Remote calibration system for direct current charging pile of new energy automobile

Abstract

The invention discloses a remote calibration system for a direct-current charging pile of a new energy automobile, and relates to the technical field of electrical measurement calibration. The system comprises a laboratory end and a plurality of field ends respectively connected with the laboratory end, each field end comprises a sampling circuit formed by a resistance voltage dividing method and a shunt method, and is provided with a band-pass filter for separating sampled composite signals; wherein the laboratory end is used for carrying out remote calibration on the field ends according to a satellite common-view method, and in each field end, cyclic calibration is completed by using a second frequency counter, a reference voltage source and a second self-calibration voltage-frequency conversion module which are calibrated by a second pulse self-calibration high-precision frequency measurement method; and signal separation and error calculation are sequentially carried out by an excitation signal output by the reference voltage source and a sampling signal of the direct-current charging pile, so that independent metering calibration is realized. According to the invention, steps and processes required for calibrating traceability can be simplified, and time and cost for metering calibration are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical measurement and calibration, and in particular to a remote calibration system for a DC charging pile of a new energy vehicle. Background Art

[0002] At present, the technologies that can be applied in the field of measurement and calibration mainly include remote metering technology, voltage source remote calibration technology based on common view method, self-calibration electric energy metering technology, self-calibration frequency counting technology, DC charging pile charging technology, signal multiplexing technology, signal separation technology, etc.

[0003] With the rapid development of social economy, as a device for directly transmitting DC power to new energy electric vehicles, DC charging piles for electric vehicles are an important part of the development of electric vehicles as a whole. DC charging piles are analogous to gas pumps and are measuring instruments for trade settlement. At present, the traditional metrological verification method uses a load to simulate the charging of electric vehicles, connects standard measuring instruments in series into the circuit, and compares the display value of the standard measuring instrument with the display value of the charging pile after charging the set electric energy, so as to determine the display error of the charging pile. Due to the rapid development of electric vehicles and the surge in the number of DC charging piles, traditional on-site measurement methods have the problems of long time and low efficiency. At the same time, DC charging pile transactions are all settled remotely in the background. On-site verification can only guarantee the measurement accuracy at the current moment, and cannot obtain the additional error of the instrument in the industrial application site, nor can it avoid the additional error introduced by the standard instrument being transported to the calibration site. Summary of the invention

[0004] The purpose of the present invention is to provide a remote calibration system for a DC charging pile of a new energy vehicle, which can simplify the steps and processes required for calibration traceability and reduce the time and cost of metrological calibration.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A remote calibration system for a DC charging pile of a new energy vehicle comprises: a laboratory end and a plurality of field ends respectively connected to the laboratory end; each of the field ends comprises a sampling circuit composed of a resistor voltage divider method and a shunt method, and is provided with a bandpass filter to separate the sampled composite signal, so as to facilitate error monitoring using an excitation signal extracted from the separated signal;

[0007] Among them, the laboratory end is used to remotely calibrate the voltage source of the field end according to the satellite common view method, and in each of the field ends, the reference voltage source signal calibrated by the second pulse self-calibration high-precision frequency measurement method and the sampling signal of the DC charging pile are used to perform signal separation and error calculation in turn to achieve independent measurement and calibration.

[0008] Optionally, the laboratory end includes a standard voltage source, a laboratory end satellite second pulse receiving module, a computer, a software system and a calibration database connected in sequence; the laboratory end satellite second pulse receiving module is also connected to each of the field ends via wireless communication.

[0009] Optionally, the laboratory-end satellite second pulse receiving module specifically includes: a first self-calibration voltage-frequency conversion module, a first pulse counter, a first time interval counter, a first frequency counter, a first Beidou satellite receiver, a first CPU and a first communication module; the first self-calibration voltage-frequency conversion module is respectively connected to the standard voltage source, the first pulse counter, the first time interval counter, the first frequency counter and the first CPU; the first pulse counter and the first time interval counter are also connected to the Beidou satellite receiver; the first CPU is also respectively connected to the computer and the first communication module; the first communication module is also connected to each of the field ends.

[0010] Optionally, each of the field ends includes: a DC charging pile, a sampling circuit, an electric energy metering chip, a reference voltage source, a second frequency counter, a second CPU, a second communication module and a calibration end satellite second pulse receiving module; the DC charging pile, the sampling circuit and the electric energy metering chip are connected in sequence; the electric energy metering chip is also connected to the second CPU; the second CPU is also respectively connected to the calibration end satellite second pulse receiving module and the second communication module; the calibration end satellite second pulse receiving module is also respectively connected to the second communication module and the reference voltage source; the reference voltage source is also connected to the sampling circuit; the second communication module is also connected to the laboratory end.

