一种混合式光伏逆变器反孤岛策略

逆变输出同本地消纳功率平衡时,被动式反孤岛策略会出现非检测区,而主动式反孤岛策略对电能质量有影响。文章提出一种基于过欠电压/频率和功率扰动相联合的混合式光伏逆变器反孤岛策略,该控制策略是将逆变器输出功率与负载功率进行比较,得到控制信号,进而在孤岛发生时根据不同工况在两种检测方法中切换。建立了光伏逆变器孤岛检测仿真模型,仿真结果表明,文章反孤岛策略具有无检测盲区、产生谐波小等优点。     

单相光伏并网发电系统孤岛检测仿真分析

基于单相单级光伏并网发电系统,针对传统主动式频率偏移法控制的复杂性,采用了一种新颖的带反馈的主动式频率偏移法。利用Matlab／simulink,对新颖的带反馈的主动式频率偏移法进行孤岛检测仿真分析。仿真结果表明,该方法能够有效、准确地检测孤岛效应。     

一种基于锁相角扰动的主动式反孤岛策略

为减小并网电流畸变率,提高孤岛检测的响应速度,以满足不同类型负载的要求,提出一种基于锁相角扰动的主动式反孤岛策略。通过对参考电流锁相角引入一个微小的随正弦规律变化的扰动,使得参考电流到达峰值的时间向左或向右偏移,同时其频率又不受影响,由于逆变器输出电流是跟随参考电流的变化而变化,因而在主电网断电时,公共点电压过峰值的时间会有一个小角度的偏移,当偏移程度超过设定阈值范围,逆变器断开,停止向主电网供电。在PSCAD中搭建了单相光伏逆变器孤岛检测仿真模型,对多种类型的负载进行了仿真,结果表明,该方法具有对电网产生的谐波小、无检测盲区、算法简单易实现等优点。     

多机光伏并网逆变器并联运行的孤岛检测方法研究

针对传统带正反馈的主动移频(Active Frequency Drift Positive Feedback,AFDPF)方法的不足,提出了改进型正反馈主动频率偏移孤岛检测方法,分析了改进型AFDPF孤岛检测方法的基本原理和孤岛检测盲区(Non-Detection Zone,NDZ)。通过Matlab/Simulink仿真软件建立了两台光伏并网逆变器并联的仿真模型,在单台逆变器和两台逆变器运行情况下分别对传统AFDPF和改进型AFDPF孤岛检测方法进行了仿真研究。仿真结果表明,改进型AFDPF孤岛检测方法在单台和两台逆变器运行情况下均能够准确检测出孤岛,且满足IEEE std.929-2000标准。     

传统的分布式光伏并网孤岛效应检测方法正确率的研究

近年来,针对分布式光伏并网孤岛效应的检测方法在不断优化。在针对分布式光伏并网的传统防孤岛保护技术中,基于光伏逆变器本身的孤岛效应检测方法主要有被动孤岛检测方法和主动孤岛检测方法,对二者的基本原理进行分析,并对不同判断依据及影响因素进行设置,然后采用仿真算例得到不同判断依据时孤岛效应检测方法的相对动作正确率,以期通过此方法为分布式光伏并网防孤岛保护的优化和完善提供一定的参考。     

改进的正反馈主动频移孤岛检测方法的仿真分析

结合光伏并网系统逆变器的并网控制过程,分析了一种改进的正反馈频率漂移孤岛检测方法,详细阐述了该方法的原理和负载性质对其的影响,通过仿真分析表明所采用的孤岛检测方法的有效性,改进后的方法加快了检测速度,减少了检测盲区和对电力系统的谐波污染.     

