CN111077375B - On-line identification method of power grid impedance under the influence of background harmonics based on frequency domain subtraction - Google Patents

On-line identification method of power grid impedance under the influence of background harmonics based on frequency domain subtraction Download PDF

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CN111077375B
CN111077375B CN201911280166.2A CN201911280166A CN111077375B CN 111077375 B CN111077375 B CN 111077375B CN 201911280166 A CN201911280166 A CN 201911280166A CN 111077375 B CN111077375 B CN 111077375B
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张兴
陈少龙
郭梓暄
潘海龙
付新鑫
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Hefei University of Technology
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Abstract

本发明公开了一种基于频域减的背景谐波影响下电网阻抗在线辨识方法,该方法所研究的系统包含直流侧电压源,三相全桥逆变电路,三相LC滤波器,三相电网阻抗和三相电网。该方法通过一次采样,注入频率与背景频率f相等的扰动分量后再次采样,仅通过检测PCC点电压、电流来估计背景谐波影响下的电网阻抗的大小,进而用于逆变器自适应控制,提升并网系统稳定性,同时不增加成本。

Figure 201911280166

The invention discloses an on-line identification method of power grid impedance under the influence of background harmonics based on frequency domain subtraction. The system studied by the method includes a DC side voltage source, a three-phase full-bridge inverter circuit, a three-phase LC filter, a three-phase Grid impedance and three-phase grid. This method uses one sampling, injects a disturbance component whose frequency is equal to the background frequency f, and then samples again, and estimates the magnitude of the grid impedance under the influence of background harmonics only by detecting the voltage and current of the PCC point, which is then used for inverter adaptive control. , improve the stability of the grid-connected system without increasing the cost.

Figure 201911280166

Description

基于频域减的背景谐波影响下电网阻抗在线辨识方法On-line identification method of power grid impedance under the influence of background harmonics based on frequency domain subtraction

技术领域technical field

本发明属于电网质量分析及信号处理领域,尤其是涉及考虑背景谐波条件下,通过谐波注入准确测量出电网阻抗的在线辨识方法。The invention belongs to the field of power grid quality analysis and signal processing, and particularly relates to an online identification method for accurately measuring power grid impedance through harmonic injection under the condition of background harmonics.

背景技术Background technique

随着光伏发电、风力发电等新能源发电在电力系统中占据越来越大的比重,以及新能源发电本地消纳能力有限,需要进行远距离输电,线路感抗增大。对于逆变器而言,较大的线路阻抗会降低并网逆变器的稳定性,甚至会失稳。因此逆变器应具有在线估计电网阻抗的能力。As photovoltaic power generation, wind power generation and other new energy power generation occupy a larger and larger proportion in the power system, and the local consumption capacity of new energy power generation is limited, long-distance power transmission is required, and the line inductive reactance increases. For the inverter, the larger line impedance will reduce the stability of the grid-connected inverter, or even cause instability. Therefore, the inverter should have the ability to estimate the grid impedance online.

此外,由于电网所带负载的多样性和不确定性,导致电网中除基波以外还含有丰富的背景谐波。这些背景谐波使得传统的扰动注入的方法测量出现较大误差,甚至可能导致电网阻抗估计错误。基于以上两点,在考虑背景谐波条件下如何准确测量出电网阻抗就显得十分必要。In addition, due to the diversity and uncertainty of the load carried by the power grid, the power grid also contains abundant background harmonics in addition to the fundamental wave. These background harmonics make the traditional disturbance injection method have large errors in measurement, and may even lead to wrong estimation of grid impedance. Based on the above two points, it is very necessary to accurately measure the power grid impedance considering the background harmonics.

目前,对于电网阻抗的在线辨识已有多篇学术论文进行研究,例如:At present, there have been many academic papers on the online identification of power grid impedance, such as:

1、题为“基于复数滤波器和非特征次谐波注入的电网阻抗估算方法”(《电网技术》,2013年第10期2796~2801页)的文章。采用注入非特征次谐波,复数滤波器提取注入谐波响应的电网阻抗估算方法,但是未考虑到电网中存在的背景谐波影响。1. The article titled "Grid Impedance Estimation Method Based on Complex Filter and Non-characteristic Subharmonic Injection" ("Power Grid Technology", No. 10, 2013, pp. 2796-2801). The grid impedance estimation method uses the injection of non-characteristic harmonics and the complex filter to extract the injected harmonic response, but the influence of background harmonics in the grid is not considered.

