WO2022247088A1

WO2022247088A1 - Source-free calibration method for smart meter

Info

Publication number: WO2022247088A1
Application number: PCT/CN2021/121549
Authority: WO
Inventors: 王宜怀; 史洪玮; 施连敏; 喻炳政
Original assignee: 苏州大学
Priority date: 2021-05-24
Filing date: 2021-09-29
Publication date: 2022-12-01
Also published as: CN113176531A

Abstract

A source-free calibration method for a smart meter, comprising: generating voltage by a stabilized voltage supply and inputting the voltage to a load having a specified power factor; separately using a standard commercial electricity meter and an electricity meter to be calibrated to measure electricity data of the load; and calculating an error between the electricity meter to be calibrated and the standard commercial electricity meter according to the electricity data as a gain value. Calibrating a metering chip of the electricity meter comprises: parameter setting, comprising mode configuration, channel gain configuration, EMU unit configuration, high frequency pulse output configuration, voltage loss threshold setting, and start threshold setting; A phase correction, comprising power gain correction, voltage correction, and current correction; and B phase correction and C phase correction. Compared with conventional calibration, the source-free calibration method has lower costs, and the current, voltage, and power can meet the requirements of level-2 electricity meters.

Description

A passive calibration method for smart meters

technical field

The invention relates to the technical field of smart meters, in particular to a passive calibration method for smart meters.

Background technique

The sampling circuit of the power quality acquisition terminal is composed of current transformers, sampling resistors, and metering chip ADC modules. The components that make up these parts have precision levels and discreteness. In addition, the PCB impedance and the error of the metering chip will lead to differences in accuracy. Due to the existence of these factors, the measurement results of the power grid data will be affected to a certain extent, making the sampling data inaccurate. This problem can be solved by calibrating each terminal.

At present, the calibration of power quality terminals is mainly active calibration. Active calibration uses a three-phase standard source to output specified current voltage, phase, etc. The power quality acquisition terminal can be calibrated accurately through the three-phase standard source, but the cost of the three-phase standard source is relatively high, which indirectly increases the development cost.

technical solution

The purpose of the present invention is achieved through the following technical solutions.

The invention uses passive calibration and cooperates with the calibration program, which can make up for the low efficiency of passive calibration and further improve the calibration accuracy.

The invention provides a passive calibration method for a smart meter, comprising:

Generate a voltage input load with a specified power factor through a regulated source;

Measure the electric energy data of the load by using standard commercial electric meters and electric meters to be calibrated respectively;

Calculate the error between the electric meter to be calibrated and the standard commercial electric meter according to the electric energy data, and use it as a gain value.

Write the gain value into the MCU designated sector of the meter to be calibrated to complete the calibration;

The meter to be calibrated uses an HT7036 metering chip, and the method further includes calibrating the metering chip, including:

Parameter settings, including mode configuration, channel gain configuration, EMU unit configuration, high-frequency pulse output configuration, voltage loss threshold setting, and startup threshold setting;

Phase A correction, including power gain correction, voltage correction, current correction;

B-phase correction and C-phase correction.

Further, the electric energy data includes: voltage, current, power, frequency, and/or harmonics.

Further, the meter to be calibrated uses the HT7036 metering chip.

Further, when the electric energy data is voltage, it is assumed that the effective value of the voltage of the standard commercial electric meter is Ur, the measured voltage of the electric meter to be calibrated is Urms, the voltage calibration coefficient is Ugain, and INT is a rounding function. The calculation formula of the voltage calibration coefficient is as follows :

Further, when the electric energy data is current, it is assumed that the effective value of the current of the standard commercial electric meter is Ir, the measured current of the electric meter to be calibrated is Irms, the current calibration coefficient is Igain, and the calculation formula of the current calibration coefficient is as follows;

Further, when the electric energy data is power, it is assumed that the active power value of the commercial electric meter is Preal, the power value of the electric meter to be calibrated is DataP, and the power calibration coefficient is Pgain. The calculation formula of the power calibration coefficient is as follows:

Further, there is a relationship between Ugain', Igain', and Pgain' as shown in the following formula 2-9. The HFconst used in formula 2-9 is a high-frequency pulse constant, and the calculation formula is shown in formula 2-7; In 2-7, U _n is the actual access voltage of the meter terminal, I _b is the actual access current, Vu and Vi are the input voltages of the metering chip voltage channel and current channel respectively; N used in formula 2-9 is the proportional coefficient , the calculation formula is shown in the following formula 2-8; T _A in formula 2-8 is the transformation ratio of the current transformer, and R is the resistance of the current sampling circuit;

Further, when the electric meter to be calibrated measures the electric energy data of the load, a median mean filtering algorithm is used.

