A method for compensating the self-heating error of electric energy meters

Abstract

The present invention relates to an error compensation method for self-heating of an electric energy meter, comprising the following steps: under the self-heating condition of the electric energy meter, obtaining a reference energy pulse within the electric energy meter acquisition cycle and saving the initial value of a power gain register in the electric energy meter metering chip; performing periodic statistics on the energy pulses generated after the self-heating condition of the electric energy meter is triggered; performing position-based PID control on the power gain of the electric energy meter based on the numerical error between the periodic energy pulses generated by the self-heating of the electric energy meter and the reference energy pulse measured by the electric energy meter to obtain a new power gain; writing the new power gain into the power gain register in the electric energy meter metering chip; determining whether the self-heating condition has been exited; if so, restoring the power gain register to the initial value and terminating the position-based PID control; if not, continuing the position-based PID control. This method facilitates standardization of test methods and greatly saves time and energy costs for R&D personnel.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy meters, and in particular to an error compensation method for electric energy meters under self-heating conditions. Background Art

[0002] Due to the resistance characteristics of the sampling device in the metering circuit of the electricity meter, self-heating effect will occur when a large current passes through it for a long time, causing the metering accuracy to deteriorate sharply in a short period of time and cannot be recovered for a long time.

[0003] The current common error compensation scheme for self-heating of electric energy meters is as follows:

[0004] 1. Use the temperature-error compensation method; that is, place at least one electric energy meter sample in a temperature control box, pre-set temperature test points within a certain range, and then form a temperature compensation curve based on the temperature-variation data of these temperature points under self-heating conditions;

[0005] 2. Use a time-variation compensation method; that is, observe and count the time-variation data of at least one electric energy meter sample under self-heating conditions, and fit a time-compensation value curve based on the errors at these time points, so as to minimize the average self-heating error of each electric energy meter sample.

[0006] However, there are still some shortcomings in adopting these two traditional compensation schemes:

[0007] 1. Using the temperature compensation curve, in actual applications, due to factors such as the placement of the temperature sensor, sensor accuracy, manganese copper circuit material, and ambient temperature, the actual compensation effect is poor, and the error regression characteristics and compensation response characteristics are poor;

[0008] 2. Compensation curves created by error fitting time-variation data can be used when the sample size is sufficient and the equipment consistency is good enough. However, this method is essentially an open-loop control method and lacks the "robustness" of system control. It is only suitable for situations with a large number of samples and good equipment consistency, and cannot automatically determine the control effect of errors outside the compensation curve range.

[0009] In summary, due to the low cost of sales required for overseas metering, any cost reductions involving changes to current parameters (such as manganese copper sampling resistors and relays) require R&D to re-test for error compensation, which is time-consuming and labor-intensive. Lack of sufficient statistical samples, poor consistency in error trends under high current conditions, or the effects of uncontrollable initial and ambient temperatures will prevent the two aforementioned self-heating compensation methods from being effectively implemented in a standardized, mass-produced manner.

[0010] Therefore, it is necessary to further improve the existing self-heating error compensation method of electricity meters. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method for compensating for the self-heating error of an electric energy meter, which can achieve accurate compensation under self-heating conditions, in response to the above-mentioned prior art.

[0012] The technical solution adopted by the present invention to solve the above technical problems is: a method for compensating the self-heating error of an electric energy meter, which is used to compensate the measurement error of the electric energy meter under self-heating conditions, and is characterized by comprising the following steps:

[0013] Step 1: Collect the current value of the electric energy meter and determine whether the current value of the electric energy meter is greater than a preset threshold. If so, proceed to step 2; if not, continue to collect the current value of the electric energy meter;

[0014] Step 2: Determine whether the duration of the current value of the electric energy meter being greater than the preset threshold value is greater than the preset time. If so, the self-heating condition is triggered and the process proceeds to step 3. If not, the self-heating condition is not triggered and the process proceeds to step 1.

