Charging pile remote calibration system and calibration method

Abstract

The application provides a charging pile remote calibration system and a calibration method. The system is realized based on a satellite common view method, a high-precision voltage frequency conversion module and a current frequency conversion module, and can calibrate the electric energy of the calibrated charging pile in real time. In the frequency deviation measurement, the pulse counter and the time interval counter work together, the decimal part of the frequency value is measured by the time interval counter, and the number of continuous square wave pulses in the second pulse period is measured by the pulse counter as the integer part of the frequency value, and the remote calibration of the voltage value / current value is completed. The application designs a high-precision voltage frequency conversion module and a current frequency conversion module, converts the electrical parameters output by the standard voltage source, the current source and the to-be-tested voltage source, the current source into corresponding frequency signals respectively by using the two modules, and then completes the remote calibration process of the charging pile based on the Beidou satellite common view method and related algorithms.

Description

Technical Field

[0001] This invention relates to the field of electrical metrology and calibration, specifically to a remote calibration system and method for charging piles. Background Technology

[0002] As environmental issues come to the public's attention, the market for new energy electric vehicles is expanding rapidly, and the number of supporting electric vehicle charging infrastructure is also growing exponentially. With the increase in the number of electric vehicle charging stations (referred to as charging piles), the demand for their calibration will inevitably also increase.

[0003] Currently, charging pile verification uses traditional DC charging pile verification technology. This traditional technology involves converting the grid input voltage into DC voltage output through a series of transformations within the DC charging pile, such as a transformer. This output voltage is then connected to a testing instrument via a standard charging interface. Simultaneously, the testing instrument is connected to an electronic load (simulating a car battery load) via a standard interface, forming a convenient and fast DC charging pile verification system. After the entire system is successfully connected, the charging pile internally performs a series of conversions and filtering processes on the grid input, then outputs high voltage and high current into the testing instrument, which is then connected in series with an electronic load to form a complete testing loop. This method requires metrology personnel to bring a standard instrument to the site for verification; the standard instrument can be manual or fully automatic testing equipment. The advantage of this method is accurate verification results, but the disadvantages are a long verification cycle, low efficiency, and the need for significant manpower and resources. Furthermore, the skill level of the metrology personnel has a significant impact on the verification results. Specifically, this is reflected in the following aspects:

[0004] (1) It takes a long time and increases costs. In the traditional verification of DC charging piles, metrology staff need to bring the standard to the site for verification, which undoubtedly increases the labor and logistics costs of the verification work. Against the backdrop of increasingly severe energy shortages and environmental pollution, and facing the potential verification needs of tens of thousands of charging piles in the future, the traditional method has an excessively long verification cycle, which will greatly increase the time cost and reduce the efficiency of metrology work.

[0005] (2) Logistics transportation causes instrument damage. Although it is not necessary to disassemble and transport the charging piles to the superior testing institution when carrying out traditional calibration work, metrology personnel still need to carry the standard device to the calibration site through logistics transportation. Multiple transportation and handling can easily cause irreversible instrument damage, especially for high-precision instruments, which will greatly reduce the accuracy of the metrology instruments and affect the calibration results.

[0006] (3) Offline calibration leads to energy waste. Test loads are an indispensable piece of equipment in the calibration of charging piles. Test loads can typically be electric vehicles, power battery packs, DC electronic loads, or resistive loads. Traditional calibration methods require offline calibration of charging piles, which makes it impossible for charging piles to perform normal operation and metrological calibration simultaneously. Therefore, test loads need to be connected to simulate the load conditions of electric vehicles under different charging states, which will cause a certain degree of energy waste.

[0007] Against the backdrop of global warming and increasingly severe environmental pollution, countries around the world have begun to vigorously promote the development of electric vehicles, and electric vehicle charging stations, as supporting facilities for new energy vehicles, have also developed rapidly. Simultaneously, as a metrological tool for trade settlement, they have been included in the national mandatory verification metrological instrument catalog. According to JJG1148-2018 "Verification Procedure for AC Charging Stations for Electric Vehicles" and JJG1149-2018 "Verification Procedure for Off-board Chargers for Electric Vehicles," preliminary calculations indicate that it takes at least 0.5 hours for two skilled verification personnel to verify each charging station. However, facing tens of thousands of charging facilities, the verification and testing capabilities of legal metrological verification institutions are inadequate, and management is difficult, costly, and inefficient. Summary of the Invention

[0008] The purpose of this invention is to provide a remote calibration system and method for charging piles to solve the problems of low efficiency and high cost of existing calibration methods.

[0009] The present invention is implemented as follows: a remote calibration system for charging piles, comprising a laboratory end and a calibration end;

[0010] The laboratory is equipped with a standard voltage source, a standard current source, a first voltage-to-frequency converter, a first current-to-frequency converter, a first satellite synchronization clock source, a first time accumulation module, a second time accumulation module, a first pulse counter, a second pulse counter, a first time interval counter, a second time interval counter, and a computer.

[0011] A standard voltage source is connected to a first time accumulation module and a first voltage-frequency converter. The standard voltage source outputs a standard voltage value to both the first time accumulation module and the first voltage-frequency converter simultaneously. The first time accumulation module calculates the calibration duration based on the output signal of the standard voltage source and outputs the signal to a computer. The first voltage-frequency converter is also connected to a first pulse counter and a first time interval counter. The first voltage-frequency converter converts the standard voltage value into a pulse signal and outputs it to the first pulse counter and the first time interval counter respectively. The first pulse counter and the first time interval counter are also connected to a first satellite synchronization clock source. The first satellite synchronization clock source receives BeiDou satellite signals and outputs satellite synchronization second pulse signals to the first pulse counter and the first time interval counter. The first pulse counter measures the number of pulses in each complete cycle of the satellite synchronization second pulse signal output by the first voltage-frequency converter and sends the pulse count to the computer. The first time interval counter measures the time interval between the pulse signal output by the first voltage-frequency converter and the satellite synchronization second pulse signal and sends the time interval to the computer.

