A high-precision current sampling system based on series connection of bidirectional power supply

Abstract

The utility model discloses a kind of high-precision current sampling systems applied to series formation bidirectional power supply, including low ripple power supply circuit, high-precision current sampling circuit, filter circuit, ADC drive circuit and data conversion and processing system, ADC drive circuit converts power output current into high-precision, low temperature drift's voltage signal that can be sampled;Switching power supply, LDO composition low ripple, supply high-precision, high stability, low ripple, low noise power supply to entire system;DSP digital signal processing control chip, ADC are responsible for AD conversion and digital signal transmission and acquisition, carry out digital filtering by digital signal processing, can make current data more stable.The utility model realizes high-speed current sampling in battery series formation system, can be as loop control feedback current, and keep effective precision in full current range.

Description

Technical Field

[0001] This utility model belongs to the field of sampling technology of charging and discharging power supply current signal chain of lithium battery formation and capacity equipment, specifically involving a high-precision current sampling system based on series-connected bidirectional power supply. Background Technology

[0002] Battery formation is a crucial step in lithium-ion battery production. Series formation involves connecting lithium-ion batteries in series within a single circuit for simultaneous formation. Because all batteries in a series circuit experience equal charging and discharging currents, the consistency of the lithium-ion batteries is better. Therefore, series formation technology is increasingly used in lithium-ion battery formation. In series formation, the current in the power supply box is particularly important, serving as a key parameter determining the capacity and consistency of the lithium-ion batteries.

[0003] Traditional shunts offer good accuracy and linearity on a single-cell 5V platform. However, since the common-mode voltage in series-formed power systems can reach up to 250V, the high-side sampling circuit of traditional shunts cannot maintain current sampling accuracy under such high common-mode voltages, while the low-side sampling circuit cannot achieve parallel connection between channels. Therefore, a new high-precision high-side current sampling method is needed in series-formed power supply systems. Summary of the Invention

[0004] To address the technical problem of low sampling accuracy in the power supply box during existing lithium battery series formation, this invention provides a high-precision current sampling system based on a bidirectional power supply during series formation. This system enables high-side current sampling and achieves a current sampling accuracy of 0.02%FS across the entire current range (-240A to +240A).

[0005] The technical solution adopted in this utility model is:

[0006] A high-precision current sampling system based on a series bidirectional power supply is characterized by comprising: a low-ripple power supply circuit (1), a high-precision current sampling circuit (2), a filter circuit (3), an ADC drive circuit (4), and a data conversion and processing system (5), wherein:

[0007] The low ripple power supply circuit (1) includes a switching power supply I, a switching power supply II, C4, C5, a decoupling capacitor C8, a decoupling capacitor C9, an LDO1, and an LDO2. The first terminal of the switching power supply I is grounded, and the second terminal is connected to the first terminal of C4. The second terminal of C4 is connected to the first terminal of the decoupling capacitor C9 after passing through LDO1. The second terminal of the decoupling capacitor C9 is grounded, and the third terminal of C4 is grounded. The first terminal of the switching power supply II is grounded, and the second terminal is connected to the first terminal of C5. The second terminal of C5 is connected to the first terminal of the decoupling capacitor C8 after passing through LDO2. The second terminal of the decoupling capacitor C8 is grounded.

[0008] The high-precision current sampling circuit (2) includes a fluxgate current sensor CT1 and a platinum resistance resistor R1. The first end of the fluxgate current sensor CT1 is connected to the third end of the decoupling capacitor C9, and the second end of the fluxgate current sensor CT1 is connected to the third end of the decoupling capacitor C8. The output end of the fluxgate current sensor CT1 is converted into a voltage signal through the platinum resistance resistor R1.

[0009] The filter circuit (3) includes R2, R3, C1, C2, and C3. The first ends of R2 and R3 are connected to R1, the second end of R2 is connected to the first end of C2 and the first end of C3, the second end of C2 is connected to the first end of C1, the second end of C3 is grounded, the second end of R3 is connected to the third end of C2 and the second end of C1, and the third end of C1 is grounded.

