CN112834807B - Flicker emission level measurement method and device based on instantaneous power - Google Patents

Flicker emission level measurement method and device based on instantaneous power Download PDF

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CN112834807B
CN112834807B CN202110023375.XA CN202110023375A CN112834807B CN 112834807 B CN112834807 B CN 112834807B CN 202110023375 A CN202110023375 A CN 202110023375A CN 112834807 B CN112834807 B CN 112834807B
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instantaneous
voltage
power
flicker
reactive power
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CN112834807A (en
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徐斌
甄超
朱明星
王小明
张毅恒
田宇
潘东
谢毓广
王坤
李坚林
高博
计长安
王刘芳
汪胜和
陈庆涛
胡翀
李金中
刘星
郑浩
毛荀
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Electric Power Research Institute of State Grid Anhui Electric Power Co Ltd
State Grid Anhui Electric Power Co Ltd
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Electric Power Research Institute of State Grid Anhui Electric Power Co Ltd
State Grid Anhui Electric Power Co Ltd
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Abstract

The invention discloses a flicker emission level measuring method and a flicker emission level measuring device based on instantaneous power, wherein the method comprises the following steps: measuring the digital quantity of the three-phase voltage of the discretization fluctuating load bus and the incoming line current of the fluctuating load by using an electric energy quality recorder; filtering the digital values of the three-phase voltage and the fluctuating load incoming line current; sampling the filtered voltage and current signals to obtain three-phase voltage and three-phase current of each sampling point after pretreatment; calculating instantaneous active power and instantaneous reactive power of the three-phase voltage and the three-phase current of the preprocessed system to be tested; calculating a power supply bus voltage fluctuation value sequence caused by injecting the fluctuation amount of instantaneous active power and instantaneous reactive power into a system to be tested; calculating a short-time voltage flicker value and a long-time voltage flicker value according to the CPF curve, and further drawing a fluctuating load flicker emission level curve; the invention has the advantages that: the accuracy of the voltage flicker calculation result is improved.

Description

Flicker emission level measurement method and device based on instantaneous power
Technical Field
The invention relates to the technical field of power systems, new energy photovoltaic power generation and wind power generation, in particular to a flicker emission level measurement method and device based on instantaneous power.
Background
The fluctuating load refers to a load with periodic or aperiodic working current change and sudden change, such as an electric arc furnace, a steel rolling mill, an electrified traction load, new energy photovoltaic power generation, wind power generation and the like, and the running process of the fluctuating load is generally seriously intermittent. Due to the tendency of gradual increase of the access proportion of the fluctuating load in the power system, the capacity of the single body is also continuously increased, and the influence and the harm to the power grid are possibly more and more serious. The main adverse effect is that the stability of system operation voltage is destroyed by the active power and the reactive power of volatility, so that the voltage fluctuation and flicker of the power supply bus are caused, and the safe and stable operation of all electric equipment under the bus is further influenced.
The existing fluctuating load voltage flicker emission level calculation method is mainly focused on extraction of power supply bus envelope lines and optimization of parameter calculation processes, voltage fluctuation and flicker of buses are caused after all fluctuating loads carried by power supply buses are superposed, the voltage flicker of the power supply buses is directly measured by an instrument, only the influence results of all loads on the power supply buses can be examined, and the problem of flicker responsibility apportionment such as contribution rate of a plurality of fluctuating loads to the flicker of the power supply buses cannot be solved. The research related to the calculation of the multi-fluctuation load flicker value also has certain problems, for example, the measurement method of the fluctuation load flicker emission level disclosed in the Chinese patent publication No. CN107390014 only calculates the active power and the reactive power of the fundamental wave, and further calculates the voltage fluctuation and the flicker value caused by the fundamental wave power, and the method ignores the influence of the inter-harmonic waves near the fundamental wave on the accuracy of the voltage flicker calculation result; if the voltage fluctuation and flicker are calculated by an instantaneous reactive method by directly using the digital quantity of the voltage and the current, the instantaneous power fluctuation caused by harmonic voltage and current can be caused, and the accuracy problem of the voltage flicker calculation result can be further caused.
The input proportion of the impact load in a new generation of electric power system is gradually improved, when some impact load flicker emission characteristics are evaluated, the impact load must be put into operation together with the dynamic reactive power compensation device, the direct measurement of the voltage flicker of the power supply bus is the flicker value which is already treated by the dynamic reactive power compensation device, and the voltage flicker level caused by the impact load alone cannot be accurately evaluated, so that a high-accuracy evaluation method for the voltage flicker emission level of the impact load is urgently needed in engineering application.
Disclosure of Invention
The invention aims to solve the technical problem that a method for evaluating the flicker emission level of the impact load voltage with higher accuracy is lacked in the prior art.
The invention solves the technical problems through the following technical means: a method of transient power-based flicker emission level measurement, the method comprising: measuring the digital quantity of the three-phase voltage of the discretization fluctuating load bus and the incoming line current of the fluctuating load by using an electric energy quality recorder;
the digital values of the three-phase voltage and the fluctuating load incoming line current pass through a low-pass filter to inhibit the influence of harmonic voltage and current on instantaneous reactive fluctuation;
taking a calculation point for every several sampling points of the filtered voltage and current signals, thereby obtaining the preprocessed three-phase voltage and three-phase current of each sampling point;
calculating instantaneous active power and instantaneous reactive power of the three-phase voltage and the three-phase current of the preprocessed system to be tested;
carrying out differential operation on the instantaneous active power and the instantaneous reactive power obtained by calculation to obtain the fluctuation quantity of the instantaneous active power and the reactive power at unit time intervals, calculating corresponding short-circuit impedance of the running system according to the running short-circuit capacity of the tested system, and then calculating a power supply bus voltage fluctuation value sequence caused by injecting the fluctuation quantity of the instantaneous active power and the instantaneous reactive power into the tested system;
and the voltage fluctuation value sequence is subjected to a series of processing by a digital visibility weighting filter, a squarer and a smooth filtering digital filter to obtain instantaneous flicker visibility and fit a CPF curve, and a short-time voltage flicker value and a long-time voltage flicker value are calculated according to the CPF curve to further draw a fluctuating load flicker emission level curve.