[0012] A standard current source is connected to a second time accumulation module and a first current frequency converter. The standard current source outputs a standard current value to both the second time accumulation module and the first current frequency converter simultaneously. The second time accumulation module calculates the calibration duration based on the output signal of the standard current source and outputs the signal to the computer. The first current frequency converter is also connected to a second pulse counter and a second time interval counter. The first current frequency converter converts the standard current value into a pulse signal and outputs it to the second pulse counter and the second time interval counter respectively. The second pulse counter and the second time interval counter are also connected to a first satellite synchronization clock source. The first satellite synchronization clock source receives BeiDou satellite signals and outputs satellite synchronization second pulse signals to the second pulse counter and the second time interval counter. The second pulse counter measures the number of pulses in each complete cycle of the satellite synchronization second pulse signal output by the first current frequency converter and sends the pulse count to the computer. The second time interval counter measures the time interval between the pulse signal output by the first current frequency converter and the satellite synchronization second pulse signal and sends the time interval to the computer.

[0013] The calibration end is equipped with a second voltage-frequency converter, a second current-frequency converter, a second satellite synchronization clock source, a third time accumulation module, a fourth time accumulation module, a third pulse counter, a fourth pulse counter, a third time interval counter, and a fourth time interval counter; the charging pile is located at the calibration end;

[0014] The charging pile's voltage output terminal is connected to the third time accumulation module and the second voltage-frequency converter. The charging pile outputs its voltage value to the third time accumulation module and the second voltage-frequency converter through its voltage output terminal. The third time accumulation module calculates the calibration duration based on the voltage value output by the charging pile and transmits the output signal to the computer through the data pass-through module. The second voltage-frequency converter is also connected to the third pulse counter and the third time interval counter. The second voltage-frequency converter converts the voltage value into a pulse signal and outputs it to the third pulse counter and the third time interval counter respectively. The third pulse counter and the third time interval counter are also connected to the second satellite synchronization clock source. The second satellite synchronization clock source receives BeiDou satellite signals and outputs satellite synchronization second pulse signals to the third pulse counter and the third time interval counter. The third pulse counter measures the number of pulses in each complete cycle of the satellite synchronization second pulse signal output by the second voltage-frequency converter and transmits the pulse count to the computer through the data pass-through module. The third time interval counter measures the time interval between the pulse signal output by the second voltage-frequency converter and the satellite synchronization second pulse signal and transmits the time interval to the computer through the data pass-through module.

[0015] The charging pile's current output terminal is connected to the fourth time accumulation module and the second current frequency converter. The charging pile outputs its current value to the fourth time accumulation module and the second current frequency converter through its current output terminal. The fourth time accumulation module calculates the calibration duration based on the current value output by the charging pile and transmits the output signal to the computer through the data pass-through module. The second current frequency converter is also connected to the fourth pulse counter and the fourth time interval counter. The second current frequency converter converts the current value into a pulse signal and outputs it to the fourth pulse counter and the fourth time interval counter respectively. The fourth pulse counter and the fourth time interval counter are also connected to the second satellite synchronization clock source. The second satellite synchronization clock source receives BeiDou satellite signals and outputs satellite synchronization second pulse signals to the fourth pulse counter and the fourth time interval counter. The fourth pulse counter measures the number of pulses of the pulse signal output by the second current frequency converter within each complete cycle of the satellite synchronization second pulse signal and transmits the pulse count to the computer through the data pass-through module. The fourth time interval counter measures the time interval between the pulse signal output by the second current frequency converter and the satellite synchronization second pulse signal and sends the time interval to the computer through the data pass-through module.

[0016] The computer calculates the standard electrical energy based on the pulse count and time interval data transmitted from the laboratory end, and calculates the charging pile's electrical energy based on the pulse count and time interval data transmitted from the calibrated end. Finally, it calculates the deviation between the standard electrical energy and the charging pile's electrical energy, thus realizing remote calibration of the charging pile.

[0017] Preferably, each time accumulation module is composed of a time counter circuit; when the input signal is high, the time accumulation module starts timing; when the input signal is low, the time accumulation module stops timing.

[0018] Preferably, the core of both the first voltage-frequency converter and the second voltage-frequency converter is the LM331 chip; the LM331 chip uses a temperature-compensated bandgap reference circuit.

[0019] Preferably, both the first current-frequency converter and the second current-frequency converter are composed of an integrator circuit, a comparator circuit, a synchronization circuit, a timing distribution circuit, an electronic switch, and a constant current source circuit.

[0020] The present invention also provides a remote calibration method for charging piles, which uses the aforementioned remote calibration system for charging piles and includes the following steps:

[0021] ① At the laboratory end, the standard electrical energy output is as follows:

[0022]

[0023] In the formula, W A This refers to the electrical energy output from the laboratory during the calibration period. This represents the average value of the output voltage at the laboratory terminal. The average value of the output current at the laboratory terminal, Δt A For calibration duration;

[0024] The standard voltage is converted into a pulse signal by a first voltage-to-frequency converter. The conversion relationship model with pulse signals is as follows:

[0025]

[0026]

[0027] In the formula, The time interval between the pulse signal output by the first voltage-frequency converter and the satellite synchronization second pulse signal, as measured by the first time interval counter at time i. Let n be the number of pulses in the pulse signal output by the first voltage-frequency converter, measured by the first pulse counter at time i, within a complete cycle of each satellite synchronization second pulse signal; and let n be the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the pulse signal. U That is the voltage-to-frequency conversion coefficient of the first voltage-to-frequency converter;

[0028] Using the same principle, the current is converted into a pulse signal by a first current-to-frequency converter. The conversion relationship model with pulse signals is as follows:

[0029]

[0030]

[0031] In the formula, The time interval between the pulse signal output by the first current-frequency converter and the satellite synchronization second pulse signal, as measured by the second time interval counter at time i, is given. Let be the number of pulses in the pulse signal output by the first current-frequency converter, measured by the second pulse counter at time i, within a complete cycle of each satellite synchronization second pulse signal; n be the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the pulse signal; and k be the number of pulses in the second pulse signal. I That is the current-frequency conversion coefficient of the first current-frequency converter;

[0032] ② At the calibrated end, the formula for the electrical energy output by the charging pile is as follows:

[0033]

[0034] In the formula, W B This refers to the electrical energy output by the standard charging station within the calibration time. The average value of the output voltage of the charging pile being calibrated. The average value of the output current of the charging pile being calibrated is Δt. B For calibration duration;

[0035] The voltage output from the charging station is converted into a pulse signal by a second voltage-to-frequency converter. The conversion relationship model with pulse signals is as follows:

[0036]

[0037]

[0038] In the formula, The time interval between the pulse signal output by the second voltage-frequency converter and the satellite synchronization second pulse signal, as measured by the third time interval counter at time i, is given. Let be the number of pulses in the second voltage-frequency converter output signal measured by the third pulse counter at time i within a complete cycle of each satellite synchronization second pulse signal, and let n be the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the pulse signal. U This is the voltage-to-frequency conversion coefficient of the second voltage-to-frequency converter;

