuit 112 is coupled to ground.

[0035] Compared with using a resistor stage, the use of the resetable capacitive gain amplifier circuit 110 can advantageously block DC and only allow AC signals to pass through. In addition, the self-restoring capacitive gain amplifier circuit 110 can operate well at higher frequencies because the time for any DC leakage current to affect the output signal is shorter.

[0036] The control circuit 118 can output a control signal to control the operation of a switching element 120 (e.g., a transistor) that can be coupled to the inverting input of the amplifier circuit 112, which can periodically reset the feedback capacitor 116 to control the DC bias voltage, e.g., by preventing the output of the amplifier from saturating due to DC leakage current at the inverting input terminal of the amplifier circuit 112. The DC leakage current at the inverting input terminal of the amplifier circuit 112 can cause a ramp on top of the amplified battery response signal, which makes it difficult to detect the sinusoidal tone of the excitation signal from the output signal of the amplifier circuit 112.

[0037] The input voltage applied to the capacitive gain amplifier circuit 110 is the AC response signal of the battery 102. Once the switching element 120 is turned off, the output signal Vamp_out of the capacitive gain amplifier circuit 110, which is an amplified version of the AC response signal of the battery 102, can follow the input voltage, having a certain amount of gain determined by the ratio of the input capacitor 114 to the feedback capacitor 116.

[0038] The system 100 may further include a backend circuit 122 to use the output signal Vamp_out of the capacitive gain amplifier circuit 110 to determine battery characteristics representative of the state of health of the battery. In some examples, the characteristics of the battery 102 may include the impedance of the battery, e.g., the complex impedance of the battery 102.

[0039] In Figure 1 the example shown, the backend circuit 122 may include an anti-aliasing filter 124, an ADC circuit 126, and a single-point discrete Fourier transform (DFT) filter 128. The single-point DFT filter 128 can process the output of the ADC circuit 126 to determine the amplitude and phase of the excitation signal from the excitation signal generator circuit 108 at the excitation frequency, which is present in the output signal Vam pout. The single-point DFT filter 128 can multiply the received signal by the excitation (and its quadrature component) over an integer number of cycles. The resulting in-phase and quadrature components can be combined to generate the phase and amplitude of the received signal. Detecting the presence of a single sinusoidal tone may also be referred to as synchronous detection or synchronous demodulation.

[0040] The backend circuit 122 may further include a processor 130, which can receive the output of the single-point DFT filter 128. Using the known excitation signal generated by the excitation signal generator circuit 108 and the measured response signal Vamp_out of the capacitive gain amplifier circuit 110, the processor 130 can process the output signal of the first capacitive gain amplifier circuit to determine battery characteristics representative of the state of health of the battery 102, e.g., the impedance of the battery 102.

[0041] In some examples, it may be necessary to use excitations at different frequencies to determine battery characteristics representative of the health state of battery 102, such as the impedance of battery 102. For example, control circuit 118 may control excitation signal generator circuit 108 to output a current having a first frequency, and processor 130 may determine the battery's response to the first frequency. Similarly, control circuit 118 may control excitation signal generator circuit 108 to output currents having second, third, and fourth frequencies (or more), and processor 130 may determine the battery's responses to these frequencies. In this way, multiple characteristics (such as impedance) of battery 102 can be determined as a function of frequency.

[0042] Figure 1 The system example shown in includes a single channel. In some implementations, it may be necessary to use two (or more) channels. For example, using two channels in a ping-pong operation can overcome DC current leakage at the virtual ground of the amplifier circuit, thereby supporting very low frequency implementations, such as approximately 10 Hz or less, as described below with respect to Figure 2 shown and described.

[0043] Figure 2 is a schematic diagram of another example of system 200 for determining the health state of battery 102. System 200 is a two-channel implementation. Figure 2 The system includes some components similar to those Figure 1 shown, with the same numbers used for similar components and different letter suffixes representing different instances of similar components.

[0044] As described above with respect to Figure 1 The switching element 120 may periodically reset the feedback capacitor 116 to control the DC bias voltage. However, in some embodiments, resetting the feedback capacitor 116 has a negative impact on the AC battery response signal. To address this issue, the inventors have recognized that in a ping-pong operation, when the switching element of the first channel is reset, the second channel can be used to observe the AC battery response signal, and vice versa. As described below, the derivative information of the AC battery response signal can be saved by both channels and can be extracted through digital post-processing using backend circuitry.

[0045] System 200 may include a first channel, generally designated as 202A, which may include a first capacitive gain amplifier circuit coupled to excitation signal generator circuit 108, generally designated as 110A. The first capacitive gain amplifier circuit may include amplifier circuit 112A, an input capacitor 114A coupled between the excitation signal generator circuit 108 and the inverting input of amplifier circuit 112A, and a feedback capacitor 116A coupled between the inverting input of amplifier circuit 112A and the output of amplifier circuit 112A. The first channel 202A may generate a first output signal d1.