The invention obtains the digital quantity of the three-phase voltage of the discretization fluctuating load bus and the inlet wire current of the fluctuating load through the measurement of an electric energy quality recorder, inhibits the influence of harmonic voltage and current on instantaneous reactive power fluctuation through a low-pass filter, directly adopts the digital quantity of the voltage and the current to calculate the voltage fluctuation and flicker by an instantaneous reactive power method, avoids the influence of inter-harmonics near fundamental waves on the accuracy of a voltage flicker calculation result, filters high-frequency harmonic voltage and current in a digital filtering mode, avoids instantaneous power fluctuation caused by the harmonic voltage and current, and further improves the accuracy of the voltage flicker calculation result.
Further, the expression of the low-pass filter is:
Figure BDA0002889372660000031
wherein x (n +1-r) represents the input response of the filter, y (n +1-l) represents the full response of the filter, n represents the nth sample point, l represents the order of the input response, r represents the order of the full response, alCoefficient representing input response, brCoefficient representing the full response, alAnd blAre all real constants, a1＝1，a2＝-5.8198，a3＝14.1153，a4＝-18.2620，a5＝13.2925，a6＝-5.1611，a7＝0.8351；b1＝1.47e-10，b2＝8.8201e-10，b3＝2.2050e-09，b4＝2.9400e-08，b5＝2.2050e-08，b6＝48.8201e-10，b7＝1.4700e-10。
Further, the calculating instantaneous active power and instantaneous reactive power of the three-phase voltage and the three-phase current of the preprocessed system to be tested includes:
by the formula p (n) ═ ua(n)ia(n)+ub(n)ib(n)+uc(n)ic(n) obtaining the instantaneous active power of each preprocessed sampling point, wherein p (n) represents the instantaneous active power of the nth sampling point, ua(n)、ub(n)、uc(n) the preprocessed three-phase voltages, i, of the nth sampling point, respectivelya(n)、ib(n)、ic(n) represents the preprocessed three-phase current of the nth sampling point;
by the formula
Figure BDA0002889372660000041
And acquiring the instantaneous reactive power of each preprocessed sampling point, wherein q (n) represents the instantaneous reactive power of the nth sampling point.
Further, the differential operation of the calculated instantaneous active power and instantaneous reactive power to obtain the fluctuation amount of the instantaneous active power and reactive power per unit time interval includes:
by the formula
Figure BDA0002889372660000042
Acquiring the fluctuation quantity of instantaneous active power and reactive power in unit time; wherein, p (m) and q (m) are respectively the instantaneous active power and the instantaneous reactive power after the pretreatment of the mth sampling point; and p (m +1) and q (m +1) are respectively the instantaneous active power and the instantaneous reactive power of the next time after the m +1 th sampling point is preprocessed.
Further, the calculating the corresponding operating system short-circuit impedance according to the measured system operating short-circuit capacity includes:
determining the operation short-circuit capacity S of the system to be tested according to the voltage grade of the power system accessed by the fluctuating loaddThen combining with the nominal voltage U of the system to be testedNBy the formula
Figure BDA0002889372660000043
Calculating the impedance X of the reference system of the system to be measureds。
Further, the calculating the power supply bus voltage fluctuation value sequence caused by injecting the fluctuation amount of the instantaneous active power and the instantaneous reactive power into the tested system comprises:
by the formula
Figure BDA0002889372660000051
Obtaining the supply caused by injecting the fluctuation quantity of the instantaneous active power and the instantaneous reactive power into the system to be testedA sequence of electrical bus voltage fluctuation values; wherein R isSFor the equivalent resistance component of the system to be measured, take the value as
Figure BDA0002889372660000052
Further, the transfer function of the digitized perceptibility weighting filter is:
Figure BDA0002889372660000053
wherein Z is a variable of the transfer function;
the transfer function of a smooth filtered digital filter is:
Figure BDA0002889372660000054
by the formula
Figure BDA0002889372660000055
Obtaining a short-time voltage flicker value, wherein PstRepresenting the short-time voltage flicker value, P0.1、P1s、P3s、P10s、P50sThe perceived unit values representing the instantaneous flicker visual acuity exceeding 0.1%, 1%, 3%, 10%, 50% of the time, respectively;
short-time voltage flicker value obtained by statistics in measurement time period is calculated by formula
Figure BDA0002889372660000056
Obtaining a long-term voltage flicker value, wherein PltRepresenting the long-term voltage flicker value, PstiAnd the ith short-time voltage flicker value is represented, and N represents the total number of the short-time voltage flicker values in the measurement period.
The invention also provides a flicker emission level measuring device based on instantaneous power, which comprises:
the preprocessing module is used for measuring and obtaining digital quantities of three-phase voltage of a discretized fluctuating load bus and the fluctuating load incoming line current through an electric energy quality wave recording instrument;
the digital values of the three-phase voltage and the fluctuating load incoming line current pass through a low-pass filter to inhibit the influence of harmonic voltage and current on instantaneous reactive fluctuation;
taking a calculation point for every several sampling points of the filtered voltage and current signals, thereby obtaining the preprocessed three-phase voltage and three-phase current of each sampling point;
the instantaneous power acquisition module is used for calculating instantaneous active power and instantaneous reactive power of the three-phase voltage and three-phase current of the preprocessed system to be tested;
the voltage fluctuation value sequence acquisition module is used for carrying out differential operation on the instantaneous active power and the instantaneous reactive power obtained by calculation to obtain the fluctuation quantity of the instantaneous active power and the reactive power at unit time intervals, calculating corresponding short-circuit impedance of the operation system according to the operation short-circuit capacity of the system to be measured, and then calculating a power supply bus voltage fluctuation value sequence caused by injecting the fluctuation quantity of the instantaneous active power and the instantaneous reactive power into the system to be measured;
and the flicker emission level acquisition module is used for obtaining instantaneous flicker visibility and fitting a CPF curve after the voltage fluctuation value sequence is subjected to a series of processing by a digital visibility weighting filter, a squarer and a smooth filtering digital filter, calculating a short-time voltage flicker value and a long-time voltage flicker value according to the CPF curve and further drawing a fluctuating load flicker emission level curve.
