CN114859093A

CN114859093A - Current sensing based on current divider

Info

Publication number: CN114859093A
Application number: CN202210475342.3A
Authority: CN
Inventors: 徐久方; 凌欢; 吴瑞; 张秀清
Original assignee: Anhui Hongtron New Energy Power Co ltd
Current assignee: Anhui Hongtron New Energy Power Co ltd
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2022-08-05

Abstract

The invention discloses a current sensor based on a shunt, wherein the current sensor is provided with two copper bars for connecting a device to be acquired, two ends of a sampling resistor of the shunt are respectively connected to the two copper bars, the output end of the shunt is connected to the input end of an MCU (microprogrammed control unit) through a filter circuit, an A/D (analog/digital) conversion circuit and an isolation circuit, the output end of the MCU is connected with a CAN (controller area network) interface, and the CAN interface is used for connecting an automobile CAN bus. The current sensor can measure bidirectional direct current through the shunt, and the module is completely isolated from high and low voltages and can be applied to the total positive end or the total negative end of a battery system. The power supply voltage range of the current sensor module is + 3.3V- + 5V. The module will minimize the resistance variation due to temperature variation, and the module communication is external communication using a CAN2.0B interface.

Description

Current sensing based on shunt

Technical Field

The invention relates to the field of component measurement, in particular to a device for measuring current in a circuit by using a current divider.

Background

Nowadays, the mileage and torque requirements of electric vehicles are higher and higher, which correspondingly requires that a battery pack provides higher power, and the higher the power and the higher the current, which correspondingly requires that a current sensor needs to measure a larger measurement range, and the controller volume of the motor is smaller, which requires that the volume of the current sensor is smaller under the condition of the larger measurement range.

The current is measured by a Hall current sensor which is provided in the market at present, the measurement of the Hall current sensor is based on the Hall principle, namely, a bus penetrates through the Hall sensor, and the current value is obtained through electromagnetic induction. The hall sensor has the disadvantages of not particularly high precision, not high flexibility, temperature drift, zero drift and the like.

The current divider is manufactured according to the principle that voltage is formed at two ends of a resistor when current passes through the resistor, is commonly used for current sharing sampling detection and has two types of slot type and non-slot type. The current divider is used for measuring the current, and the good linearity can be kept in the whole measuring range, but the measuring accuracy is slightly poor.

Disclosure of Invention

The invention aims to solve the technical problem of realizing a high-precision current sensor based on a shunt, which is used for solving the defects of monitoring and feedback of current in a high-precision current loop, thereby improving the input and output precision of the current and meeting the technical requirements of products.

In order to achieve the purpose, the technical scheme adopted by the invention is that the current sensor based on the shunt is provided with two copper bars for connecting a device to be acquired, two ends of a sampling resistor of the shunt are respectively connected to the two copper bars, an output end of the shunt is connected to an input end of an MCU (microprogrammed control unit) through a filter circuit, an A/D (analog/digital) conversion circuit and an isolation circuit, an output end of the MCU is connected with a CAN (controller area network) interface, and the CAN interface is used for connecting an automobile CAN bus.

Two the copper bar is fixed outside current sensor's casing, shunt, filter circuit, AD converting circuit, buffer circuit, MCU are fixed in the casing, the CAN interface is fixed at the casing tip.

Each copper bar is provided with a bus current connecting hole, and the two ends of each copper bar are welded to the corresponding copper bar in a welding mode.

The current sensor monolithic stationary is in the casing based on the shunt, the casing is the cuboid structure, and only one end opening is used for fixed CAN interface, the copper bar is fixed at housing face and is stretched out the casing, the connecting hole stretches out the part of casing at the copper bar, housing face has paintd the shielding lacquer layer, sampling resistance is high-accuracy low temperature ticket resistance, sampling resistance terminal connection voltage sampling circuit, voltage sampling circuit are symmetrical difference amplifier circuit, difference amplifier circuit supply voltage 7V, low temperature ticket resistance terminal connection difference amplifier circuit Vin1 and Vin 2. And the output tail end V0 of the differential amplification circuit is connected with the Ui end of the filter circuit, the tail end U0+ of the filter circuit is connected with the input end of the A/D converter, and the filter circuit U0-is grounded.