[0015] Step 3: Obtain the reference energy pulse within the energy meter acquisition period and save the initial value of the power gain register in the energy meter measurement chip;

[0016] Step 4: Periodically count the energy pulses generated after the self-heating condition of the electric energy meter is triggered;

[0017] Step 5: Perform positional PID control on the power gain of the electric energy meter according to the numerical error between the periodic energy pulses generated by the self-heating of the electric energy meter and the reference energy pulse measured by the electric energy meter to obtain a new power gain;

[0018] Step 6: Write the new power gain into the power gain register in the energy meter chip;

[0019] Step 7: Determine whether the self-heating condition has exited. If so, the power gain register is restored to the initial value and the position PID control is ended; if not, go to step 4.

[0020] The specific process of PID control is: The formula for position PID control of the power gain of the energy meter is:

[0021]

[0022] Where u(k) is the power gain control output of the kth acquisition cycle; e(k) = the sampling pulse value of this cycle - the reference pulse value; e(k-1) is the energy pulse comparison difference of the previous cycle; K p , K iand K d are the proportional coefficient, integral coefficient and differential coefficient respectively.

[0023] In order to achieve the accuracy of error compensation, the proportional coefficient K p The setting method is:

[0024] Let K i =0,K d =0;

[0025] According to the first step adjustment amount a, gradually increase the proportional coefficient K p , adjust the proportional coefficient to a*K p 、2a*K p 、…、(j*a)*K p , a>0, j is the number of increases; finally, the proportional coefficient corresponding to when the PID control system starts to oscillate is obtained;

[0026] The proportional coefficient of the PID control system oscillation is gradually reduced according to the second step adjustment amount b, b>0, and the proportional coefficient corresponding to the disappearance of the PID control system oscillation is obtained. Finally, the proportional coefficient K p Set to n% of the proportional coefficient corresponding to the disappearance of oscillation in the PID control system, where n is a preset value.

[0027] Preferably, the value range of n is: 60%≤n%≤70%.

[0028] Furthermore, the integral coefficient K i The setting method is:

[0029] Set the integral coefficient K i The initial value of the integral coefficient K is gradually increased according to the third step adjustment amount c. i , c>0, obtain the integral coefficient corresponding to when the PID control system starts to oscillate;

[0030] The integral coefficient of the PID control system that oscillates is gradually reduced according to the fourth step adjustment amount d, d>0, and the integral coefficient corresponding to the disappearance of the PID control system oscillation is obtained. Finally, the integral coefficient K i Set to m%, the integral coefficient corresponding to when the oscillation of the PID control system disappears, where m is a preset value.

[0031] Preferably, the value range of m is: 150%≤n%≤180%.

[0032] Preferably, the differential coefficient K d The setting method is:

[0033] The differential coefficient K d Set the integral coefficient K when no PID control system oscillation occursi p%, where p is a preset value, 0<p%≤100%.

[0034] In this solution, the reference energy pulse in step 3 is the initial energy pulse statistic obtained when the metering chip is in a self-heating condition and is just triggered.

[0035] In this solution, the method for acquiring the energy pulses generated by the self-heating of the electric energy meter in step 4 is: after the self-heating condition occurs, the statistical value of the energy pulses output by the metering chip after working for at least one acquisition cycle is collected.

[0036] The PID control execution mechanism in step 5 is the power gain register inside the metering chip.

[0037] Compared with existing technologies, the advantages of this invention are: using energy pulses as the error signal input source, it achieves standardized error calculation, eliminating the need for type testing after replacing the current sampling device; and through PID automatic control, it avoids the inevitable open-loop control defects of traditional manual error fitting methods. Its closed-loop control characteristics can compare the adjustment results with the reference pulse value in real time, ultimately achieving the goal of firmly controlling the error within the standard error range. Therefore, this method easily achieves standardization of test methods, greatly saving the time and energy costs of R&D personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Flowchart of the error compensation method for self-heating of an electric energy meter in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0040] like Figure 1 As shown, the error compensation method for self-heating of an electric energy meter in this embodiment is used to compensate for the measurement error of the electric energy meter under self-heating conditions, and includes the following steps:

[0041] Step 1: Collect the current value of the electric energy meter and determine whether the current value of the electric energy meter is greater than a preset threshold value. If so, proceed to step 2; if not, continue to collect the current value of the electric energy meter. The preset threshold value can be determined based on experiments or work experience.

