Calculation and design method based on zero sequence current in electric energy meter

Abstract

The present invention relates to a calculation and design method for an electric energy meter based on zero-sequence current. The metering module includes an interface register, an FPCnt register, and a pulse power register. The metering module comprises an I-ADC module, a U-ADC module, a multiplier for representing the multiplication of current and voltage, and an FPCnt calculator. The present invention has a reasonable design, a compact structure, and is easy to use.

Description

Technical Field

[0001] The invention relates to a calculation and design method in an electric energy meter based on zero-sequence current. Background Art

[0002] The current power design is that when one pulse flashes, the power increases by 1. However, in reality, it is impossible to reach a power level that is less than one pulse. In order to meet customers' requirements for the power accuracy of electricity meters, the present invention proposes a high-precision power design method to improve the power accuracy by one level. However, the current highest power resolution is that when one pulse flashes, the power increases by 1.

[0003] The zero-sequence current in the energy meter is directly obtained by the metering chip. The currents of phases A, B, and C are all the maximum current I max When the zero-sequence current is 60A, it should be 0, but the zero-sequence current obtained from the metering chip is more than 2A. As the currents of the ABC phases increase, the zero-sequence current value also increases, resulting in inaccurate zero-sequence current and causing the electric energy meter to misjudge the abnormal zero-line current event.

[0004] The main reasons for inaccurate zero-sequence current are: losses in the current transformer's magnetic core material lead to errors in current sampling; the current ADC sampling in the metering chip also suffers from errors caused by ADC conversion losses and noise; and the metering chip has issues with its zero-sequence current algorithm. All of these factors contribute to inaccurate zero-sequence current.

[0005] The present invention proposes a design method for high-precision electric quantity, which can accurately calculate the electric quantity that is less than a full pulse. Summary of the Invention

[0006] The technical problem to be solved by the present invention is generally to provide a calculation and design method based on zero-sequence current in an electric energy meter.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is:

[0008] A metering module based on zero-sequence current in an electric energy meter includes an interface register, an FPCnt register, and a pulse power register; the metering module includes an I-ADC module, a U-ADC module, a multiplier for multiplying current and voltage, and an FPCnt calculator;

[0009] The collected current signal is converted into digital form by the I-ADC module and then input into the X multiplier.

[0010] The voltage signal of Egypt is converted into digital form by the U-ADC module and then input into the X multiplier.

[0011] After the current and voltage pass through the X multiplier, the output signal is sent to the FPCnt calculator for calculation to determine whether there is / is a complete pulse. If there is a complete pulse, the pulse power increment is 1 and the FPCnt calculator is cleared;

[0012] There is a 10-fold relationship between the fractional pulse and the pulse power. When the fractional pulse reaches 10, the pulse power increments by 1, the fractional pulse register is cleared, and counting starts again.

[0013] A method for measuring zero-sequence current in an electric energy meter, S1. First, a fractional pulse FPCF takes out the pulse number, determines that the pulse number exceeds the fractional pulse minimum resolution 1, and increments the fractional pulse register by 1; then, if the fractional pulse register does not receive a pulse, the pulse power is 0; wherein the power in the fractional pulse register is a high-precision power;

[0014] S2. First, the pulse power register reads the pulse power and makes a judgment. When there is pulse power, the minimum resolution of the pulse power is 1, and the pulse power increment is 10, that is, the pulse power minus the decimal pulse register, and the difference is the high-precision power; then, the direction is judged. If the direction is positive, the high-precision power is placed in the positive high-precision power; if the direction is reverse, the high-precision power is placed in the reverse high-precision power.

[0015] A measurement method based on zero-sequence current in electric energy meters. The phasor expressions of each phase current are as follows:

[0016] i A =I A cosθ+I A sinθ;

[0017] i B =I B cosθ+I B sinθ;

[0018] i C =I C cosθ+I C sinθ;

[0019] In the expression

[0020] From the phasor expressions of the currents of each phase, we can get the current values ​​on the X and Y axes respectively.

[0021] The current value of the X-axis is as follows,

[0022]

[0023]

[0024]

[0025] i X =i XA +i XB +i XC Expression 4;

[0026] The current value of the Y axis is as follows,

[0027]

[0028]

[0029]

[0030] i Y =i YA +i YB +i YC Expression 8;

[0031] Zero-sequence current

[0032] In the data of expression 1-9, according to the phase angle before the voltage Angle between voltage and current Current I, the metering chip provides the output phase angle Angle Current I data, according to expression 1-9, get the zero-sequence current Is value;

[0033] In the electric energy meter, the requirement for the abnormal neutral current event is the ratio of the absolute value of the difference between the neutral current and the live current to the maximum value of the neutral current and the live current;

[0034] Abnormal ratio of neutral current When the current of any phase line A, B, or C exceeds 1A, the abnormal current ratio of the neutral line is calculated.