Further, the expression of the low-pass filter is:
Figure BDA0002889372660000061
wherein x (n +1-r) represents the input response of the filter, y (n +1-l) represents the full response of the filter, n represents the nth sample point, l represents the order of the input response, r represents the order of the full response, alCoefficient representing input response, brCoefficient representing the full response, alAnd blAre all real constants, a1＝1，a2＝-5.8198，a3＝14.1153，a4＝-18.2620，a5＝13.2925，a6＝-5.1611，a7＝0.8351；b1＝1.47e-10，b2＝8.8201e-10，b3＝2.2050e-09，b4＝2.9400e-08，b5＝2.2050e-08，b6＝48.8201e-10，b7＝1.4700e-10。
Further, the instantaneous power acquisition module is further configured to:
by the formula p (n) ═ ua(n)ia(n)+ub(n)ib(n)+uc(n)ic(n) obtaining the instantaneous active power of each preprocessed sampling point, wherein p (n) represents the instantaneous active power of the nth sampling point, ua(n)、ub(n)、uc(n) the preprocessed three-phase voltages, i, of the nth sampling point, respectivelya(n)、ib(n)、ic(n) represents the preprocessed three-phase current of the nth sampling point;
by the formula
Figure BDA0002889372660000071
And acquiring the instantaneous reactive power of each preprocessed sampling point, wherein q (n) represents the instantaneous reactive power of the nth sampling point.
Further, the differential operation of the calculated instantaneous active power and instantaneous reactive power to obtain the fluctuation amount of the instantaneous active power and reactive power per unit time interval includes:
by the formula
Figure BDA0002889372660000072
Acquiring the fluctuation quantity of instantaneous active power and reactive power in unit time; wherein, p (m) and q (m) are respectively the instantaneous active power and the instantaneous reactive power after the pretreatment of the mth sampling point; and p (m +1) and q (m +1) are respectively the instantaneous active power and the instantaneous reactive power of the next time after the m +1 th sampling point is preprocessed.
Further, the calculating the corresponding operating system short-circuit impedance according to the measured system operating short-circuit capacity includes:
according toMethod for determining running short-circuit capacity S of tested system by accessing voltage grade of power system through fluctuating loaddThen combining with the nominal voltage U of the system to be testedNBy the formula
Figure BDA0002889372660000073
Calculating the impedance X of the reference system of the system to be measureds。
Further, the calculating the power supply bus voltage fluctuation value sequence caused by injecting the fluctuation amount of the instantaneous active power and the instantaneous reactive power into the tested system comprises:
by the formula
Figure BDA0002889372660000081
Acquiring a power supply bus voltage fluctuation value sequence caused by injecting fluctuation amounts of instantaneous active power and instantaneous reactive power into a system to be tested; wherein R isSFor the equivalent resistance component of the system to be measured, take the value as
Figure BDA0002889372660000082
Further, the transfer function of the digitized perceptibility weighting filter is:
Figure BDA0002889372660000083
wherein Z is a variable of the transfer function;
the transfer function of a smooth filtered digital filter is:
Figure BDA0002889372660000084
by the formula
Figure BDA0002889372660000085
Obtaining a short-time voltage flicker value, wherein PstRepresenting the short-time voltage flicker value, P0.1、P1s、P3s、P10s、P50sRespectively indicates that the instantaneous flicker visual sensitivity exceeds 0.1%,Perceived unit values at 1%, 3%, 10%, 50% of time;
short-time voltage flicker value obtained by statistics in measurement time period is calculated by formula
Figure BDA0002889372660000086
Obtaining a long-term voltage flicker value, wherein PltRepresenting the long-term voltage flicker value, PstiAnd the ith short-time voltage flicker value is represented, and N represents the total number of the short-time voltage flicker values in the measurement period.
The invention has the advantages that:
(1) the invention obtains the digital quantity of the three-phase voltage of the discretization fluctuating load bus and the inlet wire current of the fluctuating load through the measurement of an electric energy quality recorder, inhibits the influence of harmonic voltage and current on instantaneous reactive power fluctuation through a low-pass filter, directly adopts the digital quantity of the voltage and the current to calculate the voltage fluctuation and flicker by an instantaneous reactive power method, avoids the influence of inter-harmonics near fundamental waves on the accuracy of a voltage flicker calculation result, filters high-frequency harmonic voltage and current in a digital filtering mode, avoids instantaneous power fluctuation caused by the harmonic voltage and current, and further improves the accuracy of the voltage flicker calculation result.
(2) The invention carries out online real-time measurement on the flicker emission level of the fluctuating load, is beneficial to evaluating the responsibility apportionment of various fluctuating loads on the voltage flicker of the public power grid, thereby evaluating the treatment effect of the electric energy quality treatment device on the voltage flicker, better carrying out electric energy quality technical supervision and management on the fluctuating load, reducing the influence of the fluctuating load on the voltage stability of the power grid and ensuring the safe and stable operation of power supply and utilization equipment.
