Andreas D. Theocharis

Three-Phase Transformer Model Including Magnetic Hysteresis and Eddy Currents Effects

In this paper, a three-phase transformer model is developed to be suitable for slow transient and power-quality studies. The proposed model takes into account the eddy currents, the magnetic core topology, and the nonlinear characteristics of the core material. In order to model the eddy currents effects in the magnetic core, Bertottis work for the eddy currents is used and nonlinear resistors dependent on the magnetic core topology are proposed. A systematic procedure is developed for the determination of the incremental self and mutual inductances of the windings. The nonlinear characteristics of the core material are represented either by a magnetization curve or by a hysteresis loop. The hysteresis loop is introduced either by the mathematical model proposed by Tellinen or by the macroscopic model presented by Jiles-Atherton. Simulations results are compared to published measurements in order to verify the proposed model.

Modeling and simulation of a single-phase residential photovoltaic system

A grid connected single-phase residential photovoltaic system is modeled and simulated using a detailed transformer model. The transformer model takes into account the non-linearity of the core material, which further affects the harmonic currents injected into the utility grid. Furthermore, suitable models for the photovoltaic array and the inverter have been used to assemble a system model in the field of standard form state equations. Comparison with published results has been made with a prototype installation of the same configuration. Very good agreement is accomplished between the predicted and measured values. Thus, a valid powerful tool is given for studies of such grid connected single-phase photovoltaic systems.

Transformer modeling based on incremental reluctances

This paper is the completion of a previous work, published recently, on transformer modeling where the magnetic core topology is taken into account. A new circuit, that represents the magnetic core, is proposed, more easily handled mathematically in antithesis to the conventional magnetic circuit that is used in the literature. The proposed circuit has the same topology with the nonlinear magnetic circuit of the core and, in each time interval of a dynamic simulation, it is considered as linear circuit. Its excitations and responses are the time derivatives of both the magnetomotive forces and the magnetic fluxes, respectively. This modeling approach helps power engineers to construct easily a nonlinear transformer model. Applying any method of circuit analysis on the proposed circuit, one can directly write linear differential equations, in each time interval Δt, for the magnetic core and the state equations of the electrical part are written in standard form.

Equivalent circuit of photovoltaic generator using Newton‐Raphson algorithm

Purpose - The purpose of this paper is to develop a linearized equivalent electrical circuit of a photovoltaic generator. This circuit is appropriate to confront problems such as numerical instabil ...