[0010] The ADC driving circuit (4) includes an instrumentation amplifier U1, R4 and C6. The fourth terminal of C1 and the fourth terminal of C3 are respectively connected to the first terminal of the instrumentation amplifier U1. The second terminal of the instrumentation amplifier U1 is connected to the first terminal of R4. The second terminal of R4 is connected to the first terminal of C6. The second terminal of C6 is grounded.

[0011] The data conversion and processing system (5) includes ADC1 and DSP. The third terminal of C6 is connected to the first terminal of ADC1, the second terminal of ADC1 is connected to instrumentation amplifier U1, and the third terminal of instrumentation amplifier U1 is connected to DSP through a data bus.

[0012] Furthermore, the typical cutoff frequency of the filter circuit (3) is 10kHz.

[0013] Furthermore, the digital value converted by ADC1 is read back to the DSP via a 16-bit data bus, and the read-back digital value is converted into a real current value, as shown in formula (1):

[0014] (1)

[0015] In the formula, This is the actual current value. For the digital quantity converted by ADC, This represents the current coefficient of the sampling circuit. It is determined by the fluxgate current sensor's multiplier and the resistance of R1;

[0016] Calculated true current value The current is fed into the PWM current loop for current control. Further, the calculated actual current value is... Digital filtering is performed using a first-order low-pass filter. Discretization is performed using the backward Euler formula, and the discretized formula is shown in formula (2):

[0017] (2)

[0018] Since the typical cutoff frequency of the filter used is 10Hz and the sampling frequency is 25kHz, the result obtained through the backward Euler formula is... , .

[0019] Furthermore, the data conversion and processing system (5) uses a 16-bit SAR-type ADC for AD conversion, and performs digital filtering processing via a DSP before sending the data to the human-computer interaction system. The SAR-type ADC has a high conversion rate, which meets the system's conversion time requirements, and its 16-bit accuracy meets the system requirements.

[0020] In the battery formation industry, the main power supply is mostly an industrial switching power supply with a switching frequency of approximately 50kHz to 100kHz and an output voltage ripple of approximately 120 to 150mVp-p. However, existing precision operational amplifiers (op-amps) have a power supply rejection ratio (PSRR) of only 20dB to 30dB at frequencies of 50kHz to 100kHz. Therefore, directly powering the precision op-amp with a switching power supply will introduce an output ripple of 3 to 15mV. This ripple, introduced into the current sampling signal chain, will severely affect the current sampling accuracy. This invention incorporates an LDO (Low-Noise Discharge Loop) into the existing switching power supply system, effectively suppressing the ripple of the industrial switching power supply before it is fed into the signal chain power supply system. Simultaneously, this LDO is required to have a PSRR greater than 40dB at frequencies of 50kHz to 100kHz. In this case, the LDO will provide a highly stable, low-noise power supply to the entire signal chain circuit, thereby improving the system's sampling accuracy.

[0021] A zero-fluxgate sensor is used for current sampling in the current sampling circuit. The zero-fluxgate sensor offers significantly improved accuracy compared to traditional Hall effect current sensors, achieving a linearity of up to 50 ppm and a zero-point drift current of less than 50 PPM. Furthermore, the current sampling is isolated, eliminating common-mode voltage interference. Therefore, the zero-fluxgate sensor is well-suited for high-precision series formation systems. A low-temperature-drift platinum resistance thermometer is used as the secondary current sampling resistor to convert the current signal into a voltage signal. The use of a low-temperature-drift platinum resistance thermometer reduces the system's temperature drift, improving system accuracy. This voltage signal is then properly filtered, amplified, and fed into an ADC for AD conversion.

[0022] Compared with the prior art, the beneficial effects of this utility model are reflected in:

[0023] 1. This invention incorporates an LDO into the existing switching power supply system, effectively suppressing the ripple of the industrial switching power supply before it is fed into the signal chain power supply system. Simultaneously, the LDO is required to have a rejection ratio greater than 40dB at frequencies between 50kHz and 100kHz. In this case, the LDO will provide a highly stable, low-noise power supply to the entire signal chain circuit, thereby improving the system's sampling accuracy.