[0046] System 200 may also include a second channel, generally designated as 202B, which may include a second capacitive gain amplifier circuit coupled to signal generator circuit 108, generally designated as 110B. The second capacitive gain amplifier circuit may include amplifier circuit 112B, an input capacitor 114B coupled between the excitation signal generating circuit 108 and the inverting input of amplifier circuit 112B, and a feedback capacitor 116B coupled between the inverting input of amplifier circuit 112B and the output of amplifier circuit 112B. The second channel 202B may generate a second output signal d2.

[0047] During a ping operation of the first channel 202A, control circuit 118 may output a signal to control the operation of a switching element 120A that may be coupled to the inverting input of amplifier circuit 112A, which may periodically reset the feedback capacitor 116A in the first channel 202A to control the DC bias voltage at the inverting input of amplifier circuit 112A. Similarly, during a pong operation of the second channel 202B, control circuit 118 may output a signal to control the operation of a switching element 120B that may be coupled to the inverting input of amplifier circuit 112B, which may periodically reset the feedback capacitor 116B in the second channel 202B to control the DC bias voltage at the inverting input of amplifier circuit 112B.

[0048] In some examples, the excitation signal is an AC signal having a first frequency, wherein control circuit 118 is configured to control the operation of the first switching element 120A and the second switching element 120B at a second frequency, and wherein the second frequency is greater than the first frequency or wherein the second frequency is less than the first frequency. In some examples, the first frequency and the second frequency may be equal.

[0049] In some examples, the measurement may be a single frequency data point or a measurement over a certain number of excitation periods. Subsequently, further measurements may be made, e.g., each measurement at another excitation frequency. For example, the change in frequency may be a step change in frequency.

[0050] System 200 may also include backend circuitry 222 to determine battery characteristics representative of the state of health of the battery using the output signals of the capacitive gain amplifier circuits 110A, 110B. In some examples, the characteristics of the battery 102 may include the impedance of the battery, such as the complex impedance of the battery 102.

[0051] In Figure 2 In the example shown, the backend circuitry 222 may include components of both the first channel 202A and the second channel 202B, namely the anti-aliasing filters 124A, 124B and the ADCs 126A, 126B, as well as components shared by the first channel 202A and the second channel 202B, namely the waveform reconstruction circuit 204, the single-point DFT filter 128, and the processor 130.

[0052] The ADCs 126A, 126B output digital signals d1, d2, which are periodic offsets or periodic reset versions of the representation of the AC battery response signal of the battery 102. The waveform reconstruction circuit 204 may receive the outputs d1, d2 of the ADCs 126A, 126B respectively, and reconstruct the digital representation of the AC battery response signal, as described in more detail below with respect to Figure 3 The waveform reconstruction circuit 204 may monitor the rate of change in the two channels 202A, 202B and use the rate of change information to reconstruct the AC response signal of the battery 102.

[0053] The digital representation of the reconstructed AC battery response signal determined by the waveform reconstruction circuit 204 may be applied to the single-point DFT filter 128. The single-point DFT filter 128 may detect the presence of a single sine tone in the output of the digital representation of the reconstructed AC battery response signal to determine whether there is a frequency of the excitation signal from the excitation signal generator circuit 108 and to quantify its phase and amplitude.

[0054] The backend circuitry may also include a processor 130, which may receive the output of the single-point DFT filter 128. In some examples, the waveform reconstruction circuit 204 and the single-point DFT filter 128 are part of the processor 130. In some examples, the processor 130 is a field programmable gate array (FPGA). Thus, the processor 130 may receive a first representation of the first output signal, such as the first representation d1, and a second representation of the second output signal, such as the second representation d2. Using the first representation and the second representation, the processor 130 may determine a representation of the battery response signal in response to the excitation signal, such as the derivative described below with respect to Figure 3 and determine the characteristics of the battery, such as the impedance of the battery 102, using the representation of the battery response signal and the excitation signal.

[0055] Using the known excitation signal generated by the excitation signal generator circuit 108 and the measured battery response signals Vamp_out1 of the capacitive gain amplifier circuit 110A and Vamp_out2 of the capacitive gain amplifier circuit 110B, the processor 130 can process the output signals of the first capacitive gain amplifier circuit and the second capacitive gain amplifier circuit to determine battery characteristics representative of the health state of the battery 102, such as the impedance of the battery 102.

