Analysis of Double-Bridge Inverters for Drive Systems With Open-End Winding Motors

The double-bridge voltage source inverter (DB-VSI) is a promising inverter topology for high performing motor drives. A DB-VSI comprises two VSIs, connected to the opposite sides of an open-end winding motor (no floating neutral point). Due to its inherent properties, a DB-VSI requires only half dc supply voltage, compared with a simple VSI, in order to generate the same motor voltage. Thereafter, by processing/switching only half of the dc supply voltage, the DB-VSI benefits from significantly lower semiconductor devices’ switching losses. The DB-VSI technology is the main focus of this article. Namely, two different DB-VSI variants and/or modulation strategies are comparatively evaluated. After detailing the operating principle of each modulation strategy, the stresses on the inverter components are analytically derived. It is shown that the selection of the DB-VSI modulation strategy impacts the efficiency/power density of the inverter and the voltage quality of the motor. The theoretical considerations are subsequently verified within the context of a high-speed motor drive. In the investigated drive system, a fuel-cell supplies the inverter, which in return controls a 280-kr/min 1-kW electric compressor. Two DB-VSI hardware prototypes are purposely assembled and compared against a third state-of-the-art hardware prototype of the same specifications. It is shown that due to the DB-VSI technology, it is possible to reduce simultaneously the volume and the losses by up to 50% compared with the state-of-the-art solution. The low DB-VSI volume enables a seamless integration of the inverter in the motor housing. Accordingly, the open-end winding motor is directly attached to the inverter, eliminating the need for cumbersome and costly interconnecting cables. A final, integrated (inverter/motor) hardware prototype is presented, which further highlights the advantages of DB-VSI technology.