[0011] Optionally, the sampling circuit specifically includes: a shunt and a voltage-dividing resistor; input ends of the shunt and the voltage-dividing resistor are respectively connected to the DC charging pile and the reference voltage source; output ends of the shunt and the voltage-dividing resistor are connected to the electric energy metering chip.

[0012] Optionally, the calibration-end satellite second pulse receiving module specifically includes: a second self-calibration voltage-frequency conversion module, a second pulse counter, a second time interval counter and a second Beidou satellite receiver; the second Beidou satellite receiver is respectively connected to the second pulse counter and the second time interval counter; the second pulse counter and the second time interval counter are also both connected to the second self-calibration voltage-frequency conversion module; the second self-calibration voltage-frequency conversion module is also respectively connected to the reference voltage source, the second frequency counter, the second CPU and the second communication module.

[0013] Optionally, the sampling circuit adopts a high voltage attenuation sampling circuit, and realizes voltage division of the DC voltage signal through a voltage divider network composed of multiple high-precision resistors.

[0014] Optionally, after extracting the excitation signal of the separated signal, the field end calculates the excitation signal measurement value based on the factory calibration parameters, compares it with the excitation signal output by the reference signal source, thereby calculating the monitoring error and restoring the load signal, thereby measuring the errors generated in the voltage sampling and current sampling circuits, and finally calculating the electric energy value by the self-calibration electric energy metering chip to complete the electric energy metering.

[0015] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0016] The present invention discloses a remote calibration system for a DC charging pile of a new energy vehicle, the system comprising a laboratory end and a plurality of field ends respectively connected to the laboratory end; each of the field ends comprises a sampling circuit composed of a resistor voltage divider method and a shunt method, and is provided with a bandpass filter to separate the sampled composite signal, so as to facilitate error monitoring using an excitation signal extracted from the separated signal; wherein the laboratory end is used to remotely calibrate the field end according to a satellite common view method, and in each of the field ends, a second frequency counter, a reference voltage source and a second self-calibration voltage-frequency conversion module calibrated by a second pulse self-calibration high-precision frequency measurement method are used to complete a cyclic calibration, and the excitation signal output by the reference voltage source and the sampling signal of the DC charging pile are sequentially subjected to signal separation and error calculation to realize independent metrological calibration. The present invention can simplify the steps and processes required for calibration traceability, and reduce the time and cost of metrological calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. 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 paying creative labor.

[0018] Figure 1 This is a schematic diagram of the structure of the remote calibration system for a DC charging pile of a new energy vehicle of the present invention;

[0019] Figure 2 This is a flowchart of the execution of the host computer software of the DC charging pile remote calibration system in this embodiment. DETAILED DESCRIPTION

[0020] The following will be combined with the 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 described embodiments 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 creative work are within the scope of protection of the present invention.

[0021] The purpose of the present invention is to provide a remote calibration system for a DC charging pile of a new energy vehicle, which can simplify the steps and processes required for calibration traceability and reduce the time and cost of metrological calibration.

[0022] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown, the present invention is mainly based on a high-precision electric energy metering chip, which integrates an advanced analog-to-digital converter (ADC) and an internal computing unit, and can quickly process signals and achieve high-precision electric energy metering. In order to cope with the challenges of wide-range voltage (0-1000V) that may be encountered during the charging process of electric vehicles, the present invention adopts a resistor voltage divider method to design a large voltage attenuation sampling circuit, and safely reduces the high voltage signal to the acceptable input range of the ADC (-10V~10V) through a precise voltage divider network, and further improves the signal quality in combination with a signal conditioning circuit. At the same time, in response to the difficulty of large current collection, the system innovatively applies the shunt method to convert large currents into small currents in proportion for sampling to ensure the accuracy of current measurement. In terms of electric energy metering algorithms, a new FFT electric energy calculation algorithm combining EWT and K-RV interconvolution windows is selected to cope with the ripple signals that may be carried by DC signals in actual environments, ensuring that high-precision electric energy metering can still be achieved in complex environments.

[0024] In addition, in order to improve the efficiency and capacity of signal transmission, the system also incorporates signal multiplexing technology. Through various technical means such as time division multiplexing and frequency division multiplexing, the system can cleverly merge multiple originally independent signals into one signal for efficient transmission, greatly improving the efficiency and reliability of signal transmission. Signal separation technology, as a key solution for the signal receiving end, uses a series of mathematical and algorithmic tools to conduct in-depth analysis of mixed signals and extract original, independent signal sources. In this process, the system not only needs to deal with challenges such as environmental noise and mutual interference between signals, but also needs to use advanced methods such as blind source separation and time-frequency analysis to ensure the accuracy and reliability of signal separation.

