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The inverter with critical loads should be able to provide critical loads with a stable and seamless voltage during control mode change as well as clearing time. The indirect current control has been proposed for providing stable voltage with critical load during clearing time and seamless control mode transfer of inverters. However, the islanding detection is difficult since with the indirect current...
The Distributed power supply has an increasing influence on the stability of the micro-grid. Virtual synchronous generator technology can improve the stability of power grid with large inertia of synchronous generator. This paper describes the principle of virtual synchronous generator technology, as well as a detailed description of the control strategy of power frequency control and excitation control...
This paper introduces a mathematical model and a voltage/frequency control scheme for inverter interfacing Grid Forming DG (VF) unit. The introduced control scheme utilizes the well understood and optimized dq-frame current control scheme that is used with inverter interfacing Grid Following DG (PQ) units. Minimum modifications are made to the control software to allow grid isolation operation of...
This paper proposes a method to determine the optimum Battery Energy Storage System (BESS) size, considering how the location of BESS affects the micro-grid and analysis of power loss for the consideration of different locations of BESS. The possibility of installing an optimum BESS as the distributed BESS at different locations is proposed. Artificial neural network (ANN) was established to evaluate...
With large amount of power electronic devices applied in distributed generations or micro-grid, harmonics pollution is becoming a more and more serious problem which limits their widely application. Frequency dividing droop controller is proposed to eliminate voltage harmonics, according droop control theory. But it failed to give an expected index to represent its harmonic suppression ability. In...
This paper proposes a micro-grid structure of EV charging station, which combined with new energy sources and energy storage. The core bi-directional converters DC/DC and AC/DC are introduced, with their principles and control strategies detailed. Among them, a kind of current limited closed-loop control strategy is adopted to control DC/DC, while double-loop control strategy of voltage outer inductor...
Micro-grid is a system with various distributed energy sources integrated. Due to its inherent distributed and heterogeneous nature, the micro-grid becomes ideal platform for consensus-based multi-agent control. Conventionally, power sharing in a micro-grid is achieved by autonomous P-f and Q-V droop control on individual inverters, which suffers from lack of frequency restoration mechanism and dependence...
This paper considers the power sharing stability of a grid connected Micro-grid (MG) system with three Distributed Generation (DG) units via Power System Stabilizer (PSS). Various PSS structures are employed and compared in order to achieve the best transient response under different DG penetration levels. Particle Swarm Optimization (PSO) is used to tune to controller parameters. The optimal controller's...
Micro-grids (MGs) are active networks known as an effective solution for the control of grids including high levels of Distributed Generation (DG). In off-grid MGs, DGs connected to Voltage Source Inverters (VSIs) enroll as controllers of voltage and frequency. These VSIs should share power between the DGs fairly. A precise power sharing may increase frequency drop. In this paper, a trade-off is obtained...
Renewable energies such as wind power and PV energy sources are valuable energy resources which can contribute to improvement of self-sufficiency rate of energy and can be used to reverse global warming. However, when there is a large amount of penetration of renewable energy generations into a grid, some problems will arise in the present distribution power network, due to instability of power output...
The “communication mechanism” to realize the power share of grid-forming inverters is analyzed and a droop control method through active and reactive current is proposed in this paper. The control strategies of inverters connected in parallel forming a micro-grid are described in detail. The droop controller is divided into three units that are current (power) decoupling, the first-order inertia and...
The future power system integrated a large share of distributed generation (DG) may causes a reduction of the system rotational inertia, resulting in high frequency variations with any disturbances. An additional rotational inertia will be provided to the system if many DG units combined with relative small storage systems operate like virtual synchronous generators (VSG). This paper presents the...
Inverters are a universal interface to inject the power produced by distributed power generation in stand-alone loads, micro-grid or the main electrical grid. The control system of a universal inverter should be designed in order to manage the different connections. This paper is an attempt to provide an overview with attention paid to current/voltage control of the converter and direct/inverse droop...
A new type of micro-grid called “Electricity Cluster-oriented Network” is proposed. The proposed Electricity Cluster-Oriented Network is the aggregation of the loosely-coupled, autonomous and independent local network called “cluster”, and the expansion in the scale is easily achieved as the additional power demand arises. This approach will be possible to hold down initial investment. Mathematical...
This paper presents a novel control strategy to operate a low-voltage (LV) micro-grid in grid connected operation mode as well as autonomous operation mode. Depending on the inverter output impedance which is mainly resistive due to the LV cables a proper control strategy based on an unbalanced resistive droop approach is developed. The control strategy is verified by simulating fast changes of power...
In the last years the power system industry is rapidly changing. The traditional centralized systems, which grew as a result of large-scale integration, are going to be replaced by the dispersed or distributed generation that is situated closer to the consumers. The future power supplying will be done by the combination of well-established central power networks and micro grids (MG), with the maximal...
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