CN100489555C - Universal electric power mutual-inductor verification device - Google Patents

Abstract

The apparatus comprises: a signal modulating unit, a check meter circuit, a digital signal process unit, a display unit and a network interface unit. The analog output signals from the mutual inductor under test and the standard transformer are inputted to the signal modulating unit to make modulation; the modulated signals are inputted to the check meter circuit; the digital signals from the mutual inductor are directly inputted into the check meter circuit; the modulated analog signals and/or the un-modulated digital signals are processed by the check meter circuit to form the digital signals in clock and data synchronization; the obtained synchronous digital signals are outputted to the signal processing unit; after processed to get the amplitude, frequency and phase information of the tested signals, then figuring out the ratio difference and angle difference; comparing the index result obtained from the mutual inductor under test with the measurement result of the standard mutual inductor to evaluate the precise level of the mutual inductor under test.

Description

The universal electric power mutual-inductor calibration equipment

Technical field

The present invention relates to the transducer check technology in power system automation technology field, particularly a kind of device that the measuring accuracy of electromagnetic type and electronic type electric power mutual-inductor is measured.

Background technology

A large amount of electric power mutual-inductors will be produced and use to the Automation of Electric Systems construction field all every year; electric power mutual-inductor is the visual plant of electric energy metrical and relay protection in the electric system; calibration equipment is the special-purpose exact instrument that is used to check and measure transformer error; therefore; greatly develop the transducer check device, all significant to the development and the production level that improve mutual inductor.

Present electric power mutual-inductor mainly contains two big classes: a class is an electromagnetic transformer, and another kind of is electronic mutual inductor, and according to the difference of measured signal form, every class electric power mutual-inductor can be divided into two kinds of voltage transformer (VT) summation current transformers again.Electromagnetic transformer is based on the electric power mutual-inductor that electromagnetic induction principle is made, in electric system, obtained widespread use, but, be difficult to satisfy the demand of electric system fast development because of there are deficiencies such as magnetic saturation, ferroresonance, dynamic range are little, insulating Design difficulty in it; Electronic mutual inductor is based on advanced sensing technology and photoelectron technology and the electric power mutual-inductor made, is thought to substitute the optimal selection of electromagnetic transformer at present by International Electrotechnical Commission.Two class mutual inductors are mainly reflected in following several aspect because the principle of work difference also has a great difference on the output signal type separately:

The specified output of the simulating signal of the voltage/current mutual inductor of electromagnetic type and electronic mutual inductor: electromagnetic potential transformer rated secondary voltage outputting standard value is line voltage 100V, and electromagnetic current transducer rated secondary current outputting standard value is 1～5A; Electronic type voltage transformer rated secondary voltage outputting standard value is 1.625～6.5V, current transformer rated secondary voltage outputting standard value is 22.5mV～4V, and the current/voltage mutual inductor has been divided into a series of output levels in above-mentioned output area, but the simulation of electronic mutual inductor is output as weak electric signal, driving force is poor, is difficult to realize verification with traditional electromagnetic transformer method of calibration.

The output of the digital signal of electromagnetic type and electronic mutual inductor: electromagnetic transformer does not have digital output interface; Electronic mutual inductor has the form of numeral output, and at the electronic mutual inductor of measuring and protect usefulness, its digital output signal is easy to and digital facility interface, meets the development trend of electric power digitalization.

Because the difference of the output signal type of two class electric power mutual-inductors, new-type electronic mutual inductor is difficult to carry out verification with the calibration equipment of traditional electromagnetic transformer, therefore, development is a kind of can carry out verification to electromagnetic transformer and can the device that electronic mutual inductor carries out verification be very important again.

Existing transducer check Design of device method mainly contains two kinds, and a kind of is differential technique, and another kind is a direct method.Because differential technique requires specified output of standard mutual inductor and the specified secondary output of to-be-tested transformer strictness to equate, this point difficulty accomplishes that therefore, transducer check device major part is to adopt the direct method design at present.So-called direct method is meant and obtains standard mutual inductor and to-be-tested transformer output, and calculates both amplitudes and phase place according to respective algorithms, obtains to-be-tested transformer ratio and angular difference thus.Described ratio is a range error, is an index of weighing its precision level from the amplitude angle; So-called angular difference is a phase error, is an index of weighing its precision level from phase angle.Adopting the calibration equipment of direct method design is to rely on computing machine or microprocessor technology, and the computer based virtual instrument is achieved, and it is powerful, but hardware investment is big, cost is high; The checkschema of existing portable power mutual inductor based on microprocessor is function singleness, algorithm imperfection then, and for guaranteeing checking precision, required sampling number is many, the processing time is long, and precision is subject to also that mains frequency fluctuates and the influence of higher hamonic wave.

Calibration technology about electromagnetic type and electronic type voltage/current transformer, in Chinese patent application number is 02279384.4,97109217.6,92229682.0,88200388.7,87108187,86108441,96237737.6 and 03156895.5 application documents, disclosure is arranged all, but still do not have can compatible the above mutual inductor of two types to realize the transducer check device of field calibration at present.

