CN103235172A - Current measuring method and measuring device - Google Patents

Abstract

The invention discloses a current measuring method and belongs to the technical field of electrical measurement. According to the current measuring method, a Rogowski coil is adopted to sample the current to be measured, an integral circuit is utilized to carry out integral reduction on a sample signal of the Rogowski coil, the current to be measured is figured out according to the amplitude of the integral reduction signal, the amplitude of the integral reduction signal for figuring out the measured current is the product of the amplitude of a signal outputted by the integral circuit and a compensation factor A, and the compensation factor A is figured out according to the frequency of the current to be measured and the cut-off angular frequency of the integral circuit. The invention also discloses a current measuring device. The current measuring method and the measuring device can be used for accurately measuring current with frequency being as low as a few hertz in a similar wind power generation system, and the safety of a power system is improved; and according to the current measuring method and the current measuring device, an existing measuring device does not need to be modified greatly, and the low cost is realized.

Description

A kind of current measuring method and measurement mechanism

Technical field

The present invention relates to a kind of electric measurement method, relate in particular to a kind of current measuring method and measurement mechanism, be applicable to the bigger occasions of power frequency variation range such as wind generator system.

Background technology

Intelligent controller is the critical component of low-voltage intelligent circuit breaker, generally is applicable to the 50/60Hz electrical network, mainly as distribution, feed or generating protection.Along with becoming increasingly conspicuous of environment and energy problem; renewable energy power generation develops rapidly in the world; wherein with fastest developing speed, the technology of wind-power electricity generation is the most ripe; for protect the wind-powered electricity generation unit normal use to avoid damaging and be convenient to wind power generating set is safeguarded or serves that blower fan system must be equipped for example isolating switch of some electric protection products.But; when low-voltage intelligent circuit breaker is applied to the generating pusher side of wind power generating set; particularly when Electrified Transmission is full power convertor; generator has been cancelled step-up gear; generator shaft is directly connected on the impeller shaft; the rotating speed of rotor changes with wind speed; the ac current signal frequency that the isolating switch mounting points is passed through (for example several Hz are to hundreds of Hz) within the specific limits changes; and existing intelligent controller is measured limited bandwidth; the general current signal that only is suitable for measuring 50/60Hz; therefore intelligent controller just can not correctly be measured current signal when the current signal frequency range exceeds the measurement bandwidth of intelligent controller; thereby can not protect the wind-powered electricity generation unit, bring loss to the user.At present, it is that hollow coil (seeing accompanying drawing 1) carries out once the measurement of big electric current that the circuit breaker intelligent controller great majority adopt Rogowski coil (or claiming Luo-coil), the Luo-coil wide frequency range, general scope of design is from more than 0.1Hz～100MHz, the wideband that therefore can satisfy above-mentioned occasion is fully measured and is required, but Luo-coil secondary output voltage signal e (t) is the differential of primary current signal, if true reduction just must be added corresponding integrating circuit (seeing accompanying drawing 2) with the directly proportional signal of primary current, but there is a cutoff frequency f in integrating circuit _L, its computing formula as the formula (1):

$f_L=\frac{1}{2\mathrm{\πRC}}---\left(1\right)$

Signal frequency through integrating circuit is lower than cutoff frequency f _L, signal amplitude will decay significantly, can be found out that by formula (1) size of cutoff frequency is determined by R, C.Many producers all can select a suitable integration time constant for example about T=R*C=0.01 when the design integrating circuit; can obtain cutoff frequency about 16Hz by formula (1); can guarantee the sensitivity of circuit protection like this; can guarantee that again measured signal (frequency 50/60Hz) can not be attenuated and reduced really; but when the current measuring device with above-mentioned integrating circuit is applied to the generating pusher side of picture wind-power electricity generation; for example be applied to the intelligent breaker of wind-power electricity generation pusher side; because flowing into the frequency of the once big electric current of isolating switch may low excessively (even can be low to moderate several Hz); Luo-coil secondary output voltage signal e (t) is through inevitable significantly decay behind the integrating circuit so; thereby influence is to the correct measurement of primary current; isolating switch was measured the distortion tripping when particularly primary current was short-circuited fault, and that is breakneck.