[0056] In some examples, it may be necessary to use excitations at different frequencies to determine battery characteristics representative of the health state of the battery 102, such as the impedance of the battery 102. For example, the control circuit 118 can control the excitation signal generator circuit 108 to output a current having a first frequency, and the processor 130 can determine the battery's response to the first frequency. Similarly, the control circuit 118 can control the excitation signal generator circuit 108 to output currents having second, third, and fourth frequencies, and the processor 130 can determine the battery's responses to these frequencies. In this way, multiple characteristics of the battery (such as impedance) can be determined as a function of frequency.

[0057] For a dual-channel implementation, such as Figure 2 the system 200, in some examples, the control circuit 118 can use a fixed ping-pong rate, i.e., the channel selection rate, and vary the frequency of the excitation signal. In other examples, the control circuit 118 can use a ping-pong that varies and also varies the frequency of the excitation signal.

[0058] Figure 3 is a diagram illustrating an example of a timing diagram 300 that shows the relationship between the timing of the switches and channels and the corresponding output signals d1, d2 of the ADCs 126A, 126B. Figure 3 Depicts the timing of the channel selection signal 302 (select_ch), which is Figure 2 the rate at which the control circuit 118 of Figure 3 performs ping-pong, for example, between the first and second channels 202A, 202B. Figure 2 Also depicts the two switch signals 304, 306 that control the Figure 3 switching elements 120A, 120B. Also depicts the timing of the output signals d1(n) 308, d2(n) 310 of the ADCs 126A, 126B, respectively. The output signals d1(n), d2(n) are periodic offset or periodic reset versions of the AC battery response signals of the battery presented at the input terminals of the first capacitive gain amplifier circuit 110A and the second capacitive gain amplifier circuit 110B, respectively.

[0059] Each output signal d1(n), d2(n) is represented by a dot. When using an ADC sampling rate that is relatively high compared to the excitation frequency, the difference between adjacent dots can approximate the derivative of the AC battery response signal. Since it is established from the corresponding reset signal (such as signal ), Figure 2 's waveform reconstruction circuit 204 does not use some dots. However, because Figure 2 's control circuit 118 switches back and forth between the first and second channels 202A, 202B, derivative information can always be obtained. For example, even if the information in signal d2(n) cannot be used when signal goes high, the information in signal d1(n) is available at the same time. This is shown graphically at 312. Similarly, even if the information in signal d1(n) cannot be used when signal goes high, the information in signal d2(n) is also available.

[0060] Figure 2 's waveform reconstruction circuit 204 can reconstruct the waveform of the AC battery response signal of the battery according to the differential information. For example, Figure 2 's waveform reconstruction circuit 204 can include an integrator circuit, such as Figure 4 's integrator circuit 204, to continuously accumulate the differences with one or other channels in front of it. In this way, Figure 2 's waveform reconstruction circuit 204 integrates the difference signal to reconstruct the AC battery response signal.

[0061] Figure 4 are examples of waveform reconstruction circuits that can be used to reconstruct the waveform of the AC battery response signal of the battery. The waveform reconstruction circuit 400 can be Figure 2 's waveform reconstruction circuit 204 example.

[0062] The waveform reconstruction circuit 400 can receive a first digitized output signal d1(n), such as the output of ADC 126A of the first channel 202A of Figure 2 , and a second digitized output signal d2(n), such as Figure 2 's output of ADC126B of the second channel 202B. The first digitized output signal d1(n) is added to the adder block 402A, and using the delay element 404A, a delayed version d1(n - 1) of the first digitized output signal is subtracted from the adder block 402A to obtain d1(n) - d1(n - 1), which is the difference between two consecutive points in the output signal d1. The first digitized output signal difference is applied to the first input terminal of the multiplexer 406. Therefore, the first input terminal of the multiplexer 406 can receive the first representation of the first output signal d1.

[0063] Similarly, the second digitized output signal d2(n) is added to adder block 402B, and using delay element 404B, a delayed version d2(n-1) of the second digitized output signal is subtracted from adder block 402B to obtain d2(n)-d2(n-1), which is the difference between two consecutive points in the output signal d2. The second digitized output signal difference is applied to the second input of multiplexer 406. Thus, the second input of multiplexer 406 can receive a second representation of the second output signal d2.

[0064] A control circuit, such as Figure 2 control circuit 118, can output a channel selection signal (select_ch) to multiplexer 406 to select one of the two inputs of the multiplexer. The output of multiplexer 406 can be applied to adder block 408. Second delay element 410 can be coupled to adder block 408 and the output of second delay element 410 can be fed back to adder block 408, thereby forming an integrator and generating output d(n), which is a representation of the AC battery response signal reconstructed from signals d1, d2 of the battery.