From as can be seen above-mentioned, mainly there is the deficiency of following aspect in existing electric power mutual-inductor calibration equipment:

Existing power transducer check device can only be realized the verification of electronic type or electromagnetic transformer, perhaps can only realize the verification of curtage mutual inductor wherein.Existing portable calibration equipment is simple in structure at present, and function ratio is more single, is subjected to the influence of multiple error component to be difficult to guarantee checking precision easily; And computer based virtual instrument checkschema, though powerful, with high costs, and can not satisfy the requirement of all kinds of electric power mutual-inductors being carried out precision determination at present.

Summary of the invention

In view of this, fundamental purpose of the present invention is to provide a kind of general electronic type voltage/current transformer and the calibration equipment of electromagnetic potential/current transformer, is used to evaluate the measuring accuracy level of all kinds of electric power mutual-inductors.

For achieving the above object, technical scheme of the present invention is achieved in that

The invention discloses a kind of universal electric power mutual-inductor calibration equipment, this device comprises:

The signal condition unit is used for the analog output signal of standard mutual inductor and the analog output signal of electromagnetic type to be measured and electronic mutual inductor are nursed one's health;

The tester circuit unit is used for the analog output signal of the digital output signal of electronic mutual inductor to be measured, standard mutual inductor simulating signal after the conditioning of signal condition unit and electromagnetic type to be measured, electronic mutual inductor is converted to synchronous digital signal;

Digital signal processing unit is used for the synchronous digital signal by the output of tester circuit unit is carried out pre-service, least-squares algorithm and accurate discrete Fourier algorithm process synchronously;

Display unit is used for the object information of display digit signal Processing; And

Network interface unit is used for providing to the electric power digital interface result of digital signal processing;

Wherein, signal condition unit, tester circuit unit and digital signal processing unit link to each other successively, and display unit and network interface unit link to each other with digital signal processing unit respectively.

Described signal condition unit further comprises:

First voltage transformer (VT) is used for voltage signal with standard mutual inductor output and is converted to voltage signal less than 5V;

First current transformer is used for current signal with 1～5A of standard current transformer output and is converted to current signal less than 25mA;

The first current/voltage transducer is used for current signal with first current transformer output and is converted to voltage signal less than 5V;

Second voltage transformer (VT) is used for voltage signal with to-be-tested transformer output and is converted to voltage signal less than 5V;

Second current transformer is used for current signal with 1～5A of current transformer to be measured output and is converted to current signal less than 25mA;

The second current/voltage transducer is used for current signal with second current transformer output and is converted to voltage signal less than 5V; And

Automatic gain is adjusted circuit, be used to receive the analog output signal of first voltage transformer (VT), the first current/voltage transducer, second voltage transformer (VT), the second current/voltage transducer and electronic mutual inductor to be measured and the amplitude of signal is adjusted to-5V～+ the 5V scope selects output again.

Described signal condition unit is nursed one's health analog output signal, be meant that the analog output signal with standard potential transformer signal, standard current transformer, electromagnetic potential transformer, electromagnetic current transducer and electronic mutual inductor is converted into-5V～+ the 5V scope.

Wherein, described tester circuit unit further comprises:

The clock source is used to this tester circuit that required work clock signal is provided;

Frequency divider, the clock signal that is used for the receive clock source is also handled this signal according to the different frequency divisions that carry out of measure analog signals and digital signal;

The light-coupled isolation unit is used for the electronic mutual inductor to be measured and output of monostable timing control unit and multi channel selecting unit and the digital signal processing of input is become not isolation altogether;

Monostable timing control unit is used for coordinating control tester circuit and carries out work;

The one A/D converting unit is used for the analog output signal of standard mutual inductor is converted to synchronous digital signal;

The 2nd A/D converting unit is used for the analog output signal of tested mutual inductor is converted to synchronous digital signal; And

The multi channel selecting unit is used to select two-way signal or selection through an A/D converting unit and the output of the 2nd A/D converting unit to carry out synchronous digital signal output through an A/D converting unit with through the two-way signal that the light-coupled isolation unit is exported.

Wherein, described tester circuit unit also includes switch, is used to realize the type selecting of electromagnetic type to be verified or electronic mutual inductor.

Described digital signal processing unit utilization Signal Pretreatment algorithm, least-squares algorithm and accurate discrete Fourier algorithm synchronously obtain amplitude, frequency and the phase information of measured signal, and calculate ratio and angular difference by the contrast with standard potential transformer or current transformer output signal.

Described display unit comprises display driver circuit and LCD or cathode-ray tube display.

Adopt the calibration equipment of the present invention of direct method design, by being classified, the simulating signal of to-be-tested transformer and digital signal handle the digital signal that produces clock and data sync, and realize various types of signal is carried out general verification in conjunction with the digital signal corresponding disposal route, both avoided problem based on investment of virtual instrument calibration equipment and cost, enriched again in the past based on digital signal processing (DSP, Digital Signal Processing) function of calibration equipment, so the present invention has the following advantages:

1) adopts the signal condition unit of versatility that all kinds of mutual inductor analog output signals are nursed one's health, when suppressing undesired signal, signal is suitably amplified, strengthened opsonizing capacity to measured signal.