Summary of the invention

Technical matters to be solved by this invention is to overcome the prior art deficiency, and a kind of current measuring method and measurement mechanism are provided, and can accurately measure the frequency conversion electric current (for example above-mentioned wind generator system) that changes in big frequency range.

The present invention is specifically by the following technical solutions:

A kind of current measuring method, utilize Luo-coil that electric current to be measured is sampled, and utilize integrating circuit that the sampled signal of Luo-coil output is carried out the integration reduction, at last calculate electric current to be measured according to the crest meter of integration recovering signal, amplitude that be used for to calculate the integration recovering signal of electric current to be measured is the amplitude and the product of penalty coefficient A of the signal of described integrating circuit output, and described penalty coefficient A is definite according to following formula:

$A=\left\{\begin{array}{cc}1& \mathrm{if}\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\&GreaterEqual;\mathrm{\&lambda;}\\ \sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}\&times;\frac{{\mathrm{\&omega;}}_0}{\mathrm{\&omega;}}& \mathrm{if}\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}<\mathrm{\&lambda;}\end{array}\right.,$

In the formula, ω is the current angular frequency of electric current to be measured; ω ₀Cut-off angular frequency for described integrating circuit; λ is preset threshold value, and its span is λ 〉=1.5.

A kind of current measuring device comprises the Luo-coil of sampling for to electric current to be measured, and the integrating circuit, amplifying circuit, analog to digital conversion circuit, the computing unit that are connected successively with the output terminal of described Luo-coil; Integrating circuit carries out the integration reduction to the sampled signal of Luo-coil, amplify and analog to digital conversion by amplifying circuit, analog to digital conversion circuit then, export computing unit to, computing unit is calculated electric current to be measured according to the crest meter of integration recovering signal, the amplitude that computing unit be used for to calculate the integration recovering signal of electric current to be measured is the amplitude and the product of penalty coefficient A of the signal of described integrating circuit output, and described penalty coefficient A is definite according to following formula:

$A=\left\{\begin{array}{cc}1& \mathrm{if}\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\&GreaterEqual;\mathrm{\&lambda;}\\ \sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}\&times;\frac{{\mathrm{\&omega;}}_0}{\mathrm{\&omega;}}& \mathrm{if}\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}<\mathrm{\&lambda;}\end{array}\right.,$ In the formula, ω is the current angular frequency of electric current to be measured; ω ₀Cut-off angular frequency for described integrating circuit; λ is preset threshold value, and its span is λ 〉=1.5.

Compared to existing technology, the present invention has following beneficial effect:

(1) the present invention can accurately measure the frequency conversion electric current of big frequency range, and for example power frequency can be changed under several hertz the situation in wind generator system, also can obtain the exact current measurement result.

(2) the present invention realizes simply, only needs existing current measurement protective device (for example intelligent circuit breaker) is improved a little, increases cost hardly.

Description of drawings

Fig. 1 is the structural representation of Rogowski air core coil;

Fig. 2 is a kind of existing passive integrator;

Fig. 3 is for being with the also equivalent electrical circuit of the Rogowski coil of primary circuit of integration;

Fig. 4 is a kind of existing active integrating circuit;

Fig. 5 is the process flow diagram of current measuring method of the present invention.

Embodiment

Below in conjunction with accompanying drawing technical scheme of the present invention is elaborated:

The band integration also the equivalent electrical circuit of the Rogowski coil of primary circuit referring to Fig. 3, L _O, R _O, Co is respectively self-induction, internal resistance, the stray capacitance of coil, M is the mutual inductance between bus and the coil, at sample resistance Rs of Rogowski coil two terminations, R, C are respectively integrating resistor and integrating capacitor.

