Isolation type current sampling device based on shunt

Abstract

The invention discloses an isolated current sampling device based on a shunt, and relates to the technical field of current detection. The device comprises a diverter connected in a loop to be tested, wherein the output end of the diverter is connected with an isolation amplifier; the output end of the isolation amplifier is connected with an operational amplifier; the operational amplifier is also connected with the 2.5 V reference chip; and the output end of the operational amplifier is connected with the MCU. The shunt is connected in series in a loop to be measured, current flows through the shunt, voltage difference is generated at the two ends of the shunt, the tiny voltage difference is output after being isolated and amplified, actual voltage at the two ends of the shunt is obtained by detecting output voltage and dividing the output voltage by amplification times, the resistance value of the shunt is known, and the current value to be measured can be obtained according to the Ohm law I = U / R. High-precision current detection is realized through a safety architecture of signal isolation and power supply isolation and a self-adaptive temperature compensation system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of current detection, and particularly relates to an isolated current sampling device based on a shunt. BACKGROUND

[0002] In the fields of industrial control, new energy, power electronics, etc., high-precision current detection is a core requirement for realizing safe operation and efficient regulation of a system. Traditional current detection technologies mainly rely on shunts, Hall sensors or current transformers, but all have significant limitations.

[0003] Although the shunt method has simple structure and low cost, its small differential pressure signal (usually only millivolt level) is easily affected by common-mode interference and temperature drift; the Hall sensor has electrical isolation advantages, but has nonlinear error, large temperature drift and high cost; the current transformer is only suitable for AC scenarios, and has a risk of magnetic saturation. Especially in high-dynamic and wide-temperature environments such as electric vehicles and energy storage systems, the precision and stability of existing technologies are difficult to meet the requirements.

[0004] For example, Chinese Patent CN205786808U provides a separated current sampling device. The separated current sampling device includes a shunt, a PCB board and a three-wire connection harness. The shunt and the PCB board are separately arranged. The three-wire connection harness includes a twisted sampling line and a system ground loop. The shunt converts the current on the main loop into a weak voltage signal and transmits the weak voltage signal to the sampling circuit on the PCB board through the twisted sampling line. The separated design of the shunt and the PCB board and the three-wire connection between the shunt and the PCB board can reduce the influence of thermoelectric potential on the current sampling accuracy. Also, Chinese Patent CN201788230U provides a double-manganese-copper current sampling circuit, which includes a live line manganese-copper current sampling part and a neutral line current sampling part for providing a current sampling signal to a metering management MCU. The neutral line current sampling part includes a manganese-copper shunt, a sampling chip and an isolation transformer. The manganese-copper shunt samples the neutral line current, the sampling chip processes the sampling signal, and the isolation transformer isolates and couples the processed sampling signal to the metering management MCU.

[0005] However, the resistance value of the shunt (usually manganese-copper alloy) changes significantly with temperature (typical temperature drift coefficient is ±50ppm / ℃), and the current measurement error can exceed 5% under high-temperature working conditions, which seriously affects the SOC estimation accuracy and overcurrent protection reliability of the battery management system (BMS). The micro-voltage difference signal output by the shunt needs to be amplified by more than 100 times to be collected by the ADC, but the conventional amplification circuit is easy to introduce noise, and the common-mode voltage (such as hundreds of volts in motor driving) between the high-voltage side and the low-voltage side will damage the collection circuit. The existing isolation amplifier has limited bandwidth and high cost.

[0006] Therefore, the application provides a shunt-based isolated current sampling device, which solves the core pain points of high-precision current detection in a wide temperature range and a high-noise environment. SUMMARY

[0007] The application aims to provide a shunt-based isolated current sampling device, which calculates the current by combining shunt temperature drift compensation with amplification of the shunt voltage, thereby solving the problems of existing high-precision current detection in a wide temperature range and a high-noise environment.

