CN112269052A - Harmonic and reactive current detection method - Google Patents
Harmonic and reactive current detection method Download PDFInfo
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- CN112269052A CN112269052A CN202011024572.5A CN202011024572A CN112269052A CN 112269052 A CN112269052 A CN 112269052A CN 202011024572 A CN202011024572 A CN 202011024572A CN 112269052 A CN112269052 A CN 112269052A
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Abstract
The invention relates to a harmonic and reactive current detection method, which comprises the following steps: step 1, separating positive and negative sequence voltage and current based on a signal T/3 delay algorithm, and extracting a positive sequence component; step 2, filtering harmonic components in the load current by using a moving average filter to obtain fundamental current direct-current components; and 3, directly obtaining active and reactive current signals through coordinate transformation. When the three-phase load voltage of the system is asymmetric, the invention can quickly and accurately detect the harmonic wave and the reactive current in the system, lays a foundation for subsequent filtering and reactive compensation, and ensures the stable operation of the system while improving the quality of electric energy.
Description
Technical Field
The invention relates to the technical field of power systems, in particular to a harmonic and reactive current detection method.
Background
In recent years, the use of nonlinear elements of an electric power system is increasingly frequent, so that the problems of reactive power and harmonic pollution become more serious, the electric energy quality is affected, and the safe and stable operation of the system is threatened. In order to improve the quality of electric energy and the stability of the system, accurate and rapid detection and compensation of reactive current become necessary.
At present, a main filtering and reactive current compensation mode is that a Static Var Generator (SVG) is matched with a low-pass active filter, and the real-time detection and compensation of harmonic waves and reactive current are realized by adopting an ip-iq theory, so that the safety and stability of a system are ensured while the electric energy quality is improved. As shown in fig. 1, according to the operation principle, the core link is the real-time and accurate detection of the harmonic and reactive current in the system, and the result directly affects the compensation effect. The traditional ip-iq principle reactive current detection method can be used for the situation that voltage is distorted, but when three-phase voltage is asymmetric, the method has large errors in extraction of active current and reactive current, and the real-time detection effect is poor due to the existence of a low filter.
Disclosure of Invention
The invention aims to provide a harmonic and reactive current detection method, which is used for realizing rapid and accurate detection of harmonic and reactive current when three phases of a system are asymmetric on the basis of an ip-iq theory harmonic and reactive current detection method, thereby laying a foundation for subsequent reactive compensation.
The invention provides a harmonic and reactive current detection method, which comprises the following steps:
and 3, directly obtaining active and reactive current signals through coordinate transformation.
Further, the step 1 comprises:
under a two-phase static coordinate system, power grid voltage and current signals are delayed by 1/3 power frequency periods T, and are combined according to a three-phase symmetry principle, positive sequence components and negative sequence components in three-phase power grid voltage are separated, and A-phase voltage positive sequence components are extracted.
Further, the step 2 comprises:
based on the moving average filter, the fundamental current direct-current component is acquired under the condition that only the sampling frequency and the sliding window width are determined.
By means of the scheme, the harmonic and reactive current detection method can quickly and accurately detect the harmonic and reactive current in the system when the three-phase load voltage of the system is asymmetric, lays a foundation for subsequent filtering and reactive compensation, and ensures the stable operation of the system while improving the power quality.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.
Drawings
FIG. 1 is based on the prior art ip-iqA theoretical harmonic wave and reactive current detection method schematic diagram;
FIG. 2 is a schematic diagram of the harmonic and reactive current detection method of the present invention.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Referring to fig. 2, the embodiment provides a method for detecting a harmonic and a reactive current, including:
Under a two-phase static coordinate system, power grid voltage and current signals are delayed for 1/3 power frequency periods T, and then are combined according to a three-phase symmetry principle, so that the purpose of separating positive sequence components and negative sequence components in three-phase power grid voltage is finally achieved, and extraction of A-phase voltage positive sequence components is realized. The problem that in a traditional phase-locked loop link, errors exist in voltage phase angles of sampling due to the existence of negative sequence voltage in voltage, and therefore detection results of harmonic waves and reactive current are affected is solved.
Setting three-phase voltage as Ua、Ub、Uc；
In the formula: u + and U-are the maximum values of positive and negative sequence fundamental wave electromotive force; theta 0+And theta 0-Initial phase angles of positive and negative sequence electromotive force; time-delaying it, the following equation can be derived:
the positive sequence component of the voltage is calculated simultaneously:
the obtained Ua + is used as the input quantity of Clark conversion, the method saves the traditional phase-locked loop link (phase-locked loop module), can obtain correct harmonic and reactive current components, and avoids the problem of phase difference caused by negative sequence components when the voltage of the three-phase power grid is asymmetric.
And 2, filtering harmonic components in the load current by using a moving average filter to obtain fundamental current direct-current components.
Aiming at the problem of time delay caused by extracting a direct current component by using a low-pass filter in the traditional method, the embodiment adopts the Moving Average Filter (MAF) to replace the traditional low-pass filter, only needs to determine the sampling frequency and the width of a sliding window, has higher dynamic response speed and higher filtering precision than the traditional low-pass filter, and reduces the operation amount.
The basic principle of the Moving Average Filter (MAF) is:
in the formula: x (tau) is the input signal,
to output the signal, T is the window width period of MAF.
