Bidirectional high-frequency current detection circuit of electric vehicle charging pile

Abstract

The utility model relates to the technical field of electric automobile charging piles, in particular to a bidirectional high-frequency current detection circuit for an electric automobile charging pile. The bidirectional high-frequency current detection circuit comprises a voltage boosting module, a signal amplification module, an impedance isolation module and an ADC conversion module, current on a direct-current bus is converted into a small voltage signal through a diverter and then is input into a signal amplification module for signal amplification, and the amplified voltage signal is subjected to voltage boosting through a voltage boosting module and then is input into an impedance isolation module; a voltage signal output by the impedance isolation module is input into the ADC conversion module, and the analog voltage signal is converted into a digital signal; the ADC conversion module is connected to the main controller in an SPI communication mode. The circuit can be applied to a direct current charging pile capable of charging or discharging or charging and discharging, monitors and records instantaneous current change in the operation process of charging equipment, improves the state monitoring level and fault tracing capability of the charging equipment, and supports the realization of intelligent operation and maintenance of the charging equipment.

Description

Technical Field

[0001] The utility model relates to the technical field of electric vehicle charging piles, in particular to a bidirectional high-frequency current detection circuit for an electric vehicle charging pile. Background Art

[0002] In recent years, with the explosive growth of new energy vehicles and the resulting increase in charging voltage and current, current charging equipment generally uses shunts as current collection devices. The maximum collected current is the shunt's range. For example, a charging device rated for 250A typically uses a 300A shunt, with a current collection range of 0-300A. However, when a surge or reverse current occurs, the current value may exceed 300A or become negative, exceeding the collection range of current solutions. In addition, conventional current collection solutions typically have a frequency of 100ms and are unable to capture current changes when instantaneous current changes occur, affecting the ability to trace charging equipment faults.

[0003] Current DC charging pile current collection uses a shunt, and the current range is consistent with the shunt. For example, using a 300A / 75mV shunt, it can only collect currents from 0 to 300A and cannot collect currents less than 0A. In addition, if a current fault occurs, if the fault current exceeds 300A, the charging equipment cannot collect current values ​​greater than 300A, nor can it collect negative current values ​​caused by current backflow. The hardware architecture of the existing solution is shown in Figure 1. The existing solution has certain shortcomings:

[0004] (1) It is impossible to collect reverse current. When a short circuit or other factors cause current backflow, it is impossible to determine the direction and magnitude of the current at that time.

[0005] (2) Slow sampling speed: The current sampling frequency of the conventional scheme is 100ms, while the occurrence of faults is often instantaneous, at least at the ms level. Utility Model Content

[0006] This utility model aims to provide a bidirectional, high-frequency current detection circuit for electric vehicle charging stations. This circuit implements high-precision, bidirectional, wide-range instantaneous current detection, extending the conventional 0-300A current detection range to -500A to +500A. This circuit also enables precise recording of the 200µs current during vehicle charging, supporting accurate location and source tracing of charging equipment faults. Furthermore, this solution can be applied to bidirectional vehicle-to-gear (V2G) charging and discharging equipment for electric vehicles, demonstrating its broad potential for application.

[0007] The utility model adopts the following technical solutions:

[0008] A bidirectional high-frequency current detection circuit for an electric vehicle charging pile includes a voltage boost module, a signal amplification module, an impedance isolation module, and an ADC conversion module. The current on the DC bus is converted to a low-voltage signal by a shunt and then input into the signal amplification module for signal amplification. The amplified voltage signal is then boosted by the voltage boost module and input into the impedance isolation module. The voltage signal output by the impedance isolation module is input into the ADC conversion module, which converts the analog voltage signal into a digital signal. The ADC conversion module is connected to a main controller via SPI communication. Data exchange between the main controller and the ADC conversion module occurs via SPI communication. The ADC conversion module sends the converted digital signal to the main controller, which then converts it to the actual current value, thereby enabling current sampling during the charging and discharging process.

