CN103364618B - A kind of HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method - Google Patents

Abstract

The invention provides a kind of HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method, be specially: in the branch road of the wave filter on DC side of HVDC (High Voltage Direct Current) transmission system, seal in current transformer, utilize the electric current measured and obtain, in conjunction with each device parameter values of wave filter on DC side or the frequency versus impedance characteristic of known wave filter on DC side, calculate the harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side.The present invention is simple to operate, and only need carry out simple transformation on the basis of Traditional DC side filter can realize, and the precision measuring harmonic voltage is high, extends the function of wave filter on DC side, has comparatively high performance-price ratio; The present invention has very high using value and marketing prospect in the occasion of HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement.

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 have circuit cost low, be applicable to long distance power transmission, there is no system stability problem, regulate the advantages such as quick, reliable, be applied to long distance power transmission and the interconnected occasion of AC system more and more.But because the current conversion station be made up of power electronic devices used in DC transmission system can produce a large amount of harmonic waves, Harmfulness Caused by Harmonics is produced to whole DC transmission system.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 harness of harmonic wave targetedly, the correctness of checking wave filter on DC side design and validity.

But in the measuring method of currently used high pressure harmonic voltage and equipment, adopt the scheme of resistor divider and capacitor dividing potential drop to need to adopt special equipment, and these equipment volume are large, expensive.Capacitance type potential transformer is adopted to carry out the method that high pressure harmonic voltage measurement is most convenient economy, but because the internal resonance condition of capacitance type potential transformer under harmonic condition will be destroyed, measuring harmonic wave by there is larger error, directly cannot apply capacitance type potential transformer and carrying out 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 up of multiple branch circuit parallel connection again that (impedance of fundamental frequency is respectively Z _{l1 (1)}, Z _{l2 (1)}..., Z _{ln (1)}).Therefore, if simply can transform wave filter on DC side widely used in current HVDC (High Voltage Direct Current) transmission system, design the wave filter simultaneously taking into account customary DC side harmonic and DC side harmonics measurement function, high-precision high voltage direct current harmonic voltage measurement can be provided while carrying out harmonic filtration.Thus provide for realizing the voltage measurement of HVDC (High Voltage Direct Current) transmission system DC side harmonics the scheme that a kind of cost performance is very high, have great practical value and marketing prospect.

Summary of the invention

For background technology Problems existing, 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 up of multiple branch circuit parallel connection 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 DC side filter, Fourier decomposition is carried out to measuring the electric current obtained, obtain individual harmonic current, according to composition and the component parameters of wave filter on DC side, calculate each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side.Also can utilize the impedance frequency characteristics measuring electric current and the known wave filter on DC side obtained, calculate each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side.The invention provides the high voltage direct current harmonic voltage measurement means that a kind of cost performance is higher, to provide the necessary technical means for analyzing HVDC (High Voltage Direct Current) transmission system DC side harmonics situation.

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 current transformer S in each parallel branch in second branch road of wave filter on DC side respectively ₁, S ₂..., S _n, and each current transformer seals in the earth terminal of each parallel branch; Measure the electric current flowing through current transformer, and utilize each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side recorded.

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

Step 1, solve the current i that first branch road of obtaining wave filter on DC side flows through _zH;

Step 2, the parallel branch k selected in second branch road, utilize Fourier transformation method to the current i of this parallel branch _zLkcarry out Harmonic Decomposition, and by current i _zLkin h subharmonic be written as phasor form;

Step 3, solve and obtain second branch voltage u _zLin h subharmonic;

Step 4, utilize Fourier transformation method, to current i _zHcarry out Harmonic Decomposition, and by current i _zHin h subharmonic be written as phasor form;

Step 5, solve and obtain first branch voltage u _zHin h subharmonic;

Step 6, by the results added in step 3 and step 5, try to achieve HVDC (High Voltage Direct Current) transmission system DC voltage u _sh subharmonic voltage;

Step 7, repetition step 1-6, try to achieve HVDC (High Voltage Direct Current) transmission system DC voltage u _seach harmonic voltage.

