CN103308806A - Islanding detection method based on fundamental frequency and switching-frequency sub-impedance - Google Patents

Abstract

Translated fromChinese

本发明涉及一种基于基频与开关频率次阻抗的孤岛检测法，属于并网逆变器在电力系统应用中的保护与控制领域。本发明针对并网逆变器，提出利用并网逆变器基波频率处电流成分与开关频率处存在的谐波成分，通过傅里叶级数中三角函数的关系取代傅里叶变换，只需在时域内将采样得到的公共连接点(PCC)电压与并网电流信号送至DSP处理芯片进行软件运算，即可由阻抗的变化快速有效的判断孤岛发生。本发明有益之处在于：突破传统被动孤岛检测法弊端，且不需外加扰动信号，从而避免主动孤岛检测法中的扰动影响，无需在频域内计算阻抗，快速的运算及动作保证了系统运行的稳定性及可靠性，具有良好的工程借鉴价值。

The invention relates to an islanding detection method based on fundamental frequency and switching frequency secondary impedance, and belongs to the field of protection and control of grid-connected inverters in power system applications. The present invention aims at the grid-connected inverter, and proposes to use the current component at the fundamental frequency of the grid-connected inverter and the harmonic component at the switching frequency to replace the Fourier transform by the relationship of the trigonometric function in the Fourier series. It is necessary to send the sampled common connection point (PCC) voltage and grid-connected current signal to the DSP processing chip for software calculation in the time domain, and the occurrence of islanding can be quickly and effectively judged by the change of impedance. The invention is beneficial in that it breaks through the disadvantages of the traditional passive island detection method, and does not need to add a disturbance signal, thereby avoiding the disturbance influence in the active island detection method, and does not need to calculate the impedance in the frequency domain, and the fast calculation and action ensure the smooth operation of the system. Stability and reliability have good engineering reference value.

Description

Translated fromChinese

一种基于基频与开关频率次阻抗的孤岛检测法An Islanding Detection Method Based on the Fundamental Frequency and Switching Frequency Secondary Impedance

技术领域technical field

本发明涉及一种基于基频与开关频率次阻抗的孤岛检测法，属于并网逆变器在电力系统应用中的保护与控制领域。The invention relates to an islanding detection method based on fundamental frequency and switching frequency secondary impedance, and belongs to the field of protection and control of grid-connected inverters in power system applications.

背景技术`Background technology`

分布式发电并网系统因其设计灵活、电能利用形式来源多样而受到人们越来越多的关注，但也由此带来了孤岛的问题。目前，孤岛检测主要有基于本地电气量特征(包括频率、电压、谐波、阻抗等)的本地检测方法和基于通信技术的远程检测两种方法，基于通信技术的远程检测多用于电力公司对分布式发电系统及配电网电能传输运行的监测与维护，也称电网端检测法。现如今，国内外各类并网标准亦对各独立的并网逆变器提出了诸多并网要求与指标。Distributed generation grid-connected system has attracted more and more attention because of its flexible design and diverse sources of power utilization, but it also brings the problem of isolated islands. At present, islanding detection mainly includes local detection methods based on local electrical quantity characteristics (including frequency, voltage, harmonics, impedance, etc.) and remote detection methods based on communication technology. The monitoring and maintenance of power generation system and distribution network power transmission operation, also known as grid end detection method. Nowadays, various grid-connected standards at home and abroad also put forward many grid-connected requirements and indicators for independent grid-connected inverters.

并网逆变器多采用本地检测方法，包括了被动式孤岛检测与主动式孤岛检测。被动式孤岛检测法通过检测并网系统中与电网接口处的电压幅值、频率、相位等异常来检测孤岛效应，此类方法简单，无需添加外部硬件，但检测实时性差，存在十分明显的检测盲区；而主动式检测法利用主动式的频率偏移、功率扰动等方法改进了被动式检测法，盲区有效减小，精确度得到提高，但主动检测法引入了外部的扰动量，增加了检测复杂性的同时带来了并网质量的下降。Grid-connected inverters mostly use local detection methods, including passive island detection and active island detection. The passive islanding detection method detects the islanding effect by detecting abnormalities such as voltage amplitude, frequency, and phase at the interface between the grid-connected system and the grid. This method is simple and does not need to add external hardware, but the real-time detection is poor, and there are obvious detection blind spots ; while the active detection method uses active frequency offset, power disturbance and other methods to improve the passive detection method, the blind area is effectively reduced, and the accuracy is improved, but the active detection method introduces external disturbances, which increases the detection complexity. At the same time, it brings a decline in the quality of grid connection.

目前较新的LCL型滤波结构并网逆变器相对传统L及LC型滤波结构并网逆变器来说，其谐波抑制效果有了明显的改善，对于LCL型三阶滤波结构的谐振尖峰问题也有了较好的解决，其开关频率次的谐波能够符合相关入网规范要求，但仍然无法完全消除，无论L型、LC型、LCL型，其开关频率次谐波特征都可作为LCL型逆变器具有的特征存在，同时，并网电流中以基波为主，采用基波电流来检测基频阻抗是一种较好的方法，不需要外加谐波，但单一的基频阻抗检测存在盲区，需与其他检测配合使用。Compared with the traditional L and LC filter structure grid-connected inverters, the newer LCL filter structure grid-connected inverters have significantly improved harmonic suppression effect. The problem has also been better solved. The harmonics of the switching frequency can meet the requirements of the relevant network access specifications, but they still cannot be completely eliminated. Regardless of the L type, LC type, or LCL type, the switching frequency sub-harmonic characteristics can be used as LCL type The characteristics of the inverter exist. At the same time, the grid-connected current is dominated by the fundamental wave. It is a better method to use the fundamental wave current to detect the fundamental frequency impedance. No additional harmonics are required, but the single fundamental frequency impedance detection There are blind spots and need to be used in conjunction with other tests.

