DC signal measurement and battery formation / testing

Abstract

The invention relates to DC signal measurement and battery formation / testing. The present disclosure relates to accurately determining a DC energy signal, such as a DC current or a DC voltage, which may be particularly useful in controlling the formation / test current of a battery cell during formation and / or testing. In a battery formation / test environment, a current sensor is used to measure the current of a battery cell, which serves as a feedback signal to control the current to achieve a target current. The transfer function of the current sensor is used to improve the accuracy of current measurement. Since the transfer function can be determined periodically during formation / testing, a low cost current sensor with a relatively poor temperature coefficient can be used. Any change in current sensor gain can be detected and corrected by transfer function determination. Therefore, high current control precision can be realized with low cost.

Description

[0001] This application is a divisional application of the invention patent application with application date of September 28, 2021, application number 202111141464.0, and invention name “DC signal measurement and battery formation / testing”. Technical Field

[0002] The present disclosure relates to measuring DC current and, in particular aspects, to controlling battery current during battery formation and / or testing. Background Art

[0003] Battery formation is performed during the manufacturing process of batteries, such as lithium-ion (Li-Ion) batteries. Battery formation is the process of performing initial charge / discharge operations on a battery cell. During battery formation, a specific charging current and / or voltage is applied to the battery cell for a period of time, for example, a charging current of 0.1C (where C is the battery capacity) may be applied for a period of time. The battery can then be controlled to discharge at a specific discharge current for a further period of time to complete a full charge and discharge cycle, which may take up to about 20 hours. Battery cells can also be tested in a similar manner by applying a specific charging current and / or voltage to the battery for a period of time and then controlling the discharge current and / or voltage to a specific discharge curve for the battery to determine whether the battery meets specific charging and discharging requirements.

[0004] It may be beneficial to measure and control current and voltage to achieve a high level of accuracy during the formation and / or testing of a battery cell. For example, it may be necessary to maintain the current and voltage within ±0.05% of the target value. This is particularly true in cases where many battery cells will be used together and should therefore operate as similarly as possible, such as tens, hundreds, or thousands of battery cells together in an electric vehicle. Controlling the current and / or voltage with high accuracy typically requires very precise measurement of the voltage and / or current of the battery cell. However, the relatively high currents typically involved in formation / testing typically result in increased temperatures during formation / testing. Therefore, current and / or voltage sensors with a stable temperature coefficient (tempco) (e.g., 15ppm / °C) can typically be used. Summary of the invention

[0005] The present disclosure relates to accurately determining a DC energy signal, such as a DC current or a DC voltage, which can be particularly useful in controlling the formation / test current of a battery cell during formation and / or testing. In a battery formation / testing environment, a current sensor is used to measure the current of a battery cell, which is used as a feedback signal to control the current to achieve a target current. The transfer function of the current sensor is used to improve the accuracy of the current measurement. Since the transfer function can be determined regularly during formation / testing, low-cost current sensors with relatively poor temperature coefficients can be used. Any changes in the current sensor gain can be detected and corrected by the transfer function determination. Therefore, high current control accuracy can be achieved at a lower cost.

[0006] In a first aspect of the present disclosure, a battery formation / test controller is provided for controlling a formation / test current of a battery cell and coupled to a current sensor, the current sensor being arranged to output a measurement value of a current flowing through the battery cell, the battery formation / test controller being configured to: determine a current feedback measurement indicative of the formation / test current of the battery cell, wherein the determination of the current feedback measurement is based on a transfer function of the current sensor and a measurement of the battery cell current; and control the formation / test current applied to the battery cell based on a target formation / test current and the determined current feedback measurement.

[0007] The battery formation / test controller may also be configured to determine a transfer function of the current sensor.

[0008] The current sensor may include an analog-to-digital converter ADC having a non-linear input range for the input signal, wherein the analog input signal is non-linearly converted into a digital output signal, and the battery formation / test controller is also configured to: compare the measured value of the battery cell current with the non-linear input range; and if the measured value of the battery cell current exceeds the non-linear input range: determine the transfer function of the current sensor.

[0009] The battery formation / test controller may also be configured to determine the transfer function of the current sensor by: applying a reference input signal to the current sensor so that a current feedback measurement includes a formation / test current signal and a reference output signal corresponding to the reference input signal; extracting a reference output signal from the current feedback measurement; and determining a transfer function based on the reference input signal and the reference output signal.

[0010] The current sensor may include an analog-to-digital converter (ADC), and the battery formation / test controller may be further configured to: apply jitter to the reference input signal. Applying jitter to the reference input signal may include at least one of: converting the reference input signal between at least two signal levels; modulating the amplitude of the reference input signal.

[0011] The battery formation / test controller may be further configured to read the transfer function of the current sensor from the memory.

[0012] The battery formation / test controller may also be configured to: determine a further transfer function of the current sensor; determine a further current feedback measurement based on the further transfer function and a further measurement of the battery current output by the current sensor; and control the formation / test current of the battery cell based on the target formation / test current and the determined further current feedback measurement.

[0013] The battery formation / test controller may also be configured to store further transfer functions in memory for use in determining future current feedback measurements.

[0014] The battery formation / test controller may also be configured to control the formation / test current of the battery cell by controlling the operation of one or more transistors configured to control the magnitude of the formation / test current.

[0015] The forming / testing current may be a charging current applied to the battery cell or a discharging current output from the battery cell.

[0016] The battery formation / test controller may also be configured to: determine a voltage feedback measurement indicative of a formation / test voltage across the battery cell, wherein the voltage feedback measurement is determined based on a transfer function of a voltage sensor coupled across the battery cell and a measurement of the voltage across the battery cell from the voltage sensor; and control the formation / test voltage across the battery cell based on a target formation / test voltage and the determined voltage feedback measurement.

