CN110244116B - DC instantaneous power metering circuit and quasi-synchronous calculation method thereof - Google Patents
DC instantaneous power metering circuit and quasi-synchronous calculation method thereof Download PDFInfo
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R21/00—Arrangements for measuring electric power or power factor
- G01R21/06—Arrangements for measuring electric power or power factor by measuring current and voltage
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention discloses a metering circuit of direct current instantaneous power, which firstly utilizes a low-frequency alternating voltage signal and an alternating current signal with known phase included angles to calculate the delay or advance phase difference of the two signals, then utilizes linear interpolation to compensate the phase in a mode of reconstructing sampling data by a software, calculates a phase compensation coefficient, and uses the phase compensation coefficient as a synchronous compensation coefficient of direct current voltage and direct current sampling to calculate the direct current instantaneous power after compensating the sampling data. The high-precision instantaneous power calculated by the method can realize the high precision of the pulse output of the high-precision direct current standard electric energy meter. The method has the characteristics of easy realization, high synchronization accuracy and good practicability, and can be applied to the synchronization of different channels in a single analog-digital conversion chip and the synchronization of sampling signals in a scheme adopting a plurality of analog-digital conversion chips.
Description
Technical Field
The invention relates to the technical field of analog-digital signal processing in alternating current and direct current signal measurement, in particular to a metering circuit of direct current instantaneous power and a quasi-synchronous calculation method thereof.
Background
With the vigorous development of new energy, high-precision direct current measurement is increasingly important. In a DC system containing various clutters, the accuracy of DC power measurement is directly related to the synchronism of the data obtained after sampling by a DC voltage channel and a DC current channel.
The multi-channel synchronous sampling is to sample data of a plurality of sampling channels at the same time, and the sampling periods among the multiple channels are the same. Depending on the manner in which the synchronous sampling is provided, both hardware synchronous sampling and software synchronous sampling may be employed.
The hardware synchronous sampling is to generate sampling pulse synchronous with the tested signal by a special hardware circuit, the hardware design is complex and the synchronous timeliness is easily affected by the consistency of the parameters of the hardware circuit.
The software synchronous sampling corrects the sampling value by using a linear interpolation method to the sampled value, so that the obtained sampling value is maximally close to the ideal sampling time.
In order to obtain high-precision direct-current instantaneous power, accurate assurance of the sampling data of the direct-current voltage and the direct-current are required to be at the same time. In the circuit design, the difference of the performances and parameters of the sampling component, the gain adjusting circuit and the filter circuit exists in the real-time performance of the signal reaction, so that errors exist between the sampled direct-current voltage data and the sampled direct-current data and the actual moment.
Disclosure of Invention
Aiming at the defects existing in the technology, the invention provides the direct current instantaneous power metering circuit with high synchronization accuracy and good practicability and the quasi-synchronization calculation method thereof.
In order to achieve the above purpose, the invention provides a metering circuit of direct current instantaneous power, which comprises a voltage sampling component, a current sampling component, a first gain adjusting circuit, a second gain adjusting circuit, a first filter circuit, a second filter circuit, a digital-to-analog conversion chip, a magnetic isolation chip and a processor, wherein the input end of the first gain adjusting circuit is connected with the output end of the voltage sampling component, the output end of the first gain adjusting circuit is connected with the input end of the first filter circuit, the input end of the second gain adjusting circuit is connected with the output end of the current sampling component, the output end of the second gain adjusting circuit is connected with the input end of the second filter circuit, the output end of the first filter circuit and the output end of the second filter circuit are both connected with the input end of the digital-to-analog conversion chip, the input end of the magnetic isolation chip is connected with the output end of the digital-to-analog conversion chip, and the output end of the magnetic isolation chip is connected with the input end of the processor.
The first gain adjusting circuit and the second gain adjusting circuit have the same circuit structure, and each of the first gain adjusting circuit and the second gain adjusting circuit comprises a signal amplifying unit and a negative signal to positive signal unit, and the output end of the signal amplifying unit is connected with the input end of the negative signal to positive signal unit.
