CN116609597A - Nonlinear load power loss metering method and device for power distribution network - Google Patents
Nonlinear load power loss metering method and device for power distribution network Download PDFInfo
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Abstract
The application discloses a method and a device for measuring nonlinear load active loss of a power distribution network, which relate to the field of power transmission line loss measurement and solve the problem of errors in the measurement of nonlinear load active loss, and are characterized in that: acquiring a current parameter of the nonlinear load equivalent circuit model under a harmonic condition; decomposing the current parameters to obtain a total harmonic current effective value and a fundamental current effective value of the power transmission line; determining the total harmonic current distortion rate of the power transmission line according to the total harmonic current effective value and the fundamental current effective value; determining and calculating a correction factor of the active loss of the nonlinear load according to the current distortion rate; and correcting the fundamental wave active power of the nonlinear load equivalent circuit model according to the correction factor, and determining the active loss of the nonlinear load of the power distribution network.
Description
Technical Field
The application relates to the field of power transmission line loss measurement, in particular to a method and a device for measuring nonlinear load active loss of a power distribution network.
Background
With the influx of a large number of power electronics, power distribution networks have become increasingly contaminated with harmonics. In 2010, IEEE issued IEEE1459 formal standard emphasizes that under a non-sinusoidal system, fundamental wave active power, reactive power and other apparent power components are decomposed, the power factor is redefined, and a solid theoretical basis is provided for the research of power theory and the development of intelligent electric meters. IEEE1459 decomposes voltages and currents into the sum of the sub-harmonics, i.e.:
V(t)＝V 0 cos(ω 0 t+α 0 )+V 1 cos(ω 1 t+α 1 )+…+V n cos(ω n t+α n ) (1)；
I(t)＝I 0 cos(ω 0 t+β 0 )+I 1 cos(ω 1 t+β 1 )+…+I n cos(ω n t+β n ) (2)；
wherein V (t) and I (t) are respectively corresponding to the instantaneous values of voltage and current at the moment t, I 0 、I 1 、I n The current amplitudes of the harmonic currents are respectively 0 times, 1 time and n times, V 0 、V 1 、V n The amplitudes of the harmonic voltages, omega, are respectively 0 times, 1 time and n times 0 、ω 1 、ω n Angular velocity, alpha, of each subharmonic 0 、α 1 、α n Respectively corresponding order harmonic voltage initial phase angle beta 0 、β 1 、β n The initial phase angles of the corresponding subharmonic currents are respectively, and the power factors under the corresponding subharmonics are obtained through the phase difference angles of the voltage currents of the subharmonics, so that the total active loss can be expressed as: p=v 0 I 0 cosθ 0 +V 1 I 1 cosθ 1 +…+V n I n cosθ n (3)；
θ n ＝α n -β n (n＝0,1,2…) (4)；
The harmonic active loss is:IEEE1459 definesThe method for calculating the harmonic active power is not proposed for the nonlinear load, but the harmonic active loss of the nonlinear load is not specified as the sum of products of voltage and current and power factors at two ends of the nonlinear load.
At present, a great deal of literature and a plurality of harmonic metering chips on the market at present, such as ATT2026A developed by Haijquan phototechnology company and ADE7880 developed by Adenode company of America, are all used for metering and defining harmonic active power according to IEEE1459 standard, and the harmonic active power of a nonlinear load is directly calculated according to formula (5) by utilizing collected voltage, current and phase angle data at two ends of the nonlinear load without considering the influence of an internal equivalent model of the nonlinear load on active power loss metering.
Thus, the nonlinear load active power loss calculated based on the IEEE1459 standard is not equal to the harmonic active power dissipated on the nonlinear load, resulting in errors in the metering of the nonlinear load active power loss.
Disclosure of Invention
In order to solve the defects of the prior art, the application provides a method and a device for measuring the nonlinear load active loss of a power distribution network.
The technical aim of the application is realized by the following technical scheme:
the application provides a nonlinear load active loss metering method of a power distribution network, which is applied to a nonlinear load equivalent circuit model, wherein an equivalent resistance, an equivalent inductance and fundamental wave voltage and harmonic voltage generated by a nonlinear load of a power transmission line are sequentially connected in series to form the nonlinear load equivalent circuit model, and the method comprises the following steps:
acquiring a current parameter of the nonlinear load equivalent circuit model under a harmonic condition;
decomposing the current parameters to obtain a total harmonic current effective value and a fundamental current effective value of the power transmission line;
determining the total harmonic current distortion rate of the power transmission line according to the total harmonic current effective value and the fundamental current effective value;
determining and calculating a correction factor of the active loss of the nonlinear load according to the current distortion rate;
and correcting the fundamental wave active power of the nonlinear load equivalent circuit model according to the correction factor to determine the active loss of the nonlinear load of the power distribution network, wherein the active loss of the nonlinear load comprises the fundamental wave active loss of the nonlinear load and the harmonic active loss of the nonlinear load.
