技术领域technical field
本发明涉及分布式电源孤岛检测技术领域，尤其涉及一种基于并网点特征谐波电压测量的分布式电源孤岛检测方法。The invention relates to the technical field of distributed power island detection, in particular to a method for detecting distributed power islands based on the measurement of characteristic harmonic voltages of grid-connected points.
背景技术Background technique
近年来，随着能源短缺和环境问题的日益突出，新能源发电技术在国家政策的大力支持下得到了迅猛的发展，大量的新能源发电装置以分布式电源(DistributedGeneration，DG)的形式接入到电网中，在缓解电网压力的同时也给电网带来了电能质量和运营规划方面的问题，其中孤岛效应就是一个主要问题。In recent years, with the increasingly prominent energy shortage and environmental problems, new energy power generation technology has developed rapidly with the strong support of national policies, and a large number of new energy power generation devices are connected in the form of distributed generation (DG) Into the power grid, while relieving the pressure on the power grid, it also brings problems in power quality and operation planning to the power grid, among which the island effect is a major problem.
在光伏发电、风力发电、燃料电池发电等分布式发电并网发电系统中，当电网供电过程中因故障事故或停电维修而跳脱时，未能即时检测出停电状态将自身切离供电网络，形成由分布电站并网发电系统和周围的负载组成的一个自给供电的孤岛，即孤岛效应。In distributed generation grid-connected power generation systems such as photovoltaic power generation, wind power generation, and fuel cell power generation, when the grid power supply process is tripped due to a fault accident or power outage maintenance, it cannot immediately detect the power outage state and cut itself off from the power supply network. Form a self-sufficient power supply island composed of distributed power station grid-connected power generation system and surrounding loads, that is, the island effect.
孤岛运行时会给用户设备带来安全隐患，同时非计划孤岛运行对检修人员的人身安全也会构成潜在的威胁，因此需要采取相关的孤岛控制措施。孤岛后的相关控制也要保证在整个系统扰动切除后，各个孤岛可以较快的进行并网操作，使整个电网恢复到正常的安全运行状态。Island operation will bring safety hazards to user equipment, and unplanned island operation will also pose a potential threat to the personal safety of maintenance personnel, so relevant island control measures need to be taken. The relevant control after the islands should also ensure that after the disturbance of the entire system is removed, each island can be quickly connected to the grid, so that the entire grid can return to a normal and safe operating state.
孤岛检测方法主要有被动式和主动式。现有的被动式孤岛检测办法，通过检测分布式电源并网逆变器输出电压、频率或者相位的数据与设立的标准阈值进行对比，判定是否发生孤岛效应。这种方法的缺陷是由于电网正常运行时的波动也可能造成误判。另外，若分布式电源的输出功率与负载功率相匹配，则当电网供电中断，并网点电压和频率变化很小不足以检测出是否发生孤岛效应，即存在很大的检测盲区。现有的主动式孤岛检测办法是对逆变器输出电流的幅值、频率、相位给一定的扰动，使输出电压的频率或相位发生相应偏移，来确定是否发生孤岛效应，但是该检测方法由于扰动量的加入，将影响电网的电能质量。Islanding detection methods mainly include passive and active. The existing passive islanding detection method compares the output voltage, frequency or phase data of the distributed power grid-connected inverter with the established standard threshold to determine whether the islanding effect occurs. The defect of this method is that the fluctuation during the normal operation of the power grid may also cause misjudgment. In addition, if the output power of the distributed power source matches the load power, when the grid power supply is interrupted, the voltage and frequency changes at the grid-connected point are too small to detect whether the islanding effect occurs, that is, there is a large detection blind zone. The existing active islanding detection method is to give a certain disturbance to the amplitude, frequency, and phase of the inverter output current, so that the frequency or phase of the output voltage will be shifted accordingly to determine whether the islanding effect occurs, but the detection method Due to the addition of the disturbance, it will affect the power quality of the grid.
因此，如何在不影响电网电能质量的前提下准确检测孤岛，是分布式电源并网研究的重点。Therefore, how to accurately detect islands without affecting the power quality of the grid is the focus of research on grid-connected distributed generation.
发明内容Contents of the invention
本发明的目的是提供一种基于并网点特征谐波电压测量的分布式电源孤岛检测方法，该方法可靠并易于实现，对电网适应性强，适合工程实际使用。The purpose of the present invention is to provide a distributed power island detection method based on the measurement of the characteristic harmonic voltage of the grid-connected point. The method is reliable and easy to implement, has strong adaptability to the power grid, and is suitable for actual engineering use.