The voltage sampling component is a voltage sampling resistor, the current sampling component is a current sampling resistor, the first filter circuit and the second filter circuit are low-pass filters, and the digital-to-analog conversion chip is a 16-bit SAR analog-to-digital converter.
The invention discloses a quasi-synchronous calculation method of direct current instantaneous power, which comprises the following calculation steps:
s1, respectively inputting an alternating voltage signal and an alternating current signal into an analog signal board aiming at a voltage sampling channel and a current sampling channel, wherein the phase angle phi a between the alternating voltage signal and the alternating current signal is definitely known;
S2, starting sampling of alternating voltage signals and alternating current signals at the same moment, wherein the sampling moment is consistent with the sampling frequency, and after obtaining sampling data, a processor processes the data by utilizing a digital filtering technology so as to filter out higher harmonics;
s3, precisely calculating the frequency and the period of the voltage signal and the current signal by using a zero crossing point periodic measurement method;
S4, respectively carrying out linear interpolation reconstruction on the alternating voltage signal and the alternating current signal according to the sampling period of the alternating voltage signal and the current signal, and then carrying out FFT analysis to obtain an included angle phi b between the alternating voltage signal and the alternating current signal;
S5, taking the alternating voltage sampling signal as a reference, carrying out linear interpolation translation on the alternating current sampling data to enable the phase included angle between the translated alternating voltage and the alternating current signal to be phi a, determining an interpolation revision coefficient K at the moment, and storing the interpolation revision coefficient K in equipment;
S6, after the analog-to-digital conversion chip finishes the analog-to-digital conversion of a fixed number, automatically calling an interpolation revision coefficient K and reconstructing a current sampling signal by using an interpolation algorithm to enable voltage sampling data and current sampling data to achieve quasi-synchronization;
and S7, in the direct current power calculation, automatically calling an interpolation revision coefficient K, reconstructing a current sampling signal by using an interpolation algorithm, and obtaining the direct current power by using a direct current power calculation formula.
In step S2, the digital filter used in the processing of the data by the digital filtering technique is an FIR finite length unit impulse response filter.
In S3, the frequency of the ac signal is calculated according to the following zero-crossing period measurement method:
Setting the time of each sampling point at equal intervals as Finding out two zero crossing points in the same direction in one cycle, and then the points/>Sum dot/>The sampling time between two zero crossing points is (N-1)Then calculate/>, through the front and back zero crossing pointsThe time distance from the zero crossing point is/>Similarly/>The time distance from the zero crossing point is/>Is called/>The sampling time of the whole period and the remainder time of the non-whole period in one period are the actual sampling time in one period, and the actual measuring frequency of the signal is calculated according to the actual sampling time; n is the number of samples of the analog-to-digital conversion chip in a certain short time.
In S3, the ac signal continues to calculate the period according to the following zero-crossing period measurement method:
the sampling period Ts is very short and, And/>The line approximation of (a) is regarded as a straight line, the slope of the line between two points is calculated, and the signal period to the starting point/> can be approximatedTime points/>The method comprises the following steps:
；
Can also be obtained By the end time point of the signal period/>The method comprises the following steps:
；
the sampling time T for one complete sampling period is:
。
In step S7, the dc instantaneous power calculation formula is as follows:
And/> The sampling values of the voltage channel and the current channel at the same time are respectively obtained.
