WO2014000359A1 - 孤岛检测方法及系统 - Google Patents

孤岛检测方法及系统 Download PDF

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Publication number
WO2014000359A1
WO2014000359A1 PCT/CN2012/084168 CN2012084168W WO2014000359A1 WO 2014000359 A1 WO2014000359 A1 WO 2014000359A1 CN 2012084168 W CN2012084168 W CN 2012084168W WO 2014000359 A1 WO2014000359 A1 WO 2014000359A1
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Prior art keywords
voltage
signal
frequency
grid
disturbance signal
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PCT/CN2012/084168
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English (en)
French (fr)
Inventor
郑平
崔明
赵鹏
汪旭洋
杨培环
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BOE Technology Group Co Ltd
Beijing BOE Energy Technology Co Ltd
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BOE Technology Group Co Ltd
Beijing BOE Energy Technology Co Ltd
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Priority to US13/876,914 priority Critical patent/US9170306B2/en
Publication of WO2014000359A1 publication Critical patent/WO2014000359A1/zh
Anticipated expiration legal-status Critical
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/381—Dispersed generators
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/40—Testing power supplies
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2101/00—Supply or distribution of decentralised, dispersed or local electric power generation
    • H02J2101/20—Dispersed power generation using renewable energy sources
    • H02J2101/22—Solar energy
    • H02J2101/24—Photovoltaics
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/388—Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Definitions

  • Embodiments of the present invention relate to an island detecting method and system. Background technique
  • the photovoltaic grid-connected inverter converts the direct current generated by the solar panel into alternating current with the same frequency and phase in the grid voltage, and feeds the alternating current back to the grid.
  • the inverter still transmits power to the grid.
  • the inverter and the local load form a self-supplied island of power that cannot be controlled by the public grid system. This phenomenon is called the island phenomenon (isknd g phenomenon). . If there is no island detection or protection technology, the inverter will continue to supply local and local grid loads.
  • the PV grid-connected power generation system is in an island operation state, it will have serious consequences: The grid cannot control the voltage and frequency in the island.
  • the inverter is designed to have a fast and accurate island detection response function, which can reduce the harm caused by the island.
  • the existing island detection methods mainly include passive detection and active detection.
  • Passive detection refers to the island effect detection by the change of voltage, frequency, phase or harmonic of the inverter output when the grid is powered off.
  • the method is a method for detecting whether or not an islanding phenomenon is mainly caused by over/under voltage and over/under frequency detection, and stopping the grid connection operation when the voltage amplitude and frequency of the common coupling point exceed the normal range. .
  • the inverter is working, the working range of voltage and frequency should be set reasonably. If the voltage or frequency offset reaches the island detection setting threshold, the island can be detected.
  • the local load of the inverter is close to its output power, the voltage and frequency offset will be very small or even zero. Therefore, there is a large dead zone in this method.
  • Embodiments of the present invention provide an island detecting method and system, which can avoid detecting dead zones, and has simple control, and can perform island detecting of the inverter quickly and accurately.
  • An aspect of the present invention provides an island detecting method, comprising: collecting a voltage signal of a grid point of a power generation system, and extracting phase information of the voltage signal; and constructing a sliding manner by using a quadratic function according to the phase information; a mode frequency offset island detection curve; and an inverter that generates a disturbance signal according to the sliding mode frequency offset island detection curve and transmits the signal to the power generation system.
  • the sliding mode frequency offset island detection curve constructed by means of a quadratic function is as follows:
  • 0 is the phase of the disturbance signal
  • / is the frequency of the current voltage signal collected
  • a, b is the preset parameter.
  • the generated 4 special signals are as follows:
  • ( ⁇ )' is the generated disturbance signal, which is the phase of the disturbance signal.
  • the detecting method further includes: obtaining a voltage peak and a frequency according to the collected voltage signal and the extracted phase information, if the voltage peak of the voltage signal of the grid point exceeds a preset voltage range, or the frequency of the voltage signal of the grid point exceeds the pre- Setting the frequency range cuts off the connection between the inverter and the local load in the power generation system.
  • the preset voltage range is [0.8V, 1.2V] and the preset frequency range is [49.5Hz, 50.5Hz].