2) in the signal processing, adopt least-squares algorithm that the frequency of measured signal is carried out accurately measuring in real time and utilizing accurate discrete Fourier transform (DFT) (DFT synchronously, Discrete Fourier Transformation) non-synchronous sampling that causes of algorithm blanketing frequency fluctuation is to spectrum analysis result's influence, the combination of two kinds of algorithms has not only improved the arithmetic speed of signal Processing and the precision of operation result, and the frequency jitter and the high frequency interference of measured signal played stronger inhibiting effect, thereby guaranteed the precision level of checking algorithm.

3) the output result of digital signal processing unit adopts liquid crystal display, and display result is divided into simulation, digital dual mode, thereby not only satisfies the requirement that real-time shows, but also has enriched the information that shows; In addition, because that liquid crystal display has a volume is little and be not subjected to electromagnetic radiation, thereby strengthen also that it is portable and stable.

4) the output result of digital signal processing unit can export by network interface unit with the form of digital signal, is easy to and other digital facility interfaces, thereby satisfies the development trend of electric power digitalization.

Description of drawings

Fig. 1 is the overall circuit structural representation of calibration equipment of the present invention;

Fig. 2 (a) is the signal wire line synoptic diagram of signal condition of the present invention unit;

Fig. 2 (b) is a signal condition element circuit illustrative view of functional configuration of the present invention;

Fig. 3 is a tester circuit function structural representation of the present invention;

Fig. 4 is the signal processing flow figure of digital signal processing unit of the present invention;

Fig. 5 is the liquid crystal drive process flow diagram of display unit of the present invention;

Fig. 6 (a) is the error testing result schematic diagram of apparatus of the present invention verification current transformer;

Fig. 6 (b) is the error testing result schematic diagram of apparatus of the present invention calibration potential transformator.

Embodiment

Core concept of the present invention is: different according to the output signal type of electromagnetic type and electronic mutual inductor, with the processing of classifying of the digital signal of the simulating signal of standard mutual inductor, to-be-tested transformer output and electronic mutual inductor to be measured; At first, the simulating signal of standard mutual inductor and to-be-tested transformer is inserted export the tester circuit unit to after the signal condition unit makes signal amplitude nurse one's health certain scope; Secondly, simulating signal to be measured is accessed to the tester circuit unit, behind process analog to digital conversion, multi channel selecting unit under the effect of sequential control, export signal to digital signal processing unit; The to-be-tested transformer digital signal is directly inserted the tester circuit unit, under the sequential control effect, export digital signal processing unit to by the multi channel selecting one-cell switching, so far, the digital output signal of the analog output signal of standard mutual inductor, to-be-tested transformer and electronic mutual inductor all is transformed into the digital signal of clock and data sync; At last, described synchronous digital signal is inputed to digital signal processing unit to be handled, obtain amplitude, frequency and phase information by utilization corresponding signal process algorithm, calculate ratio and angular difference according to the essential information that is obtained then, and intuitive measurement results is shown by display unit.

The invention will be further described below in conjunction with accompanying drawing.

Fig. 1 is the overall circuit structural representation of calibration equipment of the present invention, and as shown in Figure 1, this circuit comprises signal condition unit 101, tester circuit unit 102, digital signal processing unit 103, display unit 104 and network interface unit 105.In the described circuit, signal condition unit 101, tester circuit unit 102 and digital signal processing unit 103 link to each other successively, display unit 104, network interface unit 105 link to each other with digital signal processing unit 103 respectively, wherein, tester circuit unit 102 has the interface of the digital signal of direct reception electronic mutual inductor to be measured, makes tester circuit unit 102 can select to handle simulating signal to be measured or digital signal under the effect of gauge tap.

As shown in Figure 1, involved in the present invention to circuit in the effect of each functional unit respectively as follows:

Signal condition unit 101: will nurse one's health from the simulating signal of electromagnetic potential/current transformer or electronic type voltage/current transformer output, in the amplitude range that the analog to digital conversion circuit that makes amplitude output signal be adjusted to tester circuit unit 102 can be gathered.

Tester circuit unit 102: will pass through modulus (A/D) conversion, sequential control and multi channel selecting effect through the standard mutual inductor of conditioning, the simulating signal of to-be-tested transformer, and be transformed to clock and data sync digital signal; With digital signal to be measured by the time about control and multi channel selecting effect be transformed to the digital signal of clock and data sync.

Digital signal processing unit 103: the digital signal of clock and data sync is obtained the essential informations such as amplitude, frequency and phase place of standard mutual inductor and to-be-tested transformer signal through Preprocessing Algorithm, least-squares algorithm, accurate discrete Fourier algorithm synchronously, calculate angular difference, ratio then.

Display unit 104: will show by the object informations such as waveform, frequency, ratio and angular difference that digital signal processing unit 103 obtains.

Network interface unit 105: will export with the form of digital signal by the output object information of digital signal processing unit 103, as the interface of electric power digitalization.

The course of work that calibration equipment of the present invention is measured the mutual inductor precision is as follows:

Step 1: the analog output signal of to-be-tested transformer is inserted signal condition unit 101, and the analog output signal of conditioning mutual inductor is nursed one's health the range of signal that A/D converter can be accepted with output signal, promptly-5V～+ 5V between.

