RU2573706C2 - Method of identification of higher harmonics source - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relaters to electric engineering and electric power industry, namely to methods of the assessment of electric energy quality. The method can be used in power supply systems of industrial enterprises with permanent load to determine the source of harmonic distortions both at the power grid side, and from the non-linear load side of the enterprise. The method of the higher harmonics source identification means the determination of a position of the distortion source in AC grid, containing distortion loads, a source of grid voltage of a sine shape, a power line with an end value of internal active and reactive impedances, and connected in parallel power consumers, a part of them is assumed as the distortion loads with nonsinusoidal current at the grid input. Wherein for the analysis of the higher harmonics source in the grid control point in parallel to the load a filter is connected, it is set to series resonance to the frequency of the studied harmonic. Further a relationship between the current of the studied system harmonic I_S and active impedance of the filter R_f, is determined, based on the analysis of the system current at the higher harmonic relationship to the active impedance of the filter the position of the source of harmonic distortions is determined.

EFFECT: simplified identification of the higher harmonics source, possibility of use without the termination of power supply, and use at operated objects with installed filter compensating devices.

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Description

The invention relates to electrical engineering and the electric power industry, and in particular to methods for evaluating the quality of electric power. The method can be used in power supply systems of industrial enterprises with a constant load to determine the source of non-linear distortions both from the supply network and from the non-linear load of the enterprise itself.

A known method of accounting for the consumption of active electric energy (patent WO 2012148316 A1, publ. 01.11.13), which consists in taking into account the consumption of active electric energy, in which the active power is measured by continuously measuring the voltage and current in the connected load, multiplying the measured voltage and current with multiplying by the load power factor (cosine of the load angle), the subsequent integration over time of the measured power, which gives the recorded consumption of active electric energy consumed by the load mains, characterized in that the non-sinusoidal voltages and currents of electric networks above multiplication is performed only for the values of the main (first) harmonic voltage and current and the cosine of the angle between them. This method allows you to evaluate the active power consumed at the fundamental.

The disadvantage of this method is the inability to assess the contribution of the distortion source both from the supply network and from the load side.

A known method of harmonic signal analysis (RF patent No. 2010246, publ. 30.03.1994), which consists in comparing the signal under study with a reference sinusoidal signal with the frequency of the first harmonic, while at certain times for different phase shifts between the signals determine the modules of the ratio of the instantaneous values of the two signals and by deviating the values of these modules of relations between themselves, one judges the degree of higher harmonics in the signal under study.

The disadvantage of this method is the inability to identify the source of distortion in the electrical network of the enterprise.

There is a method of identifying and evaluating distorting loads in AC power (RF patent No. 2206099, publ. 06/10/2003), adopted as a prototype. The principle of operation of this method is to determine the connection point of the distorting load to the feeder line by determining the sign and magnitude of the active power of the higher harmonics. To simplify the analysis, the search for the power of higher harmonics is proposed to be replaced by measuring the component of the active power of the main harmonic of an ideal symmetrical valve, the proposed introduction of which could lead to the existing value and form of voltage and current at the network reference point. To assess the total power of the higher harmonics of the distorting load, the indicated power of the first harmonic of the valve is multiplied by a proportionality coefficient, which depends on the values of the active resistances of the network sections from different sides from the connection point of the specified load.

The disadvantages of this method include the need for interruption of power supply for the time the valve is connected to the network, as well as the need to determine the proportionality coefficients for assessing the power of distortions introduced from different sides of the measurement site to estimate the total power of the higher harmonics.

The technical result of the invention is to identify the source of higher harmonics by including in the network a filter compensating device tuned to the frequency of the harmonic under study, and assessing the dependence of the system current on the active resistance of the filter compensating device. According to the results of the analysis of the dependence, the source of higher harmonics is identified with the aim of their further compensation.

The technical result is achieved by the fact that, as a device for analyzing the sources of higher harmonics at the control point of the network, a filter connected in series with the resonance to the frequency of the harmonic being studied is connected in parallel to the load, then the dependence of the current of the investigated harmonic of the system I _S on the active resistance of the filter R _{Ф is} removed according to the analysis the dependences of the system current at higher harmonics on the active resistance of the filter determine the location of the source of nonlinear distortion.