  • an island detecting system comprising: a collection module, a voltage signal for collecting the grid point of the power generation system, and extracting phase information of the voltage signal; an island detecting module, configured to construct a sliding mode frequency offset island detecting curve according to the phase information and using a quadratic function; And a driving module, configured to generate a disturbance signal according to the sliding mode frequency offset island detecting curve and send the signal to an inverter of the power generation system.
  • the island detecting module uses a quadratic function to construct a sliding mode frequency offset island detecting curve as follows:
  • 0 is the phase of the disturbance signal
  • / is the frequency of the current voltage signal collected by the clamp
  • a, b is the preset parameter.
  • the disturbance signal generated by the driving module according to the sliding mode frequency offset island detection curve is as follows:
  • Cot is the extracted phase information
  • ( ⁇ )' is the generated disturbance signal, which is the phase of the disturbance signal.
  • the island detecting module is further configured to determine, according to the voltage peak and the frequency obtained by the collected voltage signal and the extracted phase information, if the voltage peak of the voltage signal of the grid point exceeds a preset voltage range, or a voltage of the grid point If the frequency of the signal exceeds the preset frequency range, the connection between the inverter and the local load in the power generation system is cut off.
  • the collection module includes sensors, a conditioning circuit, and a phase locked loop that are sequentially connected.
  • FIG. 1 is a flow chart of an island detecting method according to an embodiment of the present invention.
  • FIG. 2 is a schematic diagram showing the relationship between an SMS curve and a load curve generated by an island detecting method according to an embodiment of the present invention
  • FIG. 3 is a conventional photovoltaic power generation system and an island inspection 'J system according to an embodiment of the present invention A combined structural block diagram. detailed description
  • the method and system of the present invention use an active and passive detection method to perform islanding detection of a grid-connected inverter, and mainly utilizes a Slip-Mode Frequency Shift (SMS) detection method in an active detection method.
  • SMS detection method is an active island detection method, which controls the output current of the inverter, introduces a small phase shift disturbance, and has a certain phase difference between the voltage of the grid and the grid, and connects the inverter to the grid.
  • the output current of the inverter is in phase with the grid voltage, and the output frequency remains stable and is at the same frequency as the grid.
  • the inverter and the local load form an island system.
  • the active island detection disturbance based on SMS forms a positive feedback between the phase angle and the frequency.
  • the change triggers the over/under voltage, over/under frequency fault, the inverter is cut off. The connection to the local load.
  • the method and system of the present invention constructs an SMS curve by means of a quadratic function, and by adjusting the control parameters, when there is an island, there is positive feedback between the output frequency and the phase information of the inverter, thereby triggering over/under frequency or over / Undervoltage fault, thereby cutting off the connection between the inverter and the load, so that the inverter stops supplying power to the load, thereby improving the safety of the photovoltaic system.
  • the photovoltaic power generation system will be taken as an example to illustrate the technology of the present invention.
  • Other technologies such as a wind power generation system and the like may still be used, and the present invention is not limited thereto.
  • the photovoltaic grid-connected inverter islanding detection method includes:
  • the voltage signal of the grid-connected point of the photovoltaic power generation system is collected, and the phase information is extracted, wherein the grid-connected point refers to a node that is processed by filtering and the like, and the output signal of the inverter is connected to the power grid and the local load.
  • the SMS curve is constructed by using a quadratic function. as well as
  • a disturbance signal is generated from the SMS curve and sent to the inverter of the photovoltaic power generation system.
  • the islanding detection is a continuous process in real time, that is, the invention generates a disturbance signal according to the SMS curve based on the voltage signal collected at the previous moment, the phase information and the frequency of the voltage signal, and generates The disturbance signal is sent to the inverter, and then the disturbed voltage signal, the phase information and the frequency of the voltage signal are collected during the next cycle, and detected, and thus reciprocated.
  • the island detecting method may further include: determining, according to the collected grid point voltage signal and the extracted phase information and frequency, if the current grid point is collected The voltage peak value Vp of the voltage signal (beyond the preset voltage range (over/undervoltage threshold), or the frequency of the current grid-connected voltage signal exceeds the preset frequency range (over/under frequency threshold), then cut off the photovoltaic system The connection of the inverter to the local load.
  • the shut-off process is performed by the circuit breaker.
  • the voltage peak value Vp can be calculated based on phase information extracted from the grid-connected point voltage signal using prior art in the art.
