Power-Sharing Enhancement Using Harmonized Membership Fuzzy Logic Droop Control Based Micro-Grid

The contribution of Renewable Energy Resources(RER)in the process of power generation is significantly high in the recent days since it paves the way for overcoming the issues like serious energy crisis and natural contamination.This paper deals with the renewable energy based micro-grid as it is regarded as the apt solution for integrating the RER with the electrical frameworks.As thefixed droop coefficients in conventional droop control approaches have caused various limitations like low power-sharing and sudden drops of grid voltage in the Direct Current(DC)side,the Harmonized Membership Fuzzy Logic(MFL)droop control is employed in this present study.This proposed droop control for the hybrid PV-wind-battery system with MFL assists in achieving proper power-sharing and minimizing Total Harmonic Distortion(THD)in the emer-gency micro-grid.It eradicates the deviations in voltage and frequency with itsflexible and robust operation.The THD is reduced and attains the value of 3.1%compared to the traditional droop control.The simulation results of harmo-nized MFL droop control are analogized with the conventional approaches to vali-date the performance of the proposed method.In addition,the experimental results provided by the Field Programmable Gate Array(FPGA)based laboratory setup built using a solar photovoltaic(PV)and wind Permanent Magnet Synchro-nous Generator(PMSG)reaffirms the design.

A Qualitative Examination of Teacher-Student Power-Sharing in Chinese Classrooms:A Study in Hong Kong

This article explores the dynamics of power-sharing between teacher and students in learning and teaching situations,and describes the theoretical bases,implementation,and results of an empirical study in three elementary schools in Hong Kong Special Administrative Region of the People’s Republic of China.Findings from 58 class observations and interviews with 50 students,25 teachers,and three school principals suggest that teachers can empower students by acknowledging their right to and responsibility for learning and by sharing power with students.Power-sharing classroom practice requires the dual efforts of teachers and students,and can be facilitated by the teachers’interactive teaching mode,students’cooperation and willingness to engage in learning,and school policy and culture,etc.In the power-sharing classrooms,teachers played the role of facilitators and students played as collaborators.In this article,theoretical implications for understanding power-sharing and critical pedagogy are discussed.The empirical evidence from this Hong Kong study contributes to an understanding of teacher-initiated power-sharing in the Chinese context,and the practice of critical pedagogy in classrooms.

Adaptive Reference Power Based Voltage Droop Control for VSC-MTDC Systems

Featuring low communication requirements and high reliability,the voltage droop control method is widely adopted in the voltage source converter based multi-terminal direct current(VSC-MTDC)system for autonomous DC voltage regulation and power-sharing.However,the traditional voltage droop control method with fixed droop gain is criticized for over-limit DC voltage deviation in case of large power disturbances,which can threaten stable operation of the entire VSCMTDC system.To tackle this problem,this paper proposes an adaptive reference power based voltage droop control method,which changes the reference power to compensate the power deviation for droop-controlled voltage source converters(VSCs).Besides retaining the merits of the traditional voltage droop control method,both DC voltage deviation reduction and power distribution improvement can be achieved by utilizing local information and a specific control factor in the proposed method.Basic principles and key features of the proposed method are described.Detailed analyses on the effects of the control factor on DC voltage deviation and imbalanced power-sharing are discussed,and the selection principle of the control factor is proposed.Finally,the effectiveness of the proposed method is validated by the simulations on a five-terminal VSC based high-voltage direct current(VSC-HVDC)system.

An Improved Reactive Power Sharing in an Isolated Microgrid with a Local Load Detection

Accurate reactive power sharing is one of the main issues in isolated microgrids to avoid circulating currents and overloading small distributed generation(DG)units.A simple and enhanced method for improving reactive power sharing among parallel-connected DG systems in an isolated microgrid was proposed.The proposed method uses a compensator term with an integral action to minimize the reactive power-sharing error internally without any need for communication or information shared among the DG units.Moreover,a small disturbance carrying part of the reactive power-sharing error is injected into the active power-droop controller,maintaining the essential system parameters within their allowable limits.Consequently,a simple compensation trigger system is proposed to effectively detect any local load change in the network and provide compensation gains to activate the proposed control method.The stability of the proposed method was verified and analyzed using a detailed small-signal model.Moreover,the effectiveness and robustness of the proposed method were validated through comprehensive simulation studies and comparisons with other related techniques.

Exponential-function-based droop control for islanded microgrids

An exponential-function-based droop control strategy for the distributed energy resources(DERs)is proposed to reduce the reactive power-sharing deviation,limit the minimum value of frequency/voltage,whilst improving the utilization rate of renewable energy.Both DERs and loads are interconnected to achieve a power exchange by converters,where the power management system should accurately share the active/reactive power demand.However,the proportional reactive power sharing often deteriorates due to its dependence on the line impedances.Thus,an exponential-function-based droop control is proposed to(1)prevent voltage and frequency from falling to the lower restraint,(2)achieve accurate reactive power sharing,(3)eliminate communication and improve the usage ratio of renewable energy.Furthermore,its stability is analyzed,and the application in islanded AC/DC hybrid microgrids is investigated to achieve the bidirectional power flow.The simulation and experimental results show that the reactive power sharing deviation can be reduced,and the utilization rate of renewable energy is improved by using the proposed method.Moreover,the simulation results illustrate that the system can maintain stable operation when the microgrid is switched from one supplied energy operation condition to another absorbed one.

Load shedding strategy coordinated with storage device and D-STATCOM to enhance the microgrid stability

Recently microgrids have drawn a potential attraction by fulfilling the environmental demands and the increasing energy demands of the end-users. It is necessary to focus on various protection and control aspects of a microgrid. During the transition between the grid-following and grid-forming modes, the voltage and the frequency instability due to the power mismatch condition becomes the major point of concern. Therefore, the paper executes a frequency-active power and voltage-reactive power drooping control strategy for the precise power-sharing among the distributed power generators. Furthermore, to handle the power deficit scenarios and to maintain the system stability, a system independent and priority-based adaptive three-stage load shedding strategy is proposed. The sensitivity of the strategy depends on the system inertia and is computed according to the varying absolute rate-of-change-of-frequency. The strategy incorporates the operation of battery storage system and distributed static compensator (D-STATCOM) in the microgrid, to provide a reliable power supply to the customers for a considerable time instead of a sudden load shedding. The effectiveness of the proposed strategies is investigated on a scaled-down modified IEEE 13-bus microgrid system on the podium of MATLAB 2015b through the time-domain simulation.