CN103344825A - Electric energy measuring system based on alternating-current sampling - Google Patents

Abstract

The invention discloses an electric energy measuring system based on alternating-current sampling. The electric energy measuring system comprises a voltage sampling part, a current sampling part, a voltage signal processing part, a current signal processing part and a zero passage signal processing part, wherein the voltage sampling part is used for sampling signals which are connected into the system and are from the power grid so as to obtain a voltage analog quantity sampling value, the current sampling part is used for sampling the signals which are connected into the system and are from the power grid so as to obtain a current analog quantity sampling value, the voltage signal processing part is used for conditioning the obtained voltage analog quantity sampling value and biasing the voltage analog quantity sampling value to be the voltage analog quantity sampling value within the preset threshold value, the current signal processing part is used for conditioning the obtained current analog quantity sampling value and biasing the current analog quantity sampling value to be the current analog quantity sampling value within the preset threshold value, the zero passage signal processing part receives the voltage analog quantity sampling value from the voltage sampling part, conducts zero passage comparison and shaping filtering on the voltage analog quantity sampling value and obtains a zero passage pulse signal to be sent to a processor part to conduct voltage zero passage detection. The electric energy measuring system further comprises the processor part based on an ARM and provided with an analog-digital converter. The electric energy measuring system based on the alternating-current sampling has the advantage of being short in response time.

Description

Electric energy metered system based on AC sampling

Technical field

The invention belongs to the electric energy metrical sampling system, concretely, belong to the electric energy metered system based on AC sampling.

Background technology

Along with the raising day by day of Automation of Electric Systems level, parameters of electric power obtain and management becomes more and more important.The popularization and application of microcomputer technology in electric system makes the measurement of electric system and monitoring technique obtain fast development.Obtain the requirement that parameters of electric power can not satisfy system from conventional instrument various in style, development high precision, multiparameter, multi-functional, digitized modularization electric instrument have become a current heat subject.

Usually adopt electric energy computation chip ADE7753 as electric power side control instrument scheme in the prior art, the release of ADE7753 is provided convenience to electric energy exploitation, but as the electric power observation and control instrument scheme, it exists response time and harmonic measure and cost aspect and exists certain limitation.

STMicw Electronics releases the Cortex of 32 of STM32 series ^TMThe ARM of-M3 kernel be ST Microelectronics in the industry cycle release at first based on nucleus product in the ARM Cortex-M3, inherited the good blood lineage of Cortex-M3 kernel, increased the high performance peripheral hardware resource of ST simultaneously, FLASH, SRAM storer, abundant serial communication interface, as IIC, SPI, USART, CAN, USB etc., and 12 ADC and DAC module, the controller of the static memory flexibly FSMC of support external memory access.The sampling rate of its 1M, two ADC provide the basis for realizing the AC synchronous sampling.Powerful peripheral functionality forms a reliable and stable SOC (system on a chip), has the formedness price ratio, develops the electrical measuring instrument platform of AC sampling.

Summary of the invention

The present invention is intended to solve foregoing problems, and a kind of electric energy metered system based on AC sampling is provided, and its response time is short.

One aspect of the present invention provides a kind of electric energy metered system based on AC sampling, and it comprises

The voltage sample part is used for the signal from electrical network that inserts is sampled to obtain the voltage analog sampled value;

The current sample part is used for the signal from electrical network that inserts is sampled to obtain current analog amount sampled value;

Voltage analog sampled value in the predetermined threshold value is nursed one's health and be biased in the voltage signal processing section to the voltage analog sampled value that obtains;

Current analog amount sampled value in the predetermined threshold value is nursed one's health and be biased in the current signal processing section to the current analog amount sampled value that obtains;

The zero cross signal processing section receives the voltage analog sampled value from the voltage sample part, and the voltage analog sampled value was carried out zero balancing and shaping filter, obtains the zero-crossing pulse signal and gives the detection of processor part voltage zero-cross;