[0024] 2. A zero-fluxgate sensor is used for current sampling in the current sampling circuit. The zero-fluxgate sensor offers significantly improved accuracy compared to traditional Hall effect current sensors, achieving a linearity of up to 50 ppm and a zero-point drift current of less than 50 PPM. Current sampling is isolated, eliminating common-mode voltage interference. Therefore, the zero-fluxgate sensor is well-suited for high-precision series formation systems. A low-temperature-drift platinum resistance thermometer is used as the secondary current sampling resistor to convert the current signal into a voltage signal. Using a low-temperature-drift platinum resistance thermometer reduces the system's temperature drift, improving system accuracy. This voltage signal is then properly filtered, amplified, and fed into an ADC for AD conversion. Attached Figure Description

[0025] Figure 1 This is an implementation circuit of the present invention applied in a series-connected power supply.

[0026] Figure 2 This is a software processing flowchart of this utility model.

[0027] Figure 3 This refers to the charging current accuracy of this utility model.

[0028] Figure 4 This refers to the discharge current accuracy of this utility model. Detailed Implementation

[0029] The specific implementation of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] refer to Figure 1 This utility model discloses a high-precision current sampling system based on a series bidirectional power supply, comprising: a low-ripple power supply circuit 1, a high-precision current sampling circuit 2, a filter circuit 3, an ADC drive circuit 4, and a data conversion and processing system 5, wherein:

[0031] The low-ripple power supply circuit 1 includes a first switching power supply, a second switching power supply, capacitors C4 and C5, decoupling capacitors C8 and C9, an LDO1, and an LDO2. The first terminal of the first switching power supply is grounded, and the second terminal is connected to the first terminal of capacitor C4. The second terminal of capacitor C4 is connected to the first terminal of decoupling capacitor C9 via LDO1. The second terminal of decoupling capacitor C9 is grounded, and the third terminal of capacitor C4 is grounded. The first terminal of the second switching power supply is grounded, and the second terminal is connected to the first terminal of capacitor C5. The second terminal of capacitor C5 is connected to the first terminal of decoupling capacitor C8 via LDO2. The second terminal of decoupling capacitor C8 is grounded.

[0032] The high-precision current sampling circuit 2 includes a fluxgate current sensor CT1 and a platinum resistance resistor R1. The first end of the fluxgate current sensor CT1 is connected to the third end of the decoupling capacitor C9, and the second end of the fluxgate current sensor CT1 is connected to the third end of the decoupling capacitor C8. The output of the fluxgate current sensor CT1 is converted into a voltage signal through the platinum resistance resistor R1.

[0033] The filter circuit 3 includes R2, R3, C1, C2, and C3. The first ends of R2 and R3 are connected to R1, the second end of R2 is connected to the first end of C2 and the first end of C3, the second end of C2 is connected to the first end of C1, the second end of C3 is grounded, the second end of R3 is connected to the third end of C2 and the second end of C1, and the third end of C1 is grounded.

[0034] The ADC driver circuit 4 includes an instrumentation amplifier U1, R4, and C6. The fourth terminal of C1 and the fourth terminal of C3 are respectively connected to the first terminal of the instrumentation amplifier U1. The second terminal of the instrumentation amplifier U1 is connected to the first terminal of R4. The second terminal of R4 is connected to the first terminal of C6. The second terminal of C6 is grounded.

[0035] The data conversion and processing system 5 includes an ADC1 and a DSP. The third terminal of the C6 is connected to the first terminal of the ADC1, the second terminal of the ADC1 is connected to the instrumentation amplifier U1, and the third terminal of the instrumentation amplifier U1 is connected to the DSP via a data bus.

[0036] In one embodiment, the typical cutoff frequency of the filter circuit 3 is 10 kHz.

[0037] In one embodiment, the digital value converted by the ADC1 is read back to the DSP via a 16-bit data bus, and the read-back digital value is converted into a real current value, as shown in formula (1):

[0038] (1)

[0039] In the formula, This is the actual current value. For the digital quantity converted by ADC, This represents the current coefficient of the sampling circuit. It is determined by the fluxgate current sensor's multiplier and the resistance of R1;

[0040] Calculated true current value The current is fed into the PWM current loop for current control.

