CN114859093A - Current sensing based on current divider - Google Patents

Abstract

The invention discloses a current sensor based on a shunt. The current sensor is provided with two copper bars for connecting a device to be collected, and two ends of a sampling resistor of the shunt are respectively connected to the two copper bars. The output end of the shunt The filter circuit, the A/D conversion circuit, and the isolation circuit are connected to the input end of the MCU, and the output end of the MCU is connected to the CAN interface, and the CAN interface is used to connect the vehicle CAN bus. The current sensor of the present invention can measure bidirectional DC current through a shunt, the module is completely isolated from high and low voltage, and can be used in the total positive terminal or the total negative terminal of the battery system. The supply voltage range of the current sensor module is +3.3V to +5V. The module will minimize the resistance change caused by temperature changes, and the module communication uses a CAN2.0B interface to communicate externally.

Description

A shunt-based current sensing

technical field

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

Background technique

Nowadays, the mileage and torque requirements of electric vehicles are getting higher and higher, which accordingly requires the battery pack to provide higher power, and the higher the power, the higher the current, which requires our current sensor to measure a larger The measurement range, and the volume of the motor controller is also getting smaller and smaller, which requires our current sensor to be smaller and smaller when the measurement range is larger.

At present, all Hall current sensors on the market measure the current. The Hall current sensor measurement is based on the Hall principle, that is, passing the bus through the Hall sensor and obtaining the current value through electromagnetic induction. The disadvantage of the Hall sensor is that the accuracy is not particularly high, and the flexibility is not high, and it has problems such as temperature drift and zero drift.

The principle of the shunt to measure the current is based on the formation of a voltage across the resistor when the current passes through the resistor. Using a shunt to measure the current can maintain good linearity over the entire range, but the measurement accuracy is slightly worse.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to realize a high-precision current sensor based on a shunt, which is used to solve the insufficiency of current monitoring and feedback in the high-precision current loop, thereby improving the current input and output accuracy and meeting product technical requirements.

In order to achieve the above purpose, the technical solution adopted in the present invention is a current sensor based on a shunt. The current sensor is provided with two copper bars for connecting the device to be collected, and both ends of the sampling resistor of the shunt are respectively connected to the two copper bars. Above, the output end of the shunt is connected to the input end of the MCU through a filter circuit, an A/D conversion circuit, and an isolation circuit, and the output end of the MCU is connected to a CAN interface, and the CAN interface is used to connect to the car CAN bus.

The two copper bars are fixed outside the casing of the current sensor, the shunt, the filter circuit, the A/D conversion circuit, the isolation circuit and the MCU are fixed in the casing, and the CAN interface is fixed at the end of the casing.

Each of the copper bars is provided with a busbar current connection hole, and both ends of each of the copper bars are welded to the copper bars by welding.

The shunt-based current sensor is integrally fixed in the casing, the casing is a cuboid structure, and only one end is open for fixing the CAN interface. The copper bar is fixed on the surface of the casing and protrudes out of the casing. On the part of the copper bar extending out of the casing, the casing surface is coated with a shielding paint layer, the sampling resistor is a high-precision low-temperature ticket resistance, and the terminal terminal of the sampling resistor is connected to a voltage sampling circuit, and the voltage sampling circuit is a symmetrical differential Amplifying circuit, the power supply voltage of the differential amplifying circuit is 7V, and the low-temperature ticket resistance terminal is connected to the differential amplifying circuit Vin1 and Vin2. The output terminal V0 of the differential amplifier circuit is connected to the terminal Ui of the filter circuit, the terminal U0+ of the filter circuit is connected to the input terminal of the A/D converter, and the filter circuit U0- is grounded.

The shunt is composed of two identical A1 operational amplifier circuits and A2 operational amplifier circuits as an input stage. The positive pole of the input terminal of the A1 operational amplifier circuit is connected to a sampling resistor binding post through the resistor R1, and the input of the A2 operational amplifier circuit is connected. The positive terminal of the terminal is connected to another sampling resistor terminal through the resistor R2. The output end of the A1 operational amplifier circuit is connected to the output end of the A2 operational amplifier circuit through the resistor R4, the resistor R3 and the resistor R5 in series in sequence. The negative pole of the input terminal is connected between the resistor R4 and the resistor R3, the negative pole of the input terminal of the A2 operational amplifier circuit is connected between the resistor R5 and the resistor R3, and the resistor R4, the resistor R3 and the resistor R5 in series are connected in parallel with the capacitor C1, The output terminal of the A1 operational amplifier circuit is connected to the positive terminal of the input terminal of the A3 operational amplifier circuit through the resistor R6, the output terminal of the A2 operational amplifier circuit is connected to the negative terminal of the input terminal of the A3 operational amplifier circuit through the resistor R7, and the A1 operational amplifier circuit is connected. The output terminal of the A2 is connected to the ground through the resistor R6 and the resistor R9, and the output terminal of the A2 operational amplifier circuit is connected to the output terminal of the A3 operational amplifier circuit through the resistor R7 and the resistor R8.