The processor part based on ARM of band analog to digital converter; Comprise current sampling data analog to digital converter, current sampling data analog to digital converter, zero passage interrupt unit and parameter arithmetic section; Wherein, voltage sample value analog to digital converter is used for by the zero-crossing pulse signal enabling carrying out analog to digital conversion from the voltage analog sampled value in the predetermined threshold value of voltage signal processing section and digitized voltage sample value being kept at a magnitude of voltage storage part; The current sampling data analog to digital converter is used for by the zero-crossing pulse signal enabling carrying out analog to digital conversion and digitized current sampling data is kept at a current value storage part from the current analog amount sampled value in the predetermined threshold value of current signal processing section; This parameter arithmetic section calculates electric energy metrical parameter at this electrical network according to the digitized voltage sample value that obtains and digitized current sampling data according to the AC sampling principle.

This voltage sample part also comprises phase compensation portion.

This current sample part also comprises phase compensation portion.

AC sample system and method based on arm processor of the present invention, adopted the arm processor STM32F103RC of ST company, set up the public sample circuit that exchanges data acquisition, software algorithm platform, powerful peripheral functionality and the processing speed of STM32, can conveniently realize electric power observation and control instrument, multifunctional electric energy meter, standardized sampling module has been set up in the exploitation of electrical measuring instruments such as read out instrument and harmonic wave instrument, realize resource reuse, improved product development speed and development quality.

Description of drawings

Fig. 1 is according to the theory diagram based on the AC sampling electric energy metered system of the present invention;

Fig. 2 is the circuit diagram according to a kind of embodiment of the voltage sample part based on the AC sampling electric energy metered system of the present invention and voltage signal processing section;

Fig. 3 is the circuit diagram according to a kind of embodiment of the current sample part based on the AC sampling electric energy metered system of the present invention and current signal processing section;

Fig. 4 is the circuit diagram of a kind of embodiment of zero cross signal processing section;

Fig. 5 is according to the process flow diagram based on the AC sampling electric energy gauging method of the present invention.

Fig. 6 is the process flow diagram of the method for sampling one embodiment.

Embodiment

A kind of embodiment of AC sample system of the present invention as shown in Figure 1, wherein, the hardware of this AC sample system comprises sample circuits such as voltage sample part, current sample part; Voltage signal processing section, current signal processing section and the zero cross signal handling part front-end processing circuit of grading; And the processor part (MCU) based on ARM of band analog to digital converter, for example can be the processor module of the STM32F103RC of STMicw Electronics (TM).

Voltage sample can obtain by electric resistance partial pressure, as shown in Figure 2.Wherein, be sampled as example with the A phase voltage, by resistance R 6, R9, R23, R11, R24, R25, R27, R28 dividing potential drop, signal is through VREF bias voltage 1.65VDC, after R24, R25 picked up signal conversion process, after being amplified by filter amplifier U4-B filtering again, one the tunnel sends the ADC1 sampling of processor calculating part (MCU) to, another road is passed to zero cross signal treatment circuit (Fig. 4) UA_PLUS and is crossed zero balancing and shaping filter through U1-B, obtain UA-INT zero-crossing pulse signal and give the external interrupt IO mouth of MCU, carry out A phase voltage zero passage detection.

Fig. 3 shows at a certain phase, A phase for example, the current sample part and the circuit diagram of a kind of embodiment of current signal processing section.Wherein, be example with the A phase current, the A phase current after amplifying by U4-A filtering, sends the ADC2 sampling of MCU through current transformer T2 sampling to again;

Above-mentioned is example with A phase current voltage, and the sample circuit of voltage, electric current is described, and B, C phase current voltage sampling circuit principle, realizing can be mutually in full accord with A, repeats no more here.

Three-phase voltage and three-phase current become 0V～1.65V～3.3V voltage through signal conditioning circuit and 1.65V reference offset circuit conversion, send into ADC1 and ADC2 converter respectively, realize 6 tunnel simulating signal in-phase sampling and conversions, guaranteed that every phase voltage, current detecting are same-phases, its precision is 12; For eliminating the phase delay that mutual inductor and circuit produce, can when circuit design, provide phase compensation, as the capacitor C 10 among Fig. 2, as the capacitor C 14 among Fig. 3.