Further, the registers of the metering chip are divided into two parts, namely metering parameter registers and meter calibration parameter registers.

Beneficial effect

The advantages of the present invention are: compared with the traditional calibration, the cost of the passive calibration method adopted by the present invention is lower, and the current, voltage and power can all meet the requirements of a Class 2 electric energy meter.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment. The drawings are only for the purpose of illustrating a preferred embodiment and are not to be considered as limiting the invention. Also throughout the drawings, the same reference numerals are used to designate the same components. In the attached picture:

Figure 1 shows a schematic diagram of the principle of passive calibration according to an embodiment of the present invention.

Fig. 2 shows a schematic diagram of a metering chip calibration process according to an embodiment of the present invention.

Fig. 3 shows a schematic diagram of a single-phase data calibration interface according to an embodiment of the present invention.

Embodiments of the present invention

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided for more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

The invention proposes a passive calibration method, using an ACR330ELH commercial electric meter and a specified power factor load to realize electric meter calibration. The calibration process is combined with special calibration software to calculate the gain coefficient and write to the serial port to improve development efficiency. Compared with traditional calibration, the cost of passive calibration is lower, and the current, voltage, and power can all meet the requirements of Class 2 electric energy meters.

Figure 1 shows the calibration principle, including the following steps:

S1. Generate a voltage through a voltage stabilizer and input it to a load with a specified power factor.

S2. Measure the electric energy data of the load using a standard commercial electric meter and an electric meter to be calibrated respectively; the electric energy data includes: voltage, current, power, frequency, harmonics, etc.

S3. Calculate the error between the electric meter to be calibrated and the standard commercial electric meter according to the electric energy data as a gain value.

S4. Write the gain value into the designated sector of the MCU of the electric meter to be calibrated, and complete the calibration.

The calibration tool in Figure 1 is a WinForm window program, which communicates with the meter to be calibrated through the serial port. According to the input information, the gain value is automatically determined, and it is directly written into the designated sector of the MCU of the meter to be calibrated in a partial update mode to improve development efficiency.

The meter to be calibrated in the present invention uses the HT7036 metering chip, and the metering chip also needs to be calibrated before the meter to be calibrated is formally calibrated. The calibration process mainly performs power, current and voltage calibration. When calibrating the power, you only need to calibrate the active power gain register, and write the same coefficient in the reactive power register and apparent power gain register. The metering chip calibration process is shown in Figure 2 below, including:

B-phase correction and C-phase correction.

In the actual calibration, a stable voltage source is used to output a stable voltage, and a high-power sliding rheostat with a power factor of 1 is used for calibration to set the specified current, voltage, and power parameters. During the actual measurement, according to the data of the commercial electric meter and the electric meter to be calibrated, the calibration tool is used to calculate the error and update the gain parameters of the electric meter to be calibrated. When performing passive calibration, it is assumed that the effective value of the commercial meter voltage is Ur, the measured voltage of the meter is Urms, the voltage calibration coefficient is Ugain, and INT is a rounding function. The calculation formula of the voltage calibration coefficient is as follows.

Assume that the effective value of the commercial electric meter current is Ir, the measured current of the electric meter is Irms, and the current calibration coefficient is Igain. The calculation formula of the current calibration coefficient is as follows.

Assume that the active power value of the commercial electric meter is Preal, the power value is DataP, and the power calibration coefficient is Pgain. The calculation formula of the power calibration coefficient is as follows.