[0039] Using the same principle, a second current-frequency converter converts the current output from the charging pile into a pulse signal. The conversion relationship model with pulse signals is as follows:

[0040]

[0041]

[0042] In the formula, The time interval between the pulse signal output by the second current-frequency converter and the satellite synchronization second pulse signal, as measured by the fourth time interval counter at time i, is given. Let be the number of pulses in the second current-frequency converter output signal measured by the fourth pulse counter at time i within a complete cycle of each satellite synchronization second pulse signal, and let n be the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the pulse signal. I This is the current-frequency conversion coefficient of the second current-frequency converter;

[0043] ③ The difference between the standard electrical energy output from the laboratory end and the electrical energy output from the DC charging pile at the calibrated end is the electrical energy deviation, i.e., ΔW, as follows:

[0044] ΔW=W A -W B

[0045] At this point, the power calibration of the charging pile is complete.

[0046] This invention addresses the increasing demand for electric vehicle charging pile verification while traditional verification methods suffer from low efficiency and high costs. It explores a remote calibration system and method for charging piles by closely integrating Internet of Things (IoT) technology and remote calibration technology. This method enables online calibration without the need to transport the standard instrument to the calibration site via logistics, thereby changing the traceability process, improving calibration efficiency, and reliably achieving remote verification of the energy metering device of electric vehicle DC charging piles.

[0047] This system is based on the satellite common-view method, a high-precision voltage-frequency conversion module, and a current-frequency conversion module, enabling real-time power calibration of the charging pile being calibrated. Its significant advantages are:

[0048] (1) No metrology personnel are required to bring standard devices to the site for on-site verification. Calibration can be completed remotely through software operations in a laboratory. This significantly reduces costs in terms of manpower, transportation, and time. Furthermore, the standard devices will not suffer irreversible instrument damage due to frequent transportation, effectively improving metrological verification efficiency and creating possibilities to meet the future verification needs of a large number of charging piles.

[0049] (2) Online testing has been achieved, and the calibration results of DC charging piles can be obtained in real time. Electric vehicles can be used as test loads in the calibration process, and metrology work can be carried out simultaneously during the charging process without causing additional energy waste. This effectively solves the problem that the normal operation of charging piles and metrology calibration cannot be taken into account at the same time, and improves the calibration efficiency from another perspective.

[0050] (3) This system can simultaneously calibrate multiple DC charging piles. By connecting the interfaces of multiple charging piles to the system hardware interface installed at the calibration site, real-time calibration data of multiple charging piles can be obtained, which greatly improves the calibration efficiency of DC charging piles and effectively reduces metrology costs.

[0051] After collecting calibration data, this system transmits it back to the laboratory via network communication technology. Data processing and calibration are then performed on a computer, taking into full account additional errors caused by environmental factors at the calibrated end to ensure the accuracy of the calibration results. Simultaneously, it significantly shortens the calibration cycle, reduces labor costs, and improves calibration efficiency, truly realizing remote metering and calibration of electrical energy. Attached Figure Description

[0052] Figure 1 The flowchart of the remote calibration system for charging piles.

[0053] Figure 2 This is a hardware structure diagram of a remote calibration system for charging piles.

[0054] Figure 3 Flowchart of the host computer software execution for remote calibration of charging piles. Detailed Implementation

[0055] Based on theoretical analysis and prior work experience, this invention designs and optimizes the design scheme for a remote calibration system for charging piles. There are three existing methods for implementing remote measurement value transfer and traceability technology for metrological instruments: The first is to use a standard meter for on-site verification and calibration. This method is low-cost and easy to implement, but it cannot detect the additional errors of the standard meter, and the measurement value may change during the transfer process. The second method involves placing the standard meter on-site, requiring it to be periodically verified in a central laboratory. This method is also easy to implement, but it shares the same disadvantages as the first method, and the measurement cost increases. The third method involves having the metrological standard in the laboratory, and using IoT-based remote measurement value transfer and traceability to remotely calibrate the on-site instrument via the network. This method is efficient and low-cost, but it presents some technical challenges. Currently, time-frequency remote calibration can achieve the level of the third scheme. The principle is to calculate the time difference between the reference time at the calibrated instrument and the reference time of the standard using the satellite common-view method, and then use a corresponding algorithm to process the frequency difference to complete the calibration process.

[0056] The remote calibration system for charging piles provided by this invention is based on remote measurement and traceability technology of the Internet of Things (IoT). This invention designs a high-precision voltage-to-frequency conversion module and a current-to-frequency conversion module, simultaneously converting the voltage output from the DC voltage source and the current output from the DC current source into corresponding frequency signals. Furthermore, based on the BeiDou satellite common-view method and related data processing algorithms, the design of the remote calibration system for charging piles is completed. This invention can save time and labor costs, improve verification efficiency, and promote the development of testing and calibration technology in my country.

[0057] This invention designs a remote calibration system for charging piles based on the common-view method. Combined with... Figure 2 The entire system hardware consists of the device being calibrated, a standard source device, a voltage-to-frequency conversion module, a current-to-frequency conversion module, a pulse counter, a time interval counter, and a BeiDou satellite common-view receiver. In the voltage source remote calibration system and calibration method (CN 113156356 B) previously proposed by the research team at Hebei University, voltage source calibration requires measuring the voltage difference between the two voltage sources. The voltage deviation between the two ends corresponds to the frequency deviation, which in turn causes a time deviation in the comparison between the pulse signals at both ends and the satellite pulse signal. Frequency deviation is a key factor for the system to accurately achieve remote calibration, and its accuracy must be guaranteed. In the frequency deviation calibration model, the accuracy of the time difference value (the time difference between the output pulse of the local voltage-to-frequency converter or current-to-frequency converter and the receiver synchronization pulse) has a significant impact on the calibration results. The time difference data acquisition period is 960s. The time difference value is obtained by performing least-squares linear fitting on the 960s of data received by the time interval counters at both ends, and the midpoint value of the fitted line is recorded as the final fitting result. Therefore, the time difference value obtained through data fitting is not accurate enough. The calibration model for frequency deviation also revealed some problems in practical applications and experimental verification: (1) Inaccuracy: Since the calibration model assumes a linear functional relationship between frequency deviation and time deviation and is obtained by fitting a large amount of experimental data, it reduces the accuracy of frequency deviation measurement in the system. (2) Non-uniqueness: At each calibration point, a corresponding calibration model needs to be fitted with a large amount of experimental data, which cannot guarantee the stability of the calibration model. (3) Long time consumption: Since the accuracy of the calibration model is limited, it is necessary to obtain more experimental data over a longer period of time to ensure the relative accuracy of the calibration results.

