CN1881729B - Harmonic measuring method for AC filter protection - Google Patents

Abstract

The invention relates to a harmonic wave measure method used in alternative-current filter projection, which comprises: dividing the TA converted current of filter into two parts which independently pass two different filter circuits. Wherein one path passes relative filter circuit into the multi-path convert switch, via A/D converter, be converted into digit value, and via digit filter, to be the base wave current effective value; another path passes relative filter circuit, via the effective value calculating circuit, multi-path convert switch and A/D converter, to be the effective values of each harmonic wave current. The invention uses hardware circuit to calculate the harmonic wave current effective value of filter, and via software modification, to confirm the accuracy of heat emission calculation, to meet the demand of filter protection in direct-current transmission project.

Description

The harmonic measuring method that is used for AC filter protection

Technical field

The present invention relates to a kind of harmonic measuring method that is used for AC filter protection.

Background technology

In present DC transmission engineering, for preventing the influence of each harmonic that AC rectification and dc inversion produce to the AC system power supply quality, the filter of different resonance frequencys generally all will be set in AC side, be used for the each harmonic that produces in the filtering ac-dc conversion process, the position of filter in system as shown in Figure 1.The measuring position of flowing through inductive current in the filter as shown in Figure 2.Inductance in the filter, each harmonic electric current to identical amplitude, different frequency has different heat absorption capacity coefficients, for prevent inductance under the bigger situation of harmonic current because of heating damages, will measure the caloric value summation of the each harmonic electric current that flows through inductance more accurately.Way common in microcomputer protecting device is: improve sample frequency and deposit data district, accurately calculate the content of each harmonic electric current in the electric current, multiply by the heat absorption capacity coefficient of each harmonic respectively, obtain a total heating value, computing formula is

K wherein _nHeat absorption capacity coefficient for certain subharmonic.The subject matter that this method exists is to need the sample frequency of handle assembly to promote significantly, makes installation cost significantly improve; Simultaneously, for calculating the each harmonic content in the electric current, need take the processing time of CPU in a large number.

Summary of the invention

For overcoming the problem that existing method exists; the object of the invention is to propose a kind of harmonic measure technical method that is used for AC filter protection; utilize the numerical procedure of comparatively simple and reliable hardware circuit; on the basis of not improving hardware cost; utilize the operating experience in the direct current system engineering; comparatively accurately measure the thermal effect summation of each harmonic electric current, prevent the damage of inductance in running, improved reliability of system operation.

For achieving the above object, technical scheme of the present invention is: a kind of harmonic measuring method that is used for AC filter protection, the step of this method is: the electric current that will flow through filter is divided into two parts after through the TA conversion, respectively through two filter circuits that characteristic is different, directly enter multicircuit switch behind one tunnel its corresponding filter circuit of process, become digital quantity by the A/D converter, behind digital filtering, obtain the fundamental current effective value; Another road directly obtains the effective value of each harmonic electric current through after passing through effective value counting circuit, multicircuit switch and A/D converter again behind its corresponding filter circuit.

When the alternating current-direct current transmission system was moved, the secondary current that will flow through filter directly entered effective value hardware counter circuit device, calculates the summation of each harmonic electric current

Device is in the summation of foundation each harmonic electric current When calculating the thermal effect value of each harmonic electric current, according to the different operating conditions of system, the percentage of the shared fundamental current of each harmonic electric current under every kind of known operating mode that comparable device inside sets is according to fitting algorithm, that is:

$Q=i_1^2+k_2*i_2^2-k_3*i_3^2+...+k_{50}*i_{50}^2$

$=i_1^2+k_2*m_2^2*i_1^2+k_3*m_3^2*i_1^2+...+k_{50}*m_{50}^2*i_1^2$

$=i_1^2(1+k_2*m_2^2+k_3*m_3^2+...+k_{50}*m_{50}^2)=k_{\mathrm{sum}}*i_{\mathrm{sum}}^2$

$=k_{\mathrm{sum}}*(i_1^2+m_2^2*i_1^2+m_3^2*i_1^2+...+m_{50}^2*i_1^2)$

m _nAccount for the percentage of fundamental current for each harmonic

$k_{\mathrm{sum}}=(1+k_2{m}_2^2+k_3{m}_3^2+..+k_{50}{m}_{50}^2)/(1+m_2^2+m_3^2+...+m_{50}^2)$

Device can increase the hardware circuit that calculates the each harmonic effective value on the basis of original hardware platform, saved owing to improve the lifting of sample frequency to hardware cost.The loop is simple, is easy to realize; Only original circuit is simply transformed.For the different problem of each harmonic electric current content under the different ruuning situations, can revise heat absorption capacity coefficient by software, guarantee the accuracy that caloric value is calculated.For the fundamental current that flows through filter, can calculate by original circuit.

After obtaining the fundamental current and each harmonic current effective value that flows through filter, by calculating the current harmonics effective value that can obtain except that first-harmonic.Computing and correction through the device in house software, can comparatively accurately calculate each harmonic and flow through the caloric value that filter produces, under the situation of conditions permit, send tripping operation or warning message, prevent filter because the harmonic wave overcurrent causes temperature too high and damage.

The present invention has adopted the harmonic current effective value of hardware circuit convection current wave filter to calculate, and the accuracy by the method assurance caloric value of software correction is calculated has satisfied the requirement of DC transmission engineering to filter protection, and method is simple, realizes easily.

