CN103364618A - Measuring method for harmonic voltage on direct current side of high-voltage direct current power transmission system - Google Patents

Abstract

The invention provides a measuring method for harmonic voltage on a direct current side of a high-voltage direct current power transmission system. The measuring method specifically comprises the following steps of: connecting a current transformer in series with a branch of a direct current side filter of the high-voltage direct current power transmission system; and calculating the harmonic voltage on the direct current side of the high-voltage direct current power transmission system by using the measured electric current in combination with each element parameter value of the direct current side filter or the known frequency-impedance characteristic of the direct current side filter. The measuring method is easy to operate and can be realized by only performing simple transformation on the basis of the conventional direct current side filter, the precision for measuring the harmonic voltage is high, the function of the direct current side filter is expanded, and the measuring method has higher cost performance; and the measuring method has extremely high application value and market promotion prospect on occasions for measuring the harmonic voltage on the direct current side of the high-voltage direct current power transmission system.

Description

A kind of HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method

Technical field

The present invention relates to a kind of HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method.

Technical background

DC transmission system has low, the suitable long distance power transmission of circuit cost, does not have the system stability problem, regulates the advantages such as quick, reliable, is applied to more and more the interconnected occasion of long distance power transmission and AC system.But because the current conversion station that is made of power electronic devices that uses in the DC transmission system can produce a large amount of harmonic waves, whole DC transmission system is produced Harmfulness Caused by Harmonics.Power supply department and scientific research institution are in the urgent need to measuring the voltage harmonic of HVDC (High Voltage Direct Current) transmission system DC side, to understand the voltage harmonic situation of high voltage power transmisson system DC side, make targetedly harness of harmonic wave, correctness and the validity of the design of checking wave filter on DC side.

But in the measuring method and equipment of currently used high pressure harmonic voltage, adopt the scheme of resistor dividing potential drop and capacitor dividing potential drop need to adopt special equipment, and these equipment volume are large, expensive.Adopt capacitance type potential transformer to carry out the method that the high pressure harmonic voltage measurement is most convenient economy, but because the internal resonance condition of capacitance type potential transformer under harmonic condition is with destroyed, measure harmonic wave and larger error will occur, can't directly use capacitance type potential transformer and carry out the high pressure harmonic measure.

Currently used all wave filter on DC sides all can be divided into two parts, and namely (impedance of fundamental frequency is Z to first branch road _{H (1)}, China's fundamental frequency is 50Hz) and second branch road.Wherein second branch road is made of a plurality of branch circuit parallel connections again that (impedance of fundamental frequency is respectively Z _{L1 (1)}, Z _{L2 (1)}..., Z _{Ln (1)}).Therefore, if can simply transform widely used wave filter on DC side in the present HVDC (High Voltage Direct Current) transmission system, design the wave filter of taking into account simultaneously conventional DC side harmonics filtering and DC side harmonics measurement function, high-precision high voltage direct current harmonic voltage measurement can be provided when carrying out harmonic filtration.Thereby for realizing that the voltage measurement of HVDC (High Voltage Direct Current) transmission system DC side harmonics provides a kind of cost performance very high scheme, has great practical value and the marketing prospect.

Summary of the invention

For the problem that background technology exists, the invention provides a kind of harmonic voltage measurement method of HVDC (High Voltage Direct Current) transmission system DC side.

Currently used all wave filter on DC sides all can be divided into two parts, and namely (impedance of fundamental frequency is Z to first branch road _{H (1)}, China's fundamental frequency is 50Hz) and second branch road.Wherein second branch road is made of a plurality of branch circuit parallel connections again that (impedance of fundamental frequency is respectively Z _{L1 (1)}, Z _{L2 (1)}..., Z _{Ln (1)}).The present invention seals in current transformer in each parallel branch in second branch road of traditional wave filter on DC side, the electric current that measures is carried out Fourier decomposition, obtain individual harmonic current, according to composition and the component parameters of wave filter on DC side, calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side.Also can utilize the impedance frequency characteristics of the electric current that measures and known wave filter on DC side, calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side.The invention provides the higher high voltage direct current harmonic voltage measurement means of a kind of cost performance, for analyzing the HVDC (High Voltage Direct Current) transmission system DC side harmonics situation means that provide the necessary technical.