本发明的目的是通过以下技术方案实现的：The purpose of the present invention is achieved through the following technical solutions:
一种基于并网点特征谐波电压测量的分布式电源孤岛检测方法，该分布式电源与逆变器相连，该逆变器依次通过入口滤波器与变压器接入电网组成分布式电源并网系统，该方法包括：A distributed power island detection method based on the characteristic harmonic voltage measurement of the grid-connected point. The distributed power is connected to the inverter, and the inverter is connected to the grid through the inlet filter and the transformer in turn to form a distributed power grid-connected system. The method includes:
根据逆变器IGBT开关频率选取至少两组特征谐波次数作为参考次谐波来进行孤岛检测；According to the inverter IGBT switching frequency, at least two groups of characteristic harmonic times are selected as reference harmonics for islanding detection;
对逆变器输出端与位于变压器与电网之间的并网点的电压进行同步采样，并通过转换与分解后，获得所选取的至少两组特征谐波次数对应的参考次谐波电压值；Synchronously sample the voltage at the output terminal of the inverter and the grid-connected point between the transformer and the grid, and obtain reference sub-harmonic voltage values corresponding to at least two groups of selected characteristic harmonic orders after conversion and decomposition;
判断各组参考次谐波电压值大小是否均超出预先设定的该组谐波电压检测阈值范围；Judging whether the reference harmonic voltage values of each group exceed the preset detection threshold range of the harmonic voltage of the group;
若是，且持续时间均超过设定的时间限值，则判定发生孤岛效应。If yes, and the duration exceeds the set time limit, it is determined that the islanding effect occurs.
进一步的，进行同步采样之前包括：Further, before synchronous sampling includes:
根据逆变器IGBT开关频率确定采样分析截止频率fh与采样频率fs，其中，fs≥2fh；Determine the sampling analysis cut-off frequency fh and sampling frequency fs according to the inverter IGBT switching frequency, where fs ≥ 2fh ;
设置采样间隔Ts，采样点为且N等于2的整数次幂，f0为基波频率。Set the sampling interval Ts , the sampling point is And N is equal to an integer power of 2, and f0 is the fundamental frequency.
进一步的，该方法还包括确定谐波电压检测阈值范围，其步骤为：Further, the method also includes determining the harmonic voltage detection threshold range, the steps of which are:
建立系统阻抗模型，其中，该系统阻抗模型中的参数均折算至同一电压等级，电网端等效为电压源与系统阻抗串联，逆变器等效为谐波电压源；Establish a system impedance model, in which the parameters in the system impedance model are converted to the same voltage level, the grid terminal is equivalent to a voltage source connected in series with the system impedance, and the inverter is equivalent to a harmonic voltage source;
根据该系统阻抗模型建立未发生孤岛与发生孤岛时系统谐波阻抗模型，并以此计算所选取的至少两组特征谐波次数在未发生孤岛与发生孤岛时对应的并网点参考次谐波电压；Based on the system impedance model, establish the harmonic impedance model of the system without islanding and when islanding occurs, and calculate the reference sub-harmonic voltage of the grid-connected point corresponding to at least two groups of characteristic harmonic orders when no islanding occurs and when islanding occurs ;
根据每一组特征谐波次数在未发生孤岛与发生孤岛时并网点参考次谐波电压来确定该组谐波电压检测阈值范围。According to each group of characteristic harmonic orders, the reference harmonic voltage of the grid-connected point when no islanding occurs and when islanding occurs is used to determine the detection threshold range of the group of harmonic voltages.
