RU2569179C1 - Method for determining static load characteristics against voltage - Google Patents

Abstract

FIELD: electricity.SUBSTANCE: method for determining static load characteristics against voltage consists in in-series changes in voltage carried out in the load node, voltage and power are measured and translated into relative units. At that voltage and power are measured before and upon each measurement of voltage, load controlling effect is defined for each pair of measured voltage and power values and obtained pairs of measurements are filtered using values of load controlling effect. Then at translation of power values into relative units the first approximation of base power value Cis determined for each pair of measurements, the obtained values of voltage and power in relative units are approximated by polynom P(U)=a+a·U+a·U, at that coefficients a, a, aare defined by least-squares technique. Mean-square deviation is defined for values of voltage and power in relative units from the obtained polynom and the second approximation of the base power value is determined for each pair of measurements. Then translation of power values to relative units is repeated, coefficients a, a, aand mean-square deviation are defined, and the next approximation of the base power value is repeated till mean-square deviation is reduced with each next stage. Polynom with coefficients a, a, acorresponding to minimum mean-square deviation is taken as the target static load characteristic.EFFECT: determination of static load characteristic against voltage at non-regular oscillations and drift of power.3 dwg, 2 tbl

Description

The invention relates to the field of 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 .: publishing house ELEKS-KM, 2008. - p. 211-215], [Experimental studies of power systems / L.M. Gorbunova, M.G. Tailor, R.S. Rabinovich and others; under the editorship of S.A. Sovalova, - M.: Energoatomizdat, 1985. - p. 45-48], in which successive voltage changes are made in the load node and voltage and power values are measured. Then the measured 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 repeat experiment is required. Repeated experiment 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 and power 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 for each pair of measured values of voltage and power are determined, and the resulting pairs of measurements are filtered by the values of the regulatory effect of the load. Then, when converting the power values to relative units, they determine the first approximation of their base power value R _{BAZ (i)} for each pair of measurements, approximate the obtained voltage and power values in relative units by a polynomial

, $$P_{*}\left(U_{*}=a_0+a_{\mathrm{one}}\cdot U_{*}+a_2\cdot U_{*}^2\right)$$

,

moreover, the coefficients a ₀ , a ₁ , and _{2 are} determined by the least squares method according to the dependencies:

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

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

The standard deviation of the voltage and power values in relative units from the obtained polynomial is determined and the second approximation of its base power value for each pair of measurements is determined:

Next, the translation of the power values into relative units, determination of the coefficients a ₀ , a ₁ , and ₂ , determination of the standard deviation and determination of the next approximation of the basis power values are repeated until the standard deviation decreases. The polynomial with the coefficients a ₀ , a _x , and ₂ corresponding to the minimum standard deviation is taken as the desired static characteristic of the voltage load.

The proposed method allows to determine the static characteristics of the load voltage even in the presence of irregular fluctuations and power drift due to the fact that the measurement of voltage and power is carried out before and after each voltage change, after which the resulting pairs of measurements are filtered by the values of the regulatory effect of the load, and when translating power values in relative units for each pair of measurements, the values of the basis powers are chosen such that the standard deviation of the cut measurement measurements in relative units of the obtained static load characteristics were minimal.

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 standard deviation 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 shows a diagram of a device that implements the proposed method.

In FIG. Figure 2 shows the static characteristic of the load and the results of voltage and power measurements obtained as a first approximation of the basis power values.

In FIG. Figure 3 shows the static characteristic of the load and the results of voltage and power measurements obtained from the basis power values corresponding to the minimum standard deviation.

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

Table 2 shows the first approximation of the basis power value R _{BAZ (i)} for each pair of measurements.

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 effects unit bis the input of the filtering unit 7. The output of the control effects unit 6 nen with the input of the filtering unit 7, the output of which is connected to the input of the unit for setting the base power values 8, the output of which is connected to the first input of the casting unit 9, the output of which is connected to the input of the coefficient determination unit 10. The output of the coefficient determination unit 10 is connected to the input of the error determination unit 11, the output of which is connected to the input of the refinement unit of the base power values 12, the output of which is connected to the second input of the cast unit 9.

Measurement block 3 can be performed using an AR5 power analyzer. Control unit 1, control effects unit 6, filtering unit 7, basis power value setting unit 8, reduction unit 9, coefficient determination unit 10, error determination unit 11, basis power value refinement unit 12 can be performed on atmel AT89S53 series microcontrollers 51 .