The process of 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 recorded and in conjunction with the impedance frequency characteristics of known wave filter on DC side, calculate each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, specifically comprise the following steps:

Step 1, solve 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, the impedance frequency characteristics curve of wave filter on DC side is utilized to find the impedance magnitude Z of wave filter on DC side under 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 _sh subharmonic voltage;

Step 4, repetition step 1-3, try 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 need seal in current transformer in Traditional DC side filter, utilizes the electric current of the current transformer recorded can calculate 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, and measuring voltage harmonic wave precision is high, makes wave filter on DC side while having traditional harmonic filtration function, there is high voltage direct current harmonic voltage measurement function, in the occasion of high voltage harmonic voltage measurement, there is very high using value and marketing prospect.

Accompanying drawing explanation

Fig. 1 is schematic diagram of the present invention;

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

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

Embodiment

Below in conjunction with accompanying drawing, the present invention will be further described.

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 up of multiple branch circuit parallel connection again that (impedance of fundamental frequency is respectively Z _{l1 (1)}, Z _{l2 (1)}..., Z _{ln (1)}).The present invention seals in current transformer S respectively in each parallel branch of second branch road ₁, S ₂..., S _n.Should be noted to reduce current transformer S simultaneously ₁, S ₂..., S _ninsulating requirements, each current transformer need seal in the part of each parallel branch near earth point.

The invention provides two embodiments to solve high-pressure side DC voltage u _sharmonic content.

Embodiment 1

Step 1, solve the current i obtaining first branch road and flow through _zH:

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

Wherein, i _zLkfor the electric current of a kth parallel branch in second branch road of recording, k=1,2 ..., n;

Step 2, voltage u due to each parallel branch of second branch road _zLbe identical, the electric current of arbitrary branch road can be utilized to solve this voltage, be described for the current i ZL1 of impedance of fundamental frequency in second branch road for the parallel branch of ZL1 (1): utilize Fourier Transform Technique, can to the current i recorded _zL1carry out Harmonic Decomposition:

$i_{\mathrm{ZL}1}=\sqrt{2}\·\underset{h=1}{\overset{m}{\mathrm{\Σ}}}\·(I_{\mathrm{ZL}1\left(h\right)}\·\sin ({\mathrm{\ω}}_{h}t+{\mathrm{\θ}}_{\mathrm{ZL}1\left(h\right)}))---\left(2\right)$

Wherein: h is overtone order, m is paid close attention to most higher harmonics number of times (generally get 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 the effective value of h subharmonic and phasing degree.

By current i _zL1in h subharmonic be written as 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, solve and obtain u _zLin h subharmonic be:

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

Wherein Z _{l1 (h)}for impedance of fundamental frequency is Z _{l1 (1)}the impedance of parallel branch under h subharmonic.Because all parallel branches are all be made up of resistance, electric capacity and inductance element, when these component parameters known, be easy to solve and obtain Z _{l1 (h)}.

Step 4, utilize Fourier Transform Technique, can solve to according to formula (1) current i obtained _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 the effective value of h subharmonic and phasing degree.

By current i _zHin h subharmonic be written as 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, solve and obtain first branch voltage u _zHin h subharmonic be:

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

Wherein Z _{h (h)}for impedance of fundamental frequency is Z _{h (1)}the impedance of first branch road under h subharmonic.Because first all branch roads is all be made up of resistance, electric capacity and inductance element, when these component parameters known, be easy to solve and obtain Z _{h (h)}.

Step 6, by the results added in step 3 and step 5, try to achieve HVDC (High Voltage Direct Current) transmission system DC voltage u _sh subharmonic voltage;

Then ac high-voltage side voltage u _sin 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, repeat step 1-6, to all subharmonic (h=1,2 ..., m) all carry out above-mentioned shown calculating, HVDC (High Voltage Direct Current) transmission system DC voltage u can be calculated _seach harmonic voltage, namely these voltages are carry out the value required for frequency analysis.