[0017] In a second aspect of the present disclosure, a battery forming / testing system is provided, comprising: an analog-to-digital converter ADC for coupling to a current sensor arranged to generate an analog signal indicative of a current flowing through a battery cell; and a battery forming / testing controller coupled to a digital output of the ADC and configured to: determine a current feedback measurement indicative of a forming / testing current of the battery cell, wherein the determination of the current feedback measurement is based on a transfer function of the current sensor and the digital output of the ADC; and control the forming / testing current of the battery cell based on a target forming / testing current and the determined current feedback measurement. The current sensor may include a shunt resistor.

[0018] In a third aspect of the present disclosure, a method for controlling a forming / test current of a battery cell is provided, the method comprising: determining a current feedback measurement indicative of a forming / test current applied to the battery cell, wherein the determination of the current feedback measurement is based on a transfer function of a current sensor arranged to output a measurement value of a current flowing through the battery cell and a measurement value of a current flowing through the battery cell; and controlling the forming / test current of the battery cell based on a target forming / test current and the determined current feedback measurement.

[0019] The method may also include determining a transfer function of the current sensor.

[0020] The current sensor may include an analog-to-digital converter ADC having a nonlinear input range for an input signal, wherein the analog input signal is nonlinearly converted into a digital output signal, and the method may further include: comparing a measured current value flowing through the battery cell with the nonlinear input range; if the measured current value passing through the battery cell exceeds the nonlinear input range: determining a transfer function of the current sensor.

[0021] The method can also be configured to determine the transfer function of the current sensor by: applying a reference input signal to the current sensor so that the measurement of the current flowing through the battery cell includes forming / testing the current signal and a reference output signal corresponding to the reference input signal; extracting the reference output signal from the measurement of the current flowing through the unit battery; and determining the transfer function based on the reference input signal and the reference output signal.

[0022] The current sensor may include an analog-to-digital converter (ADC), and the method may further include applying dithering to the reference input signal.

[0023] In a fourth aspect of the present disclosure, a battery formation / test controller is provided for controlling a formation / test voltage of a battery cell and for coupling to a voltage sensor, which is arranged to output a measurement of the voltage across the battery cell, the battery formation / test controller being configured to: determine a voltage feedback measurement indicative of a formation / test voltage of the battery cell, wherein the determination of the voltage feedback measurement is based on a transfer function of the voltage sensor and a measurement of the voltage across the battery cell; and control the formation / test voltage of the battery cell based on a target formation / test voltage and the determined voltage feedback measurement.

[0024] The battery formation / test controller may also be configured to determine a transfer function of the voltage sensor.

[0025] The voltage sensor may include an analog-to-digital converter ADC having a nonlinear input range for an input signal, wherein the analog input signal is nonlinearly converted into a digital output signal, and the battery formation / test controller is further configured to: compare the voltage measurement across the battery cell with the nonlinear input range; if the voltage measurement across the battery cell exceeds the nonlinear input range: determine the transfer function of the voltage sensor.

[0026] The battery formation / test controller may also be configured to determine a transfer function of the voltage sensor by: applying a reference input signal to the voltage sensor so that a voltage measurement across the battery cell includes a formation / test voltage signal and a reference output signal corresponding to the reference input signal; extracting a reference output signal from the voltage measurement across the battery cell; and determining a transfer function based on the reference input signal and the reference output signal.

[0027] The voltage sensor may include an analog-to-digital converter ADC, wherein the battery formation / test controller is further configured to apply dithering to the reference input signal. Applying dithering to the reference input signal may include transforming the reference input signal between at least two signal levels and / or modulating the amplitude of the reference input signal.

[0028] The battery formation / test controller may also be configured to read the transfer function of the voltage sensor from the memory.

[0029] The battery formation / test controller may also be configured to: determine a further transfer function of the voltage sensor; determine a further voltage feedback measurement based on the further transfer function and further measurements of the voltage across the battery cell by the voltage sensor; and control the formation / test voltage of the battery cell based on the target formation / test voltage and the determined further voltage feedback measurements.

[0030] The battery formation / test controller may also be configured to store a further transfer function of the voltage sensor in the memory for use in determining future voltage feedback measurements.

[0031] The battery formation / test controller may also be configured to control the formation / test voltage of the battery cell by controlling the operation of one or more transistors configured to control the magnitude of the formation / test voltage of the battery cell.

[0032] In a fifth aspect of the present disclosure, a battery formation / test system is provided, comprising: a voltage sensor, including an analog-to-digital converter ADC, for coupling to a battery cell to measure a voltage across the battery cell; and a battery formation / test controller, coupled to a digital output of the ADC and configured to: determine a voltage feedback measurement indicating a formation / test voltage of the battery cell, wherein the determination of the voltage feedback measurement is based on a transfer function of the voltage sensor and the digital output of the ADC; and control the formation / test voltage of the battery cell based on a target formation / test voltage and the determined voltage feedback measurement.

[0033] In a sixth aspect of the present disclosure, a method for controlling a forming / testing voltage of a battery cell is provided, the method comprising: determining a voltage feedback measurement value indicative of the forming / testing voltage of the battery cell, wherein the determining the voltage feedback measurement is based on a transfer function of a voltage sensor, the voltage sensor being arranged to output a measurement value of a voltage across the battery cell and a measurement value of the voltage across the battery cell; and controlling the forming / testing voltage of the battery cell based on the target forming / testing voltage and the determined voltage feedback measurement.

[0034] The method may also include determining a transfer function of the voltage sensor.

[0035] The voltage sensor may include an analog-to-digital converter ADC having a nonlinear input range for an input signal, wherein the analog input signal is nonlinearly converted into a digital output signal, and the method may further include: comparing the voltage across the battery cell relative to the nonlinear input range; if the voltage measurement across the battery cell exceeds the nonlinear input range: determining a transfer function of the voltage sensor.

