Research On Characteristics Of Novel Hybrid Excitation Synchronous Machines

Hybrid excitation is an organic combination of permanent magnet excitation and electric excitation. While maintaining the merits of permanent magnet synchronous machine (PMSM), hybrid excitation synchronous machine (HESM) also combines the regulation capacity of air gap magnetic field and has important potential application prospects in aviation and space, alternative energy power generation, motor drive and other fields. Study of reasonable HESM structure is an important part in promoting the development and application of HESM technology. New HESM structure and topology is discussed in this paper. In-depth study into magnetic circuit calculation, 3D finite element analysis, structure optimization, modeling methods are presented and verified by experiments and analysis.Excitation features of hybrid excitation machines are described and common requirements are summarized. Based on two typical structures of PMSM, magnet-shunting radial structure HESM and magnet-shunting tangential structure HESM are proposed. Detailed elaboration of structure characteristics and operational principles are given. Regulation principle and operational feature of the air gap magnetic field are analyzed according to the radial/axial distribution of magnetic field.Equivalent magnetic circuit models of magnet-shunting HESM under different excitation are constructed and equivalent magnetic circuit calculation program are completed to get the magnetic circuit state and no-load output characteristics of the machine. Basic constraint relation affecting the new type of machine is deduced and systematic research of influence law on magnet regulation features by key structure parameters, such as rotor length-diameter ratio, pole number, permanent magnet structure parameters, main air gap/additional air gap length, section area of rotor magnetizer extension, are carried out. Basic methods of determining excitation magnetic potential based on armature reaction calculation is studied and regulation characteristics curve under loads with different features.A 3D finite element model of the new magnet-shunting HESM is constructed with MAXWELL 3D. Through comprehensive analysis of static magnetic field, good air gap magnetic field regulation capacity is verified; variation characteristics and rules of internal magnetic field distribution under bi-directional excitation magnetic potential is deduced; optimization methods and principles of magnetic bridge, rotor magnetizer and some other structures are introduced. The method of adding compensation alnico is proposed to address flux linkage of rotor magnetizer. Research findings indicate that compensation alnico can effectively increase air gap flux density and has little influence on magnetic field regulation range. A 3D transient field circuit coupled analysis model of magnet-shunting tangential structure HESM is constructed. Simulation analysis and experiment verification of no-load output characteristics, external characteristics and short-circuit characteristics are carried out. Methods of calculating synchronous reactance based on transient field analysis are studied and MATLAB/SIMULINK model of tangential structure HESM are built with calculation results of static magnetic field and voltage equation, which provide important analysis means to simulation analysis and rapid calculation of closed-loop systems of this new type of machine.A novel coordinate structure HESM is proposed. Internal magnetic field distribution features are studied by 3D finite element calculation and design principles of iron core length are reached by comparison analysis. Axial flux leakage, a problem unique to coordinate structure HESM is pointed out and variation principle of axial flux linkage under bi-directional excitation is revealed by 3D static magnetic field analysis, providing theoretical references for determining the axial distance between permanent magnet and electric excitation.A BLDC generator structure is proposed consisted of a synchronous generator with common-anode 12-phase half-wave rectified output. Systematic comparison of features such as generator losses, rectifier diode current stresses and fault-torelent ability are carried out under 6-phase double-star rectified output and 12-phase zero-type rectified output structures, which demonstrate the superiority of 12-phase zero-type rectified output BLDC generator's application in low voltage DC power system. 3D field-circuit coupled analysis and experiment verification of coordinate structure hybrid excitation BLDC machine are presented, which shows that the machine inherits permanent magnet machine advantages of low voltage regulation ratio and good complementary regulation capacity of excitation current. It also has been pointed out that with the coordinate structure HESM, rotor magnetic poles should be precisely even, so as to avoid phase electric potential distortion, which will undermine output voltage quality.