[0025] Therefore, the present invention provides a remote calibration system for a new energy vehicle DC charging pile, comprising: a laboratory end and a plurality of field ends respectively connected to the laboratory end; each of the field ends comprises a sampling circuit composed of a resistance voltage division method and a shunt method.

[0026] Among them, the laboratory end is used to remotely calibrate the voltage source of the field end according to the satellite common view method, and in each of the field ends, the voltage source signal calibrated by the second pulse self-calibration high-precision frequency measurement method and the sampling signal of the DC charging pile are used to perform signal separation and error calculation in turn to achieve independent measurement and calibration.

[0027] Based on the above technical solution, the working principle of the system is provided:

[0028] The present invention realizes remote calibration of DC charging piles based on the remote value transmission and traceability method of the Internet of Things. First, it is necessary to design a high-precision voltage-frequency conversion module, which is used to convert the voltage output by the standard voltage source and the voltage source to be tested into corresponding frequency signals respectively, and then realize remote calibration of the reference voltage source based on the mathematical model established by the satellite common view method and related algorithms. Next, the reference voltage is used as the reference signal to calibrate the electric energy metering chip. At the same time, the voltage and current at the measured end are sampled through the voltage divider resistor and the shunt and sent to the electric energy metering chip together with the reference signal. After the electric energy metering chip, the original reference signal is separated by the signal separation technology and compared with the original reference signal to calculate the error between the two, so as to obtain the overall error through the sampling circuit. The error is analyzed and processed to calculate the original standard voltage and current values, and then the standard electric energy value can be calculated. This process realizes remote calibration of the DC charging pile.

[0029] (1) Voltage-frequency conversion module (VFC) principle:

[0030] The basic principle of the charge-balanced VFC is based on the characteristics of the capacitor as a charge storage medium: the input voltage VIN drives a current IIN proportional to it to charge the capacitor. At the same time, a constant current source IREF (where IREF>IINmax) is used to periodically reverse charge the capacitor at a fixed time Tc to ensure that the charge input and output on the capacitor reach a balanced state in each or several cycles. This cycle directly corresponds to the cycle of the output signal, so that the frequency or average frequency of the output signal maintains a strict proportional relationship with the input voltage VIN. In fact, the V / F converter itself only converts the voltage signal into a series of pulse signals. To obtain the specific frequency value, it is necessary to use a counter to count these pulses and further calculate them. This process ensures the accurate implementation of the conversion from voltage to frequency, providing a solid foundation for various applications.

[0031] (2) Principle of Beidou satellite common-view method: Beidou satellite common-view method time and frequency transfer is currently one of the main methods for long-distance time and frequency value transfer. The basic principle of common-view technology is that within the field of view of a Beidou satellite, atomic clocks at any two locations on the earth can use the time signal from the same satellite received at the same time to compare time and frequency. The receivers at locations A and B receive the same Beidou satellite signal at the same time under the same common-view time table. Its built-in time interval counter measures the time difference Δt between the Beidou satellite second pulse and the local atomic clock second pulse ABD , Δt BBD The data from location B is transmitted to location A through the communication network, and then the time difference between the two atomic clocks can be obtained by subtracting them. Assume that the clock times at locations A and B are t A and t B , Beidou time is t GBD ,Δt ABD =t A -t BD ; Δt BBD =t B -t BD ; Δt ABD -Δt BBD =t A -t B =Δt AB ; After multiple measurements, a series of Δt ABi , from which we can calculate the average relative frequency difference between the two atomic clocks over a period of time Where f A , f B are the frequencies of the two clocks respectively; τ is the average time interval.

[0032] (3) Self-calibration frequency counting principle:

[0033] The present invention innovatively proposes a pulse-per-second self-calibration high-precision frequency measurement method. This method uses the pulse-per-second (pps) received by the three-mode satellite positioning module as a reference to correct the measured frequency, effectively solving the problem of ±1 unit counting error in frequency counting. At the same time, this method can automatically select the most suitable measurement method according to the measured frequency, which not only makes up for the shortcomings of traditional methods, but also ensures measurement accuracy while greatly reducing costs. After pulse-per-second correction, compared with high-precision frequency measuring instruments with built-in cesium atomic clocks, the measurement accuracy achieved by the present invention is as high as 10 -7 It achieves the perfect combination of low cost and high precision.

[0034] (4) Principle of signal multiplexing technology:

[0035] Signal multiplexing technology is mainly achieved through channel division, signal modulation, spectrum shifting, signal synthesis, signal transmission, and signal reception and demodulation.