[0036] The method may also be configured to determine a transfer function of a voltage sensor by: applying a reference input signal to the voltage sensor so that a voltage measurement across the battery cell includes a formed / tested voltage signal and a reference output signal corresponding to the reference input signal; extracting a reference output signal from the voltage measurement across the battery cell; and determining a transfer function based on the reference input signal and the reference output signal.

[0037] The voltage sensor may include an analog-to-digital converter (ADC), wherein the method may further include applying dithering to the reference input signal.

[0038] In a sixth aspect of the present disclosure, a system for measuring a DC energy signal in a circuit is provided, the system comprising: a sensor, comprising an analog-to-digital converter ADC, configured to receive an analog voltage that depends at least on the DC energy signal and output a digital value corresponding to the analog voltage; a signal generator for coupling to an input end of the sensor, wherein the signal generator is configured to generate an oscillating reference input signal with jitter; and a controller coupled to the ADC and the signal generator, wherein the controller is configured to: determine a transfer function of the sensor; and determine a measure of the DC energy signal based on the determined transfer function and the output of the ADC, wherein the controller is configured to determine the transfer function of the sensor in the following manner: control the signal generator to apply a reference input signal to the input end of the sensor so that the digital value output by the ADC includes a DC signal that depends on the DC energy signal and an oscillating reference output signal that depends on the oscillating reference input signal; extract the oscillating reference output signal from the digital output of the ADC; and determine the transfer function based on the oscillating reference input signal and the oscillating reference output signal.

[0039] The ADC may be used to couple to a component in a circuit such that the analog voltage received by the ADC is the voltage across the component, and wherein the ADC and component together form a sensor.

[0040] The dithering of the oscillation reference signal may include transposing the oscillation reference input signal so that the oscillation reference input signal has an average value of a first signal level in a first time period and the oscillation reference input signal has an average value of a second signal level in a second time period.

[0041] The oscillating reference input signal may have a constant peak-to-peak amplitude.

[0042] Dithering of the oscillating reference input signal may include modulating the amplitude of the oscillating reference input signal.

[0043] An oscillating reference input signal may be applied to an input of the sensor over a period of time, and the controller is configured to determine a transfer function of the sensor by comparing an average value of the oscillating reference input signal over the period of time to an average value of the oscillating reference output signal over the period of time.

[0044] The DC energy signal may be a DC current or a DC voltage.

[0045] In a seventh aspect of the present disclosure, a system for measuring a DC energy signal in a circuit is provided, the system comprising: a sensor, including an analog-to-digital converter ADC, configured to receive an analog voltage at least dependent on the DC energy signal and output a digital value corresponding to the analog voltage; a controller coupled to the ADC digital output, wherein the controller is configured to: determine whether the digital output of the ADC indicates that the ADC operates within its non-linear range; and if the ADC is determined to operate outside its non-linear range, determine a transfer function of the sensor and determine a measurement of the DC energy signal based on the determined transfer function and the digital output of the ADC.

[0046] The controller may be configured to determine a measured value of the DC energy signal based on the digital output of the ADC and a stored value of the transfer function of the sensor if the ADC is determined to be operating in its non-linear region.

[0047] The system may further include: a signal generator coupled to the input of the sensor and configured to generate an oscillating reference input signal, wherein the controller is configured to determine the transfer function of the sensor by: applying the oscillating reference input signal to the input of the sensor; extracting a synthesized oscillating reference output signal from the digital output of the ADC; and determining the transfer function based on the oscillating reference input signal and the oscillating reference output signal.

[0048] The ADC may be used to couple to a component in a circuit such that the analog voltage received by the ADC is the voltage across the component, the ADC and component together forming a sensor and the component being at the input of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] By way of example only, aspects of the present disclosure are described with reference to the following drawings, in which:

[0050] Figure 1 shows an example battery cell charging curve that may be used during battery formation and / or testing;

[0051] Figure 2 An example battery formation / testing system according to one aspect of the present disclosure is shown;

[0052] Figure 3 Shown by Figure 2 Representation of example processes performed by a battery formation / test controller of a battery formation / test system;

[0053] Figure 4 Shown by Figure 2 Representation of further example processes performed by a battery formation / test controller of a battery formation / test system;

[0054] Figure 5 shows the transfer function that can be applied to Figure 2 Example representation of different types of jitter of the reference input signal of a current sensor. DETAILED DESCRIPTION

[0055] The battery formation / test controller of the present disclosure is configured to determine the transfer function of the current sensor used to measure the battery cell during formation / testing. The transfer function can be determined periodically or intermittently, so that any changes in the current sensor can be detected and the output of the current sensor can be corrected to compensate for any changes in the current sensor, thereby maintaining accurate measurement of the current. The inventors have recognized that by implementing the battery formation / test controller in this manner, a high-quality, stable current sensor is no longer required. For example, a current sensor that is more susceptible to changes with temperature changes can be accommodated because any changes in the current sensor can be detected and compensated. As a result, high-precision measurement of current can still be achieved with a relatively low-cost current sensor, which means that it is possible to achieve high-precision current control at a relatively low cost during formation / testing. In addition, any other causes of current sensor changes, such as sensor drift, can also be corrected by transfer function determination, and recalibration of the system can also be achieved more directly by transfer function determination.

[0056] More generally, accurately determining the transfer function of a sensor used to measure a DC energy signal (e.g., a DC current or voltage) can be challenging when an analog-to-digital converter (ADC) is used in the process. In particular, many ADCs include a nonlinear region where the input signal does not convert linearly to a digital value, which can result in an inaccurate transfer function, which is determined by applying an oscillating reference to the input of the sensor and observing the resultant oscillating signal at the ADC digital output. This problem may exist not only in DC energy sensors used for battery formation / testing purposes, but more broadly when measuring any DC energy signal based on the measured output of the sensor and the transfer function of the sensor. The present disclosure includes various techniques and systems for addressing this issue to maintain high accuracy in DC energy signal measurements, such as by applying dithering to the input reference signal, or by determining the transfer function of the sensor only when the ADC is operating outside of its nonlinear region, and using previously determined transfer function values ​​when the ADC is operating in its nonlinear region.