发明内容Contents of the invention

本发明的主要目的是：针对以上所述传统方法和其他已存在方法中的问题，结合LCL型并网逆变器特点，提出了一种快速检测并网逆变器孤岛效应的新方法。The main purpose of the present invention is to propose a new method for quickly detecting the islanding effect of grid-connected inverters in view of the problems in the above-mentioned traditional methods and other existing methods, combined with the characteristics of LCL grid-connected inverters.

本发明提供的快速孤岛检测法，包括以下几个步骤：The fast island detection method provided by the present invention comprises the following steps:

一种基于基频与开关频率次阻抗的孤岛检测法，包括如下步骤：An islanding detection method based on fundamental frequency and switching frequency secondary impedance, comprising the following steps:

（1）并网逆变器与低压电网并联，同时两者中间并接本地负载若干，所述并网逆变器、低压电网、本地负载的公共连接点为PCC，在PCC和低压电网之间设置接触开关，用以切换并网模式与孤岛模式；(1) The grid-connected inverter is connected in parallel with the low-voltage grid, and a number of local loads are connected in parallel between the two. The common connection point of the grid-connected inverter, the low-voltage grid, and the local load is PCC, between PCC and the low-voltage grid Set the contact switch to switch between grid-connected mode and island mode;

（2）采样PCC处的电压V_PCC与并网逆变器的输出电流I_inv，将信号送至DSP2808核心控制芯片进行并网控制的相关软件运算，输出SPWM驱动信号驱动各桥臂开关管导通与关断，同时利用傅里叶级数的三角函数关系，由以上两个采样参数V_PCC和I_inv进行快速孤岛计算，获得基波频率和开关频率下的阻抗值；(2) Sampling the voltage V_PCC at the PCC and the output current I_inv of the grid-connected inverter, sending the signal to the DSP2808 core control chip for related software calculations of grid-connected control, outputting the SPWM drive signal to drive the switch tubes of each bridge arm On and off, while using the trigonometric function relationship of the Fourier series, fast island calculation is performed by the above two sampling parameters V_PCC and I_inv , and the impedance value at the fundamental frequency and the switching frequency is obtained;

（3）判断基波频率处阻抗变化率、开关频率次阻抗变化率是否超出阈值，只要基波频率处阻抗变化率或开关频率次阻抗变化率中有一个值超出阈值，则判定孤岛发生，DSP2808核心控制芯片立刻输出并网逆变器继电器跳变动作信号S_relay给逆变器，关断其内部的继电器，从PCC处切除设备；若快速阻抗计算数据显示正常，则电网没有发生故障，并网逆变器继续正常工作。(3) Determine whether the impedance change rate at the fundamental frequency and the secondary impedance change rate at the switching frequency exceed the threshold. As long as one of the impedance change rate at the fundamental frequency or the secondary impedance change rate at the switching frequency exceeds the threshold, it is determined that islanding occurs. DSP2808 The core control chip immediately outputs the jump action signal S_relay of the grid-connected inverter relay to the inverter, turns off the internal relay, and removes the device from the PCC; if the fast impedance calculation data shows normal, the power grid is not faulty, and The grid inverter continues to work normally.

本发明的具体方案如下：Concrete scheme of the present invention is as follows:

通常情况下的分布式并网系统中，电网(主网)系统的容量非常大，内部等效阻抗非常小，可视为一个很大的电压源，而分布式并网系统容量有限，且网络等值阻抗较大；In a distributed grid-connected system under normal circumstances, the capacity of the power grid (main grid) system is very large, and the internal equivalent impedance is very small, which can be regarded as a large voltage source. However, the capacity of a distributed grid-connected system is limited, and the network The equivalent impedance is larger;

当正常工作时，系统处于并网运行状态，公共连接点(PCC)处阻抗Z_PCC相当于分布式并网系统与主网系统并联，阻抗值低，此时的公共连接点处阻抗表达式为：When working normally, the system is in grid-connected operation state, and the impedance Z_PCC at the common connection point (PCC) is equivalent to the parallel connection between the distributed grid-connected system and the main grid system, and the impedance value is low. At this time, the impedance at the common connection point is expressed as :

其中，Z_{PCC|Connecting}为系统并网时公共连接点(PCC)处等效阻抗，Z_load为本地负载处阻抗，Z_grid为电网阻抗；Among them, Z_{PCC|Connecting} is the equivalent impedance at the point of common connection (PCC) when the system is connected to the grid, Z_load is the impedance at the local load, and Z_grid is the grid impedance;

在当孤岛发生后，主网脱离分布式发电系统，测得的Z_PCC即为负载阻抗值，此时孤岛下的阻抗表达式为：When the island occurs, the main grid is separated from the distributed power generation system, and the measured Z_PCC is the load impedance value. At this time, the impedance expression under the island is:

Z_{PCC|Islanding}=Z_load   (2)Z_{PCC|Islanding} = Z_load (2)

其中，Z_{PCC|Islanding}为孤岛时公共连接点处(PCC)等效阻抗，Z_load为负载处阻抗。Among them, Z_{PCC|Islanding} is the equivalent impedance at the point of common connection (PCC) during islanding, and Z_load is the impedance at the load.

通常情况下负载阻抗值远大于断网前阻抗，但不论哪种频率下的阻抗检测都存在一定孤岛盲区，导致检测失效。传统的阻抗检测法需要外部注入特征次的谐波，来引起公共点电压的变化，若所选频率过低，则稍加扰动即会对电能质量产生明显干扰；若选取频率过高，则很可能无法保证规范要求。Usually, the load impedance value is much greater than the impedance before the network is disconnected, but there is a certain island blind area in the impedance detection no matter what frequency, which leads to the detection failure. The traditional impedance detection method requires external injection of characteristic harmonics to cause changes in the common point voltage. If the selected frequency is too low, a slight disturbance will cause obvious interference to the power quality; if the selected frequency is too high, it will be very difficult. Specification requirements may not be guaranteed.

