Isolated swiss-forward three-phase rectifier for aircraft applicationsanalysis, design and validation

Resumen

In the last decades, there has been important interest in improving electrical system both in commercial and military aircrafts. These improvements have been driven by economic and environmental issues because replacing mechanic, pneumatic or hydraulic actuator by electric systems bring efficiency improvements reducing CO2 emissions and flying costs. The tendency of replacing mechanical, pneumatic and hydraulic system by electric one is commonly called MEA or more electric aircraft. In addition, electric actuators are more reliable and require less costs in maintenance. In aircraft applications, the electric power distribution is done using either three-phase or dc sources. Classically, the ac power line uses 115Vac and in dc the voltage used is 28Vdc. However in some of the modern aircrafts, the voltage levels have been increased to 230Vac and 270Vdc and 540vdc, in order to reduce the weight of the wiring. Following the MEA concept, this work analyses and develop a new converter topology of an isolated threephase rectifier focusing in aircraft applications. As reference design for the analysis and development of an experimental demonstrator prototype, this work considers a three-phase main of 115Vdc @ 400Hz and 270Vdc for the output voltage and a load power of 3.3kW. In this work, different solutions of an isolated three-phase rectifier have been studied including passive rectifiers, a two-stage topology or a single stage configuration. The two-stage topology can be assemble using an active rectifier with an isolated dc-dc converter or using a diode bridge plus an active power filter with an isolated dc-dc converter. On the other hand, in a single stage configuration both the ac input current shaping and the output voltage control are performed by the same converter leading to a less complex and more reliable and more efficient system. In this work, a single stage solution has been selected because this kind of configuration have several benefits in terms of efficiency, simplicity and power density. There are several single stage isolated three-phase rectifiers in the power electronic literature, they can be classified in three groups: the DCM type, Matrix-type and Unidirectional family. In aircraft applications, the unidirectionally is needed because it is not allowed regenerate power back to the acside, for this reason Matrix-type rectifiers have been discarded. DCM rectifiers do not have current-voltage angle compensation therefore at light load these systems have a poor power factor. In this work, a new isolated three-phase rectifier that belong to the unidirectional family has selected. The Swiss Forward rectifier is an adaption of the novel non-isolated Swiss rectifier. In order to add the isolation feature in the system, a forward converter with resonant reset has been used because this topology allows to take advantage of the new semiconductor material such as the SiC. In this work, the principle of operation of the Swiss-Forward rectifier is discussed as well as a converter modulation that allows the current-voltage angle compensation. In addition, in this work is discussed a reduce order model of a buck-type rectifier system is used to design of the control. Finally, a demonstrator prototype has been designed and the experimental results obtained with prototype confirm that the proposed rectifier topology is a good alternative to classical single stage topologies.