[0057] Figure 1An example battery cell charging curve that can be used during battery formation and / or testing is shown. It should be understood that similar battery cell current discharge curves can also be used during battery formation and / or testing. The values ​​of time, current, and voltage are only non-limiting examples, and charging / discharging may require any suitable time, current, and voltage relationship, for example, depending on the properties of the battery cell. In order to control the current applied during charging (or control the current of discharge), a current sensor can be used to measure the battery current. The current sensor can measure the current applied to the battery cell during charging as a positive current and the current output from the battery cell during discharge as a negative current (or vice versa). The current sensor can include a current transducer, such as a shunt resistor, an amplifier that amplifies the transducer signal, and an analog-to-digital converter (ADC) that measures the amplified signal and outputs a digital measurement of the battery current. As explained in the background, high currents during the formation / testing process can cause significant temperature increases, which can be problematic for maintaining high measurement accuracy and repeatability over time. The ADC can be a high-precision design with a high-precision reference signal, such as having a temperature coefficient of approximately 3ppm / ℃. The shunt resistor can also be selected to have a relatively stable temperature coefficient, such as 15ppm / ℃. However, this type of shunt resistor tends to be much more expensive than shunt resistors with less stable temperature coefficients. For example, a shunt resistor with a temperature coefficient of approximately 15ppm / °C may be an order of magnitude more expensive than a shunt resistor with a temperature coefficient of approximately 75ppm / °C.

[0058] Figure 2 An example battery formation / test system 200 according to one aspect of the present disclosure is shown. System 200 includes a battery formation / test controller 210, a reference signal generator 220, an amplifier 230 (e.g., a PGA or any other suitable type of amplifier), an analog-to-digital converter (ADC) 235 (e.g., a SAR ADC, or a SigmaDelta ADC, or a pipeline ADC, or any other suitable type of ADC), and a memory 240 (e.g., a volatile memory, such as RAM, or a non-volatile memory, such as flash memory, or any other suitable memory type). System 200 is suitable for coupling to a battery charge / discharge circuit. Figure 2 The example battery charge / discharge circuit shown in includes one or more battery cells 250, a current sensor 260 (a shunt resistor in this example, but may alternatively be a current transformer or any other suitable type of current sensor), a FET driver 270, FETS 275, and a current / voltage source 280 (a capacitor and a DC power supply +V in this example, but may alternatively be any suitable type of current / voltage source). It should be understood that Figure 2One non-limiting example of a circuit that can be used to control a battery cell current and / or voltage during formation / testing is shown. Those skilled in the art will appreciate that there are various other circuit configurations that can be used so that the system 200 can control at least a portion of the circuit to control the battery formation / testing current and / or voltage. The current sensor 260, the amplifier 230, and the ADC 235 together constitute a current sensor that outputs a digital signal indicating the current flowing through the battery cell 250 (i.e., a measurement of the battery cell current) to the formation / test controller 210.

[0059] The formation / test controller 210 is adapted to be coupled to the FET driver 270 to control the operation of the FET 275 and, therefore, control the current and / or voltage applied to the battery cell 250 during charging and / or control the current and / or voltage discharged from the battery cell 250 during discharging. For example, the duty cycle of the two FETs 275 may determine the average voltage at the switch node of the two FETs 275. The controller 210 may control the FETs 275 to set the average voltage to be higher than the battery cell voltage during charging in order to drive the desired charging formation / test current into the battery cell 250. Alternatively, it may control the FETs 275 to set the average voltage to be lower than the battery cell voltage during discharging in order to control the desired discharge battery cell current from the battery cell 250. Figure 2 The circuit also includes an inductor to slow the rate of change of the current, although this is optional. Amplifier 230 is adapted to be coupled to current sensor 260 via electrical connection 232 so that an analog voltage signal indicative of the current flowing through battery cell 250 is received at amplifier 230. This measurement is used by controller 210 in controlling the forming / testing current of battery cell 250 to achieve a target charge or discharge current, for example, in Figure 1 . In this example embodiment, the amplifier 230 is also adapted to be coupled to the battery cell 250 via the electrical connection 234 so as to receive an analog signal of the voltage across the battery cell 250 at the amplifier 230, so that the amplifier 230 and the ADC 235 can also be used to measure the voltage of the battery cell 250 (e.g., by multiplexing the ADC 235 between current signal and voltage signal conversion). However, in alternative embodiments, the battery cell voltage may not be measured, or may be measured by a different system or a dedicated voltage sensor component in the system 250.

[0060] The system 200 is configured so that the battery formation / test controller 210 can determine the transfer function of the current sensor (which may include the entire current measurement signal chain including the current sensor 260, the amplifier 230, and the ADC 235). The inventors have recognized that by configuring the system 200 in this manner, any changes in the transfer function of the current sensor (e.g., temperature changes due to the charging current) can be detected and corrected during the formation / test process. Therefore, a current sensor 260 with a worse temperature coefficient than the previous system can be used, thereby saving costs. For example, a shunt resistor with a temperature coefficient of about 15ppm / ℃ may have been required previously, with a unit cost of about 10USD. However, by configuring the system to determine and track the transfer function of the current sensor, a shunt resistor with a temperature coefficient of about 75ppm / ℃ (as a non-limiting example) can be used, with a unit cost of about 1USD. In the case where multiple battery cells (e.g., 10s, 100s, or 1000s) are formed / tested in parallel, each battery cell may require its own charge / discharge circuit with its own shunt resistor. Therefore, the cost savings of the shunt resistor can quickly save significant overall costs. Likewise, if current sensor 260 is changed to a current transformer, a current transformer with a worse temperature coefficient than was previously possible may be used.

