M. J. Resende

Self-Excited Induction Generator for Micro-Hydro Plants Using Water Current Turbines Type

A study of a micro-hydro run-of-the-river project using a squirrel cage induction generator is presented. A water current turbine, propeller type, is considered. A three-phase voltage source inverter is used to establish with deadbeat control on the AC side, the required currents to excite the generator. A DC control loop with PI controller is used to maintain the DC bus voltage constant with rotor speed. The control strategy is developed using the field orientation technique which is provided by a digital signal processor (DSP). The proposed model and adopted control strategy are validated both by numerical simulation and experimental results from a laboratory prototype

Fault-tolerant design of a classical voltage-source inverter using z-source and standby redundancy

This paper proposes modifications of the classical two-level three-phase voltage-source inverter topology structure with the aim of increasing its reliability to safety-critical applications. This solution intends to achieve fast changing and “soft” commutation between main and redundant branches through the combination of mechanical commutators and power devices. Also, important modifications in the power supply stage will allow to withstand severe short-circuit conditions. With those modifications, the energy processing capability can be maintained for most common failure modes. Several aspects of failure modes, detection and isolation processes within voltage-source inverters are also discussed regarding the requirements of safety related applications. Experimental results from a prototype are included to confirm the validity of the proposed solution.

Asynchronous Generator Excited by Current Controlled Voltage Source Inverter using Rotor Field Oriented Control

This paper presents a strategy used to appropriately excite and control the desired output active power of an asynchronous generator fed by a current controlled three-phase voltage source inverter. A DC voltage control loop, with a classical PI controller, is used to maintain at a reference value the DC bus voltage of the source inverter under a large rotor speed variation. The proposed asynchronous generator control strategy is developed using rotor field orientation technique and carried out by a digital signal processor (DSP). The proposed control strategy and adopted system models are validated by numerical simulation and experimental results obtained from a laboratory prototype

Combining mechanical commutators and semiconductors in fast changing redundant inverter topologies

This paper presents some solutions for fast changing and “soft” commutation between main and redundant branches in fault-tolerant inverter topologies through the combination of mechanical commutators and semiconductors. The present study deals with redundant two-level three-phase voltage-source inverters. Experimental results confirm the validity of the proposed solutions.

Measuring the value of intermittent generation technology

This paper analyses the application of levelized costs criterion to energy markets when there is a significant share of production from intermittent technologies in the power generation system. Under such scenario, the share of dispatchable technologies is often reduced, and producers may face difficulties to recover their production costs trough market.

Continuity of supply indices

With the growing importance of electric energy on society, industry and transportation services, it is essential to assure a high quality service level. This work focuses specifically on one of the service quality parameters of the electricity network, the service continuity, aiming to contribute to its clarification. First part focuses on the analysis and benchmarking of indicators from different European countries. Portugal strong positive evolution regarding other countries is also analysed. Finally, the planned interruption concepts and exceptional events are studied as well as inherent country conditions regarding the service continuity. In an European context, it is necessary to harmonize and uniform each country methodologies, regarding the service continuity, so that European comparisons can be meaningful.

UNBALANCE AND HARMONIC DISTORTION ON AC TRACTION SYSTEMS: A STATISTICAL APPROACH

From the utility network point of view, the alternating current (AC) catenary of a traction system power supply is one of the most severe consumers because of the unbalance and harmonic distortion is generates. This paper analyzes the unbalance and harmonic distortion introduced by a suburban traction system with several trains in service. Each train is considered as a harmonic and unbalance generator. Because of the high number of trains in service, a deterministic approach to quantify the disturbances introduced by the whole set may produce a fastidious result; therefore, this paper shows that this quantification may be achieved by using a probabilistic methodology. For the presented case study, it is concluded that the most severe disturbance is introduced by harmonic generation.