2、题为“Grid impedance estimation for islanding detection and adaptivecontrol of converters”,A.Ghanem,M.Rashed,M.Sumner,M.A.Elsayes,andI.I.I.Mansy,IET Power Electronics,2017:1279-1288(“基于电网阻抗估计的变换器孤岛检测与自适应控制”,《IET学报电力电子期刊》,2017年网络发表)的文章,通过采样开关频率级电压电流,利用开关管开通关断时的电路方程估算电网阻抗,虽然该方法可以忽略电网中的背景谐波影响,但是需要高精度传感器采样,不利于工程应用。2. Titled "Grid impedance estimation for islanding detection and adaptivecontrol of converters", A.Ghanem, M.Rashed, M.Sumner, M.A.Elsayes, and I.I.I.Mansy, IET Power Electronics, 2017:1279-1288 ("Grid-based "Islanding Detection and Adaptive Control of Converters Based on Impedance Estimation", "IET Journal of Power Electronics", published online in 2017), by sampling the switching frequency level voltage and current, and using the circuit equation when the switch is turned on and off to estimate the grid impedance , although this method can ignore the influence of background harmonics in the power grid, but it requires high-precision sensor sampling, which is not conducive to engineering applications.

3、中国发明专利文献(公开号CN 110112776 A)于2019年8月9日公开的《考虑电网背景谐波的并网逆变器电网阻抗的辨识方法》,提出了一种向电网中注入高频电压信号,使用复数滤波器提取出高频谐波分量的方法来测量电网阻抗。虽然该方法考虑了电网中的背景谐波影响,但是该发明是通过注入高频信号来忽略可能存在的较低频背景谐波的影响。3. "Identification Method of Grid-connected Inverter Grid Impedance Considering Grid Background Harmonics" published on August 9, 2019 by Chinese invention patent document (publication number CN 110112776 A), which proposes a method of injecting high voltage into the grid. The power grid impedance is measured by using a complex filter to extract high-frequency harmonic components. Although this method takes into account the influence of background harmonics in the grid, the invention ignores the influence of possible lower frequency background harmonics by injecting a high frequency signal.

综合以上文献,现有的技术存在以下不足:Based on the above literature, the existing technology has the following shortcomings:

1、现有基于非特征次谐波扰动注入的电网阻抗估计方法,未考虑到电网中含有的背景谐波的影响,有必要研究在背景谐波不可忽略的条件下电网阻抗估计方法。1. The existing grid impedance estimation methods based on non-characteristic harmonic disturbance injection do not consider the influence of background harmonics contained in the grid. It is necessary to study the grid impedance estimation method under the condition that the background harmonics cannot be ignored.

2、现有的考虑背景谐波影响的方法,采用的是高频次的谐波电压电流的注入、提取和分析,避开背景谐波频率与注入频率之间的混叠影响,因此有必要研究背景谐波频率与注入频率交互时的阻抗估计方法。2. The existing method for considering the influence of background harmonics adopts the injection, extraction and analysis of high-frequency harmonic voltage and current to avoid the aliasing effect between the background harmonic frequency and the injection frequency, so it is necessary to Study the impedance estimation method when the background harmonic frequency interacts with the injection frequency.

发明内容SUMMARY OF THE INVENTION

本发明提出了一种基于频域减的背景谐波影响下电网阻抗在线辨识方法,该方法考虑电网中含有的背景谐波,并且不需要注入高频信号来估算电网阻抗。通过本方法估算出的电网阻抗准确,并且可用于逆变器自适应控制,提升并网系统稳定性,同时不增加成本。The invention proposes an on-line identification method of power grid impedance under the influence of background harmonics based on frequency domain subtraction. The method considers the background harmonics contained in the power grid and does not need to inject high-frequency signals to estimate the power grid impedance. The grid impedance estimated by the method is accurate, and can be used for the adaptive control of the inverter to improve the stability of the grid-connected system without increasing the cost.