  • the preset voltage range is [0.8V, 1.2V] and the preset frequency range [49.5Hz, 50.5Hz].
  • the method of the embodiment of Figure 1 uses a quadratic function to construct a new SMS curve:
  • 0 is the phase of the disturbance signal
  • / is the frequency of the current voltage signal collected by the clamp
  • a, b are preset parameters.
  • the generated SMS curve is a quadratic curve, and its relationship with the load curve is shown in Figure 2. As shown in Figure 2, the SMS quadratic slope constructed by the method of the embodiment of Figure 1 is greater than the slope of the load curve. When an island is present, the phase information of the inverter output signal forms a positive feedback with the frequency until the over/under voltage or over/under frequency protection is triggered.
  • the a, b, and three parameters can be preset based on the required detection time (the detection time is defined as the time from when the islanding phenomenon occurs to when the circuit breaker is turned off).
  • the detection time is defined as the time from when the islanding phenomenon occurs to when the circuit breaker is turned off.
  • a, b value is larger, the detection time is shorter, the M value affects the harmonic content of the inverter output current, and the M value should be at the inverter output current harmonic content. Meet the requirements within the scope of the setting.
  • the disturbance signal ( ⁇ ) generated according to the SMS curve is:
  • ( ⁇ )' is the generated disturbance signal, which is the phase of the disturbance signal.
  • Fig. 3 is a block diagram showing the structure of a conventional photovoltaic power generation system in combination with an island detecting system in accordance with an embodiment of the present invention.
  • a conventional photovoltaic power generation system includes a photovoltaic panel 1, an inverter 2, a filter 3, and a transformer 4.
  • the output of transformer 4 is connected to the grid and local load (RLC), which is the grid point.
  • An island detecting system according to an embodiment of the present invention includes: a collecting module 5, an island detecting module 6, and a driving module 7.
  • the collection module 5 includes, but is not limited to, a sensor connected in sequence, a conditioning circuit, and a phase-locked loop.
  • the collection module 5 collects a voltage signal Vab of a grid point (dotted elliptical box in the figure) through a sensor.
  • the phase information and the frequency f are extracted by the phase locked loop, and the output of the phase locked loop is used as the input of the island detecting module 6.
  • the phase locked loop is implemented in digital signal processing (DSP).
  • the island detecting module 6 calculates the target phase of the disturbance signal according to the formula (1) based on the phase information input from the clustering module 5, and constructs the SMS curve by the above-described quadratic function.
  • the phase-locked loop in the island detecting module 6 and the clustering module 5 can be implemented in the same DSP, or the island detecting module 6 can be implemented in other ways.
  • the driving module 7 generates a final disturbance signal according to the SMS curve and the formula (2) and transmits it to the inverter 2 of the photovoltaic power generation system, and simultaneously drives the inverter 2 to output a corresponding current, thereby causing the active island to detect the phase information of the disturbance. Form positive feedback with frequency.
  • the island detecting module 6 detects the occurrence of the islanding phenomenon at any time, and when the frequency caused by the island and the voltage change at the grid-connecting point trigger the occurrence of over/under voltage, over/under frequency fault, the circuit breaker 8 is disconnected, and the inverter 2 is cut off. With the connection to the local load, the inverter 2 stops supplying power to the load side until the grid is restored.
  • the drive module 7 uses Pulse Width Modulation (PWM) to generate a disturbance signal.
  • PWM Pulse Width Modulation
  • a conventional PWM circuit can be used to generate a disturbance signal.
  • the method and system disclosed by the present invention use an active and passive detection method to avoid The blind area is detected and the control is simple, and the inverter island detection can be performed quickly and accurately.
  • the quadratic function is used to construct the SMS curve.