[0058] This invention upgrades both the calibration model construction and the hardware structure. Regarding the calibration model, to improve the accuracy of frequency deviation measurement, the experimental data fitting method is no longer used. Instead, more reference values ​​are added to the frequency deviation measurement, and the frequency deviation is split into integer and fractional parts for separate measurement, achieving quantitative calculation of the frequency deviation. Correspondingly, a pulse counter is added to the hardware structure. The pulse counter measures the number of pulses in the complete cycle of each satellite synchronization second pulse from the pulse signal output by the voltage-frequency converter. The time interval counter measures the time interval between each pulse signal output by the voltage-frequency converter and the non-complete cycle of the satellite synchronization second pulse. The pulse counter and the time interval counter work together. The fractional part of the frequency value is measured by the time interval counter, and the number of consecutive square wave pulses within the second pulse cycle is used as the integer part of the frequency value and measured by the pulse counter, completing the remote calibration of the voltage value. This method perfectly solves the above problems, significantly improving the accuracy of frequency deviation measurement and effectively reducing calibration time. The remote calibration of the current value is calculated using the same mathematical model. In summary, by using the BeiDou satellite synchronous second pulse signal as the reference signal for common observation, and combining the pulse signals of the voltage and current sources at corresponding frequencies with the satellite second pulse signal for remote comparison, and then calculating the energy deviation between the standard end and the calibrated end based on the constructed energy deviation calibration model, remote calibration of charging piles can be effectively achieved. This invention not only ensures the accuracy and reliability of measurement data but also effectively improves calibration efficiency, laying the foundation for the intelligent application of instruments.

[0059] The present invention first requires the design of a high-precision voltage-frequency conversion module and a current-frequency conversion module. These two modules are used to convert the electrical parameters output by the standard voltage source, current source and the voltage source and current source under test into corresponding frequency signals. Then, based on the Beidou satellite common-view method and related algorithms, the remote calibration process of the charging pile is completed.

[0060] (1) Principle of BeiDou Satellite Common View Method:

[0061] The common-view method for time and frequency transfer using the BeiDou satellite is one of the main methods for long-distance time and frequency measurement. The basic principle of the common-view method is that, within the perspective of a single BeiDou satellite, atomic clocks located in two different locations can compare their time and frequency using the satellite's time signal received at the same time. Under the same common-view timer, the common-view receivers at the calibration laboratory and the laboratory being calibrated receive the same BeiDou satellite signal at the same time. They use a time interval counter and a pulse counter to measure the time difference between the BeiDou satellite's second pulse and the local atomic clock's second pulse. After each measurement cycle, the data from the laboratory being calibrated is transmitted to the calibration laboratory via the internet. The time difference between the two atomic clocks is then calculated by subtracting the time difference data from both ends. Let t be the clock time at the calibration laboratory and the laboratory being calibrated. A and tB The BeiDou satellite time is t BDS The time difference between the second pulse of the atomic clock at the calibration laboratory and the second pulse of the BeiDou satellite is Δt. ABDS and Δt BBDS Then we have:

[0062] Δt ABDS =t A -t BDS

[0063] Δt BBDS =t B -t BDS

[0064] Δt ABDS -Δt BBDS =t A -t B =Δt AB

[0065] After multiple measurements, a series of Δt values ​​can be obtained. ABi From this, the average relative frequency deviation between the two atomic clocks over a period of time can be calculated.

[0066]

[0067] Where f A f B τ represents the frequency of the clocks at the calibration laboratory and the calibrated laboratory, respectively, and τ is the average time interval.

[0068] (2) Principle of voltage-to-frequency conversion module (V / F):

[0069] Monolithic integrated V / F converters are widely used in automatic control, digital instruments, and wireless equipment to convert voltage to frequency. Converting voltage to frequency signals enhances their anti-interference capabilities and makes them extremely convenient to use. In practical signal conversion, the main conversion methods include multivibrator and charge-balanced conversion. Because charge-balanced VFC devices have higher accuracy than other devices, this invention selects a charge-balanced voltage-to-frequency conversion module. Its basic principle is: using a capacitor as the charge carrier, the input voltage V... IN A current I is generated that is proportional to it. IN The capacitor is charged simultaneously using a known constant current source I. REF (where I) REF >I INmax The capacitor is periodically reverse-charged, with each charging session lasting a fixed time of T. cThis achieves a balance of input and output charges on the capacitor within each cycle or several cycles. Simultaneously, this cycle is also the cycle of the output signal, and the frequency or average frequency of the output signal is related to the input voltage V. IN It is directly proportional. The voltage-frequency converter actually only converts voltage into a pulse train; the final frequency value still needs to be calculated by counting the pulses using a time interval counter and a pulse counter.

[0070] Based on comprehensive research, the LM331 chip manufactured by NS Corporation was selected as the core for the design of the voltage-to-frequency conversion module. The LM331 chip is a cost-effective integrated circuit. When used as a voltage-to-frequency converter, its output is a pulse train, the frequency of which is proportional to the input voltage. The pulse output is compatible with all logic forms, providing the inherent advantages of all voltage-to-frequency conversion technologies and allowing for easy application in various voltage-to-frequency converters. The LM331 chip employs a new temperature-compensated bandgap reference circuit, resulting in excellent temperature stability and high accuracy across the entire operating temperature range and at low power supply voltages, up to ±50ppm / ℃. Simultaneously, the chip has a wide dynamic range of 100dB. The chip offers high voltage-to-frequency conversion accuracy with a digital resolution of up to 12 bits. Furthermore, the chip exhibits good voltage-to-frequency conversion linearity, with a maximum nonlinear distortion of less than 0.01%.