基于正反馈频率漂移的光伏并网逆变器反孤岛控制

结合光伏并网逆变器的并网控制过程提出了一种正反馈频率漂移反孤岛检测方法，并详细介绍了该方法的原理和实现过程，然后按照IEEE Std．20130-929标准中规定的测试电路对并网逆变器的反孤岛控制能力进行了测试，测试结果表明该方法是可行的并且达到了IEEE Std．2000-929标准的规定。     

基于群控扰动的微型并网逆变器防孤岛方法

主要介绍在安装于同一并网点、由大量微型并网逆变器构成的光伏并网发电系统防孤岛效应方面引入群控理念,通过控制中枢保证整个系统内微型并网逆变器在被动检测到电网异常时,统一步径共同主动扰动,实现电网孤岛检测的更准确、更安全。     

光伏多逆变器并网系统的孤岛检测方法研究

针对孤岛检测方法应用于多逆变器并网系统可能失效的问题,文章对孤岛检测方法进行了系统地分析,探讨了滑模频率漂移法和无功扰动法相互影响的机理,指出了被动法、双向无功扰动法、阻抗测量法应用于多逆变器并网系统存在一定的局限性,然后提出了Sandia频移法、滑模频率漂移法的有关参数设计方法,最后对其进行了实验验证,实验结果表明所选孤岛检测方法的有效性和合理性。     

多逆变器并网光伏系统孤岛检测技术研究

针对当前常用多逆变器并网孤岛检测方法的不足,提出一种基于小波变换与神经网络的孤岛检测方法。该法利用小波变换提取公共耦合点(PCC)处的电压信号与逆变器输出电流信号的特征量,再采用BP神经网络通过模式识别以判断孤岛现象是否发生。Matlab仿真和实验结果表明,该方法能快速检测出孤岛状态,检测盲区小且对电能质量无影响,有较高的准确性和可靠性。     

Improved SMS islanding detection method for grid-connected converters

Islanding detection is a mandatory function for grid-connected converters. The popular slip mode frequency shift (SMS) and auto phase shift active islanding detection methods are investigated and an improved (IM)-SMS strategy is proposed in this study. In the proposed method, additional phase shift is introduced to help in stimulating the action of the islanding detection and the algorithm is simplified as well. When the utility grid is disconnected, the algorithm keeps the frequency of the converter output voltage deviating until the frequency protection relay is triggered. The working principle of the method is introduced and the guidance of parameters selection and optimisation is also provided. The islanding detection performance is evaluated through theoretical analysis and verified by digital simulation and experimental results. The IM-SMS method exhibits features of simplicity, easy implementation and high reliability.     

光伏发电系统孤岛保护建模与仿真研究

通过理论分析,对孤岛保护建立了仿真模型。孤岛检测采用具有过/欠电压检测功能的电压相位突变检测方法,该检测方法克服了采用单一的电压相位突变检测方法在阻性负载下失效的问题,可以实现快速有效的孤岛检测功能,分析了孤岛检测盲区的负载参数范围,同时,提出了防止由于电网不稳定与大负载的突然投入或切除引起电网波动导致的虚假孤岛现象的误保护措施。本文通过理论分析、建模和仿真实验研究,验证了提出的孤岛保护模型的有效性和实用性。     

UK scenario of islanded operation of active distribution networks with renewable distributed generators

This paper reports on the current UK scenario of islanded operation of active distribution networks with renewable distributed generators (RDGs). Different surveys indicate that the present scenario does not economically justify islanding operation of active distribution networks with RDGs. Anti-islanding protection schemes currently enforce the renewable distributed generators (RDGs) to disconnect immediately and stop generation for grid faults through loss of grid (LOG) protection system. This greatly reduces the benefits of RDG deployment. With rising RDG penetration, much benefit would be lost if the RDGs are not allowed to island only due to conventional operational requirement of utilities. For preventing disconnection of RDGs during LOG, several islanding operation, control and protection schemes are being developed. Technical studies clearly indicate the need to review parts of the ESQCR (Electricity Safety, Quality and Continuity Regulations) for successful islanded operations. Commercial viability of islanding operation must be assessed in relation to enhancement of power quality, system reliability and supply of potential ancillary services through network support. Demonstration projects under Registered Power Zone and Technical Architecture Projects should be initiated to investigate the usefulness of DG islanding. However these efforts should be compounded with a realistic judgement of the associated technical and economic issues for the development of future power networks.     