[0036] First, the total bandwidth of the communication system is divided into several non-overlapping sub-bands according to the total bandwidth of the communication system and the number of signals to be transmitted. For each signal to be transmitted, a different carrier frequency is used for modulation. The modulation method can be amplitude modulation (AM), frequency modulation (FM) or phase modulation (PM), or a combination of these modulation methods. The modulated signal is moved to the corresponding sub-band.

[0037] At the transmitting end, spectrum shifting technology (such as modulator) is used to shift the spectrum of each signal to a specified sub-band. This usually involves multiplying the baseband signal with the corresponding carrier signal to achieve spectrum shifting. All modulated signals are synthesized to form a composite signal. This composite signal contains the signals transmitted on all sub-channels, and the signals on each sub-channel do not overlap in the spectrum. The synthesized composite signal is sent to the channel for transmission.

[0038] At the receiving end, a bandpass filter is used to separate the subchannel signals from the composite signal. The center frequency of each bandpass filter matches the carrier frequency corresponding to the transmitting end, and is used to extract the signal on the corresponding subchannel. Then, the signal on each subchannel is demodulated to restore the original baseband signal. The demodulation process is the opposite of the modulation process at the transmitting end.

[0039] (5) Signal separation technology principle:

[0040] The main implementation process of signal separation technology includes signal preprocessing and feature extraction, selection of appropriate separation algorithm, result evaluation and subsequent processing.

[0041] The first step of signal separation technology is signal preprocessing and feature extraction. The received mixed signal needs to be preprocessed to remove noise, interference and unnecessary components to make the signal purer and clearer. Then, through time domain analysis, frequency domain analysis or statistical characteristics analysis, the key features of the signal are extracted, such as frequency, amplitude, phase and statistical relationship between signals. These features provide an important basis for subsequent signal separation.

[0042] After signal preprocessing and feature extraction, it is necessary to select a suitable separation algorithm based on the characteristics of the signal and the separation target. Common signal separation algorithms include independent component analysis (ICA), principal component analysis (PCA), non-negative matrix factorization (NMF), etc. After selecting the algorithm, the corresponding mathematical model is established, and the model parameters such as the mixing matrix and separation matrix are estimated through optimization algorithms (such as gradient descent method, Newton method, etc.). Through the iterative optimization process, the parameters are continuously adjusted to achieve the maximum independence between the separated signals or other predetermined optimization goals. Finally, the mixed signal is reconstructed using the estimated parameters to obtain the separated source signal.

[0043] After the signal separation is completed, the separation results need to be evaluated. By calculating the performance indicators such as the signal-to-noise ratio (SNR) and distortion of the separated signal, the separation effect can be evaluated. At the same time, the original signal, mixed signal and separated signal can be visually compared to intuitively demonstrate the effect of signal separation. If the separation result does not meet the requirements, it may be necessary to adjust the preprocessing steps, feature extraction methods or separation algorithm parameters, and re-perform signal separation. Finally, according to the actual application requirements, the separated signal is further processed, such as enhancement, recognition, analysis, etc., to meet the needs of subsequent applications.

[0044] (6) Signal separation error analysis model:

[0045] The error assessment model is based on the error propagation theory and can perform systematic error analysis on each link in a complex system. By identifying and quantifying the errors of each subsystem or component and combining these independent error sources, the model can effectively predict the overall error of the system. Using the error propagation formula, the error sources in the system are analyzed, mainly including the error of the excitation signal source, the error introduced when the signal passes through the shunt or voltage divider network, the error that may be introduced when the excitation signal is superimposed on the load signal, the A / D converter error, and the excitation signal extraction error. The various error terms in the system are reasonably integrated to provide a theoretical basis for the accuracy optimization of the electric energy metering system.

[0046] According to the above error sources, assuming that all error sources are independent, an error propagation model is constructed.

[0047]

[0048] In the formula, E total is the total error of the system, E source The error of the reference voltage source, E divider Represents the error of the voltage divider network, E shunt represents the error of the current shunt, E ADC Represents the error of the A / D converter, E extract Represents the error in the process of extracting the excitation signal.

[0049] (7) Principle of electric energy metering technology:

[0050] According to the on-site characteristics of the DC charging pile, the voltage and current signals are set as follows.

[0051] u(t)=U d +∑u k (t)+u s (t)

[0052] i(t)=I d +∑i k (t)+i s (t)

[0053] In the above formula, U k (t), i k (t) is the kth harmonic voltage and current component, k = 1, 2, ...; U s (t), i k (t) is the non-steady-state voltage and current component.

[0054] The signal power is shown in the following formula.