In one implementation, the total harmonic current distortion of the transmission line is calculated byWherein I is H Representing the effective value of the total harmonic current, I 1 Representing the fundamental current effective value, I h The effective value of each subharmonic current is represented, h represents the harmonic frequency, THD I Indicating the current distortion rate.
In one implementation, the correction factor for the active loss of the nonlinear load is calculated asWherein K represents a correction factor, THD I Indicating the current distortion rate.
In one implementation, the calculation formula of the fundamental active loss of the nonlinear load of the power distribution network is p=kp 1 ＝KV 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
In one implementation, the harmonic active loss of the nonlinear load of the power distribution network is calculated as P H ＝(K-1)P 1 ＝(K-1)V 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
In a second aspect of the present application, there is provided a nonlinear load active loss measurement device for a power distribution network, applied to a nonlinear load equivalent circuit model, in which an equivalent resistance, an equivalent inductance, and a fundamental voltage and a harmonic voltage generated by a nonlinear load of a power transmission line are sequentially connected in series to form the nonlinear load equivalent circuit model, the device comprising:
the data acquisition module is used for acquiring current parameters of the nonlinear load equivalent circuit model under the harmonic condition;
the parameter decomposition unit is used for decomposing the current parameter to obtain a total harmonic current effective value and a fundamental current effective value of the power transmission line;
the current distortion rate determining module is used for determining the total harmonic current distortion rate of the power transmission line according to the total harmonic current effective value and the fundamental current effective value;
the correction factor calculation module is used for determining and calculating a correction factor of the active loss of the nonlinear load according to the current distortion rate;
and the active loss metering module is used for correcting the fundamental active power of the nonlinear load equivalent circuit model according to the correction factor to determine the active loss of the nonlinear load of the power distribution network, wherein the active loss of the nonlinear load comprises the fundamental active loss of the nonlinear load and the harmonic active loss of the nonlinear load.
In one embodiment, the current distortion rate determination module is calculated by the formulaWherein I is H Representing the effective value of the total harmonic current, I 1 Representing the fundamental current effective value, I h The effective value of each subharmonic current is represented, h represents the harmonic frequency, THD I Indicating the current distortion rate.
In one implementation, the correction factor calculation module has a formula ofWherein K represents a correction factor, THD I Indicating the current distortion rate.
In one embodiment, the active loss measurement module has a calculation formula of p=kp 1 ＝KV 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
In one implementation, the active loss metering module has a calculation formula of P H ＝(K-1)P 1 ＝(K-1)V 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
Compared with the prior art, the application has the following beneficial effects:
the correction factor of the active loss of the nonlinear load is determined and calculated through the total harmonic current distortion rate, and the fundamental active power of the nonlinear load equivalent circuit model is corrected through the correction factor, so that errors in the measurement of the nonlinear load active loss are further compensated.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:
FIG. 1 is a circuit diagram of a nonlinear load equivalent circuit model provided in the prior art;
FIG. 2 is a non-linear load power flow diagram provided by the prior art;
FIG. 3 is a circuit diagram of yet another nonlinear load equivalent circuit model provided by the prior art;
FIG. 4 is an equivalent circuit diagram of a harmonic source alone action of yet another nonlinear load equivalent circuit model provided by the prior art;
FIG. 5 is a prior art harmonic apparent power plot of various components;
fig. 6 is a schematic flow chart of a method for measuring nonlinear load active loss of a power distribution network according to an embodiment of the present application;
FIG. 7 is a graph comparing harmonic apparent power with load harmonic power provided by an embodiment of the present application;
FIG. 8 is a graph showing the relationship between correction factors and voltage-current distortion ratios according to an embodiment of the present application;
FIG. 9 is a simulation model diagram of nonlinear load loss measurement provided by an embodiment of the present application;
FIG. 10 is a waveform diagram of a low side simulation voltage provided by an embodiment of the present application;
FIG. 11 is a waveform diagram of a low-side simulated current provided by an embodiment of the present application;
fig. 12 is a schematic diagram of a metering point of a power distribution network structure according to an embodiment of the present application;
FIG. 13 is a graph of measured current provided by an embodiment of the present application;
FIG. 14 is a graph of measured voltage provided by an embodiment of the present application;
FIG. 15 is a graph of measured harmonic current content provided by an embodiment of the present application;
FIG. 16 is a graph of measured harmonic voltage content provided by an embodiment of the present application;
fig. 17 is a graph of total active power of a measured load of a power distribution network according to an embodiment of the present application;
fig. 18 is a schematic block diagram of a nonlinear load power loss metering device for a power distribution network according to an embodiment of the present application.