本发明的目的是这样实现的。本发明提供了一种基于频域减的背景谐波影响下电网阻抗在线辨识方法,应用该方法的并网逆变器主电路拓扑结构包括直流侧电压源、三相全桥逆变电路、三相LC滤波器、三相电网阻抗和三相电网,所述直流侧电压源与三相全桥逆变电路连接,三相全桥逆变电路经三相LC滤波器与三相电网阻抗连接后接入三相电网;The object of the present invention is achieved in this way. The invention provides an on-line identification method for power grid impedance under the influence of background harmonics based on frequency domain subtraction. The main circuit topology structure of the grid-connected inverter using the method includes a DC side voltage source, a three-phase full-bridge inverter circuit, a three-phase full-bridge inverter circuit, and a three-phase full-bridge inverter circuit. Phase LC filter, three-phase grid impedance and three-phase grid, the DC side voltage source is connected with the three-phase full-bridge inverter circuit, and the three-phase full-bridge inverter circuit is connected with the three-phase grid impedance through the three-phase LC filter Access to three-phase power grid;

定时对背景谐波影响下的电网阻抗进行在线辨识,即预先设定一个辨识间隔时间T,辨识间隔时间T到,启动一次采样、扰动注入、二次采样、电网阻抗在线辨识:On-line identification of power grid impedance under the influence of background harmonics is performed regularly, that is, an identification interval time T is preset, and when the identification interval time T arrives, first sampling, disturbance injection, second sampling, and online identification of power grid impedance are started:

具体的,一个背景谐波影响下的电网阻抗在线辨识周期的步骤如下:Specifically, the steps for the online identification cycle of grid impedance under the influence of a background harmonic are as follows:

步骤1,设逆变器并网处于稳定工作状态,对三相LC滤波器电容的A相输出端电压进行一次采样,记为PCC点A相电压UPCC_A1,对流过三相电网阻抗的A相电流进行一次采样,记为PCC点A相电流IPCC_A1Step 1, set the inverter grid-connected to be in a stable working state, sample the voltage of the A-phase output terminal of the three-phase LC filter capacitor once, record it as the A-phase voltage U PCC_A1 at the PCC point, and measure the A-phase flowing through the three-phase grid impedance. The current is sampled once, and is recorded as the A-phase current I PCC_A1 at the PCC point;

步骤2,设电网中含有背景谐波,将该背景谐波的频率记为背景频率f,对步骤1中采集得到的PCC点A相电压UPCC_A1,在背景频率f的频率点做傅里叶分析得到未注入扰动时频率为f的谐波电压矢量

Figure BDA0002316527870000031
其中U1f是未注入扰动时频率为f的谐波电压矢量
Figure BDA0002316527870000032
的模值,θu1f是未注入扰动时频率为f的谐波电压矢量
Figure BDA0002316527870000033
相角;对步骤1中采集得到的PCC点A相电流IPCC_A1,在f频率点做傅里叶分析得到未注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000034
其中I1f是未注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000035
的模值,
Figure BDA0002316527870000036
是未注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000037
的相角;Step 2: Suppose the power grid contains background harmonics, denote the frequency of the background harmonics as the background frequency f, and perform a Fourier transform on the phase A voltage U PCC_A1 of the PCC point collected in step 1 at the frequency point of the background frequency f. The harmonic voltage vector with frequency f when no disturbance is injected is obtained by analysis
Figure BDA0002316527870000031
where U 1f is the harmonic voltage vector of frequency f when no disturbance is injected
Figure BDA0002316527870000032
The modulo value of , θ u1f is the harmonic voltage vector of frequency f when no disturbance is injected
Figure BDA0002316527870000033
Phase angle; for the phase A current I PCC_A1 at the PCC point collected in step 1, perform Fourier analysis at the frequency point f to obtain the harmonic current vector with frequency f when no disturbance is injected
Figure BDA0002316527870000034
where I 1f is the harmonic current vector of frequency f when no disturbance is injected
Figure BDA0002316527870000035
the modulo value of ,
Figure BDA0002316527870000036
is the harmonic current vector of frequency f when no disturbance is injected
Figure BDA0002316527870000037
the phase angle;

步骤3,在逆变器调制波信号上注入频率与背景频率f相等的扰动分量,对三相LC滤波器电容的A相输出端电压进行二次采样并记为二次PCC点A相电压UPCC_A2,对流过三相电网阻抗的A相电流进行二次采样并记为二次PCC点A相电流IPCC_A2Step 3: Inject a disturbance component whose frequency is equal to the background frequency f on the modulated wave signal of the inverter, re-sample the voltage of the A-phase output terminal of the three-phase LC filter capacitor and record it as the A-phase voltage U at the secondary PCC point. PCC_A2 , the A-phase current flowing through the impedance of the three-phase power grid is sampled twice and recorded as the A-phase current I PCC_A2 at the secondary PCC point;