进一步的，该方法还包括：将系统阻抗模型中的参数均折算至同一电压等级；Further, the method also includes: converting the parameters in the system impedance model to the same voltage level;
其中，电压等级记为UN，系统短路容量为Sd，则系统阻抗XS为：Among them, the voltage level is recorded as UN , and the system short-circuit capacity is Sd , then the system impedance XS is:
入口滤波器的电感值与电容值分别记为L与C，系统频率记为f0，则入口滤波器感抗XL与容抗XC分别为：The inductance and capacitance of the inlet filter are denoted as L and C respectively, and the system frequency is denoted as f0 , then the inductive reactance XL and capacitive reactance XC of the inlet filter are respectively:
XL＝2πf0L；XL = 2πf0 L;
变压器额定容量记为SN，短路阻抗记为Uk，则变压器阻抗XT为：The transformer rated capacity is denoted as SN , and the short-circuit impedance is denoted as Uk , then the transformer impedance XT is:
系统负载容量记为SL，基波功率因数记为则等效负载电阻Rload和等效电抗Xload为：The system load capacity is denoted as SL , and the fundamental wave power factor is denoted as Then the equivalent load resistance Rload and equivalent reactance Xload are:
进一步的，该方法还包括计算所选取的至少两组特征谐波次数在未发生孤岛时对应的并网点参考次谐波电压，其包括：Further, the method also includes calculating the reference sub-harmonic voltage of the grid-connected point corresponding to at least two groups of selected characteristic harmonic orders when no islanding occurs, which includes:
未发生孤岛时系统谐波阻抗模型中系统负载等效为开路，其中的参数与所选取的特征谐波次数h相关：系统阻抗XS,h＝jhXS；变压器阻抗XT,h＝jhXT；入口滤波器的容抗XC,h＝-j(XC/h)；入口滤波器感抗XL,h＝jhXL；负载阻抗为逆变器输出谐波电压；When islanding does not occur, the system load in the system harmonic impedance model is equivalent to an open circuit, and the parameters are related to the selected characteristic harmonic order h: system impedance XS,h =jhXS ; transformer impedance XT,h =jhXT ;Inlet filter capacitive reactance XC,h ＝-j(XC /h); Inlet filter inductance XL,h ＝jhXL ;Load impedance Output harmonic voltage for inverter;
计算逆变器并网点a的谐波电压Calculate the harmonic voltage of the grid-connected point a of the inverter
将逆变器并网点a的谐波电压转换为并网点参考次谐波电压Harmonic voltage of the grid-connected point a of the inverter Convert to grid-connected point reference sub-harmonic voltage
其中，n为变压器一次侧对二次侧变比。Among them, n is the transformation ratio of the primary side of the transformer to the secondary side.
进一步的，该方法还包括：计算所选取的至少两组特征谐波次数在发生孤岛时对应的并网点参考次谐波电压，其包括：Further, the method also includes: calculating the reference sub-harmonic voltage of the grid-connected point corresponding to at least two groups of selected characteristic harmonic orders when islanding occurs, which includes:
发生孤岛时系统谐波阻抗模型中系统阻抗与系统分离，分布式电源通过逆变器对负载直接供电，其中的参数与所选取的特征谐波次数h相关：系统阻抗XS,h＝jhXS；变压器阻抗XT,h＝jhXT；入口滤波器的容抗XC,h＝-j(XC/h)；入口滤波器感抗XL,h＝jhXL；负载最小阻抗In the system harmonic impedance model, when islanding occurs, the system impedance is separated from the system, and the distributed power supply directly supplies power to the load through the inverter, and the parameters are related to the selected characteristic harmonic order h: system impedance XS,h = jhXS ;Transformer impedance XT,h ＝jhXT ;Inlet filter capacitive reactance XC,h ＝-j(XC /h); Inlet filter inductance XL,h ＝jhXL ;Load minimum impedance
计算逆变器并网点a的谐波电压Calculate the harmonic voltage of the grid-connected point a of the inverter
将逆变器并网点a的谐波电压转换为并网点参考次谐波电压Harmonic voltage of the grid-connected point a of the inverter Convert to grid-connected point reference sub-harmonic voltage
其中，n为变压器一次侧对二次侧变比。Among them, n is the transformation ratio of the primary side of the transformer to the secondary side.
进一步的，所述根据每一组特征谐波次数在未发生孤岛与发生孤岛时并网点参考次谐波电压来确定该组谐波电压检测阈值范围包括：Further, the determination of the harmonic voltage detection threshold range of the group of harmonic voltages based on the reference sub-harmonic voltage of the grid-connected point when no islanding occurs or when islanding occurs according to each group of characteristic harmonic orders includes:
根据所选取的特征谐波次数h未发生孤岛时与发生孤岛时并网点参考次谐波电压有效值Upcc,h与U'pcc,h确定对应的谐波电压检测阈值范围为Upcc,h～U'pcc,h。According to the selected characteristic harmonic order h when no islanding occurs and when islanding occurs, the reference sub-harmonic voltage effective value Upcc,h and U'pcc,h determine the corresponding harmonic voltage detection threshold range as Upcc,h ~U'pcc,h .
由上述本发明提供的技术方案可以看出，该方法适用于通过逆变器并网的分布式电源发电系统，该方法既可避免逆变器并网输出功率与负载功率匹配时现有被动检测办法存在的检测盲区，又可解决主动式检测办法所带来的电能质量扰动问题；同时，该方法可靠并易于实现，对电网适应性强，适合工程实际使用。It can be seen from the above-mentioned technical solution provided by the present invention that this method is suitable for a distributed power generation system connected to the grid through an inverter. This method can avoid the existing passive detection when the inverter grid-connected output power matches the load power. The detection blind area of the method can solve the power quality disturbance problem caused by the active detection method; at the same time, the method is reliable and easy to implement, has strong adaptability to the power grid, and is suitable for actual engineering use.