[0071] (3) Principle of current-frequency conversion module (I / F):

[0072] The current-frequency converter consists of an integrator circuit, a comparator circuit, a synchronization circuit, a timing distribution circuit, an electronic switch, and a constant current source circuit. Its working principle is: when the input current I... in When the integrating capacitor of the integrator is charged (assuming a positive current), it becomes charged, generating a corresponding voltage at the output of the operational amplifier in the integrator. This voltage is compared with the reference voltage of the comparator circuit. One comparator circuit will produce a pulse output (while the other will not). This output signal is sent to the synchronization circuit for synchronization with the system clock. The pulse signal output by the trigger in the synchronization circuit is shaped by the timing distribution circuit to obtain the positive frequency output signal F+. Simultaneously, the pulse signal generated by the timing distribution circuit controls the constant current source to discharge the integrating capacitor through an electronic switch. When the charge on the integrating capacitor is completely released, the input current will charge the integrating capacitor again, causing the circuit to enter the next cycle. Similarly, when the input current is negative, another part of the circuit performs the above work and outputs a negative frequency signal F-.

[0073] (4) Time accumulation module

[0074] The time accumulation module mainly consists of a counter circuit. This module is used in both the laboratory and the calibrated end to calculate the calibration duration. Specifically, the time accumulation module starts timing when the input signal is high and stops timing when the input signal is low. Furthermore, this module can transmit the measured experimental data to the laboratory computer via a serial port connection.

[0075] (5) Principle of power deviation measurement

[0076] The DC charging energy metering algorithm is the core of the high-precision metering verification system design. This system references the average value method, and its calculation expression is:

[0077]

[0078] In the formula, W represents the average value method for measuring electrical energy. P represents the average voltage, average current, and average power over the time interval Δt.

[0079] ① At the laboratory end, the electrical energy output by the standard device is expressed according to the above formula:

[0080]

[0081] In the formula, W A The electrical energy output by the standard terminal within the calibration time. This represents the average value of the output voltage at the standard terminal. The average value of the output current at the standard terminal, Δt A For calibration duration.

[0082] The voltage is converted into a pulse signal using a high-precision voltage-to-frequency conversion module. The conversion relationship model with pulse signals is as follows:

[0083]

[0084]

[0085] In the formula, Let be the time interval between the pulse signal output by the voltage-frequency converter measured by the time interval counter at time i and the satellite synchronization second pulse. denoted as the number of pulses in the voltage-frequency converter output pulse signal measured by the pulse counter at time i within a complete cycle of each satellite synchronization second pulse. It is an abstract function consisting of time interval and pulse number as dependent variables, Δt Ai This represents the difference between the (i+1)th time interval and the ith time interval at the laboratory end (i.e., ), where n is the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the pulse signal output by the voltage-frequency converter, and k is the number of pulses per second. U This refers to the voltage-to-frequency conversion coefficient of the voltage-to-frequency converter. In this calibration system, the coefficient k... U It can be adjusted through configuration, and the default value is a constant.

[0086] Using the same principle, a high-precision current-to-frequency conversion module converts the current into a pulse signal. The conversion relationship model with pulse signals is as follows:

[0087] The conversion relationship model with pulse signals is as follows:

[0088]

[0089]

[0090] In the formula, The time interval between the pulse signal output by the current-frequency converter, measured by the time interval counter at time i, and the satellite synchronization second pulse is given. Let i be the number of pulses of the pulse signal output by the current-frequency converter, measured by the pulse counter at time i, within each complete cycle of the satellite synchronization second pulse. It is an abstract function consisting of time interval and pulse number as dependent variables, Δt Ai This represents the difference between the (i+1)th time interval and the ith time interval at the laboratory end (i.e., ), where n is the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the pulse signal output by the current-frequency converter, and k is the number of pulses per second. I This refers to the current-to-frequency conversion coefficient of the current-to-frequency converter. In this calibration system, the coefficient k... I It can be adjusted through configuration, and the default value is a constant.

[0091] ② At the calibration end, the electrical energy output by the calibrated charging pile is expressed using the average value method and the electrical energy measurement formula as follows:

[0092]

[0093] In the formula, W B The electrical energy output by the standard terminal within the calibration time. The average value of the output voltage at the calibrated terminal. The average value of the output current at the calibrated terminal, Δt B For calibration duration.

[0094] The voltage is converted into a pulse signal using a high-precision voltage-to-frequency conversion module. The conversion relationship model with pulse signals is as follows:

[0095]

[0096]

[0097] In the formula, Let be the time interval between the pulse signal output by the voltage-frequency converter measured by the time interval counter at time i and the satellite synchronization second pulse. denoted as the number of pulses in the voltage-frequency converter output pulse signal measured by the pulse counter at time i within a complete cycle of each satellite synchronization second pulse. It is an abstract function consisting of time interval and pulse number as dependent variables, Δt Bi This represents the difference between the (i+1)th time and the ith time at the calibrated end (i.e., ), where n is the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the pulse signal output by the voltage-frequency converter, and k is the number of pulses per second. U This refers to the voltage-to-frequency conversion coefficient of the voltage-to-frequency converter. In this calibration system, the coefficient k... U It can be adjusted through configuration, and the default value is a constant.

[0098] Using the same principle, a high-precision current-to-frequency conversion module converts the current into a pulse signal. The conversion relationship model with pulse signals is as follows:

[0099]

[0100]

[0101] In the formula, The time interval between the pulse signal output by the current-frequency converter, measured by the time interval counter at time i, and the satellite synchronization second pulse is given. denoted as the number of pulses in the pulse signal output by the current-frequency converter, measured by the pulse counter at time i, within each complete cycle of the satellite synchronization second pulse. It is an abstract function consisting of time interval and pulse number as dependent variables, Δt Bi This represents the difference between the (i+1)th time and the ith time at the calibrated end (i.e., ), where n is the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the pulse signal output by the current-frequency converter, and k is the number of pulses per second. I This refers to the current-to-frequency conversion coefficient of the current-to-frequency converter. In this calibration system, the coefficient k... I It can be adjusted through configuration, and the default value is a constant.

[0102] ③ The difference between the output power of the standard device at the laboratory end and the output power of the DC charging pile at the calibrated end is the power deviation, i.e., ΔW in the formula. Thus, this system completes the power calibration work.