Detailed Description
For the purpose of making apparent the objects, technical solutions and advantages of the present application, the present application will be further described in detail with reference to the following examples and the accompanying drawings, wherein the exemplary embodiments of the present application and the descriptions thereof are for illustrating the present application only and are not to be construed as limiting the present application.
As described in the background, power distribution networks have become increasingly contaminated with harmonics as a result of the influx of a large number of power electronics. In 2010, IEEE issued IEEE1459 formal standard emphasizes that under a non-sinusoidal system, fundamental wave active power, reactive power and other apparent power components are decomposed, the power factor is redefined, and a solid theoretical basis is provided for the research of power theory and the development of intelligent electric meters. IEEE1459 decomposes voltages and currents into the sum of the sub-harmonics, i.e.: v (t) =v 0 cos(ω 0 t+α 0 )+V 1 cos(ω 1 t+α 1 )+…+V n cos(ω n t+α n ) (1)；
I(t)＝I 0 cos(ω 0 t+β 0 )+I 1 cos(ω 1 t+β 1 )+…+I n cos(ω n t+β n ) (2)；
Wherein V (t) and I (t) are instantaneous values of voltage and current corresponding to the moment t, I 0 、I 1 、I n The current amplitudes of the harmonic currents are respectively 0 times, 1 time and n times, V 0 、V 1 、V n The amplitudes of the harmonic voltages, omega, are respectively 0 times, 1 time and n times 0 、ω 1 、ω n Angular velocity, alpha, of each subharmonic 0 、α 1 、α n Respectively corresponding order harmonic voltage initial phase angle beta 0 、β 1 、β n The initial phase angles of the corresponding subharmonic currents are respectively, and the power factors under the corresponding subharmonics are obtained through the phase difference angles of the voltage currents of the subharmonics, so that the total active loss can be expressed as: p=v 0 I 0 cosθ 0 +V 1 I 1 cosθ 1 +…+V n I n cosθ n (3)；
θ n ＝α n -β n (n＝0,1,2…) (4)；
The harmonic active loss is:IEEE1459 defines a method for calculating harmonic active power, but the method is not proposed for a nonlinear load, and does not specify that the harmonic active loss of the nonlinear load is the sum of products of voltage and current and power factors at both ends of the nonlinear load.
At present, a great deal of literature and a plurality of harmonic metering chips on the market at present, such as ATT2026A developed by Haijquan phototechnology company and ADE7880 developed by Adenode company of America, are all used for metering and defining harmonic active power according to IEEE1459 standard, and the harmonic active power of a nonlinear load is directly calculated according to formula (5) by utilizing collected voltage, current and phase angle data at two ends of the nonlinear load without considering the influence of an internal equivalent model of the nonlinear load on active power loss metering.
Thus, the nonlinear load active power loss calculated based on the IEEE1459 standard is not equal to the harmonic active power dissipated on the nonlinear load, resulting in errors in the metering of the nonlinear load active power loss.
In summary, based on the shortcomings of the prior art, the method for measuring the nonlinear load active loss of the power distribution network provided by the embodiment determines and calculates the correction factor of the active loss of the nonlinear load through the total harmonic current distortion rate, corrects the fundamental active power of the nonlinear load equivalent circuit model through the correction factor, and further compensates the error existing in the measurement of the nonlinear load active loss.
Referring to fig. 6, fig. 6 is a schematic flow chart of a method for measuring nonlinear load active loss of a power distribution network according to an embodiment of the present application, where the method provided in the embodiment is applied to a nonlinear load equivalent circuit model shown in fig. 1, and an equivalent resistance, an equivalent inductance, and a fundamental voltage and a harmonic voltage generated by a nonlinear load of a power transmission line are sequentially connected in series to form the nonlinear load equivalent circuit model, and the method includes:
s610, acquiring current parameters of the nonlinear load equivalent circuit model under a harmonic condition.