The beneficial effects of the invention are as follows:
Compared with the prior art, the invention carries out a series of treatments such as gain adjustment, low-pass filtering and the like on the output signals of the tested voltage signal and the current sampling component, converts the signals into analog signals suitable for the input range of the analog-to-digital converter, sends the analog signals into the analog-to-digital converter, and then converts the analog signals into digital signals through the analog-to-digital converter to be sent to a processor for processing. In the processor, firstly, a low-frequency alternating voltage signal and an alternating current signal with known phase angles are used for calculating the delay or advance phase difference of the low-frequency alternating voltage signal and the alternating current signal, then the linear interpolation is used for compensating the phase in a mode of reconstructing sampling data through a software, a phase compensation coefficient is calculated, the phase compensation coefficient is used as a synchronous compensation coefficient of sampling direct current voltage and direct current, and the sampling data is compensated to calculate the direct current instantaneous power. The method has the characteristics of easy realization, high synchronization accuracy and good practicability, and can be applied to the synchronization of different channels in a single analog-digital conversion chip and the synchronization of sampling signals in a scheme adopting a plurality of analog-digital conversion chips.
Drawings
FIG. 1 is a schematic diagram of a DC instantaneous power metering circuit according to the present invention;
FIG. 2 is a schematic circuit diagram of a DC instantaneous power metering circuit according to the present invention;
FIG. 3 is a flow chart of a quasi-synchronous calculation method of the DC instantaneous power of the invention;
FIG. 4 is an auxiliary graph of the signal sampling period and frequency calculation process of the present invention.
The main reference numerals are as follows:
10. Voltage sampling unit 11 and current sampling unit
12. First gain adjustment circuit 13 and second gain adjustment circuit
14. First filter circuit 15, second filter circuit
16. Digital-to-analog conversion chip 17 and magnetic isolation chip
18. A processor.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below with reference to the accompanying drawings.
Referring to fig. 1, the metering circuit for dc transient power of the present invention includes a voltage sampling unit 10, a current sampling unit 11, a first gain adjustment circuit 12, a second gain adjustment circuit 13, a first filter circuit 14, a second filter circuit 15, a digital-to-analog conversion chip 16, a magnetic isolation chip 17, and a processor 18, wherein an input end of the first gain adjustment circuit 12 is connected to an output end of the voltage sampling unit 10, an output end of the first gain adjustment circuit 12 is connected to an input end of the first filter circuit 14, an input end of the second gain adjustment circuit 13 is connected to an output end of the current sampling unit 11, an output end of the second gain adjustment circuit 13 is connected to an input end of the second filter circuit 15, an output end of the first filter circuit 14 and an output end of the second filter circuit 15 are both connected to an input end of the digital-to-analog conversion chip 16, an input end of the magnetic isolation chip 17 is connected to an output end of the digital-to-analog conversion chip 16, and an output end of the magnetic isolation chip 17 is connected to an input end of the processor 18.
Compared with the prior art, the invention performs a series of processes such as gain adjustment, low-pass filtering and the like on the output signals of the tested voltage signal and the current sampling component, converts the output signals into analog signals suitable for the input range of the analog-to-digital converter, sends the analog signals into the analog-to-digital converter, and then converts the analog signals into digital signals through the analog-to-digital converter to be sent to the processor 18 for processing. The processor 18 first calculates the delay or advance phase difference of the low-frequency ac voltage signal and the ac current signal with known phase angles, compensates the phase by linear interpolation through the mode of reconstructing the sampled data by the software, calculates a phase compensation coefficient, uses the phase compensation coefficient as a synchronous compensation coefficient of the dc voltage and the dc current, compensates the sampled data, and calculates the dc instantaneous power. The method has the characteristics of easy realization, high synchronization accuracy and good practicability, and can be applied to the synchronization of different channels in a single analog-digital conversion chip and the synchronization of sampling signals in a scheme adopting a plurality of analog-digital conversion chips.