Step 2: will insert tester circuit unit 102 through the standard mutual inductor of conditioning and the analog output signal of to-be-tested transformer, maybe will insert tester circuit unit 102 through the analog output signal of standard mutual inductor of conditioning and the digital signal of undressed to-be-tested transformer, utilize in the circuit switch closure or open this two states in measure analog signals or measure between the digital signal and switch, to realize fast processing unlike signal; By modulus (A/D) conversion, sequential control and multi channel selecting effect in the tester circuit unit 102, simulating signal is transformed to clock and data sync digital signal or the digital signal of to-be-tested transformer is transformed to the digital signal of clock and data sync by sequential control, and by this synchronizing signal of output behind the multi channel selecting one-cell switching.

Step 3:DSP unit 103 is finished and is gathered and signal processing function, adopt Preprocessing Algorithm to remove the influence of higher harmonic components respectively, adopt least-squares algorithm signal calculated frequency, adopt the amplitude and the phase place of accurate DFT algorithm computation standard mutual inductor synchronously and to-be-tested transformer signal, the combination by various algorithms has effectively suppressed the influence to check results of the non-synchronous sampling that causes because of the mains frequency fluctuation.

Step 4: adopt liquid crystal display or cathode ray tube (CRT) display to show waveform, frequency, ratio and the angular difference parameter of tested mutual inductor in real time.

Below in conjunction with the main circuit unit in Fig. 1 circuit, comprise that the composition structure and the course of work thereof of signal condition unit 101, tester circuit unit 102 and digital signal processing unit 103 further described.

Fig. 2 (a) is the signal wire line synoptic diagram of signal condition of the present invention unit, shown in Fig. 2 (a), signal condition unit 101 is divided between three sub-functional areas according to the source difference of institute's input signal, wherein, the left side is a standard mutual inductor voltage synoptic diagram, center section is electromagnetic potential to be measured/current transformer wiring schematic diagram, and the right side is electronic type voltage to be measured/current transformer signal input wires synoptic diagram.More than in three funtion parts, each part is divided into voltage/current input, output terminal two classes again, for example, is example with mutual inductor in scheming, the public ground of solid circles representative, empty circles representative simulation signal voltage/electric current input or output end.

Fig. 2 (b) is a signal condition element circuit illustrative view of functional configuration of the present invention, shown in Fig. 2 (b), signal condition unit 101 circuit comprise first voltage transformer (VT) 201, first current transformer 202, the first current/voltage conversion 203, second voltage transformer (VT) 204, second current transformer 205, the second current/voltage conversion 206, automatic gain adjustment circuit 207.

Wherein, first voltage transformer (VT) 201, be used for

The output voltage signal of standard potential transformer be converted to less than the light current of 5V and press signal; First current transformer 202 is used for current signal with 1～5A of standard current transformer output and is converted to weak current signal less than 25mA; The first current/voltage conversion 203, the weak current signal transformation that is used for the output of first current transformer is that voltage signal is further handled for automatic gain adjustment circuit 207; Second voltage transformer (VT) 204, be used for

The output voltage signal of electromagnetic potential transformer to be measured be converted to less than the light current of 5V and press signal; Second current transformer 205 is used for current signal with 1～5A of electromagnetic current transducer to be measured output and is converted to weak current signal less than 25mA; The second current/voltage conversion 206, the weak current signal transformation that is used for the output of second current transformer is that voltage signal is further handled for automatic gain adjustment circuit 207; Automatic gain is adjusted circuit 207, being used to receive from the light current of normal voltage/current transformer, electromagnetic potential/current transformer to be measured presses signal and the light current after conversion to press signal and from the analog output signal of electronic mutual inductor to be measured, and the amplitude of each voltage signal is adjusted to-5V～+ 5V between, select signal to be measured to export the tester circuit to as required.In addition, Electrical Instrument Transducers with Digital output signal direct puncture signal condition unit to be measured and need in signal condition unit 101, not handling.

First voltage transformer (VT) 201, second voltage transformer (VT) 204 that adopt in this conditioning unit are the high-accuracy voltage mutual inductor, and first current transformer 202, second current transformer 205 are high precision current transformer.

The voltage range that can accept to the A/D change-over circuit can be nursed one's health with the output signal of dissimilar electric power mutual-inductors in signal condition unit 101, promptly-5V～+ 5V between.The course of work of signal condition unit is as follows: for for the electromagnetic transformer of standard signal, the conditioning unit is adjusted into weak electric signal by high precision mutual inductor (accuracy class be ten thousand/) with it, the current transformer conditioning of 5A output is the little current signal of 25mA, be transformed to the voltage signal that peak value is 5V through behind the sampling resistor then, and incite somebody to action

Voltage transformer (VT) output signal conditioning be the voltage signal of 5V for peak value, so just finished the conditioning of standard road electric power mutual-inductor output signal.For to-be-tested transformer, when it is electronic mutual inductor, no matter be current transformer or voltage transformer (VT), because electronic mutual inductor output directly is weak electric signal, so can be adjusted to the voltage signal that peak value is 5V through behind the gain adjustment circuit, send into the follow-up signal treatment circuit, promptly finished signal condition work.And if to-be-tested transformer is an electromagnetic transformer, then the process of signal condition is with standard road electromagnetic transformer, also be earlier to be weak electric signal, send into the follow-up signal treatment circuit through sampling resistor (during the current transformer verification with) or direct (during the voltage transformer (VT) verification with) again and carry out analyzing and processing by the conditioning of high precision mutual inductor.The output signal of modulate circuit unit is the voltage signal that meets the follow-up signal treatment circuit.