步骤4,对步骤2中得到的二次PCC点A相电压UPCC_A2,在背景频率f的频率点做傅里叶分析得到注入扰动时频率为f的谐波电压矢量

Figure BDA0002316527870000041
其中U2f是注入扰动时频率为f的电压矢量
Figure BDA0002316527870000042
的模值,θu2f是注入扰动时频率为f的谐波电压矢量
Figure BDA0002316527870000043
的相角;对步骤2中得到的二次PCC点A相电流IPCC_A2,在背景频率f的频率点做傅里叶分析得到注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000044
其中I2f是注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000045
的模值,
Figure BDA0002316527870000046
是注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000047
的相角;Step 4: Perform Fourier analysis on the phase A voltage U PCC_A2 at the secondary PCC point obtained in step 2 at the frequency point of the background frequency f to obtain the harmonic voltage vector with frequency f when the disturbance is injected.
Figure BDA0002316527870000041
where U 2f is the voltage vector of frequency f when the perturbation is injected
Figure BDA0002316527870000042
The modulo value of , θ u2f is the harmonic voltage vector of frequency f when the disturbance is injected
Figure BDA0002316527870000043
The phase angle of the second PCC point A obtained in step 2, I PCC_A2 , do Fourier analysis at the frequency point of the background frequency f to obtain the harmonic current vector with the frequency f when the disturbance is injected
Figure BDA0002316527870000044
where I 2f is the harmonic current vector at frequency f when the disturbance is injected
Figure BDA0002316527870000045
the modulo value of ,
Figure BDA0002316527870000046
is the harmonic current vector of frequency f when the disturbance is injected
Figure BDA0002316527870000047
the phase angle;

步骤5,将三相电网阻抗的数值记为阻抗值Z,利用步骤2中得到未注入扰动时频率为f的谐波电压矢量

Figure BDA0002316527870000048
和未注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000049
步骤4中得到的注入扰动时频率为f的谐波电压矢量
Figure BDA00023165278700000410
和注入扰动时频率为f的谐波电流矢量
Figure BDA00023165278700000411
计算阻抗值Z,计算式如下:Step 5, record the value of the impedance of the three-phase power grid as the impedance value Z, and use the harmonic voltage vector with frequency f obtained in step 2 when no disturbance is injected.
Figure BDA0002316527870000048
and the harmonic current vector of frequency f when no disturbance is injected
Figure BDA0002316527870000049
The harmonic voltage vector of frequency f obtained in step 4 when the perturbation is injected
Figure BDA00023165278700000410
and the harmonic current vector of frequency f when the disturbance is injected
Figure BDA00023165278700000411
Calculate the impedance value Z, the formula is as follows:

Figure BDA00023165278700000412
Figure BDA00023165278700000412

其中,|Z|为阻抗值Z的模值,δ为阻抗值Z的相角,Rg为阻抗值Z的阻性成分,Lg为阻抗值Z的感性成分,j是虚数单位,j2=-1。Among them, |Z| is the modulus value of the impedance value Z, δ is the phase angle of the impedance value Z, R g is the resistive component of the impedance value Z, L g is the inductive component of the impedance value Z, j is the imaginary unit, j 2 =-1.

相对于现有技术,本发明的有益效果为:Compared with the prior art, the beneficial effects of the present invention are:

1、本发明所述的基于频域减的背景谐波影响下电网阻抗在线辨识方法,该方法通过检测PCC点电压电流可以准确估计电网阻抗,进而用于逆变器自适应控制,提升并网系统稳定性;1. The method for online identification of power grid impedance under the influence of background harmonics based on frequency domain subtraction according to the present invention can accurately estimate the power grid impedance by detecting the voltage and current of the PCC point, which is then used for inverter adaptive control to improve grid connection. system stability;

2、本发明通过分析PCC点电压电流幅值相角特征,两次测量、计算谐波电压电流幅值相角,解决了电网中可能一直存在的背景谐波对电网阻抗辨识的影响;2. The present invention solves the influence of the background harmonics that may always exist in the power grid on the power grid impedance identification by analyzing the phase angle characteristics of the voltage and current amplitude at the PCC point, and measuring and calculating the harmonic voltage and current amplitude phase angle twice;

3、本发明所述的基于频域减的背景谐波影响下电网阻抗在线辨识方法仅在现有电力电子变换器系统的算法上进行改进,无需增加额外设备,如传感器等;3. The on-line identification method of power grid impedance under the influence of background harmonics based on frequency domain subtraction according to the present invention is only improved on the algorithm of the existing power electronic converter system, without adding additional equipment, such as sensors, etc.;

附图说明Description of drawings

图1为应用本发明基于频域减的背景谐波影响下电网阻抗在线辨识方法的并网逆变器主电路拓扑图。FIG. 1 is a topology diagram of a main circuit of a grid-connected inverter using the method for online identification of grid impedance under the influence of background harmonics based on frequency domain subtraction according to the present invention.