Referring to fig. 2, the first gain adjusting circuit 12 and the second gain adjusting circuit 13 have the same circuit structure, and the first gain adjusting circuit 12 and the second gain adjusting circuit 13 each include a signal amplifying unit and a negative signal to positive signal unit, and an output end of the signal amplifying unit is connected to an input end of the negative signal to positive signal unit. As shown in fig. 2, the interconnections among the capacitor C9, the capacitor C10, the capacitor C11, the capacitor C12, the capacitor C13, the capacitor C14, the resistor R10, the resistor R11, the resistor R12, the resistor R13, the chip U, and one amplifier form a signal amplifying unit; the mutual connection among the capacitor C1, the capacitor C2, the capacitor C3, the capacitor C4, the capacitor C5, the capacitor C6, the capacitor C7, the capacitor C8, the resistor R1, the resistor R2, the resistor R3, the resistor R4, the resistor R5, the resistor R6, the resistor R7, the resistor R8, the resistor R9 and one amplifier forms a negative signal to positive signal unit.
In this embodiment, the voltage sampling unit 10 is a voltage sampling resistor, the current sampling unit 11 is a current sampling resistor, the first filter circuit 14 and the second filter circuit 15 are low-pass filters, and the digital-to-analog conversion chip 16 is a 16-bit SAR analog-to-digital converter.
Referring further to fig. 3, the quasi-synchronous calculation method of the direct current instantaneous power of the present invention comprises the following calculation steps:
s1, respectively inputting an alternating voltage signal and an alternating current signal into an analog signal board aiming at a voltage sampling channel and a current sampling channel, wherein the phase angle phi a between the alternating voltage signal and the alternating current signal is definitely known;
S2, starting sampling of alternating voltage signals and alternating current signals at the same moment, wherein the sampling moment is consistent with the sampling frequency, and after obtaining sampling data, the processor 18 processes the data by utilizing a digital filtering technology so as to filter out higher harmonics;
s3, precisely calculating the frequency and the period of the voltage signal and the current signal by using a zero crossing point periodic measurement method;
S4, respectively carrying out linear interpolation reconstruction on the alternating voltage signal and the alternating current signal according to the sampling period of the alternating voltage signal and the current signal, and then carrying out FFT analysis to obtain an included angle phi b between the alternating voltage signal and the alternating current signal;
Aiming at the constraint condition that the length of a signal is required to be an integer power of 2 by an FFT algorithm, an FFT improvement strategy for carrying out a linear interpolation reconstruction mode on a sampling signal is provided.
Linear interpolation is an interpolation method widely used in the fields of mathematics, computer graphics and the like. If the function value y corresponding to a certain position x in the interval [ x0, x1] is obtained, the known coordinate points (x 0, y 0) and (x 1, y 1) can be calculated by the formula:
；
let the ratio of two sides of the equation be Then
；
When the spectrum analysis is sampled, the sampling frequency can be set to 12.8K, the time interval between sampling points is very small, and the linear fitting degree is very high, so that the error of an algorithm for performing linear interpolation in the interval of the time interval between the sampling points is very small. Through a linear interpolation method, an analysis sample with the integer power length of 2 can be obtained, so that the analysis sample meets the calculation constraint condition of an FFT algorithm.
The improved FFT algorithm based on linear interpolation resampling can obtain an integer period of an analysis signal and is suitable for a sampling sequence of FFT, so that errors of leakage effect and fence effect are suppressed, and the spectrum and phase analysis processing of the signal can be completed rapidly, and the method has high accuracy and instantaneity. The included angle phi b between the alternating voltage signal and the alternating current signal with high precision can be calculated by utilizing an FFT algorithm according to the method.
S5, taking the alternating voltage sampling signal as a reference, carrying out linear interpolation translation on the alternating current sampling data to enable the phase included angle between the translated alternating voltage and the alternating current signal to be phi a, determining an interpolation revision coefficient K at the moment, and storing the interpolation revision coefficient K in equipment;
S6, after the analog-to-digital conversion chip finishes the analog-to-digital conversion of a fixed number, automatically calling an interpolation revision coefficient K and reconstructing a current sampling signal by using an interpolation algorithm to enable voltage sampling data and current sampling data to achieve quasi-synchronization; the method eliminates the influence of signal delay generated by a hardware circuit and a software sampling control time sequence;
and S7, in the direct current power calculation, the interpolation revision coefficient K is automatically called, the interpolation algorithm is utilized to reconstruct the current sampling signal, and the direct current power obtained by utilizing the direct current power calculation formula has very high instantaneous precision, so that the high precision of the pulse output of the high-precision direct current standard electric energy meter can be realized by utilizing the high-precision instantaneous power.
