G. Ricco Galluzzo

A suitable control technique for fault-tolerant converters in Distributed Generation

The penetration of Distributed Generation (DG) in power systems is deeply changing the existing distribution networks which is becoming a very sophisticated and complex systems incorporating both active (generators) and passive systems (distribution systems, converters and loads). The necessary simplification can be obtained dealing with small networks, namely Micro-Grids, reproducing, in a smaller scale, the structure and the problems of large networks including production, transmission and distribution of the electrical energy. In order to achieve an adequate level of reliability, fault-tolerant operations of micro-grids become very important. This result can be achieved only using power converters with fault-tolerance capabilities. Therefore, this paper, presents a control algorithm for fault tolerant converters suitable for micro-grids. After describing the model of the power converter reformulated in terms of healthy leg binary variable, the paper shows how this control preserves power quality when the converter works in the linear range. The effectiveness of the proposed approach is shown through computer simulations.

Computer aided optimization via simulation tools of energy generation systems with universal small wind turbines

This paper considers the general issues in the project and the optimization of energy generation systems using small universal wind turbines, suitable in Distributed Generation (DG) and computer aided optimization for a better exploitation of wind source. Optimization in this field reveal to be more and more important because the local generation and consumption of electrical power, even for grid connected generators can suffers for unevenness of wind source exploitation, also in terms of wrong directions and in not regular wind flows. Computer aided design and optimization of small plants may give significant improvements in the development of the wind source also in accordance with the projections of future energy policies that foresee a significant increase of the wind generated energy for the future market. The effectiveness of computer aided optimization tools is illustrated in the present paper with the exposition of two case studies. In the first of them a Wind Electrical Energy Generating System is moved by a Modular Multiple Blade Fixed Pitch Wind Turbine coupled with an asynchronous wound rotor generator. In the second case study the optimization regards a Savonius wind turbine and a PM synchronous generator with particular reference to the development of wind source for the wind turbine and the reduction of saturation and of harmonic content in the emf for the electrical machines.

Efficiency Maximization of Permanent Magnet Synchronous Generators Coupled Coupled to Wind Turbines

In this paper a control algorithm for the efficiency improvement of permanent magnet synchronous generators (PMSG), the relative simulations and their results are presented. The proposed algorithm reduces the losses of the generator without affecting its performances. In details, after a description of a dynamic model of the PMSG, which has been modified in order to take into account the iron losses, the basic methodologies to obtain the loss minimization are presented and discussed. Many simulations of a specific PMSG employing the proposed algorithm were carried out and are presented. The results of these simulations show that enhancement of the efficiency up to 3% and more can be reached in comparison to a PMSG using a traditional control strategy. The control algorithm has been tested through simulations in order to demonstrate its validity when the generator is coupled to wind turbines.

Development of diagnostic systems for the fault tolerant operation of Micro-Grids.

The progressive penetration level of Distributed Generation (DG) is destined to cause deep changes in the existing distribution networks no longer considered as passive terminations of the whole electrical system. A possible solution is the realization of small networks, namely the Micro-Grids, reproducing in themselves the structure of the main production and distribution of the electrical energy system. In order to gain an adequate reliability level of the micro-grids the individuation and the management of the faults with the goal of maintaining the micro-grid operation (fault tolerant operation) is quite important. In the present paper after the introduction of the aims of several diagnostic systems, the main available diagnostic techniques are examined with particular references to those applied to the fault diagnosis of the electrical machines and finally the Authors also present an approach for the fault tolerant exercise of the micro-grid.

An IPMSM torque/weight and torque/moment of inertia ratio optimization

In this paper, a torque/weight and torque/moment of inertia ratio optimization procedure for interior permanent magnet syncronous motors (IPMSMs) is presented. More in detail, a performance comparison between several IPMSM rotor structures has been carried out in order to determine the optimum geometry that can maximize the torque/weight and torque/moment of inertia ratios. A commercial motor, with known electrical and mechanical characteristics, has been taken as reference. Its rotor structure has been modified several times, obtaining different rotor geometries and, therefore, many IPMSM models with different electrical and mechanical characteristics. The finite element method (FEM) analysis of each IPMSMs has been performed using the software FEMM, allowing to determine the related torque/load-angle characteristics. From the comparison between the torque/load-angle characteristics of the different IPMSM structures, it can be stated that significant performance improvements can be obtained in dependence not only of the type of permanent magnets and their direction of magnetization, but also of the PM displacement within the rotor.