附图说明Description of drawings
为了更清楚地说明本发明实施例的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域的普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他附图。In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings on the premise of not paying creative work.
图1为本发明实施例提供的分布式电源并网系统的孤岛检测原理图；FIG. 1 is a schematic diagram of an island detection principle of a distributed power grid-connected system provided by an embodiment of the present invention;
图2为本发明实施例提供的一种基于并网点特征谐波电压测量的分布式电源孤岛检测方法的流程图；Fig. 2 is a flow chart of a distributed power island detection method based on grid-connected point characteristic harmonic voltage measurement provided by an embodiment of the present invention;
图3为本发明实施例提供的系统阻抗模型的示意图；FIG. 3 is a schematic diagram of a system impedance model provided by an embodiment of the present invention;
图4为本发明实施例提供的未发生孤岛时系统谐波阻抗模型的示意图；FIG. 4 is a schematic diagram of a system harmonic impedance model when no islanding occurs according to an embodiment of the present invention;
图5为本发明实施例提供的发生孤岛时系统谐波阻抗模型的示意图；5 is a schematic diagram of a system harmonic impedance model when islanding occurs according to an embodiment of the present invention;
图6为本发明实施例提供的基于并网点特征谐波电压测量的分布式电源孤岛检测的步骤流程图。FIG. 6 is a flow chart of steps for islanding detection of distributed power sources based on the measurement of characteristic harmonic voltages of grid-connected points provided by an embodiment of the present invention.
具体实施方式detailed description
下面结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明的保护范围。The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.
分布式电源并网系统中，分布式电源与逆变器相连，该逆变器依次通过入口滤波器与变压器接入电网。分布式电源通过逆变器并网时，由于负载阻抗远远大于系统阻抗，在未发生孤岛时等效为开路，逆变器产生特定谐波注入系统，在并网点产生相应谐波电压。发生孤岛时，分布式电源通过逆变器对负载直接供电，系统阻抗分离，并网点谐波电压将迅速增加，本发明通过检测并网点特征谐波电压变化确定是否孤岛。因此，针对含逆变器并网的分布式电源并网系统的孤岛检测原理图如图1，需要测量逆变器输出端和并网点参考次谐波电压大小，并计算出未发生孤岛和发生孤岛两种情况下并网点参考次谐波电压大小，确定特征谐波电压比较阈值范围，从而判定是否发生孤岛效应。下面通过具体实施例来对本发明做详细的介绍。In the distributed power grid-connected system, the distributed power is connected to the inverter, and the inverter is connected to the grid through the inlet filter and the transformer in turn. When the distributed power supply is connected to the grid through the inverter, since the load impedance is much larger than the system impedance, it is equivalent to an open circuit when no islanding occurs. The inverter generates specific harmonics and injects them into the system, generating corresponding harmonic voltages at the grid connection point. When islanding occurs, the distributed power supply directly supplies power to the load through the inverter, the system impedance is separated, and the harmonic voltage at the grid-connected point will increase rapidly. The invention determines whether it is an island by detecting the characteristic harmonic voltage change of the grid-connected point. Therefore, the islanding detection schematic diagram for the distributed power grid-connected system with inverter grid-connected is shown in Fig. In the two cases of islanding, the grid-connected point refers to the magnitude of the sub-harmonic voltage, and determines the comparison threshold range of the characteristic harmonic voltage, so as to determine whether the islanding effect occurs. The present invention will be described in detail below through specific embodiments.
图2为本发明实施例提供的一种基于并网点特征谐波电压测量的分布式电源孤岛检测方法的流程图。如图2所示，该方法主要包括如下步骤：Fig. 2 is a flow chart of a distributed power island detection method based on the measurement of the characteristic harmonic voltage of the grid-connected point provided by the embodiment of the present invention. As shown in Figure 2, the method mainly includes the following steps:
步骤21、根据逆变器IGBT开关频率选取至少两组特征谐波次数作为参考次谐波来进行孤岛检测。Step 21. Select at least two groups of characteristic harmonic orders as reference harmonics according to the IGBT switching frequency of the inverter to perform islanding detection.