Fig. 3 is a tester circuit function structural representation of the present invention, as shown in Figure 3, this tester circuit 102 comprises clock source 300, frequency divider 301, light-coupled isolation unit 302, monostable timing control unit 303, an A/D converting unit 304, the 2nd A/D converting unit 305 and multi channel selecting unit 306.

Wherein, clock source 300 is used to entire circuit that reference clock signal is provided; Frequency divider 301 is used to receive the clock signal in self-clock source 300, and this signal is handled the back through frequency division and provided the work clock signal for an A/D converting unit 304, the 2nd A/D converting unit 305 under the control of switch or monostable timing control unit 303; Light-coupled isolation unit 302, be used for electronic mutual inductor to be measured and monostable timing control unit 303 and multi channel selecting unit 306 are treated to not state altogether, realize electronic mutual inductor digital signal to be measured and the digital output signal that strengthens electronic mutual inductor to be measured and the antijamming capability of monostable timing control unit 303 and multi channel selecting unit 306 received signals; Monostable timing control unit 303, the circuit that is used for united and coordinating control tester circuit unit carries out work, each signal is finished under its effect simulating signal to be measured or digital signal are exported to digital signal processing unit by multi channel selecting unit 306; The one A/D converting unit 304 is used under the control of frequency divider 301 output signals, the analog output signal of standard mutual inductor is converted to the synchronous digital signal of suitable digital signal processing; The 2nd A/D converting unit 305 is used under the control of frequency divider 301 output signals, the analog output signal of to-be-tested transformer is converted to the synchronous digital signal of suitable digital signal processing; Multi channel selecting unit 306 is used to select to export through digital signal that obtains after an A/D converting unit 304 and 305 conversions of the 2nd A/D converting unit or digital signal and the Electrical Instrument Transducers with Digital to be measured of selecting output to obtain through an A/D converting unit 304 output signal to digital signal processing unit.

According to the disconnection of switch in this circuit, the signal type that closure state is selected electric power mutual-inductor to be verified, two kinds of functions of alignment processing digital signal when alignment processing simulating signal, off-state when promptly switch is in closure state; Through the tester circuit unit mutual inductor to be verified and standard mutual inductor output signal are changed then.The effect of the circuit of tester circuit unit is to select corresponding modulate circuit and enlargement factor according on off state, with conditioning standard mutual inductor output signal and mutual inductor to be verified output signal to scope-5V that A/D converter can be accepted among the DSP～+ 5V between.For guaranteeing the conditioning precision, the output working voltage mutual inductor summation current transformer of electromagnetic transformer is nursed one's health, current signal is adopted accurate I/V (current/voltage) varying circuit.To the components and parts heating problem in the conditioning process, can solve by setting up constant-temperature circuit, because there is different brackets in mutual inductor output, also there is the amplifying circuit of optional multiple in the conditioning part.

Its concrete course of work is as follows: as shown in Figure 3, the to-be-tested transformer signal is a simulating signal during switch closure, the circuit of representing with solid line among the figure is started working, the signal that draw in the clock source is through frequency division and sequential selection effect, gating two-way on two different time points, be that the analog output signal of standard mutual inductor and the analog output signal of to-be-tested transformer input to an A/D converting unit and the 2nd A/D converting unit, and the signal after will changing is introduced the multi channel selecting unit, and under the sequential control of monostable timing control unit, control described two paths of signals by logical circuit and export from the multi channel selecting unit; The to-be-tested transformer signal was a digital signal when switch disconnected, the signal flow that the digital circuit that is represented by dotted lines among the figure is started working to, digital output signal to be measured is through after the light-coupled isolation, producing control signal by monostable timing control unit again starts working frequency dividing circuit, through sequential selection effect, the one A/D conversion work of control criterion mutual inductor output, the digital signal that obtains and the digital signal of to-be-tested transformer after the conversion are entered the multi channel selecting unit, and under the effect of monostable timing control unit, control described two paths of signals by logical circuit and export to through the multi channel selecting unit and carry out subsequent analysis in the DSP unit and handle.

Fig. 4 is the signal processing flow figure of digital signal processing unit of the present invention, the core concept of its digital signal processing is as follows: at first will carry out the pre-service computing from the data that measured signal collects, make signal when enlarging first-harmonic and DC component, higher hamonic wave is decayed to zero, thereby suppress the influence of higher hamonic wave signal processing algorithm; Then, carry out least-squares algorithm,, utilize the trigonometric function relation, try to achieve the frequency of electrical network median generatrix electric current indirectly by least square fitting by adopting the method for tectonic sequence; At last, utilize accurate DFT algorithm synchronously to reduce non-integer-period sampled error, to realize the pin-point accuracy frequency analysis, the result of Huo Deing shows by display unit the most at last.As shown in Figure 4, digital signal processing of the present invention comprises the steps:

Step 400: digital signal processing unit is carried out initialization;

Step 401: then response external is interrupted, and carries out interrupt service routine;

Step 402: judge whether external interrupt finishes, if do not finish, then by interrupt service routine execution in step 403, if external interrupt finishes, then execution in step 404;

Step 403: interrupt service routine is carried out the signals collecting function, interrupts at one that data acquisition finishes in the performance period, end interrupt program then, and return master routine;

Step 404: begin to carry out signal Processing, carry out the Signal Pretreatment algorithm, carry out least-squares algorithm and accurate DFT algorithm synchronously then.