Flexible power converters for the fault tolerant operation of Micro-Grids

The progressive penetration level of Distributed Generation (DG) is destined to cause deep changes in the existing distribution networks no longer considered as passive terminations of the whole electrical system. A possible solution is the realization of small networks, namely the Micro-Grids, reproducing in themselves the structure of the main production and distribution of the electrical energy system.

Experimental validation of a general model for three phase inverters operating in healthy and faulty modes

The paper presents the experimental verification of a general mathematical model of Voltage Source Inverters (VSI) able to simulate fault conditions and which is also useful for the simulation of fault-tolerant systems for different applications. In general, in the past, the problem of faulty inverters modeling has been addressed specifically by considering faults on the different phases as separate cases. Furthermore, traditional models include only the faulty mode and not the healthy mode, so resulting then not able to predict transient phenomena. The model hereafter presented overcomes this drawback. It was formulated by introducing the concept of “healthy leg binary variables”. Such variables allow the management of both unfaulted and faulted conditions regardless of what is the faulty phase. Experimental tests were used to verify the correctness of the followed modeling approach and the ability of the model to predict transients before, during and after the application of a fault tolerant control.

Monitoring and diagnosis of failures in squirrel-cage induction motors due to cracked or broken bars

In this paper three diagnostic procedures, based on on the vibration, current and instantaneous power monitoring for the detection and monitoring of incipient faults as cracks or bar breaks on squirrel cage motors are briefly reminded. The experimental investigations, carried out at the SDESLab (Sustainable Development Energy Savings Laboratory) of the University of Palermo in order to underline merits and drawbacks of the methods applied to the same die cast squirrel cage induction motor, are presented. The results of the investigations confirmed the effectiveness of the diagnostic procedures here considered.

A photovoltaic charging system of an electrically assisted tricycle for touristic purposes

In this paper the design, realization and testing of a photovoltaic charging system suitable for the management of an electrically power assisted tricycle are described. This vehicle uses a photovoltaic module as a source of electric energy for the battery recharging. In this work, an overview on the needs of sustainable mobility and on the commercial electrically power assisted velocipedes is presented. The electrical rickshaw prototype, developed in the SDELab laboratory of the University of Palermo, is presented in detail, underlining the design, implementation and developing phases of the photovoltaic charging system assembled on the velocipede. Moreover, tests oriented on the setting up of the whole system and validation tests on the prototype are described, with the aim of determining the growing up of performances. Particular attention is dedicated to the vehicle autonomy, by using the management system here proposed. The results show how is possible to reach an increase of the 30% of the electrical rickshaw autonomy by using the management system conceived by the Authors. Furthermore, these tests are carried out in order to demonstrate that the electrical rickshaw vehicle supported by the PV charging system could be targeted for touristic purposes.

Parametrical study of multilayer structures for CIGS solar cells

In this paper, a numerical analysis of relevant electrical parameters of multilayer structures for CIGS-based solar cells was carried out, employing the simulation software wxAMPS. In particular, we have focused on thin film cells having a ZnO:Al/ZnO/CdS/CIGS structure with a Molybdenum back contact. The aim of this work is to establish good theoretical reference values for an ongoing experimental activity, where our technology of choice is the single-step electrodeposition. In detail, we have analyzed how the main electrical properties change with the bang gap and the thickness of the absorber layer, for such a type of solar cell structure. Our results show that both efficiency and fill factor strongly depend on the energy gap. Instead, the absorber thickness plays a role up to a few microns, after which the cell parameters remain almost constant. As expected, the theoretical peak efficiency was found for a band gap value of 1.40 eV, corresponding to a Ga/(In+Ga) ratio of 0.66.