[0008] To solve the above technical problems, the application is implemented by the following technical scheme: The application is a shunt-based isolated current sampling device, which comprises: A shunt connected in a to-be-measured circuit, wherein an output end of the shunt is connected with an isolation amplifier; An output end of the isolation amplifier is connected with an operational amplifier, and the operational amplifier is further connected with a 2.5V reference chip; An output end of the operational amplifier is connected with an MCU; When the current flows through the shunt, a voltage difference generated across the shunt is isolated and amplified by the isolation amplifier, and then transmitted to the operational amplifier, and the output signal of the operational amplifier is output to the MCU after being raised by 2.5V by the reference chip for calculation of the to-be-measured current value, and the resistance of the shunt is compensated by detecting the temperature of the shunt.

[0009] Further, a thermistor is arranged on the shunt, the resistance of the thermistor is detected, the real-time temperature of the shunt is obtained according to an RT fitting curve, and the resistance of the shunt is compensated.

[0010] Further, the resistance of the thermistor is converted into a voltage by a voltage dividing circuit, the converted voltage is collected by an ADC of the MCU, the temperature corresponding to the thermistor is obtained by the MCU by looking up a table, and the resistance of the shunt is calculated according to the obtained temperature.

[0011] Further, a temperature acquisition module is further included, and the temperature acquisition module is connected with the MCU.

[0012] Further, the temperature value of the shunt is detected in real time by the temperature acquisition module, and the resistance of the shunt is compensated.

[0013] Further, the shunt is connected in series in the to-be-measured circuit, and the voltage difference generated after the current I flows through the shunt is V 压差 =I*R 分流器 , wherein R 分流器 is the resistance of the shunt.

[0014] Further, the isolation amplifier is powered by a 5V power supply, and a power supply isolation module is arranged to supply power to the high-voltage side of the isolation amplifier, and an isolation type DC-DC converter is usually used.

[0015] Further, the isolation amplifier isolates and amplifies the voltage difference generated across the shunt by 8 times, and the output voltage is: 8* the voltage difference generated across the shunt.

[0016] Further, the operational amplifier amplifies the voltage output by the isolation amplifier by 4 times, and after superimposing a 2.5V reference, the output voltage range is 0.34-4.66V.

[0017] Further, the MCU calculates the measured current value according to the voltage output by the operational amplifier in combination with the compensated shunt resistance.

[0018] The present application has the following beneficial effects: The present application has the following beneficial effects:

[0019] Of course, any product implementing the present application does not necessarily need to achieve all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 The schematic diagram of the shunt-based isolation type current sampling device of the present application; Figure 2 The flow chart of the shunt-based isolation type current sampling device of the present application. DETAILED DESCRIPTION

[0022] In the following description, specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. However, persons skilled in the art will understand that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits and methods are omitted so as not to obscure the description of the present application with unnecessary details.

[0023] It should be understood that the word “comprise” or variations such as “comprises” or “comprising”, when used in this specification and in the accompanying claims, indicate the presence of the described features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0024] It should also be understood that the term “and / or” when used in this specification and in the following claims is intended to mean one or the other or both of the associated listed items and includes the possibility of combinations thereof.

[0025] As used in this specification and in the appended claims, the term “if’ can be interpreted as meaning “when” or “once” or “in response to determining” or “in response to detecting”, depending on the context. Similarly, the phrase “if it is determined” or “if [the described condition or event] is detected” can be interpreted as meaning “once it is determined” or “in response to determining” or “once [the described condition or event] is detected” or “in response to detecting [the described condition or event]”, depending on the context.

[0026] In addition, the terms “first”, “second”, “third”, etc. as used in the description of the application and the appended claims are only used to distinguish descriptions, and cannot be understood as indicating or implying relative importance.

[0027] Reference in the specification to “one embodiment” or “some embodiments” or “an embodiment” or “some embodiments” etc. means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. Thus, the appearances of the phrases “in one embodiment”, “in some embodiments”, “in other embodiments”, “in additional embodiments”, etc. in various places in the specification are not necessarily all referring to the same embodiment, unless otherwise specifically noted. The terms “comprise”, “comprises”, “comprising”, “include”, “includes”, “including” and variants thereof are meant to be open-ended, meaning that they include but are not limited to the listed features, integers, steps, operations, elements, and / or components, unless otherwise specifically noted.