The current divider comprises two identical A1 operational amplifier circuits and an A2 operational amplifier circuit to form an input stage, the anode of the input end of the A1 operational amplifier circuit is connected with a sampling resistance binding post through a resistor R1, the anode of the input end of the A2 operational amplifier circuit is connected with the other sampling resistance binding post through a resistor R2, the output end of the A1 operational amplifier circuit is connected with the output end of the A2 operational amplifier circuit through a resistor R4, a resistor R3 and a resistor R5 which are sequentially connected in series, the cathode of the input end of the A1 operational amplifier circuit is connected between the resistor R4 and the resistor R3, the cathode of the input end of the A2 operational amplifier circuit is connected between a resistor R5 and a resistor R3, the series-connected resistor R4, a resistor R3 and a resistor R5 are connected in parallel with a capacitor C1, the output end of the A1 operational amplifier circuit is connected with the anode of the input end of the A3 operational amplifier circuit through a resistor R6, the output end of the A2 operational amplifier circuit is connected with the cathode of the input end of the A3 through a resistor R7, the output end of the A1 operational amplifier circuit is grounded through a resistor R6 and a resistor R9, and the output end of the A2 operational amplifier circuit is connected with the output end of the A3 operational amplifier circuit through a resistor R7 and a resistor R8.

A3 operational amplifier circuit is low temperature ticket low gain operational amplifier circuit, A1 and A2 operational amplifier circuit are low temperature ticket, high gain's operational amplifier circuit, electric capacity C1 is filter capacitor, resistance R1, resistance R2, resistance R6, resistance R7, resistance R9 are balanced resistance, resistance R3, resistance R4, resistance R5, resistance R8 are divider resistance, balanced resistance is used for balanced input end offset current.

The A/D conversion circuit selects a highly integrated analog-to-digital converter CS5460A with a conversion bit number of 24 bits, a high-speed electric energy calculation function and a serial interface. The A/D conversion circuit converts the analog signal into a digital signal and is connected with the VI port of the isolation circuit through the output port.

The isolation circuit selects a four-channel digital isolator with multi-channel configuration and output enabling functions for isolation and connection, a logic memory in the isolation circuit is an RAM memory, and the isolation circuit connects an output port V0 of the isolator with an input end SPI of the MCU.

The MCU is used for carrying out logic judgment on input signals, a timer, a communication interface, a power manager and a watchdog timer are arranged in the MCU, and the MCU is used for connecting the output end SPI of the micro control unit with the input port of the CAN.

The CAN interface output port is connected with the outside through a connector, the CAN interface is a connector provided with four Pin pins, wherein Pin a is a power supply VCC, Pin b is CAN _ L, Pin c is CAN _ H, and Pin d is GND.

The current sensor can measure bidirectional direct current through the shunt, and the module is completely isolated from high and low voltages and can be applied to the total positive end or the total negative end of a battery system. The power supply voltage range of the current sensor module is + 3.3V- + 5V. The module can reduce the resistance value change caused by temperature change to the minimum, and module communication adopts a CAN2.0B interface to communicate with the outside (default is 500kbit/s, and configurable).

Drawings

The following is a brief description of the contents of each figure and the symbols in the figures in the description of the invention:

FIG. 1 is a schematic diagram of a circuit of an internal structure of a sensor;

FIG. 2 is a schematic diagram of the structural form of the appearance of the sensor;

FIG. 3 is a schematic diagram of the internal structure of the sensor;

FIG. 4 is a schematic diagram of a low pass filter circuit;

FIG. 5 is a schematic diagram of a high pass filter circuit;

FIG. 6 is a block diagram of an A/D converter of the present invention;

FIG. 7 is a schematic diagram of an isolation circuit;

FIG. 8 is a block diagram of an MCU of the present invention;

FIG. 9 is a schematic diagram of a CAN interface structure of the present invention;

FIG. 10 is a schematic view of a diverter according to the present invention

The labels in the above figures are: 1. copper bars; 2. a current wiring hole; 3. sampling a resistor; 4. a measuring unit; 5. a voltage acquisition module; 6. and a CAN interface.