图2为电网背景谐波对阻抗测量影响的对比分析图。Figure 2 is a comparative analysis diagram of the influence of power grid background harmonics on impedance measurement.

图3为测量出来的电网阻抗Z的模值|Z|和阻抗角图。Fig. 3 is a graph of the modulus value |Z| and the impedance angle of the measured grid impedance Z.

图4为图3中区域A的放大部分图。FIG. 4 is an enlarged partial view of area A in FIG. 3 .

图5为电网阻抗Z的电感Lg部分和电阻Rg部分的测试图。FIG. 5 is a test diagram of the inductance L g part and the resistance R g part of the grid impedance Z.

图6为图5中区域B的放大部分图。FIG. 6 is an enlarged partial view of area B in FIG. 5 .

具体实施方式Detailed ways

下面结合附图对本实施例进行具体的描述。The present embodiment will be described in detail below with reference to the accompanying drawings.

图1是应用本发明的并网逆变器主电路的拓扑结构图,由图可见,该拓扑结构包括直流侧电压源10、三相全桥逆变电路20、三相LC滤波器30、三相电网阻抗40和三相电网50。1 is a topological structure diagram of the main circuit of a grid-connected inverter to which the present invention is applied. As can be seen from the figure, the topological structure includes a DC side voltage source 10, a three-phase full-bridge inverter circuit 20, a three-phase LC filter 30, and a three-phase LC filter. Phase grid impedance 40 and three-phase grid 50 .

所述直流侧电压源10与三相全桥逆变电路20连接,三相全桥逆变电路20经三相LC滤波器30与三相电网阻抗40连接后接入三相电网50。在图1中,Vdc为直流侧电压源10,Lf为三相LC滤波器30桥臂侧电感,Cf为三相LC滤波器30滤波电容,r为三相LC滤波器30无源阻尼电阻,Rg为三相线路阻抗40中的电阻,Lg为三相电网阻抗40中的电感,Grid为三相电网50。The DC side voltage source 10 is connected to the three-phase full-bridge inverter circuit 20 , and the three-phase full-bridge inverter circuit 20 is connected to the three-phase grid 50 after being connected to the three-phase grid impedance 40 through the three-phase LC filter 30 . In FIG. 1 , V dc is the DC side voltage source 10 , L f is the bridge arm side inductance of the three-phase LC filter 30 , C f is the filter capacitor of the three-phase LC filter 30 , and r is the passive source of the three-phase LC filter 30 . Damping resistance, R g is the resistance in the three-phase line impedance 40 , L g is the inductance in the three-phase grid impedance 40 , and Grid is the three-phase grid 50 .

本实施例中主电路参数为:直流侧电压Vdc为800V,逆变器额定输出线电压为380V/50Hz,逆变器额定功率为100kW,滤波电感Lf为0.56mH,滤波电容Cf及无源阻尼电阻r为270uF/0.3Ω,三相电网阻抗中电感部分Lg=0.1mH及电阻部分Rg=0.1Ω。In this embodiment, the main circuit parameters are: the DC side voltage V dc is 800V, the rated output line voltage of the inverter is 380V/50Hz, the rated power of the inverter is 100kW, the filter inductance L f is 0.56mH, the filter capacitor C f and The passive damping resistance r is 270uF/0.3Ω, the inductance part L g =0.1mH and the resistance part R g =0.1Ω in the three-phase power grid impedance.

本发明所述基于频域减的背景谐波影响下电网阻抗在线辨识方法,定时对背景谐波影响下的电网阻抗进行在线辨识,即预先设定一个辨识间隔时间T,辨识间隔时间T到,启动一次采样、扰动注入、二次采样、电网阻抗在线辨识。在本实施例中,选择T为16个基波周期周期T0The method for online identification of power grid impedance under the influence of background harmonics based on frequency domain subtraction according to the present invention regularly performs online identification of power grid impedance under the influence of background harmonics, that is, an identification interval time T is preset, and the identification interval time T reaches, Start primary sampling, disturbance injection, secondary sampling, and online identification of grid impedance. In this embodiment, T is selected to be 16 fundamental wave period periods T 0 .

