• Energy Research

The use of a suitable modeling technique for the optimized design of a magnetic gear is essential to simulate its electromagnetic behavior and to predict its satisfactory performance. This paper presents the design optimization of an axial flux magnetic gear (AFMG) using a two-dimensional (2D) magnetic equivalent circuit model (MEC) and a Multi-objective Genetic Algorithm (MOGA). The proposed MEC model is configured as a meshed reluctance network (RN) with permanent magnet magnetomotive force sources. The non-linearity in the ferromagnetic materials is accounted for by the MEC. The MEC model based on reluctance networks (RN) is considered to be a good compromise between accuracy and computational effort. This new model will allow a faster analysis and design for the AFMG. A multi-objective optimization is carried out to achieve an optimal volume-focused design of the AFMG for future practical applications. The performance of the optimized model is then verified by establishing flux density comparisons with finite element simulations. This study shows that with the combination of an MEC-RN model and a GA for its optimization, a satisfactory accuracy can be achieved compared to that of the finite element analysis (FEA), but with only a fraction of the computational time.

Abstract The parameter estimation of a synchronous generator using the dc-step voltage is presented in this paper. The dc-step voltage is a standstill experiment needed to generate the required data to estimate the fundamental parameters of the d–q axis equivalent circuits. A hybrid Genetic Algorithm is used in the estimation process. A model with one damper winding along each axis is adopted. The unequal mutual effect of field and d-axis damper windings is taken into account. To check the validity of the estimated parameters, a sudden three-phase short-circuit test is applied at the generator terminals. The measured data are compared against the simulation response of the machine model using the parameters estimated from the dc-step voltage. Furthermore, the description of the developed experimental setups for both standstill and online tests is presented. A synchronous generator of 7 kVA, 220 V, 1800 rpm, 60 Hz was used in the study.

Este artículo presenta el diseño, desarrollo, y construcción de un sistema de ahorro de energía para un climatizador evaporativo. El sistema de ahorro está diseñado para disminuir la energía eléctrica consumida por el enfriador de aire. En el sistema propuesto se sustituye el motor de inducción monofásico de fase partida que se emplea comúnmente por un motor de inducción trifásico, el cual es accionado por un inversor de tensión y un rectificador ca/cd controlado. El control del sistema de ahorro de energía se lleva a cabo por un controlador digital de señales el cual el operado con base a un sistema operativo en tiempo real, que administra las diferentes tareas del sistema de ahorro de energía del climatizador. El uso del motor trifásico y de un inversor permite una operación en un rango continuo de velocidades de acuerdo a la temperatura ambiente, en contraste con el equipo convencional que solo cuenta con dos velocidades fijas. Adicionalmente, la presencia del sistema operativo en tiempo real permite ejecutar diferentes tareas de forma simultánea y segura. Las tareas que se ejecutan son: el controlador de la velocidad del motor, el control del inversor y del rectificador así como el registro de variables del sistema. Las pruebas experimentales realizadas muestran que el sistema propuesto permite un ahorro de un 45% de la energía consumida en comparación con los sistemas empleados tradicionalmente. Palabras clave: Motor de inducción, inversor de tensión, ahorro de energía, rectificador controlado, sistema operativo en tiempo real, climatizador evaporativo

This paper presents a novel single-phase grid-tied neutral-point-clamped (NPC) five-level converter (SPFLC). Unlike the literature on five-level NPC topologies, the proposed one is capable of inherently balancing the voltage of the DC-link split capacitors. For this purpose, a simple Multicarrier Phase Disposition (MPD) Pulse Width Modulation (PWM) technique is used, thus avoiding both complex modifications to the Space Vector Modulation (SVM) and offset voltage injections into the carrier based (CB) PWM, as commonly done in most conventional balancing algorithms. Bearing in mind that the proposed balancing strategy only requires measuring the capacitors’ voltages and the sign of the converter output current, it has a very low complexity. The developed strategy is not only straightforwardly implemented but is also very effective for obtaining symmetrical and undistorted voltage levels from the proposed multilevel converter, as well as for significantly improving the power quality of the SPFLC output voltage and, in turn, of the grid current. The simulation results obtained with MATLAB-SimPowerSystems as well as the experimental results obtained with the prototype built in the laboratory validate the topology of the proposed NPC five-level converter and the voltage balancing strategy, by showing a good performance under step-changes and exhaustive operating test conditions.

A time-domain parameter calculation of a turbogenerator state-space model is presented. The finite-element (FE) method has been used to simulate a two-dimensional (2-D) nonlinear transient condition of the turbogenerator. An open-circuit transient excitation of the machine in closed-loop conditions (excitation system and unloaded synchronous generator) was reproduced to extract flux linkages, power losses, and eddy currents produced within the generator, which allowed the computation of the parameters of an electrical circuit. An electrical circuit structure with one d-axis damper winding is proposed. New parameter behavior profiles were found for the fictitious damper winding, and the saturation effects on the field winding reactance were determined. FE commercial software is employed during the research as a validation tool. It is found that the simulated time-domain response of the lumped model closely follows the time-stepping FE model. The research was carried out for a large turbine generator of 150 MVA, 13.8 kV, 50 Hz, and two poles.

This paper presents the development of a single-phase grid-connected wind energy conversion system (WECS) that uses a modified PLL. The WECS development is based on the use of the low cost 30 MIPS Digital Signal controller (DSC) dsPIC30f3011. The modified single-phase PLL is based on the PQ theory, where a lag structure based on an integrator is proposed instead of a conventional lag structure. The voltage source inverter (VSI) is driven by a Space Vector Pulse Width Modulation (SVPWM). The maximum power transfer is achieved by using a Maximum Power Point Tracking (MPPT) algorithm based on the steepest ascent method. The tasks related to the SVPWM algorithm, the PLL, the MPPT algorithm, and the monitoring of the DC voltage were successfully implemented in the DSC.

This paper presents a virtual instrument (VI) to carry out the frequency response test and parameter estimation. The VI was used for parameter estimation of induction, synchronous and direct current machines. The constrained least square algorithm was used for the parameter estimation of the linear machine models. In each machine test, a variable frequency alternating current was applied through the machine terminals while it was at the standstill condition. The obtained voltage and current responses were used to calculate the magnitude and the phase angle of the relevant transfer function. The frequency domain response was measured from 1 mHz through 1 kHz. The VI was implemented in the programming environment of LabVIEW. It can generate the excitation signal, acquire the necessary signals, process the signals for frequency response and carry out the parameter estimation.

A new steady-state model describes synchronous reactance over the whole operating region of the machine. The model takes into account main and cross-axis magnetic saturation. An analysis is presented of saturation as a function of the total air gap ampere-turns which shows that complicated relationships exist at leading power factors making such relationships unuseful. Two large turbogenerators of 13.8 kV, 150 MVA and 22 kV, 588 MVA are studied.

The paper presents the development of a computational program that simulates the electromechanical dynamics of an electric power system (EPS). It allows the evaluation of the transient stability and will be integrated into an on-line security assessment system in the northern control area of the Mexican Electric Utility (CFE). Initially, the program was developed for research and academic purposes. The program was written in MATLAB and then in C++ using available public license compiler and numerical libraries. The power system model structure for transient stability analysis is defined by a set of algebraic and differential-ordinary equations (ADOE). This model structure allows the study of several solution algorithms, here an algorithm is used and its particular features are explained. The simulation results of the developed model are validated against the commercial software PSS/E, where good agreement was found.