For example: when the sampling frequency of the analog-to-digital conversion chip is 12.8kHz, sampling data of 256 voltages and currents at the same time after quasi-synchronization are taken for operation (N=256), and then high-precision direct-current instantaneous power within 20 milliseconds can be calculated.
In this embodiment, in step S2, the digital filter used in processing the data using the digital filtering technique is an FIR finite length unit impulse response filter. The digital filtering mode is adopted to save cost, the modification is convenient, and the stability is good. The common digital filtering has two types of infinite impulse response filter of IIR and finite impulse response filter of FIR, and both have the advantages and disadvantages. The IIR digital filtering has the characteristics of good amplitude-frequency effect, low filtering order and the like, but the phase is nonlinear, the phase characteristic is not well controlled, the phase changes along with the change of the cut-off frequency, and a phase calibration network is needed when the phase requirement is high. The FIR digital filtering is absolutely stable, has strict linear phase, and can ensure accurate linear phase while the amplitude characteristic is set randomly, but the filtering order is larger. In contrast, the software digital filtering adopts FIR digital low-pass filtering to avoid the interference of higher harmonics.
With further reference to fig. 4, in S3, the frequency of the ac signal is calculated according to the zero-crossing periodic method:
Setting the time of each sampling point at equal intervals as Finding out two zero crossing points in the same direction in one cycle, and then the points/>Sum dot/>The sampling time between two zero crossings is/>Then calculate/>, through the front and back zero crossing pointsThe time distance from the zero crossing point is/>Similarly/>The time distance from the zero crossing point is/>Is called/>The sampling time of the whole period and the remainder time of the non-whole period in one period are the actual sampling time in one period, and the actual measuring frequency of the signal is calculated according to the actual sampling time; n is the number of samples of the analog-to-digital conversion chip in a certain short time.
In this embodiment, in S3, the ac signal continues to calculate the period according to the zero-crossing period measurement method as follows:
the sampling period Ts is very short and, And/>The line approximation of (a) is regarded as a straight line, the slope of the line between two points is calculated, and the signal period to the starting point/> can be approximatedTime points/>The method comprises the following steps:
；
Can also be obtained By the end time point of the signal period/>The method comprises the following steps:
；
the sampling time T for one complete sampling period is:
。
in this embodiment, in step S7, the dc instantaneous power calculation formula is as follows:
And/> The sampling values of the voltage channel and the current channel at the same time are respectively obtained.
The above disclosure is only a few specific embodiments of the present invention, but the present invention is not limited thereto, and any changes that can be thought by those skilled in the art should fall within the protection scope of the present invention.