The data that obtain can shift through DMA formation memory, and are few to the cpu resource occupancy; Voltage signal becomes square wave to send STM32 external interrupt input port to detect through the zero balancing circuit conversion, obtains the cycle of AC signal;

STM32 has powerful peripheral hardware and calculation process ability, realizes that easily instrument measures in real time, analyzes: U, I, P, Q, S, COS Φ, F, parameters of electric power such as kWh, kvarh.

STM32 processor working procedure is finished in the system: control the A/D data sampling, sampled result is carried out the FFT computing, according to all parameters in the hardware parameter calculating electric weight of AC sampling principle coupling system, it is standby that the result is sent into RAM.Its flow process is illustrated in fig. 5 shown below.

This method comprises: the signal from electrical network that inserts is sampled to obtain the voltage analog sampled value; The signal from electrical network that inserts is sampled to obtain current analog amount sampled value; Voltage analog sampled value in the predetermined threshold value is nursed one's health and be biased to the voltage analog sampled value that obtains; Current analog amount sampled value in the predetermined threshold value is nursed one's health and be biased to the current analog amount sampled value that obtains; Reception was carried out zero balancing and shaping filter from the voltage analog sampled value of voltage sample part to the voltage analog sampled value, obtained the zero-crossing pulse signal and gave the detection of processor part voltage zero-cross; And by the zero-crossing pulse signal enabling to carrying out analog to digital conversion from the voltage analog sampled value in the predetermined threshold value of voltage signal processing section and digitized voltage sample value being kept at a magnitude of voltage storage part; By the zero-crossing pulse signal enabling to carrying out analog to digital conversion and digitized current sampling data be kept at a current value storage part from the current analog amount sampled value in the predetermined threshold value of current signal processing section; Calculate electric energy metrical parameter at this electrical network according to the digitized voltage sample value that obtains and digitized current sampling data according to the AC sampling principle.

Wherein, also comprise the phase differential that produces in the elimination voltage sample process.

Wherein, also comprise the phase differential that produces in the elimination current sample process.

Wherein, also comprise carrying out FFT through digitized voltage and current sampled value.

Wherein, according to the frequency of the electrical network of real-time detection the sample frequency of voltage, current signal is adjusted in real time.

Specifically the method for sampling is, as shown in Figure 6:

At first, by DMA1 constantly with voltage, the AD value of electric current is put into an array AD_Value[7] S101, interrupt finding to open an initial point by the outside zero passage of a UA_INT then, in one-period, adopt 128 times by a timer, and 7 data will sampling each time are put into a Tmp_AD_Value[128*7] array in, enable DMA2 simultaneously with Tmp_AD_Value[128*7 during in one-period the 128th time sampling] array in data be put into Cal_AD_Value[128*7] in, use when being used for calculating, finish at DMA2 and forbid DMA2 in the interruption and start computation process S103.

Wherein, interrupt finding out T cycle length by the outside zero passage of a UA_INT, then frequency is exactly F=1/T;

Interrupt finding out the phase angle of UA and UC by the zero passage of external interrupt UC-INT under another;

Interrupt finding out the phase angle of U and I by the zero passage of external interrupt IA-INT under another;

Ac cycle detects, and the external hardware that the square-wave signal that voltage transitions becomes is sent into STM32 interrupts, and reads the count value of timer in interrupt service routine, converts the cycle (frequency) to, according to the cycle of cycle Adjustment System sampling.

Adopt AC sampling on the hardware circuit basis, by the very convenient acquisition of 1-15 formula U, I, P, Q, S, COS Φ, F, parameters of electric power such as kWh, kvarh

AC sampling is according to certain rules the instantaneous value of measured signal to be sampled, and tries to achieve measured value with certain numerical algorithm again, with respect to more accurate through the direct current sampling of carrying out sampled measurements after the direct current rectification again.