[0035] In a three-phase system, when the voltage and current are balanced and the power factor is Right now

[0036] In a three-phase system, the phase angle between the voltages is 120 degrees when they are balanced; The voltage phase angle of the energy meter takes phase A as the reference point.

[0037] Right now

[0038] The present invention can accurately calculate the amount of electricity that is less than a full pulse. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a metering schematic diagram of the present invention.

[0040] Figure 2 It is a high-precision electricity diagram of the present invention.

[0041] Figure 3 The power factor of the present invention is Schematic diagram showing the phasor relationship between voltage and current.

[0042] Figure 4 Schematic diagram of the zero-sequence current Is of the present invention.

[0043] Figure 5 It is the phasor diagram of the present invention. DETAILED DESCRIPTION

[0044] like Figure 1-5 As shown, the calculation and design method of the zero-sequence current in the electric energy meter of this embodiment is as follows:

[0045] The present invention proposes a design method for high-precision electrical quantity, such as Figure 1 To illustrate the relationship between the FPCnt register and the pulse power register, the metering module includes an interface register, an FPCnt register, and a pulse power register; the metering module has an I-ADC module, a U-ADC module, a multiplier for multiplying current and voltage, and an FPCnt calculator;

[0046] The collected current signal is converted into digital form by the I-ADC module and then input into the X multiplier.

[0047] The voltage signal of Egypt is converted into digital form by the U-ADC module.

[0048] After the current and voltage pass through the X multiplier, the output signal is sent to the FPCnt calculator for calculation to determine whether a complete pulse is present / output. If a complete pulse is present, the pulse charge is incremented by 1 and the FPCnt calculator is cleared. Specifically, the relationship between the fractional pulse and the pulse charge is 10 times. When the fractional pulse reaches 10, the pulse charge is incremented by 1, the fractional pulse register is cleared, and counting begins again.

[0049] The design steps of the present invention are as follows:

[0050] S1, FPCF (fractional pulse) takes out the pulse number, determines that the pulse number exceeds the minimum resolution of the fractional pulse by 1, and increments the fractional pulse register by 1; if the fractional pulse register does not receive a pulse, the pulse power is 0; the power in the fractional pulse register is a high-precision power;

[0051] S2. The pulse power register reads the pulse power and makes a judgment. When there is pulse power, the minimum resolution of the pulse power is 1, and the pulse power increment is 10. Since the pulse power increment is 1 (including decimal pulses), the pulse power minus the decimal pulse register, the difference is the high-precision power. Finally, the direction is judged. If the direction is positive, the high-precision power is placed in the positive high-precision power; otherwise, the high-precision power is placed in the reverse high-precision power.

[0052] Figure 3 The relationship shown is when the current and voltage are in the same direction and the angle between them is zero degrees, the power factor at this time is Right now

[0053] In a three-phase system, the phase angle between the voltages is 120 degrees when they are balanced; The voltage phase angle of the energy meter takes phase A as the reference point, that is,

[0054] According to the symmetrical component method, which is basic knowledge, the phasor expressions of each phase current are as follows: A =I A cosθ+I A sinθ

[0055] i B =I B cosθ+I B sinθ

[0056] i C =I C cosθ+I C sinθ

[0057] In the expression

[0058] From the phasor expressions of each phase current, we can see the current values ​​on the X and Y axes respectively.

[0059] The current value of the X-axis is as follows

[0060]

[0061]

[0062]

[0063] i X =i XA +i XB +i XC Expression 4

[0064] The current value of the Y axis is as follows

[0065]

[0066]

[0067]

[0068] i Y =i YA +i YB +i YC Expression 8

[0069] Zero-sequence current

[0070] From the data of the above expression, the phase angle before the voltage Angle between voltage and current Current I; because the expression contains an angle, the current value is an unsigned absolute value. The metering chip provides the output phase angle Angle Current I data, and then according to expressions 1 to 9, the zero-sequence current Is value is obtained, such as Figure 4 shown.

[0071] The current is 60A, the angle between voltage and current is 0 degrees or 360 degrees, and the voltage phase angle is symmetrical. Figure 1 The zero-sequence current I can be obtained s =0; draw the phasor diagram as Figure 5 shown.

[0072] The phase quantity obtained by Ia and Ib is Iab, and the phase quantity Iab is the same as Ic in magnitude but opposite in direction, and finally the zero-sequence current Is=0 is obtained.

[0073] Let's verify it from expressions 1 to 9, which are as follows.