Drawings
FIG. 1 is a flow chart of a method for measuring a flicker emission level based on instantaneous power according to an embodiment of the present invention;
FIG. 2 is a test chart of an electric arc furnace power distribution system provided by an embodiment of the present invention;
FIG. 3 is a schematic diagram of voltage fluctuations on a 33kV bus caused solely by an EAF furnace instantaneous active and reactive power fluctuation injection system in an electric arc furnace power distribution system provided by an embodiment of the present invention;
fig. 4 is a schematic diagram of voltage fluctuation of a 33kV bus caused by an LF furnace instantaneous active and reactive power fluctuation injection system provided in an embodiment of the present invention alone;
fig. 5 is a schematic diagram of voltage fluctuation of a 33kV bus caused by instantaneous active and reactive power fluctuation amount injection systems of an EAF furnace and an LF furnace according to an embodiment of the present invention;
FIG. 6 is a diagram illustrating a voltage short-time flicker value of a 33kV bus caused by an EAF furnace alone, measured by a flicker emission level measurement method based on instantaneous power according to an embodiment of the present invention;
fig. 7 is a voltage short-time flicker value of a 33kV bus caused by an LF furnace alone measured by the flicker emission level measurement method based on instantaneous power according to the embodiment of the present invention.
Fig. 8 shows a short-time flicker value of the voltage of the 33kV bus caused by the EAF furnace and the LF furnace measured by the transient power-based flicker emission level measurement method according to the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
As shown in fig. 1, a method of transient power based flicker emission level measurement, the method comprising:
step S1, measuring by a power quality wave recording instrument to obtain digital quantities of three-phase voltage of a discretized fluctuating load bus and the incoming line current of the fluctuating load, wherein the sampling rate of the power quality wave recording instrument is 12.8kHz, and each power frequency cycle is sampled at 256 points; in order to inhibit the influence of harmonic voltage and current above 100Hz on instantaneous reactive power fluctuation, the embodiment introduces the three-phase voltage and fluctuation load into the lineThe digital quantity of the flow passes through a 6-order Butterworth low-pass filter with a cutoff frequency of 95 Hz; in order to further reduce the calculated amount, a calculated point is taken for each 8 sampling points at intervals of the filtered voltage and current signals, and therefore the three-phase voltage u of each sampling point after pretreatment is obtaineda(n)、ub(n)、uc(n) and three-phase current ia(n)、ib(n)、ic(n)。
In the embodiment of the invention, a synchronous parallel acquisition mode is adopted to acquire the analog signals of the voltage of the power supply bus and the fluctuating load current of the system to be detected, and the analog signals are converted into digital signals through the corresponding filter circuit and the synchronous analog-to-digital conversion circuit.
The expression of the 6 th order butterworth filter with the cut-off frequency of 95Hz is as follows:
Figure BDA0002889372660000101
wherein x (n +1-r) represents the input response of the filter, y (n +1-l) represents the full response of the filter, n represents the nth sample point, l represents the order of the input response, r represents the order of the full response, alCoefficient representing input response, brCoefficient representing the full response, alAnd blAre all real constants, a1＝1，a2＝-5.8198，a3＝14.1153，a4＝-18.2620，a5＝13.2925，a6＝-5.1611，a7＝0.8351；b1＝1.47e-10，b2＝8.8201e-10，b3＝2.2050e-09，b4＝2.9400e-08，b5＝2.2050e-08，b6＝48.8201e-10，b7＝1.4700e-10。
Step S2, instantaneous active power and instantaneous reactive power calculation are carried out on the three-phase voltage and the three-phase current of the preprocessed system to be tested, the calculated instantaneous active power and instantaneous reactive power are subjected to differential operation, and fluctuation quantity of the instantaneous active power and reactive power at unit time interval is obtained, and the specific process is as follows:
by the formula p (n) ═ ua(n)ia(n)+ub(n)ib(n)+uc(n)ic(n) obtaining the instantaneous active power of each preprocessed sampling point, wherein p (n) represents the instantaneous active power of the nth sampling point, ua(n)、ub(n)、uc(n) the preprocessed three-phase voltages, i, of the nth sampling point, respectivelya(n)、ib(n)、ic(n) represents the preprocessed three-phase current of the nth sampling point;
by the formula
Figure BDA0002889372660000111
And acquiring the instantaneous reactive power of each preprocessed sampling point, wherein q (n) represents the instantaneous reactive power of the nth sampling point.
Carrying out difference operation of adjacent points on the instantaneous active power sequence p (n) and the instantaneous reactive power sequence q (n) obtained by calculation, and obtaining the difference value of the adjacent points by a formula
Figure BDA0002889372660000112
Acquiring the fluctuation quantity of instantaneous active power and reactive power in unit time; wherein, p (m) and q (m) are respectively the instantaneous active power and the instantaneous reactive power after the pretreatment of the mth sampling point; and p (m +1) and q (m +1) are respectively the instantaneous active power and the instantaneous reactive power of the next time after the m +1 th sampling point is preprocessed.