The described signal Processing of carrying out, its concrete implementation is as follows:

At first, carry out Preprocessing Algorithm, suppose that the signal v (t) that DSP gathers has following form by the structure new function:

$v\left(t\right)=\underset{L=1}{\overset{N}{\mathrm{\Σ}}}{A}_L\sin (2\mathrm{\πL}{f}_{0}t+{\mathrm{\θ}}_L)+D$

Wherein: N is an overtone order; A _LBe L subharmonic amplitude; θ _LBe L subharmonic phase place;

f ₀Be fundamental frequency; D is a DC component.

Then the sequence v (n) after the sampling is:

Wherein: , f _sBe sample frequency;

For the k subharmonic, determine real number x _k, make:

Then: x _k=f _s/ 2kf ₀

And then make up following sequence:

v ₁(n)＝v(n)+v(n-x _k)

v ₂(n)＝v ₁(n)+v ₁(n-x _k)

v(n)＝v ₂(n)

Work as x _kWhen being not integer, v (n-x _k) can use

With

Linear fit represent;

Get k from 2 to N above-mentioned three sequences that circulate successively, can get:

Wherein:

D _N=4 ^ND;

Get L=1, A _N1Fundamental voltage amplitude for signal after the circular treatment:

$A_{N1}=4^N{A}_1\underset{k=2}{\overset{N}{\mathrm{\Π}}}{\cos }^2\left(\frac{\mathrm{\π}}{2\×k}\right);$ And then try to achieve: A _N12 ^N+1A ₁Arrive the N subharmonic, its amplitude for 2:

The aforementioned calculation process makes higher hamonic wave almost decay to zero when having enlarged first-harmonic and DC component, and in cyclic process the choosing of parameter without any restriction.

Then, after cyclic process, promptly adopt the least square fitting algorithm to obtain high-precision frequency measurement;

Pretreated measured signal is:

v(n)＝A _N1sin(nω+θ _N1)+D _N

In the formula: A _N1Be pretreated fundamental voltage amplitude, θ _N1Be pretreated fundamental phase, D _NBe pretreated direct current amplitude.

Come tectonic sequence x (n) and y (n) by v (n):

x(n)＝2v(n-1)

y(n)＝v(n)+v(n-2)

Utilize least-squares algorithm, and can obtain following formula according to the trigonometric function relation:

y(n)＝x(n)cosΩ+2D(1-cosΩ)

Make a=cos Ω, b=2D (1-cos Ω) then can be expressed as:

y(n)＝ax(n)+b

As seen, there are linear relationship in x (n) and y (n), thereby can try to achieve a by least square fitting.Because: a=cos Ω=cos2 π f Δ T

Can get: f=arccosa/ (2 π f Δ T) can draw the fundamental frequency f of bus current ₀

At last, on the basis that obtains the accurate measurement result of frequency, utilize accurate DFT algorithm synchronously to solve the influence of frequency jitter targetedly again to signal processing results.

Introduce periodic function g (t), its mean value in one-period is:

$\stackrel{\&OverBar;}{g\left(t\right)}=\frac{1}{T}{\&Integral;}_{T_0}^{{\mathrm{<figure-callout\; id="0"\; label="T"\; filenames="C200710119585E00241.png,C200710119585E00242.png"\; state="\{\{state\}\}">T</figure-callout>}}_0+T}g\left(t\right)\mathrm{dt}=\frac{1}{2\mathrm{\&pi;}}{\&Integral;}_0^{2\mathrm{\&pi;}}g(x/\mathrm{\&Omega;})\mathrm{dx}=\frac{1}{2\mathrm{\&pi;}}{\&Integral;}_0^{2\mathrm{\&pi;}}f\left(x\right)\mathrm{dx}=\stackrel{\&OverBar;}{f\left(x\right)}$

In the formula, t=x/ Ω, f (x)=g (x/ Ω), the cycle is 2 π;

$\stackrel{\&OverBar;}{f\left(x\right)}=\frac{1}{2\mathrm{\&pi;}}{\&Integral;}_0^{2\mathrm{\&pi;}}f\left(x\right)\mathrm{dx}=\frac{1}{2\mathrm{\&pi;}}{\&Integral;}_{\mathrm{\&alpha;}}^{\mathrm{\&alpha;}+2\mathrm{\&pi;}}f\left(x\right)\mathrm{dx}$

Integer-period sampled as if failing, there is error delta, then:

$\stackrel{\&OverBar;}{f\left(x\right)}\&NotEqual;\frac{1}{2\mathrm{\&pi;}+\mathrm{\&Delta;}}{\&Integral;}_{\mathrm{\&alpha;}}^{\mathrm{\&alpha;}+2\mathrm{\&pi;}+\mathrm{\&Delta;}}f\left(x\right)\mathrm{dx}$

Order: $F^1\left(\mathrm{\&alpha;}\right)=\frac{1}{2\mathrm{\&pi;}+\mathrm{\&Delta;}}{\&Integral;}_{\mathrm{\&alpha;}}^{\mathrm{\&alpha;}+2\mathrm{\&pi;}+\mathrm{\&Delta;}}f\left(x\right)\mathrm{dx}$