Commonly used Fourier method-based decomposition metering single-phase nonlinear loadThe active loss method is to equivalent a nonlinear load as shown in figure 1, R S And L is equal to S The equivalent resistance and the equivalent inductance of the power transmission line are respectively. The nonlinear load is equivalent to a fundamental wave voltage source and a harmonic wave voltage source which are connected in series, and because the harmonic wave is generated by the nonlinear load, the harmonic wave voltage source and the power supply voltage are in the same direction and reverse to the equivalent fundamental wave voltage source, so that the current parameters of the nonlinear load equivalent circuit model under the harmonic wave condition are acquired through a measuring instrument.
S620, decomposing the current parameters to obtain a total harmonic current effective value and a fundamental current effective value of the power transmission line.
According to the IEEE1459 standard, the current parameter and the voltage parameter are decomposed into:
wherein I is H 、V H Respectively the effective values of the total harmonic current and the voltage, I h 、V h Respectively the effective values of current and voltage of each subharmonic, I 1 、V 1 The fundamental current and the voltage effective values are respectively, H represents the total harmonic frequency, and H represents the H-th harmonic.
S630, determining the total harmonic current distortion rate of the power transmission line according to the total harmonic current effective value and the fundamental wave current effective value.
Line total harmonic voltage distortion rate THD in nonlinear load system V And total harmonic current distortion rate THD I Respectively defined as:
the apparent power S is decomposed:
wherein D is I The power for current distortion is:
D V the power for voltage distortion is:
S H for harmonic apparent power:
harmonic distortion power D H The method comprises the following steps:
further, the method comprises the steps of,
the nonlinear load energy conversion schematic diagram is shown in fig. 2, and in order to determine the internal active loss of the nonlinear load, V in fig. 1 1 Equivalent to resistance R L And inductance L L Is then in series with the harmonic source V H source Form an equivalent circuit in series when the current I 1 Flow through R L 、L L When generating V 1 As shown in fig. 3, the circuit is actually the Thevenin conversion of a nonlinear load Norton equivalent circuit, compared with the equivalent model in fig. 1, the equivalent circuit is used for calculating nonlinear load loss, the conversion process of nonlinear load internal loss can be more closely described, the fig. 3 is further equivalent to two conditions of independent action of a power supply and independent action of a harmonic source by utilizing the superposition principle, when the harmonic source is independently acted, the equivalent circuit is shown in fig. 4, and the voltage V at two ends of a measuring instrument can be obtained by combining fig. 3 and fig. 4 C On-line equal to harmonic sourceVoltage V generated on road HX Each subharmonic voltage V at two ends of measuring instrument c And the current I of each subharmonic h The relation is:
V c ＝V hx ＝I h (R L +jω h L L )-V hy (16)；
wherein V is hy Is equivalent to a harmonic source V HY The emitted subharmonic voltages, V hx Is the voltage of each subharmonic on the line. From the above analysis, the measured subharmonic voltages V c Harmonic source V hy And equivalent resistance R L Harmonic current I h Co-influencing and equivalent resistance value R L Is based on nonlinear load fundamental wave active power P 1 The relation is obtained as follows:
the analysis shows that the content of the harmonic voltage and the harmonic current of the actual nonlinear load has a certain relation with the fundamental active power operated by the load, and the relation is also consistent with the actual situation.
When the harmonic source acts alone, the harmonic apparent power of each component is shown in fig. 5. As can be seen from fig. 5, the voltage V across the nonlinear load C To calculate the obtained harmonic apparent power as the actual harmonic apparent power S of the line HX ：
Theoretically nonlinear load harmonic apparent power S H Apparent power S to be supplied with harmonic source HY Separately consider, S H Should be equivalent resistance R L And L L Harmonic apparent power consumed above:
thus using the harmonic voltage V across the measuring instrument C The nonlinear load harmonic active loss obtained through calculation is likely to cause errors, and the calculation result is shown in the formula (20).
Measuring result P of measuring instrument C The harmonic active power loss for the line is not equal to the harmonic active power dissipated on the nonlinear load.
And S640, determining and calculating a correction factor of the active loss of the nonlinear load according to the current distortion rate.