[0103] ΔW=W A -W B

[0104] This invention utilizes LabVIEW-based system software to control the setting of various calibration parameters. During calibration, the standard emits a standard signal, the DC charging pile under test emits a test signal, and the signals are acquired in real time by a time interval counter and a pulse counter. The calibration software calculates the error and uncertainty, and completes the measurement of power deviation in the computer, thus completing the remote calibration of the charging pile. Figure 1 The complete calibration process of this system is as follows: (1) System initialization: Start the client calibration program, the system's device management module sends an initialization command to the system hardware, completes the functional testing of each test instrument interface, and records the parameter information of the standard device and the DC charging pile under test. (2) System test point setting: On the main page of the calibration system, select and set the power calibration point and the corresponding model of the calibration point, as well as the relevant parameters such as the acquisition time, and automatically detect whether the remote calibration instrument is started normally. (3) Send calibration command and collect power deviation data: The system's calibration control module sends a calibration start command, reads the set test point, collects the average voltage, average current, calibration time and other data of the standard end and the DC charging pile under test, and stores them in the corresponding path. (4) Calibration data processing and report generation: At the end of each test cycle, the system's real-time test module analyzes the calibration data according to the set data algorithm and determines the test results. Then, the power deviation at both ends is obtained through software algorithm processing and the corresponding error and uncertainty analysis is given, generating the corresponding report or calibration certificate to complete the remote calibration process of the DC charging pile.

[0105] Figure 2 This is a hardware structure diagram of a remote calibration system for charging piles. The system hardware consists of a standard voltage source, a standard current source, a time counter, a voltage-to-frequency converter, a current-to-frequency converter, a time interval counter, a pulse counter, and a BeiDou satellite receiver. Both the BeiDou satellite receivers at the calibrated end and the laboratory end have built-in atomic clocks, allowing them to receive synchronous satellite clock signals simultaneously. The BeiDou satellite synchronous second pulse signal is used as the reference signal for this system. The control computer acquires data from the time interval counter and pulse counter at the laboratory end through a standard interface and uses remote data transmission technology to obtain the pulse frequency at the calibrated end in real time, completing the calibration calculations.

[0106] (1) Remote calibration of charging pile output voltage value

[0107] At the laboratory end, a standard voltage source simultaneously outputs voltage values ​​to a high-precision voltage-to-frequency converter and a time accumulation module. Channels 3 and 1 of the voltage-to-frequency converter are connected to channels 2 of the pulse counter and time interval counter, respectively. This module converts the voltage into pulse signals and outputs them to the pulse counter and time interval counter, respectively. The time accumulation module mainly consists of a time counter circuit and is used to calculate the calibration duration. When the input signal is high, the time accumulation module starts timing; when the input signal is low, the time accumulation module stops timing. For other hardware connections, channels 1 and 2 of the satellite synchronization clock source are connected to channels 1 of the time counter and pulse counter, respectively, providing them with the synchronization second pulse frequency signal. The pulse counter measures the number of pulses in the pulse signal output by the voltage-to-frequency converter within each complete cycle of the satellite synchronization second pulse. The time interval counter measures the time interval between the pulse signal output by the voltage-to-frequency converter and the satellite synchronization second pulse. Thus, the pulse signal of the voltage source at the corresponding frequency is compared with the satellite second pulse signal in the two hardware devices. The output interfaces of the time interval counter and pulse counter are connected to serial ports 1 and 2 of the computer, respectively, transmitting the time interval data and pulse count data to the computer.

[0108] At the calibration end, the actual voltage value of the charging pile is simultaneously output to a high-precision voltage-to-frequency converter and a time accumulation module. Channels 3 and 1 of the voltage-to-frequency converter are connected to channels 2 of the pulse counter and time interval counter, respectively. This module converts the voltage into pulse signals and outputs them to the pulse counter and time interval counter, respectively. The time accumulation module mainly consists of a time counter circuit and is used to calculate the calibration duration. When the input signal is high, the time accumulation module starts timing; when the input signal is low, the time accumulation module stops timing. The time accumulation modules at both the laboratory end and the calibration end keep timing simultaneously, enabling bidirectional comparison of the calibration duration to ensure the accuracy of time measurement. Channels 1 and 2 of the satellite synchronization clock source are connected to channels 1 of the time interval counter and pulse counter, respectively, providing them with a synchronization second pulse frequency signal. The pulse counter and time interval counter at the calibration end have the same hardware functions as the device at the laboratory end. Thus, the actual output voltage of the charging pile is converted into a pulse signal of the corresponding frequency and compared with the satellite second pulse signal in the two hardware devices mentioned above. The output interfaces of the time interval counter and pulse counter are connected to serial port 1 and serial port 2 of the data pass-through module, respectively, and the processed time interval data and pulse count data are transmitted to the data pass-through module. After acquiring the data, the data pass-through module transmits it to the laboratory computer via a mobile communication network.

[0109] (2) Remote calibration of charging pile output current value

[0110] In the standard current source section, the standard current value from the laboratory end is simultaneously output to a high-precision current-to-frequency converter and a time accumulation module. Channels 3 and 1 of the current-to-frequency converter are connected to channels 2 of the pulse counter and time interval counter, respectively. This module converts the current into pulse signals and outputs them to the pulse counter and time interval counter, respectively. The time accumulation module mainly consists of a time counter circuit and is used to calculate the calibration duration. Similarly, channels 4 and 3 of the satellite synchronization clock source are connected to channels 1 of the pulse counter and time interval counter, respectively, to achieve synchronous output of the second pulse frequency signal. Thus, the pulse signal of the current source corresponding to the frequency is combined with the satellite second pulse signal to complete signal comparison in the two hardware devices mentioned above. The output interfaces of the time interval counter and the pulse counter are then connected to serial ports 4 and 5 of the computer, respectively, and the time interval data and pulse count data are transmitted to the computer.

[0111] At the calibration end, the actual current value of the charging pile is simultaneously output to a high-precision current-frequency converter and a time accumulation module. Channels 3 and 1 of the current-frequency converter are connected to channels 2 of the pulse counter and time interval counter, respectively. This module converts the current into pulse signals and outputs them to the pulse counter and time interval counter, respectively. The time accumulation module mainly consists of a time counter circuit and is used to calculate the calibration duration. The time accumulation modules at both the laboratory end and the calibration end keep time simultaneously, enabling bidirectional comparison of the calibration duration to ensure the accuracy of time measurement. Channels 3 and 4 of the satellite synchronization clock source are connected to channels 1 of the time interval counter and pulse counter, respectively, and provide them with a synchronization second pulse frequency signal. The pulse counter and time interval counter at the calibration end have the same hardware functions as the device at the laboratory end. Thus, the actual output current of the charging pile is converted into a pulse signal of the corresponding frequency and compared with the satellite second pulse signal in the two hardware devices mentioned above. The output interfaces of the time interval counter and pulse counter are connected to serial ports 4 and 5 of the data pass-through module, respectively, and the processed time interval data and pulse count data are transmitted to the data pass-through module. After the data transmission module collects the data, it transmits it to the laboratory computer via a mobile communication network.