[0061] Further benefits include the ability to continuously or intermittently update the determined transfer function without the need for time-consuming, complex system recalibration, so that any long-term sensor drift can be easily corrected. In addition, it is possible to extend the time period between recalibrations because it is possible to detect whether recalibration is required, rather than simply following a set recalibration schedule. In addition, any changes in any part of the current measurement signal chain can be detected by determining the transfer function and compensated for accordingly. As a result, the control accuracy of the formation / test current of the battery cell 250 can be further improved.

[0062] Figure 3 1 shows a representation of an example process performed by the battery formation / test controller 210 according to an aspect of the present disclosure. In step S310, a transfer function of the current sensor is determined. The transfer function of the current sensor may be determined in any suitable manner. Figure 2In the specific example system 200 configuration represented in FIG. 2 , the reference signal generator 220 is adapted to be coupled to the current sensor 260 via an electrical connection 222 so that it can apply / inject a reference input signal M1 to the input of the current sensor. The reference input signal M1 can be any suitable time-varying signal, such as a square wave signal, a trapezoidal signal, a sinusoidal signal, etc. Thus, the measurement of the current flowing through the battery cell 250 will include two main components: primarily the battery cell current signal X (the formation / test current signal, which can be, for example, a DC or low-frequency current signal); and a reference output signal M2 that corresponds to the reference input signal M1 and has a different frequency characteristic than signal X (for example, it can be a higher frequency component in the battery current measurement caused by the injected reference input signal M1). The reference signal generator 220 can apply the reference input signal to the current sensor for a period of time, during which the battery formation / test controller 210 can sample and average the measurement of the battery cell current. The battery formation / test controller 210 can then extract the reference output signal M2 from the average measurement of the battery cell current (e.g., using a time domain algorithm, such as piecewise accumulation, or a frequency domain algorithm, such as FFT / Goertzel analysis) and determine the transfer function by comparing M1 to M2. For example, the transfer function can be determined by comparing the magnitudes of M1 and M2.

[0063] Further details of how to determine the transfer function of a current sensor by applying a reference input signal to the current sensor are given in patent application WO2013 / 038176A2, which is incorporated herein by reference in its entirety. For example, line 14 of page 49 to line 5 of page 51 describe an example process by which the transfer function of a current sensor can be determined using a known reference input signal.

[0064] Optionally, the process may proceed to step S315 where the determined transfer function is stored in the memory 240 for later use.

[0065] In step S320, a current feedback measurement is determined by the battery formation / test controller 210. The current feedback measurement represents the formation / test current of the battery cell (i.e., the current applied to the battery cell 250 during charging, or the current output from the battery cell 250 during discharging). The determination of the current feedback measurement is based on the transfer function of the current sensor and the measurement of the battery cell current (i.e., the signal output by the current sensor). If the reference signal generator 220 is still operating to apply the reference input signal to the current sensor, the measurement of the battery cell current may include two main components, M2 and X (as described above). The formation / test current signal (component X) may be isolated or extracted in any suitable manner, such as by filtering or removing the reference output signal (component M2) by FFT, etc. Alternatively, once step S310 is completed, the controller 210 may turn off the reference signal generator, or disconnect it from the current sensor, in which case the measurement of the battery cell current may include only the formation / test current. The previously determined transfer function of the current sensor may then be used to appropriately modify the formation / test current signal (component X) in order to arrive at a more accurate current feedback measurement that accounts for any changes or drift in the current sensor transfer function.

[0066] For example, at the time of initial calibration of the system 200 and circuit, the transfer function of the current sensor may be determined to be TF0. This value may be stored in the memory 240. During formation / testing, the transfer function may be determined to be TF1. The ratio of TF1 / TF0 may represent any change in the gain of the current sensor compared to the initial calibration. Any change in gain may then be corrected in the formation / test current signal (component X) so that the determined current feedback measurement has been corrected for the gain change.

[0067] In step S330, the formation / test controller 210 uses the determined current feedback measurement and the target formation / test current to control the formation / test current of the battery cell 250. For example, a specific target formation / test current may be required, such as Figure 1 , and may be stored in memory 240. The current feedback measurement may be compared to the target, and controller 210 may adjust its control timing of FET 275 to increase or decrease the battery cell current as desired.

[0068] During battery formation / testing, steps S320 and S330 may be repeated intermittently or periodically. In this case, if the transfer function determined in step S310 is stored in memory 240 in step S315, the most recently determined transfer function may be obtained from memory 240 in step S320 and used to determine the current feedback measurement. Steps S320 and S330 may use a single sample of the output of ADC 235 and use that single sample to determine the current feedback measurement, or may average multiple samples over time and determine the current feedback measurement from the average. The process may periodically or intermittently determine further or updated transfer functions by returning to step S310. For example, every minute, or every two minutes, or every five minutes, etc., the process may return to step S310 to determine an updated transfer function, which is then stored in step S315. Steps S320 and S330 may then be repeated cyclically between transfer function updates. Alternatively, upon completion of S330, the process may always return to S310, thereby continuously updating the transfer function.

[0069] Optionally, during steps S320 and S330, the controller 210 may turn off or disconnect the reference signal generator 220 so that the reference input signal is no longer applied to the current sensor. Alternatively, the reference signal generator 220 may always apply the reference input signal and the formed / test current signal (component X) extracted from the measurement of the current flowing through the battery cell, such as by filtering or FFT, etc.

[0070] according to Figure 3 By using a process for determining an initial transfer function TF0 of the current sensor and storing it in the memory 240, any changes in the current sensor can be detected and compensated for periodically or continuously. In this way, a lower cost current sensor 260 can be used with a relatively poor temperature coefficient while still maintaining a high level of current control accuracy. In addition, other contributors to gain changes in the current sensor can also be detected and compensated, thereby even further improving the accuracy of current control. In addition, the initial calibration of the system 200 and circuit can be simplified by using a process for determining an initial transfer function TF0 of the current sensor and storing it in the memory 240. In addition, by recalculating TF0 at any appropriate time and updating the TF0 value stored in the memory 240, a more straightforward recalibration can be achieved throughout the life cycle of the system 200 and circuit.