本发明直接利用并网逆变器输出电流中的基波以及开关频率次谐波成分，就可以完全不需外部注入扰动，阻抗检测法可以简化很多。The present invention directly utilizes the fundamental wave and the sub-harmonic component of the switching frequency in the output current of the grid-connected inverter, so that no external disturbance injection is required at all, and the impedance detection method can be greatly simplified.

定义h次谐波下公共连接点处阻抗为：Define the impedance at the common connection point under the hth harmonic as:

Z_PCC(h)|_Islanding=Z_load(h)    (3)Z_PCC(h) |_Islanding =Z_load(h) (3)

利用基波信号检测基波频率下阻抗值，即令h=f1，则基波频率阻抗可表示为Z_PCC(f1)；利用开关频率检测h次频率下公共连接点处阻抗，即令h=sw，则开关频率处阻抗即为Z_PCC(sw)。Utilize the fundamental wave signal to detect the impedance value under the fundamental frequency, that is, make h=f1, then the fundamental frequency impedance can be expressed as Z_PCC(f1) ; use the switching frequency to detect the impedance at the common connection point under h times of frequency, that is, make h=sw, Then the impedance at the switching frequency is Z_PCC(sw) .

同时，传统的阻抗测量法为了获取所需的阻抗值，需要进行快速傅里叶变换(FFT)。At the same time, in order to obtain the required impedance value in the traditional impedance measurement method, a fast Fourier transform (FFT) is required.

$\mathrm{<span><span>Z</span>Z</span>}<span><span>(</span>(</span>\mathrm{<span><span>f</span>f</span>}<span><span>)</span>)</span><span><span>=</span>=</span>\frac{\mathrm{<span><span>F</span>f</span>}<span><span>(</span>(</span>\mathrm{<span><span>U</span>u</span>}<span><span>(</span>(</span>\mathrm{<span><span>t</span>t</span>}<span><span>)</span>)</span><span><span>)</span>)</span>}{\mathrm{<span><span>F</span>f</span>}<span><span>(</span>(</span>\mathrm{<span><span>I</span>I</span>}<span><span>(</span>(</span>\mathrm{<span><span>t</span>t</span>}<span><span>)</span>)</span><span><span>)</span>)</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>4</span>4</span>}<span><span>)</span>)</span>$

虽然这种方法可以将各次频率阻抗全部计算出来，但需要大量的采样时间变换到频域内进行计算，运算过程复杂，造成保护动作时间迟缓，影响保护效果。Although this method can calculate all frequency impedances, it requires a large amount of sampling time to transform into the frequency domain for calculation. The calculation process is complicated, resulting in slow protection action time and affecting the protection effect.

本发明的新方法是利用傅里叶级数中三角函数之间的关系，结合开关频率处谐波含量，快速有效实现阻抗计算。The new method of the invention uses the relationship between trigonometric functions in the Fourier series and combines the harmonic content at the switching frequency to quickly and effectively realize impedance calculation.

由三角函数在任意单周期内的特性；by the properties of trigonometric functions in any single period;

${<span><span>\&Integral;</span>\&Integral;</span>}_{\mathrm{<span><span>t</span>t</span>}}^{\mathrm{<span><span>t</span>t</span>}<span><span>+</span>+</span>\mathrm{<span><span>T</span>T</span>}}\mathrm{<span><span>sin</span>sin</span>}\mathrm{<span><span>kx</span>x</span>}\mathrm{<span><span>cos</span>cos</span>}\mathrm{<span><span>nxdx</span>wxya</span>}<span><span>=</span>=</span>\mathrm{<span><span>0</span>0</span>}<span><span>(</span>(</span>\mathrm{<span><span>k</span>k</span>}<span><span>,</span>,</span>\mathrm{<span><span>n</span>no</span>}<span><span>=</span>=</span>\mathrm{<span><span>1.2.3</span>1.2.3</span>}<span><span>\&CenterDot;</span>\&CenterDot;</span><span><span>\&CenterDot;</span>\&Center\; Dot;</span><span><span>\&CenterDot;</span>\&Center\; Dot;</span><span><span>)</span>)</span>$

${<span><span>\&Integral;</span>\&Integral;</span>}_{\mathrm{<span><span>t</span>t</span>}}^{\mathrm{<span><span>t</span>t</span>}<span><span>+</span>+</span>\mathrm{<span><span>T</span>T</span>}}\mathrm{<span><span>cos</span>cos</span>}\mathrm{<span><span>kx</span>x</span>}\mathrm{<span><span>cos</span>cos</span>}\mathrm{<span><span>nxdx</span>wxya</span>}<span><span>=</span>=</span>\mathrm{<span><span>0</span>0</span>}<span><span>(</span>(</span>\mathrm{<span><span>k</span>k</span>}<span><span>,</span>,</span>\mathrm{<span><span>n</span>no</span>}<span><span>=</span>=</span>\mathrm{<span><span>1.2.3</span>1.2.3</span>}<span><span>\&CenterDot;</span>\&Center\; Dot;</span><span><span>\&CenterDot;</span>\&Center\; Dot;</span><span><span>\&CenterDot;</span>\&CenterDot;</span><span><span>,</span>,</span>\mathrm{<span><span>k</span>k</span>}<span><span>\&NotEqual;</span>\&NotEqual;</span>\mathrm{<span><span>n</span>no</span>}<span><span>)</span>)</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>5</span>5</span>}<span><span>)</span>)</span>$

