The demand and acceptance of the renewable energy power plants are steadily increasing because of its positive environmental impacts and free availability of fuels such as wind and solar. Because of the intermittent and volatile nature of the output of these plants, neighboring plants are interconnected and controlled simultaneously using intelligent controllers. Loads and other conventional generators like diesel generators are also connected to this network and forms a microgrid which may or may not be connected to the main utility grid. For effectively controlling the resources and the loads connected to a microgrids, many control strategies are developed and successfully implemented nowadays. This paper looks at the possible control schemes used in an AC microgrid.

A review on control of ac microgrid

Power flow control in grid-connected microgrid operation using Particle Swarm Optimization under variable load conditions

This paper presents an optimal power control strategy for an autonomous microgrid operation based on a real-time self-tuning method. The purpose of this work is to improve the quality of power supply of the microgrid where some Distributed Generation (DG) units are connected to the grid. Voltage and frequency regulation, and power sharing are the main performance parameters which are considered in this work, particularly during the transition from grid-connected to islanding operation mode and also during load change. In this work, two typical DG units are connected in parallel to configure the microgrid. The controller scheme is composed of an inner current control loop and an outer power control loop based on a synchronous reference frame and the conventional PI regulators. The power controller employs two typical strategies: active–reactive power (PQ) control strategy and voltage–frequency (Vf) control strategy. Particle Swarm Optimization (PSO) is an intelligent searching algorithm that is applied for real-time self-tuning of the power control parameters. The proposed strategy in this paper is that both DG units adopt the Vf control mode once the microgrid is islanded in order to regulate the microgrid voltage and frequency, whereas during the load change, only the second DG unit invokes the PQ control mode to ensure maximum power exportation. The results show that the proposed controller offers an excellent response to satisfy the power quality requirements and proves the validity of the proposed strategy.

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Power quality enhancement in autonomous microgrid operation using Particle Swarm Optimization

Renewable energy based Distributed Generation (DG) has been the solution to researchers to combat the problem of increasing load. In DG based microgrids, the loads and generators are in the close vicinity to aid continuous power supply. However, the power electronic interfacing towards DG systems gives rise to some of the serious power quality problems, such as, the reactive power compensation and the generation of harmonics that pollutes the power distribution system. Reactive power compensation is becoming a challenging task to sustain an acceptable degree of power quality in microgrids due to tightly coupled generation and distribution. Therefore, current research is to cope up with the expanding microgrid system and mitigation of these concerned issues. Recent trends are geared towards the realization of multitasking devices to tackle several power quality problems simultaneously. Hence, the objective of this paper is to present an overview of a microgrid and its modeling utilizing the actual environmental data. Subsequently, the challenges and power quality issues faced in the microgrid are observed and succeeded by a review of compensation methods against these concerns using various control techniques, algorithms, and devices.

A review of reactive power compensation techniques in microgrids

Voltage and frequency regulation based DG unit in an autonomous microgrid operation using Particle Swarm Optimization

This paper proposes an appropriate control systems aiming at the control demands of distributed generation (DG) unit in the micro-grid. When the micro-grid is connected to the main grid, PQ control with droop characteristic is adopted for the inverter; When micro-grid separates from the main grid, Vf control with droop characteristic is used. Also, the controller can make the conversion between different modes seamless. The grid-connected mode, islanding mode and transition from grid-connected to an islanding operation are simulation by PSIM software. The simulation results verify that the proposed control strategy is right and feasible.

Research on the Control Strategy of Inverters in the Micro-Grid

This paper proposes the intermittent step-varied search of maximum power point tracking (MPPT) method to solve the problem of the tracking speed and power oscillation, it is composed of three control processes including startup stage, step-varied timing search and constant duty ratio timing control. When the photovoltaic (PV) system starts up or the environment changes strongly, step-varied search is implemented at intervals of the shorter timing to track the maximum power point (MPP) quickly. When the environment changes slightly, the optimal constant duty ratio is utilized for a longer timing. The simulation and experimental results prove that this method can reduce the tracking power loss caused by the continuous perturbation, and track the MPP fast even under the quick environment change.

XiangDong Sun

Papers

Research on the Control Strategy of Inverters in the Micro-Grid

Maximum Power Point Tracking Method Based on the Intermittent Step-varied Search for PV Array