设计了一种具有零稳态误差的并网逆变器系统，系统控制器由比例调节器P和谐振调节器R组成。与传统的PI控制器比较，该比例谐振控制器(PR)在基波频率处增益无穷大，因此可以完全消除稳态误差。通过理论分析，系统中采用了一种更易实现的准谐振控制器，并给出控制器参数具体的设计方法。此外，为了消除电网电压畸变或扰动对逆变器输出电流的影响，系统中引入了电网电压前馈解耦控制，改善了系统输出电流的质量。理论分析和实验结果验证了系统具有较好的稳态性能和抗扰性能。

设计了一种具有零稳态误差的并网逆变器系统，系统控制器由比例调节器P和谐振调节器R组成。与传统的PI控制器比较，该比例谐振控制器(PR)在基波频率处增益无穷大，因此可以完全消除稳态误差。通过理论分析，系统中采用了一种更易实现的准谐振控制器，并给出控制器参数具体的设计方法。此外，为了消除电网电压畸变或扰动对逆变器输出电流的影响，系统中引入了电网电压前馈解耦控制，改善了系统输出电流的质量。理论分析和实验结果验证了系统具有较好的稳态性能和抗扰性能。

On the basis of traditional active frequency drift（AFD） method， an improved islanding detection method is presented adopting the pulse current amplitude disturbance. The method to inject the current amplitude disturbance is introduced， especially the method to choose disturbance time. The islanding detection is simulated in combination with over-voltage protection /under-voltage protection（OVP/UVP） and over-frequency protection /under-frequency protection（OFP/UFP）. The results show that the combined method overcomes the problems associated with AFD or the current disturbing method. Islanding occurrence can be detected effectively with the presented method， and the photovoltaic system can be disconnected from the system before high-speed auto-reclosing， with limited harmonics and reduced non-detection zone.

On the basis of traditional active frequency drift（AFD） method， an improved islanding detection method is presented adopting the pulse current amplitude disturbance. The method to inject the current amplitude disturbance is introduced， especially the method to choose disturbance time. The islanding detection is simulated in combination with over-voltage protection /under-voltage protection（OVP/UVP） and over-frequency protection /under-frequency protection（OFP/UFP）. The results show that the combined method overcomes the problems associated with AFD or the current disturbing method. Islanding occurrence can be detected effectively with the presented method， and the photovoltaic system can be disconnected from the system before high-speed auto-reclosing， with limited harmonics and reduced non-detection zone.

Since passive islanding detection methods have non-detection zone and traditional active frequency drift（AFD） methods may cause active current fluctuation， an improved AFD islanding detection algorithm is proposed. The algorithm realizes current frequency drift by controlling reactive current， so as to achieve positive feedback of voltage frequency at the point of common coupling（PCC） in islanding state and realize anti-islanding function. To reduce reactive current injection to the power system， the improved AFD algorithm should be combined with traditional passive islanding detection algorithm. Simulation and experiment results show that the improved algorithm can not only eliminate the non-detection zone of passive islanding detection algorithms when the loads power and the inverter power match， but also overcome the active current fluctuation of traditional AFD algorithms and improve the stability of DC bus voltage.

Since passive islanding detection methods have non-detection zone and traditional active frequency drift（AFD） methods may cause active current fluctuation， an improved AFD islanding detection algorithm is proposed. The algorithm realizes current frequency drift by controlling reactive current， so as to achieve positive feedback of voltage frequency at the point of common coupling（PCC） in islanding state and realize anti-islanding function. To reduce reactive current injection to the power system， the improved AFD algorithm should be combined with traditional passive islanding detection algorithm. Simulation and experiment results show that the improved algorithm can not only eliminate the non-detection zone of passive islanding detection algorithms when the loads power and the inverter power match， but also overcome the active current fluctuation of traditional AFD algorithms and improve the stability of DC bus voltage.

当分布式发电系统提供的功率与本地负载所需功率匹配, 且负载角和扰动角度相等时, 即使发生孤岛现象, 公共耦合点电压也一直处于非检测区内, 从而导致主动频率偏移法无法识别孤岛效应的问题。针对上述问题, 本文提出了一种新颖的2N电压周期电流扰动方法, 即第2N电压周期采用主动频率偏移方法, 第2N+1电压周期的电流与电压同步。根据公共耦合点相邻周期间的电压频率差是否正负连续交替变化来识别孤岛现象。仿真和实验结果证明该方法很大程度上解决了非检测区的问题, 而且适用于多台逆变器的并网运行情况。

当分布式发电系统提供的功率与本地负载所需功率匹配, 且负载角和扰动角度相等时, 即使发生孤岛现象, 公共耦合点电压也一直处于非检测区内, 从而导致主动频率偏移法无法识别孤岛效应的问题。针对上述问题, 本文提出了一种新颖的2N电压周期电流扰动方法, 即第2N电压周期采用主动频率偏移方法, 第2N+1电压周期的电流与电压同步。根据公共耦合点相邻周期间的电压频率差是否正负连续交替变化来识别孤岛现象。仿真和实验结果证明该方法很大程度上解决了非检测区的问题, 而且适用于多台逆变器的并网运行情况。

孤岛检测是光伏并网逆变器所必备的功能。在各种孤岛检测技术中，主动移频法及改进后的带正反馈主动移频法被广泛采用。该类方法通过对逆变器输出电流的频率进行扰动来实现孤岛检测。目前针对该类方法的研究主要集中在单台逆变器。该文采用相位原理和基于负载品质因数与谐振频率坐标系的盲区空间理论，对多机并联工作方式下主动移频法及带正反馈的主动移频法之间的相互影响及孤岛检测有效性进行深入理论分析，揭示了多机并联下孤岛检测可靠性与工作条件的关系，仿真与实验验证了理论分析的正确性。