${<span><span>\&Integral;</span>\&Integral;</span>}_{\mathrm{<span><span>t</span>t</span>}}^{\mathrm{<span><span>t</span>t</span>}<span><span>+</span>+</span>\mathrm{<span><span>T</span>T</span>}}\mathrm{<span><span>sin</span>sin</span>}\mathrm{<span><span>kx</span>x</span>}\mathrm{<span><span>sin</span>sin</span>}\mathrm{<span><span>nxdx</span>wxya</span>}<span><span>=</span>=</span>\mathrm{<span><span>0</span>0</span>}<span><span>(</span>(</span>\mathrm{<span><span>k</span>k</span>}<span><span>,</span>,</span>\mathrm{<span><span>n</span>no</span>}<span><span>=</span>=</span>\mathrm{<span><span>1.2.3</span>1.2.3</span>}<span><span>\&CenterDot;</span>\&Center\; Dot;</span><span><span>\&CenterDot;</span>\&Center\; Dot;</span><span><span>\&CenterDot;</span>\&CenterDot;</span><span><span>,</span>,</span>\mathrm{<span><span>k</span>k</span>}<span><span>\&NotEqual;</span>\&NotEqual;</span>\mathrm{<span><span>n</span>no</span>}<span><span>)</span>)</span>$

式中，t为任意时刻点，T为基波频率下周期值，k，n为任意次谐波次数。In the formula, t is any time point, T is the period value under the fundamental frequency, k, n are the harmonic times of any order.

因此，可以进一步写出开关频率处阻抗表达式：Therefore, the impedance expression at the switching frequency can be further written as:

${\mathrm{<span><span>Z</span>Z</span>}}_{\mathrm{<span><span>PCC</span>PCC</span>}<span><span>(</span>(</span>\mathrm{<span><span>fl</span>fl</span>}<span><span>)</span>)</span>}<span><span>(</span>(</span>\mathrm{<span><span>t</span>t</span>}<span><span>)</span>)</span><span><span>=</span>=</span>\frac{{\mathrm{<span><span>V</span>V</span>}}_{\mathrm{<span><span>fl</span>fl</span>}}<span><span>(</span>(</span>\mathrm{<span><span>t</span>t</span>}<span><span>)</span>)</span>}{{\mathrm{<span><span>I</span>I</span>}}_{\mathrm{<span><span>fl</span>fl</span>}}<span><span>(</span>(</span>\mathrm{<span><span>t</span>t</span>}<span><span>)</span>)</span>}<span><span>=</span>=</span>$

$\frac{\sqrt{{(\underset{t_0}{\overset{t_0+T}{\&Integral;}}v\left({\mathrm{\&omega;}}_h\mathrm{\&tau;}\right)\&CenterDot;\sin \left({\mathrm{\&omega;}}_1\mathrm{\&tau;}\right)\mathrm{d\&tau;})}^2+{(\underset{t_0}{\overset{t_0+T}{\&Integral;}}v\left({\mathrm{\&omega;}}_h\mathrm{\&tau;}\right)\&CenterDot;\cos \left({\mathrm{\&omega;}}_1\mathrm{\&tau;}\right)\mathrm{d\&tau;})}^2}}{\sqrt{{(\underset{t_0}{\overset{t_0+T}{\&Integral;}}i\left({\mathrm{\&omega;}}_h\mathrm{\&tau;}\right)\&CenterDot;\sin \left({\mathrm{\&omega;}}_1\mathrm{\&tau;}\right)\mathrm{d\&tau;})}^2+{(\underset{t_0}{\overset{t_0+T}{\&Integral;}}i\left({\mathrm{\&omega;}}_h\mathrm{\&tau;}\right)\&CenterDot;\cos \left({\mathrm{\&omega;}}_1\mathrm{\&tau;}\right)\mathrm{d\&tau;})}^2}}$(6)$\frac{\sqrt{{(\underset{t_0}{\overset{t_0+T}{\&Integral;}}v\left({\mathrm{\&omega;}}_h\mathrm{\&tau;}\right)\&Center\; Dot;\sin \left({\mathrm{\&omega;}}_1\mathrm{\&tau;}\right)\mathrm{d\&tau;})}^2+{(\underset{t_0}{\overset{t_0+T}{\&Integral;}}v\left({\mathrm{\&omega;}}_h\mathrm{\&tau;}\right)\&Center\; Dot;\cos \left({\mathrm{\&omega;}}_1\mathrm{\&tau;}\right)\mathrm{d\&tau;})}^2}}{\sqrt{{(\underset{t_0}{\overset{t_0+T}{\&Integral;}}i\left({\mathrm{\&omega;}}_h\mathrm{\&tau;}\right)\&Center\; Dot;\sin \left({\mathrm{\&omega;}}_1\mathrm{\&tau;}\right)\mathrm{d\&tau;})}^2+{(\underset{t_0}{\overset{t_0+T}{\&Integral;}}i\left({\mathrm{\&omega;}}_h\mathrm{\&tau;}\right)\&Center\; Dot;\cos \left({\mathrm{\&omega;}}_1\mathrm{\&tau;}\right)\mathrm{d\&tau;})}^2}}$ (6)

${\mathrm{<span><span>Z</span>Z</span>}}_{\mathrm{<span><span>PCC</span>PCC</span>}<span><span>(</span>(</span>\mathrm{<span><span>sw</span>sw</span>}<span><span>)</span>)</span>}<span><span>(</span>(</span>\mathrm{<span><span>t</span>t</span>}<span><span>)</span>)</span><span><span>=</span>=</span>\frac{{\mathrm{<span><span>V</span>V</span>}}_{\mathrm{<span><span>sw</span>sw</span>}}<span><span>(</span>(</span>\mathrm{<span><span>t</span>t</span>}<span><span>)</span>)</span>}{{\mathrm{<span><span>I</span>I</span>}}_{\mathrm{<span><span>sw</span>sw</span>}}<span><span>(</span>(</span>\mathrm{<span><span>t</span>t</span>}<span><span>)</span>)</span>}<span><span>=</span>=</span>$