[0028] Embodiment One: Referring to Figure 1 The present application provides a shunt-based isolated current sampling device; As an embodiment of the application, the shunt-based isolated current sampling device specifically comprises: a shunt, an isolation amplifier, an operational amplifier, a reference chip, a thermistor, a current measurement module, a temperature acquisition module, a power supply isolation module, and a 5V power supply; both isolation amplification and anti-interference are realized, and real-time temperature compensation is performed to suppress drift, thereby solving the problem of current detection in a wide temperature range and a high-noise environment. In new energy automobile electric control systems, intelligent power grid protection devices, industrial robot servo drives, and other scenarios, the response speed of overcurrent protection, the accuracy of energy management, and the service life of equipment can be significantly improved.

[0029] The shunt is connected in a to-be-detected circuit, and an output end of the shunt is connected with the isolation amplifier; An output end of the isolation amplifier is connected with the operational amplifier; the operational amplifier is also connected with the 2.5V reference chip; An output end of the operational amplifier is connected with the MCU; When current flows through the shunt, a voltage difference generated at both ends of the shunt is isolated and amplified by the isolation amplifier, and then transmitted to the operational amplifier; the operational amplifier outputs a signal after the signal is raised by 2.5V by the reference chip, and then outputs the signal to the MCU for to-be-detected current value calculation; the resistance value of the shunt is compensated by detecting the temperature of the shunt; the calibration process is simplified and the BOM cost is reduced by the device, and the device is particularly suitable for compact devices (such as unmanned aerial vehicle electric governors and servo drives) with limited space.

[0030] As an embodiment provided by the application, preferably, an isolated precision amplifier is adopted to process millivolt-level voltage differences, so that common-mode interference is suppressed and high and low voltage electrical isolation is realized, thereby ensuring the stability of the system in a complex EMC environment such as a frequency converter or a photovoltaic inverter.

[0031] As an embodiment provided by the application, preferably, the device further comprises a thermistor arranged on the shunt; the resistance value of the thermistor is detected, the real-time temperature of the shunt is obtained according to an RT fitting curve, and the resistance value of the shunt is compensated.

[0032] As an embodiment provided by the application, preferably, the resistance value of the thermistor is converted into a voltage through a voltage dividing circuit, the converted voltage is collected by an ADC of the MCU, the temperature corresponding to the thermistor is obtained by the MCU through table lookup, and the resistance value of the shunt is calculated according to the obtained temperature.

[0033] As an embodiment provided by the application, preferably, the device further comprises a temperature acquisition module, and the temperature acquisition module is connected with the MCU.

[0034] As an embodiment provided by the application, preferably, the temperature value of the shunt is detected in real time by the temperature acquisition module, and the resistance value of the shunt is compensated.

[0035] As an embodiment provided by the present application, preferably, the temperature of the shunt is monitored in real time by the integrated temperature acquisition module, and the R value is dynamically corrected in combination with a preset resistance-temperature curve (such as a quadratic fitting formula), so that the measurement error in the full temperature range (-40℃-125℃) is compressed to within 1%.

[0036] As an embodiment provided by the present application, preferably, the shunt is connected in series in the loop to be measured, and the voltage difference generated after the current I flows through the shunt is: V 压差 =I*R 分流器 , wherein R 分流器 is the resistance of the shunt.

[0037] As an embodiment provided by the present application, preferably, the resistance R 分流器 of the shunt is usually small (milliohm level), for example, 2 mΩ. When the current I flows through, the voltage difference generated is: V 压差 =I*R 分流器 . If the current is 50 A, then: V 压差 =50A*0.002Ω=100mV.

[0038] As an embodiment provided by the present application, preferably, the isolation amplifier is powered by a 5V power supply, and a power isolation module is arranged to supply power to the high-voltage side of the isolation amplifier. An isolated DC-DC converter is usually used.