Step S3, calculating the corresponding short-circuit impedance of the operation system according to the operation short-circuit capacity of the system to be tested, and then calculating the fluctuation value sequence of the power supply bus voltage caused by injecting the fluctuation quantity of instantaneous active power and instantaneous reactive power into the system to be tested; the specific process is as follows:
determining the operation short-circuit capacity S of the system to be tested according to the voltage grade of the power system accessed by the fluctuating loaddThen combining with the nominal voltage U of the system to be testedNBy the formula
Figure BDA0002889372660000121
Calculating the impedance X of the reference system of the system to be measureds。
Thus, calculating a voltage fluctuation value sequence caused by injecting instantaneous active power delta p (m) and instantaneous reactive power delta q (m) at unit time interval into the tested system independently:
by the formula
Figure BDA0002889372660000122
Wherein R isSFor the equivalent resistance component of the system to be measured, take the value as
Figure BDA0002889372660000123
And step S4, the voltage fluctuation value sequence is subjected to a series of processing of a digital visibility weighting filter, a squarer and a smooth filtering digital filter to obtain instantaneous flicker visibility and fit a CPF curve, and the short-time voltage flicker value and the long-time voltage flicker value are calculated according to the CPF curve to draw a fluctuating load flicker emission level curve. The specific process is as follows:
the voltage fluctuation value sequence d (m) obtained in step S3 is subjected to a series of processing according to the method given in IEC 61000-4-15 standard: firstly, z-transform is performed on the voltage fluctuation value sequence d (m) calculated in the step S3 to obtain
Figure BDA0002889372660000124
Wherein the transfer function of the digitized perceptibility weighting filter is:
Figure BDA0002889372660000125
wherein Z is a variable of the transfer function;
the voltage fluctuation value sequence is processed by a digital visual sensitivity weighting filter to obtain an expression D (z) of which the expression D passes through a transfer function1(z)＝D(z)H1(z)；
And then z inverse transformation is carried out on the D (z), and the output of voltage fluctuation passing through the visual sensitivity weighting filter is obtained as follows:
d1(m)＝Z-1[D1(z)]；
the output of the vision sensitivity weighting filter passes through a squarer to obtain the output of the squarer
Figure BDA0002889372660000133
A digital filter that subjects the output of the squarer to smoothing filtering, wherein the transfer function of the smoothing filtered digital filter is:
Figure BDA0002889372660000131
to d2(m) z-transforming to obtain
Figure BDA0002889372660000132
To obtain D2(z) expression D after passing through transfer function3(z)＝D2(z)H2(z)；
Then to D3(z) performing z-inverse transformation to obtain d3(m)＝Z-1[D3(z)]The final smoothed digital filter output signal is the instantaneous flicker visual sensitivity s (t) sequence.
And step S5, grading the instantaneous flicker visibility S (t) obtained in the step 4 according to IEC requirements, wherein the grading quantity is not less than 64, for the graded data, the percentage of the instantaneous flicker visibility S (t) corresponding to each grade to the total quantity is respectively calculated, a frequency distribution histogram is constructed, and the CPF (probability cumulative histogram) recommended by the IEC can be obtained according to the histogram.
From the fitted CPF curve, 5 values specified by IEC for calculating the short-time flicker values can be obtained, respectively: p0.1、P1s、P3s、P10s、P50sFor these 5 values, by formula
Figure BDA0002889372660000134
Obtaining a short-time voltage flicker value, wherein PstRepresenting the short-time voltage flicker value, P0.1、P1s、P3s、P10s、P50sRespectively indicates that the instantaneous flicker visual acuity exceeds 0.1 percent1%, 3%, 10%, 50% of the time perceived Unit value, P1s、P3s、P10s、P50sThe subscript s of (a) indicates that smooth values should be used, which values are obtained using the following formula:
P1s＝(P0.7+P1+P1.5)/3；
P3s＝(P2.2+P3+P4)/3；
P10s＝(P6+P8+P10+P13+P17)/5；
P1s＝(P30+P50+P80)/3；
wherein P is0.7Equivalent meanings to the above P0.1And the like, and will not be described in detail.
When the amplitude and frequency of the voltage fluctuation signal in the original voltage signal are stable and unchanged, the following can be considered:
P0.1＝P1s＝P3s＝P10s＝P50s＝S(t)；
substitution formula
Figure BDA0002889372660000141
Then there are:
Figure BDA0002889372660000142
short-time voltage flicker value obtained by statistics in measurement time period is calculated by formula
Figure BDA0002889372660000143
Obtaining a long-term voltage flicker value, wherein PltRepresenting the long-term voltage flicker value, PstiAnd the ith short-time voltage flicker value is represented, and N represents the total number of the short-time voltage flicker values in the measurement period.
And drawing a fluctuating load flicker emission level curve according to the calculated short-time voltage flicker value and the long-time voltage flicker value, then evaluating responsibility share of various fluctuating loads on the voltage flicker of the public power grid, evaluating the treatment effect of the electric energy quality treatment device on the voltage flicker, better performing electric energy quality technical supervision and management on the fluctuating loads, reducing the influence of the fluctuating loads on the voltage stability of the power grid, and ensuring safe and stable operation of power supply and utilization equipment.
For ease of understanding, the following description is made in conjunction with a specific example; it should be noted that the numerical values used in the following examples are only examples, and the user may make corresponding changes according to actual needs.
This example is a 150 ton ac arc furnace in an enterprise, the distribution system has a 33kV bus that is powered by a 180MVA transformer, with the main loads on site being the EAF furnace, LF furnace and SVC plant. The schematic diagram of the test wiring of a 150 ton ac electric arc furnace power supply and distribution system of a certain enterprise is shown in fig. 2.
By adopting the scheme provided by the embodiment of the invention, the running data of the incoming line current of the EAF furnace and the LF furnace and the 33kV bus voltage can be obtained through testing.
(1) The three-phase voltage u of the 33kV bus of the electric arc furnace is measured by the instrumenta(t)、ub(t)、uc(t) incoming current i of EAF furnace and LF furnaceEAFa(t)、iEAFb(t)、iEAFc(t)、iLFa(t)、iLFb(t)、iLFc(t) converting the analog quantity into digital quantity, passing the digital quantity of the three-phase bus voltage and the incoming line current through a 6-order Butterworth filter with the cut-off frequency of 95Hz, and then taking a calculation point every other 8 sampling points for reducing the calculation quantity to obtain the processed three-phase voltage digital quantity u of the system to be measureda(n)、ub(n)、uc(n) and iEAFa(n)、iEAFb(n)、iEAFc(n)、iLFa(n)、iLFb(n)、iLFcAnd (n) is the processed sampling sequence number.