$\frac{\sqrt{{<span><span>(</span>(</span>\underset{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>0</span>0</span>}}}{\overset{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>+</span>+</span>\mathrm{<span><span>T</span>T</span>}}{<span><span>\&Integral;</span>\&Integral;</span>}}\mathrm{<span><span>v</span>v</span>}<span><span>(</span>(</span>{\mathrm{<span><span>\&omega;</span>\&omega;</span>}}_{\mathrm{<span><span>h</span>h</span>}}\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span><span><span>\&CenterDot;</span>\&Center\; Dot;</span>\mathrm{<span><span>sin</span>sin</span>}<span><span>(</span>(</span>{\mathrm{<span><span>\&omega;</span>\&omega;</span>}}_{\mathrm{<span><span>sw</span>sw</span>}}\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span>\mathrm{<span><span>d\&tau;</span>d\&tau;</span>}<span><span>)</span>)</span>}^{\mathrm{<span><span>2</span>2</span>}}<span><span>+</span>+</span>{<span><span>(</span>(</span>\underset{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>0</span>0</span>}}}{\overset{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>+</span>+</span>\mathrm{<span><span>T</span>T</span>}}{<span><span>\&Integral;</span>\&Integral;</span>}}\mathrm{<span><span>v</span>v</span>}<span><span>(</span>(</span>{\mathrm{<span><span>\&omega;</span>\&omega;</span>}}_{\mathrm{<span><span>h</span>h</span>}}\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span><span><span>\&CenterDot;</span>\&Center\; Dot;</span>\mathrm{<span><span>cos</span>cos</span>}<span><span>(</span>(</span>{\mathrm{<span><span>\&omega;</span>\&omega;</span>}}_{\mathrm{<span><span>sw</span>sw</span>}}\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span>\mathrm{<span><span>d\&tau;</span>d\&tau;</span>}<span><span>)</span>)</span>}^{\mathrm{<span><span>2</span>2</span>}}}}{\sqrt{{<span><span>(</span>(</span>\underset{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>0</span>0</span>}}}{\overset{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>+</span>+</span>\mathrm{<span><span>T</span>T</span>}}{<span><span>\&Integral;</span>\&Integral;</span>}}\mathrm{<span><span>i</span>i</span>}<span><span>(</span>(</span>{\mathrm{<span><span>\&omega;</span>\&omega;</span>}}_{\mathrm{<span><span>h</span>h</span>}}\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span><span><span>\&CenterDot;</span>\&Center\; Dot;</span>\mathrm{<span><span>sin</span>sin</span>}<span><span>(</span>(</span>{\mathrm{<span><span>\&omega;</span>\&omega;</span>}}_{\mathrm{<span><span>sw</span>sw</span>}}\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span>\mathrm{<span><span>d\&tau;</span>d\&tau;</span>}<span><span>)</span>)</span>}^{\mathrm{<span><span>2</span>2</span>}}<span><span>+</span>+</span>{<span><span>(</span>(</span>\underset{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>0</span>0</span>}}}{\overset{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>+</span>+</span>\mathrm{<span><span>T</span>T</span>}}{<span><span>\&Integral;</span>\&Integral;</span>}}\mathrm{<span><span>i</span>i</span>}<span><span>(</span>(</span>{\mathrm{<span><span>\&omega;</span>\&omega;</span>}}_{\mathrm{<span><span>h</span>h</span>}}\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span><span><span>\&CenterDot;</span>\&Center\; Dot;</span>\mathrm{<span><span>cos</span>cos</span>}<span><span>(</span>(</span>{\mathrm{<span><span>\&omega;</span>\&omega;</span>}}_{\mathrm{<span><span>sw</span>sw</span>}}\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span>\mathrm{<span><span>d\&tau;</span>d\&tau;</span>}<span><span>)</span>)</span>}^{\mathrm{<span><span>2</span>2</span>}}}}$

式中，Z_PCC(f1)(t)是时域内公共连接点基波频率处阻抗的计算值，Z_PCC(sw)(t)是时域内公共连接点开关频率处阻抗的计算值，V_f1(t)是基波频率处电压的有效值，I_f1(t)是基波频率处电流的有效值，V_sw(t)是开关频率处电压的有效值，I_sw(t)是开关频率处电流的有效值。In the formula, Z_PCC(f1) (t) is the calculated value of the impedance at the fundamental frequency of the common connection point in the time domain, Z_PCC(sw) (t) is the calculated value of the impedance at the switching frequency of the common connection point in the time domain, V_f1 (t) is the effective value of the voltage at the fundamental frequency, I_f1 (t) is the effective value of the current at the fundamental frequency, V_sw (t) is the effective value of the voltage at the switching frequency, and I_sw (t) is the switching frequency effective value of the current.

只要通过时域内，将采样获得的电压电流信号与根据实际并网逆变器基波及开关频率所生成的正余弦参考值进行计算，即可直接获得基波与开关频率处的阻抗值，并求出新的周期下阻抗变化率。根据并网逆变器实际参数设置合适的动作阈值，当所计算得出的阻抗变化率超出安全范围后，控制系统输出动作信号，控制继电器动作，切除并网设备，保护相关用电设备及人员安全。As long as the voltage and current signals obtained by sampling are calculated with the sine and cosine reference values generated according to the fundamental wave and switching frequency of the actual grid-connected inverter in the time domain, the impedance value at the fundamental wave and switching frequency can be directly obtained, and calculated The impedance change rate under the new cycle. Set the appropriate action threshold according to the actual parameters of the grid-connected inverter. When the calculated impedance change rate exceeds the safe range, the control system outputs an action signal to control the action of the relay, cut off the grid-connected equipment, and protect the safety of related electrical equipment and personnel. .

