Islanding detection is a mandatory component in grid-connected photovoltaic （PV） inverters. It is also a key issue in the photovoltaic agriculture. In this work, an overview on the islanding effect in grid-connected...Islanding detection is a mandatory component in grid-connected photovoltaic （PV） inverters. It is also a key issue in the photovoltaic agriculture. In this work, an overview on the islanding effect in grid-connected PV power systems was provided. Various islanding detection methods were introduced and their strength and weakness were dicussed. An improved islanding detection method was proposed based on active frequency drift （AFD）. The new method tolerated capacitive and inductive loads, because its perturbation signal was not offset by the non-resistive load. The new method through simulation in MATLAB/Simulink was evaluated and the advantages of the new method were demonstrated.展开更多
Micro-grids comprise low voltage distribution systems with distributed energy resources(DERs) and controllable loads which can operate connected to the medium voltage grid or islanded in a controlled coordinated way. ...Micro-grids comprise low voltage distribution systems with distributed energy resources(DERs) and controllable loads which can operate connected to the medium voltage grid or islanded in a controlled coordinated way. This concept aims to move from "connect and forget" philosophy towards a full integration of DERs. Micro-grids can provide numerous economic and environmental benefits for end-customers, utilities and society. However, their implementation poses great technical challenges, such as a new philosophy in design of protection systems. In this work, a micro-grid protection scheme is presented based on positive-sequence component using phasor measurement units(PMUs) and a central protection unit(CPU). The salient feature of the proposed scheme in comparison with the previous works is that it has the ability to protect both radial and looped micro-grids against different types of faults with the capability of single-phase tripping. Furthermore, since the CPU is capable of updating its pickup values(upstream and downstream equivalent positive-sequence impedances of each line) after the first change in the micro-grid configuration(such as transferring from grid-connected to islanded mode and or disconnection of a line, bus, or DER either in grid-connected mode or in islanded mode), it can protect micro-grid against subsequent faults. Finally, in order to verify the effectiveness of the suggested scheme and the CPU, several simulations have been undertaken by using DIg SILENT Power Factory and MATLAB software packages.展开更多
Virtual synchronous generator(VSG)technology is an effective way to realize coordinated energy supply of active distribution networks and comprehensive energy at present.This paper starts from the two perspectives of ...Virtual synchronous generator(VSG)technology is an effective way to realize coordinated energy supply of active distribution networks and comprehensive energy at present.This paper starts from the two perspectives of grid-connected operational modes and island operational modes.Based on the mathematical model of VSG,referring to existing grid standards,comprehensively considering its active and reactive-power loop stability and dynamic performance,the influencing factors of the related control parameters K,Dq,J,Dp are analyzed.And selection range for K,Dq,J,Dp is proposed,which ensures stability and robustness in grid-connected and island operational modes.In this paper,this method can be used as a reference for control strategy research and practical engineering applications of VSG.Finally,effects of parameter selection on stability and dynamic performance of active and reactive-power loops are analyzed by using the zero-pole map and Bode diagram,and feasibility of the scheme is verified by PSCAD/EMTDC.展开更多
基金Supported by the National Science and Technology Support Program(2014BAD06B04-1-09)China Postdoctoral Fund(2016M601406)Heilongjiang Postdoctoral Fund(LBHZ15024)
文摘Islanding detection is a mandatory component in grid-connected photovoltaic （PV） inverters. It is also a key issue in the photovoltaic agriculture. In this work, an overview on the islanding effect in grid-connected PV power systems was provided. Various islanding detection methods were introduced and their strength and weakness were dicussed. An improved islanding detection method was proposed based on active frequency drift （AFD）. The new method tolerated capacitive and inductive loads, because its perturbation signal was not offset by the non-resistive load. The new method through simulation in MATLAB/Simulink was evaluated and the advantages of the new method were demonstrated.
文摘Micro-grids comprise low voltage distribution systems with distributed energy resources(DERs) and controllable loads which can operate connected to the medium voltage grid or islanded in a controlled coordinated way. This concept aims to move from "connect and forget" philosophy towards a full integration of DERs. Micro-grids can provide numerous economic and environmental benefits for end-customers, utilities and society. However, their implementation poses great technical challenges, such as a new philosophy in design of protection systems. In this work, a micro-grid protection scheme is presented based on positive-sequence component using phasor measurement units(PMUs) and a central protection unit(CPU). The salient feature of the proposed scheme in comparison with the previous works is that it has the ability to protect both radial and looped micro-grids against different types of faults with the capability of single-phase tripping. Furthermore, since the CPU is capable of updating its pickup values(upstream and downstream equivalent positive-sequence impedances of each line) after the first change in the micro-grid configuration(such as transferring from grid-connected to islanded mode and or disconnection of a line, bus, or DER either in grid-connected mode or in islanded mode), it can protect micro-grid against subsequent faults. Finally, in order to verify the effectiveness of the suggested scheme and the CPU, several simulations have been undertaken by using DIg SILENT Power Factory and MATLAB software packages.
基金the Technology Project of SGCC:Research on fast inertia response and flexible interaction technology for large-scale charging facilities connected to distribution network(5400-202155459A-0-0-00)。
文摘Virtual synchronous generator(VSG)technology is an effective way to realize coordinated energy supply of active distribution networks and comprehensive energy at present.This paper starts from the two perspectives of grid-connected operational modes and island operational modes.Based on the mathematical model of VSG,referring to existing grid standards,comprehensively considering its active and reactive-power loop stability and dynamic performance,the influencing factors of the related control parameters K,Dq,J,Dp are analyzed.And selection range for K,Dq,J,Dp is proposed,which ensures stability and robustness in grid-connected and island operational modes.In this paper,this method can be used as a reference for control strategy research and practical engineering applications of VSG.Finally,effects of parameter selection on stability and dynamic performance of active and reactive-power loops are analyzed by using the zero-pole map and Bode diagram,and feasibility of the scheme is verified by PSCAD/EMTDC.