  • the occupied CPU resources are small, which facilitates the development of the embedded system;
  • the required parameter response time can be obtained by setting the relevant parameters.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Inverter Devices (AREA)

Abstract

一种孤岛检测方法及系统。该方法包括：采集发电系统并网点的电压信号，并提取该信号的相位信息；根据所述相位信息，采用二次函数的方式构建滑模频率偏移孤岛检测曲线；以及根据所述滑模频率偏移孤岛检测曲线生成扰动信号并发送至发电系统的逆变器。该方法及系统能够避免检测盲区，并且控制简单，能够快速、准确地进行逆变器的孤岛检测。

Description

孤岛检测方法及系统 技术领域
本发明的实施例涉及一种孤岛检测方法及系统。 背景技术
光伏并网逆变器作为光伏发电系统的关键部件， 其作用是将太阳能电池 板发出的直流电转换成与电网电压同频率、 同相位的交流电， 并将该交流电 反馈至电网。 当电网因故中断供电时， 逆变器仍向电网传输电能， 该逆变器 将和本地负载形成一个公共电网系统无法控制的自给供电孤岛， 这种现象即 称为孤岛现象（ isknd g phenomenon )。 如果没有任何孤岛检测或保护技术， 逆变器会持续给本地负载和局部电网负载供电。 光伏并网发电系统处于孤岛 运行状态时会产生严重的后果： 电网无法控制孤岛中的电压和频率， 若电压 和频率超出允许的范围， 可能会对用户的设备造成损坏； 若负载容量大于光 伏发电系统容量， 光伏发电系统过载运行， 易被烧毁； 与光伏发电系统相连 的线路仍然带电， 对检修人员造成危险， 降低电网的安全性； 对孤岛进行重 合闸操作会导致线路再次跳闸， 还有可能损坏光伏发电系统和其他设备。 可 见， 将逆变器设计为具有快速准确的孤岛检测响应功能， 可以降低孤岛产生 的危害。
现有孤岛检测方法主要有被动检测和主动检测两种方法。 被动检测是指 利用电网断电时逆变器输出端的电压、 频率、 相位或谐波的变化进行孤岛效 应检测。该方法是一种主要通过过 /欠电压和过 /欠频检测法来确定是否发生孤 岛现象， 在公共耦合点的电压幅值和频率超过正常范围时， 停止逆变器并网 运行的检测方法。 逆变器工作时， 电压、 频率的工作范围要合理设置， 如果 电压或频率偏移达到孤岛检测设定阀值， 则可检测到孤岛发生。 然而当逆变 器所带的本地负荷与其输出功率接近于匹配时， 电压和频率的偏移将非常小 甚至为零， 因此该方法存在着较大的盲区， 对于负载匹配很好的系统， 被动 检测方法失效。 主动检测方法是指通过控制逆变器， 使其输出功率、 频率或相位存在一 定的扰动。 电网正常工作时， 由于电网的平衡作用， 检测不到这些扰动。 一 旦电网出现故障， 逆变器输出的扰动将快速累积并超出允许范围， 从而触发 孤岛效应检测电路。 该方法检测精度高， 非检测区小， 但是控制较复杂， 且 降低了逆变器输出电能的质量。 发明内容
本发明的实施例提供了一种孤岛检测方法及系统， 其能够避免检测盲区， 且控制简单， 能够快速、 准确地进行逆变器的孤岛检测。
本发明的一个方面提供了一种孤岛检测方法， 包括： 釆集发电系统并网 点的电压信号， 并提取该电压信号的相位信息； 才艮据该相位信息， 釆用二次 函数的方式构建滑模频率偏移孤岛检测曲线； 以及根据所述滑模频率偏移孤 岛检测曲线生成扰动信号并发送至发电系统的逆变器。
例如， 釆用二次函数的方式构建的滑模频率偏移孤岛检测曲线如下：
Figure imgf000004_0001
其中， 0为所述扰动信号的相位， Δ/ = / - ， 是电网额定频率， /是 当前釆集到的电压信号的频率， 为预设的扰动信号最大幅值， a、 b为预设 参数。
例如， 生成的 4尤动信号如下：