为了验证所述方法的理论正确性与各种情况下的检测效果，分别测试单机与多机工作模式下并网逆变器工作状态，其中单机工作包括单机带阻性负载、单机带阻感性负载、单机带阻容性负载等情况；多机工作包括多台并网逆变器工作在相同开关频率状态、多台并网逆变器工作在不同开关频率状态，以及多台逆变器或者负载的切入与切出状态。In order to verify the theoretical correctness of the method and the detection effect in various situations, the working status of the grid-connected inverter under the single-machine and multi-machine working modes were respectively tested, and the single-machine work includes the single-machine resistive load and the single-machine band-resistance inductive load. , single machine with resistive and capacitive loads, etc.; multi-machine work includes multiple grid-connected inverters working at the same switching frequency state, multiple grid-connected inverters working at different switching frequency states, and multiple inverters or loads cut-in and cut-out states.

本发明的有益效果是：在控制系统中加入针对基波与开关频率特征的阻抗检测算法，突破了被动孤岛检测法的弊端，同时不需外加扰动信号，避免主动检测法中的扰动影响。快速的运算及动作保证了系统运行的稳定性及可靠性，具有良好的工程借鉴价值。The beneficial effects of the invention are: adding an impedance detection algorithm aimed at the characteristics of the fundamental wave and switching frequency into the control system, breaking through the disadvantages of the passive island detection method, and at the same time, no external disturbance signal is required to avoid the disturbance effect in the active detection method. Fast calculation and action ensure the stability and reliability of the system operation, and have good engineering reference value.

附图说明Description of drawings

图1为本发明的并网逆变器工作与测试结构框图；Fig. 1 is a block diagram of grid-connected inverter work and test structure of the present invention;

图2为本发明的并网逆变器并网电流的FFT分析例图；Fig. 2 is the FFT analysis example diagram of grid-connected inverter grid-connected current of the present invention;

图3为本发明的并网逆变器新型阻抗检测算法实现图；Fig. 3 is the implementation diagram of the novel impedance detection algorithm of the grid-connected inverter of the present invention;

图4为本发明的并网逆变器工作及孤岛检测流程图。Fig. 4 is a flow chart of grid-connected inverter operation and islanding detection in the present invention.

本发明主要组成及说明包括：1-以LCL型滤波结构为例的并网逆变器；2-并网逆变器、电网、本地负载的公共连接点(PCC)；3-电网与公共连接点(PCC)的接触开关；4-电网端等效阻抗；5-负载端等效阻抗；6-低压电网；7-DSP TMS320F2808核心控制芯片。The main composition and description of the present invention include: 1-grid-connected inverter taking LCL filter structure as an example; 2-common connection point (PCC) of grid-connected inverter, power grid and local load; 3-grid and public connection Point (PCC) contact switch; 4-grid end equivalent impedance; 5-load end equivalent impedance; 6-low voltage power grid; 7-DSP TMS320F2808 core control chip.

图中所述字母符号分别表示为：V_PCC---公共连接点(PCC)处电压值；I_inv---并网逆变器逆变电流值；I_grid---实际的并网电流；V_grid---低压电网电压值；Z_grid---低压电网的等效阻抗值；Z_load---本地负载的等效阻抗值；I_load---本地负载的电流值；SPWM---DSP2808运算处理后输出的各逆变桥臂开关管驱动信号；S_relay---并网逆变器继电器跳变动作信号。The letters and symbols in the figure are respectively expressed as: V_PCC --- the voltage value at the common connection point (PCC); I_inv --- the inverter current value of the grid-connected inverter; I_grid --- the actual grid-connected current ; V_grid --- voltage value of low voltage grid; Z_grid --- equivalent impedance value of low voltage grid; Z_load --- equivalent impedance value of local load; I_load --- current value of local load; SPWM- --DSP2808 operation and processing the drive signal of each inverter bridge arm switch tube output; S_relay --- grid-connected inverter relay jump action signal.

具体实施方式Detailed ways

以下结合附图对本发明的系统实验平台进行详细描述。The system experiment platform of the present invention will be described in detail below in conjunction with the accompanying drawings.

附图1为本发明的并网逆变器工作与测试结构框图：Accompanying drawing 1 is grid-connected inverter work and test structural block diagram of the present invention:

所述并网逆变器1与所述低压电网6并联，同时中间并接相关本地负载若干，其公共连接端即为公共连接点(PCC)2，在公共连接点(PCC)2、低压电网6之间设置接触开关3，用以切换并网与孤岛模式的发生。将低压电网端等效阻抗4等效为一阻抗Z_grid，本地负载的等效阻抗5等效为Z_load，系统采样所述公共连接点(PCC)2处的电压V_PCC与逆变器输出电流I_inv，将信号送至DSP2808核心控制芯片7进行并网控制的相关运算，输出SPWM驱动信号驱动各桥臂开关管导通与关断，同时由以上两个参数进行快速孤岛计算，判断基波频率处阻抗变化率以及开关频率次阻抗变化率是否超出阈值，若二者有一个变化超出阈值，则判定孤岛发生，立刻输出S_relay信号给逆变器，关断其内部的继电器，从PCC处切除设备。The grid-connected inverter 1 is connected in parallel with the low-voltage grid 6, and at the same time, a number of related local loads are connected in parallel, and its common connection end is the common connection point (PCC) 2. Acontact switch 3 is set between 6 to switch between grid-connected and island modes. The equivalent impedance 4 of the low-voltage grid end is equivalent to an impedance Z_grid , theequivalent impedance 5 of the local load is equivalent to Z_load , the system samples the voltage V_PCC at the common connection point (PCC) 2 and the output of the inverter The current I_inv sends the signal to the DSP2808core control chip 7 for grid-connected control related calculations, outputs the SPWM drive signal to drive the switch tubes of each bridge arm to turn on and off, and performs fast island calculation based on the above two parameters to judge the basic Whether the impedance change rate at the wave frequency and the switching frequency sub-impedance change rate exceed the threshold value. If one of the two changes exceeds the threshold value, it is determined that islanding occurs, and the S_relay signal is output to the inverter immediately, and the internal relay is turned off. From the PCC Remove the device.

