Proposition of Structures for Brushless Hybrid-Excitation Synchronous Motors With Improved Rotor

Recently, studies on the hybrid excitation synchronous motor using permanent magnet (PM) together with field windings have been actively conducted. In this regard, this paper seeks to investigate brushless hybrid excitation synchronous motors with improved rotors. The design was performed using an equivalent magnetic circuit to determine the best of four possible different structures. Using a finite-element analysis (FEA), the back electromotive force (EMF) per PM usage and the phase back EMF of each type were calculated and compared, and the design that can best reduce costs and increase torque density was determined. A detailed design of one of the four structures with excellent characteristics was performed, and the associated characteristics and problems were verified. An improved rotor structure was proposed to resolve the identified problems and improve performance. The phase back EMF and the total harmonic distortion of the phase back EMF, cogging torque, load torque, and torque ripple of the improved rotor structure were verified through the application of the FEA. In addition, the prototype motor was fabricated, and a no-load test was conducted to compare the test results and analysis results on the phase back EMF. The reliability of the analysis results was confirmed by comparison between test results and analysis results on the input current, line to line voltage, and efficiency under the same output conditions through the load test.