Lately, there has been increased interest in hybrid excitation electrical machines. Hybrid excitation is a construction that combines permanent magnet excitation with wound field excitation. Within the general classification, these machines can be classified as modified synchronous machines or inductor machines. These machines may be applied as motors and generators. The complexity of electromagnetic phenomena which occur as a result of coupling of magnetic fluxes of separate excitation systems with perpendicular magnetic axis is a motivation to formulate various mathematical models of these machines. The presented paper discusses the construction of a unipolar hybrid excitation synchronous machine. The magnetic equivalent circuit model including nonlinear magnetization curves is presented. Based on this model, it is possible to determine the multi-parameter relationships between the induced voltage and magnetomotive force in the excitation winding. Particular attention has been paid to the analysis of the impact of additional stator and rotor yokes on above relationship. Induced voltage determines the remaining operating parameters of the machine, both in the motor and generator mode of operation. The analysis of chosen correlations results in an identification of the effective control range of electromotive force of the machine.

The hybrid excitation synchronous motor (HESM), which aim at combining the advantages of permanent magnet motor and wound excitation motor, have the characteristics of low-speed high-torque hill climbing and wide speed range. Firstly, a new kind of HESM is presented in the paper, and its structure and mathematical model are illustrated. Then, based on a space voltage vector control, a novel flux-weakening method for speed adjustment in the high speed region is presented. The unique feature of the proposed control method is that the HESM driving system keeps the q-axis back-EMF components invariable during the flux-weakening operation process. Moreover, a copper loss minimization algorithm is adopted to reduce the copper loss of the HESM in the high speed region. Lastly, the proposed method is validated by the simulation and the experimental results.

To further enhance the speed regulation range of the hybrid excited machine (HEM), the structure of a magnetic ring is optimized using a combination of the magnetic circuit method (MCM) and numerical analysis method in this paper, and a disc magnetic ring (DMR) is proposed. The magnetic density distribution of the proposed disc magnetic ring hybrid excited machine (DMRHEM) is compared to the radial-axial hybrid excited machine (RAHEM), and the superiority of alleviating a saturation problem in the proposed DMRHEM is determined. To improve the power density, the spoke-type permanent magnet (PM) rotor is applied. The influence of the proposed DMR on the HEM is analyzed, and the field adjustment capability of the proposed DMRHEM is better. Based on this, by combining the bypass principle, the analytical expressions for the relations between the rotor pole-pair number and the motor axial length/stator inner diameter (MAL/SID) as well as flux regulation capability are derived to further explore the superiority of the proposed DMRHEM. The influence mechanism of the rotor pole-pair number and the MAL/SID on the proposed DRMHEM is determined. The optimal MAL/SID and pole-pair number are obtained.