In the present invention, can use STM32F103RC is instrument intelligent kernel parts, adopts the A/D transducer of this chip internal as data acquisition unit, and the electric signal in the electrical network that inserts is carried out the pointwise instantaneous sampling, calculate voltage, current effective value by single-chip microcomputer again, active power, reactive power, applied power, power factor, signal frequency, active energy, reactive energy and frequency analysis etc.

Wherein, the calculation procedure of voltage effective value is as follows:

At first, with the voltage effective value formula

$U=\sqrt{\frac{1}{T}{\∫}_0^T{u}^2\left(t\right)\mathrm{dt}}---\left(1\right)$

Discretize replaces continually varying function of voltage value in the one-period with limited sampled voltage digital quantity in the one-period, then obtains

$U_c\&ap;\sqrt{\frac{1}{T}\underset{m=1}{\overset{N}{\mathrm{\&Sigma;}}}{u}_{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="HDA00003480578900031.png"\; state="\{\{state\}\}">m</figure-callout>}}^2\mathrm{\&Delta;}{T}_m}---\left(2\right)$

In the formula: Δ Tm is the time interval of adjacent double sampling; u _mIt is the voltage sample instantaneous value in m-1 the time interval; N is the sampling number in 1 cycle.Make the time interval of adjacent two samplings equate that namely Δ Tm is constant Δ T, considers N=(T/ Δ T)+1, then has

$U_c=\sqrt{\frac{1}{N-1}\underset{m=1}{\overset{N}{\mathrm{\&Sigma;}}}{u}_m^2}---\left(3\right)$

Formula (3) is exactly to reach the formula of phase sampling number calculating voltage signal effective value weekly according to each sampled instantaneous value of one-period.

In like manner, the current effective value computing formula is as follows:

$I_c=\sqrt{\frac{1}{N-1}\underset{m=1}{\overset{N}{\mathrm{\&Sigma;}}}{i}_m^2}---\left(4\right)$

Formula (1) is exactly to reach the formula of phase sampling number calculating voltage signal effective value weekly according to each sampled instantaneous value of one-period.

Calculate a certain phase active power, the calculating of power is from the definition of consecutive periods signal effective value and the definition of power, with the approximate continuous integration that replaces of numerical integration.The computing formula of active power is suc as formula (5)

$P=\frac{1}{T}{\&Integral;}_0^T\mathrm{iudt}---\left(5\right)$

After the discretize be

$P=\frac{1}{N-1}\underset{m=1}{\overset{N}{\mathrm{\&Sigma;}}}{i}_m{u}_m---\left(6\right)$

In the formula: im, um are electric current, the voltage sample value of synchronization.

Applied power: S=UI

U in the formula, I are the effective value of voltage and current;

Power factor can be tried to achieve by following formula:

cosφ=P/S=P/UI

Calculating reactive power has multiple algorithm, adopts digital phase shift method Microcomputer Calculation amount less, and it is good that data are handled real-time.Because active power P and reactive power Q only differ from 90 ° in the voltage and current phase place, reactive power is write as

$Q=\frac{1}{N}\underset{K=1}{\overset{N}{\mathrm{\&Sigma;}}}(u_K\&times;i_{(K+\frac{N}{4})})---\left(7\right)$

I in the formula _(k+N/4) inferior current sampling data of expression (k+N/4) (phase shift 90 ° after sampled value), as (k+N/4) during greater than N, (k+N/4) be taken as (k-3N/4).

In three-phase four-wire system, use the ternary method, ask the expression formula of power as follows after dispersing:

$Q=\frac{1}{N}\underset{K=1}{\overset{N}{\mathrm{\&Sigma;}}}(u_{\mathrm{UK}}\&times;i_{U(K+\frac{N}{4})})+u_{\mathrm{VK}}\&times;i_{V(K+\frac{N}{4})}+u_{\mathrm{WK}}\&times;i_{W(K+\frac{N}{4})}---\left(9\right)$

Uuk in the formula, Uvk, Uwk represent the k time sampled value of three phase voltages in the one-period; i _UK, i _VK, i _WKThe k time sampled value of three phase currents in the expression one-period.

