M. Valverde

Voltage sag correction by dynamic voltage restorer based on fuzzy logic control

In basic applications, the fuzzy logic controller is used as a substitute for the conventional Pl compensator. The voltage error and its derivative are the fuzzy logic controller input crisp values. When a fuzzy logic controller is used, the tracking error and transient overshoots of PWM can be considerably reduced. The simulations carried out show that the dynamic voltage restorer provides excellent voltage regulation capabilities. This paper demonstrates that the transient response of the fuzzy logic control is better than that of PI.

Fuzzy logic control of a dynamic voltage restorer

Dynamic voltage restorer can provide the most cost effective solution to mitigate voltage sags by establishing the proper voltage quality level that is required by customer. This device is connected in series with the distribution feeder at medium voltage. A fuzzy logic control is proposed. As is known, the PWM converter is actually non-linear, but the PI is a linear controller, so it can only guarantee the stability of this converter in a local area. Simulation results are shown to validate these control methods.

Combined molten carbonate fuel cell and gas turbine systems for efficient power and heat generation using biomass

Abstract When used in combination with turbines, fuel cells can produce from 55 to 90% of the electricity of the system while turbines produce the remainder. Fuel flexibility enables the use of low-cost indigenous fuels, renewables, and waste materials. The characteristics of gas from biomass gasification may vary significantly. Most real systems cannot be modeled exactly. Errors arise from unmodeled or unknown parameters. From another point of view, robust control incorporates the varying or uncertain parameters of the model. The advantage of this uncertainty representation is that it provides a good representation of the uncertainty arising in many real control problems.

Fuzzy logic inverter flux control of fuel cell plants in distributed generation

The use of advanced power converters at the front end of distributed generation is constantly increasing, posing harmonic control requirements for their connection to the grid. This work shows the design of a new fuzzy logic regulator for a three-phase inverter using the strategy of inverter flux vector control method. Criteria for designing the fuzzy controller are given and a comparison with the hysteresis method is introduced. Harmonic characteristics in steady state and transient characteristics of system voltage sag are analyzed. The results reveal that the inverter system has capabilities to reduce harmonics and to control system disturbances. In order to highlight the comparative study a simulation is accomplished using MATLAB.

Multiobjective Genetic Algorithm for Three-Phase PWM Inverter in Microturbines

In this article, authors present a new design method for PWM inverters in microturbines by using a multiobjective genetic algorithm. More precisely, the design problem is converted to an equivalent optimization problem, and then a multiobjective genetic algorithm is adopted to find a solution. The genetic algorithm is proposed to design a fuzzy controller. In this genetic algorithm approach, an individual is constructed to represent the fuzzy controller. A short coded string is proposed such that it is associated with an individual can map, a fuzzy controller structure, including the membership functions, and the scaling factors. Multiobjective genetic algorithm confers a number of advantages over conventional multiobjective optimization methods by evolving a family of Pareto-optimal solutions rather than a single solution estimate. This optimal fuzzy controller is suitable for the specific harmonic elimination pulse width modulation technology, as demonstrated by the examples given in this article.

Identification of Hammerstein Model for Solid Oxide Fuel Cells

There is a consensus within the industry that the development of accurate models for solid oxide fuel cells is a key step in understanding the operation of these devices. The Hammerstein model configuration, which includes a nonlinear static block followed by a linear dynamic block, is applied to model the static and dynamic characteristics of the solid oxide fuel cell. The performance of the proposed identification algorithms is illustrated through simulation

Effect of the fuel cell on distribution system stability

When connected in small amounts, the impact of distributed generation on distribution system stability is negligible. However, if its penetration level becomes higher, distributed generation may start to influence the dynamic behavior of the system as a whole. The paper presents a mathematical representation of a solid oxide fuel cell plant that is suitable for use in distribution system stability studies. The model is applied to a distributed utility grid that uses a solid oxide fuel cell plant as distributed resource. Examinations include transient stability and voltage stability of the system.

Applications of signal processing tools in a power systems course

The scope of a modern electrical engineering curriculum presents a challenging problem. It is quite difficult to design a well rounded and all-encompassing curriculum in a rapidly evolving field such as electrical engineering. In this paper, signal processing tools are presented that allow the student to see immediately the advantages and limitations of these techniques for electric power ‘quality’. Three signal processing techniques are considered: discrete Fourier transforms, wavelet filters, and discrete short-time Fourier transforms. The paper explains how the course material and teaching style respond to various requirements for an integrated design experience.

A method for the identification of micro-turbines using a Hammerstein model

Accurate modeling of micro-turbines is a relevant problem, because of their nonlinear behavior. This paper examines Hammerstein model identification in frequency domain using the sampled input-output data. A modeling approach for a micro-turbine system for the analysis of its dynamic performance is presented. Functioning of the distribution system under fault and load disconnection scenarios are investigated. MATLABtrade software environment is used for the studies

A Fuzzy Flux Control to Reduce Harmonics in the Utility Interface of Fuel Cell Power Systems

The deregulation and unbundling of electricity markets in many countries worldwide brings new perspectives for fuel cells. This article presents a new flux modulation approach for the closed-loop control of the output voltage of inverters for fuel cells, using the flux vector control method. Criteria for designing a fuzzy controller are established, and a comparison with the conventional flux control method is shown. The proposed control scheme can achieve fast transient responses and, at the same time, have low total harmonic distortion in output current during steady-state operation. The performance of the new modulator has been verified in simulation.