Its cycle is 2 π, averages in one-period, still equals f (x), makes that the integration starting point is β, then:

$\stackrel{\&OverBar;}{f\left(x\right)}=\stackrel{\&OverBar;}{F^1\left(\mathrm{\&alpha;}\right)}=\frac{1}{2\mathrm{\&pi;}}{\&Integral;}_{\mathrm{\&beta;}}^{\mathrm{\&beta;}+2\mathrm{\&pi;}}{F}^1\left(\mathrm{\&alpha;}\right)\mathrm{d\&alpha;}$

Owing to still can not realize integration complete cycle, then have:

$\stackrel{\&OverBar;}{f\left(x\right)}=\stackrel{\&OverBar;}{F^1\left(\mathrm{\&alpha;}\right)}\&NotEqual;\frac{1}{2\mathrm{\&pi;}+\mathrm{\&Delta;}}{\&Integral;}_{\mathrm{\&beta;}}^{\mathrm{\&beta;}+2\mathrm{\&pi;}+\mathrm{\&Delta;}}{F}^1\left(\mathrm{\&alpha;}\right)\mathrm{d\&alpha;}$

Integral result is relevant with β, still is to be the function of 2 π in the cycle, and mean value equals f (x), obtains following recursion formula by that analogy:

$F^n\left(x\right)=\frac{1}{2\mathrm{\&pi;}+\mathrm{\&Delta;}}{\&Integral;}_x^{x+2\mathrm{\&pi;}+\mathrm{\&Delta;}}{F}^{n-1}(x\&prime;)\mathrm{dx}\&prime;$

Can prove:

$\underset{n\&RightArrow;\&infin;}{\lim }{F}^n\left(x\right)=\stackrel{\&OverBar;}{f\left(x\right)}={\mathrm{<figure-callout\; id="0"\; label="A"\; filenames="C200710119585E00241.png,C200710119585E00242.png"\; state="\{\{state\}\}">A</figure-callout>}}_0$

Wherein: A ₀Be the DC component amplitude;

If with quasi-synchronous algorithm and discrete Fourier transformation combination, find the solution the formula of coefficient by Fourier transform:

$a_k=\frac{2}{T}{\&Integral;}_0^{T}f\left(t\right)\cos \left(\mathrm{k\&Omega;t}\right)\mathrm{dt}$

And supposition: g (t)=f (t) cos (k Ω t) is that one-period is the function of T, then a _k=2g (t), finding the solution of g (t) can be with reference to above-mentioned quasi-synchronous algorithm.

Step 405: the ratio, the angular difference that calculate measured signal;

By aforesaid signal processing algorithm process, draw the first harmonic magnitude and the fundamental phase value of standard signal and measured signal, range value and phase value with standard signal are standard value, and the range error that utilizes the key concept of error analysis can obtain measured signal again is that ratio and phase error are angular difference.

Step 406: the result of signal Processing is sent to the display unit demonstration;

Step 407: produce and interrupt enable signal, return step 401.

Breadboard simulation result shows, precision based on pre-service and least-squares algorithm survey frequency can reach 2/100000ths, the result who carries out signal analysis in conjunction with accurate DFT synchronously more afterwards, range error is no more than 0.0033%, phase angle error is no more than 0.1 ', this is the hard-wired theoretical foundation of calibration equipment of the present invention.

Fig. 5 is the liquid crystal drive process flow diagram of display unit of the present invention, and as shown in Figure 5, DSP at first finishes initialization, comprises the setting that shows with constant.Then carry out the liquid crystal initialization, comprise time constant, some line number, the shared byte number of delegation, viewing area first address, viewing area synthesis mode etc., because of data such as the real-time display frequency of needs, angular difference, ratios, also to realize the dynamic demonstration of waveform simultaneously, so two viewing areas are set, two viewing areas all cover whole liquid crystal display fully, are the relation of logical "or" between the two.Like this, thick-and-thin displaying contents is arranged on same viewing area as grid and Chinese character, and other need the content of real-time change, are set to another viewing area as signal waveform and calculation result data.When moving continuously, constantly refresh dynamic display area and get final product.Described liquid crystal drive and LCD also can be common display driving circuit and cathode ray tube (CRT) display, are referred to as display unit.

Calibration equipment of the present invention has carried out full test in the laboratory, use multi-function calibrator generation calibration equipment input end required voltage and the current analog signal of the model of U.S.'s fluke (FLUKE) company production as FLUKE 5500A, the model of utilizing the said firm to produce is tested the amplitude of simulating signal for eight half word multimeters of FLUKE 8508A, the amplitude of the output signal that test result and calibration equipment are shown on LCD compares the precision level of verifying calibration equipment self, obtains the display result shown in Fig. 6 (a) and Fig. 6 (b) thus:

Fig. 6 (a) is the error testing result schematic diagram of apparatus of the present invention verification current transformer, be depicted as the measurement result of current transformer passage as Fig. 6 (a), shown calibration equipment of the present invention and the follow-up signal Processing Algorithm overall accuracy when carrying out the current transformer calibration, the result shows, standard and current transformer to be measured corresponding check device passage precision level respectively all satisfy the accuracy requirement of 0.02 grade of current transformer in the national standard.

