José Cidrás

A third order model for the doubly-fed induction machine

Abstract Induction generators are generally simulated by means of a well-known model described by Brereton et al. [1] , based on the induction motor equations derived by Stanley [2] . In this model the possibility of opening the rotor circuit in order to inject a voltage source is not taken into account, although there are other models where it is dealt with [3] . This paper presents an alternative way of obtaining the mentioned model and introduces the possibility of modeling voltage sources in the rotor circuit, which can be very useful when simulating some generating schemes, such as variable speed asynchronous wind turbines.

An improved branch-exchange algorithm for large-scale distribution network planning

Design of optimal layout for medium-voltage (MV) power networks is a common issue in electrical distribution planning. Technical constraints (radial structure, voltage drops, and equipment capacity) and reliability limits must be fulfilled. The function for minimizing includes investments, power losses, and quality of supply costs. We present an improved algorithm based on a branch exchange technique to solve large-scale problems. A heuristic algorithm for solving a Euclidean Steiner problem is used to improve the network by including transshipment nodes.

Nodal frequency analysis of grounding systems considering the soil ionization effect

Soil ionization takes place when the current leaking into the earth is high enough to produce an electric field intensity greater than a critical value. This phenomenon lowers the ground impedance and it is similar to an apparent increase in the electrode dimensions. Soil ionization has a great influence on the performance of small grounding electrodes fed by currents of high magnitude (i.e., lightning waves). In this paper, a new way of including the nonlinear soil ionization in the grounding system analysis is proposed. The study of the grounding system is performed in the frequency domain by means of an equivalent electric circuit.

Influence of the shadows in photovoltaic systems with different configurations of bypass diodes

The IU characteristic curve of a photovoltaic module is affected by shadows, depending on the shaded area of the PV module, and the radiation received by the shaded areas. Another factor in the shape of the I-V curve of a PV module, is the configuration of the electrical connection between its cells and bypass diodes. Bypass diodes are installed in the modules to prevent power consumption when they are shaded or damaged; they also prevent cells from working near the avalanche zone. This paper examines the performance of a photovoltaic array. A PV array consists of modules connected between them. Particularly, the configuration with bypass diodes overlapped is analysed, showing that totally or partially shaded modules can consume some of the power generated by other modules of the PV array. This effect is also present in low power PV arrays. In these cases, the power dissipated by a diode is small; but if there are many diodes, the power dissipated by all the diodes can be comparable with the power produced by various PV modules. Additionally, this article deals with the influence of the inverter in the MPP tracking.

Low-frequency magnetic fields from electrical appliances and power lines

The relationship between magnetic fields and the health of people is increasingly being investigated. International organizations have proposed bylaws that put limits on the value of the generated magnetic field. In this work, we measure the magnetic field created by electrical appliances and high voltage lines and we analyze the degree of compliance with recent applicable European regulation. The simulation of the magnetic field generated by electrical lines through a simple model accurately predicts the measured values. The model is used to simulate the behavior of the lines under given conditions. In both cases, an FFT analysis of the magnetic field waveform was performed to study the frequency and amplitude of the possible induced currents.

Theoretical model to calculate steady-state and transient ampacity and temperature in buried cables

The temperature distribution and ampacity in a multilayered soil surrounding a system of three cables is calculated in the steady state in emergency situations. We present the mathematical model that solves the heat diffusion equation in cylindrical coordinates inside the cables and in Cartesian coordinates in the surrounding soil. The finite difference method is used to solve the equations. In order to reduce the number of points studied that are of no interest to the results, a variable step discretization is used. We present the development of the model and the effect of some of the parameters that influence the convergence and accuracy of the method. The application of the model in different configurations and situations is given in the second part of this work. The model is applicable to the study of buried cab in both the steady state and transient states for short circuit and overload situations.

A linear dynamic model for asynchronous wind turbines with mechanical fluctuations

A specific linear dynamic model for an asynchronous machine is presented. This model is based on the balanced dynamic model of the asynchronous machine, and it is developed for asynchronous wind turbines when the mechanical power (wind power) has sinusoidal fluctuations. The dynamic and the proposed linear models for real and reactive powers and voltage fluctuations analysis are considered and compared.

Synchronization of asynchronous wind turbines

In this paper, a theoretical analysis and explanation of synchronization phenomena in wind parks with asynchronous generators is presented.

Design of Large Rural Low-Voltage Networks Using Dynamic Programming Optimization

The purpose of this paper is to establish algorithms in the design of rural low-voltage (lv) distribution networks. Planning of rural lv distribution networks involves the optimal design of radial configuration and location of mv/lv substations considering cost functions. In this work both goals are considered by taking into account different conductors, voltage drop constraints, power losses in lines, and deterministic loads. The algorithms developed in this paper are based on dynamic programming and were implemented on large-scale rural lv distribution networks, but they could also be used for other network optimization.

An application of an evolution strategy in power distribution system planning

The optimal location and sizing of power distribution substations and feeder layouts is a common problem in new expansion planning. This paper is an application of a type of evolutionary algorithm called an evolution strategy (ES), to obtain optimal locations and sizes for power distribution substations such that the demand is met at minimum cost. The cost function for minimization includes substation investments, medium-voltage network costs and power losses.