In this embodiment, considering starting from the power flow decomposition method, the nonlinear load active loss P can be obtained as
Formulas (7) to (14) are combined to obtain:
the combination of formulas (21), (22) can be achieved:
analyzing the equivalent circuits of fig. 3 and 4, the nonlinear load active loss P is defined by ohm's law:
the result obtained by the power flow decomposition calculation method and the ohm law calculation method is the same, and the accuracy of the nonlinear load harmonic active loss calculation formula (23) is verified.
Therefore, the correction factor K is
And S650, correcting the fundamental wave active power of the nonlinear load equivalent circuit model according to the correction factor, and determining the active loss of the nonlinear load of the power distribution network, wherein the active loss of the nonlinear load comprises the fundamental wave active loss of the nonlinear load and the harmonic active loss of the nonlinear load.
Specifically, if the correction factor is determined according to the above formula (25), the total nonlinear load loss P measured based on the power flow decomposition method can be expressed as a product of the correction factor and the conventional fundamental active loss, as follows:
P＝KP 1 ＝KV 1 I 1 cosθ 1 (26) Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
Nonlinear load harmonic loss P H Can be expressed as P H ＝(K-1)P 1 ＝(K-1)V 1 I 1 cosθ 1 (27) Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Representing the effective value of the fundamental wave voltage, R L Represents the equivalent resistance, θ, of the fundamental voltage generated by a nonlinear load 1 The phase difference between the harmonic voltage and the fundamental current is represented.
Further, the calculation formula of the total harmonic current distortion rate of the power transmission line is as followsWherein I is H Representing the effective value of the total harmonic current, I 1 Representing the fundamental current effective value, I h The effective value of each subharmonic current is represented, h represents the harmonic frequency, THD I Indicating the current distortion rate.
Further, the calculation formula of the correction factor of the active loss of the nonlinear load is as followsWherein K represents a correction factor, THD I Indicating the current distortion rate.
Further, the calculation formula of the fundamental wave active loss of the nonlinear load of the power distribution network is p=kp 1 ＝KV 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
In one implementation, the harmonic active loss of the nonlinear load of the power distribution network is calculated as P H ＝(K-1)P 1 ＝(K-1)V 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
The present embodiment also provides simulation analysis for the method provided in the present embodiment, as follows:
comparing and analyzing the metering result based on the power flow decomposition method and the Fourier decomposition method, and setting nonlinear load fundamental wave apparent power S 1 For 800KVA, the fundamental wave active loss is 760KW (fundamental wave power factor 0.95), and the fundamental wave active loss is substituted into the formula (14) and the formula (27), and the randomness of the power angles of each subharmonic is large and is difficult to be assumed, so that the nonlinear load harmonic active power metered based on the Fourier decomposition method is difficult to determine, and only a curve diagram of the change of the nonlinear load harmonic active loss metered based on the power flow method and the nonlinear load harmonic apparent power metered based on the Fourier decomposition method along with the current distortion of different voltages is made, thereby comparing and analyzing the accuracy of the two metering modes, as shown in figure 7.
As can be seen from fig. 7, the two spatial planes intersect when the harmonic voltage distortion rate THDV is equal to the current distortion rate THDI, THDI>The apparent power of the nonlinear load harmonic measured by the THDV area Fourier decomposition measuring module is smaller than the active loss of the nonlinear load harmonic measured by the power flow measuring module; in THDV>The nonlinear load harmonic apparent power measured by the Fourier decomposition measuring module in the THDI area is larger than the load harmonic active loss. It can be seen that the harmonic voltage V across the meter (non-linearity) is measured C The calculation method substituted into equation (20) to obtain nonlinear load harmonic loss is erroneous, and the nonlinear load harmonic active loss is not correctly measured. The method for measuring the active loss provided by the embodiment is considered to be not only theoretically based, but also can better evaluate the economic benefit of nonlinear load harmonic loss.
As can be seen from the above equations (25) and (26), when calculating nonlinear load loss, only the fundamental wave active loss and the current distortion rate of the user are known, and the harmonic loss of the load can be accurately measured by K coefficient correction. The operation method not only accurately measures the load active loss caused by the harmonic wave, but also avoids the complicated calculation of the voltage distortion rate and the introduction of unnecessary measurement errors, and the theoretical basis is more convincing. Fig. 8 is a three-dimensional perspective view of the change of the correction factor K along with the voltage-current distortion rate, and it can be seen that the correction factor K is affected by the current distortion rate, and the correction factor K gradually increases along with the increase of the current distortion rate.