孤岛检测是光伏并网逆变器所必备的功能。在各种孤岛检测技术中，主动移频法及改进后的带正反馈主动移频法被广泛采用。该类方法通过对逆变器输出电流的频率进行扰动来实现孤岛检测。目前针对该类方法的研究主要集中在单台逆变器。该文采用相位原理和基于负载品质因数与谐振频率坐标系的盲区空间理论，对多机并联工作方式下主动移频法及带正反馈的主动移频法之间的相互影响及孤岛检测有效性进行深入理论分析，揭示了多机并联下孤岛检测可靠性与工作条件的关系，仿真与实验验证了理论分析的正确性。

As more distributed generators join the utility grid, the concern of possible undetected islanding operation increases. This concern is due to the safety hazards this phenomenon imposes on the personnel and equipment. Passive anti-islanding detection methods monitor grid parameters to detect islanding, whereas active methods inject a perturbation into the current waveform to drive these parameters out of limit when islanding occurs. The performance of active methods, such as conventional active frequency drift (AFD), is limited by the amount of total harmonic distortion (THD) they inject into the grid, which defines its nondetection zone. In this paper, an improved AFD anti-islanding method is presented based on a different current distortion injection waveform. The proposed method generates 30% less THD compared to classic AFD, resulting in faster island detection and improved nondetection zone. The performance of the proposed method is derived analytically, simulated using Matlab and verified experimentally using a prototype setup. A single-phase grid-tied photovoltaic distributed generation system is used for the simulation and experimental setup, and considered as potential application.

传统无源孤岛检测方法存在检测盲区，有源孤岛检测方法可减小或消除检测盲区，但其机制是将系统电压幅值或频率偏离至故障运行范围，从而判断孤岛发生，其本质属于破坏性孤岛检测方法。然而，微电网应用场合需要无盲区且非破坏性孤岛检测方法。为了解决该问题，提出一种基于负序电压正反馈(negative-sequence voltage positive feedback，NSVPF)的孤岛检测方法，并根据IEEE Std.1547测试标准对提出的方法进行理论分析及仿真研究。结果表明，在IEEE Std.1547规定的最差情况下，提出的NSVPF孤岛检测方法在电压处于正常运行范围的情况下仍可快速有效地检测到孤岛的发生，从而实现了非破坏性无盲区孤岛检测。此外，该文提出的孤岛检测方法在电网单相和两相断路情况下仍然有效，最后探讨了如何防止伪孤岛的问题。

传统无源孤岛检测方法存在检测盲区，有源孤岛检测方法可减小或消除检测盲区，但其机制是将系统电压幅值或频率偏离至故障运行范围，从而判断孤岛发生，其本质属于破坏性孤岛检测方法。然而，微电网应用场合需要无盲区且非破坏性孤岛检测方法。为了解决该问题，提出一种基于负序电压正反馈(negative-sequence voltage positive feedback，NSVPF)的孤岛检测方法，并根据IEEE Std.1547测试标准对提出的方法进行理论分析及仿真研究。结果表明，在IEEE Std.1547规定的最差情况下，提出的NSVPF孤岛检测方法在电压处于正常运行范围的情况下仍可快速有效地检测到孤岛的发生，从而实现了非破坏性无盲区孤岛检测。此外，该文提出的孤岛检测方法在电网单相和两相断路情况下仍然有效，最后探讨了如何防止伪孤岛的问题。

Islanding protection is necessary for the distributed generation (DG) systems, but it is difficult for some traditional methods such as frequency or phase variation methods to detect the islanding effect when the power generated by the DG systems matches with the demand power of the local load. The islanding detection capabilities about different disturbing signals are analyzed and even harmonic current disturbing signal suiting to multi-inverter DG system is available in this paper. Combining with a zero-crossing frequency detector, the positive feedback loop with even harmonic current disturbance is introduced to detect the islanding phenomenon. Output current reference in the grid-connected inverter is affected by a minute disturbance signal in general. Once the islanding occurs, the positive feedback of disturbance current makes the voltage frequency at the point of common coupling go beyond a preset threshold value. It is easy to design the software program, less to inject the current harmonics into the grid, quick to detect the islanding effect, equal to form the multi-inverter system. Simulation and experimental results verify that the method is effective and reliable.

Islanding protection is necessary for the distributed generation (DG) systems, but it is difficult for some traditional methods such as frequency or phase variation methods to detect the islanding effect when the power generated by the DG systems matches with the demand power of the local load. The islanding detection capabilities about different disturbing signals are analyzed and even harmonic current disturbing signal suiting to multi-inverter DG system is available in this paper. Combining with a zero-crossing frequency detector, the positive feedback loop with even harmonic current disturbance is introduced to detect the islanding phenomenon. Output current reference in the grid-connected inverter is affected by a minute disturbance signal in general. Once the islanding occurs, the positive feedback of disturbance current makes the voltage frequency at the point of common coupling go beyond a preset threshold value. It is easy to design the software program, less to inject the current harmonics into the grid, quick to detect the islanding effect, equal to form the multi-inverter system. Simulation and experimental results verify that the method is effective and reliable.

This paper presents a new active anti-islanding detection method for distributed power generation systems. This method is based on introducing a disturbance at the inverter output and observing the behavior of the voltage at the point of common coupling (PCC), which depends on the impedance connected to the PCC in an islanding situation. The islanding detection is based on the Goertzel algorithm.