[0065] Figure 5 is a schematic diagram of another example of a system 500 for determining the health state of battery 102. System 500 is another two-channel ping-pong implementation. Similar to Figure 2 system 200, system 500 includes a shared ADC. Figure 5 System 500 of Figure 1 and Figure 3 includes some components similar to those shown in

[0066] Similar to Figure 2 two-channel system 200, two-channel system 500 includes an ADC 126 shared by two channels 502A, 502B. To share ADC 126, each channel 502A, 502B can include corresponding sample and hold (S / H) circuits 504A, 504B. S / H circuits 504A, 504B can hold samples of the corresponding representations of the AC response signal of battery 102 until ADC126 needs these samples. Switching elements 506A, 506B (after the corresponding S / H circuits 504A, 504B) can each receive a channel selection signal from control circuit 118.

[0067] In some examples, it may be necessary to disable one of the two channels, such as in Figure 2 system 200 or Figure 5In system 500. For example, when the frequency of the excitation signal is high enough, such as higher than about 10 Hz, the DC leakage current problem may no longer be an issue. Therefore, it may not be necessary to perform a ping-pong operation between the two channels. Using a system capable of performing a ping-pong operation, such as Figure 2 system 200 or Figure 5 system 500, the control circuit can disable one of the two channels based on the frequency of the AC excitation signal, for example, by holding the channel selection signal at a constant logic level, thereby enabling only one of the two channels and disabling the other channel.

[0068] Figure 6 is a diagram showing an example of using a channel selection signal that changes phase with respect to the excitation signal to determine battery characteristics representing the battery health state. The excitation signal generator circuit, such as Figure 2 excitation signal generator circuit 108, can generate an excitation signal 600, which is shown together with the channel selection signal 602 (select_ch). After an initial stabilization period, the first measurement 604 can start at a 0-degree phase. After a period of time, the phase of the channel selection signal 602 can change between the first measurement 604 and the second measurement 606, while the phase of the excitation signal 600 remains unchanged. In other words, the phase of the second measurement 606 is opposite to the phase of the first measurement 604.

[0069] Any DC leakage current will cause the rising slope of the battery AC response signal. Here, by performing two measurements at opposite phases, subtracting the results, and then taking the average, the DC leakage current error can be eliminated. In some examples, the SNR measurement result can be improved by 3 dB.

[0070] Figure 7 is a diagram showing an example of using an excitation signal with a changing phase to determine battery characteristics representing the battery health state. In , after an initial stabilization period 700, the first measurement 702 can be determined by the processor, such as Figure 7 processor 130. After the first measurement 702 and before the second setup time 704, the excitation signal generator circuit, such as Figure 1 excitation signal generator circuit 108, can change the phase of the excitation signal 706, as shown at 708, such that the excitation signal 706 is 180 degrees different from its previous phase. After the second stabilization time 704, the processor can determine the second measurement 710. The data corresponding to each measurement can be determined after the initial stabilization corresponding to that measurement.

[0071] In some examples, the gain between pings can cause aliasing of the ping frequency (channel selection frequency). Therefore, gain calibration may be needed to reduce this type of aliasing. For example, the control circuit can cause the excitation signal generator circuit to generate a square wave at half of the ping frequency. Then, the processor can determine the amplitude of the square wave in each channel to derive the gain mismatch. Then, the processor can apply gain correction to the data using this gain mismatch information.

[0072] Filter bandwidth mismatch can cause a similar problem. Filter bandwidth mismatch can be solved by oversampling and applying well-controlled digital filtering after the ADC and before signal reconstruction.

[0073] Although the above system is a single-ended system, the techniques of the present disclosure are not limited to single-ended systems. As Figure 1 shown, these techniques are also applicable to differential systems.

[0074] Figure 8 is a schematic diagram of another example of a system 800 for determining the health state of a battery 102. The system 800 is Figure 8 a differential version of the single-ended system 100. The capacitive gain amplifier circuit 810 includes an amplifier circuit 812 having differential output terminals to generate an output voltage Vout. The amplifier circuit 812 may also include a common-mode input terminal to receive a common-mode voltage Vcm.

[0075] The inverting input of the differential system 800 is coupled to the components in a manner similar to Figure 1 the single-ended system 100, and for the sake of brevity, will not be described again. Instead of coupling the non-inverting input to ground, as in Figure 1 the single-ended system 100, the non-inverting input of the differential system 800 can be coupled to the capacitive gain amplifier circuit like the inverting input. The capacitive gain amplifier circuit 810 also includes an input capacitor 114B coupled between the excitation signal generator circuit 108 and the in-phase input terminal of the amplifier circuit 812, and a feedback capacitor 116B coupled between the non-inverting input terminal of the amplifier circuit 812 and the output terminal of the amplifier circuit 812. The in-phase input terminal of the amplifier circuit 812 is coupled to a switching element 120B that can periodically reset the feedback capacitor 116B to control the DC bias voltage at the in-phase input terminal of the amplifier circuit 812.