[0039] As an embodiment provided by the present application, preferably, the isolation amplifier isolates and amplifies the voltage difference generated across the shunt by 8 times, and the output voltage is: 8*the voltage difference generated across the shunt.

[0040] As an embodiment provided by the present application, preferably, the isolation amplifier adopts magnetic isolation or capacitive isolation technology, such as ADI's ADuM3190 or TI's AMC3330, to provide isolation between the high-voltage side and the low-voltage side, ensuring safety. The output of the isolation amplifier is: V 隔离放大器 = 8 * V 压差 .

[0041] As an embodiment provided by the present application, preferably, the operational amplifier amplifies the voltage output by the isolation amplifier by 4 times, and after superimposing a 2.5V reference, the output voltage range is 0.34-4.66V.

[0042] As an embodiment provided by the present application, preferably, a 2.5V reference source (such as REF5025) is connected to the operational amplifier circuit for level lifting, and the output of the operational amplifier is: V_out = 2.5V + (V 压差 * total gain).

[0043] As an embodiment provided by the application, preferably, total gain = isolation amplifier gain * operational amplifier gain = 8 * 4 = 32 times, and the operational amplifier output is: V_out = 2.5V + (I * R 分流器 * 32).

[0044] As an embodiment provided by the application, preferably, the MCU calculates the measured current value according to the voltage output by the operational amplifier and the compensated shunt resistance value.

[0045] Embodiment two: As embodiment two of the application, it specifically includes: The shunt is connected in series in the measured circuit, and the output end of the shunt is connected with the isolation amplifier; the output end of the isolation amplifier is connected with the operational amplifier; the operational amplifier is further connected with the 2.5V reference chip; the voltage difference generated at both ends of the shunt is transmitted to the operational amplifier after isolation and amplification by the isolation amplifier; The current measurement module is a current sensor; The input end of the isolation amplifier is connected with the shunt, and the power supply used is the isolated 5V power supply; the output end is connected with the amplifier, and the power supply used is the non-isolated 5V power supply; The output side power supply pin (VCC_OUT) of the isolation amplifier is connected to the output end of the power supply isolation module, and the power supply isolation module usually adopts transformer isolation, and the output side is before isolation and the input side is after isolation; The output of the 5V power supply is connected to the input end of the power supply isolation module through a wire, such as the VIN+ and VIN- of the DC-DC module, to provide input power for it.

[0046] The output end of the power supply isolation module, such as VOUT+ and VOUT-, has no direct electrical connection with the input end of the 5V power supply; The output signal of the isolation amplifier, that is, the differential signal, is connected to the input end of the operational amplifier (OPA).

[0047] The 2.5V reference source is used as the bias voltage of the OPA, and is usually connected to the positive input end of the OPA or used for level offset, to adjust the signal to the single-ended voltage range suitable for the MCU.

[0048] The output end (labeled as OUT, ranging from 0.34V to 4.66V) of the OPA is directly connected to the analog input pin (ADC) of the MCU, for subsequent sampling and processing. The Vout and thermistor signals are respectively connected to the ADC; and T→R 分流器 →I is calculated in real time through software, to improve flexibility.

[0049] An operational amplifier (OPA) is used to combine a 2.5V reference source to perform signal level shift or proportional adjustment, so as to ensure that the output voltage is within the compatible range of the MCU ADC. The 2.5V reference source provides a bias voltage for the operational amplifier, so as to ensure that the output signal is positive, facilitating the measurement of the alternating current signal. Embodiment three Please refer to Figure 2 The application provides a sampling flowchart of the shunt-based isolated current sampling device. As embodiment three of the application, the specific method for sampling of the shunt-based isolated current sampling device comprises the following steps: The shunt is connected in series in the to-be-measured circuit. When the current flows through the shunt, a voltage difference is generated at both ends of the shunt. The tiny voltage difference is isolated, amplified and then output. By detecting the output voltage and dividing the amplification multiple, the actual voltage at both ends of the shunt is obtained. According to Ohm's law I=U / R, the to-be-measured current value can be obtained. The shunt is connected in series in the to-be-measured circuit. When the current flows through the shunt, a tiny voltage difference is generated at both ends of the shunt. The voltage difference signal is isolated and amplified by the isolation voltage amplifier and then transmitted to the operational amplifier. The 2.5V reference chip is connected with the operational amplifier. The output signal of the operational amplifier is lifted by 2.5V. Through the formula: to-be-measured current=(output signal-2.5V) / (amplification multiple*R), the to-be-measured current can be obtained.