(ωή '=ωί+θ
其中， 为提取的相位信息， （ωί)'为生成的扰动信号， 为所述扰动信 号的相位。
例如， =50Ηζ。
例如， 检测方法还包括： 根据釆集到的电压信号和提取的相位信息得到 电压峰值和频率， 若并网点的电压信号的电压峰值超出预设电压范围， 或并 网点的电压信号的频率超出预设频率范围， 则切断发电系统中逆变器与本地 负载的连接。
例如， 预设电压范围为 [0.8V, 1.2V] , 预设频率范围 [49.5Hz, 50.5Hz]。 本发明的另一方面提供了一种孤岛检测系统， 该系统包括： 釆集模块， 用于釆集发电系统并网点的电压信号， 并提取该电压信号的相位信息； 孤岛 检测模块， 用于根据所述相位信息， 釆用二次函数的方式构建滑模频率偏移 孤岛检测曲线； 以及驱动模块， 用于根据所述滑模频率偏移孤岛检测曲线生 成扰动信号并发送至发电系统的逆变器。
例如， 所述孤岛检测模块釆用二次函数的方式构建的滑模频率偏移孤岛 检测曲线如下：
Figure imgf000005_0001
其中， 0为所述扰动信号的相位， Δ/ = / - ， 是电网额定频率， /是 釆集到的当前电压信号的频率， 为预设的扰动信号最大幅值， a、 b为预设 参数。
例如， 所述驱动模块根据所述滑模频率偏移孤岛检测曲线生成的扰动信 号如下：
Figure imgf000005_0002
cot为提取的相位信息， （ωί)'为生成的扰动信号， 为所述扰动信号的相 位。
例如， 所述孤岛检测模块还用于根据釆集到的电压信号和提取的相位信 息得到的电压峰值和频率判断， 若并网点的电压信号的电压峰值超出预设电 压范围， 或并网点的电压信号的频率超出预设频率范围， 则切断发电系统中 逆变器与本地负载的连接。
例如， 所述釆集模块包括依次连接的传感器、 调理电路以及锁相环。 附图说明
为了更清楚地说明本发明实施例的技术方案， 下面将对实施例的附图作 简单地介绍， 显而易见地， 下面描述中的附图仅仅涉及本发明的一些实施例， 而非对本发明的限制。
图 1为依照本发明一种实施方式的孤岛检测方法流程图；
图 2为依照本发明一种实施方式的孤岛检测方法所生的 SMS曲线与负载 曲线的关系示意图；
图 3为传统的光伏发电系统与依照本发明一种实施方式的孤岛检 'J系统 相结合的结构框图。 具体实施方式
为使本发明实施例的目的、 技术方案和优点更加清楚， 下面将结合本发 明实施例的附图， 对本发明实施例的技术方案进行清楚、 完整地描述。 显然， 所描述的实施例是本发明的一部分实施例， 而不是全部的实施例。 基于所描 述的本发明的实施例， 本领域普通技术人员在无需创造性劳动的前提下所获 得的所有其他实施例， 都属于本发明保护的范围。
本发明的方法及系统釆用主动与被动结合的检测方法进行并网逆变器的 孤岛检测，且主要利用主动检测方法中的滑模频率偏移（ Slip-Mode Frequency Shift, SMS )检测法。 SMS检测法是一种主动式孤岛检测方法， 该方法控制 逆变器的输出电流， 引入一个小的相移扰动， 使其与并网点电压间存在一定 的相位差， 在逆变器与电网连接的情况下， 由于电网的钳位作用， 逆变器输 出的电流与电网电压同相位， 输出频率保持稳定且与电网同频。 当电网发生 故障时， 且逆变器运行于本地负载匹配艮好的情况下， 逆变器与本地负载形 成孤岛系统， 此时基于 SMS的主动孤岛检测扰动使相角与频率形成正反馈， 从而导致逆变器的输出电流的频率和并网点处电压的变化， 并根据该频率或 电压的变化来检测孤岛， 当该变化触发过 /欠压、 过 /欠频故障的发生时， 切断 逆变器与本地负载的连接。 本发明的方法及系统利用二次函数的方式构建 SMS曲线， 通过调整控制参数， 使在孤岛发生时， 逆变器的输出频率与相位 信息之间存在正反馈， 进而触发过 /欠频或过 /欠压故障， 由此切断逆变器与负 载之间的连接， 使逆变器停止向负载供电， 从而提高光伏系发电系统的安全 性。
下面以光伏发电系统为例， 来说明本发明的技术， 其它例如风力发电系 统等仍可使用本发明的技术， 在此不作为对本发明的限制。