[0076] Although Figure 1 and 5 the two-channel implementations shown in are described in a single-ended configuration, in some examples, Figure 2 and 5 each channel of the systems 200, 500 can be in a differential configuration, as Figure 2 shown.

[0077] Figure 8 FIG. 1 is a schematic diagram of another example of a system 900 for determining the health state of a battery 102. The system 900 is a single-ended configuration using a capacitive gain amplifier circuit 910 and is another example of a reset circuit that can be used to periodically reset a feedback capacitor 116 to prevent the output of the amplifier circuit 912 from saturating due to leakage current at the negative input of the amplifier. The system 900 may include three switching elements 120A - 120C controlled by control signals and The control circuit 118 may output a control signal to open (or close) the switching elements 120A, 120B, while the control circuit 118 outputs a complementary control signal to close (or open) the switching element 120C.

[0078] Closing the switching element 120A using the control signal couples the summing node 914 to the first voltage V1. The summing node 914 is the node between the input capacitor 114, the feedback capacitor 116, and the inverting terminal of the amplifier circuit 912. Closing the switching element 120B using the control signal while the switching element 120C is open couples the terminals of the feedback capacitor 116 to the second voltage V2. Figure 9 The switching element configuration shown in FIG. 1 can reset the input of the amplifier circuit 912 to a voltage level different from the output to accommodate the operating range of the amplifier circuit 912.

[0079] Figure 9 FIG. 2 is a block diagram of an example of a system 1000 that can implement various techniques of the present disclosure to determine the health state of a battery 102. The system 1000 can be used to implement the systems 100, 200, 500, 800, or 900 described above.

[0080] The system 1000 may include a processor 1002, such as an FPGA, which can implement various functions, including a waveform generator 1004 and a timing generator 1006. The waveform generator 1004 can generate signals applied to a current-mode digital-to-analog converter (IDAC) 1010 using a look-up table 1008 (or some other data structure stored in a memory), thereby forming an example of an excitation signal generator circuit.

[0081] The timing generator can also generate and apply signals, such as gain setting signals and reset pulses, to the capacitive gain amplifier circuit, represented by the analog front end (AFE) circuit 1012. The timing generator can also generate and apply signals (e.g., conversion start, sdata, sclk) to the ADC 126 to control the conversion. The timing generator can also generate signals and apply them to the programmable decimator 1014, which can reduce quantization noise. The output of the programmable decimator 1014 can then be applied to the FIFO register 1016, and the FIFO register 1016 can output the data to the computer 1018.

[0082] Although many of the above systems are regarding a single energy storage battery, such as a battery pack cell or a fuel cell, the techniques of the present disclosure are not limited to use with a single energy storage battery, such as a battery pack cell or a fuel cell. Instead, the techniques can be used with an energy storage battery pack, such as a battery pack battery pack or a fuel cell stack, as Figure 10 shown.

[0083] Figures 11 - 14 is a schematic diagram of another example of a system for determining the health state of one or more cells of an energy storage battery stack. The energy storage device 1100 can include a stack of two or more energy storage cells coupled in series, as Figure 11 shown by cells 1102A - 1102E. The energy storage device 1100 can be coupled to the load 106.

[0084] The excitation signal generator circuit 108 can generate an excitation signal, such as an AC current, and apply it to the energy storage device 1100. In one non - limiting example, the excitation signal can be 100 mA and have a frequency between approximately 0.1 Hertz (Hz) and approximately 1 kHz. In Figure 11 the example shown, all cells 1102A - 1102E of the energy storage device 1100 see the same current injected by the excitation signal generator circuit 108, which is common to all cells 1102A - 1102E.

[0085] The system 800 can be used to monitor the health of individual cells of the energy storage device 1100, similar to the differential system 800 described above with respect to Figure 11 . Other systems described above can also be used. By monitoring the voltage across an individual cell (e.g., cell 1102B) of the energy storage device 1100 for a given current from the excitation signal generator circuit 108, the system 800 can measure the impedance of the individual cell.

[0086] In some examples, there may be a system 800 associated with each of the units in units 1102A - 1102E. For example, for an energy storage device 1100 having units 1102A - 1102E, each unit may be associated with a corresponding system 800. In other examples, a multiplexer may couple a single system 800 to multiple units 1102A - 1102E.

[0087] Figure 8 is a schematic diagram of another example of a system for determining the health state of one or more cells of an energy storage battery stack. The energy storage device 1200 may include a stack of two or more energy storage cells coupled in series, as shown by the cells 1202A - 1202E in Figure 12 . The energy storage device 1200 may be coupled to a load 106.

[0088] The excitation signal generator circuit 108 may generate an excitation signal, such as an alternating current, and apply it to the energy storage device 1200. In one non - limiting example, the excitation signal may be 100 mA and have a frequency between approximately 0.1 Hertz (Hz) and approximately 1 kHz. In Figure 12 the example shown, all of the cells 1202A - 1202E of the energy storage device 1200 see the same current injected by the excitation signal generator circuit 108, which is common to all of the cells 1202A - 1202E.