Detailed Description

The following description of the embodiments with reference to the drawings is provided to describe the embodiments of the present invention, and the embodiments of the present invention, such as the shapes and configurations of the components, the mutual positions and connection relationships of the components, the functions and working principles of the components, the manufacturing processes and the operation and use methods, etc., will be further described in detail to help those skilled in the art to more completely, accurately and deeply understand the inventive concept and technical solutions of the present invention.

The invention is a current sensor based on a shunt, and changes the traditional measuring method into the method that the measuring part of the shunt is completely integrated on the shunt, thus the whole current measuring and feedback loop can be shortened, and the voltage acquisition uses a differential amplifying circuit to reduce the signal interference factor and the measuring error.

The current sensor is mainly divided into three parts, wherein the first part is a large-current connecting copper bar 1, the second part is a measuring unit 4 and is also the core of the whole sensor, and the third part is a CAN communication part. The measuring unit 4 comprises a current divider, a filter circuit, an A/D conversion circuit and an isolation circuit. And (3) current measurement process: the method comprises the steps of firstly electrifying a current sensor, when current passes through a shunt, the current passes through a low-temperature drift resistor, the shunt measures a voltage signal, the voltage signal is amplified by a differential amplification circuit and then sent to a filter circuit to filter noise waves, then the voltage signal is connected to an analog quantity input end of an A/D (analog-to-digital) converter, a digital signal is obtained after the voltage signal passes through an analog-to-digital converter, the digital signal is output by the A/D converter and then output to an MCU (microprogrammed control unit) through an isolation circuit, and after the MCU performs logic judgment, data is output to a CAN (controller area network) bus through a CAN interface 6.

As shown in fig. 10, the shunt is formed by two identical a1 operational amplifier circuits and a2 operational amplifier circuits as input stages, the anode of the input terminal of the a1 operational amplifier circuit is connected to a sampling resistor binding post through a resistor R1, the anode of the input terminal of the a2 operational amplifier circuit is connected to another sampling resistor binding post through a resistor R2, the output terminal of the a1 operational amplifier circuit is connected to the output terminal of the a2 operational amplifier circuit through a resistor R4, a resistor R3 and a resistor R5 which are connected in series in sequence, the cathode of the input terminal of the a1 operational amplifier circuit is connected between a resistor R4 and a resistor R4, the cathode of the input terminal of the a 4 operational amplifier circuit is connected to the anode of the input terminal of the a 4 operational amplifier circuit, the output terminal of the a 4 operational amplifier circuit is connected to the anode of the input terminal of the a 4 operational amplifier circuit through a resistor R4, the cathode of the operational amplifier circuit of the a 4 is connected to the input terminal of the a 4 operational amplifier circuit through a 4, and the cathode of the resistor R4 circuit is connected to the input terminal of the operational amplifier circuit through a 4, the resistor R4, The resistor R9 is grounded, and the output end of the A2 operational amplifier circuit is connected with the output end of the A3 operational amplifier circuit through the resistor R7 and the resistor R8.

The operational amplifier differential amplification circuit is added at the sampling end, so that the effect of stabilizing working voltage can be achieved, small current measurement can be performed, the design enables the measurement range to be wider, the precision to be higher, the A1 and A2 two identical operational amplifier circuits form an input stage, the input stage and the differential amplifier A3 are connected in series to form a three-operational amplifier differential amplification circuit, and the input stage resistance in the circuit is kept symmetrical and equal.

C1 is a filter capacitor, A1 and A2 select a low-temperature ticket and a high-gain operational amplifier, A3 is a low-temperature ticket and a low-gain operational amplifier, R1, R2, R6, R7 and R9 are balance resistors and are used for balancing input end offset current, and R3, R4, R5 and R8 are divider resistors.

A1 and A2 improve the ratio of differential mode signals to common mode signals, under the condition that the input stage of the circuit is symmetrical, errors of resistance values of the resistors have no influence on common mode rejection of the circuit, the circuit has almost no amplification effect on the common mode signals, and the gain of common mode voltage is very small.