[0071] Figure 4A representation of an example process for improving the measurement accuracy of a DC energy signal such as a current or voltage according to one aspect of the present disclosure is shown. In one particular aspect, it can be implemented as a further process performed by the battery formation / test controller 210. Many types of ADCs 235 can have a non-linear input range of an input signal, where the analog input signal is converted non-linearly to a digital output signal. For example, the ADC can have a specific range of input signals where a linear change in the input analog signal does not result in a linear change in the output digital signal. This may cause some inaccuracies in the determination of the current sensor transfer function.

[0072] For example, the reference input signal may be a square wave signal that varies between two levels, level 1 and level 2. ADC 235 converts a signal generated by level 1 (we call this signal level 1') in the voltage at the input of ADC 235 into data1 = level1' + error1, where error1 is the ADC conversion error. ADC 235 converts a signal generated by level 2 (we call this signal level2') in the voltage at the input of ADC 235 into data2 = level2' + error2, where error2 is the ADC conversion error. In order to determine the transfer function of the current sensor, the controller 210 may compare the amplitude of the reference input signal (i.e., level2-level1) with the amplitude of the M2 component of the current flowing through the shunt 260 (i.e., the current flowing through the battery cell 250). In other words, data2-data1 = (level2'-level1') + (error2-error1).

[0073] If the ADC 235 operates in its linear region, error2 and error1 should be similar, such as both positive or both negative. This should result in a relatively small overall error in data2-data1, so that data2-data1 is a relatively accurate representation of level2'-level1'. For example, if error1 = +0.3LSB and error2 = 0.2LSB, the overall error in data2-data1 may be 0.1LSB. However, if the ADC 235 operates in its nonlinear region, error2 and error1 may be completely different, such as one is positive and the other is negative. This may result in a relatively large overall error in data2-data1, so that data2-data1 is a less accurate representation of level2'-level1'. For example, if error1 = +0.3LSB and error2 = -0.2LSB, the overall error in data2-data1 may be 0.5LSB.

[0074] return Figure 4 In step S410, the controller 210 may compare the analog voltage indicated by the digital output of the ADC 230 with the nonlinear input range of the ADC 210 (e.g., the “measurement of the cell current” mentioned above, which may be just the formation / test current signal (component X), or the entire signal X+M2). The comparison may be based on an average value, such as RMS, a digital output, or any other suitable characteristic. The nonlinear input ranges of different types of ADCs may be known, such as from tests or data tables, and stored in the memory 240 during manufacture or calibration of the system 200. If the input to the ADC exceeds the nonlinear input range (i.e., the ADC 235 operates in its linear region), the process may proceed to step S310, where the transfer function of the current sensor is determined as described above. If the input to the ADC is within the nonlinear input range (e.g., the measurement of the battery cell current described above), the process may proceed to step S320. In this case, the previously determined transfer function value stored in the memory 240 is used to determine the measured value of the DC current (e.g., the current feedback measurement described above). For example, each time a transfer function is determined in step S310, it may be stored in memory as the most recently determined transfer function (step S315), and then the stored most recently determined transfer function may be used to determine the current feedback measurement in step S320. In this way, the transfer function may be determined only when the ADC 235 is operating in its linear region, thereby improving the accuracy of the determined transfer function.

[0075] Once step S330 is completed, the process can return to step S320, and / or can periodically or intermittently return to step S410 when the transfer function needs to be updated. In this way, the transfer function can be accurately determined and the current applied to the battery cell 250 can be accurately controlled throughout the formation / testing process.

[0076] In further example embodiments of the present disclosure, dithering may be applied to the reference input signal to improve randomization of quantization noise in the output of ADC 235 and thereby improve the accuracy of transfer function determination. This is particularly described in the context of battery formation / testing, but may equally be used for any purpose as part of a process for measuring a DC energy signal (e.g., a DC current or voltage). During battery formation / testing, the formation / test current of the battery cell 250 may be primarily a DC signal or a low frequency signal, sometimes with very little ripple (e.g., a sine wave of approximately 2 mVpp). The primarily DC nature of the signal may result in a lack of randomization and overdetermination of the quantization noise in the output of ADC 235. Randomization of the quantization noise may be beneficial to noise reduction / elimination when multiple samples of the output of ADC 235 are averaged in the process of determining the transfer function and / or current feedback measurement.

[0077] To improve the randomization of the quantization noise, the reference signal generator 220 may apply dithering to the reference input signal. Various different types of dithering may be applied.

[0078] Figure 5 An example representation of two different types of dithering that can be applied to a reference input signal is shown. One or both of these different types can be used. In this example, the reference input signal is a square wave signal, but the same principles can also be applied to any other suitable type of reference input signal.

[0079] Reference numeral 510 relates to the jitter of the transposed reference input signal. In this example, the reference input signal is converted between three signal levels, but any number of signal levels (two or more) may be used. The term "transposed" describes the jitter of the reference input signal ( Figure 5 The peak-to-peak amplitude of the signal level remains constant, but the average value of the signal level varies between the three signal levels ( Figure 5 'ped1', 'ped2', 'ped3' in ' . In this particular example, for the first second the reference input signal has a first average signal level, which then increases to a second average signal level in the next second, which then increases to a third average signal level in the next second. In this example, because the peak-to-peak amplitude of the input reference signal has not changed, no modification is required to the transfer function determination process, since this accounts for the difference between the peak-to-peak amplitudes of the reference input signal and the reference output signal.