A combined active anti-islanding method for photovoltaic systems

In a modern power system, photovoltaic as distributed generated source is growing larger and it can cause a variety of problems. The most important problem is that of the islanding phenomenon. In order to prevent islanding phenomenon, three kinds of active islanding detection methods have been studied. These are, respectively, to change magnitude, frequency, and the start phase of inverter output current. Among those, both a frequency variation method and a start-phase variation anti-islanding method make the islanding frequency drift away from the trip window of the frequency relay if islanding occurs. This paper presents a novel combined active anti-islanding method, which consists of a frequency variation method active frequency drift (AFD) and a start-phase variation method slip-mode frequency shift (SMS). Clearly, the proposed anti-islanding method shows the islanding detection ability to IEEE 1547 Standard. To validate the performance of the proposed method, simulations and experiments were performed. Possible islanding conditions are implemented with a unity quality factor by the IEEE Standard 1547. The methodology presented can be extended to the other active anti-islanding methods.     

Automatic phase-shift method for islanding detection of grid-connected photovoltaic inverters

The traditional frequency-shift methods for islanding detection of grid-connected PV inverters-the active frequency drift method and the slip-mode frequency-shift method-become ineffective under certain paralleled RLC loads. The automatic phase-shift method is proposed in this paper to alleviate this problem. The method is based on the phase shift of the sinusoidal inverter output current. When the utility malfunctions, the phase-shift algorithm keeps the frequency of the inverter terminal voltage deviating until the protection circuit is triggered. Simulation and experiments are performed for verification.     

Microgrid Dynamic Performance Improvement Using a Doubly Fed Induction Wind Generator

This paper describes a control approach applied on a doubly fed induction generator (DFIG) to provide both voltage and frequency regulation capabilities, and hence, an improvement in the dynamic behavior of a microgrid system. The microgrid system is assumed to be a portion of a medium voltage distribution feeder and is supplied by two distributed generation (DG) units, i.e., a gas-turbine synchronous generator and a variable-speed wind turbine with DFIG. A control approach algorithm is proposed for the DFIG unit to improve both voltage and primary frequency controls. Two distinct operation modes, i.e., grid-connected and islanding mode, are used in the proposed approach for proper transfer from normal to islanding operation. Case studies are simulated based on both planned and unplanned islanding scenarios to evaluate the performance of the control approach. The study results show that the proposed control approach for DGs in the microgrid increase the microgrid system's dynamic performance, reduce frequency changes, and improve bus voltages regulation during islanding and autonomous operations.      

Harmonic distortion-based island detection technique for inverter-based distributed generation

A harmonic distortion-based island detection technique for inverter-based distributed generation (IBDG) is proposed. The proposed technique is classified as an active island detection technique and it is based on the voltage change at the point of common coupling (PCC) that occurs in islanding. To avoid island detection failure in case of a close matching between IBDG-generated power and load power, an active power-voltage locus is introduced to shift the reference active power for PCC voltage change, therefore breaking the IBDG-load power balance and transferring the operating point outside the non-detection zone. A new harmonic performance index, named harmonic amplification factor, is introduced to detect the island. This factor amplifies each harmonic component by its order. Besides the ability of detecting short circuit, the proposed technique can discriminate between islanding and other disturbances, as load change, grid voltage distortion and unbalance, and capacitor bank switching. The proposed technique is validated by Matlab/Simulink simulation and practically as well.     

Study on the operation control strategies of microgrid islanding of photovoltaic and energy storage

主要讨论了光储微网在孤岛运行模式下的控制策略,分别对光伏逆变器进行PQ控制,对储能变流器进行恒压恒频控制实现微网在孤岛模式下对负载的稳定供电.在Simulink中搭建仿真平台对所提出理论进行仿真,对仿真结果进行分析,验证了所提控制策略的正确性和有效性.     

Testing the islanding protection function of photovoltaic inverters

A major safety issue in grid-connected photovoltaics is to avoid nonintentional operation in islanding mode when the grid is being tripped. Worst-case conditions under which islanding can occur are specified analytically. The circuit that is commonly used for testing is described. The issue of appropriate test conditions with regard to reactive-power injection to the grid is discussed and the stabilizing impact of rotating machines and resonant circuits is evaluated in detail. Islanding test results for small inverters are presented. They confirm that very simple islanding protection methods that are commonly used, are likely to fail, if inverters are loaded with considerable capacitance. The obtained results support the assessment of the islanding protection function. They emphasize important points when defining new certification procedures for upcoming guidelines and standards.