如图 1 所示， 依照本发明的实施方式的光伏并网逆变器孤岛检测方法包 括：
釆集光伏发电系统并网点的电压信号， 并提取其相位信息， 其中， 并网 点是指经过滤波等处理后的逆变器输出信号接入电网以及本地负载的节点。 根据该并网点电压信号的相位信息 OJt和频率 f , 釆用二次函数的方式构 建 SMS曲线。 以及
根据 SMS曲线生成扰动信号并发送至光伏发电系统的逆变器。
需要说明的是， 孤岛检测是一个实时进行的连续过程， 即本发明基于前 一时刻釆集到的电压信号、 该电压信号的相位信息和频率， 才艮据 SMS曲线生 成扰动信号， 并将生成的扰动信号发送至逆变器， 然后在下一次循环过程中 釆集受到扰动后的电压信号、 该电压信号的相位信息和频率， 进行检测， 如 此往复循环。
如图 1 所示， 根据本发明的实施例的孤岛检测方法， 还可以包括： 根据 釆集到的并网点电压信号和提取的相位信息和频率进行判断——若釆集到的 当前并网点的电压信号的电压峰值 Vp (超出预设电压范围 （过 /欠压阔值）， 或当前并网点的电压信号的频率超出预设频率范围（过 /欠频阔值），则切断光 伏发电系统中逆变器与本地负载的连接。 该切断过程由断路器执行。 又例如， 可以利用本领域的现有技术基于从所述并网点电压信号提取的相位信息来计 算电压峰值 Vp。
例如， 根据并入的电网电压及其频率， 预设电压范围为 [0.8V, 1.2V] , 预 设频率范围 [49.5Hz, 50.5Hz]。
例如， 图 1中实施方式的方法釆用二次函数的方式构建新型的 SMS曲线 下：
Figure imgf000007_0001
其中， 0为扰动信号的相位， Δ/ = / _ ， 是电网额定频率，例如为 50Hz 或 60Hz, /是釆集到的当前电压信号的频率， 为预设的扰动信号最大幅值 (限幅值）， a、 b、 均为预设参数。 生成的 SMS曲线为二次曲线， 其与负 载曲线关系如图 2所示。如图 2中所示，图 1中实施方式的方法所构建的 SMS 二次曲线斜率要大于负载曲线斜率。 当出现孤岛时， 逆变器输出信号的相位 信息与频率形成正反馈， 直至触发过 /欠压或过 /欠频保护。
a、 b以及 三个参数可以根据所需要的检测时间（检测时间定义为从出 现孤岛现象到断路器关断的时间）来预先设置。 a、 b值越大，检测时间越短， M值影响逆变器输出电流的谐波含量， M值应当在逆变器输出电流谐波含量 符合要求的范围内设置。
根据 SMS曲线生成的扰动信号 (ωΐ)'为：
Figure imgf000008_0001
其中， 为提取的相位信息， （ωί)'为生成的扰动信号， 为扰动信号的 相位。
图 3示出了传统的光伏发电系统与依照本发明一种实施方式的孤岛检测 系统相结合的结构框图。 如图 3所示， 传统的光伏发电系统包括光伏电池板 1、 逆变器 2、滤波器 3、 以及变压器 4。变压器 4的输出与电网以及本地负载（RLC ) 相连接， 连接点即为并网点。 依照本发明一种实施方式的孤岛检测系统包括： 釆集模块 5、 孤岛检测模块 6、 以及驱动模块 7。
例如， 釆集模块 5包括但不限于依次连接的传感器、 调理电路、 以及锁相 环构成，该釆集模块 5通过传感器釆集光伏发电系统并网点（图中虚线椭圓框） 的电压信号 Vab, 并经过调理电路处理后由锁相环提取其相位信息 以及频率 f, 锁相环的输出作为孤岛检测模块 6的输入。 例如， 在数字信号处理（DSP ) 中实现该锁相环。
孤岛检测模块 6基于从釆集模块 5输入的相位信息， 根据公式 ( 1 )计算出 扰动信号的目标相位 6>, 并釆用上述二次函数的方式构建 SMS曲线。 例如， 可 以在同一块 DSP中实现孤岛检测模块 6和釆集模块 5中的锁相环，也可以通过其 他方式实现孤岛检测模块 6。
驱动模块 7根据该 SMS曲线和公式（2 )生成最终的扰动信号并发送至光 伏发电系统的逆变器 2 , 同时驱动逆变器 2以输出相应的电流， 从而使主动孤 岛检测扰动的相位信息与频率形成正反馈。