[0080] Reference numeral 520 relates to a jitter in which the reference input signal is modulated. In particular, the peak-to-peak amplitude of the reference input signal is changed compared to the signal represented in reference numeral 510 (in this example it is reduced to "ms2", but it could also be increased). In this particular example, signal 520 then also transitions between three different signal levels, as described above. In the case where the jitter involves a variation in the peak-to-peak amplitude of the reference input signal, the transfer function determination performed by controller 210 may need to be modified. Figure 5 In the example shown, each of the six different reference input signals is applied for one second. The output of the ADC 235 can be sampled and averaged over the entire six second period, and the average reference output signal M2 is extracted. The amplitude of the average reference output signal M2 can be compared to the average of the amplitudes of the reference input signals during the six second period (in this example, it would be halfway between the amplitude of the reference input signal during the first three seconds and the amplitude of the reference input signal during the last three seconds). This is merely a non-limiting example, and any number of changes to the amplitude of the reference input signals can be applied, each change can last for any suitable amount of time (all the same amount of time, or different amounts of time), and the reference input signals can be applied for any suitable amount of time (not just a total of six seconds).

[0081] It should be understood that the dithering applied to the reference input signal may include transposing the reference input signal between two or more different signal levels and / or modulating the amplitude of the reference input signal between two or more different amplitudes. Additionally or alternatively, any other suitable type of dithering may be applied to the reference input signal. The controller 210 may be configured to control the operation of the reference signal generator 220 during the transfer function determination, such as setting the type of dithering used, so that any changes in the amplitude of the reference input signal may be properly accounted for during the transfer function determination.

[0082] It will be easily understood by those skilled in the art that various changes or modifications may be made to the above-mentioned aspects of the present disclosure without departing from the scope of the present disclosure.

[0083] The functions of the controller 210 may be implemented by software, hardware, or a combination of software and hardware. For example, its functions may be implemented by software including computer readable code, which, when executed on a processor of any electronic device, performs the above functions. The software may be stored on any suitable computer readable medium, such as a non-transitory computer readable medium, such as a read-only memory, a random access memory, a CD-ROM, a DVD, a Blu-ray, a tape, a hard drive, a solid-state drive, and an optical drive. Therefore, the system 200 may include any suitable hardware, such as one or more processors, or a microcontroller, or any other suitable form of logic, which is configured to perform the above functions, or execute software configured to perform the above functions.

[0084] The components represented in system 200 may all be implemented within a single device or IC. Alternatively, one or more of the represented components may form part of a separate device or IC suitable for coupling to a host device or IC. System 200 may optionally include any number of additional components or devices related or unrelated to the battery formation / testing functionality. In addition, Figure 2 The different logical entities within the system 200 are represented as independent entities that are interconnected. It should be understood that Figure 2 The specific representation of is provided merely for the benefit of understanding the operation of the system 200, and any one or more of the represented entities may be combined into a single entity, or subdivided into two or more sub-entities.

[0085] System 200 may optionally not include amplifier 230, such as where the received analog signal does not require amplification. Additionally or alternatively, ADC 235 may be omitted, such as where controller 210 is configured to operate in the analog domain.

[0086] Optionally, the above process may also be applied to control the forming / testing voltage across the battery cell 250 and / or may be applied to control the voltage across the battery cell 250 during discharge. In particular, the transfer function of a voltage sensor arranged to measure the voltage across the battery cell may be determined in any suitable manner (e.g., amplifier 230 and ADC 235, coupled to the battery cell 250 via electrical connection 234), such as by injecting a reference input signal into the voltage sensor in a manner similar to the reference signal implementation described above. Some example processes for determining the transfer function of a voltage sensor are disclosed in WO2014 / 072733, in particular with respect to Figure 4A-4F, 5A-5C, 6A and 6B, the entire contents of which are incorporated herein by reference. The voltage feedback measurement value can then be determined based on the determined transfer function of the voltage sensor and the measurement of the voltage across the battery cell 250 output from the voltage sensor. Optionally, the voltage sensor can also include a voltage divider coupled across the battery cell 250 to divide the voltage measured by the ADC 235, wherein the ADC 235 is coupled in parallel with one of the resistors of the voltage divider using the electrical connection 234. In this case, a reference input signal can be injected on one side of the voltage divider, such as the reference WO2014 / 072733 Figure 4 A-4F is described in more detail. The controller 210 can then control the operation of the FET 275 or any other suitable component based on the voltage feedback measurement and the target forming / testing voltage to achieve the desired forming / testing voltage. Optionally, a similar process can be used during the discharge cycle to additionally or alternatively more accurately monitor / set the voltage across the battery cell 250. In addition, any of the optional processes described earlier, such as determining the transfer function when the analog input to the ADC exceeds the non-linear input range, or applying dithering to the reference input signal, can be used to determine the voltage sensor transfer function.

[0087] The controller 210 can be configured to control / measure only the voltage across the battery cell 250 in this manner, or to control / measure only the current flowing through the battery cell 250 in this manner, or can be configured to control / measure both the current flowing through the battery cell 250 and the voltage across the battery cell 250 in this manner (for example, by determining the transfer function of the current sensor by applying a reference input signal to at least a portion of the current sensor, and by determining the transfer function of the voltage sensor by applying the same or different reference input signal to at least a portion of the voltage sensor).