[0042] Step 2: Determine whether the duration of the current value of the electric energy meter being greater than the preset threshold value is greater than the preset time. If so, the self-heating condition is triggered and the process proceeds to step 3. If not, the self-heating condition is not triggered and the process proceeds to step 1. The preset time can be determined based on experiments or work experience.

[0043] The metering error is only compensated after the self-heating condition of the electric energy meter is triggered, and no compensation is performed when the self-heating condition is not triggered, thereby making the metering of the electric energy meter more accurate and not affecting the normal use of the electric energy meter;

[0044] Step 3: Obtain the reference energy pulse within the energy meter acquisition period and save the initial value of the power gain register in the energy meter measurement chip;

[0045] In this embodiment, the reference energy pulse is the statistical value of the initial energy pulse obtained when the metering chip is in a self-heating condition and is just triggered. This reference pulse value is a reference pulse value within a measurement cycle. As an error judgment standard for automatic control, it can be automatically adjusted according to the actual working state of the electric energy meter, rather than a fixed theoretical calculated value. The method for obtaining the energy pulse generated by the self-heating of the electric energy meter is: after the self-heating condition occurs, the statistical value of the energy pulse output by the metering chip after at least one acquisition cycle is collected;

[0046] And the method for determining the acquisition period in step 3 is: taking the self-heating conditions Un=220V, Imax=85A, C=1000ipm / h as an example, then it can be calculated that the theoretical number of pulses of the metering chip in 1 minute is 311.666.

[0047] Considering the relationship between the number of pulses as the sampling granularity and the error accuracy, if the number of pulses is an integer, the sampling error is the smallest. Therefore, the acquisition period can be determined to be 3 minutes, and about 935 pulse values ​​(934.9999 pulses) can be used as the reference pulse value.

[0048] Step 4: Periodically count the energy pulses generated after the self-heating condition of the electric energy meter is triggered;

[0049] Step 5: Perform positional PID control on the power gain of the electric energy meter according to the numerical error between the periodic energy pulses generated by the self-heating of the electric energy meter and the reference energy pulse measured by the electric energy meter to obtain a new power gain;

[0050] In this embodiment, the PID control actuator is the power gain correction register inside the metering chip, which realizes precise control under high-precision error conditions;

[0051] The formula for position PID control of the power gain of the energy meter is:

[0052]

[0053] Where u(k) is the power gain output of the kth acquisition cycle; e(k) = the sampling pulse value of this cycle - the reference pulse value; e(k-1) is the energy pulse comparison difference of the previous cycle; K p , K i and Kd are the proportional coefficient, integral coefficient and differential coefficient respectively;

[0054] Step 6: Write the new power gain into the power gain register in the energy meter chip;

[0055] Step 7: Determine whether the self-heating condition has exited. If so, the power gain register is restored to the initial value and the position PID control is ended; if not, go to step 4.

[0056] In this embodiment, to prevent the "accumulated integral error" saturation phenomenon in position-based PID control, the output must be limited beforehand. The aforementioned limiting threshold is determined based on the boundary value of the actual electric energy meter's error range. After position-based PID calculation, the controlled output directly reflects the difference between the error-compensated energy pulse value and the reference energy pulse value. The control output of this cycle is then "integrated limited" based on the maximum error range of the electric energy meter. The adjusted value written to the power gain register is then calculated using the "power gain - power" proportional conversion relationship, and position-based PID control is then repeated. In this way, through a continuous, successive "error negative feedback" approximation process, the goal of error elimination is ultimately achieved.

[0057] The oscillation of the PID control system is defined as: after each measurement cycle is reached, the error of the electric energy meter calibration platform is centered on the actual error and is displayed alternately in positive and reverse directions.