Embodiment 2

Step 1, solve the current i obtaining first branch road and flow through according to formula (1) _zH;

Step 2, to i _zHcarry out Fourier decomposition, solve 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, the impedance frequency characteristics curve of wave filter on DC side is utilized to find the impedance magnitude Z of wave filter on DC side under 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 _sh subharmonic voltage;

For designed DC filter, its impedance frequency characteristics is very important characteristic, know when designing, impedance magnitude and the phasing degree value under different harmonic frequency of what impedance frequency characteristics provided is whole wave filter on DC side, and be depicted as the form of curve.Therefore, the impedance magnitude Z of wave filter on DC side under h subharmonic can be found by this family curve _(h)and phasing degree , utilize following formula to calculate HVDC (High Voltage Direct Current) transmission system DC voltage u _sin h subharmonic voltage be:

Step 4, repeat step 1-3, to all subharmonic (h=1,2 ..., m) all carry out above-mentioned shown calculating, HVDC (High Voltage Direct Current) transmission system DC voltage u can be calculated _seach harmonic voltage, namely these voltages are carry out the value required for frequency analysis.

The concrete computation process of embodiment 2 is described below in conjunction with Fig. 2 and Fig. 3.C in Fig. 2 ₁, L ₁, R ₁, C ₂, L ₂, R ₂the element of customary DC side double-tuned filter, S ₁and S ₂for the current transformer sealed in.Fig. 3 is the impedance frequency characteristics of this double-tuned filter.Such as, impedance magnitude and phasing degree 378 Ω and 89 ° respectively of this wave filter under 15 subharmonic can be found, in conjunction with the current i calculated _zHthe effective value I of the 15th subharmonic _{zH (15)}with phasing degree θ _{zH (15)}, according to formula (9), HVDC (High Voltage Direct Current) transmission system DC voltage u can be calculated _s15 subharmonic voltages be:

Can see, this method can carry 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 customary DC side filter branch road, Fourier decomposition is carried out to measuring the electric current obtained, obtain individual harmonic current, according to composition and the component parameters of wave filter on DC side, each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side can be calculated.Also can utilize the impedance frequency characteristics of known wave filter on DC side, calculate each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, thus the analysis of high-pressure system direct current harmonic voltage can be carried out.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 simply need be improved on the basis of customary DC side filter, realize simple, for the accurate measurement realizing high voltage direct current harmonic voltage provides important technological means, there is very high practical value and wide marketing application prospect.

Above embodiment is used for illustrative purposes only, but not limitation of the present invention, person skilled in the relevant technique, without departing from the spirit and scope of the present invention, can also make various conversion or modification, therefore all equivalent technical schemes also should belong within category of the present invention.

Claims (2)

1. a HVDC (High Voltage Direct Current) transmission system DC side harmonics voltage measurement method, is characterized in that: seal in current transformer S respectively 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; Measure the electric current flowing through current transformer, and utilize each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side recorded; Utilize each harmonic voltage of the Current calculation HVDC (High Voltage Direct Current) transmission system DC side recorded, detailed process is: carry out Fourier decomposition to measuring the electric current obtained, obtain individual harmonic current, according to composition and the component parameters of wave filter on DC side, calculate each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, specifically comprise the following steps: step 1, solve the current i that first branch road of obtaining wave filter on DC side flows through _zH;

Step 2, the parallel branch k selected in second branch road, utilize Fourier decomposition method to the current i of this parallel branch _zLkcarry out Harmonic Decomposition, and by current i _zLkin h subharmonic be written as phasor form;

Step 3, solve and obtain second branch voltage u _zLin h subharmonic;

Step 4, utilize Fourier decomposition method, to current i _zHcarry out Harmonic Decomposition, and by current i _zHin h subharmonic be written as phasor form;

Step 5, solve and obtain first branch voltage u _zHin h subharmonic;

Step 6, by the results added in step 3 and step 5, try to achieve HVDC (High Voltage Direct Current) transmission system DC voltage u _sh subharmonic voltage;

Step 7, repetition step 1-6, try to achieve HVDC (High Voltage Direct Current) transmission system DC voltage u _seach harmonic voltage.

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 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 recorded and in conjunction with the impedance frequency characteristics of known wave filter on DC side, calculate each harmonic voltage of HVDC (High Voltage Direct Current) transmission system DC side, specifically comprise the following steps:

Step 1, solve 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, the impedance frequency characteristics curve of wave filter on DC side is utilized to find the impedance magnitude Z of wave filter on DC side under 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 _sh subharmonic voltage;

Step 4, repetition step 1-3, try to achieve HVDC (High Voltage Direct Current) transmission system DC voltage u _seach harmonic voltage.