Description of drawings

Fig. 1 is the position of filter in AC system;

Fig. 2 is the measuring position of inductive current in the filter;

Fig. 3 measures loop hardware circuit principle figure for harmonic current.

Embodiment

The invention provides a kind ofly under supplied by AC/DC electricity system service conditions, comparatively accurately measure the computational methods of the total amount of heat that the each harmonic electric current that flows through filter produces on inductance, computing formula is Ensure that filter element is not damaged, improved the reliability of system stable operation.For the filter that is too much caused by harmonic content is overheated higher use value arranged.

The hardware circuit principle that among the present invention harmonic current is detected is as shown in Figure 3: the electric current that flows through filter is divided into two parts after through the TA conversion, respectively through behind the different filter circuit of two characteristics, one the tunnel directly enters multicircuit switch, become digital quantity by the A/D converter, behind digital filtering, obtain the fundamental current effective value; Lead up in addition behind effective value counting circuit, multicircuit switch and the A/D converter, directly obtain the effective value of each harmonic electric current.

Specific implementation method of the present invention is: when the alternating current-direct current transmission system was moved, the secondary current that flows through filter directly entered the effective value counter circuit, calculates the summation of each harmonic electric current by hardware-in-the-loop Device is when calculating the thermal effect value of each harmonic electric current, and according to the different operating conditions of system, the engineering experience parameter that comparable device inside sets (percentage of the shared fundamental current of each harmonic electric current is known under every kind of operating mode) is according to fitting algorithm, that is:

$Q=i_1^2+k_2*i_2^2-k_3*i_3^2+...+k_{50}*i_{50}^2$

$=i_1^2+k_2*m_2^2*i_1^2+k_3*m_3^2*i_1^2+...+k_{50}*m_{50}^2*i_1^2$

$=i_1^2(1+k_2*m_2^2+k_3*m_3^2+...+k_{50}*m_{50}^2)=k_{\mathrm{sum}}*i_{\mathrm{sum}}^2$

$=k_{\mathrm{sum}}*(i_1^2+m_2^2*i_1^2+m_3^2*i_1^2+...+m_{50}^2*i_1^2)$

m _nAccount for the percentage of fundamental current for each harmonic

Can obtain: $k_{\mathrm{sum}}=(1+k_2{m}_2^2+k_3{m}_3^2+..+k_{50}{m}_{50}^2)/(1+m_2^2+m_3^2+...+m_{50}^2)$

Because k _nBe known quantity, m _nParameter under different operating modes can obtain in advance, just can be at known i _SumSituation under comparatively accurately measure the thermal effect value of harmonic current, thereby obtain generating heat actual influence to protective device, ensure that filter element can not improve the reliability of system stable operation because of overheated and damage.

It should be noted last that: above embodiment is the unrestricted technical scheme of the present invention in order to explanation only, although the present invention is had been described in detail with reference to the foregoing description, those of ordinary skill in the art is to be understood that: still can make amendment or be equal to replacement the present invention, and not breaking away from any modification or partial replacement of the spirit and scope of the present invention, it all should be encompassed in the middle of the claim scope of the present invention.

Claims (3)

1. harmonic measuring method that is used for AC filter protection, it is characterized in that, the step of this method is: the electric current that will flow through filter is divided into two parts after through the current transformer conversion, respectively through two filter circuits that characteristic is different, directly enter multicircuit switch behind one tunnel its corresponding filter circuit of process, be transformed into digital quantity by the A/D converter, behind digital filtering, obtain the fundamental current effective value; Another road again by behind effective value counting circuit, multicircuit switch and the A/D converter, directly obtains the effective value of each harmonic electric current through its corresponding filter circuit.

2. the harmonic measuring method that is used for AC filter protection according to claim 1; it is characterized in that; when the alternating current-direct current transmission system was moved, the secondary current that will flow through filter directly entered effective value hardware counter circuit device, calculates the summation of fundamental current and each harmonic electric current

Wherein, i ₁Be fundamental current, i ₂～i ₅₀Be followed successively by the each harmonic electric current.

3. the harmonic measuring method that is used for AC filter protection according to claim 2 is characterized in that, device is in the summation of foundation fundamental current and each harmonic electric current

When calculating the thermal effect value of each harmonic electric current, according to the different operating conditions of system, the percentage of the shared fundamental current of each harmonic electric current under every kind of known operating mode that comparable device inside sets is according to fitting algorithm, that is:

$Q=i_1^2+k_2*i_2^2+k_3*i_3^2+...+k_{50}*i_{50}^2$

$=i_1^2+k_2*m_2^2*i_1^2+k_3*m_3^2*i_1^2+...+k_{50}*m_{50}^2*i_1^2$

$=i_1^2(1+k_2*m_2^2+k_3*m_3^2+...+k_{50}*m_{50}^2)=k_{\mathrm{sum}}*i_{\mathrm{sum}}^2$

$=k_{\mathrm{sum}}*(i_1^2+m_2^2*i_1^2+m_3^2*i_1^2+...+m_{50}^2*i_1^2)$

Wherein, Q is the caloric value summation that flows through the fundamental current and the each harmonic electric current of inductance;

m ₂～m ₅₀Be followed successively by each harmonic and account for the percentage of fundamental current;

k ₂～k ₅₀Be followed successively by inductance in the filter to the heat absorption capacity coefficient of each harmonic electric current;

$k_{\mathrm{sum}}=(1+k_2*m_2^2+k_2*m_3^2+...+k_{50}*m_{50}^2)/(1+m_2^2+m_3^2+...+m_{50}^2).$

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