[0041] Specifically, the software flowchart of this utility model is as follows: Figure 2 As shown, the software code runs in a 25kHz PWM interrupt. When the interrupt service function is triggered, the ADC conversion is triggered first. When the ADC conversion is complete, the digital value converted by the ADC is read back to the DSP via a 16-bit data bus. Then, the read-back digital value is converted into the actual current value, as shown in Formula 1.

[0042] The calculated actual current value is fed into the PWM current loop for current control. Since this invention does not involve PWM loop control, this part will not be described in detail.

[0043] In one embodiment, the calculated true current value Digital filtering is performed using a first-order low-pass filter. Discretization is performed using the backward Euler formula, and the discretized formula is shown in formula (2):

[0044] (2)

[0045] Since the typical cutoff frequency of the filter used is 10Hz and the sampling frequency is 25kHz, the result obtained through the backward Euler formula is... , .

[0046] In one embodiment, the data conversion and processing system 5 uses a 16-bit SAR-type ADC for AD conversion and performs digital filtering processing via a DSP before sending the data to the human-computer interaction system.

[0047] Figure 3 and Figure 4 To ensure the actual metering accuracy of this invention when applied to a series-connected power supply, it can be seen that the accuracy requirement of 0.02%Fs (48mA) is met in all current ranges (±100mA~±240A) during charging and discharging.

Claims

1. A high-precision current sampling system based on a series-connected bidirectional power supply, characterized in that, include: The system comprises a low-ripple power supply circuit (1), a high-precision current sampling circuit (2), a filter circuit (3), an ADC drive circuit (4), and a data conversion and processing system (5), wherein: The low ripple power supply circuit (1) includes a switching power supply I, a switching power supply II, C4, C5, a decoupling capacitor C8, a decoupling capacitor C9, an LDO1, and an LDO2. The first terminal of the switching power supply I is grounded, and the second terminal is connected to the first terminal of C4. The second terminal of C4 is connected to the first terminal of the decoupling capacitor C9 after passing through LDO1. The second terminal of the decoupling capacitor C9 is grounded, and the third terminal of C4 is grounded. The first terminal of the switching power supply II is grounded, and the second terminal is connected to the first terminal of C5. The second terminal of C5 is connected to the first terminal of the decoupling capacitor C8 after passing through LDO2. The second terminal of the decoupling capacitor C8 is grounded. The high-precision current sampling circuit (2) includes a fluxgate current sensor CT1 and a platinum resistance resistor R1. The first end of the fluxgate current sensor CT1 is connected to the third end of the decoupling capacitor C9, and the second end of the fluxgate current sensor CT1 is connected to the third end of the decoupling capacitor C8. The output end of the fluxgate current sensor CT1 is converted into a voltage signal through the platinum resistance resistor R1. The filter circuit (3) includes R2, R3, C1, C2, and C3. The first ends of R2 and R3 are connected to R1, the second end of R2 is connected to the first end of C2 and the first end of C3, the second end of C2 is connected to the first end of C1, the second end of C3 is grounded, the second end of R3 is connected to the third end of C2 and the second end of C1, and the third end of C1 is grounded. The ADC driving circuit (4) includes an instrumentation amplifier U1, R4 and C6. The fourth terminal of C1 and the fourth terminal of C3 are respectively connected to the first terminal of the instrumentation amplifier U1. The second terminal of the instrumentation amplifier U1 is connected to the first terminal of R4. The second terminal of R4 is connected to the first terminal of C6. The second terminal of C6 is grounded. The data conversion and processing system (5) includes an ADC1 and a DSP. The third terminal of the C6 is connected to the first terminal of the ADC1, the second terminal of the ADC1 is connected to the instrumentation amplifier U1, and the third terminal of the instrumentation amplifier U1 is connected to the DSP via a data bus.

2. The high-precision current sampling system based on a series-connected bidirectional power supply as described in claim 1, characterized in that, The typical cutoff frequency of the filter circuit (3) is 10kHz.

3. A high-precision current sampling system based on a series-connected bidirectional power supply as described in claim 1, characterized in that, The data conversion and processing system (5) uses a 16-bit SAR ADC for AD conversion and performs digital filtering by a DSP before sending the data to the human-computer interaction system.

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