If the dependence is convex in nature, distortions from the load side prevail, if the dependence is concave or concave with the presence of an extremum, the mains contributes most to the distortions, this experiment is carried out for all harmonics whose contribution to the overall shape of the current and voltage curves is most significant , on the basis of these conclusions, a further method of devices for suppressing and compensating for higher harmonics and their installation location is made in order to improve the quality of electricity. It is possible to judge the location of the source of distortion both from the supply network and from the load side without interruption of power supply to the facility, the use of complex computing devices, there is a basis for a more appropriate choice of devices for suppressing and compensating for higher harmonics and their installation location to improve the quality of electricity, which leads to an increase in the resource of electrical equipment, a decrease in the number of false positives of automation devices, and an improvement in the quality of products and in the enterprise

The proposed method is illustrated by the drawings shown in FIG. 1 and FIG. 2, where in FIG. 1 shows an equivalent circuit of an electric network, including a voltage source, a power line with a finite value of internal active and reactive resistance and consumers connected in parallel, some of which belong to the category of distorting loads with a non-sinusoidal current shape at the network input, FIG. 1: U ₁ , U ₂ , ..., U _n - voltage sources of various harmonics representing the parameters of the supply network, R _S , X _S - active and reactive resistance of the system (internal resistance of the source and supply line), R _H , X _H - parameters linear load, I ₁ , I ₂ , ... I _n - current sources representing a non-linear load with a non-sinusoidal current shape at the network input, X _C , X _L , R _Ф - filter compensating device parameters. The power supply circuit is shown in the form shown in FIG. 1, then a filter-compensating device tuned to the frequency of the harmonic under study is connected at the measurement point, i.e. the following inequality is necessary:

where ω _res is the resonance frequency of the filter compensating device.

To obtain the dependences of the current of the system at the harmonic under study on the active resistance of the filter shown in FIG. 2, an analysis was made of the equation expressing the current of the system as a function of the active resistance of the filter.

The equation has the form:

; $$\dot{I}=I$$

).We consider the resistance of the installed filter to be purely active, since the filter is tuned to the harmonic under study. We also take into account the assumptions according to which the phase angles of the current source (non-linear load) and voltage source (mains) are taken equal to zero ( $$\dot{U}=U$$

; $$\dot{I}=I$$

)

As a result of the transformations, the dependence of the system current module on the active resistance of the filter in the analytical form is obtained:

where the coefficients are respectively equal to:

a = (U · R _H ) ² + (I · R _H · X _H + U · X _H ) ² ;

b = 2 · (U · R _H · X _H ) · (I · R _H · X _H + U · X _H );

c = (U · R _H · X _H ) ² ;

d = (R _S · R _H -X _S · X _H ) + (R _H · X _H + R _S · X _H + R _H · X _S );

e = 2 [(R _S · R _H -X _S · X _H ) (- X _S · X _H · R _H ) + R _S · X _H · R _H (R _H · X _H + R _S · X _H + R _H · X _S )];

f = (- X _S · X _H · R _H ) ² + (R _S · X _H · R _H ) ² .

The dependences of the system current modulus on the active resistance of the filter-compensating device turned on for various combinations of distortion sources are shown in FIG. 2, where the upper curve is the dependence of the current module of the system at the harmonic under study on the active resistance of the filter compensating device at the source of distortion from the mains, the lower curve is the same dependence at the source of distortion only from the side of the nonlinear load, the dashed line indicates the system current without connecting the filtering device , intermediate curves were obtained for various combinations of distortions both from the mains and from the load side.

The method is as follows - the presence of higher harmonics in the electric network is estimated, the filter-compensating device is calculated and selected, then included in the network and the current module of the system depends on the active resistance of the filter at the harmonic under study. By analyzing this dependence, the contribution of both the supply network and the non-linear load is estimated in order to select means for compensating for non-linear distortions and the installation location.

From the results obtained by calculation it follows that a function that has a concave or convex shape with an extremum (dependences indicated by a solid line in Fig. 2) indicates a voltage distortion caused by the mains if the function is convex in nature, without extrema (dependencies , indicated by the dashed-dotted line in Fig. 2), the current distortion caused by the nonlinear load has the greatest effect.

The advantage of the method for identifying the source of higher harmonics is the simplicity of its implementation, the cost-effectiveness of the device for its implementation, the possibility of its application without interruption in power supply, as well as the use of existing facilities with installed filter compensating devices.

Claims (1)

A method for identifying a source of higher harmonics, which consists in determining the location of the source of distortion in an alternating current electric network containing distorting loads, a sinusoidal mains voltage source, a supply line with a finite value of internal active and reactive resistance and parallel-connected electricity consumers, some of which belong to the category distorting loads with a non-sinusoidal current shape at the network input, characterized in that as a device for analysis Source of higher harmonics in the control point of the network parallel to the load connected filter tuned to series resonance at the frequency of the harmonic, then remove the dependence of the current study harmonic system I _S by R _F active filter resistance, the analysis function of the system current higher harmonic of the active filter resistance determined location of the source of nonlinear distortion.

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