Design and Optimization of a High Performance Isolated Three Phase AC/DC Converter
In modern aircraft power systems, transformer rectifier units are widely adopted to perform AC/DC power conversion while also providing galvanic isolation. Recent research shows that active rectifiers are promising replace-ments for transformer rectifier units concerning efficiency and weight. Fur-thermore, active rectifiers can perform online current shaping and output voltage regulation, which is out of reach for transformer rectifier units. To exploit the benefits of active rectifiers, converter design and optimization should be carefully made under the requirements of aircraft applications: electromagnetic interference (EMI) standards, power quality standards, etc. Moreover, certain applications may have strict limits on converter specifica-tions: weight, size, converter loss, etc. This paper focuses on the design and optimization of a free convection cooled isolated three-phase active AC/DC converter that delivers maximum power within the given dimensions (8 inches * 7.5 inches * 1 inch), loss (35 W) limits and operation (EMI, power quality) requirements.
A two-stage structure (shown in Fig. 1), where an active front-end (AFE) converter is joined with an isolated DC/DC converter, was employed in this design. The AFE stage converts a three-phase variable frequency (360 Hz ~ 800 Hz) AC voltage (115 Vrms) into a regulated DC voltage while perform-ing a power factor correction for the inputs. An isolated DC/DC stage con-verts internal DC bus voltage into output DC bus voltage (28 V) while providing galvanic isolation. Input EMI filters were added to meet EMI standard. A complete design and optimization method was developed in search of the relationship between the converter rated power, full load loss and converter size of this multi-converter system. A 1.2 kW converter proto-type (shown in Fig. 2) was constructed based on the design and optimization results. The 1.2 kW free convection cooled prototype exhibits a 97.1% full load efficiency and a 22 W/inch3 power density. The compliance of EMI standards and power quality standards was verified experimentally.