Contributions to power conditioning tecniques in two-phase three-wire eletric networks

Abstract

This doctoral thesis deals with power conditioning applications in two-phase three-wire electric circuits derived from three-phase four-wire systems. This kind of application can be useful in modern electricity networks, specially for residential and small commercial consumers. An adaptation of the pq Theory is proposed to use the concepts of instantaneous powers in twophase three-wire circuits. A linear transformation is proposed to map two-phase voltages and currents into an orthogonal ab reference frame. Time-domain mathematical analyses are used to present the behaviour and interpretation of two-phase instantaneous powers, comparing the proposed definitions with single-phase and three-phase instantaneous powers theories found in the literature. The concepts of two-phase instantaneous powers are used to design algorithms to control a shunt grid-connected converter, specially to be used as active power filter. It is also proposed an algorithm to detect fundamental-frequency positive-sequence voltages by measuring only two phase-voltages of the grid. Two different strategies are presented to control the shunt active power filter: double single-phase strategy and zero neutral current strategy. The adapted two-phase positive-sequence detector is implemented in a laboratory prototype and experimental results validate the effectiveness of the proposed positive-sequence detector. Simulation studies are also performed to validate the proposed control algorithms for two-phase power conditioning equipment. The obtained results confirm the effectiveness of the two proposed control strategies to compensate load reactive power and currents’ harmonic components and unbalances. Furthermore, the zero-neutral current strategy shows to be suitable to avoid or reduce zero-sequence unbalances in distribution grids and microgrids. Proposals for future studies include further experimental implementation, active power injection applications and field measurements to evaluate the influence of zero-sequence voltage unbalances in the proposed controllers.