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This article presents the electrical power planning, tests and analysis for a micro-grid (MG) in the distribution system. The MG of the Institute of Nuclear Energy Research has been selected for study. To enhance the MG reliability, two power sources are used for connecting to the utility power grid. The two power sources are currently interlocked, one for the regular and the other for the standby. Firstly, the phase sequence tests of the two power sources were performed to avoid the failure and damage of the equipment during power transfer. After that, the control logic planning between the two power sources is done to maintain the power supply of the MG. Finally, the reliability analysis for the load in the MG is performed to examine the effectiveness of the two power sources configuration. [ABSTRACT FROM AUTHOR]

Microgrid operation is challenging because the amount of electricity that is produced from renewables is uncertain and the inertia of distributed generation resources is very small. Energy storage systems can regulate energy, improve the reliability of the power systemand enhance the transient stability. This paper determines the optimal capacities of energy storage systems in an islanded microgrid that is composed of wind-turbine generators, photovoltaic arrays, and micro-turbine generators. The energy storage system can enhance the reliability of the microgrid and eliminate the unnecessary load shedding when a severe transient (such as a generator outage) occurs in the islanded microgrid. The studied problem is expressed as a multi-objective programming formulation, which is solved using an immunity-based algorithm. Four objective functions are optimized: minimum of energy storage capacity, minimum of load shedding, maximum of the lowest swing frequency, and minimum of the Customer Average Interruption Duration Index (CAIDI). These four objective functions are subject to both steady-state constraints and the transient-state equality constraint. The steady-state constraints include the total shed load limit, the feasible range of energy storage capacities while the transient-state equality constraint is expressed by the dynamic equation. The Pareto optimums are explored and optimality of the problem is investigated. The simulation results based on an islanded 15-bus microgrid show the applicability of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract This paper discusses the power variation of photovoltaic power plant (PVPP) impact on the frequency response of an isolated island microgrid. An island microgrid with PVPPs and diesel generators is selected for study. The power system network, diesel generation units, load and PVPP data are collected in detail. And the one-line diagram of the study system with regarding peak and off-peak loading is set up in the simulation software for the steady state load flow analysis. After that, the transient stability analysis is executed with considering the tripping and power variation of various PVPP ramp rates with and without considering the over frequency compensation of photovoltaic (PV) inverters. The dynamic response of diesel generators and system frequency are examined carefully. It is found that the over frequency phenomenon can be controlled effectively by the regulation of PV inverters to achieve better reliability of the microgrid. [ABSTRACT FROM AUTHOR]

The installation of renewable energy generation resources (such as photovoltaic arrays and wind-turbine generators) in a microgrid is important because a microgrid can increase the penetration of renewable energies in a smart grid. A community may be a grid-tied microgrid in which an energy management system may dispatch elastic loads (such as air conditioning systems). This paper investigates the optimal sizing of renewable energy generation resources in a community microgrid. The cost of renewables and community welfare are optimized while the comfort zone of indoor temperature in all homes is maintained using air conditioning systems. Community welfare is ensured by minimizing the purchased power from and maximizing the sold power to the utility grid with different time-of-use electricity tariffs. Since the problem of interest involves a large number of variables and chronological constraints, Markov models of photovoltaic power generation, wind generation, load and temperature are utilized to reduce the numbers of variables and constraints. The Markov-based optimization problem is then solved using the interior-point algorithm. The simulation results, based on a smart community of 50 homes, reveal the applicability of the proposed method. [ABSTRACT FROM AUTHOR]

In a general microgrid (MG), a step-up distribution transformer is used to facilitate integration of the low-voltage (LV) AC microgrid into a medium-voltage distribution system. On the other hand, isolation transformers are placed between distributed energy resources (DERs) (e.g. non-renewable/renewable energy resources and energy storage devices) and common AC buses/lines to eliminate DC-current components and to configure 3-phase & 4-wire, 3-phase & 3-wire, 1-phase & 2-wire, or 1-phase & 3-wire AC microgrids. When all neutral points of isolation transformers are grounded through a unique grounding system of the step-up distribution transformer, a uni-grounded AC microgrid structure is configured. This paper not only mentions advantages and shortcomings of the uni-grounded LVAC microgrid operation, but also investigates its transient operation characteristics. Transient simulation results of the uni-grounded LVAC MG are surveyed through various fault situations and operation transition tests between the grid-connected mode and the islanded mode of the microgrid. Available fault protection methods of a uni-grounded LVAC microgrid are considered. Transient simulation results from PSCAD software are used to validate the fault protection solutions developed for the uni-grounded LVAC microgrid. Last, a generalised fault protection system of uni-grounded LVAC microgrids is proposed in the paper. [ABSTRACT FROM AUTHOR]