And experimental simulation analysis is carried out, and the AC-DC-AC circuit of the frequency converter is widely applied to high-power variable frequency motors. Therefore, the AD-DC-AC frequency converter model is built by combining MATLAB/Simulink in the embodiment, and the frequency converter converts a 50HZ power grid power supply into direct current and then converts the direct current into 60HZ for three-phase load through passive inversion. The simulation model is shown in fig. 9. The high-voltage side and the low-voltage side of the 10/0.4 transformer are connected with the measuring modules, and loss measurement results of the variable frequency load (the load is a three-phase balanced load and only one phase is measured) of each measuring module are observed.
The high voltage side voltage distortion rate was 0.07%, the high voltage side current distortion rate was 7.49%, the low voltage side voltage distortion rate was 0.65%, and the low voltage side current distortion rate was 7.76%. The voltage-current waveforms of the low-voltage side simulation are shown in fig. 10 and 11.
Table 1 metering results for each metering mode on the high voltage side of the transformer
| Metering method | Metering active power | Harmonic active power |
| Traditional metering | 5235W | 0W |
| Power flow metering | 5271W | 36W (Transformer + load) |
Table 2 metering results for each metering mode on the low-voltage side of the transformer
| Metering method | Metering active power | Harmonic active power |
| Traditional metering | 4945W | 0W |
| Fourier decomposition metrology | 4947W | 2W (inside transformer) |
| Power flow metering | 4978W | 33W (load) |
As can be seen from the statistics of the above tables 1 and 2, the metering results of the three different metering modes at the low pressure side are: the nonlinear load active power metered under the fundamental wave condition is only considered as follows: 4945W; the nonlinear load active power measured based on the fourier decomposition method of equation (5) is: 4947W, the nonlinear load active power metered based on the power flow method of equation (23) is: 4978W.
The fundamental wave loss metering mode only considers fundamental wave (50 HZ) supply load loss, and 2-50 times of harmonic loss is considered based on a Fourier decomposition metering module, and the metering module meters line harmonic loss and load fundamental wave loss; and the power flow metering module meters the extra loss caused by all times of harmonic waves according to a power flow decomposition method, and the metering module meters the load harmonic loss and the load fundamental wave loss. As can be seen from simulation results, the metering module which only considers the fundamental wave to cause the loss does not meter harmonic loss, and the effective value of the voltage-current fundamental wave transmitted by the power grid is reduced due to the fact that the current and the voltage are distorted in the nonlinear load, so that the metering accuracy of the fundamental wave loss metering module is affected, and the metering result is minimum.
And comparing the metering result of the low-voltage side Fourier decomposition metering module with the fundamental wave loss metering result to obtain that the active loss power caused by 2-50 times of harmonic waves is 2W. The method is to multiply and sum the voltage and current of each subharmonic and the power factor under the correspondence of each subharmonic to obtain the harmonic active loss, and the analysis of section 2 shows that the calculation method measures the loss on the system and the line, and the calculation result is to measure the internal harmonic active loss of the transformer, not to measure the nonlinear load harmonic loss, and the measured object is wrong, so the statistical harmonic loss is relatively small.
The low-voltage side power flow metering module meters that the nonlinear load active power loss is 33W, and the harmonic active power (transformer+load) measured by the high-voltage side power flow metering module is 36W. The harmonic active loss of the transformer can be obtained by comparing the metering results of the high-voltage side power flow module and the low-voltage side power flow module as follows: the line loss (transformer) counted by the Fourier decomposition measurement is 2W, the difference between the results of measuring the harmonic active loss of the transformer by the two methods is 1W, the error is caused because the 2-50 times of harmonic waves are considered based on the Fourier decomposition method, the harmonic wave after 50 times is not unified, the harmonic active loss of the transformer measured by the low-voltage side Fourier measurement module of the transformer only measures the winding loss of the low-voltage side transformer, the harmonic wave is transmitted to the high-voltage side winding and the harmonic active loss in the magnetic core of the transformer is not counted (by the theoretical analysis of the power flow of fig. 2, a part of harmonic power is returned to the system, and thus, the leakage of 1W exists in the harmonic active loss of the transformer measured by the Fourier measurement module. Simulation results show that the object of measuring harmonic active loss by the Fourier decomposition measuring module is taken as a transformer, and the power flow measuring module measures nonlinear load harmonic active loss, so that theoretical analysis is verified.