Fig. 6 (b) is the error testing result schematic diagram of apparatus of the present invention calibration potential transformator, be depicted as the measurement result synoptic diagram of voltage transformer (VT) passage as Fig. 6 (b), shown calibration equipment circuit of the present invention and the follow-up signal Processing Algorithm overall accuracy when carrying out the voltage transformer (VT) calibration, the result shows, standard and voltage transformer (VT) to be measured corresponding check device passage precision level respectively all satisfy the accuracy requirement of 0.01 step voltage mutual inductor in the national standard.

As seen, to the analog input channel of calibration equipment, the precision level of standard mutual inductor and to-be-tested transformer passage all satisfies the error requirements of 0.02 grade of mutual inductor in the national standard; And digital input channel is nursed one's health fractional error because of no signal, is the error of DSP self algorithm therefore, can reach the accuracy requirement of 0.01 grade of mutual inductor.

The above is preferred embodiment of the present invention only, is not to be used to limit protection scope of the present invention.

Claims (7)

1, a kind of universal electric power mutual-inductor calibration equipment is characterized in that, this device comprises:

The signal condition unit is used for the analog output signal of standard mutual inductor and the analog output signal of electromagnetic type to be measured and electronic mutual inductor are nursed one's health;

The tester circuit unit is used for the analog output signal of the digital output signal of electronic mutual inductor to be measured, standard mutual inductor simulating signal after the conditioning of signal condition unit and electromagnetic type to be measured, electronic mutual inductor is converted to synchronous digital signal;

Digital signal processing unit is used for the synchronous digital signal by the output of tester circuit unit is carried out pre-service, least-squares algorithm and accurate discrete Fourier algorithm process synchronously;

Display unit is used for the object information of display digit signal Processing; And

Network interface unit is used for providing to the electric power digital interface result of digital signal processing;

Wherein, signal condition unit, tester circuit unit and digital signal processing unit link to each other successively, and display unit and network interface unit link to each other with digital signal processing unit respectively.

2, universal electric power mutual-inductor calibration equipment according to claim 1 is characterized in that, described signal condition unit further comprises:

First voltage transformer (VT) is used for voltage signal with standard mutual inductor output and is converted to voltage signal less than 5V;

First current transformer is used for current signal with the 1A～5A of standard current transformer output and is converted to current signal less than 25mA;

The first current/voltage transducer is used for current signal with first current transformer output and is converted to voltage signal less than 5V;

Second voltage transformer (VT) is used for voltage signal with to-be-tested transformer output and is converted to voltage signal less than 5V;

Second current transformer is used for current signal with the 1A～5A of current transformer to be measured output and is converted to current signal less than 25mA;

The second current/voltage transducer is used for current signal with second current transformer output and is converted to voltage signal less than 5V; And

Automatic gain is adjusted circuit, be used to receive the analog output signal of first voltage transformer (VT), the first current/voltage transducer, second voltage transformer (VT), the second current/voltage transducer and electronic mutual inductor to be measured and the amplitude of signal is adjusted to-5V～+ the 5V scope selects output again.

3, universal electric power mutual-inductor calibration equipment according to claim 1 and 2, it is characterized in that, described signal condition unit is nursed one's health analog output signal, be meant that the analog output signal with standard potential transformer signal, standard current transformer, electromagnetic potential transformer, electromagnetic current transducer and electronic mutual inductor is converted into-5V～+ the 5V scope.

4, universal electric power mutual-inductor calibration equipment according to claim 1 is characterized in that, described tester circuit unit further comprises:

The clock source is used to this tester circuit that required work clock signal is provided;

Frequency divider, the clock signal that is used for the receive clock source is also handled this signal according to the different frequency divisions that carry out of measure analog signals and digital signal;

The light-coupled isolation unit is used for the electronic mutual inductor to be measured and output of monostable timing control unit and multi channel selecting unit and the digital signal processing of input is become not isolation altogether;

Monostable timing control unit is used for coordinating control tester circuit and carries out work;

The one A/D converting unit is used for the analog output signal of standard mutual inductor is converted to synchronous digital signal;

The 2nd A/D converting unit is used for the analog output signal of tested mutual inductor is converted to synchronous digital signal; And

The multi channel selecting unit is used to select two-way signal or selection through an A/D converting unit and the output of the 2nd A/D converting unit to carry out synchronous digital signal output through an A/D converting unit with through the two-way signal that the light-coupled isolation unit is exported.

5, universal electric power mutual-inductor calibration equipment according to claim 4 is characterized in that, described tester circuit unit also includes switch, is used to realize the type selecting of electromagnetic type to be verified or electronic mutual inductor.

6, universal electric power mutual-inductor calibration equipment according to claim 1, it is characterized in that, described digital signal processing unit utilization Signal Pretreatment algorithm, least-squares algorithm and accurate discrete Fourier algorithm synchronously obtain amplitude, frequency and the phase information of measured signal, and calculate ratio and angular difference by the contrast with standard potential transformer or current transformer output signal.

7, universal electric power mutual-inductor calibration equipment according to claim 1 is characterized in that, described display unit comprises display driver circuit and LCD or cathode-ray tube display.

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