(2) And calculating instantaneous active power and instantaneous reactive power according to the processed three-phase voltage and current digital quantity of the system to be measured. And performing discrete Fourier transform on the calculated instantaneous active power sequence p (n) and the instantaneous reactive power sequence q (n), and recording the m-th instantaneous active power as p (m) and the m-th instantaneous reactive power as q (m). And performing adjacent point differential operation on the instantaneous active power and the instantaneous reactive power calculated in unit time t.
(3) The bus of the system is 33kV, the operation short circuit capacity is 1152MVA, and the impedance and the resistance of the operation system are calculated as follows:
Figure BDA0002889372660000151
Figure BDA0002889372660000152
according to the formula
Figure BDA0002889372660000153
Calculating the voltage fluctuation of the 33kV bus caused by the incoming lines of the EAF furnace and the LF furnace under the reference short-circuit capacity, and the voltage fluctuation of the 33kV bus caused by the incoming lines of the EAF furnace and the LF furnace under the reference short-circuit capacity are respectively shown in fig. 3 and fig. 4. The voltage fluctuation of the 33kV bus caused by the injection system after the instantaneous power fluctuation of the EAF furnace and the LF furnace are superposed is shown in figure 5.
(4) According to the method given in the IEC 61000-4-15 standard, the voltage fluctuation value sequence d (m) obtained in the step (3) is processed in series to obtain S (t), and then the voltage flicker value is calculated according to the formula given in the IEC 61000-4-15 standard:
Figure BDA0002889372660000161
drawing a fluctuating load flicker emission level curve according to the calculated flicker statistic value, as shown in fig. 6 and 7, fig. 6 is a voltage short-time flicker curve caused by an EAF furnace alone, fig. 7 is a voltage short-time flicker curve caused by an LF furnace incoming line alone, and fig. 8 is a voltage short-time flicker value caused by a fluctuating quantity injection system in which instantaneous power of the EAF furnace and the LF furnace are superposed.
(5) According to the fluctuating load flicker emission level curve, the responsibility of various fluctuating loads on the voltage flicker of the public power grid can be evaluated, the treatment effect of the electric energy quality treatment device on the voltage flicker can be evaluated, the electric energy quality technical supervision and management can be better carried out on the fluctuating loads, the influence of the fluctuating loads on the voltage stability of the power grid is reduced, and the safe and stable operation of power supply and utilization equipment is ensured.
The method can evaluate the responsibility share of various fluctuating load single equipment on the voltage flicker of the public power grid and evaluate the treatment effect of the electric energy quality treatment device on the voltage flicker.
According to the technical scheme, the flicker emission level measuring method based on the instantaneous power, provided by the invention, comprises the steps of measuring and obtaining digital quantities of three-phase voltage of a discretization fluctuating load bus and inlet wire current of the fluctuating load through an electric energy quality recorder, inhibiting the influence of harmonic voltage and current on instantaneous reactive power fluctuation through a low-pass filter, directly calculating the voltage fluctuation and flicker by adopting the digital quantities of the voltage and the current through an instantaneous reactive power method, avoiding the influence of inter-harmonics near fundamental waves on the accuracy of a voltage flicker calculation result, filtering high-frequency harmonic voltage and current in a digital filtering mode, avoiding the instantaneous power fluctuation caused by the harmonic voltage and the current, and further improving the accuracy of the voltage flicker calculation result.
Example 2
Corresponding to embodiment 1 of the present invention, embodiment 2 of the present invention further provides a flicker emission level measuring device based on instantaneous power, the device including:
the preprocessing module is used for measuring and obtaining digital quantities of three-phase voltage of a discretization fluctuating load bus and incoming line current of the fluctuating load through a power quality wave recording instrument, wherein the sampling rate of the power quality wave recording instrument is 12.8kHz, and each power frequency cycle samples 256 points;
the digital quantities of the three-phase voltage and the fluctuating load incoming line current pass through a 6-order Butterworth low-pass filter with the cutoff frequency of 95Hz to inhibit the influence of harmonic voltage and current above 100Hz on instantaneous reactive power fluctuation;
taking a calculation point for each 8 sampling points at intervals of the filtered voltage and current signals, thereby obtaining the preprocessed three-phase voltage and three-phase current of each sampling point;
the instantaneous power acquisition module is used for calculating instantaneous active power and instantaneous reactive power of the three-phase voltage and three-phase current of the preprocessed system to be tested;
the voltage fluctuation value sequence acquisition module is used for carrying out differential operation on the instantaneous active power and the instantaneous reactive power obtained by calculation to obtain the fluctuation quantity of the instantaneous active power and the reactive power at unit time intervals, calculating corresponding short-circuit impedance of the operation system according to the operation short-circuit capacity of the system to be measured, and then calculating a power supply bus voltage fluctuation value sequence caused by injecting the fluctuation quantity of the instantaneous active power and the instantaneous reactive power into the system to be measured;
and the flicker emission level acquisition module is used for obtaining instantaneous flicker visibility and fitting a CPF curve after the voltage fluctuation value sequence is subjected to a series of processing by a digital visibility weighting filter, a squarer and a smooth filtering digital filter, calculating a short-time voltage flicker value and a long-time voltage flicker value according to the CPF curve and further drawing a fluctuating load flicker emission level curve.
Specifically, the expression of the 6 th order butterworth filter with the cutoff frequency of 95Hz is as follows:
Figure BDA0002889372660000181
wherein x (n +1-r) represents the input response of the filter, y (n +1-l) represents the full response of the filter, n represents the nth sample point, l represents the order of the input response, r represents the order of the full response, alCoefficient representing input response, brCoefficient representing the full response, alAnd blAre all real constants, a1＝1，a2＝-5.8198，a3＝14.1153，a4＝-18.2620，a5＝13.2925，a6＝-5.1611，a7＝0.8351；b1＝1.47e-10，b2＝8.8201e-10，b3＝2.2050e-09，b4＝2.9400e-08，b5＝2.2050e-08，b6＝48.8201e-10，b7＝1.4700e-10。
Specifically, the instantaneous power obtaining module is further configured to:
by the formula p (n) ═ ua(n)ia(n)+ub(n)ib(n)+uc(n)ic(n) obtaining the instantaneous active power of each preprocessed sampling point, wherein p (n) represents the instantaneous active power of the nth sampling point, ua(n)、ub(n)、uc(n) the preprocessed three-phase voltages, i, of the nth sampling point, respectivelya(n)、ib(n)、ic(n) represents the preprocessed three-phase current of the nth sampling point;
by the formula
Figure BDA0002889372660000182
And acquiring the instantaneous reactive power of each preprocessed sampling point, wherein q (n) represents the instantaneous reactive power of the nth sampling point.
