Abstract
This paper proposes a new modified architecture for AC microgrid consisting of multiple grid-supporting master units (MUs) and multiple grid-feeding slave units (SUs). In this study, a coordinated four-layer hierarchal control (HC) approach is applied to the proposed structure for allowing the MUs, SUs and loads to be easily integrated as a microgrid and operated in both grid-integrated and standalone operation mode. The proposed structure of the AC microgrid enhances the system redundancy to prevent the single point of failure of MU and has more stability, efficiency, flexibility and reliability than the conventional structures. Furthermore, optimal design guidelines, based on a new hybrid Harries hawks and particle swarm optimization algorithm (H-HHOPSO) with the cooperation of different types of proposed multi-objective functions, are presented to fulfill the study objectives. The optimization constraints/objectives are employed for optimal parameters selection of HC controllers to improve the power quality, enhance dynamic and steady-state performance and guarantee a seamless transition between operation modes. To accomplish this work, the newly modified structure is modeled, constructed in MATLAB/SIMULINK and tested under the variations of generations and loads. This structure is also examined when the fault occurs at any one of the MUs and during the connecting and disconnecting of utility grid. This testing is to verify its flexibility and reliability, and confirm the effectiveness and robustness of the proposed optimal controllers. Additionally, the experimental work is carried out using the hardware-in-the-loop real-time emulation to prove the optimal controllers' feasibility. Finally, the experimental and simulation results are compared.
Highlights
Nowadays, the penetration of renewable energy microsources (REMSs) based distributed generation (DG) units in the utility power grid is rapidly growing
THE primary control level (PCL) AND OPTIMIZATION FOR ITS CONTROLLERS The PCL is the first control layer of hierarchal control (HC) required for satisfying the following objectives: (1) regulation and stabilization of the microgrid’s frequency and voltage via grid-supporting master units (MUs) empowered by energy storage elements (ESEs), (2) responsibility of plug and play capability of DG units and realizing accurate power-sharing among MUs via droop control method without using any communications (3) mitigation of the circulating currents among DG units (4) obtaining the maximum power from REMSs based grid-feeding slave units (SUs) and regulating the microgrid reactive power via these SUs
Three scenarios are proposed, simulated and discussed in the following subsections to investigate the feasibility of the new microgrid architecture
Summary
The penetration of renewable energy microsources (REMSs) based distributed generation (DG) units in the utility power grid is rapidly growing. 4. The new H-HHOPSO algorithm with the aid of many types of suggested multi-objective functions had been proposed to tackle one of the most complex microgrid technical problems represented in the optimum design of its controllers’ coefficients of four control levels to achieve the study objectives. THE PCL AND OPTIMIZATION FOR ITS CONTROLLERS The PCL is the first control layer of HC required for satisfying the following objectives: (1) regulation and stabilization of the microgrid’s frequency and voltage via grid-supporting MUs empowered by ESEs, (2) responsibility of plug and play capability of DG units and realizing accurate power-sharing among MUs via droop control method without using any communications (3) mitigation of the circulating currents among DG units (4) obtaining the maximum power from REMSs based grid-feeding SUs and regulating the microgrid reactive power via these SUs. two control strategies are discussed. The grid-supporting MU is controlled as a voltage source with series output impedance, whereas the grid-feeding SU is controlled as a current source with paralleled high output impedance
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