[0058] The PID control system oscillation disappearance is defined as: after each measurement cycle is reached, the error compensation effect displayed by the electric energy meter calibration platform is not obvious (the error gradually increases);

[0059] In order to determine the various coefficients in the position PID control and ultimately achieve error compensation, the proportional coefficient K p The setting method is:

[0060] Let K i =0,K d =0;

[0061] According to the first step adjustment amount a, gradually increase the proportional coefficient K p , adjust the proportional coefficient to a*K p 、2a*K p 、…、(j*a)*K p , a>0, j is the number of increases; then obtain the proportional coefficient corresponding to when the PID control system starts to oscillate;

[0062] The proportional coefficient of the PID control system oscillation is gradually reduced according to the second step adjustment amount b, b>0, and the proportional coefficient corresponding to the disappearance of the PID control system oscillation is obtained. Finally, the proportional coefficient K p Set to n% of the proportional coefficient corresponding to when the oscillation of the PID control system disappears, where n is a preset value; the value range of n is: 60%≤n%≤70%.

[0063] In this embodiment, a=0.5; b=0.2;

[0064] In addition, the above integral coefficient K i The setting method is:

[0065] According to the characteristic that the minimum error resolution is 1 pulse, first set the integral coefficient K i The initial value of the integral coefficient K is gradually increased according to the third step adjustment amount c. i , c>0, obtain the integral coefficient corresponding to when the PID control system starts to oscillate;

[0066] The integral coefficient of the PID control system that oscillates is gradually reduced according to the fourth step adjustment amount d, d>0, and the integral coefficient corresponding to the disappearance of the PID control system oscillation is obtained. Finally, the integral coefficient K i Set to m%, the integral coefficient corresponding to the disappearance of oscillation in the PID control system, where m is a preset value. The value range of m is: 150% ≤ n% ≤ 180%; in this embodiment, c = 4.5; d = 2.0;

[0067] Differential coefficient K d The setting method is:

[0068] The differential coefficient K d Set the integral coefficient K when no PID control system oscillation occurs i p% is a preset value, 0<p%≤100%. In this embodiment, 10%≤p%≤30%;

[0069] In this embodiment, K p =0.6, the PID control system oscillation disappears, take K p =0.4; K i =2, the PID control system oscillation disappears, take K i =3.0; in addition, K d =0.2; therefore, the final PID calculation formula is:

[0070] u(k)=0.4*e(k)+3.0*e SUM +0.2*e D

[0071] Among them, e SUM =eSUM +[e(k)-e(k-1)],e SUM The initial value can be set, usually the initial value is 0; D =e(k)-e(k-1), the ultimate goal is e(k-1)=e(k).

[0072] The PID algorithm signal source in this embodiment is taken from the internal electrical quantity pulse signal of the metering chip, which is unrelated to the external self-heating condition and has high isolation. Therefore, the quality judgment standard of the error signal is true and reliable, and has high anti-interference ability. In addition, the algorithm output actuator is the "power gain correction register" inside the metering chip, which can achieve high-precision and accurate control. A closed-loop control structure is created through the PID control system. It has the ability to use the output result as a feedback signal and then provide it to the input signal. The frequency and error (meter-standard meter) of the energy pulse output by the metering chip show a certain proportional trend. A position-type PID algorithm is used to periodically count, compensate and adjust the power output of the energy pulses generated under self-heating conditions. Through continuous cyclic operations, a series of "negative feedback" processes of "utilizing deviations and correcting deviations" are formed, and ultimately the control target is locked within the expected range.