[0009] Preferably, the main controller is connected to a NAND FLASH memory and a USB module. With the significant growth of high-power charging equipment and the increasing charging current, the risks in the charging process are also increasing. The status monitoring and recording of charging equipment has become an indispensable part of the operation and maintenance of charging equipment. The ADC conversion module will sample the current value at a sampling frequency of 200us. At the same time, each recorded data will be added with time and stored in the NAND FLASH memory. The memory has 16GB of memory and can achieve a minimum of 1 year of recorded data storage capacity. The stored data can be exported through the USB module. The USB module is connected to the main controller. When a fault occurs and the fault data needs to be exported, the user can insert a USB flash drive into the USB module. After the main controller recognizes the USB flash drive, it operates the NAND FLASH memory, reads the data, and synchronously imports it into the USB flash drive.

[0010] Preferably, the voltage boost module includes a first capacitor C1, a second capacitor C2, a voltage reference chip U1, a first resistor R1, a second resistor R2, and a third resistor R3; one end of the first capacitor C1 is connected to a 5V power supply, and the other end is connected to a reference ground; the first capacitor C1 acts as a filter, which can stabilize the 5V power supply. One end of the first resistor R1 is connected to a 5V power supply, and the other end is connected to pins 2 and 1 of the voltage reference chip U1, and pin 3 of the voltage reference chip is connected to the reference ground; the first resistor R1 acts as a current limiter in this process, limiting the operating current of the voltage boost module. Pin 1 of the voltage reference chip U1 is connected to the second capacitor C2 and one end of the second resistor R2, the other end of the second capacitor C2 is connected to the reference ground, and the other end of the second resistor R2 is connected to the reference ground via the third resistor R3; the voltage output from pin 1 of the voltage reference chip U1 is 2.5V; the output at the connection between the second resistor R2 and the third resistor R3 is a boost voltage for input to the signal amplification module . Raise voltage The relationship between the size of the two voltage divider resistors, the second resistor R2 and the third resistor R3, is:

[0011]

[0012] Raise voltage The function is that when the reverse voltage is input (i.e. discharge state), since the input voltage value is negative, in order to ensure that the voltage input to the signal amplification module is positive, the voltage signal is raised to a positive value. This is also a key step in realizing negative current detection.

[0013] Preferably, the signal amplification module includes a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a third capacitor C3, and a first operational amplifier U2B; the current on the DC bus is converted into a small voltage signal through a shunt; the small voltage signal is usually 0-75mV. The positive input terminal and the negative input terminal of the small voltage signal are connected to the in-phase input terminal and the reverse input terminal of the first operational amplifier U2B respectively through the fourth resistor R4 and the fifth resistor R5; the voltage of the positive input terminal and the negative input terminal of the small voltage signal is recorded as 、 ; The voltage at the non-inverting input terminal is recorded as , the reverse input voltage is recorded as . Raise voltage The voltage is input to the non-inverting input terminal of the first operational amplifier U2B through the sixth resistor R6 and the third capacitor C3 connected in parallel. The inverting input terminal of the first operational amplifier U2B is connected to the output terminal of the first operational amplifier U2B through the seventh resistor R7 to form an output voltage Output voltage It is connected to the impedance isolation module via the eighth resistor R8.

[0014] The fourth resistor R4, the fifth resistor R5, the sixth resistor R6, the seventh resistor R7, and the first operational amplifier U2B form a differential amplifier circuit. According to the characteristics of the differential amplifier circuit, R4=R5 and R6=R7. After passing through the sixth resistor R6, it is connected to the fourth resistor R4 and the non-inverting input terminal of the first operational amplifier U2B as the DC bias of the differential amplifier circuit. The amplified signal is output through the 7th pin of the first operational amplifier U2B. The output voltage is recorded as When a small voltage signal is input into the differential amplifier circuit, according to the characteristics of the differential amplifier circuit, we can get:

[0015]

[0016] According to the virtual short of the amplifier, , and according to the above R4=R5, R6=R7, formula ③ can be written as:

[0017]

[0018] Combining ②-④ gives:

[0019]

[0020] Simplifying, we get:

[0021]

[0022] In formula ⑥, when a negative voltage is input, If the value of is negative, The value of is also negative, and finally The value is a positive value With a negative value Add.

[0023] Preferably, the impedance isolation module includes a second operational amplifier U2A, the output voltage The impedance isolation module is essentially an amplifier circuit with a voltage gain of 1, that is, the input voltage is equal to the output voltage, and the output voltage after the signal amplification module is equal to the output voltage. After passing through the impedance isolation module, the output voltage signal is still , and output to the ADC conversion module through the output end of the second operational amplifier U2A.