[0055]

[0056] In the above formula, P d is the DC power, P k is the kth harmonic power, P s It is non-steady-state power.

[0057] From the above formula, it can be seen that the signal power consists of a DC part, harmonic components, and non-steady-state power. In order to accurately measure the power during the charging process, it is necessary to accurately identify and separate the DC component, harmonics, and non-steady-state signals from the composite signal. In view of the wide application and unique advantages of Fourier transform (FFT) and wavelet transform (WT) in signal processing, this innovative method combines the FFT electric energy calculation method of empirical wavelet transform (EWT) and K-RV interconvolution window technology. This method first uses the EWT technology to decompose the voltage and current signals into multiple independent modal components, and then accurately distinguishes and separates the non-steady-state signal and the DC signal by real-time monitoring of the instantaneous amplitude change rate of each modal signal. After that, the three-spectral line interpolation FFT algorithm based on the K-RV interconvolution window function is used to identify and calculate each harmonic with high precision. This method achieves high accuracy in electric energy metering.

[0058] like Figure 1As shown in the figure, the hardware of this system mainly consists of shunt, voltage divider resistor, self-calibration energy metering chip, reference voltage source, self-calibration frequency counter, Beidou satellite synchronization clock source, pulse counter, time interval counter, and self-calibration voltage-frequency converter. Under the premise of accurate measurement and collection of high voltage, high current and output power parameters of DC charging piles, the data is transmitted back to the laboratory through data remote transmission technology to complete the high-precision measurement task of voltage, current and energy.

[0059] (1) Reference voltage and voltage-to-frequency converter cyclic calibration

[0060] At the field end, the voltage source needs to be remotely calibrated, with a standard voltage source at the laboratory end as the traceability subject. The remote calibration method is to convert the voltage values ​​at both ends into frequencies through their respective voltage-frequency converters, and then receive the same satellite second pulses as reference signals through Beidou satellite receivers at both ends. The frequency values ​​converted by the voltage-frequency converter are compared with the received second pulses to obtain the difference in voltage frequency between the field end and the laboratory end, thereby calculating the voltage difference. Now, in order to ensure the accuracy of the voltage value measurement at the field end, the key components in the remote calibration link need to be self-calibrated, and the most important thing is to ensure the stability of the voltage-frequency converter.

[0061] The reference voltage and voltage-frequency converter are calibrated in a cyclic manner. The specific process is as follows:

[0062] First, the voltage source (reference voltage) at the field end is accurately calibrated in the laboratory and brought to the field, and a frequency counter is connected to the output end of the voltage-frequency converter at the field end. This frequency counter can perform self-calibration autonomously and is accurate during the entire operation process.

[0063] After the remote calibration work begins, since the voltage source (reference voltage) at the field end is calibrated at the laboratory end, it is assumed that its accuracy will not change temporarily. First, the output frequency of the voltage-to-frequency converter at the field end is measured with a self-calibration frequency meter. Since it is assumed that the voltage source at the field end does not change, the voltage-to-frequency conversion coefficient of the voltage-to-frequency converter can be calculated, that is, the voltage-to-frequency converter is assumed to be calibrated and this voltage-to-frequency conversion coefficient is trusted.

[0064] The second time, the reference voltage was remotely calibrated by the Beidou satellite common view method, and the previously obtained voltage-frequency conversion coefficient was trusted in this round of cyclic calibration. At the laboratory end, the standard voltage source outputs the voltage value to the high-precision self-calibration voltage-frequency converter and the time accumulation module at the same time. Channel 2 and channel 1 of the voltage-frequency converter are respectively connected to the channel 2 of the pulse counter and the time interval counter. The module converts the voltage into a pulse signal and outputs it to the pulse counter and the time interval counter respectively. The time accumulation module is mainly composed of a counter circuit, which is used to calculate the duration of the electric energy calibration. 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, the satellite synchronization clock source's own channel 1 and channel 2 are connected to the channel 1 of the time counter and the pulse counter, respectively, and provide the two with a synchronized second pulse frequency signal. The time interval counter measures the time interval between the pulse signal output by the voltage-frequency converter and the satellite synchronization second pulse. The satellite synchronization second pulse at one end is used as the opening pulse of the time interval counter at that end, and the pulse signal obtained by voltage-frequency conversion at the same end is used as the closing pulse of the time interval counter at that end. The time interval between the two pulses is measured by the time interval counter. The pulse counter measures the number of pulses of the pulse signal output by the voltage-frequency converter in each complete cycle of the satellite synchronization second pulse. The pulse signal obtained by voltage-frequency conversion at one end is used as the measured signal of the pulse counter at that end, and the satellite synchronization second pulse signal at the same end is used as the trigger signal of the pulse counter at that end. The field hardware system performs the above operations synchronously.

