Internal Design of a Class of Self-Excited Synchronous Generators

Licentiate thesis, 2006

INTERNAL DESIGN OF A CLASS OF SELF-EXCITED ABSTRACT With the increasing trend of distributed generation and the need for alternative and renewable energy sources, self-excited induction and synchronous reluctance generators have attracted more attention for wind, tidal and hydropower applications. This thesis is concerned with the development of a class of self-excited synchronous reluctance generators (SRG). The work provides a review of induction and synchronous generators with emphases on their ability to provide output voltage without having a dedicated exciter. Preliminary test results obtained from an experimental machine that was connected to yield a self-excited synchronous generator are presented and discussed. The shortcomings of the self-excited synchronous generator are identified as: output voltage harmonics and the risk of instable operation. Internal design parameters that have most effect on generator performance are identified and investigated. This has yielded modifications to both the stator and rotor. When such modifications are implemented, the resulting machine would exhibit a significant reluctance effect and, therefore, is referred to as synchronous reluctance generator (SRG). The advantages and disadvantages of soft magnetic composite materials (SMC) are discussed together with their possible effect on the SRG performance. The concept of SRG described in this thesis not only has the advantages of simplicity and ruggedness, but can also have enhanced steady-state characteristics and high efficiency over a wide range of operation. Additionally, its output frequency is determined only by the prime mover speed and this enables integration with power electronic devices to realise control schemes more economically. This proposed design provides a competitive alternative to both induction and conventional brushless synchronous generators used in stand-alone applications.