[0050] As an embodiment provided by the application, preferably, the temperature acquisition module can detect the temperature of the shunt in real time and compensate for the resistance value of the shunt.

[0051] As an embodiment provided by the application, preferably, when the temperature of the shunt is too high, the shunt will generate temperature drift, resulting in a large current error. By detecting the resistance value of the thermistor, the real-time temperature of the shunt can be obtained according to the RT fitting curve, so as to compensate for the shunt.

[0052] In the description of the present specification, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0053] The preferred embodiments of the application disclosed above are only to facilitate the elucidation of the application. The preferred embodiments do not describe all the details of the application and limit the application to the specific embodiments described. Obviously, many modifications and variations can be made in light of the teachings above. The description is chosen and described in order to best explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and get the best results from the application. The application is only limited by the claims and their full scope and equivalents.

Claims

1. An isolated current sampling device based on a shunt, characterized in that, The application relates to a current measurement device. The device comprises a shunt connected in a circuit to be measured, an isolation amplifier connected to the output end of the shunt, an operational amplifier connected to the output end of the isolation amplifier, a 2.5V reference chip connected to the operational amplifier, and an MCU connected to the output end of the operational amplifier. When current flows through the shunt, the voltage difference generated at the two ends of the shunt is isolated and amplified by the isolation amplifier, and then transmitted to the operational amplifier. The output signal of the operational amplifier is lifted by 2.5V by the reference chip, and then output to the MCU for calculation of the current value to be measured. The resistance value of the shunt is compensated by detecting the temperature of the shunt.

2. The shunt-based isolated current sensing device of claim 1, wherein, The device further comprises a thermistor arranged on the shunt.

3. The shunt-based isolated current sensing device of claim 2, wherein, The resistance value of the thermistor is converted into voltage by a voltage dividing circuit.

4. The shunt-based isolated current sensing device of claim 1, wherein, The converted voltage is collected by the ADC of the MCU.

5. The shunt-based isolated current sensing device of claim 4, wherein, The MCU obtains the temperature corresponding to the thermistor by looking up a table, and calculates the resistance value of the shunt according to the obtained temperature.

6. The shunt-based isolated current sensing device of claim 1, wherein, The shunt is connected in series in the loop to be measured, and the voltage difference generated after current I flows through the shunt is: 压差 =I*R 分流器 Where R 分流器 is the resistance of the shunt.

7. The shunt-based isolated current sensing device of claim 1, wherein, The device further comprises a temperature acquisition module connected to the MCU.

8. The shunt-based isolated current sensing device of claim 1, wherein, The temperature value of the shunt is detected in real time by the temperature acquisition module, and the resistance value of the shunt is compensated.

9. The shunt-based isolated current sensing device of claim 1, wherein, The isolation amplifier is powered by a 5V power supply and provided with a power isolation module to supply power to the high-voltage side of the isolation amplifier.

10. The shunt-based isolated current sensing device of claim 1, wherein, The isolation amplifier isolates and amplifies the voltage difference generated at the two ends of the shunt by 8 times, and the output voltage is 8 times the voltage difference generated at the two ends of the shunt. The operational amplifier amplifies the voltage output by the isolation amplifier by 4 times, and the output voltage range is 0.34-4.66V after superimposing the 2.5V reference. The MCU calculates the current value to be measured according to the voltage output by the operational amplifier and the compensated resistance value of the shunt.

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