Dovetail rotor poles in synchronous permanent magnet and reluctance machines

Abstract

Robust synchronous permanent magnet and reluctance machine designs are developed. In the designs, the rotor structure is simple and strong and the leakage flux is relatively small. For the new design solution, a dovetail form-blocked rotor structure, specific analyzing principles are also developed. The dovetail designs are shown to be good solutions with their lower leakage flux and at least the same strength against centrifugal forces as the conventional rotor solutions. The compared conventional solutions considered have inseparable rotor sheets in which the parts of the rotor are kept still by using bridges between them. In the dovetail rotor, the forms of the rotor parts keep them together and no bridges between them are needed for support. The simplicity of the dovetail solution has also been kept the same or better. In addition, the manufacturing method is the same for both solutions. The dovetail design can also be used for saving the magnetic material of permanent magnet synchronous machines because it has a smaller leakage flux than the conventional V-shaped designs with supporting bridges. The problem of how to compare the dovetail designs to the conventional ones is considered in depth. The strength of the dovetail structure has to be defined in a different way than in the conventional design with supporting bridges. In bridge-fixed design, the strength of the bridges is critical for rotor durability but in the dovetail design wider areas of the rotor affect the strength of the rotor. However, the basic electrical properties could be defined with the same method. Additional methods for defining the electrical properties of dovetail designs are also considered. One method is that the load angle can be defined only from the forms of phase currents in delta-connected synchronous machines and phase voltage and current in star-connected synchronous machines. The load angles defined are successfully used to find a good model for the test results. The other method is to view the normalized local torque density in the air gap as a function of time. In this work, several dovetail synchronous reluctance and permanent magnet machines are designed, manufactured, tested, and analyzed. The design, manufacturing, testing, and analysis methods are defined and developed especially for dovetail designs.