附图2为本发明的并网逆变器并网电流的FFT分析例图：Accompanying drawing 2 is the FFT analysis example figure of grid-connected inverter grid-connected current of the present invention:

通过图2需要来说明的是，不论L型、LC型、LCL型并网逆变器的输出电流，都会在开关频率处存在一定量的谐波，这类谐波量符合并网规范要求，但相比除基波以外的其他频率仍然比例较高，如图即为一种开关频率为20KHz(400次基波频率)的并网逆变器输出逆变电流波形，因而不需要额外向系统注入特征频率的扰动，就可以利用这种具有突出区别的特征来用于孤岛效应的检测。It needs to be illustrated by Figure 2 that regardless of the output current of the L-type, LC-type, and LCL-type grid-connected inverters, there will be a certain amount of harmonics at the switching frequency. This type of harmonics meets the requirements of the grid-connected regulations. However, compared with other frequencies other than the fundamental frequency, the proportion is still relatively high. As shown in the figure, a grid-connected inverter with a switching frequency of 20KHz (400 times fundamental frequency) outputs an inverter current waveform, so no additional power supply to the system is required. By injecting the perturbation of the characteristic frequency, this distinctive feature can be used to detect the islanding effect.

附图3为本发明的并网逆变器新型阻抗检测算法实现图：Accompanying drawing 3 is the implementation diagram of the novel impedance detection algorithm of the grid-connected inverter of the present invention:

Sinω_f1t与Cosω_f1t为根据系统基波频率由内部给定的正余弦数据点，Sinω_swt与Cosω_swt为根据系统开关频率由内部给定的正余弦数据点，将采样获得的PCC处电压值V_PCC以及逆变器输出电流I_inv分别与Sinω_f1t、Cosω_f1t、Sinω_swt、Cosω_swt相乘，并在单位周期内求积分，利用傅里叶级数中三角函数的正交特性，通过对基波频率次电压电流值正余弦数据求平方和，对开关频率次的电压电流值正余弦数据求平方和，求出单位周期有效值并相除，最终得到两种频率下的阻抗值。Sinω_f1 t and Cosω_f1 t are sine and cosine data points given internally according to the fundamental frequency of the system, and Sinω_sw t and Cosω_sw t are sine and cosine data points given internally according to the system switching frequency. The PCC obtained by sampling The voltage value V_PCC and the inverter output current I_inv are respectively multiplied by Sinω_f1 t, Cosω_f1 t, Sinω_sw t, and Cosω_sw t, and the integral is calculated in the unit period, using the trigonometric function in the Fourier series Orthogonal characteristics of the fundamental frequency sub-voltage and current value sine and cosine data, and the switching frequency sub-voltage and current value sine and cosine data to find the square and sum, find the effective value of the unit cycle and divide, and finally get two Impedance value at frequency.

附图4为本发明的并网逆变器工作及孤岛检测流程图：首先系统待机自检测，检查外部的并网环境及直流侧电压是否都一切正常，待检测完毕后系统先进行正常的并网工作，此时采样PCC处电压与电流数据，若此时已发现其电网电压电压、频率出现超/欠正常参数范围，则由被动孤岛检测法，判定出电网故障，直接由DSP发出切除设备指令，系统无需再进行孤岛计算；若PCC处电压与电流数据并未超出阈值，显示在正常范围，此时被动孤岛检测法失效，系统进一步将检测到的数据送至DSP进行快速阻抗计算，判定其两种特征阻抗及变化率是否超出阈值，若其中有任意一个超出阈值，则可判定电网故障，DSP发出指令，让继电器动作切除设备，若快速阻抗计算数据显示正常，则可知电网没有发生故障，并网设备继续正常工作。Accompanying drawing 4 is the flow chart of grid-connected inverter operation and island detection of the present invention: firstly, the system conducts self-test in standby, checks whether the external grid-connected environment and DC side voltage are all normal, and after the detection is completed, the system performs normal parallel operation first. At this time, the voltage and current data at the PCC are sampled. If the voltage and frequency of the grid are found to exceed/undershoot the normal parameter range at this time, the fault of the grid will be determined by the passive island detection method, and the DSP will directly send a signal to remove the device. command, the system no longer needs to perform island calculation; if the voltage and current data at the PCC do not exceed the threshold and are displayed within the normal range, then the passive island detection method fails, and the system further sends the detected data to the DSP for fast impedance calculation to determine Whether the two characteristic impedances and the rate of change exceed the threshold, if any one of them exceeds the threshold, it can be determined that the power grid is faulty, and the DSP issues an instruction to let the relay act to remove the device. If the fast impedance calculation data shows normal, it can be known that the power grid is not faulty , the grid-connected equipment continues to work normally.