The A3 op-amp circuit is a low-temperature low-gain op-amp circuit, the A1 and A2 op-amp circuits are low-temperature, high-gain op-amp circuits, the capacitor C1 is a filter capacitor, the resistor R1, resistor R2, The resistor R6, the resistor R7, and the resistor R9 are balance resistors, and the resistor R3, the resistor R4, the resistor R5, and the resistor R8 are voltage divider resistors, and the balance resistors are used to balance the offset current of the input terminal.

The A/D conversion circuit uses a highly integrated analog-to-digital converter CS5460A with 24 conversion bits, high-speed power calculation function and a serial interface. The A/D conversion circuit converts the analog signal into a digital signal, and is connected to 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, the logic memory in the isolation circuit is a RAM memory, and the isolation circuit connects the isolator output port V0 with the microcontroller. The unit MCU input terminal SPI is connected.

The MCU is used to perform logical judgment on the input signal, and the MCU is provided with a timer, a communication interface, a power manager, and a watchdog timer, and the MCU connects the output end SPI of the microcontroller unit with the CAN input port .

The CAN interface output port is connected with the outside world through a connector, and the CAN interface is a connector provided with four Pins, wherein Pin a is the power supply VCC, Pin b is CAN_L, Pin c is CAN_H, and Pin d is GND.

The current sensor of the present invention can measure bidirectional DC current through a shunt, the module is completely isolated from high and low voltage, and can be used in the total positive terminal or the total negative terminal of the battery system. The supply voltage range of the current sensor module is +3.3V to +5V. The module will minimize the resistance change caused by temperature change, and the module communication uses a CAN2.0B interface for external communication (default 500kbit/s, configurable).

Description of drawings

The content expressed in each drawing in the description of the present invention and the marks in the drawings are briefly described below:

Figure 1 is a schematic diagram of the internal structure and circuit principle of the sensor;

Fig. 2 is the schematic diagram of the appearance structure of the sensor;

Figure 3 is a schematic diagram of the internal structure of the sensor;

Figure 4 is a schematic diagram of a low-pass filter circuit;

Figure 5 is a schematic diagram of a high-pass filter circuit;

Fig. 6 is the block diagram of A/D converter of the present invention;

Figure 7 is a schematic diagram of the isolation circuit;

Fig. 8 is the MCU block diagram of the present invention;

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

Figure 10 is a schematic diagram of the shunt of the present invention

The marks in the above figures are: 1. Copper bar; 2. Current wiring hole; 3. Sampling resistor; 4. Measuring unit; 5. Voltage acquisition module; 6. CAN interface.

Detailed ways

Below with reference to the accompanying drawings, through the description of the embodiments, the specific implementation of the present invention, such as the shape and structure of each component involved, the mutual position and connection relationship between each part, the function and working principle of each part, and the manufacturing process and operation and use methods, etc., are described in further detail to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solutions of the present invention.

The present invention is a current sensor based on a shunt, and the traditional measurement method is changed to the measurement part of the shunt, all of which are integrated into the shunt, so that the entire current measurement and feedback loop can be shortened, and the voltage acquisition uses a differential amplifier circuit to make the signal Interference factors are reduced, and measurement errors are reduced.

The current sensor is mainly divided into three parts, the first part is the high current connection copper bar 1, the second part is the measurement unit 4, which is also the core of the whole sensor, and the third part is the CAN communication part. The measurement unit 4 includes a shunt, a filter circuit, an A/D conversion circuit, and an isolation circuit. Current measurement process: first power on the current sensor, when there is current passing through the shunt, the current flows through the low temperature drift resistance, the shunt measures a voltage signal, the voltage signal is amplified by the differential amplifier circuit and sent to the filter circuit to filter the clutter, and then It is connected to the analog input terminal of the A/D converter, and the digital signal is obtained after the analog-to-digital converter. The A/D converter outputs the digital signal and outputs it to the MCU through the isolation circuit. After the MCU performs logical judgment, the data is passed through the CAN Interface 6 outputs to the CAN bus.

