Excitation system technologies for wound-field synchronous machines: Survey of solutions and evolving trends

Wound-field synchronous machines (WFSMs) are included in the majority of large power generating units and special high-power motor drives, due to their high efficiency, fiexible field excitation and intrinsic fiux weakening capability. Moreover, they are employed in a wide range of high-end solutions in the low-to-medium power range. This contribution presents a comprehensive survey of classical and modern methods and technologies for excitation systems (ESs) of WFSMs. The work covers the fundamental theory, typical de-excitation methods and all the modern excitation equipment topologies in detail. It also includes a description of the state-of-the-art and the latest trends in the ESs of wound-field synchronous motors and generators. The purpose of the paper is to provide a useful and up-to-date reference for practitioners and researchers in the field.