Since R1 ═ R2, R4 ═ R5, R8 ═ R9, and R6 ═ R7, the two-stage differential mode gain Q is equal to

Q＝V0/(Vin1+Vin2)＝(R3+R4+R5)/R3*(R9/R6)

Because the first-stage gain amplification factor of the differential amplification circuit is 10-100 times, and the second-stage gain amplification factor is about 1-2 times, the voltage can obtain a very high amplification factor after passing through the first-stage and second-stage amplification circuits, and the current sensor can measure a small current of several milliamperes.

Whole current sensor fixes in the casing, and two copper bars 1 are fixed in the side of casing, and the casing encapsulating is sealed, and the other end is CAN interface 6, directly with the CAN plug connection on the car. The shunt includes sampling resistor 3 and voltage acquisition module 5, sampling resistor 3 welds both ends to copper bar 1 through the welded mode, when the electric current passes through two electric current wiring hole 2 on copper bar 1 and flows through the shunt, can form a collection voltage at sampling resistor 3 both ends, this voltage signal generally is 0-75mV, sampling resistor 3's resistance is known, voltage acquisition module 5 obtains its voltage U through wiring terminal connection sampling resistor 3 both ends, can know the current value I that flows through in the sampling resistor 3 through formula I ═ U/R. The TCR (temperature coefficient of resistance) is the key point of selection in the whole design, the low temperature drift resistance refers to the resistance with small resistance value change along with the temperature, the temperature drift of the resistance is the TCR, and the low temperature drift resistance is divided into a low temperature drift thin film resistance and a low temperature drift precision resistance.

Therefore, two schemes can be provided, the first scheme is to use a low-temperature drift film resistor as a shunt sampling resistor 3, the low-temperature drift film resistor can meet the measurement of medium and high resistance values and can have higher precision through larger current, the second scheme is to use a low-temperature ticket precision resistor, and the use of the low-temperature ticket precision resistor has the advantage of providing extremely high measurement precision which can generally reach 0.01%. Compared with the common resistor, the low-temperature drift resistor has the difference that the self temperature change of the resistor is very small along with the rise of the current, and can be widely applied to the measurement of high-temperature environments such as a motor controller and the like.

As shown in fig. 4 and 5, because noise is mixed in the filter circuit during signal transmission, a filter circuit is introduced, Ui represents an input voltage, R represents a protection resistor, C represents a filter capacitor, Uo represents a filter output voltage, RL represents an internal resistance of the circuit, a high-pass circuit allows a signal higher than a set frequency to pass through, and does not allow a signal lower than the set frequency to pass through, a low-pass circuit corresponds to a high-pass circuit, that is, the signal lower than the set frequency is blocked very little, and the signal higher than the set frequency is blocked very much, and a high-frequency signal or a low-frequency signal exceeds a limit value in an EMC battery compatibility test of an automobile part, at this time, the use of the high-pass filter circuit and the low-pass circuit can improve a test result, and the low-pass circuit and the high-pass circuit are selected according to practical application conditions.

The a/D conversion circuit is shown in fig. 6, the a/D converter has various forms, the difference of the forms can affect the precision after measurement, and its main function is to convert the analog electronic quantity into digital quantity, so that the output digital quantity is in direct proportion to the input analog electronic quantity to realize the conversion function. In the a/D conversion process, since the input analog electronic quantity signal is continuous and the output digital signal is discrete, the input analog quantity signal is sampled at a certain frequency during the analog-to-digital conversion. The a/D conversion needs to go through four stages of sampling, holding, quantizing, and encoding. Sampling is to perform timing measurement sampling on continuously-changed analog electronic signals, and the denser the sampling is, the closer the circuit output signal is to an input value, so that a certain requirement is imposed on the sampling frequency, and the sampling frequency fs is more than or equal to 2fImay, wherein fImay is the highest frequency in the frequency spectrum of the input signal; the keeping is to store the collected signals for a period of time; quantization is a process of converting a sampling voltage into integral multiples of a certain minimum unit voltage delta, and divided levels are called quantization levels, wherein the more the levels are, the better the levels are, and A is called a quantization unit; the coding is to represent the quantized quantization level by a binary code. In practical application, a highly integrated analog-to-digital converter CS5460A with a conversion bit number of 24 bits, high-speed power calculation function and a serial interface is selected.

