A Multi-Mode Stacked-Switch Inverter/Rectifier Leg for Bidirectional Power Converters

The development of renewable energy systems (e.g. wind and solar) is significant to cope with an energy crisis yet, at the same time, it presents challenges to the grid for their MW-scale integration due to their volatile characteristics. Battery energy storage systems are essential in providing sustainable power and improving the overall system reliability effectively with the large deployments of renewable energy conversion systems. Bidirectional power converters are responsible for transferring power between the battery energy storage system and the grid. Selecting an efficient and cost-effective power topology along with a reliable control system is critical to ensure that the energy storage system operates safely with prolonged service life and minimized maintenance cost. In this dissertation, a multi-mode stacked-switch leg with soft-switching capability for use in bidirectional DC/DC converters is proposed for battery energy storage applications. This dissertation consists of three parts. The first part focuses on the development of a bidirectional soft-switched converter utilizing a CLLC resonant circuit and the proposed multi-mode switching legs. The presented leg is able to facilitate multiple operating modes to enable high voltage gain under different operating conditions and allow the converter to operate with a much lower output voltage ripple (50%) compared with the conventional stacked-switches-based converter topology. In the second part of this thesis, a fault-tolerant control scheme is proposed which enables seamless post fault operation of the presented multi-mode DC/DC converter if any switches in the presented leg experience an open-circuit fault. In the third part of this thesis, a comprehensive hybrid control system is proposed so that the overall voltage gain range of the converter is widely extended with a narrow switching frequency range (less than 10% of the base frequency), while at the same time, the efficiency of the converter is improved over the whole gain range (more than 1%). The operating principles and characteristics of the proposed converter and the proposed control schemes are explained in detail in this thesis. The performance of each of the presented circuit and control concepts is verified through simulation as well as experimental results on silicon-carbide (SiC)-based proof-of-concept hardware prototypes.