Luís Monteiro

Delta Prolog: A Distributed Backtracking Extension with Events

We present Delta Prolog, a distributed logic programming language that extends Prolog to include AND-parallelism (in a single processor or across a network of processors), interprocess communication via message passing with two-way pattern matching, interprocess synchronization with simultaneous message passing, and distributed backtracking among a family of processes. The extension is achieved, at the language level, by just two additional types of goals — events and splits. The implementation is written part in Prolog and part in C, with a small number of core primitives, to help portability. It is still experimental and expected to evolve. In this work we present the languages distinguishing features, describe its semantics, exhibit programs and analyse their behaviour, examine the implementation, and mention conclusions, advantages of the approach and the next developments.

Instantaneous p–q power theory for control of compensators in micro-grids

The main objective of this tutorial is to present the basic concepts on the instantaneous p–q Theory and then show its applicability for controlling switching converters connected in a micro-grid. These converters can be used for connecting renewable energy sources (solar, wind, and others) to the micro-grids or for harmonic, reactive power or unbalance compensation, and even for voltage regulation. The emphasis is given on the compensation characteristics derived from the p–q Theory, and simulation results of test cases are shown. Special attention is put on the oscillating component of the instantaneous real power, as it may produce torque oscillations or frequency variations in weak systems (micro-grids) generators. This oscillating component, as defined in the p–q Theory, gives the amount of oscillating energy between the source and the load, and its compensation through a switching compensator must have an energy storage element to exchange it with the load. With the p–q Theory this energy storage element can be easily calculated as a function of the average component of the instantaneous real power, which depends on the observation period.

Compensation algorithms based on the p-q and CPC theories for switching compensators in micro-grids

The main objective of this paper is to compare the applicability and performance of a switching compensator when it is controlled by algorithms derived from the pq-Theory and from the Currents Physical Components Power Theory (CPC-Theory) considering a micro-grid application. Compensation characteristics derived from each one of these set of power definitions are highlighted, and simulation results of test cases are shown. Special attention is put on the oscillating instantaneous real power, as it may produce torque oscillations or frequency variations in weak systems (micro-grids) generators. The oscillating instantaneous real power, as defined in the pq-Theory, gives the amount of energy oscillating between the source and the load, and its compensation using a switching compensator must have an energy storage element to exchange it with the load. The energy storage element can be easily calculated with the pq-Theory.

A control strategy for shunt active filter

This paper describes a novel control strategy for shunt active filters the sinusoidal Fryze currents control strategy. The control strategy considers the presence of harmonics in the system voltage and load current simultaneously. Although the fundaments of the pq theory is used to better explain the proposed control strategy, it is not directly used, since the Clarke transformation (abc to /spl alpha//spl beta/0 transformation) is avoided. In fact, the fundaments of the pq theory is inserted in a minimization method - the generalized Fryze currents, which together with a robust synchronizing circuit (PLL control circuit), form a concise controller for shunt active filter. The shunt active filter provides current compensation, such that the compensated current drawn from the network is sinusoidal and balanced, corresponding to the fundamental positive-sequence component of the load current, plus an additional fundamental positive-sequence component to cover losses in the power circuit of the shunt active filter. Simulation results are presented to validate the control strategy.

A Combined Series Active Filter and Passive Filters for Harmonics, Unbalances and Flicker Compensation

This paper describes a combined operation involving a series active filter and shunt passive filters for three-phase three-wire systems. The series active filter is able to minimize Power Quality problems like unbalances, harmonics and flicker observed at the system voltages. Another task for the series active filter is to damp possible resonances involving the passive filters and the system impedance. The shunt passive filters are designed to drain harmonic current-components generated by the load. The control strategy of the series active conditioner is based on the instantaneous power theory on ¿-ß-0 reference frame, together with a robust synchronizing circuit PLL (Phase-Locked-Loop). A dc-link voltage controller, applied to the series conditioner, is also introduced due to the fact that there is only a single capacitor at the inverter dc-side. Simulation results on PSCAD®/EMTDC¿ are presented in order to verify the performance involving a combined operation of passive and active filters.

Shunt Active Power Filter with Dynamic Output Current Limitation

This paper presents a shunt active filter with a controller able to dynamically limit the output current, which allows an effective protection of the inverter semiconductors without diminishing the active filter performance. The control strategy is based on the p-q theory expanded for three-phase four-wire systems and the power stage of the active filter is composed by a two-level four-leg inverter. Simulation results on PSCADreg/EMTDCtrade are presented to demonstrate the performance of the dynamic current limitation.

Syntactic and Semantic Inheritance in Logic Programming

This paper aims at a deeper understanding of how inheritance can fit into a logic programming framework, by considering inheritance systems in terms of partially ordered sets of logic program units. We develop for such systems operational, declarative and fixed point semantics which are proven equivalent.

Experimental Results of a Single-Phase Shunt Active Filter Prototype with Different Switching Techniques

This paper presents experimental results obtained with a developed single-phase shunt active power filter laboratory prototype operating with different switching techniques. This active filter can compensate harmonic currents and power factor in single-phase electric installations. Its power circuit is based on a two-leg IGBT inverter, with a single capacitor in the dc side, and an inductor in the ac side. Its control system is based on a simple stratagem that enables the use of the traditional Theory of Instantaneous Reactive Power (p-q Theory), originally developed to three-phase power systems, in single-phase systems. The experimental results are obtained for the active filter operating with two different switching techniques: Periodic Sampling (with variable switching frequency) and Pulse Width Modulation (with constant switching frequency) for two different frequencies (8 kHz and 16 kHz). Three different types of loads are used: linear RL load, rectifier with RL load, and rectifier with RC load.

A novel selective control algorithm for the shunt active filter

This paper presents a novel selective control algorithm for a shunt active filter. Based on the proposed control algorithm, the active filter drains controlled currents in order to improve the performance of the passive filters and also to minimize a specific harmonic component of the system voltages. The controlled currents produced by the active filter are determined through the system voltages, together with the dc-link voltage. Load and system currents are no more measured. The control algorithm derives from the instantaneous power theory (pq-Theory), together with a synchronizing circuit. Comparative to similar algorithms observed in literature, the introduced one is simpler to be implemented since load-and system currents are no measured. Simulation results involving a selective active filter, with the proposed control algorithm, are presented in order to analyze its performance in transient and steady-state conditions.

Semantic domains based on sets with families of equivalences

This paper contains a preliminary study of a class of spaces that can be seen as special cases of metric spaces. These spaces seem to cover all practical needs, as exemplified e.g. by the work in 2]. Their interest lies mainly in the fact that the degree of mathematical sofistication required to develop the theory is quite small, at least as compared to the metric case. The paper recreates part of the theory developed for metric spaces, ending with a fixed-point theorem that can be used for solving “domain equations”, and a final coalgebra theorem.