Equivalent electrical circuit by Fig. 3 can obtain the also output-transfer function of primary circuit (ignoring coil stray capacitance Co) of this integration:

$H\left(s\right)=\frac{\mathrm{Uo}\left(s\right)}{I\left(s\right)}=\frac{\frac{\mathrm{Rs}*M}{\mathrm{Lo}}}{1+\frac{\mathrm{Rs}+\mathrm{Ro}}{\mathrm{Lo}*S}}*\frac{1}{R*C*S+1}---\left(2\right)$

If S=j is ω, ω ₀=1/RC=2 π * f ₀, f ₀Be the also cutoff frequency of primary circuit of integration, ask mould to get the amplitude versus frequency characte formula to formula (2) | H (s) |, namely corresponding amplitude proportion concerns between integration reduction circuit output signal Uo (t) and the primary current i (t).During practical application microprocessor by to integration also the output signal U o of primary circuit (t) carry out real-time sampling and calculate its amplitude, concern according to amplitude proportion corresponding between integration reduction circuit output signal Uo (t) and the primary current i (t) again to calculate primary current amplitude (being electric current to be measured):

$\left|\mathrm{Hs}\right|=\left|\frac{\mathrm{Uo}\left(s\right)}{I\left(s\right)}\right|=\frac{\frac{\mathrm{Rs}*M}{\mathrm{Lo}}}{\sqrt{1+{\left(\frac{\mathrm{Rs}+\mathrm{Ro}}{\mathrm{\&omega;}*\mathrm{Lo}}\right)}^2}}*\frac{1}{\sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}}---\left(3\right)$

Generally speaking, sample resistance Rs is big (hundreds of k Ω), and self-induction Lo is very little, therefore

Formula (3) can get again:

$\left|\mathrm{Hs}\right|=\frac{\mathrm{Rs}*M*\mathrm{\&omega;}}{\mathrm{Rs}+\mathrm{Ro}}*\frac{1}{\sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}}---\left(4\right)$

When the measured signal angular frequency greater than ω ₀, and (ω/ω ₀) ²1 o'clock, formula (4) can be simplified to again:

$\left|\mathrm{Hs}\right|=\left|\frac{\mathrm{Uo}\left(s\right)}{I\left(s\right)}\right|=\frac{\mathrm{Rs}*M*{\mathrm{\&omega;}}_0}{\mathrm{Rs}+\mathrm{Ro}}---\left(5\right)$

Can be at the signal angular frequency greater than ω by formula (5) ₀And (ω/ω ₀) ²1, the measured signal of different frequency equates in the amplitude of exporting after the integrating circuit reduction under the situation that the primary current amplitude equates, and the signal angular frequency is near ω ₀The time, then should calculate by formula (4), signal frequency is more low then to decay more severely.

Therefore, in order to guarantee on the one hand the sensitivity of circuit protection, guarantee on the other hand the correctness measured, thinking of the present invention be to the lower measured signal of frequency since its frequency near ω ₀Make the part that also decays behind the primary circuit through integration compensate, specifically be by multiply by a penalty coefficient A on the basis of formula (4), specifically as the formula (6), (namely | I (s) |) is constant because the amplitude of primary current, multiply by penalty coefficient A so come down to that integration is reduced the amplitude (namely | Uo (s) |) of circuit output signal.

$\left|\mathrm{Hs}\right|*A=\frac{\mathrm{Rs}*M*\mathrm{\&omega;}}{\mathrm{Rs}+\mathrm{Ro}}*\frac{1}{\sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}}*\sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}*\frac{1}{\mathrm{\&omega;}}*{\mathrm{\&omega;}}_0---\left(6\right)$

Wherein $A=\sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}*\frac{1}{\mathrm{\&omega;}}*{\mathrm{\&omega;}}_0.$

The words actual result that formula (6) is calculated approximately is exactly (5), formula (4) is that integrating circuit is to the true reduction output of different frequency signals, be desirable and multiply by the essence hypothesis integrating circuit that penalty coefficient A compensates, do not consider that cutoff frequency is to the attenuation factor of signal, why can take such indemnifying measure because of formula (5), namely different measured signal angular frequency is greater than ω o and (ω/ω ₀) ²1, equate in the amplitude through integration reduction back output under the situation that the primary current amplitude all equates, that is to say that the proportionate relationship between the signal value that primary current and integration reduce is constant, also namely irrelevant substantially with the angular frequency of measured signal.