In addition, there is also a relationship between Ugain', Igain' and Pgain' as shown in the following formula 2-9. HFconst used in Equation 2-9 is the high-frequency pulse constant, and the calculation formula is shown in Equation 2-7. In Formula 2-7, U _n is the actual access voltage of the meter terminal, I _b is the actual access current, Vu and Vi are the input voltages of the metering chip voltage channel and current channel, respectively. N used in Equation 2-9 is a proportional coefficient, and the calculation formula is shown in Equation 2-8 below. T _A in Formula 2-8 is the transformation ratio of the current transformer, and R is the resistance of the current sampling circuit.

specific embodiment

1 Preparations

The HT7036 metering chip integrates multiple 19-bit ADC modules inside, and adopts double-ended differential signal input. When calibrating, the ADC input corresponding to the voltage channel of the metering chip should be selected at an effective value of about 0.22V, and the ADC input of the current channel should be selected at an effective value of about 0.05V. In this way, good linearity characteristics can be obtained to ensure measurement accuracy. The voltage sampling circuit adopts the principle of series voltage division. The voltage sampling channel is connected in parallel with a 1.2KΩ voltage sampling resistor. The voltage dividing resistor of the voltage sampling circuit is composed of seven 330KΩ chip resistors. The voltage data sampled by the voltage channel is positively correlated with the channel gain coefficient. When using mains power for calibration, the actual input voltage is about 230V. In order to make the voltage channel as close to 0.22V as possible, the gain factor of the voltage channel should be set to 2, and the input voltage of the voltage sampling channel is about 0.2367V. The current sampling channel is connected in parallel with a 7.8Ω sampling resistor, and the input current is generated by a current transformer, which is 1/1000 of the actual current. In order to make the sampling voltage of the current channel close to 0.05V, the input current is set to 3A, and the gain factor of the current sampling channel is set to 2. The input voltage of the current sampling channel is 0.0468V.

The metering chip register is divided into two parts, namely the metering parameter register (read-only memory) and the calibration parameter register. Calibration parameters are stored in the meter calibration parameter register, and grid data are stored in the metering parameter register. The address range of the measurement parameter register is 0x00~0x7F, and the address range of the calibration parameter register is 0x00~0x71. The SPI communication format of the metering chip is 8-bit command, 24-bit data, and the data transmission adopts the high-order priority system. The highest bit of the command is 0, (Bit7: 0) indicates the read command, which is used for the external MCU to read the metering chip register data, the lower 7 bits (Bit6...0) indicate the register address, and the 24-bit data is a redundant byte (0xFF, 0xFF, 0xFF). After receiving the redundant bytes, the metering chip will reply the corresponding data. If you need to operate the meter calibration parameter register, you need to send a special command, that is, send the command 0xC6, the data is equal to 0x00005A, select SPI to read the parameters of the meter calibration data register, and you cannot read the value of the measurement parameter register at this time. Send the command 0xC6, the data is not equal to 0x000005A, and choose to read the parameters of the metering data register at the address 0x0~0x7F through SPI. After power-on reset, the parameters of the metering data register are read out by default. When choosing to read the parameters of the meter calibration data register, the value read from the 0x00 address is fixed at 0x00AAAA, otherwise the read metering parameter 0x00 address is 0x7122A0.

When writing data, the highest bit of the command is 1, and the lower 7 bits (Bit6...0) indicate the register address, which means writing data to the calibration register. When the user communicates through SPI and configures the calibration register, the calibration data needs to be placed in the lower two bytes of the 3 data bytes.

When formally calibrating the meter, it is necessary to first write the corresponding parameters to the meter calibration parameter register, the specific command is as follows.

(1) Configure the mode register (0x01 address), write the recommended value 0xB9EF. Turn on the vref chopper function to obtain a more stable reference voltage. Turn on the power RMS slow mode to reduce jitter; configure the emulator (EMU) clock to 921.6kHz to reduce power consumption; turn on the A, B, C three-phase voltage and current channel data sampling function.

(2) There are two options for calculating the apparent power, namely the PQS method and the RMS apparent method. Let the apparent power be S, the active power be P, the reactive power be Q, the measured voltage be Urms, and the current be Ims, then the calculation method of S is as follows. Write 0xFD04 to the EMU unit configuration register (0x03 address). Turn off the fundamental wave function, and select the PQS mode for apparent power energy.

(3) Write 0x3437 to the analog module enable register (0x31 address), turn on the high-pass filter; turn on the brown-out reset (Brown-out Reset, BOR) power monitoring circuit.