[0024] Preferably, the main controller adopts an ARM Cortex-A7 main controller.

[0025] The ADC conversion module converts the voltage signal into a digital quantity and transmits the data to the ARMCortex-A7 main controller via SPI communication. The ADC conversion module itself is a 24-bit ADC, and the reference voltage of the ADC conversion module is 3V. That is, when the voltage input to the ADC conversion module is 3V, the digital quantity data converted by the conversion module corresponds to 2 to the power of 24 (16777216). The sampling frequency of the ADC conversion module is 200us, that is, the ARM-A7 will obtain a sampled data every 200us. For negative current detection, since the input negative voltage signal is less than or equal to the lift voltage Therefore, after sampling, the voltage that finally enters the ADC conversion module is still a positive voltage. The ARM-A7 main control restores the digital value output by the ADC conversion module to the actual voltage value of the small voltage signal (unit: mV):

[0026]

[0027] When using a 0-75mV shunt, the actual current value in the DC circuit is:

[0028]

[0029] When the input voltage When it is positive, the final current That is positive current; when the input voltage When it is negative, the resulting current That is negative current.

[0030] The ARM Cortex-A7 main controller converts the converted data to the real current value, adds a timestamp to the current value and stores it in the NAND FLASH. This process is called wave recording.

[0031] The above detection circuit implements negative current detection in the charging pile. This helps prevent reverse overshoot currents caused by current faults. If the charging pile lacks a mechanism to handle reverse current, reverse current flowing back into the charging pile busbar can cause irreversible damage to the various components within the charging pile. Adding reverse current detection allows for real-time monitoring of current polarity. When a reverse current surge occurs, the controller immediately disconnects the circuit, protecting both the vehicle and the charging pile.

[0032] The utility model proposes a bidirectional high-frequency current detection circuit for electric vehicle charging piles. The circuit can be applied to DC charging piles with charging or discharging or both, monitors and records instantaneous current changes during the operation of charging equipment, improves the status monitoring level and fault tracing capability of charging equipment, and supports the realization of intelligent operation and maintenance of charging equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 is a circuit block diagram of an existing solution;

[0035] FIG2 is a circuit block diagram of the present utility model;

[0036] FIG3 is a circuit diagram of the present utility model. DETAILED DESCRIPTION

[0037] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] The following is a detailed description with reference to the accompanying drawings.

[0039] like Figure 2 The figure shows a bidirectional high-frequency current detection circuit for an electric vehicle charging pile, comprising a voltage boost module, a signal amplification module, an impedance isolation module, and an ADC conversion module. The current on the DC bus is converted to a low voltage signal by a shunt and then input into the signal amplification module for signal amplification. The amplified voltage signal is then boosted by the voltage boost module and input into the impedance isolation module. The voltage signal output by the impedance isolation module is input into the ADC conversion module, which converts the analog voltage signal into a digital signal. The ADC conversion module is connected to a main controller via SPI communication. The main controller and the ADC conversion module exchange data via SPI communication. The ADC conversion module sends the converted digital signal to the main controller, which converts it into the actual current value, thereby implementing current sampling during the charging and discharging process. The main controller is connected to a NAND FLASH memory and a USB module.