In three-phase three-wire system, use two-dimensional method, ask the formula of power as follows after the discretize:

$p=\frac{1}{N}\underset{K=1}{\overset{N}{\mathrm{\&Sigma;}}}(u_{\mathrm{UVK}}\&times;i_{\mathrm{UK}}+u_{\mathrm{VWK}}\&times;i_{\mathrm{WK}})---\left(10\right)$

$Q=\frac{1}{N}\underset{K=1}{\overset{N}{\mathrm{\&Sigma;}}}(u_{\mathrm{UVK}}\&times;i_{U(K+\frac{N}{4})}+u_{\mathrm{VWK}}\&times;i_{W(K+\frac{N}{4})})---\left(11\right)$

U in the formula _Uvk, u _VwkThe k time sampled value representing two line voltages in 1 cycle respectively.

Applied power S and powerfactorcos can be obtained with following formula:

$S=\sqrt{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HDA00003480578900031.png"\; state="\{\{state\}\}">P</figure-callout>}}^2+Q^2}---\left(12\right)$

Active power and reactive power just can be obtained active energy and reactive energy to time integral respectively.

The FFT computing:

The cosine signal of the voltage and current in the electric power transmission line, be subjected to the influence of nonlinear load, the waveform of electrical network can distort, it still is periodic function after the distortion, and satisfy the Di Liheli condition, the stack that can resolve into first-harmonic and a series of harmonic waves to voltage and current with the fourier series decomposition method, namely

$u\left(t\right)=U_0+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{U}_n\cos (\mathrm{n\&omega;t}+{\mathrm{\&alpha;}}_n)---\left(14\right)$

$i\left(t\right)=I_0+\underset{n=1}{\overset{m}{\mathrm{\&Sigma;}}}{I}_n\cos (\mathrm{n\&omega;t}+{\mathrm{\&beta;}}_n)---\left(15\right)$

U in the formula ₀, I ₀The DC component of-voltage, electric current;

U _n, I _nThe peak value of-each harmonic amplitude; α _n, β _nDifference be that harmonic phase is poor.

Continuous time signal to electrical network carries out the sample sequence that real-time sampling obtains dispersing, and with fft algorithm it is carried out the time-frequency domain conversion, can analyze amplitude and the phase place situation of first-harmonic and each harmonic, to realize the monitoring of harmonic wave.In addition, there is phase differential between the phase voltage on each road and the phase current in the electrical network, to voltage and current signal synchronized sampling and carry out the FFT conversion, just can calculates the phase differential of each harmonic, measure the meritorious and reactive power of each harmonic exactly.

And calculate for FFT, if the end points of sampled data set is discontinuous, just need to introduce window function, thereby increased the fussy degree of calculating.And satisfying the correlated sampling principle, and the data point set of sampling just in time is under the situation of complete cycle, the sampled data set two-end-point is continuous, just can be similar to the sampled signal sequence and regard infinite periodic signal as, thereby the FFT calculated amount is reduced.

Determining of sampling number:

According to time domain sampling theorem f, 〉=2f _m, native system requires to analyze 63 subharmonic, and therefore minimum sampling number is 78 points in one-period, and the FFT butterfly computation itself requires sampling number when being 2 power, and computing velocity is the fastest, and the sample frequency of device is 256 times of fundamental frequency.Because mains frequency can fluctuate up and down about 50Hz, therefore on hardware is realized, cannot sample to voltage, current signal with fixed frequency, and will adjust sample frequency in real time according to the frequency of electrical network.

Native system adopts 128 fft algorithms, namely finishes a FFT computing at two all after dates of sampling, and it is the result of sampling last time that one-period is wherein arranged; The time of finishing 128 FFT computings is about 0.5ms, thereby can satisfy the online detection of instrument and analysis.