Technical scheme of the present invention is as follows:

A kind of HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method seals in respectively current transformer S in each parallel branch in second branch road of wave filter on DC side ₁, S ₂..., S _n, and each current transformer seals in the earth terminal of each parallel branch; The flow through electric current of current transformer of measurement, and utilize the each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side that records.

The process of the each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side that described utilization records is: the electric current that measures is carried out Fourier decomposition, obtain individual harmonic current, composition and component parameters according to wave filter on DC side, calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, specifically may further comprise the steps:

Step 1, find the solution the current i that first branch road of obtaining wave filter on DC side flows through _ZH

Step 2, select a parallel branch k in second branch road, utilize Fourier transformation method to the current i of this parallel branch _ZLkCarry out Harmonic Decomposition, and with current i _ZLkIn the h subharmonic be written as the phasor form;

Step 3, find the solution and obtain second branch voltage u _ZLIn the h subharmonic;

Step 4, utilize Fourier transformation method, to current i _ZHCarry out Harmonic Decomposition, and with current i _ZHIn the h subharmonic be written as the phasor form;

Step 5, find the solution and obtain first branch voltage u _ZHIn the h subharmonic;

Step 6, with the results added in step 3 and the step 5, try to achieve HVDC (High Voltage Direct Current) transmission system dc voltage u _SThe h subharmonic voltage;

Step 7, repeating step 1-6 are tried to achieve HVDC (High Voltage Direct Current) transmission system dc voltage u _SEach harmonic voltage.

The process of the each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side that described utilization records is: according to the electric current that records and in conjunction with the impedance frequency characteristics of known wave filter on DC side, calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, specifically may further comprise the steps:

Step 1, find the solution the current i that first branch road of obtaining wave filter on DC side flows through _ZH

Step 2, to i _ZHCarry out Fourier decomposition, obtain current i _ZHThe effective value I of h subharmonic _{ZH (h)}With phasing degree θ _{ZH (h)}, h=1,2 ..., m;

Step 3, utilize the impedance frequency characteristics curve of wave filter on DC side to find the impedance magnitude Z of wave filter on DC side under the h subharmonic _(h)And phasing degree

, the I of integrating step 2 gained _{ZH (h)}And θ _{ZH (h)}Calculate HVDC (High Voltage Direct Current) transmission system dc voltage u _SThe h subharmonic voltage;

Step 4, repeating step 1-3 are tried to achieve HVDC (High Voltage Direct Current) transmission system dc voltage u _SEach harmonic voltage.

Compared with prior art, the invention has the beneficial effects as follows:

The present invention only needs to seal in current transformer in traditional wave filter on DC side, and the electric current of the current transformer that utilization records can calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side.The present invention is simple to operate, it is convenient to realize, measuring voltage harmonic wave precision is high, so that wave filter on DC side is when having traditional harmonic filtration function, have high voltage direct current harmonic voltage measurement function, have very high using value and marketing prospect in the occasion of high voltage harmonic voltage measurement.

Description of drawings

Fig. 1 is schematic diagram of the present invention;

Fig. 2 is the schematic diagram of the embodiment of the invention 2;

Fig. 3 is the impedance frequency characteristics figure of the double tunning wave filter on DC side of the embodiment of the invention 2.