[0089] The system 800 can be used to monitor the health of the entire energy storage battery stack of the energy storage device 1200, such as the differential system 800 described above with respect to Figure 12 . Other systems described above can also be used. By monitoring the voltages across all of the cells 1202A - 1202E of the energy storage device 1100 for a given current from the excitation signal generator circuit 108, the system 800 can measure the impedance of the entire battery stack.

[0090] Figure 8 is a schematic diagram of another example of a system for determining the health state of one or more cells of an energy storage battery stack. The energy storage device 1300 may include a stack of two or more energy storage cells coupled in series, as shown by the cells 1302A - 1302E in Figure 13 . The energy storage device 1300 may be coupled to a load 106.

[0091] The excitation signal generator circuit 108 may generate an excitation signal, such as an AC current, and apply it to the energy storage device 1300. In one non - limiting example, the excitation signal may be 100 mA and have a frequency between approximately 0.1 Hertz (Hz) and approximately 1 kHz. As with Figure 13 and12 differs from the common current excitation used in Figure 11 In the example shown, the excitation signal generator circuit 108 can apply an excitation signal to each of the cells 1302A - 1302E of the energy storage device 1300.

[0092] The system 800 can be used to monitor the health of individual cells of the energy storage device 1300, similar to the differential system 800 described above with respect to Figure 13 By monitoring the voltage across an individual cell (e.g., cell 1302B) of the energy storage device 1300 for a given current from the excitation signal generator circuit 108, the system 800 can measure the impedance of the individual cell.

[0093] In some examples, there can be a system 800 associated with each of the cells 1302A - 1302E. For example, for an energy storage device 1300 having cells 1302A - 1302E, each cell can be associated with a corresponding system 800. In other examples, a multiplexer can couple a single system 800 to multiple cells 1302A - 1302E.

[0094] Figure 8 is a schematic diagram of another example of a system for determining the health state of one or more cells of an energy storage battery stack. Figure 14 An electrolyzer 1500 is depicted, for example, for manufacturing hydrogen. The electrolyzer 1500 can include a DC current source 1502, which can inject a large current (e.g., 100 A) into the energy storage device 1504. The energy storage device 1504 can include a stack of two or more energy storage batteries, shown as Figure 14 the cells 1506A - 1506E in

[0095] The excitation signal generator circuit 108 can generate an excitation signal, such as an AC current, and apply it to the energy storage device 1504. In one non - limiting example, the excitation signal can be 100 mA and have a frequency between approximately 0.1 Hertz (Hz) and approximately 1 kHz. Different from Figure 14 and 12 the common current excitation used in Figure 11 In the example shown, the excitation signal generator circuit 108 can apply an excitation signal to each of the cells 1506A - 1506E of the energy storage device 1504.

[0096] The system 800 can be used to monitor the health of individual cells of the energy storage device 1504, similar to the differential system 800 described above with respect to Figure 14 described. Other systems described above can also be used. By monitoring the voltage across an individual cell (e.g., cell 1506B) of the energy storage device 1504 for a given current from the excitation signal generator circuit 108, the system 800 can measure the impedance of the individual cell.

[0097] In some examples, there can be a system 800 associated with each of the cells 1506A - 1506E. For example, for an energy storage device 1504 having cells 1506A - 1506E, each cell can be associated with a corresponding system 800. In other examples, a multiplexer can couple a single system 800 to multiple cells 1506A - 1506E.

[0098] Figure 8 Individual cell excitation is depicted. However, common excitation can alternatively be implemented (as in Figure 14 ).

[0099] It should be noted that Figure 12 can be modified to include a second amplifier circuit for separating the ping - pong phases, as Figures 11 - 14 shown.

[0100] The various techniques described above can use a capacitor gain amplifier to determine the health state of the battery to provide AC gain and block DC voltage. A switch can be used to periodically reset the feedback capacitor to prevent the output of the amplifier from saturating due to leakage current at the negative input of the amplifier. Advantageously, these techniques can eliminate the need for an external DC - blocking capacitor, thus allowing an embedded solution. Additionally, since there is no high - pass RC filter, there is no phase shift when using the techniques of the present invention.

[0101] Figure 2 Various Annotations

[0102] Each non - restrictive aspect or example described herein can exist independently, or can be combined in various permutations or combinations with one or more other examples.

[0103] The foregoing detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings illustrate, by way of example, specific embodiments in which the invention may be practiced. These embodiments are also referred to herein as "examples." Such examples may include elements in addition to those shown or described. However, the inventors also contemplate examples that include only those elements shown or described. In addition, the inventors also contemplate examples using any combination or arrangement (or one or more aspects thereof) of those elements shown or described, or with respect to a particular example (or one or more aspects thereof), or with respect to other examples shown or described herein (or one or more aspects thereof).