[0112] (3) Remote calibration of charging pile output power

[0113] The computer program processes the data collected from both ends. The frequency deviation of the pulse signals converted from the voltage and current parameters at both ends is used to obtain the energy deviation between the two ends based on the remote calibration model formula. The specific algorithm of the remote calibration model is as follows:

[0114] ① The average value of electrical energy is expressed as follows:

[0115]

[0116] In the formula, W represents the average value method for measuring electrical energy. P represents the average voltage, average current, and average power over the time interval Δt.

[0117] ② High-precision voltage-frequency conversion modules and current-frequency conversion modules can convert voltage and current into pulse signals. The conversion formula is as follows:

[0118]

[0119] In the formula, t i N represents the time interval between the pulse signal output by the voltage-frequency converter or current-frequency converter measured by the time interval counter at time i and the satellite synchronization second pulse. i The pulse count is the number of pulses in each complete cycle of the satellite synchronization second pulse, as measured by the pulse counter at time i, output by the voltage-frequency converter or the current-frequency converter. It is an abstract function consisting of the time interval and pulse number at time i as dependent variables. k is the conversion coefficient of the voltage / current frequency converter. In this calibration system, the coefficient k can be adjusted through configuration, and defaults to a constant.

[0120] ③ The difference between the output power of the standard device at the laboratory end and the output power of the DC charging pile at the calibrated end is the power deviation, i.e., ΔW in the formula.

[0121] ΔW=W A -W B

[0122] By completing the corresponding algorithm processing in the computer, remote power calibration between the calibrated end and the laboratory end can be achieved.

[0123] Figure 3This document presents the execution flowchart of the host computer software for remote calibration of charging piles. The host computer software system serves as the control hub for human-computer interaction. This system utilizes LabVIEW software and relevant instrument drivers to develop automatic calibration programs and software call frameworks. The software design must adhere to relevant metrological verification regulations, optimizing the system control algorithm to achieve all calibration requirements without sacrificing control accuracy, while minimizing testing time. The host computer software system primarily employs a concurrent scheme for three threads: UI interface refresh, real-time testing process, and real-time data storage. After the system officially starts, the host computer software enters the initialization program, primarily checking the functionality of each testing instrument interface. It then enters the initial calibration system homepage, providing UI interaction functions such as equipment management, real-time testing, data processing, and report management. First, the system enters the equipment management terminal to configure the parameters of the charging pile under test and the environmental parameters of the testing instruments. Next, it enters the real-time testing terminal to configure the corresponding calibration projects and items. Subsequently, the remote calibration process is initiated. During calibration, the collected data is analyzed and processed to achieve real-time display of various progress and data, including measurement progress display, measurement data display, and single-point retest display, and the data is completely saved to the database. After the test, the system can provide calibration results and fault feedback. Users can browse calibration data and export corresponding calibration reports through the historical data terminal. They can also customize calibration report templates and export reports based on the calibration data through the report terminal.

Claims

1. A remote calibration system for charging piles, characterized in that, Including the laboratory end and the calibrated end; The laboratory is equipped with a standard voltage source, a standard current source, a first voltage-to-frequency converter, a first current-to-frequency converter, a first satellite synchronization clock source, a first time accumulation module, a second time accumulation module, a first pulse counter, a second pulse counter, a first time interval counter, a second time interval counter, and a computer. The standard voltage source is connected to the first time accumulation module and the first voltage frequency converter. The standard voltage source is used to output the standard voltage value to the first time accumulation module and the first voltage frequency converter simultaneously. The first time accumulation module is used to calculate the calibration duration based on the output signal of the standard voltage source and output the signal to the computer; the first voltage frequency converter is also connected to the first pulse counter and the first time interval counter. The first voltage frequency converter is used to convert the standard voltage value into a pulse signal and output it to the first pulse counter and the first time interval counter respectively. The first pulse counter and the first time interval counter are also connected to the first satellite synchronization clock source, which is used to receive BeiDou satellite signals and output satellite synchronization second pulse signals to the first pulse counter and the first time interval counter. The first pulse counter is used to measure the number of pulses of the pulse signal output by the first voltage-frequency converter within each complete cycle of the satellite synchronization second pulse signal, and sends the pulse count to the computer; the first time interval counter is used to measure the time interval between the pulse signal output by the first voltage-frequency converter and the non-complete cycle of the satellite synchronization second pulse signal, and sends the time interval to the computer; the integer part of the frequency of the pulse signal output by the first voltage-frequency converter is measured by the first pulse counter, and its fractional part is measured by the first time interval counter; The standard current source is connected to the second time accumulation module and the first current frequency converter. The standard current source is used to output the standard current value to the second time accumulation module and the first current frequency converter simultaneously. The second time accumulation module is used to calculate the calibration duration based on the output signal of the standard current source and output the signal to the computer; the first current frequency converter is also connected to the second pulse counter and the second time interval counter. The first current frequency converter is used to convert the standard current value into a pulse signal and output it to the second pulse counter and the second time interval counter respectively. The second pulse counter and the second time interval counter are also connected to the first satellite synchronization clock source, which is used to receive BeiDou satellite signals and output satellite synchronization second pulse signals to the second pulse counter and the second time interval counter. The second pulse counter is used to measure the number of pulses of the pulse signal output by the first current frequency converter within each complete cycle of the satellite synchronization second pulse signal, and sends the pulse count to the computer; the second time interval counter is used to measure the time interval between the pulse signal output by the first current frequency converter and the non-complete cycle of the satellite synchronization second pulse signal, and sends the time interval to the computer; the integer part of the frequency of the pulse signal output by the first current frequency converter is measured by the second pulse counter, and its fractional part is measured by the second time interval counter; The calibration end is equipped with a second voltage-frequency converter, a second current-frequency converter, a second satellite synchronization clock source, a third time accumulation module, a fourth time accumulation module, a third pulse counter, a fourth pulse counter, a third time interval counter, and a fourth time interval counter; The charging station is located at the end being calibrated; The voltage output terminal of the charging pile is connected to the third time accumulation module and the second voltage frequency converter. The charging pile outputs the voltage value to the third time accumulation module and the second voltage frequency converter through its voltage output terminal. The third time accumulation module is used to calculate the calibration duration based on the voltage value output by the charging pile, and transmits the output signal to the computer through the data pass-through module; the second voltage frequency converter is also connected to the third pulse counter and the third time interval counter. The second voltage frequency converter is used to convert the voltage value into a pulse signal and output it to the third pulse counter and the third time interval counter respectively. The third pulse counter and the third time interval counter are also connected to the second satellite synchronization clock source, which is used to receive BeiDou satellite signals and output satellite synchronization second pulse signals to the third pulse counter and the third time interval counter. The third pulse counter is used to measure the number of pulses of the pulse signal output by the second voltage-frequency converter within each complete cycle of the satellite synchronization second pulse signal, and transmits the pulse count to the computer through the data pass-through module; the third time interval counter is used to measure the time interval between the pulse signal output by the second voltage-frequency converter and the non-complete cycle of the satellite synchronization second pulse signal, and transmits the time interval to the computer through the data pass-through module; the integer part of the frequency of the pulse signal output by the second voltage-frequency converter is measured by the third pulse counter, and its fractional part is measured by the third time interval counter; The charging pile's current output terminal is connected to the fourth time accumulation module and the second current frequency converter. The charging pile outputs the current value to the fourth time accumulation module and the second current frequency converter through its current output terminal. The fourth time accumulation module is used to calculate the calibration duration based on the current value output by the charging pile, and transmits the output signal to the computer through the data pass-through module; the second current frequency converter is also connected to the fourth pulse counter and the fourth time interval counter. The second current frequency converter is used to convert the current value into a pulse signal and output it to the fourth pulse counter and the fourth time interval counter respectively; the fourth pulse counter and the fourth time interval counter are also connected to the second satellite synchronization clock source. The second satellite synchronization clock source is used to receive Beidou satellite signals and output satellite synchronization second pulse signals to the fourth pulse counter and the fourth time interval counter. The fourth pulse counter is used to measure the number of pulses of the pulse signal output by the second current frequency converter within each complete cycle of the satellite synchronization second pulse signal, and transmits the pulse count to the computer through the data pass-through module; the fourth time interval counter is used to measure the time interval between the pulse signal output by the second current frequency converter and the non-complete cycle of the satellite synchronization second pulse signal, and transmits the time interval to the computer through the data pass-through module; the integer part of the frequency of the pulse signal output by the second current frequency converter is measured by the fourth pulse counter, and its fractional part is measured by the fourth time interval counter; The computer calculates the standard energy based on the number of pulses and time interval data transmitted from the laboratory end, and calculates the energy of the charging pile based on the number of pulses and time interval data transmitted from the calibrated end. Finally, it calculates the deviation between the standard energy and the charging pile energy to achieve remote calibration of the charging pile. The core of both the first and second voltage-frequency converters is the LM331 chip; the LM331 chip uses a temperature-compensated bandgap reference circuit inside. Both the first and second current-frequency converters consist of an integrator circuit, a comparator circuit, a synchronization circuit, a timing distribution circuit, an electronic switch, and a constant current source circuit.

