Load Shedding Application within a Microgrid to Assure Its Dynamic Performance during Its Transition to the Islanded Mode of Operation

This article presents the simulation results and analysis related to the response of the generators within a microgrid towards an accidental overload condition that will require some load shedding action. A microgrid overload can occur due to various reasons ranging from poor load schedule, inadequate switching of circuits within the microgrid, outage of one or more generators inside the microgrid, illegal load connections by some low voltage consumers, etc. It was observed that among the main factors that determine the survival of the microgrid during its transition from the grid connected mode to the islanded mode of operation are the size and type of the load connected (passive or dynamic load) as well as the length of time during which the unexpected load is connected. Models of a speed and voltage regulators of a diesel generator, and important for coping with the overload conditions are provided in the paper. The novelty of the work lies in the load shedding simulation and analysis of the specific generators studied herein, regarding that in many countries the microgrid technology is seen as an important alternative towards the ever increasing load demand and also to assist the system during periods of blackout.

A new hybrid control technique for operation of DC microgrid under islanded operating mode

This study proposes a novel combined primary and secondary control approach for direct current microgrids,specifi-cally in islanded mode.In primary control,this approach establishes an appropriate load power sharing between the distributed energy resources based on their rated power.Simultaneously,it considers the load voltage deviation and provides satisfactory voltage regulation in the secondary control loop.The proposed primary control is based on an efficient droop mechanism that only deploys the local variable measurements,so as to overcome the side effects caused by communication delays.In the case of secondary control,two different methods are devised.In the first,low bandwidth communication links are used to establish the minimum required data transfer between the converters.The effect of communication delay is further explored.The second method excludes any communication link and only uses local variables.Accordingly,a self-sufficient control loop is devised without any communication require-ment.The proposed control notions are investigated in MATLAB/Simulink platform to highlight system performance.The results demonstrate that both proposed approaches can effectively compensate for the voltage deviation due to the primary control task.Detailed comparisons of the two methods are also provided.

Parameters Analysis and Operational Area Calculations of VSG Applied to Distribution Networks

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.