Specifically, the differential operation of the instantaneous active power and the instantaneous reactive power obtained by calculation to obtain the fluctuation amount of the instantaneous active power and the reactive power at the unit time interval includes:
by the formula
Figure BDA0002889372660000191
Acquiring the fluctuation quantity of instantaneous active power and reactive power in unit time; wherein, p (m) and q (m) are respectively the instantaneous active power and the instantaneous reactive power after the pretreatment of the mth sampling point; and p (m +1) and q (m +1) are respectively the instantaneous active power and the instantaneous reactive power of the next time after the m +1 th sampling point is preprocessed.
Specifically, the calculating the corresponding operating system short-circuit impedance according to the operating short-circuit capacity of the system to be tested includes:
determining the operation short-circuit capacity S of the system to be tested according to the voltage grade of the power system accessed by the fluctuating loaddThen combining with the nominal voltage U of the system to be testedNBy the formula
Figure BDA0002889372660000192
Calculating the impedance X of the reference system of the system to be measureds。
Specifically, the calculating of the power supply bus voltage fluctuation value sequence caused by injecting the fluctuation amounts of the instantaneous active power and the instantaneous reactive power into the system to be tested includes:
by the formula
Figure BDA0002889372660000193
Acquiring a power supply bus voltage fluctuation value sequence caused by injecting fluctuation amounts of instantaneous active power and instantaneous reactive power into a system to be tested; wherein R isSFor the equivalent resistance component of the system to be measured, take the value as
Figure BDA0002889372660000194
Specifically, the transfer function of the digitized perceptibility weighting filter is:
Figure BDA0002889372660000195
wherein Z is a variable of the transfer function;
the transfer function of a smooth filtered digital filter is:
Figure BDA0002889372660000196
by the formula
Figure BDA0002889372660000197
Obtaining a short-time voltage flicker value, wherein PstRepresenting the short-time voltage flicker value, P0.1、P1s、P3s、P10s、P50sThe perceived unit values representing the instantaneous flicker visual acuity exceeding 0.1%, 1%, 3%, 10%, 50% of the time, respectively;
short-time voltage flicker value obtained by statistics in measurement time period is calculated by formula
Figure BDA0002889372660000201
Obtaining a long-term voltage flicker value, wherein PltRepresenting the long-term voltage flicker value, PstiAnd the ith short-time voltage flicker value is represented, and N represents the total number of the short-time voltage flicker values in the measurement period.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A method for transient power-based flicker emission level measurement, the method comprising: measuring the digital quantity of the three-phase voltage of the discretization fluctuating load bus and the incoming line current of the fluctuating load by using an electric energy quality recorder;
the digital values of the three-phase voltage and the fluctuating load incoming line current pass through a low-pass filter to inhibit the influence of harmonic voltage and current on instantaneous reactive fluctuation;
taking a calculation point for every several sampling points of the filtered voltage and current signals, thereby obtaining the preprocessed three-phase voltage and three-phase current of each sampling point;
calculating instantaneous active power and instantaneous reactive power of the three-phase voltage and the three-phase current of the preprocessed system to be tested;
carrying out differential operation on the instantaneous active power and the instantaneous reactive power obtained by calculation to obtain the fluctuation quantity of the instantaneous active power and the reactive power at unit time intervals, calculating corresponding short-circuit impedance of the running system according to the running short-circuit capacity of the tested system, and then calculating a power supply bus voltage fluctuation value sequence caused by injecting the fluctuation quantity of the instantaneous active power and the instantaneous reactive power into the tested system;
and the voltage fluctuation value sequence is subjected to a series of processing by a digital visibility weighting filter, a squarer and a smooth filtering digital filter to obtain instantaneous flicker visibility and fit a CPF curve, and a short-time voltage flicker value and a long-time voltage flicker value are calculated according to the CPF curve to further draw a fluctuating load flicker emission level curve.
2. The method of claim 1, wherein the low pass filter is expressed as:
Figure FDA0002889372650000011
wherein x (n +1-r) represents the input response of the filter, y (n +1-l) represents the full response of the filter, n represents the nth sample point, l represents the order of the input response, r represents the order of the full response, alCoefficient representing input response, brCoefficient representing the full response, alAnd blAre all real constants, a1＝1，a2＝-5.8198，a3＝14.1153，a4＝-18.2620，a5＝13.2925，a6＝-5.1611，a7＝0.8351；b1＝1.47e-10，b2＝8.8201e-10，b3＝2.2050e-09，b4＝2.9400e-08，b5＝2.2050e-08，b6＝48.8201e-10，b7＝1.4700e-10。
3. The transient power-based flicker emission level measurement method of claim 1, wherein the calculating instantaneous active power and instantaneous reactive power of the preprocessed three-phase voltage and three-phase current of the system under test comprises:
by the formula p (n) ═ ua(n)ia(n)+ub(n)ib(n)+uc(n)ic(n) obtaining the instantaneous active power of each preprocessed sampling point, wherein p (n) represents the instantaneous active power of the nth sampling point, ua(n)、ub(n)、uc(n) represents the passage of the nth sample point, respectivelyPretreated three-phase voltage ia(n)、ib(n)、ic(n) represents the preprocessed three-phase current of the nth sampling point;
by the formula
Figure FDA0002889372650000021
And acquiring the instantaneous reactive power of each preprocessed sampling point, wherein q (n) represents the instantaneous reactive power of the nth sampling point.