2. The remote calibration system for charging piles according to claim 1, characterized in that, Each time accumulation module consists of a time counter circuit; when the input signal is high, the time accumulation module starts timing; when the input signal is low, the time accumulation module stops timing.

3. A method for remote calibration of charging piles, characterized in that, The calibration method employs the remote calibration system for charging piles as described in claim 1, and the calibration method includes the following steps: ① At the laboratory end, the standard electrical energy output is as follows: ， In the formula, This refers to the electrical energy output from the laboratory during the calibration period. This represents the average value of the output voltage at the laboratory terminal. This represents the average value of the output current at the laboratory end. For calibration duration; The standard voltage is converted into a pulse signal by a first voltage-to-frequency converter. The conversion relationship model with pulse signals is as follows: ， ， In the formula, For the first The time interval between the pulse signal output by the first voltage-frequency converter, measured by the first time interval counter, and the non-complete cycle of the satellite synchronization second pulse signal. For the first The pulse signal output by the first voltage-frequency converter, measured by the first pulse counter, is the number of pulses within a complete cycle of each satellite synchronization second pulse signal; n is the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the first pulse signal. That is the voltage-to-frequency conversion coefficient of the first voltage-to-frequency converter; Using the same principle, the current is converted into a pulse signal by a first current-to-frequency converter. The conversion relationship model with pulse signals is as follows: ， ， In the formula, For the first The time interval between the pulse signal output by the first current-frequency converter and the non-complete cycle of the satellite synchronization second pulse signal, as measured by the second time interval counter. for The pulse signal output by the first current-frequency converter, measured by the second pulse counter at time t, is the number of pulses within a complete cycle of each satellite synchronization second pulse signal; n is the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the first pulse signal. That is the current-frequency conversion coefficient of the first current-frequency converter; ② At the calibrated end, the formula for the electrical energy output by the charging pile is as follows: ， In the formula, This refers to the electrical energy output by the standard charging station within the calibration time. The average value of the output voltage of the charging pile being calibrated. This represents the average output current of the charging pile at the calibrated end. For calibration duration; The voltage output from the charging station is converted into a pulse signal by a second voltage-to-frequency converter. The conversion relationship model with pulse signals is as follows: ， ， In the formula, For the first The time interval between the pulse signal output by the second voltage-frequency converter, measured by the third time interval counter, and the non-complete cycle of the satellite synchronization second pulse signal. For the first The pulse signal output by the second voltage-frequency converter, measured by the third pulse counter, is the number of pulses within a complete cycle of each satellite synchronization second pulse signal. n is the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the first pulse signal. This is the voltage-to-frequency conversion coefficient of the second voltage-to-frequency converter; Using the same principle, a second current-frequency converter converts the current output from the charging pile into a pulse signal. The conversion relationship model with pulse signals is as follows: ， ， In the formula, For the first The time interval between the pulse signal output by the second current-frequency converter and the non-complete cycle of the satellite synchronization second pulse signal, as measured by the fourth time interval counter. For the first The pulse signal output by the second current-frequency converter, measured by the fourth pulse counter, is the number of pulses within a complete cycle of each satellite synchronization second pulse signal. n is the number of second pulses when the first rising edge of the satellite second pulse signal coincides with the first pulse signal. This is the current-frequency conversion coefficient of the second current-frequency converter; ③ The difference between the standard electrical energy output from the laboratory end and the electrical energy output from the DC charging pile at the calibrated end is the electrical energy deviation, i.e. ,as follows: ， At this point, the power calibration of the charging pile is complete.

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