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Energy management system (EMS) is able to coordinate the generation and load to ensure economic and reliable operation and improve performance metrics of microgrids (MGs). However, most the previous studies have focused mainly on the optimal dispatch of the gas turbines and/or energy storage systems inside a normal MG. Very few works have been carried out to address the potential power outage in MGs. In this study, a novel optimal approach in the EMS based on online forecasts is proposed to minimise the system-wide outages of MG, specifically through pre-emptive load shedding. Online distributed generations' output forecasts are updated to predict the state of system and characterise potential upcoming outages. Proper control strategies based on receding horizon methods are introduced in this study. Outage mitigation actions using pre-emptive load shedding are then performed to avoid power outages or minimise the duration of unavoidable outages. The effectiveness of proposed approach can be demonstrated in the presence of various fluctuations, which can be easily integrated in the EMS for both islanded and grid-connected MGs.

With the widespread use of distributed generation, a large number of power electronic switches and nonlinear loads greatly deteriorate the power quality of the micro-grid(MG). In order to effectively address harmonics problems in the micro-grid, a novel control topology of the unified power quality conditioner based on photovoltaic grid-connected generation and super-capacitor energy storage (SCPV-UPQC) is proposed in this paper. The control system is able to calculate the appropriate compensation amount by extracting the fundamental and harmonic components in the current and voltage signals of the PCC point. And a fuzzy logic PI control method is proposed to adaptively adjust the parameters of the traditional PI controller to mitigate the harmonic distortion and other power quality problems of the MG. The proposed SCPV-UPQC structure based on the fuzzy PI control strategy is simulated in MATLAB/Simulink under a typical MG model, and the results illustrate that this method can significantly suppress the harmonics in the MG, verifying the validity and feasibility of the proposed UPQC structure and control strategy. The method can provide helpful assistance for harmonic control of the future AC or DC MG and even multiple parallel MGs.

As a key component of DC medium voltage breaker, the switch mechanism is required to open in high-speed and can withstand the breaking voltage which is generated during opening motion. Thus, the design of driving circuit of switch mechanism is very important to optimize the mechanism structure and improve mechanism opening characteristics. First the motion principle of high-speed switch was given in this paper, and the influence of driving circuit parameters on mechanism opening characteristics was analyzed. Then two driving circuit solutions were provided with simulation and test verification analysis. Finally, the prototype was built according to aforesaid analysis. The design of DC medium voltage breaker can be benefited by the research work in this paper.