Claims (7)
1. The quasi-synchronous calculation method of the direct current instantaneous power metering circuit is characterized in that the direct current instantaneous power metering circuit comprises a voltage sampling component, a current sampling component, a first gain adjusting circuit, a second gain adjusting circuit, a first filter circuit, a second filter circuit, a digital-to-analog conversion chip, a magnetic isolation chip and a processor, wherein the input end of the first gain adjusting circuit is connected with the output end of the voltage sampling component, the output end of the first gain adjusting circuit is connected with the input end of the first filter circuit, the input end of the second gain adjusting circuit is connected with the output end of the current sampling component, the output end of the second gain adjusting circuit is connected with the input end of the second filter circuit, the output end of the first filter circuit and the output end of the second filter circuit are both connected with the input end of the digital-to-analog conversion chip, the input end of the magnetic isolation chip is connected with the output end of the digital-to-analog conversion chip, and the output end of the magnetic isolation chip is connected with the input end of the processor;
The quasi-synchronous calculation method of the metering circuit based on the direct current instantaneous power comprises the following calculation steps:
s1, respectively inputting an alternating voltage signal and an alternating current signal into an analog signal board aiming at a voltage sampling channel and a current sampling channel, wherein the phase angle phi a between the alternating voltage signal and the alternating current signal is definitely known;
S2, starting sampling of alternating voltage signals and alternating current signals at the same moment, wherein the sampling moment is consistent with the sampling frequency, and after obtaining sampling data, a processor processes the data by utilizing a digital filtering technology so as to filter out higher harmonics;
s3, precisely calculating the frequency and the period of the voltage signal and the current signal by using a zero crossing point periodic measurement method;
S4, respectively carrying out linear interpolation reconstruction on the alternating voltage signal and the alternating current signal according to the sampling period of the alternating voltage signal and the current signal, and then carrying out FFT analysis to obtain an included angle phi b between the alternating voltage signal and the alternating current signal;
S5, taking the alternating voltage sampling signal as a reference, carrying out linear interpolation translation on the alternating current sampling data to enable the phase included angle between the translated alternating voltage and the alternating current signal to be phi a, determining an interpolation revision coefficient K at the moment, and storing the interpolation revision coefficient K in equipment;
S6, after the analog-to-digital conversion chip finishes the analog-to-digital conversion of a fixed number, automatically calling an interpolation revision coefficient K and reconstructing a current sampling signal by using an interpolation algorithm to enable voltage sampling data and current sampling data to achieve quasi-synchronization;
and S7, in the direct current power calculation, automatically calling an interpolation revision coefficient K, reconstructing a current sampling signal by using an interpolation algorithm, and obtaining the direct current power by using a direct current power calculation formula.
2. The method according to claim 1, wherein the first gain adjustment circuit and the second gain adjustment circuit have the same circuit structure, and each of the first gain adjustment circuit and the second gain adjustment circuit includes a signal amplifying unit and a negative signal to positive signal unit, and an output end of the signal amplifying unit is connected to an input end of the negative signal to positive signal unit.
3. The method of claim 2, wherein the voltage sampling component is a voltage sampling resistor, the current sampling component is a current sampling resistor, the first filter circuit and the second filter circuit are both low-pass filters, and the digital-to-analog conversion chip is a 16-bit SAR analog-to-digital converter.
4. The method according to claim 1, wherein in step S2, the digital filter used in the processing of the data by the digital filtering technique is an FIR finite length unit impulse response filter.
5. The quasi-synchronous calculation method of a direct current instantaneous power metering circuit according to claim 1, wherein in S3, the frequency is calculated for the alternating current signal according to the zero crossing period measurement method as follows:
Setting the time of each sampling point at equal intervals as Finding out two zero crossing points in the same direction in one cycle, and thenSum dot/>The sampling time between two zero crossings is/>Then calculate/>, through the front and back zero crossing pointsThe time distance from the zero crossing point is/>Similarly/>The time distance from the zero crossing point is/>Is called/>The sampling time of the whole period and the remainder time of the non-whole period in one period are the actual sampling time in one period, and the actual measuring frequency of the signal is calculated according to the actual sampling time; n is the number of samples of the analog-to-digital conversion chip in a certain short time.
6. The quasi-synchronous calculation method of a DC instantaneous power metering circuit according to claim 5, wherein in S3, the calculation period is continued for the AC signal according to the following zero-crossing period measurement method:
the sampling period Ts is very short and, And/>The line approximation of (a) is regarded as a straight line, the slope of the line between two points is calculated, and the signal period to the starting point/> can be approximatedTime points/>The method comprises the following steps:
；
Can also be obtained By the end time point of the signal period/>The method comprises the following steps:
；
the sampling time T for one complete sampling period is:
。
7. The method according to claim 1, wherein in step S7, the dc instantaneous power calculation formula is as follows:
And/> The sampling values of the voltage channel and the current channel at the same time are respectively obtained.
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