The low frequency signal of Rogowski coil secondary output through integration reduction back by the amplification of subsequent conditioning circuit handle, the input AD converter converts input microprocessor behind the digital quantity to, microprocessor is finished compensation according to penalty coefficient A and is calculated, the numerical value that obtains after the compensation calculating through microprocessor conforms to corresponding primary current amplitude, thereby reaches the requirement of measuring correctness.

When the measured signal angular frequency greater than ω o and (ω/ω ₀) ²1, penalty coefficient A ≈ 1 that is to say to compensate this moment to calculate to have little significance, and therefore can not compensate and calculate.

Above-mentioned analytic process be at integration also primary circuit be the situation of passive integrator shown in Figure 2, in fact for active integrating circuit, above-mentioned analysis result is still set up.Fig. 4 has shown a typical active integrating circuit, and following formula (7) is the output-transfer function of active integrating circuit:

$H\left(s\right)=\frac{\mathrm{Uo}\left(s\right)}{I\left(s\right)}=\frac{\frac{\mathrm{Rs}*M}{\mathrm{Lo}}}{1+\frac{\mathrm{Rs}+\mathrm{Ro}}{\mathrm{Lo}*S}}*\frac{1}{\mathrm{Rf}*C*S+1}*(-\frac{\mathrm{Rf}}{R1})---\left(7\right)$

The difference of formula 7 and the output-transfer function of the passive integrator of Fig. 2 coefficient (Rf/R1), the cut-off angular frequency ω of active integrating circuit that only has been many ₀=1/2 π Rf*C, thus when the angular frequency of measured signal near ω ₀In time, also can decay gradually, and is identical with the passive integrator of Fig. 2.

Use for the ease of reality, can be to ω/ω ₀Set a threshold value λ, certainly λ under the perfect condition ²=(ω/ω ₀) ²The 1st, leave nothing to be desired, but can set λ during practical application in certain span and satisfy measuring error under acceptable terms, can think that the value of penalty coefficient A is that 1(namely is equivalent to not the secondary current amplitude of integrating circuit output is compensated); Otherwise, then need basis

Calculate penalty coefficient, the secondary current amplitude to integrating circuit output is compensated.The span of threshold value λ is λ 〉=1.5 among the present invention, preferred λ=5.Like this, namely obtain complete technical scheme of the present invention:

A kind of current measuring method, utilize Luo-coil that electric current to be measured is sampled, and utilize integrating circuit that the sampled signal of Luo-coil output is carried out the integration reduction, at last calculate electric current to be measured according to the crest meter of integration recovering signal, amplitude that be used for to calculate the integration recovering signal of electric current to be measured is the amplitude and the product of penalty coefficient A of the signal of described integrating circuit output, and described penalty coefficient A is definite according to following formula:

$A=\left\{\begin{array}{cc}1& \mathrm{if}\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\&GreaterEqual;\mathrm{\&lambda;}\\ \sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}\&times;\frac{{\mathrm{\&omega;}}_0}{\mathrm{\&omega;}}& \mathrm{if}\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}<\mathrm{\&lambda;}\end{array}\right.,$

In the formula, ω is the current angular frequency of electric current to be measured; ω ₀Cut-off angular frequency for described integrating circuit; λ is preset threshold value, and its span is λ 〉=1.5.

A kind of current measuring device comprises the Luo-coil of sampling for to electric current to be measured, and the integrating circuit, amplifying circuit, analog to digital conversion circuit, the computing unit that are connected successively with the output terminal of described Luo-coil; Integrating circuit carries out the integration reduction to the sampled signal of Luo-coil, amplify and analog to digital conversion by amplifying circuit, analog to digital conversion circuit then, export computing unit to, computing unit is calculated electric current to be measured according to the crest meter of integration recovering signal, the amplitude that computing unit be used for to calculate the integration recovering signal of electric current to be measured is the amplitude and the product of penalty coefficient A of the signal of described integrating circuit output, and described penalty coefficient A is definite according to following formula:

