RU2584338C1 - Method for determining static load characteristics from stress - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering and can be used to determine static load voltage characteristics. Method consists in that load node voltage change produces successive measured voltage and power values and measured voltage is converted into relative units. However, voltage and power are measured before and after each change in voltage, value determined load regulating effect KP_i for each pair of measured values of voltage and power. To filter obtained pairs of measurements, values of regulatory effect of KP_i which do not fall within specified confidence interval, method includes determining coefficients a ₀, a ₁, a ₂ by least squares method. Static load voltage polynomial

is taken as desired static load voltage characteristics.

EFFECT: technical result is to determine static voltage load characteristics in presence of irregular fluctuations and power drift.

1 cl, 3 dwg, 1 tbl

Description

The invention relates to electrical engineering and can be used to determine the static characteristics of the voltage load.

A known method for determining the static characteristics of the load voltage [Gurevich Yu.E., Libova L.E. The use of mathematical models of electric load in the calculation of energy systems and the reliability of power supply to industrial consumers. - M .: ELEKS-KM, 2008. - S. 211-215], in which successive voltage changes are made in the load node, voltage and power are measured, and the measured voltage and power values are converted to relative units. The resulting characteristic is used as a static characteristic of the load.

The condition for using this method is the stationarity of the test load. If irregular fluctuations and power drift take place, then this method cannot be used. In this case, a repeated experiment is required, which is often associated with a number of technical and organizational difficulties and is not always possible. In addition, there is no guarantee that during the repeated experiment the load will be stationary and the use of this method to determine the static characteristics of the load will be successful.

No methods are known for determining the static characteristics of a voltage load under conditions of significant irregular fluctuations and power drift.

The objective of the invention is to develop a method that allows to determine the static characteristics of the voltage load in the presence of irregular fluctuations and power drift.

This is achieved by the fact that, as in the prototype, successive voltage changes are made in the load node, voltage and power are measured, and the measured voltage values are converted to relative units.

According to the invention, the voltage and power are measured before and after each voltage change, the values of the regulatory effect of the load KP _{i are} determined for each pair of measured voltage and power values in accordance with the ratio:

where U _{* 1 (i)} and P _{1 (i)} are voltage values in relative units and power in named units, measured before the i-th voltage change,

i = 1, 2, ... - serial number of the voltage change,

U _{* 2 (i)} and P _{2 (i)} are voltage values in relative units and power in named units, measured after the i-th voltage change.

Then, the obtained pairs of measurements are filtered, the values of the regulatory effect KP _{i of} which do not fall within the given confidence interval, and the coefficients a ₀ , a ₁ , a _{2 are} determined by the least squares method from the expression

_BAZ wherein P _(i) - the base power value for the i-th pair of measurements,

N is the number of measurement pairs remaining after filtering.

The polynomial voltage load is taken as the desired static characteristic of the load.

The proposed method allows to determine the static characteristics of the voltage load even in the presence of irregular fluctuations and power drift due to the fact that from the entire array of experimental data such pairs of measurements are distinguished for which the load under study is stationary, that is, P _{BAZ (i)} = const, and the values of P _{BAS (i) are} determined along with the coefficients a ₀ , a ₁ , a ₂ from the condition of minimizing the sum of squares of deviations of the measurement results in relative units from the obtained static load characteristic.

Expression (2) is a system composed of equations of the form

taking into account the fact that for each pair of measurements U _{* 1 (i)} and U _{* 2 (i)} , P _{l (i)} and P _{2 (i), the} base power P _{BAS (i)} remains constant.

Irregular fluctuations and power drift can be taken into account as a change in the value of the base power, which is used to translate the measured power values into relative units. In the proposed method, the measurement of voltage and power values is carried out immediately before and after the voltage change, which minimizes the likelihood of a change in the base power between such measurements. In order to exclude pairs of measurements between which a base power change still occurs, the proposed method provides for filtering of measurement pairs by the values of the regulatory effect of the load. Since the values of the base power for each pair of measurements are not known in advance, in the proposed method they are selected based on the condition of minimizing the sum of squares of deviations of the measurement results from the obtained static load characteristics. This allows you to minimize the effect of irregular fluctuations and power drift on the resulting static load characteristics, which expands the scope of the proposed method in comparison with the prototype.

In FIG. 1 - presents a diagram of a device that implements the proposed method.

In FIG. 2 - presents pairs of measured voltage and power values in named units.

In FIG. 3 - presents the obtained static characteristic of the load and a pair of voltage and power measurements after filtering, converted into relative units.

Table 1 shows the measured values of voltage U _{1 (i)} and U _{2 (i)} and power P _{1 (i)} and P _{2 (i)} in named units, as well as the corresponding values of the regulating effect of the load KP _i .