[0040] like Figure 3As shown, the voltage boost module includes a first capacitor C1, a second capacitor C2, a voltage reference chip U1, a first resistor R1, a second resistor R2, and a third resistor R3. The upper end of the first capacitor C1 is connected to a 5V voltage, and the lower end of the first capacitor C1 is connected to a reference ground. The first capacitor C1 acts as a filter, which can stabilize the 5V power supply; the left end of the first R1 is connected to the 5V power supply and the upper end of the first capacitor C1, and the 5V power supply is input through the left end of the first resistor R1 and output through the right end of the first resistor R1. The first resistor R1 plays a current limiting role in this process, limiting the working current of the voltage boost module; the 5V power supply is output from the right end of the first resistor R1 and connected to pins 2 and 1 of the voltage reference chip U1. Pin 3 of the voltage reference chip U1 and the lower end of the first capacitor C1 are connected to the reference ground. The 5V voltage is input through the left end of the first resistor R1 and output through the right end of the first resistor R1. The first resistor R1 plays a current limiting role in this process, limiting the working current of the voltage boost module; the 5V power supply is output from the right end of the first resistor R1 and connected to pins 2 and 1 of the voltage reference chip U1. The pin 3 of the voltage reference chip U1 and the lower end of the first capacitor C1 are connected to the reference ground. After the voltage reference chip U1 is connected, it is output through pin 1 of the voltage reference chip U1, and the output voltage is 2.5V; the 2.5V voltage output from pin 1 of the voltage reference chip U1 is connected to the upper end of the second capacitor C2, and the lower end of the second capacitor C2 is connected to the reference ground, and the second capacitor C2 plays a filtering role; the upper end of the second capacitor C2 is connected to the left end of the second resistor R2, that is, the 2.5V voltage is input to the left end of the second R2, the right end of the second R2 is connected to the upper end of the third R3, and the lower end of the third resistor R3 is connected to the reference ground. After the 2.5V voltage is input to the left end of the second resistor R2, it is divided by the second resistor R2 and the third resistor R3, and the final output is the raised voltage. ; Raise voltage Output at the common connection between the right end of the second resistor R2 and the upper end of the third resistor R3, raising the voltage The relationship between the size of the second resistor R2 and the third resistor R3 is:

[0041]

[0042] Raise voltage Finally, it is input to the signal amplification circuit. The purpose of the voltage boost is that when the reverse voltage is input (i.e., discharge state), since the input voltage value is negative, in order to ensure that the voltage input to the signal amplification module is positive, the voltage signal is boosted to a positive value. This is also a key step in realizing negative current detection.

[0043] The signal amplification module includes five resistors: a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, and an eighth resistor R8; a third capacitor C3; and a first operational amplifier U2B. After the current on the DC bus is converted into a small voltage signal (typically 0-75mV) by the shunt, the positive input and negative input of the small voltage signal are connected to the in-phase input and inverting input of the first operational amplifier U2B via the fourth resistor R4 and the fifth resistor R5, respectively. The voltages at the positive and negative inputs of the small voltage signal are recorded as 、 ; The voltage at the non-inverting input terminal is recorded as , the reverse input voltage is recorded as Resistors R4, R5, R6, R7 and the first operational amplifier U2B form a differential amplifier circuit. According to the characteristics of the differential amplifier circuit, R4=R5 and R6=R7. The input is sent to the sixth resistor R6 and the upper end of the third capacitor C3. The lower end of the capacitor C3 is connected to the 5th pin of the first operational amplifier U2B to play a filtering role. After passing through the sixth resistor R6, the lower end of the sixth resistor R6 is connected to the fourth resistor R4 and the first operational amplifier U2B amplifier 5 pin, serving as the DC bias of the differential amplifier circuit. The amplified signal is output through the first operational amplifier U2B 7 pin (the voltage at this point is recorded as ). When the signal is input into the differential amplifier circuit, according to the characteristics of the differential amplifier circuit, we can get:

[0044]

[0045] According to the virtual short of the amplifier, , and according to the above R4=R5, R6=R7, formula ③ can be written as:

[0046]

[0047] Combining ②-④ gives:

[0048]

[0049] Simplifying, we get:

[0050]

[0051] In formula ⑥, when a negative voltage is input, If the value of is negative, The value of is also negative, and finally The value is a positive value With a negative value Add.

[0052] According to the above calculation, when the current on the DC bus is converted into a small voltage signal through the shunt, and then amplified by the signal amplification module, the small voltage signal is amplified to the voltage value calculated by formula ⑥. The current is output through the 7th pin of the first operational amplifier U2B and enters the left end of the eighth resistor R8. The eighth resistor R8 is a current limiting resistor. The output is output from the right end of the eighth resistor R8 and enters the impedance isolation module at the rear.

[0053] The impedance isolation module consists of an operational amplifier U2A. The signal after passing through the signal amplification module is input to the 3rd pin of the second operational amplifier U2A in the impedance isolation module. The 2nd and 1st pins of the second operational amplifier U2A are directly connected. The impedance isolation module is essentially an amplifier circuit with a voltage gain of 1, that is, the input voltage is equal to the output voltage. After the signal after passing through the signal amplification module passes through the impedance isolation module, the output voltage signal size is still , The signal is output to the ADC conversion module through pin 1 of the second operational amplifier U2A.