From equation (7), MAF is an average of the input signal from time T-T to time T. Since the harmonics are all sinusoidal signals, it is clear that harmonics can be filtered out when T is the harmonic period. The theoretical analysis is as follows.
The Laplace transform is carried out on the formula to obtain:
let s be j ω, the MAF amplitude-frequency and phase-frequency characteristics can be obtained as:
as can be seen from equation (9), when sin (T ω/2) ═ 0, the harmonics with angular frequency ω can be completely filtered out. Then the requirement for the MAF window width period T is:
Tω＝2hπ，h＝1、2……
namely: T/Th-fh/f, h-1, 2 … …
In the formula: f is the window width frequency of MAF; fh and Th are the frequency and period of the harmonics, respectively.
After matrix transformation, the load current contains both the direct current component converted from the fundamental component and the alternating current component converted from the harmonic component, and the average value of the alternating current component in one period is zero, so that after the average value algorithm, the load current only retains the direct current component corresponding to the fundamental component. The moving average filter depends on the moving square characteristic, even if the signal changes slightly, the moving average value can also change along with the signal, so that the moving average filter approaches to a true value, and the algorithm does not need to perform circular calculation every time, so that the rapidity of data updating is embodied, and the operation efficiency is improved. By omitting the link of the low-pass filter, the problem of poor filtering timeliness caused by the complex structure of the traditional low-pass filter is avoided.
And 3, directly obtaining active and reactive current signals through coordinate transformation. Redundant calculation amount caused by Clark transformation and Park inverse transformation is avoided, and calculation speed is faster. The conversion calculation lays a foundation for accurate compensation of harmonic waves and reactive current.
Referring to fig. 2, in a specific embodiment, three-phase voltages are set as Ua, Ub, and Uc, a delay method is used to separate a fundamental positive sequence component of an a-phase voltage in the system, and an initial phase angle is obtained only through corresponding function operation, so that detection errors of the phase-locked loop when the voltages are asymmetric are avoided. Wherein
The matrices C and D of the coordinate system transformation consisting of the above functions, ω t is the synchronous rotation angle of the grid voltage, where:
three-phase load currents ia, ib and ic are set and are obtained after alpha-beta conversion:
carrying out Park transformation:
the harmonic components of ip and iq are filtered by a Moving Average Filter (MAF) to obtain a DC component
And
fundamental component is obtained by matrix transformation:
for direct reactive current only
And carrying out coordinate transformation to obtain the reactive current in the system.
The difference between the three-phase current component of the load and the fundamental component is the sum of the harmonic component and the reactive current.
According to the harmonic and reactive current detection method, a T/3 time delay algorithm is adopted to separate the three-phase voltage of the system and collect the initial phase, so that the problem that when the three-phase voltage of a phase-locked loop module is asymmetric in the system, the initial phase of the sampled voltage has a phase difference due to the existence of negative sequence voltage, so that the reactive current detection has errors, and the detection result of the harmonic and reactive current is influenced is solved; the method adopts a Moving Average Filter (MAF) to filter, utilizes the MAF sliding square characteristic to accurately filter harmonic components in the load current, and obtains a current positive sequence fundamental wave signal, so as to make up the problems that the traditional low-pass filter is complex in structure and delay exists in detection, and enable the detection of harmonic waves and reactive current to be quicker and more accurate.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (3)
1. A harmonic and reactive current detection method is characterized by comprising the following steps:
step 1, separating positive and negative sequence voltage and current based on a signal T/3 delay algorithm, and extracting a positive sequence component;
step 2, filtering harmonic components in the load current by using a moving average filter to obtain fundamental current direct-current components;
and 3, directly obtaining active and reactive current signals through coordinate transformation.
2. The harmonic and reactive current detection method of claim 1, wherein step 1 comprises:
under a two-phase static coordinate system, power grid voltage and current signals are delayed by 1/3 power frequency periods T, and are combined according to a three-phase symmetry principle, positive sequence components and negative sequence components in three-phase power grid voltage are separated, and A-phase voltage positive sequence components are extracted.
3. The harmonic and reactive current detection method of claim 2, wherein the step 2 comprises:
based on the moving average filter, the fundamental current direct-current component is acquired under the condition that only the sampling frequency and the sliding window width are determined.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112881776A (en) * | 2021-01-13 | 2021-06-01 | 国网浙江省电力有限公司湖州供电公司 | Rapid extraction method of harmonic current |
| CN116626442A (en) * | 2023-06-06 | 2023-08-22 | 国网辽宁省电力有限公司抚顺供电公司 | Novel distribution network fault indicator based on edge calculation and application method thereof |
-
2020
- 2020-09-25 CN CN202011024572.5A patent/CN112269052A/en active Pending
Non-Patent Citations (2)
| Title |
|---|
| 康小燕: "改进的谐波和无功电流检测方法", 《电测与仪表》, pages 29 - 33 * |
| 徐荣: "一种抑制无隔离并网逆变器直流分量的PIR控制策略", 《电器与能效管理技术》, pages 53 - 58 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112881776A (en) * | 2021-01-13 | 2021-06-01 | 国网浙江省电力有限公司湖州供电公司 | Rapid extraction method of harmonic current |
| CN116626442A (en) * | 2023-06-06 | 2023-08-22 | 国网辽宁省电力有限公司抚顺供电公司 | Novel distribution network fault indicator based on edge calculation and application method thereof |
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