Transmission line protection challenges influenced by inverter-based resources:a review

High penetration of renewable energy sources(RES)leads to new challenges for protection devices.Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources,while the RES dynamic response,mainly governed by inverters,is not considered.Consequently,some relevant algorithms of transmission line protection are experiencing challenges because of the fact that magnitude and phase angle com-parison,amount of negative-sequence,and short-circuit current level are affected by the RES.Therefore,an in-depth study of this issue is necessary,one which considers the main causes and new methodological criteria solutions.This work presents an extensive literature review of the evaluation of electrical protection performance and the effects of RES connected to a power grid through inverters.Bibliographic data on many representative publications related to this topic are obtained to show the current research lines and their proposed solutions.In addition,this work identi-fies the main protection functions affected and describes the new protection schemes that consider RES.Finally,an analysis and discussion of the selected bibliography are presented.

Stability analysis and decentralized control of inverter-based ac microgrid

This work considers the problem of decentralized control of inverter-based ac micro-grid in different operation modes.The main objectives are to(i)design decentralized frequency and voltage controllers,to gather with power sharing,without information exchange between microsources(ii)design passive dynamic controllers which ensure stability of the entire microgrid system(iii)capture nonlinear,interconnected and large-scale dynamic of the micro-grid system with meshed topology as a port-Hamiltonian formulation(iv)expand the property of shifted-energy function in the context of decentralized control of ac micro-grid(v)analysis of system stability in large signal point of view.More precisely,to deal with nonlinear,interconnected and large-scale structure of micro-grid systems,the port-Hamiltonian formulation is used to capture the dynamic of micro-grid components including microsource,distribution line and load dynamics as well as interconnection controllers.Furthermore,to deal with large signal stability problem of the microgrid system in the grid-connected and islanded conditions,the shifted-Hamiltonian energy function is served as a storage function to ensure incremental passivity and stability of the microgrid system.Moreover,it is shown that the aggregating of the microgrid dynamic and the decentralized controller dynamics satisfies the incremental passivity.Finally,the effectiveness of the proposed controllers is evaluated through simulation studies.The different scenarios including grid-connected and islanded modes as well as transition between both modes are simulated.The simulation conforms that the decentralized control dynamics are suited to achieve the desired objective of frequency synchronization,voltage control and power sharing in the grid-connected and islanded modes.The simulation results demonstrate the effectiveness of the proposed control strategy.

Modeling methodology and fault simulation of distribution networks integrated with inverter-based DG

The increasing penetration of inverter-based distributed generations(DGs)significantly affects the fault characteristics of distribution networks.Fault analysis is a keystone for suitable protection scheme design.This paper presents the modelling methodology for distribution networks with inverter-based DGs and performs fault simulation based on the model.Firstly,a single inverter-based DG model based on the cascaded control structure is developed.Secondly,a simulation model of distribution network with two inverter-based DGs is established.Then,different fault simulations are performed based on the Real Time Digital Simulator(RTDS).Theoretical analyses are conducted to justify the simulation results,including the equivalent circuit of distribution networks with inverter-based DGs and the solution method for loop currents.

Dual Control Strategy for Grid-tied Battery Energy Storage Systems to Comply with Emerging Grid Codes and Fault Ride Through Requirements

Battery energy storage systems(BESSs)need to comply with grid code and fault ride through(FRT)requirements during disturbances whether they are in charging or discharging mode.Previous literature has shown that constant charging current control of BESSs in charging mode can prevent BESSs from complying with emerging grid codes such as the German grid code under stringent unbalanced fault conditions.To address this challenge,this paper proposes a new FRTactivated dual control strategy that consists of switching from constant battery current control to constant DC-link voltage control through a positive droop structure.The results show that the strategy ensures proper DC-link voltage and current management as well as adequate control of the positive-and negative-sequence active and reactive currents according to the grid code priority.It is also shown that the proposed FRT control strategy is tolerant to initial operating conditions of BESS plant,grid code requirements,and fault severity.