As shown in Figure 10, the shunt is composed of two identical A1 op-amp circuits and A2 op-amp circuits as the input stage. The positive terminal of the input terminal of the A1 op-amp circuit is connected to a sampling resistor binding post through the resistor R1, and the input of the A2 op-amp circuit is connected. The positive terminal of the terminal is connected to another sampling resistor terminal through the resistor R2. The output terminal of the A1 operational amplifier circuit is connected to the output terminal of the A2 operational amplifier circuit through the resistor R4, resistor R3 and resistor R5 in series in sequence, and the input terminal of the A1 operational amplifier circuit is connected to the negative terminal. Between the resistor R4 and the resistor R3, the negative pole of the input terminal of the A2 op amp circuit is connected between the resistor R5 and the resistor R3, the resistor R4, the resistor R3, and the resistor R5 are connected in parallel with the capacitor C1, and the output terminal of the A1 op amp circuit is connected in parallel with the capacitor C1. The resistor R6 is connected to the positive terminal of the input terminal of the A3 operational amplifier circuit, the output terminal of the A2 operational amplifier circuit is connected to the negative terminal of the input terminal of the A3 operational amplifier circuit through the resistor R7, the output terminal of the A1 operational amplifier circuit is grounded through the resistor R6 and the resistor R9, and the A2 operational amplifier is connected to the ground. The output end of the circuit is connected to the output end of the A3 operational amplifier circuit through the resistor R7 and the resistor R8.

The sampling end adds an operational amplifier differential amplifier circuit, which can not only stabilize the working voltage but also perform small current measurement. This design can make the measurement range wider and higher in accuracy. Two identical operational amplifier circuits A1 and A2 form the input. stage, in series with the differential amplifier A3 to form a three-op-amp differential amplifier circuit, the input stage resistance in the circuit should be kept symmetrical and equal.

C1 is a filter capacitor, A1 and A2 use low-temperature, high-gain op amps, A3 is a low-temperature low-gain op amp, R1, R2, R6, R7, R9 are balance resistors to balance the offset current at the input end, R3, R4, R5 and R8 are voltage divider resistors.

A1 and A2 improve the ratio of differential mode signal to common mode signal. Under the condition of symmetry of the circuit input stage, the error of each resistance value has no effect on the common mode rejection of the circuit, the circuit has almost no amplifying effect on the common mode signal, and the common mode voltage gain is very high. Small.

Because R1=R2, R4=R5, R8=R9, R6=R7, the two-stage differential mode gain Q is

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

Because the first-stage gain magnification of the differential amplifier circuit is 10-100 times, and the second-stage gain magnification is about 1-2 times, the voltage can get a very high magnification after passing through the first-stage and second-stage amplifying circuits , so the current sensor can measure small currents of a few milliamps.

The entire current sensor is fixed in the casing, two copper bars 1 are fixed on the side of the casing, the casing is sealed with glue, and the other end is the CAN interface 6, which is directly connected to the CAN plug on the car. The shunt includes a sampling resistor 3 and a voltage acquisition module 5. Both ends of the sampling resistor 3 are welded to the copper bar 1 by welding. When the current flows through the shunt through the two current wiring holes 2 on the copper bar 1, it will A collection voltage is formed at both ends of the sampling resistor 3. The voltage signal is generally 0-75mV. The resistance value of the sampling resistor 3 is known. The voltage collection module 5 obtains its voltage U by connecting the two ends of the sampling resistor 3 through the binding posts. I=U/R The current value I flowing through the sampling resistor 3 can be known. In the whole design, TCR (Temperature Coefficient of Resistance) is the key point of selection. Low temperature drift resistance refers to the resistance whose resistance value changes with temperature. Drift precision resistors.

In this way, we can have two solutions. The first solution is to use the low temperature drift thin film resistor as the shunt sampling resistor 3. The low temperature drift thin film resistor can meet the measurement of medium and high resistance values, and not only can pass a large current, but also have a relatively high resistance value. The second solution is to use a low-temperature precision resistor. The advantage of using a low-temperature precision resistor is that it can provide a very high measurement accuracy, which can generally reach 0.01%. The difference between low temperature drift resistance and ordinary resistance is that the temperature of the resistance itself changes very little with the increase of current, and it can be widely used in the measurement of high temperature environments such as motor controllers.

The filter circuit is shown in Figures 4 and 5. Because there will be clutter mixed in the signal transmission process, a filter circuit is introduced. Ui represents the input voltage, R represents the protection resistor, C represents the filter capacitor, and Uo represents the filter output voltage. RL is the internal resistance of the circuit. High-pass circuit means that signals higher than the set frequency are allowed to pass, and signals below the set frequency are not allowed to pass. The low-pass circuit corresponds to the high-pass circuit, that is, the signal below the set frequency is blocked. It is very small, and the signal higher than the set frequency is very hindered. In the EMC battery compatibility test of auto parts, it is often encountered that the high frequency signal or the low frequency signal exceeds the limit. At this time, the use of high and low pass filter circuit will make the test result. Improved, low-pass and high-pass circuits are selected by the actual application situation.