Embodiment

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

As shown in Figure 1, currently used all wave filter on DC sides all can be divided into two parts, and namely (impedance of fundamental frequency is Z to first branch road _{H (1)}, China's fundamental frequency is 50Hz) and second branch road.Wherein second branch road is made of a plurality of branch circuit parallel connections again that (impedance of fundamental frequency is respectively Z _{L1 (1)}, Z _{L2 (1)}..., Z _{Ln (1)}).The present invention seals in respectively current transformer S in each parallel branch of second branch road ₁, S ₂..., S _nShould be noted simultaneously in order to reduce current transformer S ₁, S ₂..., S _nInsulating requirements, each current transformer need seal in each parallel branch near the part of earth point.

The invention provides two embodiment and find the solution high-pressure side DC voltage u _SHarmonic content.

Embodiment 1

Step 1, find the solution and obtain the current i that first branch road flows through _ZH:

$i_{\mathrm{ZH}}=\underset{k=1}{\overset{n}{\mathrm{\Σ}}}{i}_{\mathrm{ZLK}}---\left(1\right)$

Wherein, i _ZLkBe the electric current of k parallel branch in second branch road that records, k=1,2 ..., n;

Step 2, because the voltage u of second each parallel branch of branch road _ZLBe identical, can utilize the electric current of arbitrary branch road to solve this voltage, impedance of fundamental frequency describes as the current i ZL1 of the parallel branch of ZL1 (1) as example in second branch road: utilize Fourier Transform Technique, and can be to the current i that records _ZL1Carry out Harmonic Decomposition:

$i_{\mathrm{<figure-callout\; id="1"\; label="ZL"\; filenames="130726145415.png"\; state="\{\{state\}\}">ZL</figure-callout>}1}=\sqrt{2}\&CenterDot;\underset{h=1}{\overset{m}{\mathrm{\&Sigma;}}}\&CenterDot;(I_{\mathrm{ZL}1\left(h\right)}\&CenterDot;\sin ({\mathrm{\&omega;}}_{h}t+{\mathrm{\&theta;}}_{\mathrm{ZL}1\left(h\right)}))---\left(2\right)$

Wherein: h is overtone order, and m is the higher harmonics number of times paid close attention to (generally gets 30 times enough); ω _h=2 π hf are h subharmonic angular frequency, and wherein f is work frequency, and China is 50Hz; T is the time; I _{ZL1 (h)}And θ _{ZL1 (h)}Be respectively current i _ZL1In effective value and the phasing degree of h subharmonic.

With current i _ZL1In the h subharmonic be written as the phasor form:

${\stackrel{\&CenterDot;}{I}}_{\mathrm{ZL}1\left(h\right)}=I_{\mathrm{ZL}1\left(h\right)}<{\mathrm{\&theta;}}_{\mathrm{ZL}1\left(h\right)}---\left(3\right)$

Step 3, find the solution and obtain u _ZLIn the h subharmonic be:

${\stackrel{\&CenterDot;}{U}}_{\mathrm{ZL}\left(h\right)}={\stackrel{\&CenterDot;}{I}}_{\mathrm{ZL}1\left(h\right)}\&CenterDot;Z_{L1\left(h\right)}---\left(4\right)$

Z wherein _{L1 (h)}For impedance of fundamental frequency is Z _{L1 (1)}The impedance of parallel branch under the h subharmonic.Because all parallel branches all are to be made of resistance, electric capacity and inductance element, in the situation that known these component parameters, are easy to find the solution and obtain Z _{L1 (h)}

Step 4, utilize Fourier Transform Technique, can be to finding the solution the current i that obtains according to formula (1) _ZHCarry out Harmonic Decomposition:

$i_{\mathrm{ZH}}=\sqrt{2}\&CenterDot;\underset{h=1}{\overset{m}{\mathrm{\&Sigma;}}}(I_{\mathrm{ZH}\left(h\right)}\&CenterDot;\sin ({\mathrm{\&omega;}}_{h}t+{\mathrm{\&theta;}}_{\mathrm{ZH}\left(h\right)}))---\left(5\right)$

Wherein: I _{ZH (h)}And θ _{ZH (h)}Be respectively current i _ZHIn effective value and the phasing degree of h subharmonic.

