Aportaciones a los acondicionadores activos de corriente en derivación para redes trifásicas de cuatro hilos

Résumé

The aim of this work is to find some solutions in order to improve the behavior of the shunt active power filters in three-phase four-wire power systems, even if adverse conditions are present in the utility voltages or in the load currents. The calculation of the instantaneous electrical power under non-sinusoidal conditions is the basis in the analysis of power conditioners. At present, there is not a universal theory that unifies the calculation of the instantaneous power and current components. In this work, a detailed study on this field is conducted, showing the relationship between the different conventional theories, and proposing a new formulation, which offers a higher physical meaning for the calculated power and current components than if previous theories are used. The knowledge about the positive-sequence fundamental-frequency component of the utility voltage is a crucial matter in the synchronization of power electronics systems interfaced to the utility. This work presents a new detection system, which obtains, quickly and accurately, the positive-sequence fundamental-frequency utility voltage, even if utility voltage is severely distorted and unbalanced. A static converter, known as inverter, is the core of an active power filter. The potentialities of the filtering system are greatly conditioned by the technology of this inverter, by its topology, by the modulation technique, and by the characteristics of the control system that regulates the output variables of the inverter. This work proposes an alternative inverter topology suitable for active conditioners working in three-phase four-wire systems, which allows a simple control and cancels the problems shown by other topologies when zero-sequence currents are injected in the utility. Also, a new approach on the space vector modulation of three- and four-leg full-bridge inverters is proposed. The proposed technique offers a higher physical meaning than previous techniques in the synthesis of the inverter output voltage, and gives rise to a very efficient algorithm, which can be implemented in a low-cost processor. Finally, this work offers a new standpoint in the calculation of the reference currents of the active power filter. An analysis of the instantaneous power flow when the active power filter is working under generic utility voltage and load current, gives rise to a new control system, which employs an energy approach in the reference currents calculation. This energy control increases the robustness of the active power filter when sudden variations appear in the environment conditions.