$A=\left\{\begin{array}{cc}1& \mathrm{if}\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\&GreaterEqual;\mathrm{\&lambda;}\\ \sqrt{1+{\left(\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}\right)}^2}\&times;\frac{{\mathrm{\&omega;}}_0}{\mathrm{\&omega;}}& \mathrm{if}\frac{\mathrm{\&omega;}}{{\mathrm{\&omega;}}_0}<\mathrm{\&lambda;}\end{array}\right.,$

In the formula, ω is the current angular frequency of electric current to be measured; ω ₀Cut-off angular frequency for described integrating circuit; λ is preset threshold value, and its span is λ 〉=1.5.

For specific integrating circuit, its cut-off angular frequency ω ₀Be fixing known, ω then needs actual measurement, obtaining for the frequency of primary current signal generally can be by measuring busbar voltage, power frequency realization, but the more correctness that can influence frequency measurement of the harmonic content of considering current signal, the present invention preferably obtains ω by the frequency of measuring bus voltage signal (being the voltage signal in loop, electric current to be measured place).Because frequency measurement circuit repeats no more for existing mature technology herein.

Fig. 5 has shown the workflow that adopts the circuit breaker intelligent controller of current measuring method of the present invention, and as shown in the figure, intelligent controller detects the primary current amplitude I in the frequency variation signal at first synchronously _RNS, voltage angular frequency; Then judge ω/ω ₀Whether less than 5, if, then with ω substitution formula

The value of coefficient A is repaid in supplement, and the primary current amplitude that records be multiply by A value back for measuring protection calculating, showing processing etc.; If more than or equal to 5, then directly the primary current amplitude that records is calculated, shows processing etc. that for measuring protection the value that namely is equivalent to penalty coefficient A is 1.

The present invention can be low to moderate several hertz frequency conversion electric current to this frequency change of similar wind generator system and accurately measure, and improves the security of electric system; And the present invention need not existing measurement mechanism is carried out big change, realizes that cost is low.

Claims (6)

1. current measuring method, utilize Luo-coil that electric current to be measured is sampled, and utilize integrating circuit that the sampled signal of Luo-coil output is carried out the integration reduction, at last calculate electric current to be measured according to the crest meter of integration recovering signal, it is characterized in that the amplitude that is used for the integration recovering signal of calculating electric current to be measured is amplitude and the penalty coefficient of the signal of described integrating circuit output AProduct, described penalty coefficient ADetermine according to following formula:

，

In the formula,

Current angular frequency for electric current to be measured;

Cut-off angular frequency for described integrating circuit;

Be preset threshold value, its span is

〉=1.5.

2. current measuring method according to claim 1 is characterized in that the current angular frequency of described electric current to be measured Measure by voltage or current signal to loop, electric current to be measured place.

3. current measuring method according to claim 1 is characterized in that described threshold value

Value be 5.

4. a current measuring device comprises the Luo-coil of sampling for to electric current to be measured, and the integrating circuit, amplifying circuit, analog to digital conversion circuit, the computing unit that are connected successively with the output terminal of described Luo-coil; Integrating circuit carries out the integration reduction to the sampled signal of Luo-coil, amplify and analog to digital conversion by amplifying circuit, analog to digital conversion circuit then, export computing unit to, computing unit is calculated electric current to be measured according to the crest meter of integration recovering signal, it is characterized in that the amplitude that computing unit is used for the integration recovering signal of calculating electric current to be measured is amplitude and the penalty coefficient of the signal of described integrating circuit output AProduct, described penalty coefficient ADetermine according to following formula:

，

In the formula,

Current angular frequency for electric current to be measured; Cut-off angular frequency for described integrating circuit;

Be preset threshold value, its span is

〉=1.5.

5. as current measuring device as described in the claim 4, it is characterized in that the current angular frequency of electric current to be measured

Measure by voltage or current signal to loop, electric current to be measured place.

6. as current measuring device as described in the claim 4, it is characterized in that described threshold value

Value be 5.

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