[0088] As noted several times previously, many aspects of the system 200 and process described above are generally applicable to the measurement of DC energy signals, such as DC voltage or DC current, and not just in the context of battery formation / testing. In particular, when an ADC is used to measure a DC energy signal for any purpose, the above referenced Figure 4 and Figure 5The described techniques for addressing issues associated with ADC nonlinearity may be beneficial. In more detail, as previously described, an ADC may be used to convert a voltage signal that is dependent on a DC energy signal (e.g., the ADC input is coupled to a shunt or resistor across a current transformer for DC current measurement, or coupled to a voltage divider for DC voltage measurement, or a battery whose voltage is being measured, etc.), and then measure the DC energy signal based on a digital output and a transfer function of the sensor (composed of the ADC and optionally one or more other components, such as a shunt or voltage divider and / or an amplifier, etc.). Nonlinearity of the ADC may cause the determined transfer function to be inaccurate, and the system may use the previously referenced transfer function to determine the DC energy signal. Figure 4 and Figure 5 The described technology solves this problem. Thus, a system for measuring a DC energy signal in a circuit is disclosed, which is very similar to the system 220, but in which the battery formation / test controller 210 can be simply considered as a controller, which determines the transfer function of the sensor by controlling the reference signal generator 220 to apply an oscillating reference input signal to the input terminal of the sensor (for example, to a shunt or voltage divider that forms the sensor input) to determine the measured value of the DC energy signal, and measures the DC energy signal using the determined transfer function and the digital output of the ADC 230, but does not necessarily output any form of control signal external to the system 200, such as output to Figure 2 , and the control signals for the FET driver 270 shown in FIG. 2. Furthermore, the DC energy measurement system may be adapted to be coupled to any type of circuit where a DC energy signal is to be determined, not just to a battery formation / test circuit.

[0089] As a result, low cost components, such as low cost shunts, may be used within the sensor while still being able to accurately measure the DC energy signal over time by virtue of accurate transfer function determination.

[0090] Although a particular transfer function determination technique involving application of a reference input signal is described above, it should be appreciated that the system 200 may alternatively determine the transfer function of the current sensor and / or the voltage sensor in any other suitable manner.

Claims

1. A system for measuring a DC energy signal in a circuit, the system comprising: a sensor comprising an analog-to-digital converter ADC configured to receive an analog voltage at least dependent on a DC energy signal and output a digital value corresponding to the analog voltage; and A controller coupled to the digital output of the ADC, wherein the controller is configured to: determining whether a digital output of the ADC indicates that the ADC is operating within its non-linear range; as well as If the ADC is determined to be operating outside of its non-linear range, a transfer function of the sensor is determined and a measurement of the DC energy signal is determined based on the determined transfer function and the digital output of the ADC.

2. The system of claim 1, wherein the ADC is configured to be coupled to an element in the circuit such that the analog voltage received by the ADC is the voltage across the element, and wherein the ADC and the element together constitute the sensor.

3. The system of claim 1 , further configured to determine a transfer function of the current sensor by: applying a reference input signal to the sensor so that an analog voltage received by the ADC includes a DC energy signal and a reference output signal corresponding to the reference input signal; extracting the reference output signal from a digital value corresponding to the analog voltage; as well as The transfer function is determined based on the reference input signal and the reference output signal.

4. The system of claim 1, further configured to store the determined transfer function in a memory for use in determining future measurements of the DC energy signal.

5. The system of claim 1, further configured to determine the measure of the DC energy signal based on a previously determined transfer function stored in the memory if the ADC is determined to be operating in its non-linear region.

6. A method for measuring a DC energy signal in a circuit using a sensor, the sensor comprising an analog-to-digital converter (ADC), the ADC being configured to receive an analog voltage at least dependent on the DC energy signal and output a digital value corresponding to the analog voltage, the method comprising: determining whether the digital output of the ADC indicates that the ADC is operating within its nonlinear range; as well as If the ADC is determined to be operating outside of its nonlinear range, then: determining a transfer function of the sensor; and A measurement of the DC energy signal is determined based on the determined transfer function and the digital output of the ADC.

7. The method of claim 6, further comprising, if the ADC is determined to be operating in its non-linear region, determining a measure of the DC energy signal based on a previously determined transfer function stored in the memory.

8. The method of claim 6, wherein determining the transfer function of the current sensor comprises: applying a reference input signal to the sensor so that an analog voltage received by the ADC includes a DC energy signal and a reference output signal corresponding to the reference input signal; extracting the reference output signal from the digital value corresponding to the analog voltage; as well as The transfer function is determined based on the reference input signal and the reference output signal.

9. The method of claim 6, further comprising: The determined transfer function is stored in a memory for use in determining future measurements of the DC energy signal.

10. A method for measuring a DC energy signal in a circuit using a sensor, the sensor comprising an analog-to-digital converter (ADC), the ADC being configured to receive an analog voltage at least dependent on the DC energy signal and output a digital value corresponding to the analog voltage, the method comprising: The transfer function of the sensor is determined by: applying an oscillating reference input signal to an input of the sensor such that a digital value output by the ADC includes a DC signal dependent on the DC energy signal and an oscillating reference output signal dependent on the oscillating reference input signal, wherein the oscillating reference input signal includes jitter; Extracting the oscillating reference output signal from the digital output of the ADC; as well as determining a transfer function based on the oscillating reference input signal and the oscillating reference output signal; as well as A measure of the DC energy signal is determined based on the determined transfer function and the output of the ADC.

11. The method of claim 10, wherein the ADC is configured to be coupled to an element in a circuit such that the analog voltage received by the ADC is the voltage across the element, and wherein the ADC and the element together constitute the sensor.

12. The method of claim 10, wherein the dithering of the oscillation reference signal comprises shifting the oscillation reference input signal so that the oscillation reference input signal has an average value of a first signal level in a first time period and the oscillation reference input signal has an average value of a second signal level in a second time period.

13. The method of claim 12, wherein the oscillating reference input signal has a constant peak-to-peak amplitude.

14. The method of claim 10, wherein the dithering of the oscillating reference input signal comprises modulating an amplitude of the oscillating reference input signal.

15. The method of claim 10, further comprising: applying the oscillating reference input signal to the input of the sensor for a period of time, Wherein determining the transfer function of the sensor further comprises: The average value of the oscillating reference input signal during the period of time is compared with the average value of the oscillating reference output signal during the period of time.

16. A controller configured to execute the method according to any one of claims 6-15.

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