With current i _ZHIn the h subharmonic be written as the phasor form:

${\stackrel{\&CenterDot;}{I}}_{\mathrm{ZH}\left(h\right)}=I_{\mathrm{ZH}\left(h\right)}<{\mathrm{\&theta;}}_{\mathrm{ZH}\left(h\right)}---\left(6\right)$

Step 5, find the solution and obtain first branch voltage u _ZHIn the h subharmonic be:

${\stackrel{\&CenterDot;}{U}}_{\mathrm{ZH}\left(h\right)}={\stackrel{\&CenterDot;}{I}}_{\mathrm{ZH}\left(h\right)}\&CenterDot;Z_{H\left(h\right)}---\left(7\right)$

Z wherein _{H (h)}For impedance of fundamental frequency is Z _{H (1)}The impedance of first branch road under the h subharmonic.Because first all branch roads all is to be made of resistance, electric capacity and inductance element, in the situation that known these component parameters, is easy to find the solution and obtains Z _{H (h)}

Step 6, with the results added in step 3 and the step 5, try to achieve HVDC (High Voltage Direct Current) transmission system dc voltage u _SThe h subharmonic voltage;

Ac high-voltage side voltage u then _SIn the h subharmonic voltage be:

${\stackrel{\&CenterDot;}{U}}_{S\left(h\right)}={\stackrel{\&CenterDot;}{U}}_{\mathrm{ZH}\left(h\right)}+{\stackrel{\&CenterDot;}{U}}_{\mathrm{ZL}\left(h\right)}---\left(8\right)$

Step 7, repeating step 1-6, to all subharmonic (h=1,2 ..., m) all carry out the calculating shown in above-mentioned, can calculate HVDC (High Voltage Direct Current) transmission system DC voltage u _SEach harmonic voltage, these voltages namely are to carry out the needed value of frequency analysis.

Embodiment 2

Step 1, find the solution according to formula (1) and to obtain the current i that first branch road flows through _ZH

Step 2, to i _ZHCarry out Fourier decomposition, find the solution and obtain current i _ZHThe effective value I of h subharmonic _{ZH (h)}With phasing degree θ _{ZH (h)}, h=1,2 ..., m;

Step 3, utilize the impedance frequency characteristics curve of wave filter on DC side to find the impedance magnitude Z of wave filter on DC side under the h subharmonic _(h)And phasing degree

, the I of integrating step 2 gained _{ZH (h)}And θ _{ZH (h)}Calculate HVDC (High Voltage Direct Current) transmission system dc voltage u _SThe h subharmonic voltage;

For designed DC filter, its impedance frequency characteristics is very important characteristic, known when design, what impedance frequency characteristics provided is the impedance magnitude and the value of phasing degree under different harmonic frequencies of whole wave filter on DC side, and is depicted as the form of curve.Therefore, can find the impedance magnitude Z of wave filter on DC side under the h subharmonic by this family curve _(h)And phasing degree

, utilize following formula to calculate HVDC (High Voltage Direct Current) transmission system dc voltage u _SIn the h subharmonic voltage be:

Step 4, repeating step 1-3, to all subharmonic (h=1,2 ..., m) all carry out the calculating shown in above-mentioned, can calculate HVDC (High Voltage Direct Current) transmission system dc voltage u _SEach harmonic voltage, these voltages namely are to carry out the needed value of frequency analysis.

The concrete computation process of embodiment 2 is described below in conjunction with Fig. 2 and Fig. 3.C among Fig. 2 ₁, L ₁, R ₁, C ₂, L ₂, R ₂The element of conventional DC side double-tuned filter, S ₁And S ₂Be the current transformer that seals in.Fig. 3 is the impedance frequency characteristics of this double-tuned filter.For example, can find the impedance magnitude of this wave filter under 15 subharmonic and phasing degree respectively 378 Ω and 89 °, in conjunction with the current i that calculates _ZHThe effective value I of the 15th subharmonic _{ZH (15)}With phasing degree θ _{ZH (15)}, according to formula (9), can calculate HVDC (High Voltage Direct Current) transmission system dc voltage u _S15 subharmonic voltages be:

Can see, this method can be carried out HVDC (High Voltage Direct Current) transmission system dc voltage u more quickly _SEach harmonic voltage calculate.