[0065] After a calibration cycle, the time interval counters and pulse counters at both ends collect the time intervals and pulse numbers with time stamps in the same time period. In the current cycle calibration, the voltage-frequency conversion coefficient trusts the data obtained last time. The data is transmitted to the host computer at this end in real time through the network port communication and stored. Finally, after the data at the laboratory end and the field end are summarized, they are substituted into the remote measurement model through the host computer program:

[0066]

[0067] Among them, ΔU represents the voltage deviation at both ends, U A Indicates the laboratory terminal voltage, U B Indicates the field terminal voltage, λ A Indicates the laboratory end voltage-frequency conversion coefficient, λ B Indicates the field voltage-frequency conversion coefficient, N Ai Indicates the number of pulses at the laboratory end in the i-th second, N Bi Indicates the number of pulses at the field end in the i-th second, Δt Ai represents the difference between the adjacent time intervals of the ith second at the laboratory end, Δt Birepresents the difference between the adjacent time intervals of the ith second at the field end, f A , f B are the frequencies of voltage conversion at the laboratory end and the field end respectively.

[0068] The calibration result of the calibration point is obtained by solving the above method. The calibration of the field voltage source (reference voltage) is completed through the above method. After the voltage source remote calibration is completed, the field voltage source can be trusted again.

[0069] The value of the terminal voltage source (reference voltage).

[0070] The third time, trust the field voltage source (reference voltage), repeat the first operation, use the self-calibration frequency meter to test the frequency of the field voltage source, and calculate the voltage-frequency conversion coefficient of the voltage-frequency converter. It is considered that the voltage-frequency converter has been calibrated and the voltage-frequency conversion coefficient is trusted.

[0071] The fourth calibration was carried out in the same way as the second one. The calibration cycle was continued to complete the remote calibration of the voltage source (reference voltage) at the field end, and the accuracy of the key component voltage-frequency converter was ensured during the calibration process. The field end and the laboratory end performed the same operation at the same time to ensure consistency.

[0072] (2) Voltage and current sampling circuit self-calibration

[0073] During the normal charging process of electric vehicles, the operating voltage range is 0-1000V. For the measurement of 1000V DC high voltage, it is usually impossible to directly use test instruments for measurement, so appropriate attenuation conversion is required. Since the input range of ADC is -10V to 10V, each collected signal needs to be conditioned to adapt to the optimal quantization range of ADC.

[0074] In order to consider the ripple and measurement accuracy of the output DC signal and eliminate the influence of the parasitic capacitance of the resistor in the pure resistor divider, it is planned to design a high voltage attenuation sampling circuit using the resistor voltage divider method. The voltage division of the DC voltage signal is achieved through a voltage divider network composed of multiple high-precision resistors, and the voltage division ratio is set to 1000V / 10V. The attenuated signal passes through a differential sampling circuit to improve the common mode rejection ratio, and then enters the signal conditioning circuit. The signal is first amplified by 2 times through a multiplier, and then a subtractor is used to reduce the signal amplitude to 10V, which meets the optimal input range of the ADC (-10V to 10V). This method can meet the relevant index requirements of the non-physical standard transmission method in remote measurement and calibration.

[0075] In the large current collection, the present invention uses a high-precision shunt to convert the large current into a small current for sampling in proportion to ensure the accuracy of the current measurement. The resistance of the shunt changes with the temperature. Therefore, in order to obtain accurate current measurement results, the system uses a temperature coefficient resistor (TCR) to compensate the resistance of the shunt for temperature.

[0076] In order to solve the influence of the error generated in the front-end sampling circuit on the overall calibration result, the present invention generates an excitation signal through the calibrated reference voltage, injects it into the sampling circuit of the load signal, and superimposes it on the voltage or current load signal. At the back end, the digital signal collected by the measurement part is separated by signal separation technology, and the digital component of the excitation signal is extracted from it. The excitation signal measurement value is calculated according to the factory calibration parameters, and compared with the excitation signal output by the reference signal source (reference voltage), so as to calculate the monitoring error and restore the load signal, thereby measuring the error generated in the voltage sampling and current sampling circuits, and calculating the accurate electric energy value through the self-calibration electric energy metering chip.