Isolation as shown in fig. 7, communication signals of the current sensor can be interfered by various kinds during transmission, the sensor uses a signal isolator to ensure the stability of the signals, the isolator is added to separate high voltage and low voltage of the circuit and protect the low voltage circuit from being interfered by the high voltage circuit, a four-channel digital isolator with multi-channel configuration and output enabling function is selected between the a/D converter and the MCU for isolation and connection, an internal logic memory is a RAM memory, logic input and output buffers of the devices are isolated by TI silica isolation shielding, a data rate of not less than 500kbps at the lowest and various channel configurations are supported, two ends of a selected model can be powered by a 5V power supply, the model is compatible with a low voltage system and can realize a voltage conversion function, a default output control pin is required to be selected, and the pin can define a logic state adopted when no input power supply exists, meanwhile, a layer of shielding paint is uniformly coated on the sensor shell, the paint can play a role in conducting after being dried to form a paint film, so that the electromagnetic wave interference shielding function is achieved, and the shielding paint is prepared by adding conductive metal powder into a specific resin raw material to prepare a paint coating capable of being sprayed.

The MCU, i.e., the MCU, is a micro control unit, as shown in fig. 8, and the micro control unit performs logic judgment on the input signal. The Timer of MCU selects Programmable Timer, the Timer timing can be controlled by user program, the control method includes: selecting a clock source, selecting a frequency division number (Prescale), setting a preset number and the like. The external interruption is triggered by adopting a rising edge, and is automatically triggered when the input signal is greater than a set value. The communication interface adopts an SPI interface, the interface is the most basic communication mode provided by most MCUs, and data transmission is controlled by a synchronous clock. Band gap forbidden Band width, the difference in energy between the lowest point of the conduction Band and the highest point of the valence Band, also called energy gap. The IO port is directly read and written, and when an IO port reading instruction is executed, the IO port is an input port; when the write IO port instruction is executed, the write IO port instruction is automatically the output port. The RAM memory is adopted, and the stored data can be cleared after being uploaded, so that the data does not need to be stored for a long time. The power manager selects a DC/DC modulation IC, and the power supply is a direct-current power supply, so that alternating current is not involved, and only voltage rising/reduction regulation is needed. Watchdog is a basic configuration of most MCUs, and this Watchdog satisfies that it allows the program to reset and close it, and provides a self-recovery capability to guarantee that the MCU crashes due to unexpected failure.

The CAN interface 6 uses CAN transmission as shown in fig. 9 because the current sensor may work in an environment with strong electromagnetic noise or long signal transmission distance, and this problem CAN be solved well by using CAN. The CAN is composed of a male/female connector, the number of Pin pins is 4, and as shown in fig. 5, Pin a is a power supply VCC: 12V; pin b is CAN _ L; pin c is CAN _ H; pin d is GND.

And (3) current measurement process: the method comprises the steps of firstly electrifying a current sensor, when current passes through a shunt, the current passes through a low-temperature drift resistor, the shunt measures a voltage signal, the voltage signal passes through a filter circuit to filter noise waves and then is connected to an analog quantity input end of an A/D (analog-to-digital) converter, a digital signal is obtained after the voltage signal passes through an analog-to-digital converter, the A/D converter outputs the digital signal to an MCU (micro control unit) through an isolation circuit, and the MCU outputs data to a CAN bus through a CAN interface after logical judgment.

The invention has been described above with reference to the accompanying drawings, it is obvious that the invention is not limited to the specific implementation in the above-described manner, and it is within the scope of the invention to apply the inventive concept and solution to other applications without substantial modification.

Claims

1. A shunt-based current sensor, comprising: current sensor is equipped with and is used for connecting two copper bars of treating the collection device, and the sampling resistance both ends of shunt are connected to respectively on two copper bars, the shunt output is connected to the MCU input through filter circuit, AD converting circuit, buffer circuit, the CAN interface is connected to the MCU output, the CAN interface is used for connecting car CAN bus.

2. The shunt-based current sensor of claim 1, wherein: two the copper bar is fixed outside current sensor's casing, shunt, filter circuit, AD converting circuit, buffer circuit, MCU are fixed in the casing, the CAN interface is fixed at the casing tip.