The present invention seals in current transformer in conventional wave filter on DC side branch road, the electric current that measures is carried out Fourier decomposition, obtain individual harmonic current, according to composition and the component parameters of wave filter on DC side, can calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side.Also can utilize the impedance frequency characteristics of known wave filter on DC side, calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, thereby can carry out the analysis of high-pressure system direct current harmonic voltage.The harmonic voltage measurement scheme of the high voltage direct current transmission system DC side based on wave filter on DC side of the present invention only needs simply improve on the basis of conventional wave filter on DC side, realize simple, for the accurate measurement that realizes the high voltage direct current harmonic voltage provides important technological means, have very high practical value and wide marketing application prospect.

Above embodiment is only for explanation the present invention's, but not limitation of the present invention, person skilled in the relevant technique, in the situation that do not break away from the spirit and scope of the present invention, can also make various conversion or modification, so all technical schemes that are equal to should belong within the category of the present invention also.

Claims (3)

1. a HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method is characterized in that: seal in respectively current transformer S in each parallel branch in second branch road of wave filter on DC side ₁, S ₂..., S _n, and each current transformer seals in the earth terminal of each parallel branch; The flow through electric current of current transformer of measurement, and utilize the each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side that records.

2. a kind of HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method according to claim 1, it is characterized in that: the process of the each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side that described utilization records is: the electric current that measures is carried out Fourier decomposition, obtain individual harmonic current, composition and component parameters according to wave filter on DC side, calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, specifically may further comprise the steps:

Step 1, find the solution the current i that first branch road of obtaining wave filter on DC side flows through _ZH

Step 2, select a parallel branch k in second branch road, utilize Fourier transformation method to the current i of this parallel branch _ZLkCarry out Harmonic Decomposition, and with current i _ZLkIn the h subharmonic be written as the phasor form;

Step 3, find the solution and obtain second branch voltage u _ZLIn the h subharmonic;

Step 4, utilize Fourier transformation method, to current i _ZHCarry out Harmonic Decomposition, and with current i _ZHIn the h subharmonic be written as the phasor form;

Step 5, find the solution and obtain first branch voltage u _ZHIn the h subharmonic;

Step 6, with the results added in step 3 and the step 5, try to achieve HVDC (High Voltage Direct Current) transmission system dc voltage u _SThe h subharmonic voltage;

Step 7, repeating step 1-6 are tried to achieve HVDC (High Voltage Direct Current) transmission system dc voltage u _SEach harmonic voltage.

3. a kind of HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method according to claim 1, it is characterized in that: the process of the each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side that described utilization records is: according to the electric current that records and in conjunction with the impedance frequency characteristics of known wave filter on DC side, calculate the each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, specifically may further comprise the steps:

Step 1, find the solution the current i that first branch road of obtaining wave filter on DC side flows through _ZH

Step 2, to i _ZHCarry out Fourier decomposition, obtain current i _ZHThe effective value I of h subharmonic _{ZH (h)}With phasing degree θ _{ZH (h)}, h=1,2 ..., m;

Step 3, utilize the impedance frequency characteristics curve of wave filter on DC side to find the impedance magnitude Z of wave filter on DC side under the h subharmonic _(h)And phasing degree

, the I of integrating step 2 gained _{ZH (h)}And θ _{ZH (h)}Calculate HVDC (High Voltage Direct Current) transmission system dc voltage u _SThe h subharmonic voltage;

Step 4, repeating step 1-3 are tried to achieve HVDC (High Voltage Direct Current) transmission system dc voltage u _SEach harmonic voltage.

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