Isolated Swiss-Forward three-phase rectifier for aircraft applications

Recently an important increase of the electrical equipment in modern aircrafts is leading to an increase in the demand for electrical power. The usual electrical power distribution in aircraft applications is done via a three-phase 115Vac grid. A new trend of DC distribution is emerging employing a 270 Vdc grid. This yields the need for high-efficiency and high power-density AC-DC converters, connecting the two grids while providing galvanic isolation. Traditionally 12-pulse autotransformer passive rectifiers are used in aircraft applications. This converter is robust and highly reliable, however it is a non-controlled topology and it is relatively heavy because of the low frequency power transformer. Two-stage rectifier system approaches, employing three-phase PWM rectifiers or active filters and isolated DC-DC converters, are good alternatives to be applied in aircraft applications, to reduce the weight by using high frequency transformers and inductors. However, two-stage topologies process the energy twice leading to lower efficiency, power density. The reliability is also not very high due to a high semiconductor component count. This paper presents a new isolated single-stage PWM rectifier system, based on the recently presented non-isolated Swiss rectifier topology, called the Swiss-Forward rectifier. The principle of operation of this converter topology is presented together with detailed design guidelines and experimental validation on a 3.3kW 115Vac to 270Vdc prototype.