[0073] The PID algorithm is used to achieve closed-loop automatic control of the error generated under self-heating conditions, and error adjustment can be performed in a timely, efficient and automatic manner, so that the 0.5S-level single-phase electricity meter can successfully pass the self-heating error test standard specified in EN 50470-3:2006.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for compensating the self-heating error of an electric energy meter, which is used to compensate the measurement error of the electric energy meter under self-heating conditions, is characterized in that The steps include: Step 1: Collect the current value of the electric energy meter and determine whether the current value of the electric energy meter is greater than a preset threshold. If so, proceed to step 2; if not, continue to collect the current value of the electric energy meter; Step 2: Determine whether the duration of the current value of the electric energy meter being greater than the preset threshold value is greater than the preset time. If so, the self-heating condition is triggered and the process goes to step 3. If not, the self-heating condition is not triggered and the process goes to step 1; Step 3: Obtain the reference energy pulse within the energy meter acquisition period and save the initial value of the power gain register in the energy meter measurement chip; Step 4: Periodically count the energy pulses generated after the self-heating condition of the electric energy meter is triggered; Step 5: Perform positional PID control on the power gain of the electric energy meter according to the numerical error between the periodic energy pulses generated by the self-heating of the electric energy meter and the reference energy pulse measured by the electric energy meter to obtain a new power gain; The formula for position PID control of the power gain of the energy meter is: Where u(k) is the power gain control output of the kth acquisition cycle; e(k) = the sampling pulse value of this cycle - the reference pulse value; e(k-1) is the energy pulse comparison difference of the previous cycle; K p , K i and K d are the proportional coefficient, integral coefficient and differential coefficient respectively; Step 6: Write the new power gain into the power gain register in the energy meter chip; Step 7: Determine whether the self-heating condition has exited. If so, the power gain register is restored to the initial value and the position PID control is ended; if not, go to step 4.

2. The method for compensating for self-heating errors in electric energy meters according to claim 1, characterized in that: The proportionality coefficient K p The setting method is: Let K i =0,K d =0; According to the first step adjustment amount a, gradually increase the proportional coefficient K p , adjust the proportional coefficient to a*K p 、2a*K p 、…、(j*a)*K p , a>0, j is the number of increases; then obtain the proportional coefficient corresponding to when the PID control system starts to oscillate; The proportional coefficient of the PID control system oscillation is gradually reduced according to the second step adjustment amount b, b>0, and the proportional coefficient corresponding to the disappearance of the PID control system oscillation is obtained. Finally, the proportional coefficient K p Set to n% of the proportional coefficient corresponding to the disappearance of oscillation in the PID control system, where n is a preset value.

3. The method for compensating for self-heating errors in an electric energy meter according to claim 2, wherein: The value range of n is: 60%≤n%≤70%.

4. The method for compensating for self-heating errors in an electric energy meter according to claim 1, wherein: The integral coefficient K i The setting method is: Set the integral coefficient K i The initial value of the integral coefficient K is gradually increased according to the third step adjustment amount c. i , c>0, obtain the integral coefficient corresponding to when the PID control system starts to oscillate; The integral coefficient of the PID control system that oscillates is gradually reduced according to the fourth step adjustment amount d, d>0, and the integral coefficient corresponding to the disappearance of the PID control system oscillation is obtained. Finally, the integral coefficient K i Set to m%, the integral coefficient corresponding to when the oscillation of the PID control system disappears, where m is a preset value.

5. The method for compensating for self-heating errors in an electric energy meter according to claim 4, characterized in that: The value range of m is: 150%≤m%≤180%.

6. The method for compensating for self-heating errors in an electric energy meter according to claim 4, characterized in that: The differential coefficient K d The setting method is: The differential coefficient K d Set the integral coefficient K when no PID control system oscillation occurs i p%, where p is a preset value, 0<p%≤100%.

7. The method for compensating for self-heating errors in an electric energy meter according to any one of claims 1 to 6, characterized in that: The reference energy pulse in step 3 is an initial energy pulse statistic obtained when the metering chip is in a self-heating condition and is just triggered.

8. The method for compensating for self-heating errors in an electric energy meter according to claim 7, characterized in that: The method for acquiring the energy pulses generated by the self-heating of the electric energy meter in step 4 is: after the self-heating condition occurs, the statistical value of the energy pulses output by the metering chip after working for at least one acquisition cycle is collected.

9. The method for compensating for self-heating errors in an electric energy meter according to claim 8, characterized in that: The PID control execution mechanism in step 5 is the power gain register inside the metering chip.

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