本发明实施例中，为保证孤岛检测的可靠性，至少选取两组逆变器IGBT(绝缘栅双极型晶体管)开关频率附近特征谐波电压作为参考次谐波来进行孤岛检测。In the embodiment of the present invention, in order to ensure the reliability of islanding detection, at least two groups of inverter IGBT (Insulated Gate Bipolar Transistor) switching frequency near characteristic harmonic voltages are selected as reference sub-harmonics for islanding detection.
步骤22、对逆变器输出端与位于变压器与电网之间的并网点的电压进行同步采样，并通过转换与分解后，获得所选取的至少两组特征谐波次数对应的参考次谐波电压值。Step 22. Synchronously sample the voltage of the inverter output terminal and the grid-connected point between the transformer and the grid, and after conversion and decomposition, obtain the reference sub-harmonic voltage corresponding to at least two sets of characteristic harmonic orders selected value.
如图1所示，可通过PT(电压互感器)对逆变器输出端和并网点(PCC并网点)电压进行同步采样，再通过A/D转换，与傅里叶分解后，可得到各组参考次谐波电压大小。As shown in Figure 1, the voltage at the output terminal of the inverter and the grid-connected point (PCC grid-connected point) can be sampled synchronously through a PT (voltage transformer), and then through A/D conversion and Fourier decomposition, each Group reference subharmonic voltage magnitude.
示例性的，同步采样得到一个长度为S的有限长序列u(n)，通过A/D转换，进行傅里叶分解，得到各组参考次谐波电压大小：Exemplarily, synchronous sampling obtains a finite length sequence u(n) of length S, performs Fourier decomposition through A/D conversion, and obtains the magnitude of each group of reference sub-harmonic voltages:
其中，为虚单位，以下同；h为所选取的特征谐波次数。in, is the imaginary unit, the same below; h is the selected characteristic harmonic order.
另外，在进行同步采样之前需要进行相关参数的设定，具体包括：根据逆变器IGBT开关频率确定采样分析截止频率fh与采样频率fs，其中，fs≥2fh；设置采样间隔Ts，采样点为其中f0为基波频率，为减少傅里叶分解计算量和复杂程度，增加孤岛检测响应速度，采样点N还限定为等于2的整数次幂。In addition, related parameters need to be set before synchronous sampling, specifically including: determining the sampling analysis cut-off frequency fh and sampling frequency fs according to the inverter IGBT switching frequency, where fs ≥ 2fh ; setting the sampling interval Ts , the sampling point is Where f0 is the fundamental frequency. In order to reduce the calculation amount and complexity of Fourier decomposition and increase the response speed of island detection, the sampling point N is also limited to an integer power of 2.
步骤23、判断各组参考次谐波电压值大小是否均超出预先设定的该组谐波电压检测阈值范围；若是，则转入步骤24；否则，转入重复执行步骤22。Step 23. Determine whether the reference sub-harmonic voltage values of each group exceed the preset detection threshold range of the harmonic voltage; if yes, proceed to step 24; otherwise, proceed to repeat step 22.
本发明实施例中，每一组谐波电压检测阈值范围可通过相应的计算来确定，具体的步骤如下：In the embodiment of the present invention, each group of harmonic voltage detection threshold ranges can be determined through corresponding calculations, and the specific steps are as follows:
1、建立系统阻抗模型，其中，该系统阻抗模型中的参数均折算至同一电压等级，电网端等效为电压源与系统阻抗串联，逆变器等效为谐波电压源。1. Establish a system impedance model, wherein the parameters in the system impedance model are all converted to the same voltage level, the grid terminal is equivalent to a voltage source connected in series with the system impedance, and the inverter is equivalent to a harmonic voltage source.
如图3所示为系统阻抗模型的示意图，其中：XS为系统阻抗，XT为变压器阻抗，XC为入口滤波器容抗，XL为入口滤波器感抗，Rload和Xload为负载等效电阻和电抗，US为电网电压源，为逆变器等效电压源，a点为逆变器并网点。Figure 3 is a schematic diagram of the system impedance model, where: XS is the system impedance, XT is the transformer impedance, XC is the inlet filter capacitive reactance, XL is the inlet filter inductive reactance, Rload and Xload are Load equivalent resistance and reactance, US is the grid voltage source, is the equivalent voltage source of the inverter, and point a is the grid connection point of the inverter.