具体的,一个背景谐波影响下的电网阻抗在线辨识周期的步骤如下:Specifically, the steps for the online identification cycle of grid impedance under the influence of a background harmonic are as follows:

步骤1,设逆变器并网处于稳定工作状态,对三相LC滤波器30电容的A相输出端电压进行一次采样,记为PCC点A相电压UPCC_A1,对流过三相电网阻抗40的A相电流进行一次采样,记为PCC点A相电流IPCC_A1Step 1, set the inverter grid-connected to be in a stable working state, sample the voltage of the A-phase output terminal of the three-phase LC filter 30 capacitor once, record it as the A-phase voltage U PCC_A1 at the PCC point, and measure the voltage flowing through the three-phase grid impedance 40 . The A-phase current is sampled once, and is recorded as the A-phase current I PCC_A1 at the PCC point;

步骤2,设电网中含有背景谐波,将该背景谐波的频率记为背景频率f,对步骤1中采集得到的PCC点A相电压UPCC_A1,在背景频率f的频率点做傅里叶分析得到未注入扰动时频率为f的谐波电压矢量

Figure BDA0002316527870000061
其中U1f是未注入扰动时频率为f的谐波电压矢量
Figure BDA0002316527870000062
的模值,θu1f是未注入扰动时频率为f的谐波电压矢量
Figure BDA0002316527870000063
相角;对步骤1中采集得到的PCC点A相电流IPCC_A1,在f频率点做傅里叶分析得到未注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000064
其中I1f是未注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000065
的模值,
Figure BDA0002316527870000066
是未注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000067
的相角;Step 2: Suppose the power grid contains background harmonics, denote the frequency of the background harmonics as the background frequency f, and perform a Fourier transform on the phase A voltage U PCC_A1 of the PCC point collected in step 1 at the frequency point of the background frequency f. The harmonic voltage vector with frequency f when no disturbance is injected is obtained by analysis
Figure BDA0002316527870000061
where U 1f is the harmonic voltage vector of frequency f when no disturbance is injected
Figure BDA0002316527870000062
The modulo value of , θ u1f is the harmonic voltage vector of frequency f when no disturbance is injected
Figure BDA0002316527870000063
Phase angle; for the phase A current I PCC_A1 at the PCC point collected in step 1, perform Fourier analysis at the frequency point f to obtain the harmonic current vector with frequency f when no disturbance is injected
Figure BDA0002316527870000064
where I 1f is the harmonic current vector of frequency f when no disturbance is injected
Figure BDA0002316527870000065
the modulo value of ,
Figure BDA0002316527870000066
is the harmonic current vector of frequency f when no disturbance is injected
Figure BDA0002316527870000067
the phase angle;

步骤3,在逆变器调制波信号上注入频率与背景频率f相等的扰动分量,对三相LC滤波器30电容的A相输出端电压进行二次采样并记为二次PCC点A相电压UPCC_A2,对流过三相电网阻抗40的A相电流进行二次采样并记为二次PCC点A相电流IPCC_A2Step 3: Inject a disturbance component whose frequency is equal to the background frequency f on the modulated wave signal of the inverter, and resample the voltage of the phase A output terminal of the capacitor of the three-phase LC filter 30 and record it as the phase A voltage of the secondary PCC point. U PCC_A2 , the A-phase current flowing through the three-phase grid impedance 40 is sampled twice and recorded as the A-phase current I PCC_A2 at the secondary PCC point;

步骤4,对步骤2中得到的二次PCC点A相电压UPCC_A2,在背景频率f的频率点做傅里叶分析得到注入扰动时频率为f的谐波电压矢量

Figure BDA0002316527870000071
其中U2f是注入扰动时频率为f的电压矢量
Figure BDA0002316527870000072
的模值,θu2f是注入扰动时频率为f的谐波电压矢量
Figure BDA0002316527870000073
的相角;对步骤2中得到的二次PCC点A相电流IPCC_A2,在背景频率f的频率点做傅里叶分析得到注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000074
其中I2f是注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000075
的模值,
Figure BDA0002316527870000076
是注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000077
的相角;Step 4: Perform Fourier analysis on the phase A voltage U PCC_A2 at the secondary PCC point obtained in step 2 at the frequency point of the background frequency f to obtain the harmonic voltage vector with frequency f when the disturbance is injected.
Figure BDA0002316527870000071
where U 2f is the voltage vector of frequency f when the perturbation is injected
Figure BDA0002316527870000072
The modulo value of , θ u2f is the harmonic voltage vector of frequency f when the disturbance is injected
Figure BDA0002316527870000073
The phase angle of the second PCC point A obtained in step 2, I PCC_A2 , do Fourier analysis at the frequency point of the background frequency f to obtain the harmonic current vector with the frequency f when the disturbance is injected
Figure BDA0002316527870000074
where I 2f is the harmonic current vector at frequency f when the disturbance is injected
Figure BDA0002316527870000075
the modulo value of ,
Figure BDA0002316527870000076
is the harmonic current vector of frequency f when the disturbance is injected
Figure BDA0002316527870000077
the phase angle;