The measured data analysis is performed by using an instrument, and the FLUCK435 is an electric energy quality analysis instrument manufactured based on IEEE1459 standard, which can analyze the harmonic components of load current and voltage. Considering that sand field loads are processed by using special motor equipment (generating harmonic waves), the embodiment utilizes FLUCK435 to actually measure 10kV sand field loads (high-power) of a certain power grid, as shown in FIG. 12. And a FLUCK435 electric energy quality testing instrument is additionally arranged at a gateway of the power grid metering, and the harmonic content of the line is monitored. As shown in fig. 13 and 14, the voltage-current curve of the measured line and the current-current curve of the measured line are respectively.
The collected load voltage and current waveforms were subjected to harmonic analysis, and the distortion rate is as shown in fig. 15 and 16, and the distortion rate of the harmonic current is: 13.713%, harmonic voltage distortion rate is: 0.739%.
Active power at load run time deriving gateway table statistics from grid system as shown in figure17, the statistical data analysis of the time period from 13 th 45 th to 14 th the next day shows that the active power of the load fundamental wave is 400KW, the power factor is 0.87. According to (14), the apparent power of the harmonic wave measured in the Fourier decomposition measurement mode is 0.001S 1 The method comprises the steps of carrying out a first treatment on the surface of the And according to the formula (23), calculating the harmonic active loss to be 0.019P by a power flow method L It can be seen that the nonlinear load power loss measured in fourier decomposition metering must be smaller than the nonlinear load power loss measured in power flow metering. Satisfying the theoretical analysis, objects metered in a Fourier decomposition metering manner are wrong, the result is inaccurate, and in THD I >THD V The nonlinear load active loss measurement result of the area measured in a Fourier decomposition measurement mode is smaller than the standard measurement result of the power flow measurement mode, so that mistakes and few meters are caused.
In summary, the metering method provided in the embodiment is adopted to meter the harmonic active loss of the grid gateway, and the economic benefit brought by the method is evaluated. Assuming that the power grid statistics of the operation time period is 400KW of load fundamental wave average power, 7.6KW harmonic power grid gateway table is not counted. In 4.5 hours of load operation, 34.2KWH of harmonic electric quantity is not metered, and the direct economic loss of 34.5 yuan in 4.5 hours accounts for 1.9% of the metering of a power grid gateway assuming 1 yuan/KWH of industrial electric quantity. It can be seen that the metering method proposed in this embodiment can effectively meter the load harmonic loss.
As shown in fig. 18, the embodiment of the present application further provides a power distribution network nonlinear load active power loss metering device, which is applied to a nonlinear load equivalent circuit model, and corresponds to a power distribution network nonlinear auxiliary active power loss metering method described in the foregoing embodiment, wherein an equivalent resistance, an equivalent inductance, and a fundamental voltage and a harmonic voltage generated by a nonlinear load of a power transmission line are sequentially connected in series to form the nonlinear load equivalent circuit model, and the device includes:
the data acquisition module is used for acquiring current parameters of the nonlinear load equivalent circuit model under the harmonic condition;
the parameter decomposition unit is used for decomposing the current parameter to obtain a total harmonic current effective value and a fundamental current effective value of the power transmission line;
the current distortion rate determining module is used for determining the total harmonic current distortion rate of the power transmission line according to the total harmonic current effective value and the fundamental current effective value;
the correction factor calculation module is used for determining and calculating a correction factor of the active loss of the nonlinear load according to the current distortion rate;
and the active loss metering module is used for correcting the fundamental active power of the nonlinear load equivalent circuit model according to the correction factor to determine the active loss of the nonlinear load of the power distribution network, wherein the active loss of the nonlinear load comprises the fundamental active loss of the nonlinear load and the harmonic active loss of the nonlinear load.
Therefore, the measuring device provided by the embodiment determines and calculates the correction factor of the active loss of the nonlinear load through the total harmonic current distortion rate, corrects the fundamental active power of the nonlinear load equivalent circuit model through the correction factor, and further compensates the error existing in the measurement of the nonlinear load active loss.
Further, the calculation formula of the current distortion rate determination module is as followsWherein I is H Representing the effective value of the total harmonic current, I 1 Representing the fundamental current effective value, I h The effective value of each subharmonic current is represented, h represents the harmonic frequency, THD I Indicating the current distortion rate.
Further, the calculation formula of the correction factor calculation module is as followsWherein K represents a correction factor, THD I Indicating the current distortion rate.