上述参数均折算至同一电压等级，具体的：The above parameters are all converted to the same voltage level, specifically:
电压等级记为UN(低电压等级)，系统短路容量为Sd，则系统阻抗XS为：The voltage level is recorded as UN (low voltage level), and the system short-circuit capacity is Sd , then the system impedance XS is:
入口滤波器的电感值与电容值分别记为L与C(均为单相)，系统频率记为f0，则入口滤波器感抗XL与容抗XC分别为：The inductance and capacitance of the inlet filter are denoted as L and C (both are single-phase), and the system frequency is denoted as f0 , then the inductive reactance XL and capacitive reactance XC of the inlet filter are respectively:
XL＝2πf0L；XL = 2πf0 L;
变压器额定容量记为SN，短路阻抗记为Uk(％)，则变压器阻抗XT为：The rated capacity of the transformer is recorded as SN , and the short-circuit impedance is recorded as Uk (%), then the transformer impedance XT is:
系统负载容量记为SL，基波功率因数记为则负载等效电阻Rload和等效电抗Xload为：The system load capacity is denoted as SL , and the fundamental wave power factor is denoted as Then the load equivalent resistance Rload and equivalent reactance Xload are:
2、根据该系统阻抗模型建立未发生孤岛与发生孤岛时系统谐波阻抗模型，并以此计算所选取的至少两组特征谐波次数在未发生孤岛与发生孤岛时对应的并网点参考次谐波电压。2. Based on the system impedance model, establish the harmonic impedance model of the system without islanding and when islanding occurs, and calculate the selected at least two groups of characteristic harmonic orders corresponding to the reference subharmonic of the grid connection point when no islanding occurs and when islanding occurs wave voltage.
本步骤中，采用前述步骤11所选取的两组逆变器IGBT开关频率附近特征谐波电压作为检测比较的参考次谐波电压。In this step, the characteristic harmonic voltages near the IGBT switching frequency of the two groups of inverters selected in step 11 above are used as the reference sub-harmonic voltage for detection and comparison.
1)未发生孤岛时系统谐波阻抗模型(如图4所示)中负载阻抗远远大于系统阻抗，等效为开路，计算时不考虑，模型中参数与所选取的特征谐波次数h相关：系统阻抗XS,h＝jhXS；变压器阻抗XT,h＝jhXT；入口滤波器的容抗XC,h＝-j(XC/h)；入口滤波器感抗XL,h＝jhXL；为逆变器输出谐波电压；1) In the system harmonic impedance model (as shown in Figure 4) when islanding does not occur, the load impedance is far greater than the system impedance, which is equivalent to an open circuit and is not considered in the calculation. The parameters in the model are related to the selected characteristic harmonic order h : system impedance XS,h ＝jhXS ; transformer impedance XT,h ＝jhXT ; entrance filter capacitive reactance XC,h ＝-j(XC /h); entrance filter inductance XL,h =jhXL ; Output harmonic voltage for inverter;
计算逆变器并网点a的谐波电压Calculate the harmonic voltage of the grid-connected point a of the inverter
因为实际测试点设在变压器高压侧母线的并网点，因此需要将谐波电压折算到高压等级，即将逆变器并网点a的谐波电压转换为并网点参考次谐波电压Because the actual test point is set at the grid-connected point of the high-voltage side bus of the transformer, it is necessary to convert the harmonic voltage to the high-voltage level, that is, the harmonic voltage of the grid-connected point a of the inverter Convert to grid-connected point reference sub-harmonic voltage
其中，n为变压器一次侧对二次侧变比，即低电压对高电压等级变比。Among them, n is the transformation ratio of the primary side to the secondary side of the transformer, that is, the transformation ratio of low voltage to high voltage level.
2)发生孤岛时系统谐波阻抗模型(如图5所示)中系统阻抗与系统分离，分布式电源通过逆变器对负载直接供电，其中的参数与所选取的特征谐波次数h相关：系统阻抗XS,h＝jhXS；变压器阻抗XT,h＝jhXT；入口滤波器的容抗XC,h＝-j(XC/h)；入口滤波器感抗XL,h＝jhXL；负载最小阻抗2) In the system harmonic impedance model (as shown in Figure 5) when islanding occurs, the system impedance is separated from the system, and the distributed power supply directly supplies power to the load through the inverter, and the parameters are related to the selected characteristic harmonic order h: System impedance XS,h ＝jhXS ; transformer impedance XT,h ＝jhXT ; entrance filter capacitive reactance XC,h ＝-j(XC /h); entrance filter inductance XL,h ＝ jhXL ; load minimum impedance
计算逆变器并网点a的谐波电压Calculate the harmonic voltage of the grid-connected point a of the inverter
同理，将逆变器并网点a的谐波电压转换为并网点参考次谐波电压Similarly, the harmonic voltage of the grid-connected point a of the inverter Convert to grid-connected point reference sub-harmonic voltage
3、根据每一组特征谐波次数在未发生孤岛与发生孤岛时并网点参考次谐波电压来确定该组谐波电压检测阈值范围。3. Determine the detection threshold range of the harmonic voltage for each group of characteristic harmonics according to the reference harmonic voltage of the grid-connected point when no islanding occurs and when islanding occurs.