[0074] Current value of each phase on the X-axis

[0075] i XA =I A cosθ=60cos(0°+0°)=60A

[0076] i XB =I B cosθ=60cos(120°+0°)=-30A

[0077] i XC =I C cosθ=60cos(240°+0°)=-30A

[0078] i X =i XA +i XB +i XC=60-30-30=0A

[0079] Current value of each phase on the Y axis

[0080] i YA =I A Sinθ=60sin(0°+0°)=0A

[0081] i YB =I B Sinθ=60sin(120°+0°)=51.962A

[0082] i YC =I C Sinθ=60sin(240°+0°)=-51.962A

[0083] i Y =i YA +i YB +i YC =0+51.962-51.962=0A

[0084] Zero-sequence current

[0085] Zero sequence current expression verification and Figure 5 Phase Figure 1 Therefore, Is=0.

[0086] Conclusion: The zero-sequence current expression needs to provide current I, phase angle Angle The electric energy meter measures the current I and phase angle Angle There are accuracy and error requirements, with an angle error of ±0.1° and a current error of ±1%. In addition, the abnormal event requirement for the neutral current of the electricity meter is the ratio of the absolute value of the difference between the neutral current and the live current to the maximum value of the neutral current and the live current.

[0087] Abnormal ratio of neutral current To meet the ratio requirement, the current of any phase line (ABC) must exceed 1A before the calculation of the abnormal neutral current ratio begins, and a determination is made as to whether the ratio exceeds 50%. The electric energy meter uses a zero-sequence current expression method to resolve the problem of inaccurate zero-sequence current directly obtained by the metering chip, ensuring accurate judgment of abnormal zero-line current events. This invention improves the meter's energy metering accuracy. During meter settlement, the meter reduces the error precision of the energy quantity by one level, improving settlement accuracy.

[0088] The present invention is fully described for a clearer disclosure, and the prior art is not listed one by one.

[0089] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art will appreciate that the technical solutions described in the above embodiments may be modified or some of the technical features may be replaced with equivalents. It is also obvious for those skilled in the art to combine multiple technical solutions of the present invention. However, such modifications or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A metering module based on zero-sequence current in an electric energy meter, characterized by: The metering module includes an interface register, an FPCnt register, and a pulse power register; the metering module includes an I-ADC module, a U-ADC module, a multiplier for multiplying current and voltage, and an FPCnt calculator; The collected current signal is converted into digital form by the I-ADC module and then input into the X multiplier. The collected voltage signal is converted into digital form by the U-ADC module and then input into the X multiplier. The X multiplier multiplies the current and voltage and outputs a signal to the FPCnt calculator for calculation to determine whether a complete pulse has been reached or output. If a complete pulse has been reached, the pulse power increment is 1 and the FPCnt calculator is cleared. There is a 10-fold relationship between the fractional pulse and the pulse power. When the fractional pulse reaches 10, the pulse power increments by 1, the fractional pulse register is cleared, and counting starts again.

2. A method for measuring zero-sequence current in an electric energy meter, characterized in that: S1. First, the fractional pulse FPCF takes out the pulse number, determines that the pulse number exceeds the fractional pulse minimum resolution 1, and increments the fractional pulse register by 1; Then, if the fractional pulse register does not receive a pulse, the pulse power is 0; wherein, the power of the fractional pulse register is a high-precision power; S2. First, the pulse power register reads the pulse power and makes a judgment. When there is pulse power, the minimum resolution of the pulse power is 1, and the pulse power increment is 10, that is, the pulse power minus the decimal pulse register, and the difference is the high-precision power; then, the direction is judged. If the direction is positive, the high-precision power is placed in the positive high-precision power; if the direction is reverse, the high-precision power is placed in the reverse high-precision power.

3. A method for measuring zero-sequence current in an electric energy meter, characterized by: The phasor expressions of each phase current are as follows: i A =I A cosθ+I A sinθ; i B =I B cosθ+I B sinθ; i C =I C cosθ+I C sinθ; In the expression From the phasor expressions of the currents of each phase, we can get the current values ​​on the X and Y axes respectively. The current value of the X-axis is as follows, i X = i XA +i XB +i XC Expression 4; The current value of the Y axis is as follows, i Y = i YA +i YB +i YC Expression 8; Zero-sequence current In the data of expression 1-9, according to the phase angle before the voltage Angle between voltage and current Current I, the metering chip provides the output phase angle Angle Current I data, according to expression 1-9, get the zero-sequence current Is value; In the electric energy meter, the requirement for the abnormal neutral current event is the ratio of the absolute value of the difference between the neutral current and the live current to the maximum value of the neutral current and the live current; Abnormal ratio of neutral current or When the current of any phase line A, B, or C exceeds 1A, the abnormal current ratio of the neutral line is calculated.

4. The method for measuring zero-sequence current in an electric energy meter according to claim 3, characterized in that: In a three-phase system, when the voltage and current are balanced and the power factor is Right now In a three-phase system, the phase angle between the voltages is 120 degrees when they are balanced; The voltage phase angle of the energy meter takes phase A as the reference point. Right now

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