步骤5,将三相电网阻抗40的数值记为阻抗值Z,利用步骤2中得到未注入扰动时频率为f的谐波电压矢量

Figure BDA0002316527870000078
和未注入扰动时频率为f的谐波电流矢量
Figure BDA0002316527870000079
步骤4中得到的注入扰动时频率为f的谐波电压矢量
Figure BDA00023165278700000710
和注入扰动时频率为f的谐波电流矢量
Figure BDA00023165278700000711
计算阻抗值Z,计算式如下:In step 5, the value of the impedance 40 of the three-phase power grid is recorded as the impedance value Z, and the harmonic voltage vector with the frequency f when the disturbance is not injected is obtained in step 2.
Figure BDA0002316527870000078
and the harmonic current vector of frequency f when no disturbance is injected
Figure BDA0002316527870000079
The harmonic voltage vector of frequency f obtained in step 4 when the perturbation is injected
Figure BDA00023165278700000710
and the harmonic current vector of frequency f when the disturbance is injected
Figure BDA00023165278700000711
Calculate the impedance value Z, the formula is as follows:

Figure BDA00023165278700000712
Figure BDA00023165278700000712

其中,|Z|为阻抗值Z的模值,δ为阻抗值Z的相角,Rg为阻抗值Z的阻性成分,Lg为阻抗值Z的感性成分,j是虚数单位,j2=-1。Among them, |Z| is the modulus value of the impedance value Z, δ is the phase angle of the impedance value Z, R g is the resistive component of the impedance value Z, L g is the inductive component of the impedance value Z, j is the imaginary unit, j 2 =-1.

为例验证本发明的有效性,进行了仿真验证。Taking an example to verify the effectiveness of the present invention, simulation verification is carried out.

图2为电网背景谐波对阻抗测量影响的对比分析图。由图2可见,用常规扰动注入的方法测量电网阻抗,可以看出在不考虑背景谐波时,可以准确测量出电网阻抗;然而电网突然出现背景谐波,导致测量电网阻抗发生突变,测量就会出现错误。Figure 2 is a comparative analysis diagram of the influence of power grid background harmonics on impedance measurement. It can be seen from Figure 2 that the grid impedance is measured by the conventional disturbance injection method, and it can be seen that the grid impedance can be accurately measured without considering the background harmonics; however, the background harmonics suddenly appear in the grid, resulting in a sudden change in the measured grid impedance, and the measurement is An error will occur.

图3为测量出来的电网阻抗Z的模值|Z|和阻抗角图,图4为图3中区域A的放大部分图。如图3和图4可见,通过对背景谐波信息的测量,消除了背景谐波对阻抗辨识的影响,得到的电网阻抗比较准确。FIG. 3 is a graph of the modulus value |Z| and the impedance angle of the measured grid impedance Z, and FIG. 4 is an enlarged partial graph of the area A in FIG. 3 . As can be seen in Figure 3 and Figure 4, by measuring the background harmonic information, the influence of the background harmonic on the impedance identification is eliminated, and the obtained grid impedance is relatively accurate.

图5为电网阻抗Z的电感Lg部分和电阻Rg部分的测试图,图6为图5中区域B的放大部分图。由图5和图6可见,本发明方法还可以准确测量出电网阻抗中的感性成分和阻性成分的大小。FIG. 5 is a test diagram of the inductance L g part and the resistance R g part of the grid impedance Z, and FIG. 6 is an enlarged partial diagram of the area B in FIG. 5 . It can be seen from FIG. 5 and FIG. 6 that the method of the present invention can also accurately measure the magnitude of the inductive component and the resistive component in the grid impedance.