Further, the calculation formula of the active loss measurement module is p=kp 1 ＝KV 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
Further, the calculation formula of the active loss metering module is P H ＝(K-1)P 1 ＝(K-1)V 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the application, and is not meant to limit the scope of the application, but to limit the application to the particular embodiments, and any modifications, equivalents, improvements, etc. that fall within the spirit and principles of the application are intended to be included within the scope of the application.
Claims (10)
1. The utility model provides a nonlinear load active loss metering method of distribution network, is applied to nonlinear load equivalent circuit model, wherein establish ties in proper order the equivalent resistance, equivalent inductance and the fundamental wave voltage and the harmonic voltage that produce by nonlinear load of transmission line, constitute nonlinear load equivalent circuit model, its characterized in that, the method includes:
acquiring a current parameter of the nonlinear load equivalent circuit model under a harmonic condition;
decomposing the current parameters to obtain a total harmonic current effective value and a fundamental current effective value of the power transmission line;
determining the total harmonic current distortion rate of the power transmission line according to the total harmonic current effective value and the fundamental current effective value;
determining and calculating a correction factor of the active loss of the nonlinear load according to the current distortion rate;
and correcting the fundamental wave active power of the nonlinear load equivalent circuit model according to the correction factor to determine the active loss of the nonlinear load of the power distribution network, wherein the active loss of the nonlinear load comprises the fundamental wave active loss of the nonlinear load and the harmonic active loss of the nonlinear load.
2. The method according to claim 1, wherein the calculation formula of the total harmonic current distortion of the transmission line isWherein I is H Representing the effective value of the total harmonic current, I 1 Representing the fundamental current effective value, I h The effective value of each subharmonic current is represented, h represents the harmonic frequency, THD I Indicating the current distortion rate.
3. The method of claim 1, wherein the correction factor for the active loss of the nonlinear load is calculated by the formulaWherein K represents a correction factor, THD I Indicating the current distortion rate.
4. The method according to claim 1, wherein the calculation formula of the fundamental active loss of the nonlinear load of the distribution network is p=kp 1 ＝KV 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
5. The method of claim 1, wherein the harmonic active loss of the nonlinear load of the power distribution network is calculated as P H ＝(K-1)P 1 ＝(K-1)V 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
6. The utility model provides a nonlinear load active loss metering device of distribution network, is applied to nonlinear load equivalent circuit model, wherein establishes ties in proper order the equivalent resistance of transmission line, equivalent inductance and the fundamental wave voltage and the harmonic voltage that produce by nonlinear load, constitutes nonlinear load equivalent circuit model, its characterized in that, the device includes:
the data acquisition module is used for acquiring current parameters of the nonlinear load equivalent circuit model under the harmonic condition;
the parameter decomposition unit is used for decomposing the current parameter to obtain a total harmonic current effective value and a fundamental current effective value of the power transmission line;
the current distortion rate determining module is used for determining the total harmonic current distortion rate of the power transmission line according to the total harmonic current effective value and the fundamental current effective value;
the correction factor calculation module is used for determining and calculating a correction factor of the active loss of the nonlinear load according to the current distortion rate;
and the active loss metering module is used for correcting the fundamental active power of the nonlinear load equivalent circuit model according to the correction factor to determine the active loss of the nonlinear load of the power distribution network, wherein the active loss of the nonlinear load comprises the fundamental active loss of the nonlinear load and the harmonic active loss of the nonlinear load.
7. The apparatus of claim 6, wherein the current distortion rate determination module is calculated by the formulaWherein I is H Representing the effective value of the total harmonic current, I 1 Representing the fundamental current effective value, I h The effective value of each subharmonic current is represented, h represents the harmonic frequency, THD I Indicating the current distortion rate.
8. The apparatus of claim 6, wherein the correction factor calculation module has a formula ofWherein K represents a correction factor, THD I Indicating the current distortion rate.
9. The apparatus of claim 6, wherein the active loss measurement module is calculated by the formulaWherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
10. The apparatus of claim 6 wherein the active loss measurement module has a formula P H ＝(K-1)P 1 ＝(K-1)V 1 I 1 cosθ 1 Wherein K represents a correction factor, P 1 Representing fundamental active power, I 1 Representing the fundamental current effective value, V 1 Represents the effective value of fundamental wave voltage, theta 1 The phase difference between the harmonic voltage and the fundamental current is represented.
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| CN117388569B (en) * | 2023-12-11 | 2024-03-01 | 浙江宏仁电气有限公司 | Electric energy metering method, electric energy metering box and medium under waveform distortion of power grid |
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