The frequency of AC network is definite, and the method for determining is also many, and native system adopts and comes measuring period by the method for hardware, is about to alternating voltage and send STM32F103RC to carry out timing after conditioning and shaping, thereby obtain the frequency of AC network; Because the frequency change of electrical network has bigger inertia, thereby can adopt the software low-pass filter that measured data are handled.

Claims (6)

1. electric energy metered system based on AC sampling, it is characterized in that: this system comprises

The voltage sample part is used for the signal from electrical network that inserts is sampled to obtain the voltage analog sampled value with variable voltage sample frequency;

The current sample part is used for the signal from electrical network that inserts is sampled to obtain current analog amount sampled value with variable current sample frequency;

Voltage analog sampled value in the predetermined threshold value is nursed one's health and be biased in the voltage signal processing section to the voltage analog sampled value that obtains;

Current analog amount sampled value in the predetermined threshold value is nursed one's health and be biased in the current signal processing section to the current analog amount sampled value that obtains;

The zero cross signal processing section.Reception was carried out zero balancing and shaping filter from the voltage analog sampled value of voltage sample part to the voltage analog sampled value, obtained the zero-crossing pulse signal and gave the detection of processor part voltage zero-cross; And

The processor part based on ARM of band analog to digital converter; Comprise current sampling data analog to digital converter, current sampling data analog to digital converter, zero passage interrupt unit and parameter arithmetic section; Wherein, voltage sample value analog to digital converter is used for by the zero-crossing pulse signal enabling carrying out analog to digital conversion from the voltage analog sampled value in the predetermined threshold value of voltage signal processing section and digitized voltage sample value being kept at a magnitude of voltage storage part; The current sampling data analog to digital converter is used for by the zero-crossing pulse signal enabling carrying out analog to digital conversion and digitized current sampling data is kept at a current value storage part from the current analog amount sampled value in the predetermined threshold value of current signal processing section; This parameter arithmetic section calculates electric energy metrical parameter at this electrical network according to the digitized voltage sample value that obtains and digitized current sampling data according to the AC sampling principle.

2. according to the electric energy metered system based on AC sampling of claim 1, it is characterized in that: this voltage sample part comprises that also phase compensation portion is used for eliminating the phase differential that sampling process produces.

3. according to the electric energy metered system based on AC sampling of claim 1, it is characterized in that: this current sample part comprises that also phase compensation portion is used for eliminating the phase differential that sampling process produces.

4. according to the electric energy metered system based on AC sampling of claim 1, it is characterized in that: the sample frequency adjustment part is used for the frequency of real-time detection of grid, and according to the frequency of the electrical network that records the sample frequency of voltage, electric current is adjusted.

5. according to the electric energy metered system based on AC sampling of claim 1, it is characterized in that: this storage part is RAM.

6. the electric energy gauging method based on AC sampling is characterized in that: comprise

The signal from electrical network that inserts is sampled to obtain the voltage analog sampled value with variable voltage sample frequency;

The signal from electrical network that inserts is sampled to obtain current analog amount sampled value with variable current sample frequency;

Voltage analog sampled value in the predetermined threshold value is nursed one's health and be biased to the voltage analog sampled value that obtains;

Current analog amount sampled value in the predetermined threshold value is nursed one's health and be biased to the current analog amount sampled value that obtains;

Reception was carried out zero balancing and shaping filter from the voltage analog sampled value of voltage sample part to the voltage analog sampled value, obtained the zero-crossing pulse signal and gave the detection of processor part voltage zero-cross; And

By the zero-crossing pulse signal enabling to carrying out analog to digital conversion from the voltage analog sampled value in the predetermined threshold value of voltage signal processing section and digitized voltage sample value being kept at a magnitude of voltage storage part;

By the zero-crossing pulse signal enabling to carrying out analog to digital conversion and digitized current sampling data be kept at a current value storage part from the current analog amount sampled value in the predetermined threshold value of current signal processing section; And

Calculate electric energy metrical parameter at this electrical network according to the digitized voltage sample value that obtains and digitized current sampling data according to the AC sampling principle.

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