可以根据所选取的特征谐波次数h未发生孤岛时与发生孤岛时并网点参考次谐波电压有效值Upcc,h与U'pcc,h确定对应的谐波电压检测阈值范围为Upcc,h～U'pcc,h。The corresponding harmonic voltage detection threshold range can be determined as Upcc,h and U'pcc,h according to the selected characteristic harmonic order h when there is no islanding and when islanding occurs. h ~ U'pcc,h .
步骤24、若持续时间均超过设定的时间限值，则判定发生孤岛效应；否则，转入重复执行步骤22。Step 24, if the duration exceeds the set time limit, it is determined that the islanding effect occurs; otherwise, go to step 22 to repeat.
为了便于理解，下面结合一具体的示例进行说明；需要说明的是，下述示例中所采用的数值仅为举例，用户可根据实际的需求做相应的更改。For ease of understanding, a specific example is used below for illustration; it should be noted that the numerical values used in the following examples are only examples, and users can make corresponding changes according to actual needs.
本示例中的步骤如图6所示，用于某光伏并网发电配电网系统中，基本参数如下：500kW光伏逆变器通过0.27/10kV变压器接入电网，变压器额定容量SN为500kW，短路阻抗Uk(％)为6％；10kV系统短路容量Sd为198MVA；500kW光伏逆变器LC入口滤波器的电容C＝200μF，电感L＝0.150mH；10kV系统负载基波功率因数容量为5MVA；逆变器IGBT开关频率为3kHz。The steps in this example are shown in Figure 6. It is used in a photovoltaic grid-connected power generation and distribution network system. The basic parameters are as follows: a 500kW photovoltaic inverter is connected to the power grid through a 0.27/10kV transformer, and the rated capacity of the transformer is500kW . The short-circuit impedance Uk (%) is 6%; the short-circuit capacity Sd of the 10kV system is 198MVA; the capacitance C of the LC inlet filter of the 500kW photovoltaic inverter is 200μF, and the inductance L is 0.150mH; the load fundamental wave power factor of the 10kV system The capacity is 5MVA; the inverter IGBT switching frequency is 3kHz.
(1)系统初始化。(1) System initialization.
(2)根据逆变器IGBT开关频率选取至少两组谐波次数作为参考次谐波，本示例中IGBT开关频率为3kHz，系统频率f0为50Hz，故选取56次、58次、62次和64次四组谐波电压作为孤岛检测参考次谐波。(2) According to the switching frequency of the inverter IGBT, at least two groups of harmonic orders are selected as the reference harmonics. In this example, the IGBT switching frequency is 3kHz, and the system frequencyf0 is 50Hz, so the 56th, 58th, 62nd and The 64th harmonic voltage of the fourth group is used as the reference sub-harmonic for islanding detection.
(3)建立系统阻抗模型，折算到0.27kV(低电压等级)侧系统阻抗为：(3) Establish a system impedance model, converted to 0.27kV (low voltage level) side system impedance as:
LC入口滤波器感抗(单相)为：XL＝2πfL＝2π×50×0.15×10-3＝0.0471Ω，The inductive reactance (single-phase) of the LC inlet filter is: XL ＝2πfL＝2π×50×0.15×10-3 ＝0.0471Ω,
LC入口滤波器容抗(单相)为：LC inlet filter capacitive reactance (single phase) is:
变压器阻抗为：The transformer impedance is:
负载电阻和电抗为：The load resistance and reactance are:
(4)根据系统阻抗模型建立未发生孤岛时系统谐波阻抗模型，并计算未发生孤岛时并网点各组参考次谐波电压大小。本示例中，选取h＝58次为例介绍计算并网点谐波电压的过程。计算58次系统各谐波阻抗值为：(4) Based on the system impedance model, establish a system harmonic impedance model when no islanding occurs, and calculate the reference harmonic voltage of each group of grid-connected points when no islanding occurs. In this example, h=58th order is taken as an example to introduce the process of calculating the harmonic voltage of the grid-connected point. Calculate the impedance value of each harmonic of the 58th system:
在0.27kV等效系统中，未发生孤岛时逆变器并网点a的58次谐波电压为：In the 0.27kV equivalent system, the 58th harmonic voltage of the grid-connected point a of the inverter when no islanding occurs is:
计算得到：Calculated to get:
折算到10kV侧母线，PCC点58次谐波电压为：Converted to the 10kV side bus, the 58th harmonic voltage at the PCC point is:
式中为逆变器输出的58次谐波电压。In the formula It is the 58th harmonic voltage output by the inverter.