[0077] (3) Self-calibration of energy metering chip

[0078] The electric energy metering module is the core of the field end verification device of the DC charging pile. It adopts the method of combining electric energy metering chip with MCU. The electric energy metering chip integrates ADC, and the internal computing unit completes the signal processing and high-precision electric energy metering work. The advantages are short development cycle and guaranteed metering effect. In ADC, the reference voltage is the benchmark for ADC quantization, which is used to determine the digital output value corresponding to the level of the analog input signal. By completing the reference voltage and voltage-frequency converter cyclic calibration method introduced above to realize the self-calibration of the voltage-frequency converter, and remotely metering the reference voltage based on the satellite common view method, after ensuring the real-time calibration of the reference voltage, the stability of the working state of the electric energy metering chip can be guaranteed, and the real-time self-calibration of the electric energy metering chip can be realized. The selection of electric energy metering chip meets the requirements that the voltage and current measurement accuracy are both 0.02 level, and the electric energy measurement accuracy is 0.1 level. In addition, it also has SPI and UART communication interfaces to meet the functional requirements of the communication part of the field verification device.

[0079] like Figure 2As shown in the figure, the upper computer software execution flow chart of the DC charging pile remote calibration system will be built based on the open source Linux operating system and run on the ARM architecture. With its strong stability and high portability, the Linux system can ensure the reliable operation of the software on multiple platforms. The system will also use Ubuntu and combine the Qt framework as the main development tool to build a cross-compilation environment and develop user interfaces and test logic. As a high-performance cross-platform C++ application framework, Qt has good compatibility and a rich development ecosystem, and is suitable for the development of human-computer interaction interfaces. This system effectively integrates the technical advantages of Linux and Qt to ensure the efficiency of system development and resource utilization.

[0080] After the initialization self-test, the host computer software system is divided into three main execution paths. Each path is responsible for different functional modules, including information collection of standard devices and charging piles to be tested, environmental parameter collection, calibration project creation and real-time calibration operation, data processing and report management, etc. Each module completes independent tasks to realize remote calibration of DC charging pile energy metering data. After the system is powered on, it first enters the initialization self-test phase. The initialization phase requires two steps: communication interface connection test and selection of charging parameter type. The former is used to establish conventional parameters for serial port communication, including port selection, baud rate, check bit setting, etc.; the latter is used to set the indicator parameters of the charging process, including charging voltage and current, charging circuit type, etc., both of which must be given initial definitions. After the self-test is completed, the system will enter the calibration system homepage. The device management module is mainly used to manage the relevant parameter information of standard devices and charging piles to be tested. The parameter information of the standard device can include voltage and current accuracy levels, etc., and the information of the charging pile to be tested includes its basic configuration and parameters to be tested. The environmental parameter acquisition module is used to collect environmental factors such as temperature, humidity, and atmospheric pressure of the calibration environment, which have an important impact on accurate calibration. The real-time calibration process is then started, and the calibration operation is divided into two paths: creating a new calibration project and opening a calibration project. Creating a new calibration project is suitable for the first calibration or when calibration parameters need to be reconfigured, while opening a calibration project is used to continue an existing calibration project. During the calibration process, the collected data is analyzed and processed to achieve real-time display of various progress and data. The calibration data is analyzed step by step to complete the test result determination, and the calibration data is completely saved in the database. After the calibration data is stored, the user can select the storage path of the report and save it, and can also browse or extract historical data. The report usually contains all key data, environmental parameters, calibration results and uncertainty analysis of the calibration project. Finally, the system generates a calibration report export and ends the entire calibration process.

[0081] Therefore, the remote metering system designed by the present invention can realize real-time calibration of the electric energy of multiple charging piles. Its main advantages include:

[0082] The system can realize real-time calibration of the power of multiple charging piles. Its main advantages include:

[0083] (1) Remote calibration reduces costs: Instead of requiring measurement personnel to carry equipment to the site for calibration, calibration tasks can be completed through the software system in the remote laboratory. This not only greatly reduces labor, transportation and time costs, but also avoids the loss of equipment caused by frequent handling, greatly improves measurement efficiency, and provides possibilities for the calibration needs of large-scale charging piles in the future.

[0084] (2) Online real-time monitoring to improve efficiency: The system can obtain the calibration data of the DC charging pile in real time during the charging process of the electric vehicle. The electric vehicle is used as the test load, and charging and calibration are carried out simultaneously, avoiding additional energy consumption and solving the contradiction between the normal operation and metrological calibration of the charging pile, further improving the calibration efficiency.

[0085] (3) Simultaneous calibration of multiple charging piles to save resources: The system can calibrate multiple DC charging piles at the same time, standardize the connection between the communication interfaces of multiple charging piles and the system hardware interface at the calibration site, achieve stable data interaction and communication, and combine the remote control function of the software system to effectively manage and control the real-time calibration of multiple charging piles, greatly improving the efficiency of multi-pile calibration and effectively reducing the overall measurement cost.