[0054] The ADC conversion module converts the input voltage signal into a digital quantity and transmits the data to the ARM Cortex-A7 main controller via SPI communication. The ADC conversion module itself is a 24-bit ADC, and the reference voltage of the ADC conversion module is 3V. That is, when the voltage input to the ADC conversion module is 3V, the digital quantity data converted by the conversion module corresponds to 2 to the power of 24 (16777216). The sampling frequency of the ADC conversion module is 200us, that is, the ARM-A7 will obtain a sampling data every 200us. The negative current detection mentioned above is because the input negative voltage signal is less than or equal to the lift voltage. Therefore, after sampling, the voltage that finally enters the ADC conversion module is still a positive voltage. The ARM Cortex-A7 main controller restores the digital value output by the ADC conversion module to the actual voltage value (in mV) input to the sampling unit:

[0055]

[0056] When using a 0-75mV shunt, the actual current value in the DC circuit is:

[0057]

[0058] When the input voltage When it is positive, the final current That is positive current; when the input voltage When it is negative, the resulting current That is negative current.

[0059] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. The preferred embodiments do not describe all details in detail, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A bidirectional high-frequency current detection circuit for an electric vehicle charging pile, characterized by: It includes a voltage boost module, a signal amplification module, an impedance isolation module and an ADC conversion module. The current on the DC bus is converted into a small voltage signal by a shunt and then input into the signal amplification module for signal amplification. The amplified voltage signal is boosted by the voltage boost module and then input into the impedance isolation module. The voltage signal output by the impedance isolation module is input to the ADC conversion module to convert the analog voltage signal into a digital signal; the ADC conversion module is connected to the main controller via SPI communication.

2. The electric vehicle charging pile bidirectional high-frequency current detection circuit according to claim 1, characterized in that: The main controller is connected with a NAND FLASH memory and a USB module.

3. The electric vehicle charging pile bidirectional high-frequency current detection circuit according to claim 1, characterized in that: The voltage boost module includes a first capacitor C1, a second capacitor C2, a voltage reference chip U1, a first resistor R1, a second resistor R2, and a third resistor R3; one end of the first capacitor C1 is connected to a 5V power supply, and the other end is connected to a reference ground; One end of the first resistor R1 is connected to the 5V power supply, and the other end is connected to pins 2 and 1 of the voltage reference chip U1. Pin 3 of the voltage reference chip is connected to the reference ground. Pin 1 of the voltage reference chip U1 is connected to the second capacitor C2 and one end of the second resistor R2. The other end of the second capacitor C2 is connected to the reference ground. The other end of the second resistor R2 is connected to the reference ground through the third resistor R3. The connection between the second resistor R2 and the third resistor R3 outputs a boost voltage for input to the signal amplification module. .

4. The electric vehicle charging pile bidirectional high-frequency current detection circuit according to claim 3, characterized in that: The signal amplification module includes a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a third capacitor C3, and a first operational amplifier U2B; the current on the DC bus is converted into a small voltage signal through a shunt; the positive input terminal and the negative input terminal of the small voltage signal are respectively connected to the in-phase input terminal and the reverse input terminal of the first operational amplifier U2B through the fourth resistor R4 and the fifth resistor R5; the voltage is raised The voltage is input to the non-inverting input terminal of the first operational amplifier U2B through the sixth resistor R6 and the third capacitor C3 connected in parallel. The inverting input terminal of the first operational amplifier U2B is connected to the output terminal of the first operational amplifier U2B through the seventh resistor R7 to form an output voltage Output voltage It is connected to the impedance isolation module via the eighth resistor R8.

5. The electric vehicle charging pile bidirectional high-frequency current detection circuit according to claim 4, characterized in that: The impedance isolation module includes a second operational amplifier U2A, which outputs a voltage The inverting input terminal of the second operational amplifier U2A is connected to the non-inverting input terminal of the second operational amplifier U2A via the eighth resistor R8, the inverting input terminal of the second operational amplifier U2A is connected to its output terminal, and its output terminal is connected to the ADC conversion module.

6. The electric vehicle charging pile bidirectional high-frequency current detection circuit according to claim 1 or 2, characterized in that: The main controller adopts ARM Cortex-A7 main controller.

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