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 measuring unit 3. In accordance with the control actions before and after each voltage change in the measuring 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 is the serial number of the measurement pair, index 1 means that the measurement was made before the voltage changed, and index 2 means that the measurement was made after the voltage change. Further, the obtained pairs of measured values of U _{1 (i)} and U _{2 (i)} , P _{1 (i)} and P _{2 (i)} (table 1) simultaneously come from the output of measurement unit 3 to the input of the control effects unit 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 the ratio:

The values of the regulatory effects of the load KP _i (table 1) are received from the output of the regulatory effects unit 6 to the input of the filtration unit 7, where the resulting pairs of measurements U _{1 (i)} and U _{2 (i)} , P _{1 (i)} and P _{2 ( i)} according to the value of the regulatory effect of the load KP _i , excluding pairs of measurements, the values of the regulatory effect of which do not fall within the confidence interval (in this case, 0.75 ÷ 2). Excluded values are shown in bold italics in Table 1.

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 fed to the input of the unit for setting the values of the base power 8, where they determine the first approximation of their value basic power for each pair of measurements:

- для первой пары измерений,

- for the first pair of measurements,

- для последующих пар измерений.

- for subsequent pairs of measurements.

Further, the obtained values of the base power P _{BA3 (i)} (table 2) together with the values U _{1 (i)} and U _{2 (i)} , P _{1 {i)} and P _{2 (i)} from the output of the set unit of the values of the base power 8 are supplied to the input of the cast unit 9, where the measured values of voltage and power are converted into relative units:

moreover, to translate all the measured voltage values into relative units, as well as in the prototype, use the same constant value of the base voltage (in this case, U _BAZ = 6200 V).

The obtained values of U _{* 1 (i)} and U _{* 2 (i)} , P _{* 1 (i)} and P _{* 2 (i)} in relative units from the output of the cast unit 9 go to the input of the block for determining the coefficients 10, where they are approximated by the polynomial ( Fig. 2)

moreover, the coefficients a ₀ , a ₁ , and _{2 are} determined by the least squares method according to the dependencies

Then the obtained coefficients a ₀ = 1.387, and ₁ = -1.794, and ₂ = 1.392 together with the values U _{* 1 (i)} and U _{* 2 (i)} , P _{* 1 (i)} and P _{* 2 (i)} from the output the coefficient determination unit 10 is input to the error determination unit 11, where the standard deviation of the voltage and power values in relative units from the resulting polynomial is determined

where N is the number of measurement pairs remaining after filtering in the filtering unit 7. Then, the previously determined values of the coefficients a ₀ , a ₁ , and ₂ together with the values U _{* 1 (i)} and U _{* 2 (i)} , P _{* 1 (i )} and P _{* 2 (i)} come from the output of the error determination unit 11 to the input of the basis power value refinement unit 12, in which the second approximation of its base power value for each pair of measurements is determined:

с коэффициентами а₀=1,481, а₁=-2,277, а₂=1,796, соответствующими минимальному среднеквадратическому отклонению σ=0,003 (фиг. 3).The obtained values of the base power P _{BAZ (i)} come from the output of the unit for clarifying the values of the base power 12 to the input of the cast unit 9, in which the translation of the measured power values into relative units is repeated according to formulas (1) and then the device continues to work as described in accordance with the scheme FIG. 1. At the same time, the conversion of power values into relative units, determination of the coefficients a ₀ , a ₁ , a ₂ , determination of the standard deviation σ and determination of the next approximation of the basis power values P _{BAZ (i) are} repeated until the standard deviation is repeated with each subsequent repetition σ decreases. In this example, the standard deviation continued to decrease to a minimum value of σ = 0.003, after which it began to increase. Therefore, the polynomial

with coefficients a ₀ = 1.481, and ₁ = -2.277, and ₂ = 1.796, corresponding to the minimum standard deviation σ = 0.003 (Fig. 3).

Thus, the example of determining the static characteristics of the active power of a load by voltage 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 and power are converted into relative units, characterized in that the voltage and power are measured before and after each voltage change, values are determined the regulatory effect of the load for each pair of measured values of voltage and power, filter the resulting pairs of measurements by the values of the regulatory e load effect, then when translating the power values into relative units, they determine the first approximation of their base power value P _{BAZ (i)} for each pair of measurements, approximate the obtained voltage and power values in relative units by a polynomial

and the coefficients a ₀ , a ₁ , a _{2 are} determined by the least squares method according to the dependencies:

where U _{* 1 (i)} and P _{* 1 (i)} are the voltage and power values in relative units before the voltage change for the i-th measurement pair,
U _{* 2 (i)} and P _{* 2 (i)} - voltage and power values in relative units after voltage change for the i-th measurement pair,
determine the standard deviation of the voltage and power values in relative units from the polynomial obtained, determine the second approximation of its base power value for each pair of measurements:

repeat the translation of the power values into relative units, determination of the coefficients a ₀ , a ₁ , a ₂ , determination of the standard deviation and determination of the next approximation of the basis power values until the standard deviation decreases with each subsequent repetition, take as the desired static load characteristic polynomial voltage with coefficients a ₀ , a ₁ , a ₂ corresponding to the minimum standard deviation.

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