孤岛检测模块 6时刻检测孤岛现象的发生， 在孤岛导致的频率和并网点处 电压的变化触发过 /欠压、 过 /欠频故障的发生时， 使断路器 8断开， 切断逆变 器 2与本地负载之间的连接， 逆变器 2停止向负载侧供电， 直到电网恢复。
在本发明的一个实施例中， 驱动模块 7使用脉冲宽度调制 （Pulse Width Modulation, PWM )来生成扰动信号。 例如， 可使用常规的 PWM电路来生成 扰动信号。
本发明所公开的方法及系统釆用主动与被动结合的检测方法， 能够避免 检测盲区， 且控制简单， 能够快速、 准确的进行逆变器孤岛检测。 此外， 根 据当前釆样的并网点电压信号的频率， 釆用二次函数的方式构建 SMS曲线， 在方法运行过程中， 所占用的 CPU资源小， 便于嵌入式系统的开发； 并且计 算简单， 通过对相关参数的设定可获得需要的检测响应时间。
以上所述仅是本发明的示范性实施方式， 而非用于限制本发明的保护范 围， 本发明的保护范围由所附的权利要求确定。

Claims

权利要求书
1、 一种孤岛检测方法， 其中， 包括：
釆集发电系统并网点的电压信号， 并提取该电压信号的相位信息； 根据所述相位信息， 釆用二次函数的方式构建滑模频率偏移孤岛检测曲 线； 以及
根据所述滑模频率偏移孤岛检测曲线生成扰动信号并将该扰动信号发送 至发电系统的逆变器。
2、 如权利要求 1所述的方法， 所述釆用二次函数的方式构建的滑模频率 偏移孤岛检测曲线如下：
Figure imgf000010_0001
其中， 0为所述扰动信号的相位， Δ/ = / - ， 是电网额定频率， /是 当前釆集到的电压信号的频率， 为预设的扰动信号最大幅值， a、 b为预设 参数。
3、 如权利要求 2所述的方法， 所述生成的扰动信号如下：
(ωί) '=ωί+θ
其中， 为提取的相位信息， （ωί)'为生成的扰动信号， 为所述扰动信 号的相位。
4、 如权利要求 2所述的方法， 其中， =50Ηζ。
5、 如权利要求 1-4中任一项所述的方法， 其中， 所述检测方法还包括： 根据所述釆集到的电压信号和所述提取的相位信息得到电压峰值和频 率， 若所述并网点的电压信号的电压峰值超出预设电压范围， 或所述并网点 的电压信号的频率超出预设频率范围， 则切断所述发电系统中逆变器与本地 负载的连接。
6、 如权利要求 5所述的方法， 其中， 所述预设电压范围为 [0.8V, 1.2V] , 所述预设频率范围 [49.5Hz, 50.5Hz]。
7、 一种孤岛检测系统， 其中， 该系统包括：
釆集模块， 用于釆集发电系统并网点的电压信号， 并提取该电压信号的 相位信息；
孤岛检测模块， 用于根据所述相位信息， 釆用二次函数的方式构建滑模 频率偏移孤岛检测曲线； 以及
驱动模块， 用于根据所述滑模频率偏移孤岛检测曲线生成扰动信号并将 该扰动信号发送至所述发电系统的逆变器。
8、 如权利要求 7所述的系统， 所述孤岛检测模块釆用二次函数的方式构 建的滑模频率偏移孤岛检测曲线如下：
Figure imgf000011_0001
其中， 0为所述扰动信号的相位， Δ/ = / - ， 是电网额定频率， /是 釆集到的当前电压信号的频率， 为预设的扰动信号最大幅值， a、 b为预设 参数。
9、 如权利要求 8所述的系统， 所述驱动模块根据所述滑模频率偏移孤岛 检测曲线生成的扰动信号如下：
Figure imgf000011_0002
其中， 为提取的相位信息， （ωί)'为生成的扰动信号， 为所述扰动信 号的相位。
10、如权利要求 7-9中任一项所述的系统， 其中， 所述孤岛检测模块还用 于根据所述釆集到的电压信号和所述提取的相位信息得到的电压峰值和频率 来进行判断， 若所述并网点的电压信号的电压峰值超出预设电压范围， 或所 述并网点的电压信号的频率超出预设频率范围， 则切断所述发电系统中逆变 器与本地负载的连接。
11、 如权利要求 7-10中任一项所述的系统， 其中， 所述釆集模块包括依 次连接的传感器、 调理电路以及锁相环。
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