*Article* **An Extremely High Power Density Asymmetrical Back-to-Back Converter for Aerospace Motor Drive Applications**

**Yifan Zhang 1, Chushan Li 1,2, David Xu 3, Wuhua Li 1, Jian Zhang 1,\*, Hao Ma 1,2 and Xiangning He <sup>1</sup>**


Received: 26 January 2020; Accepted: 3 March 2020; Published: 10 March 2020

**Abstract:** Higher-voltage-standard and higher-power-rating aerospace power systems are being investigated intensively in the aerospace industry to address challenges in terms of improving emissions, fuel economy, and also cost. Multilevel converter topologies become attractive because of their higher efficiency under high-voltage and high-switching-frequency conditions. In this paper, an asymmetrical-voltage-level back-to-back multilevel converter is proposed, which consists of a five-level (5L) rectifier stage and a three-level (3L) inverter stage. Based on the comparison, such an asymmetrical back-to-back structure can achieve high efficiency and minimize the converter weight on both rectifier and inverter sides. A compact triple-surface-mounted heatsink structure is designed to realize high density and manufacturable thermal management. This topology and structure are evaluated with a full-rating prototype. According to the evaluation, the achieved power density is 2.61 kVA/kg, which is 30% higher than that of traditional solutions. The efficiency at the rated power of the back-to-back system is 95.8%.

**Keywords:** more electric aircraft (MEA); multilevel converter; high power density