Claims (4)

Translated fromChinese

1.一种基于基频与开关频率次阻抗的孤岛检测法，其特征在于，包括如下步骤：1. an islanding detection method based on fundamental frequency and switching frequency secondary impedance, is characterized in that, comprises the steps:（1）并网逆变器与低压电网并联，同时两者中间并接本地负载若干，所述并网逆变器、低压电网、本地负载的公共连接点为PCC，在PCC和低压电网之间设置接触开关，用以切换并网模式与孤岛模式；(1) The grid-connected inverter is connected in parallel with the low-voltage grid, and a number of local loads are connected in parallel between the two. The common connection point of the grid-connected inverter, the low-voltage grid, and the local load is PCC, between PCC and the low-voltage grid Set the contact switch to switch between grid-connected mode and island mode;（2）采样PCC处的电压V_PCC与并网逆变器的输出电流I_inv，将信号送至DSP2808核心控制芯片进行并网控制的相关软件运算，输出SPWM驱动信号驱动各桥臂开关管导通与关断，同时利用傅里叶级数的三角函数关系，由以上两个采样参数V_PCC和I_inv进行快速孤岛计算，获得基波频率和开关频率下的阻抗值；(2) Sampling the voltageV_PCC at the PCC and the output currentI_inv of the grid-connected inverter, sending the signal to the DSP2808 core control chip for related software calculations of grid-connected control, outputting the SPWM drive signal to drive the switch tubes of each bridge arm On and off, while using the trigonometric function relationship of the Fourier series, fast island calculation is performed by the above two sampling parametersV_PCC andI_inv , and the impedance value at the fundamental frequency and the switching frequency is obtained;（3）判断基波频率处的阻抗变化率和开关频率次的阻抗变化率是否超出阈值，只要基波频率处的阻抗变化率或开关频率次的阻抗变化率中有一个超出阈值，则判定孤岛发生，DSP2808核心控制芯片立刻输出并网逆变器继电器跳变动作信号S_relay给逆变器，关断其内部的继电器，从PCC处切除设备；若快速阻抗计算数据显示正常，则电网没有发生故障，并网逆变器继续正常工作。(3) Determine whether the impedance change rate at the fundamental frequency and the impedance change rate at the switching frequency exceed the threshold, as long as one of the impedance change rate at the fundamental frequency or the impedance change rate at the switching frequency exceeds the threshold, the island is determined occurs, the DSP2808 core control chip immediately outputs the jump action signalS_relay of the grid-connected inverter relay to the inverter, turns off the internal relay, and removes the device from the PCC; if the fast impedance calculation data shows normal, the power grid has not occurred fault, the grid-connected inverter continues to work normally.2.根据权利要求1所述的一种基于基频与开关频率次阻抗的孤岛检测法，其特征在于：所述步骤（2）中获得阻抗值的具体步骤为：记Sinω_f1t 与Cosω_f1t为根据系统基波频率由内部给定的正余弦数据点，Sinω_swt 与Cosω_swt为根据系统开关频率由内部给定的正余弦数据点，将采样获得的PCC处电压值V_PCC以及逆变器的输出电流I_inv分别与Sinω_f1t 、Cosω_f1t、Sinω_swt和Cosω_swt相乘，并在单位周期内求积分，利用傅里叶级数中三角函数的正交特性，通过对基波频率次电压电流值正余弦数据求平方和，对开关频率次的电压电流值正余弦数据求平方和，求出单位周期有效值并相除，最终得到基波频率和开关频率下的阻抗值。2. An islanding detection method based on fundamental frequency and switching frequency sub-impedance according to claim 1, characterized in that: the specific step of obtaining the impedance value in the step (2) is: writeS inω_f1 t andC osω_f1 t is the sine and cosine data points given internally according to the fundamental frequency of the system,S inω_sw t andC osω_sw t are the sine and cosine data points given internally according to the system switching frequency, and the voltage at PCC obtained by sampling The valueV_PCC and the output currentI_inv of the inverter are multiplied byS inω_f1 t ,C osω_f1 t ,S inω_sw t andC osω_sw t respectively, and are integrated in the unit period, using the Fourier series The orthogonality characteristic of the trigonometric function, by calculating the sum of the squares of the sine and cosine data of the voltage and current values of the fundamental frequency, and the sum of the squares of the sine and cosine data of the voltage and current values of the switching frequency, the effective value of the unit cycle is obtained and divided, and finally Obtain the impedance value at the fundamental frequency and the switching frequency.3.根据权利要求1或2所述的一种基于基频与开关频率次阻抗的孤岛检测法，其特征在于：所述方法可以分别测试单机与多机工作模式下并网逆变器工作状态，其中单机工作模式包括单机带阻性负载、单机带阻感性负载和单机带阻容性负载情况；多机工作模式包括多台并网逆变器工作在相同开关频率状态、多台并网逆变器工作在不同开关频率状态，以及多台逆变器或者负载的切入与切出状态。3. An islanding detection method based on fundamental frequency and switching frequency sub-impedance according to claim 1 or 2, characterized in that: said method can test the working status of grid-connected inverters in single-machine and multi-machine working modes respectively , where the stand-alone operating mode includes single-unit resistive load, single-unit resistive inductive load and single-unit resistive-capacitive load; multi-unit operating mode includes multiple grid-connected inverters working at the same switching frequency state, multiple grid-connected inverters The inverters work in different switching frequency states, and the cut-in and cut-out states of multiple inverters or loads.4.根据权利要求3所述的一种基于基频与开关频率次阻抗的孤岛检测法，其特征在于：先由被动孤岛检测法检测外部参数，若超出阈值范围，则直接由被动孤岛方式执行保护动作；若PCC处电压与电流幅值、频率数据并未超出阈值，显示在正常范围，则利用所述基于基频与开关频率次阻抗的孤岛检测法继续检测。4. A kind of islanding detection method based on fundamental frequency and switching frequency secondary impedance according to claim 3, characterized in that: the external parameters are detected by the passive islanding detection method first, and if it exceeds the threshold range, it is directly executed by the passive islanding method Protection action; if the voltage and current amplitudes and frequency data at the PCC do not exceed the threshold and are displayed within the normal range, then use the islanding detection method based on the fundamental frequency and switching frequency secondary impedance to continue detection.

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