The method of determining the static characteristics of the voltage load can be carried out using the device (Fig. 1), in which the first output of the control unit 1 is connected to a voltage control device under the load of the supply transformer 2. The second output of the control unit 1 is connected to the input of the measurement unit 3, inputs which are connected to the measuring transformers of current 4 and voltage 5. The output of the measuring unit 3 is connected to the input of the control unit 6 and to the input of the filtering unit 7. The output of the control unit 6 nen with an input filter unit 7, whose output is connected to an input of determination unit 8 coefficients.

Measurement block 3 can be performed using an AR5 power analyzer. The control unit 1, the control effect unit 6, the filtering unit 7, the coefficient determination unit 8 can be performed on microcontrollers of the 51 series atmel AT89S53.

As an example, a method for determining the static characteristics of the active load power of Sibkabel OJSC in Tomsk by voltage is given. The load of Sibkabel OJSC has a sharply alternating character, due to the characteristics of production, which is accompanied by irregular fluctuations and power drift, therefore, it is impossible to determine the static characteristics of the load by voltage by known methods.

The successive voltage change in the load node is performed using the voltage control device under load of the supply transformer 2, and the voltage and power are measured using the measurement unit 3. To coordinate the measurement process with the voltage change process, control unit 1 is used, in which, in accordance with the program the experiment consistently form the control actions on the measuring unit 3, the drive of the voltage regulation device under load of the supply transformer 2 and again to the measurement unit 3. In accordance with the control actions before and after each voltage change in the measurement unit 3, the values of the three-phase active power P _{1 (i)} and P _{2 (i)} and the current average phase voltage value U _{1 (i)} and U are measured _{2 (i)} , where i = 1, 2, ... is the sequence number of the voltage change, index 1 means that the measurement was made before the voltage change, and index 2 means that the measurement was made after the voltage change (table 1, FIG. 2).

In measurement unit 3, the measured voltage values are converted to relative units:

wherein for transfer of measured voltage values in relative units, as in prior art, use one and the same constant value of the base voltage (in this case U _BAZ = 6200 V).

Subsequently, the obtained pair of the measured values U _{* 1 (i)} and U _{* 2 (i),} P _{1 (i)} and P _{2 (i)} simultaneously output from the measurement unit 3 to the input of block regulatory effects 6 and to the input of the filtering unit 7. In the block of regulatory effects 6 determine the values of the regulatory effects of the load KP _i for each pair of measurements in accordance with relation (1).

The values of the regulatory effects of the load KP _i (table 1) come from the output of the regulatory effects unit 6 to the input of the filtration unit 7, where the resulting pairs of measurements are filtered U _{* 1 (i)} and U _{* 2 (i)} , P _{1 (i)} and P _{2 (i)} , the values of the regulatory effect KP _{i of} which do not fall within the specified confidence interval (in this case, 0.75 ÷ 2). The excluded measurement pairs are shown in bold italics in Table 1 and grayed out in the graph of FIG. 2.

с полученными коэффициентами a ₀=1,458, a ₁=-2,233, a ₂=1,775.From the output of the filtering unit 7, the remaining pairs of voltage values U _{* 1 (i)} and U _{* 2 (i)} , and power P _{1 (i)} and P _{2 (i)} are supplied to the input of the coefficient determination unit 8, where the coefficients a ₀ , a ₁ , a ₂ by the least squares method from expression (2). The polynomial voltage load is taken as the desired static characteristic of the load.

with the obtained coefficients a ₀ = 1.458, a ₁ = -2.233, a ₂ = 1.775.

In the graph of FIG. Figure 3 presents the obtained static characteristic of the active load power of Sibkabel OJSC by voltage, as well as the measured voltage and power values converted into relative units. The graph shows that the deviation of the measured values from the characteristics are not significant. Thus, the example of the active load power of Sibkabel OJSC shows the operability of the proposed method even in the presence of irregular load fluctuations and power drift. The operation of the device in determining the static characteristics of the reactive power of the load voltage will be similar.

Claims (1)

A method for determining the static characteristics of a voltage load, in which successive voltage changes are made in the load node, voltage and power are measured, the measured voltage values are converted into relative units, characterized in that the voltage and power are measured before and after each voltage change, and the values of the regulatory effect are determined load KP _i for each pair of measured values of voltage and power in accordance with the ratio:

where U _{* 1 (i)} and P _{1 (i)} are voltage values in relative units and power in named units, measured before the i-th voltage change,
i = 1, 2, ... - serial number of the voltage change,
U _{* 2 (i)} and F _{2 (i)} - values of voltage in arbitrary units and a power in the named units measured after i-th voltage changes,
filtering the obtained pairs of measurements, the values of the regulatory effect of CR _i which do not fall within a given confidence interval, determine the coefficients a ₀ , a ₁ , and ₂ using the least squares method from the expression

where R _{BAZ (i)} is the value of the base power for the i-th pair of measurements,
N is the number of measurement pairs remaining after filtering,
take the polynomial voltage load as the desired static characteristic $${\text{P}}_{\text{*}}{\text{(U}}_{\text{*}}\text{)}={\text{à}}_{\text{0}}+{\text{à}}_{\text{one}}\cdot U_{*}+a_2\cdot U_{*}^2$$

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