The A/D conversion circuit is shown in Figure 6. There are many forms of A/D converters, and the different methods will affect the accuracy after measurement, and its main function is to convert analog electronic quantities into digital quantities, so that the output The digital quantity is proportional to the input analog electronic quantity to realize the conversion function. In the process of A/D conversion, since the input analog electronic signal is continuous and the output digital signal is discrete, the input analog signal should be sampled according to a certain frequency during analog-to-digital conversion. A/D conversion needs to go through four stages of sampling, holding, quantization and encoding. Sampling is the timing measurement and sampling of the continuously changing analog electronic signal. The denser the sampling, the closer the circuit output signal is to the input value. Therefore, there are certain requirements for the sampling frequency. The sampling frequency fs≥2fImay, where fImay is the highest value in the input signal spectrum. Frequency; hold is to store the collected signal for a period of time; quantization is the process of converting the sampling voltage into an integer multiple of a certain minimum unit voltage △, and the divided levels are called quantization levels. The more levels, the better, A is called the quantization unit ; The so-called coding is to use binary code to represent the quantized level after quantization. In practical application, a highly integrated analog-to-digital converter CS5460A with 24-bit conversion bits, high-speed power calculation function and a serial interface is used.

Isolation As shown in Figure 7, the communication signal of the current sensor will be subject to various disturbances during the transmission process. In order to ensure the stability of the signal, the sensor uses a signal isolator, adding an isolator to separate the high and low voltages of the circuit to protect the low-voltage circuit from being damaged. Interferenced by high-voltage circuits, we choose a four-channel digital isolator with multi-channel configuration and output enable functions for isolation and connection between the A/D converter and the MCU. The internal logic memory is RAM memory. The logic input and The output buffers are separated by TI's silicon dioxide isolation shield, support a variety of channel configurations and minimum data rates of 500kbps, both ends of the selected model can be powered by 5V power supply, compatible with low voltage systems, and can achieve voltage conversion Function, the selected model needs to have a default output control pin, which can be used to define the logic state taken when there is no input power supply, and at the same time, a layer of shielding paint is evenly applied to the sensor housing, and the paint can be dried to form a paint film. Conductive effect, thus playing the role of shielding electromagnetic wave interference, shielding paint is to add conductive metal powder to specific resin raw materials to make paint that can be sprayed.

The MCU, the micro-control unit, is shown in Figure 8, and the micro-control unit performs logical judgment on the input signal. MCU's timer selection Programmable Timer (programmable timer) The timing of this type of Timer can be controlled by the user's program. The control methods include: clock source selection, frequency division (Prescale) selection and preset number selection settings etc. The external interrupt is triggered by the rising edge, and is automatically triggered when the input signal is greater than the set value. The communication interface adopts the SPI interface, which is the most basic communication method provided by most MCUs, and its data transmission is controlled by a synchronous clock. Bandgap is the energy difference between the lowest point of the conduction band and the highest point of the valence band, also known as the energy gap. Directly read and write the IO port. When the read IO port command is executed, it is an input port; when the write IO port command is executed, it is automatically an output port. RAM memory is used, because the stored data can be cleared after uploading, and it does not need to be stored for a long time. The power manager uses a DC/DC modulation IC. Since the power supply is a DC power supply, it does not involve AC power, and only needs to be adjusted up/down. Watchdog (watchdog timer) is a basic configuration of most MCUs. This Watchdog satisfies that it allows the program to reset and close it, and provides a self-recovery capability to ensure that the MCU crashes due to unexpected failures.

The CAN interface 6 is shown in Figure 9. The use of CAN transmission is because the current sensor may work in an environment with strong electromagnetic noise or a long signal transmission distance. The use of CAN can solve this problem very well. CAN consists of male/female connectors with 4 pins, as shown in Figure 5, Pin a is the power supply VCC: 12V; Pin b is CAN_L; Pin c is CAN_H; Pin d is GND.

Current measurement process: first power on the current sensor, when there is current passing through the shunt, the current flows through the low temperature drift resistance, the shunt measures a voltage signal, the voltage signal is filtered by the filter circuit, and then connected to the A/D converter The analog input terminal of the MCU obtains a digital signal after passing through the analog-to-digital converter. The A/D converter outputs the digital signal and outputs it to the MCU through the isolation circuit. After the MCU performs logical judgment, the data is output to the CAN bus through the CAN interface.

The present invention has been exemplarily described above in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above methods, as long as various insubstantial improvements made by the method concept and technical solutions of the present invention are adopted, or no improvement is made. It is within the protection scope of the present invention to directly apply the concepts and technical solutions of the present invention to other occasions.

Claims (10)

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.

Images