Claims (1)

1. A grid-connected inverter main circuit topological structure applying the method comprises a direct current side voltage source (10), a three-phase full-bridge inverter circuit (20), a three-phase LC filter (30), a three-phase grid impedance (40) and a three-phase grid (50), wherein the direct current side voltage source (10) is connected with the three-phase full-bridge inverter circuit (20), and the three-phase full-bridge inverter circuit (20) is connected with the three-phase grid impedance (40) through the three-phase LC filter (30) and then is connected with the three-phase grid (50);
the method is characterized in that the online identification is carried out on the power grid impedance under the influence of background harmonic wave at regular time, namely, an identification interval time T is preset, the identification interval time T is up, and the online identification of primary sampling, disturbance injection, secondary sampling and power grid impedance is started:
specifically, the steps of the online identification period of the power grid impedance under the influence of background harmonic waves are as follows:
step 1, setting the grid connection of an inverter to be in a stable working state, sampling the voltage of an A-phase output end of a capacitor of a three-phase LC filter (30) for one time, and marking as a PCC point A-phase voltage UPCC_A1The phase A current flowing through the three-phase network impedance (40) is sampled once and is recorded as the phase A current I of the PCC pointPCC_A1
Step 2, setting that the power grid contains background harmonic waves, recording the frequency of the background harmonic waves as background frequency f, and carrying out phase voltage U on the PCC points A phase collected in the step 1PCC_A1Fourier analysis is carried out on the frequency point of the background frequency f to obtain a harmonic voltage vector with the frequency f when no disturbance is injected
Figure FDA0002703878310000011
Wherein U is1fIs a harmonic voltage vector of frequency f without injected disturbance
Figure FDA0002703878310000012
Modulus of (e), thetau1fIs a harmonic voltage vector of frequency f without injected disturbance
Figure FDA0002703878310000013
A phase angle; for the PCC point A phase current I acquired in the step 1PCC_A1Fourier analysis is carried out at the f frequency point to obtain a harmonic current vector with the frequency of f when disturbance is not injected
Figure FDA0002703878310000014
Wherein I1fIs a harmonic current vector of frequency f when no disturbance is injected
Figure FDA0002703878310000015
The value of the modulus of the (c) component,
Figure FDA0002703878310000016
is a harmonic current vector of frequency f when no disturbance is injected
Figure FDA0002703878310000017
The phase angle of (d);
and 3, injecting disturbance components with the frequency equal to the background frequency f into the inverter modulation wave signal, performing secondary sampling on the voltage of the A-phase output end of the capacitor of the three-phase LC filter (30) and recording the voltage as the secondary PCC point A-phase voltage UPCC_A2The phase-A current flowing through the three-phase network impedance (40) is subsampled and recorded as a secondary PCC point phase-A current IPCC_A2
Step 4, carrying out phase voltage U of the secondary PCC point A phase obtained in the step 3PCC_A2Fourier analysis is carried out on frequency points of background frequency f to obtain harmonic voltage vector with frequency f when injection disturbance is carried out
Figure FDA0002703878310000021
Wherein U is2fIs a voltage vector of frequency f at the time of injection of a disturbance
Figure FDA0002703878310000022
Modulus of (e), thetau2fIs a harmonic voltage vector of frequency f when injecting a disturbance
Figure FDA0002703878310000023
The phase angle of (d); for the secondary PCC point A phase current I obtained in the step 3PCC_A2Fourier analysis is carried out on frequency points of background frequency f to obtain harmonic current vector with frequency f when disturbance is injected
Figure FDA0002703878310000024
Wherein I2fIs a harmonic current vector of frequency f when injecting a disturbance
Figure FDA0002703878310000025
The value of the modulus of the (c) component,
Figure FDA0002703878310000026
is a harmonic current vector of frequency f when injecting a disturbance
Figure FDA0002703878310000027
The phase angle of (d);
step 5, recording the numerical value of the three-phase power grid impedance (40) as an impedance value Z, and obtaining a harmonic voltage vector with the frequency f when disturbance is not injected in the step 2
Figure FDA0002703878310000028
And a harmonic current vector of frequency f when no disturbance is injected
Figure FDA0002703878310000029
The harmonic voltage vector with the frequency f during injection disturbance obtained in the step 4
Figure FDA00027038783100000210
And the harmonic current vector with frequency f when injecting disturbance
Figure FDA00027038783100000211
Calculating the impedance value Z according to the following formula:
Figure FDA00027038783100000212
wherein | Z | is a module value of the impedance value Z, and is a phase angle of the impedance value Z, RgIs a resistive component of the impedance value Z, LgIs the inductive component of the impedance value Z, j being the unit of an imaginary number, j2=-1。
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