4. The method of claim 3, wherein the step of differentiating the instantaneous active power and the instantaneous reactive power to obtain the fluctuation amount of the instantaneous active power and the reactive power per unit time interval comprises:
by the formula
Figure FDA0002889372650000022
Acquiring the fluctuation quantity of instantaneous active power and reactive power in unit time; wherein, p (m) and q (m) are respectively the instantaneous active power and the instantaneous reactive power after the pretreatment of the mth sampling point; and p (m +1) and q (m +1) are respectively the instantaneous active power and the instantaneous reactive power of the next time after the m +1 th sampling point is preprocessed.
5. The method of claim 4, wherein calculating the operating system short-circuit impedance according to the operating short-circuit capacity of the system under test comprises:
determining the operation short-circuit capacity S of the system to be tested according to the voltage grade of the power system accessed by the fluctuating loaddThen combining with the nominal voltage U of the system to be testedNBy the formula
Figure FDA0002889372650000031
Calculating the impedance X of the reference system of the system to be measureds。
6. The method of claim 5, wherein the step of calculating the sequence of supply bus voltage fluctuation values caused by injecting the fluctuation amounts of instantaneous active power and instantaneous reactive power into the system under test comprises:
by the formula
Figure FDA0002889372650000032
Acquiring a power supply bus voltage fluctuation value sequence caused by injecting fluctuation amounts of instantaneous active power and instantaneous reactive power into a system to be tested; wherein R isSFor the equivalent resistance component of the system to be measured, take the value as
Figure FDA0002889372650000033
7. The method of claim 1, wherein the transfer function of the digitized perceptibility weighting filter is:
Figure FDA0002889372650000034
wherein Z is a variable of the transfer function;
the transfer function of a smooth filtered digital filter is:
Figure FDA0002889372650000035
by the formula
Figure FDA0002889372650000036
Obtaining a short-time voltage flicker value, wherein PstRepresenting the short-time voltage flicker value, P0.1、P1s、P3s、P10s、P50sThe perceived unit values representing the instantaneous flicker visual acuity exceeding 0.1%, 1%, 3%, 10%, 50% of the time, respectively;
by measuringShort-time voltage flicker value obtained by intra-segment statistics is calculated by formula
Figure FDA0002889372650000041
Obtaining a long-term voltage flicker value, wherein PltRepresenting the long-term voltage flicker value, PstiAnd the ith short-time voltage flicker value is represented, and N represents the total number of the short-time voltage flicker values in the measurement period.
8. An instantaneous power-based flicker emission level measuring device, the device comprising:
the preprocessing module is used for measuring and obtaining digital quantities of three-phase voltage of a discretized fluctuating load bus and the fluctuating load incoming line current through an electric energy quality wave recording instrument;
the digital values of the three-phase voltage and the fluctuating load incoming line current pass through a low-pass filter to inhibit the influence of harmonic voltage and current on instantaneous reactive fluctuation;
taking a calculation point for every several sampling points of the filtered voltage and current signals, thereby obtaining the preprocessed three-phase voltage and three-phase current of each sampling point;
the instantaneous power acquisition module is used for calculating instantaneous active power and instantaneous reactive power of the three-phase voltage and three-phase current of the preprocessed system to be tested;
the voltage fluctuation value sequence acquisition module is used for carrying out differential operation on the instantaneous active power and the instantaneous reactive power obtained by calculation to obtain the fluctuation quantity of the instantaneous active power and the reactive power at unit time intervals, calculating corresponding short-circuit impedance of the operation system according to the operation short-circuit capacity of the system to be measured, and then calculating a power supply bus voltage fluctuation value sequence caused by injecting the fluctuation quantity of the instantaneous active power and the instantaneous reactive power into the system to be measured;
and the flicker emission level acquisition module is used for obtaining instantaneous flicker visibility and fitting a CPF curve after the voltage fluctuation value sequence is subjected to a series of processing by a digital visibility weighting filter, a squarer and a smooth filtering digital filter, calculating a short-time voltage flicker value and a long-time voltage flicker value according to the CPF curve and further drawing a fluctuating load flicker emission level curve.
9. An instantaneous power-based flicker emission level measuring device according to claim 8, wherein the low pass filter is expressed as:
Figure FDA0002889372650000051
wherein x (n +1-r) represents the input response of the filter, y (n +1-l) represents the full response of the filter, n represents the nth sample point, l represents the order of the input response, r represents the order of the full response, alCoefficient representing input response, brCoefficient representing the full response, alAnd blAre all real constants, a1＝1，a2＝-5.8198，a3＝14.1153，a4＝-18.2620，a5＝13.2925，a6＝-5.1611，a7＝0.8351；b1＝1.47e-10，b2＝8.8201e-10，b3＝2.2050e-09，b4＝2.9400e-08，b5＝2.2050e-08，b6＝48.8201e-10，b7＝1.4700e-10。
10. The apparatus of claim 8, wherein the instantaneous power acquisition module is further configured to:
by the formula p (n) ═ ua(n)ia(n)+ub(n)ib(n)+uc(n)ic(n) obtaining the instantaneous active power of each preprocessed sampling point, wherein p (n) represents the instantaneous active power of the nth sampling point, ua(n)、ub(n)、uc(n) the preprocessed three-phase voltages, i, of the nth sampling point, respectivelya(n)、ib(n)、ic(n) represents the preprocessed three-phase current of the nth sampling point;
by the formula
Figure FDA0002889372650000052
And acquiring the instantaneous reactive power of each preprocessed sampling point, wherein q (n) represents the instantaneous reactive power of the nth sampling point.
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