3. The shunt-based current sensor of claim 2, wherein: each copper bar is provided with a bus current connecting hole, and the two ends of each copper bar are welded to the corresponding copper bar in a welding mode.

4. The shunt-based current sensor of claim 3, wherein: the current sensor monolithic stationary is in the casing based on the shunt, the casing is the cuboid structure, and only one end opening is used for fixed CAN interface, the copper bar is fixed at housing face and is stretched out the casing, the connecting hole stretches out the part of casing at the copper bar, housing face has paintd the shielding lacquer layer, sampling resistance is high-accuracy low temperature ticket resistance, sampling resistance terminal connection voltage sampling circuit, voltage sampling circuit are symmetrical difference amplifier circuit, difference amplifier circuit supply voltage 7V, low temperature ticket resistance terminal connection difference amplifier circuit Vin1 and Vin 2. And the output tail end V0 of the differential amplification circuit is connected with the Ui end of the filter circuit, the tail end U0+ of the filter circuit is connected with the input end of the A/D converter, and the filter circuit U0-is grounded.

5. The shunt-based current sensor of any one of claims 1-4, wherein: the current divider is composed of two identical A1 operational amplifier circuits and an A2 operational amplifier circuit to form an input stage, the anode of the input end of the A1 operational amplifier circuit is connected with a sampling resistor through a resistor R1, the anode of the input end of the A2 operational amplifier circuit is connected with another sampling resistor through a resistor R2, the output end of the A1 operational amplifier circuit is connected with the output end of the A2 operational amplifier circuit through a resistor R4, a resistor R3 and a resistor R5 which are sequentially connected in series, the cathode of the input end of the A1 operational amplifier circuit is connected between a resistor R4 and a resistor R4, the cathode of the input end of the A4 operational amplifier circuit is connected between the resistor R4 and the resistor R4, the series-connected resistor R4, the resistor R4 and the resistor R4 are connected in parallel with a capacitor C4, the output end of the A4 operational amplifier circuit is connected with the anode of the input end of the A4 operational amplifier circuit through the resistor R4, the output end of the A4 operational amplifier circuit is connected with the A4 through the resistor R4, and the cathode of the output end of the A4 amplifier circuit is connected with the input end of the A4 through the resistor R4, and the output end of the A4 circuit, The resistor R9 is grounded, and the output end of the A2 operational amplifier circuit is connected with the output end of the A3 operational amplifier circuit through the resistor R7 and the resistor R8.

6. The shunt-based current sensor of claim 5, wherein: a3 operational amplifier circuit is low temperature ticket low gain operational amplifier circuit, A1 and A2 operational amplifier circuit are low temperature ticket, high gain's operational amplifier circuit, electric capacity C1 is filter capacitor, resistance R1, resistance R2, resistance R6, resistance R7, resistance R9 are balanced resistance, resistance R3, resistance R4, resistance R5, resistance R8 are divider resistance, balanced resistance is used for balanced input end offset current.

7. The shunt-based current sensor of claim 6, wherein: the A/D conversion circuit selects a highly integrated analog-to-digital converter CS5460A with a conversion bit number of 24 bits, a high-speed electric energy calculation function and a serial interface. The A/D conversion circuit converts the analog signal into a digital signal and is connected with the VI port of the isolation circuit through the output port.

8. The shunt-based current sensor of claim 7, wherein: the isolation circuit selects a four-channel digital isolator with multi-channel configuration and output enabling functions for isolation and connection, a logic memory in the isolation circuit is an RAM memory, and the isolation circuit connects an output port V0 of the isolator with an input end SPI of the MCU.

9. The shunt-based current sensor of claim 8, wherein: the MCU is used for carrying out logic judgment on input signals, a timer, a communication interface, a power manager and a watchdog timer are arranged in the MCU, and the MCU is used for connecting the output end SPI of the micro control unit with the input port of the CAN.

10. The shunt-based current sensor of claim 9, wherein: the CAN interface output port is connected with the outside through a connector, the CAN interface is a connector provided with four Pin pins, wherein Pin a is a power supply VCC, Pin b is CAN _ L, Pin c is CAN _ H, and Pin d is GND.