[0104] If there is any inconsistency in the usage between this document and any document incorporated by reference, the usage in this document shall prevail.

[0105] In this document, the terms "a" or "some" are common in patent documents and are used to include one or more, independent of any other instance or usage of "at least one" or "one or more." In this document, unless otherwise specified, the term "or" is used to refer to a non-exclusive or, e.g., "A or B" includes "A but not B," "B but not A," and "A and B." In this document, the terms "comprising" and "wherein" are used as simple equivalents of the corresponding terms "including" and "wherein." Further, in the following aspects, the terms "comprising" and "including" are open-ended, i.e., a system, apparatus, article, composition, formulation, or process that includes elements in addition to those listed after such terms in one aspect is still considered to be within the scope of that aspect. And, in the following aspects, the words "first," "second," "third," etc. are used only as labels and do not impose a numerical requirement on their objects.

[0106] The method examples described herein may be at least partially machine or computer-implemented. Some examples may include a computer-readable medium or machine-readable medium encoded with instructions that are operable to configure an electronic device to perform the methods as described in the above examples. Implementations of such methods may include code, such as microcode, assembly language code, high-level language code, etc. Such code may include computer-readable instructions for performing various methods. The code may form part of a computer program product. Further, in one example, the code may be tangibly stored on one or more volatile, non-transitory, or non-volatile tangible computer-readable media, e.g., during execution or at other times. Examples of such tangible computer-readable media may include, but are not limited to, hard disks, removable disks, removable optical disks (e.g., compact disks and digital video disks), magnetic tapes, memory cards or sticks, random access memory (RAM), read-only memory (ROM), etc.

[0107] The foregoing description is intended to be illustrative and not restrictive. For example, the above examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments may be used, such as by those of ordinary skill in the art upon reading the foregoing description. The Abstract is provided to comply with 37 C.F.R. § 1.72(b), allowing the reader to quickly ascertain the nature of the technical disclosure. It should be understood that it will not be used to interpret or limit the scope or meaning of the claims. Additionally, in the foregoing detailed description, various features may be combined together to simplify the disclosure. This should not be construed as intending that the disclosed features that are not claimed are essential to any embodiment. On the contrary, the subject matter of the present invention may lie in less than all of the features of a particular disclosed embodiment. Accordingly, the following aspects are hereby incorporated into the detailed description as examples or embodiments, each aspect standing on its own as a separate embodiment, and it is contemplated that these embodiments may be combined with each other in various combinations or permutations. The scope of the present invention should be determined with reference to the appended claims and the full scope of equivalents to which such claims are entitled.

Claims

1. A system for determining the health state of an energy storage device, the system comprising: A signal generator circuit configured to generate an excitation signal and apply the excitation signal to at least one cell of the energy storage device; A first capacitive gain amplifier circuit coupled to the signal generator circuit and configured to generate a first output signal in response to the excitation signal, the first capacitive gain amplifier circuit including a first inverting input terminal; A control circuit configured to control the operation of a first switching element coupled to the first inverting input terminal to control a DC bias voltage; And A backend circuit configured to use the first output signal of the first capacitive gain amplifier circuit to determine a characteristic of the energy storage device indicative of the health state of the energy storage device.

2. The system of claim 1, comprising: A first channel including the first capacitive gain amplifier circuit; And A second channel including a second capacitive gain amplifier circuit coupled to the signal generator circuit and configured to generate a second output signal in response to the excitation signal, the second capacitive gain amplifier circuit including a second inverting input terminal, Wherein the control circuit is configured to control the operation of a second switching element coupled to the second inverting input terminal to control a DC bias voltage on the second inverting input terminal, and Wherein the backend circuit is further configured to use the second output signal to determine the characteristic of the energy storage device.

3. The system of claim 2, wherein the backend circuit includes: A first filter circuit and a first analog-to-digital converter (ADC) circuit forming part of the first channel; And A second filter circuit and a second ADC circuit forming part of the second channel.

4. The system of claim 2, wherein the backend circuit includes: An analog-to-digital converter (ADC) circuit shared by the first channel and the second channel.

5. The system of claim 2, wherein the excitation signal is an AC signal having a first frequency, wherein the control circuit is configured to control the operation of the first switching element and the second switching element at a second frequency, and wherein the second frequency is greater than the first frequency.

6. The system of claim 2, wherein the backend circuit includes: A processor configured to: Receive a first representation of the first output signal and a second representation of the second output signal; Use the first representation and the second representation to determine a representation of an energy storage device response signal in response to the excitation signal; And Use the representation of the energy storage device response signal and the excitation signal to determine the characteristic of the energy storage device.