(5)根据系统阻抗模型建立发生孤岛时系统谐波阻抗模型，并计算发生孤岛时并网点各组参考次谐波电压大小。58次负载最小阻抗其余参数与步骤(4)中的一致。(5) Establish the system harmonic impedance model when islanding occurs according to the system impedance model, and calculate the reference harmonic voltage of each group of grid-connected points when islanding occurs. 58 load minimum impedance The remaining parameters are consistent with those in step (4).
计算在0.27kV等效系统中，发生孤岛时逆变器并网点a的58次谐波电压为：Calculated in the 0.27kV equivalent system, the 58th harmonic voltage of the grid-connected point a of the inverter when islanding occurs is:
计算得到：Calculated to get:
折算到10kV侧母线，PCC点58次谐波电压为：Converted to the 10kV side bus, the 58th harmonic voltage at the PCC point is:
(6)根据两种情况下并网点谐波电压的计算值，设定58次谐波电压检测范围为6.296×10-2U58～0.344U58，由于系统负载阻抗大于计算所采用的负载最小阻抗，所以采用这个阈值范围检测孤岛是准确可靠的。(6) According to the calculated value of the harmonic voltage at the grid-connected point in the two cases, the detection range of the 58th harmonic voltage is set to 6.296×10-2 U58 ～0.344U58 , since the system load impedance is greater than the minimum load used in the calculation Impedance, so using this threshold range to detect islands is accurate and reliable.
(7)设定同步采样频率和采样点。(7) Set the synchronous sampling frequency and sampling point.
根据IGBT开关频率，设定截止频率fh为70次基波频率，采样频率fs≥2fh，采样点要确定采样点N等于2的整数次幂，选取N＝28＝256，采样频率fs为12800Hz。According to the IGBT switching frequency, set the cut-off frequency fh as the 70th fundamental frequency, the sampling frequency fs ≥ 2fh , and the sampling point To determine that the sampling point N is equal to an integer power of 2, select N=28 =256, and the sampling frequency fs is 12800 Hz.
(8)孤岛检测时，通过PT对逆变器输出端和并网点电压进行同步采样，通过A/D转换，进行快速傅里叶分解，得到58次参考次谐波电压大小，与设定范围进行比较。另外三组56次、62次和64次谐波电压的计算比较过程与58次同理。(8) During islanding detection, the inverter output terminal and the grid-connected point voltage are sampled synchronously through PT, and fast Fourier decomposition is performed through A/D conversion to obtain the 58th reference harmonic voltage, which is consistent with the setting range Compare. The calculation and comparison process of the other three groups of 56th, 62nd and 64th harmonic voltages is the same as that of 58th.
(8)判断各组参考次谐波电压大小是否均超出设定的谐波电压检测比较范围，如未均超过则返回第(7)步；(8) Judging whether the reference harmonic voltage of each group exceeds the set harmonic voltage detection and comparison range, if not, return to step (7);
(9)如果均超出检测比较范围，并且持续时间均超过设定的时间限值，判定产生孤岛，输出警报信号或反孤岛控制信号。(9) If all exceed the detection comparison range, and the duration exceeds the set time limit, it is determined that islanding occurs, and an alarm signal or an anti-islanding control signal is output.
本发明实施例的上述方案适用范围为含逆变器并网的分布式发电系统，如光伏并网发电系统。可解决逆变器并网输出功率与负载功率匹配时现有被动检测办法存在盲区(NDZ)的问题，又可避免主动式检测办法所带来的电能质量问题，且对于GB/T 29319-2012《光伏发电系统接入配电网技术规定》中关于孤岛检测快速性和准确性要求也可满足。The above solution of the embodiment of the present invention is applicable to a grid-connected distributed power generation system including an inverter, such as a photovoltaic grid-connected power generation system. It can solve the problem of blind zone (NDZ) in the existing passive detection method when the grid-connected output power of the inverter matches the load power, and can avoid the power quality problem caused by the active detection method, and is compatible with GB/T 29319-2012 The requirements for rapidity and accuracy of island detection in the "Technical Regulations for Connecting Photovoltaic Power Generation Systems to Distribution Networks" can also be met.
以上所述，仅为本发明较佳的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明披露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应该以权利要求书的保护范围为准。The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technical field can easily conceive of changes or changes within the technical scope disclosed in the present invention. Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.
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