(4) Write 0x154 to the ADC gain configuration register (address 0x02), set the three-phase voltage and current channel gain to 2 times the gain, so that during calibration, the input voltage of the current channel is close to 0.05V, and the input voltage of the voltage channel is close to 0.5V.

(5) Write HFconst to the high-frequency pulse constant register (0x1E address).

(6) Write 0x8 to the algorithm control register (0x70 address), the chip starts the automatic compensation mechanism, automatically calculates the gain value of all channels, and writes 0x5C address, and sets the measurement mode to three-phase four-wire system.

2 Calibration procedure

When calibrating the metering chip, it is necessary to calculate the calibration parameters of the gain register of the metering chip according to the reading of the standard meter and the measured value of the meter terminal. When obtaining the calibration parameters, the calibration parameters need to be written into the terminal. If reprogramming is used, it will take a long time. The terminal described in the present invention stores various calibration parameters and calibration parameter register configuration data in the last sector of the FLASH storage area of the STM32L431 chip. After the terminal is powered on or receives the calibration command, by reading the FLASH sector information, the calibration-related data is read into the calibration structure, and the calibration is performed through the calibration function of the terminal.

When the sampling voltage of the terminal voltage channel and the current channel reaches the rated voltage in the calibration procedure, a better calibration effect will be obtained. If the rated voltage cannot be provided for the sampling channel, the actual board voltage, actual board current and voltage, and current channel input voltage should be modified. In view of the above situation, developers can modify the parameters stored in the lower computer by changing the corresponding parameters in the measurement parameter operation area in the calibration program interface diagram. Moreover, when the user is operating, he only needs to input the input voltage and input current, and then click the update button to automatically update the voltage and voltage channel input text box data.

When the user calibrates the metering chip, it needs to calibrate phase by phase. It is necessary to input the measured value of the grid data and the value of the standard meter into the designated area of the calibration program, and then click the start button, and the calibration parameters of the gain register stored in the lower computer will automatically change. The user needs to make an evaluation based on the data obtained after the operation. If there is still a large deviation from the ideal data, it is necessary to repeatedly input the measured value of the grid data and the value of the standard table to perform multiple calibrations. During the calibration process, if it is found that the calibration parameters appear cyclically, but the deviation still exists. The calibration parameters with the smallest error should be selected and written into the development board, and the input power parameters of the experiment should be adjusted. If the error remains constant, software can be used to make up for it; otherwise, the development board needs to be overhauled. When calibrating the gain register of a certain phase, if the voltage and current data measured by the development board have reached the required accuracy, you only need to check the button in front of the voltage and current calibration parameter text boxes when calibrating the power, and the subsequent calibration process will only Change power calibration parameters.

The upper computer calibration program of the present invention is a WinForm form developed by Visual Studio 2019 (VS), and the upper computer communicates with the lower computer through the SCI class. The SCI class inherits the VS system class SerialPort, and the main functions are shown in Table 1 below. The host computer program cannot operate the terminal before it is connected to the terminal. When the upper computer shakes hands with the lower computer, a single thread is used to call the SCIReceiveData function to receive the handshake information. After the connection is successful, the host computer sends commands to read and modify data through the window program button, and calls the SerialDataReceivedEventHandler event to realize asynchronous data reception.

Using the calibration program mentioned in the present invention, during the calibration process, new calibration parameters will be stored in the designated sector of FLASH, and the data will still remain after the terminal is powered on again. Compared with manually calculating the calibration parameters and reprogramming the program, the efficiency and accuracy are greatly improved by using the calibration program provided by the present invention for calibration. The calibration procedure mainly focuses on the single-phase data calibration interface, as shown in Figure 3 below.

3 Calibration process

After the hardware circuit is built, turn on the switch of the AC voltage regulator to output stable voltage and current. Record the readings of the meter terminal and the standard meter, input the corresponding parameters into the designated position of the single-phase data calibration interface, and perform calibration until the test data of the meter terminal is stable and the error is small. Then, rebuild the calibration circuit, change the access voltage and current of the meter terminal, and verify whether recalibration is required.