[0086] The system transmits the collected calibration data to the remote laboratory through the network, and the computer performs data processing and calibration analysis. Taking into account the additional errors that may be caused by different environmental factors, the system makes full corrections during the data processing process to ensure the accuracy of the calibration results. At the same time, the system significantly shortens the calibration cycle, reduces labor costs, improves overall efficiency, and realizes remote and intelligent energy metering and calibration work. The system provides a feasible technical solution for efficient and low-cost calibration of charging piles in the future.

[0087] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0088] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. New energy vehicle DC charging pile remote calibration system, characterized by: include: A laboratory end and a plurality of field ends respectively connected to the laboratory end; Each of the field terminals includes a sampling circuit composed of a resistor voltage divider method and a current divider method, and is provided with a bandpass filter to separate the sampled composite signal, so as to facilitate error monitoring using an excitation signal extracted from the separated signal; Among them, the laboratory end is used to remotely calibrate the field end according to the satellite common view method. In each of the field ends, the second frequency counter, reference voltage source and second self-calibration voltage-frequency conversion module calibrated by the second pulse self-calibration high-precision frequency measurement method are used to complete the cyclic calibration, and the excitation signal output by the reference voltage source and the sampling signal of the DC charging pile are sequentially separated and the error calculated to achieve independent measurement calibration.

2. The remote calibration system for a new energy vehicle DC charging pile according to claim 1 is characterized in that: The laboratory end includes a standard voltage source, a laboratory end satellite second pulse receiving module, a computer, a software system and a calibration database which are connected in sequence; the laboratory end satellite second pulse receiving module is also connected to each of the field ends through wireless communication.

3. The remote calibration system for a new energy vehicle DC charging pile according to claim 2 is characterized in that: The laboratory-end satellite second pulse receiving module specifically includes: a first self-calibration voltage-frequency conversion module, a first pulse counter, a first time interval counter, a first frequency counter, a first Beidou satellite receiver, a first CPU and a first communication module; the first self-calibration voltage-frequency conversion module is respectively connected to the standard voltage source, the first pulse counter, the first time interval counter, the first frequency counter and the first CPU; the first pulse counter and the first time interval counter are also connected to the Beidou satellite receiver; the first CPU is also respectively connected to the computer and the first communication module; the first communication module is also connected to each of the field ends.

4. The remote calibration system for a new energy vehicle DC charging pile according to claim 1, characterized in that: Each of the field ends includes: a DC charging pile, a sampling circuit, an electric energy metering chip, a reference voltage source, a second frequency counter, a second CPU, a second communication module and a calibration end satellite second pulse receiving module; the DC charging pile, the sampling circuit and the electric energy metering chip are connected in sequence; the electric energy metering chip is also connected to the second CPU; the second CPU is also respectively connected to the calibration end satellite second pulse receiving module and the second communication module; the calibration end satellite second pulse receiving module is also respectively connected to the second communication module and the reference voltage source; the reference voltage source is also connected to the sampling circuit; the second communication module is also connected to the laboratory end.

5. The remote calibration system for a new energy vehicle DC charging pile according to claim 4 is characterized in that: The sampling circuit specifically includes: a shunt and a voltage-dividing resistor; the input ends of the shunt and the voltage-dividing resistor are respectively connected to the DC charging pile and the reference voltage source; the output ends of the shunt and the voltage-dividing resistor are connected to the electric energy metering chip.

6. The remote calibration system for a new energy vehicle DC charging pile according to claim 4 is characterized in that: The calibration-end satellite second pulse receiving module specifically includes: a second self-calibration voltage-frequency conversion module, a second pulse counter, a second time interval counter and a second Beidou satellite receiver; the second Beidou satellite receiver is respectively connected to the second pulse counter and the second time interval counter; the second pulse counter and the second time interval counter are also both connected to the second self-calibration voltage-frequency conversion module; the second self-calibration voltage-frequency conversion module is also respectively connected to the reference voltage source, the second frequency counter, the second CPU and the second communication module.

7. The remote calibration system for a new energy vehicle DC charging pile according to claim 4 is characterized in that: The sampling circuit adopts a high voltage attenuation sampling circuit, and realizes the voltage division of the DC voltage signal through a voltage division network composed of multiple high-precision resistors.

8. The remote calibration system for a new energy vehicle DC charging pile according to claim 1, characterized in that: After extracting the excitation signal of the separation signal, the field end calculates the excitation signal measurement value according to the factory calibration parameters, compares it with the excitation signal output by the reference signal source, thereby calculating the monitoring error and restoring the load signal, thereby measuring the errors generated in the voltage sampling and current sampling circuits, and finally calculating the electric energy value by the self-calibration electric energy metering chip to complete the electric energy metering.

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