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By intensifying renewable energy sources integration to the power grid and forming the microgrids (MGs) concept, many studies have been done to investigate MGs operation, control, protection, and etc. The performance of loads can play a major role in the MG behavior. Different load models can be implemented in MGs. The voltage and frequency (VF) dependent load is a substantial load model which few...
Microgrids are a growing trend toward a new power distribution system that allows for a high penetration of renewable distributed generation, electrical energy storage systems and controllable loads. This modern concept exploits the advances in electronic technology to improve efficiency, reliability, and flexibility, while reducing cost and size. Furthermore, microgrids can operate in a grid-connected...
The current paper explores a solar and wind energy system that is capable of operating in both: on-grid and off-grid regimes. The system contains two on-grid and one off-grid inverter for that purpose. The off-grid operation of the analyzed system is more vulnerable to instabilities. Experiments where made to show how inrush currents of electrical loads cause transient processes in such a renewable...
Small signal stability of inverter based droop controlled microgrid is a major problem from past decade. In this work, an optimal state feedback controller is designed to improve the stability of the two inverter based test microgrid. The detailed full order small signal model of the test microgrid is developed in state space considering network and load dynamics. Eigen value and sensitivity analysis...
Electricity in rural area of Indonesia is mostly in small-scale with diesel generator as the main power source. These diesel generators are mostly in the latter stage of operational age, thus have limited capability and poor performance. Microgrid has been introduced lately, as a system to integrate more renewable energy sources to the existing power system. Photovoltaic (PV) source is one of the...
In cascaded-type microgrid, the synchronization and power sharing of distributed generators (DGs) become two new issues that needs to be addressed urgently. In this paper, a unified droop control is proposed and its stability is analyzed in the islanded mode. The proposed scheme can ensure the system stability and accurate power sharing without communication in four-quadrant operations. Finally, simulation...
In an islanded microgrid, harmonic current is controlled (or shared) by modifying the effective impedance in the path of harmonic current. This effective impedance includes line impedance and the internal impedance of the generation unit. Reported works consider the aforementioned impedances as separate entities and their combined effect in harmonic current flow has not been discussed so far. This...
The voltage source inverters operating in islanded microgrid are used as sources of power similar to synchronous generators (SG) in conventional power system. Unlike synchronous generators, these inverters neither have a natural droop (P-f and Q-V) characteristics nor rotational inertia. The electrical time constant is much lesser than mechanical time constant and hence the load changes will show...
The accurate and fast detection of the grid voltage attributes (e.g. frequency and amplitude) are gaining more attention in microgrids due to the new stringent amendments to the microgrid standards. In this paper, two novel observer based techniques are introduced; one for estimating the frequency and another for the amplitude of the grid voltage. The proposed observer techniques offer superior performance...
A hybrid impedance model of Islanded MicroGrid with Paralleled Inverters Controlled by Droop and PQ Strategies (IMG-PICDPS) is derived, in which the PQ-controlled Inverters (PQ-Invs) are equivalent to Norton's circuits, while the DRoop-controlled Inverters (DR-Inv) to Thevenin's circuits in this paper. An impedance-based stability analysis method is further proposed according to the Nyquist criterion...
The well-known droop control and master-slave control methods are two dominant coordinative control schemes for inverter interfacing parallel distributed energy resources (DERs) in islanded AC microgrids. However, both these two control methods have some drawbacks and inherent limitations in practical application. After analyzing their complementary strengths and weaknesses, this paper proposed a...
This paper presents a novel hybrid adaptive droop controller to simultaneously regulate both the AC-side and DC-side parameters for power electronic converters in single-phase Microgrids. The main contribution of this paper is to integrate the AC-side and DC-side controllers. Unlike previously presented control schemes, where the DC-bus is considered as an infinite bus or constant voltage bus, the...
Parallel three-level T-type inverters (3LT2Is) can increase power rating and reliability, but the circulating current problem will arise. Unbalanced conditions including unbalanced filter inductances and unbalanced grid voltage have negative effects on the operation of parallel 3LT2Is. This paper presents an improved repetitive control scheme for circulating current suppression in parallel 3LT2Is...
This paper highlights the power limited nature of the Distributed Generation inverter and demonstrates the practical way to integrate them into the microgrid. Since the energy source of Distributed Generation inverters is power limited in nature, they constrain the operation of inverters to which they are coupled. If the power demanded from these inverters is beyond their capability, their DC-link...
A novel control strategy which enables proportional linear and nonlinear loads sharing among paralleled inverters and voltage harmonic suppression is proposed in this paper. The proposed method is based on the autonomous currents sharing controller (ACSC) instead of conventional power droop control to provide fast transient response, decoupling control and large stability margin. The current components...
Power quality of ac bus voltage is a key issue for microgrids. A model-predictive-control (MPC)-based distributed bus voltage compensation methods using inverter-interfaced distributed generators (DGs) connected to the concerned bus is proposed. The presented method can compensate bus voltage unbalance and harmonics and share the compensated current between inverters autonomously, with neither communication...
This paper proposes an improvement of the finite control set model predictive control (FCS-MPC) strategy for enhancing the voltage regulation performance of a voltage source converter (VSC) used for standalone microgrid and uninterrupted power supply (UPS) applications. The modification is based on tracking the voltage reference trajectory derivative using a single step prediction horizon. The main...
Because of the differences in line impedances, parallel inverters with conventional droop control will have huge circulating current, which does not flow through the loads. To mitigate the circulating current, the research in this paper finds out that parallel-operated inverters should have the impedance in inverse proportion to their capacities, which is difficult to realize in practice. To meet...
Microgrids are seen to play an ever increasing role in providing clean energy which is essential to ensure sustainable and equitable growth. A variety of challenges need to be overcome for these microgrids to be successful, varying from stability, power quality issues to protection and management. Various control algorithms are actively being proposed, and emerging challenges still being researched...
In order to address the economical dispatch problem in cascaded microgrids, this digest proposes an optimal economical-sharing scheme via decentralized approach only with the local information. This overcomes the limitations of centralized control, where the central controller and external information exchange are needed. The frequency and current are used as carriers driven the distributed generators...
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