An approximate method for analysing non-linear systems subject to random excitation

A solution technique based on the representation of the response of the non-linear system by a polynomial of the response of the linearized system is presented. The relation between the original non-linear system and the linearized system is introduced by considering the so-called extended moment equations and their closed set is to be solved to determine unknowns. For the Vanderpol oscillator subject to white noise excitation, the technique gives good approximation to the response moments as well as the probability density function

OPTIMAL POWER FLOW IN ISLANDED MICROGRIDS

In this thesis, studies about OPF in islanded MGs have been carried out. First, an original formulation and solution approach for the OPF problem in islanded distribution systems is proposed. The methodology is well suited for AC microgrids and can be envisioned as a new hierarchical control structure comprising only two levels: primary and tertiary regulation, the latter also providing iso-frequency operating points for all units and optimized droop parameters for primary regulation. The OPF provides a minimum losses operating point for which voltage drops are limited and power sharing is carried out according to the most adequate physical properties of the infrastructure thus giving rise to increased lifetime of lines and components. Due to the fact that the solution method is based on a numerical approach, the OPF is quite fast and efficient and the operating point can be calculated in times that are comparable to the current secondary regulation level times. Two test systems, 6_bus and 38_bus, have been used. In the different applications. Different scenarios have been investigated to show: - the possibility to solve the OPF in islanded MGs - the possible link between stability of operation and minimum losses. In particular two methods for OPF have been investigated, one based on a numerical approach (Lagrange method) and one based on heuristic optimization (Glow-worm Swarm Optimization, GSO). The latter is a global optimizer that is able to identify multiple optima.Positive and negative aspects of both methods are put into evidence. Numerical optimization indeed can provide stable solutions but cannot deal with a comprehensive formulation able to optimize both active power-to-frequency and reactive power-to-voltage droop coefficient. Also the load with the numerical approach can only be balanced while heuristic optimization allows both balanced and unbalanced loading conditions. Also constraints can be easily considered using a heuristic formulation, while this is not possible using the numerical approach. The thesis is divided as follow: - In the first chapter, the motivation and scientific goals of the thesis have been presented. - In the second chapter, a parametric study changing coefficients of droop control is carried out solving the power flow for balanced and unbalanced three phase different microgrids systems using the Trust Region Method. - In the third chapter, an original formulation and solution approach for the OPF problem in islanded distribution systems based on Lagrange method is proposed. - In the fourth chapter applications of GSO method to solve the optimal power flow problem taking into account the constraints of frequency and line ampacity in three-phase islanded Microgrids with variables are both Kgs and Kds are proposed. The details of optimal results and load flow calculation results are shown in the appendix

A hierarchical architecture for increasing efficiency of large photovoltaic plants under non-homogeneous solar irradiation

Under non-homogeneous solar irradiation, photovoltaic (PV) panels receive different solar irradiance, resulting in a decrease in efficiency of the PV generation system. There are a few technical options to fix this issue that goes under the name of mismatch. One of these is the reconfiguration of the PV generation system, namely changing the connections of the PV panels from the initial configuration to the optimal one. Such technique has been widely considered for small systems, due to the excessive number of required switches. In this paper, the authors propose a new method for increasing the efficiency of large PV systems under non-homogeneous solar irradiation using Series-Parallel (SP) topology. In the first part of the paper, the authors propose a method containing two key points: a switching matrix to change the connection of PV panels based on SP topology and the proof that the SP-based reconfiguration method can increase the efficiency of the photovoltaic system up to 50%. In the second part, the authors propose the extension of the method proposed in the first part to improve the efficiency of large solar generation systems by means of a two-levels architecture to minimize the cost of fabrication of the switching matrix

Extension of method of moment equation to nonlinear deterministic vibrations

The paper present the so-called "an extended averaged equation approach" to the investigation of nonlinear vibration problems. The numerical results in analysing the vibration systems with weak, middle and strong non-linearity show the advantages of the method

Extended averaged equation method and application on analyzing some nonlinear deterministic vibrations

The paper presents an extended averaged equation approach to the investigation of nonlinear vibration problems. The proposed method is applied to some free/self excited oscillator, nonlinear free and forced oscillations of a suspension system with two-degree-of-freedom. The results in analyzing the vibration systems with different nonlinearity show the efficiency and advantages of the method

Life-Cycle Land-Use Requirement for PV in Vietnam

Over the last 15 years, photovoltaics (PV) in Vietnam has experienced development. The increased installed capacity of PV requires more land for installation sites as well as for manufacturing the plants’ component and waste treatment during the plants’ decommissioning. As a developing country, in which more than 80% of the population’s livelihood depends on agriculture, there are concerns about the competition of land for agriculture and solar development. This paper estimates the life-cycle land-use requirement for PV development in Vietnam, to provide the scientific-based evidence for policy makers on the quantity of land required, so that the land budget can be suitably allocated. The direct land-use requirement for PV ranges from 3.7 to 6.7 m2 MWh−1 year, and the total fenced area is 7.18 to 8.16 m2 MWh−1 year. Regarding the life-cycle land use, the land occupation is 241.85 m2a and land transformation is 16.17 m2 per MWh. Most of the required land area is for the installation of the PV infrastructure, while the indirect land use of the background process is inconsiderable

Optimal Power Flow in three-phase islanded microgrids with inverter interfaced units

In this paper, the solution of the optimal power flow (OPF) problem for three phase islanded microgrids is studied, the OPF being one of the core functions of the tertiary regulation level for an AC islanded microgrid with a hierarchical control architecture. The study also aims at evaluating the contextual adjustment of the droop parameters used for primary voltage and frequency regulation of inverter interfaced units. The output of the OPF provides an iso-frequential operating point for all the generation units and a set of droop parameters for primary regulation. In this way, secondary regulation can be neglected in the considered hierarchical control structure. The application section provides the solution of the OPF problem over networks of different sizes and a stability analysis of the microgrid system using the optimized droop parameters, thus giving rise to the optimized management of the system with a new hierarchical control architecture

A parametric study on unbalanced three phase islanded microgrids with inverter interfaced units

In this paper, the solution of the power flow for unbalanced three phase microgrids systems is proposed. The study aims at the integration of inverter interfaced units using the control law used for primary voltage and frequency regulation, so as to take into account possible small variations of these parameters to account for sudden load changes. The proposed study deals with unbalanced systems which is the typical case of small distribution systems and shows how the power losses term varies as the regulators parameters vary as well, thus showing that these are sensitive parameters that could have an important role in optimal management of such system

All-dielectric Metamaterial for Electromagnetically-induced Transparency in Optical Region

Metamaterial (MM) is emerging as a promising approach to manipulate electromagnetic waves, spanning from radio frequency to the optical region. In this paper, we employ an effect called electromagnetically-induced transparency (EIT) in all-dielectric MM structures to create a narrow transparent window in opaque broadband of the optical region (580-670 nm). Using dielectric materials instead of metals can mitigate the large non-radiative ohmic loss on the metal surface. The unit-cell of MM consists of Silicon (Si) bars on Silicon dioxide (SiO$_{2}$) substrate, in which two bars are directed horizontally and one bar is directed vertically. By changing the relative position and dimension of the Si bars, the EIT effect could be achieved. The optical properties of the proposed MM are investigated numerically using the finite difference method with commercial software Computer Simulation Technology (CST). Then, characteristic parameters of MM exhibiting EIT effect (EIT-MM), including Q-factor, group delay, are calculated to evaluate the applicability of EIT-MM to sensing and light confinement