7. The system of claim 6, wherein the first representation of the first output signal is a derivative of the energy storage device response signal, and the second representation of the second output signal is a derivative of the energy storage device response signal.

8. The system of claim 2, wherein the signal generator circuit includes a waveform generator coupled to a current-mode digital-to-analog converter (IDAC) circuit, the waveform generator being configured to generate and apply an excitation signal having a first phase relative to the channel selection signal to produce a first energy storage device response signal, and the waveform generator being configured to generate and apply an excitation signal having a second phase relative to the channel selection signal to produce a second energy storage device response signal, the system comprising: a processor configured to average the first and second energy storage device response signals to reduce or eliminate leakage current errors.

9. The system of claim 8, wherein the excitation signal is an AC signal having a first frequency, wherein the channel selection signal has a second frequency, wherein the control circuit is configured to control the operation of the first switching element and the second switching element at the second frequency, and wherein the second frequency is greater than the first frequency.

10. The system of claim 1, wherein a characteristic of the energy storage device representing the health state of the energy storage device includes the impedance of the energy storage device.

11. The system of claim 1, wherein a backend circuit configured to use the first output signal of the first capacitive gain amplifier circuit is configured to determine the amplitude and phase at the frequency of the excitation signal in the first output signal.

12. A system for determining the health state of an energy storage device, the system comprising: a signal generator circuit configured to generate an excitation signal and apply the excitation signal to at least one cell of the energy storage device; a first channel including a first capacitive gain amplifier circuit, the first capacitive gain amplifier circuit being coupled to the signal generator circuit and configured to produce a first output signal in response to the excitation signal, the first capacitive gain amplifier circuit including a first inverting input terminal; a second channel including a second capacitive gain amplifier circuit, the second capacitive gain amplifier circuit being coupled to the signal generator circuit and configured to produce a second output signal in response to the excitation signal, the second capacitive gain amplifier circuit including a second inverting input terminal, a control circuit configured to control the operation of: a first switching element coupled to the first inverting input terminal to control a first DC bias voltage; and a second switching element coupled to the second inverting input terminal to control a second DC bias voltage on the second inverting input terminal; and a backend circuit configured to use the first output signal of the first capacitive gain amplifier circuit and the second output signal of the second capacitive gain amplifier circuit to determine a characteristic of the energy storage device representing the health state of the energy storage device.

13. The system of claim 12, wherein the excitation signal is an AC signal having a first frequency, wherein the control circuit is configured to control the operation of the first switching element and the second switching element at a second frequency, and wherein the second frequency is greater than the first frequency.

14. The system of claim 12, wherein the excitation signal is an AC signal having a frequency, and wherein the control circuit is configured to disable the operation of the first channel and enable the operation of the second channel based on the frequency of the AC signal.

15. The system of claim 12, wherein the signal generator circuit includes a waveform generator coupled to a current mode digital-to-analog converter (IDAC) circuit, the waveform generator for generating and applying an excitation signal having a first phase relative to a channel selection signal to produce a first energy storage device response signal, and the waveform generator for generating and applying an excitation signal having a second phase relative to the channel selection signal to produce a second energy storage device response signal, the system including: a processor configured to average the first and second energy storage device response signals to reduce or eliminate leakage current error.

16. The system of claim 12, wherein a characteristic of the energy storage device representing the health state of the energy storage device includes the impedance of the energy storage device.

17. A method of determining the health state of an energy storage device, the method comprising: generating and applying an excitation signal to at least one cell of the energy storage device; using a first capacitive gain amplifier circuit to produce a first output signal in response to the excitation signal, the first capacitive gain amplifier circuit including a first inverting input terminal; controlling the operation of a first switching element coupled to the first inverting input terminal to control a first DC bias voltage; and using the first output signal of the first capacitive gain amplifier circuit to determine a characteristic of the energy storage device representing the health state of the energy storage device.

18. The method of claim 17, wherein a characteristic of the energy storage device representing the health state of the energy storage device includes the impedance of the energy storage device.

19. The method of claim 17, wherein the first channel includes the first capacitive gain amplifier circuit, the method including: using a second capacitive gain amplifier circuit in a second channel to generate a second output signal in response to the excitation signal, the second capacitive gain amplifier circuit including a second inverting input terminal; and controlling the operation of a second switching element coupled to the second inverting input terminal to control a DC bias voltage on the second inverting input terminal, and wherein determining a characteristic of the energy storage device representing the health state of the energy storage device includes using the second output signal of the second capacitive gain amplifier circuit.

20. The method of claim 19, wherein the excitation signal is an AC signal having a first frequency, the method including: controlling the operation of the first switching element and the second switching element at a second frequency, and wherein the second frequency is greater than the first frequency.

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