In order to ensure the stability of the electric energy data, an AC stabilized voltage source is used to stabilize the voltage at 220V and the current at 2.2A, and then start the calibration. The initial calibration data are shown in Table 2 below. 0xD59A, 0xE38, and 0x1312 are the initial gain parameters of current, voltage, and power set randomly. In the subsequent calibration process, it is confirmed that the current gain parameter is 0xBAAA, the active power gain parameter is 0x13EC, and the voltage gain value is 0xD579. The gain parameters of other phase-splitting reactive power and apparent power are consistent with the gain parameters of active power.

The voltage measurement error is large, after recalculation according to formula 2-9, write 0xB4B1. The holding current is 2.1A, and the data measured by adjusting the voltage across the load are shown in Table 3 below. The measurement error of the voltage is less than 2%, and the measurement accuracy reaches the level 2 standard.

Adjust the input current parameters of the point meter terminal, and observe the change law of the current and power measured by the metering chip. The power error is concentrated at about 8%, and the current power error is between 10% and 15%. The specific data are shown in Table 4 below.

After determining the gain value, use a stabilized voltage source to keep the voltage at 220V, and repeatedly adjust the resistance of the sliding rheostat to gradually increase the current and power. Through repeated experiments, the active power error is about 8%, and the current error is between 9% and 15%. When the power grid data is sampled, the median mean filtering algorithm is used. In order to determine the number of sampling times, the number of continuous reading sampling times of current and power data is changed, and the data rules are found in Table 5 below. The effect of 30 times is the worst, and the effect of 50 and 100 times is the same. In order to reduce energy consumption, the number of continuous sampling is determined to be 50 times.

After determining the number of samples, the current measurement and power measurement are compensated by software, and the specific data obtained are shown in Table 6 below. After being compensated by software, the current error is less than 5%, the power error is less than 2%, and the active power measurement meets the requirements of level 2.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims

A passive calibration method for a smart meter, characterized in that it includes: generating a voltage input to a load with a specified power factor through a stabilized voltage source; using a standard commercial meter and a meter to be calibrated to measure the electric energy data of the load; according to the electric energy The data calculates the error between the meter to be calibrated and the standard commercial meter as the gain value. Write the gain value into the MCU designated sector of the meter to be calibrated to complete the calibration; the meter to be calibrated uses an HT7036 metering chip, and the method further includes calibrating the metering chip, including: parameter setting, including mode configuration , Channel gain configuration, EMU unit configuration, high-frequency pulse output configuration, voltage loss threshold setting, start threshold setting; A-phase correction, including power gain correction, voltage correction, current correction; B-phase correction and C-phase correction.
The method according to claim 1, wherein the electric energy data includes: voltage, current, power, frequency, and/or harmonics.
The method according to claim 2, wherein when the electric energy data is voltage, it is assumed that the effective value of the voltage of the standard commercial electric meter is Ur, the measured voltage of the electric meter to be calibrated is Urms, the voltage calibration coefficient is Ugain, and INT is rounded. function, the calculation formula of the voltage calibration coefficient is as follows:
.
The method according to claim 3, characterized in that, when the electric energy data is current, assuming that the effective value of the standard commercial ammeter current is Ir, the measured current of the ammeter to be calibrated is Irms, and the current calibration coefficient is Igain, and the current calibration coefficient is calculated The formula looks like this:
.
The method according to claim 4, wherein when the electric energy data is power, the active power value of the commercial electric meter is Preal, the power value of the electric meter to be calibrated is DataP, the power calibration coefficient is Pgain, and the power calibration coefficient calculation formula As follows:
.
The method according to claim 5, characterized in that, there is a relationship shown in the following formula 2-9 between Ugain' and Igain', Pgain', and the HFconst used in the formula 2-9 is a high-frequency pulse constant, calculated The formula is shown in formula 2-7; in formula 2-7, U n is the actual access voltage of the meter terminal, I b is the actual access current, Vu and Vi are the input voltages of the metering chip voltage channel and current channel respectively; formula 2 N used in -9 is a proportional coefficient, and the calculation formula is shown in the following formula 2-8; T A in formula 2-8 is the transformation ratio of the current transformer, and R is the resistance of the current sampling circuit;
.
The method according to claim 5, characterized in that, when the electric meter to be calibrated measures the electric energy data of the load, a median mean filtering algorithm is used.
The method according to claim 1, wherein the register of the metering chip is divided into two parts, namely a metering parameter register and a calibration parameter register.