Research On The General Airgap Field Modulation Theory For Electrical Machines And Its Application Methods

The existing classical analysis theories of electric machines lack universality and unity,and features fragmentation.In the meanwhile,without powerful theoretical guidance,the analysis,design and innovation of electric machine principles and structures are confronted with certain blindness,contingency,overreliance on empirical knowledge and low efficiency.In addition,there are urgent need for expanding applications,improved electromagnetic performance requirements,and the emergence of newly-emerged electric machines featuring different principles and structures.Therefore,it is with practical significance and value to develop a generalized theoretical framework and has become an intrinsic need for the development of the electrical engineering,based on the essence of electromechanical energy conversion across the airgap,to generalize and unify the magnetic field modulation phenomenon and map it to specific electric machines.The general airgap field modulation theory has wide applicability and provides a brand new perspective and powerful tool of assisting the invention,analysis and design of almost all newly-emerged topologies.After several years of research and development,the basic framework of the general airgap field modulation theory for electric machines has been basically shaped,which is complementary to existing classical analysis theories,enriches the research content of the electrical engineering and promotes its further development.The newly-emerged topologies proposed based on the general airgap field modulation theory offer high torque density,high operation efficiency and compact structure,showing unique advantages and qualified application prospects in the fields of electric vehicles,wind power generation and servo control etc.This dissertation is closely based on the general airgap field modulation theory,analyzes the operation mechanism and general principles based on the in-depth understanding of the magnetic field modulation phenomenon,reveal the modulation behaviors and torque production mechanism,investigate the equivalence and interchangeability of different modulators etc.,in order to enrich and improve the airgap field modulation theory.In addition,this dissertation researches how to apply the general airgap field modulation theory to calculate electromagnetic performances,reveal the nature of magnetic field modulation behaviors,guide electric machine optimization,etc.,that is,to study the application method of the general airgap field modulation theory.The research results of this dissertation are as follows:1.The dialectical relationship between magnetic field modulation behavior and torque components is elucidated.Based on the judgment of the magnetic field modulation behavior natures and the analysis of torque production mechanism,the synchronous modulation and asynchronous modulation behaviors,synchronous torque and asynchronous torque components are defined,on basic of which the key differences between the modulation behaviors and torque components are compared,analyzed and revealed.The torque components of typical magnetic field modulated machines are summarized and classified based on the general airgap field modulation theory.The relationship between the magnetic field modulation behaviors and the torque components is analyzed dialectically.2.The basic laws such as equivalence and interchangeability between different modulators are revealed.On account of the knowledge of the mathematical properties of the modulation operators for different modulators,the basic magnetic field modulation behavior characteristics of the salient pole reluctance/flux barriers/short-circuited coils are systemetrically summarized.The general principles such as the relationship between the modulator magnetic field modulation ability and its own parameters,the pole pair combination are compared to reveal the equivalence and difference between different modulators.Finally,the electromagnetic performance comparison after modulator interchangeability is investigated.3.The effectiveness and unity of the general airgap field modulation theory is quantitatively verified.Applying the general airgap field modulation theory,the unified framework for performance analysis is proposed based on which the magnetic field modulation behaviors of typical electric machines featuring salient pole reluctance/flux barriers/short-circuited coils are studied and the main electromagnetic performances,such as the modulated airgap field distribution,back electromotive force,torque and inductance characters are theoretically calculated.The influence of modulator parameters on the output characteristics is discussed,and an in-depth analysis of the magnetic field modulation efficiency of different modulators is carried out to verify the validity and consistency of the general airgap field modulation theory from a quantitative perspective.In addition,the internal connection between conventional and newly-emerged magnetic field modulated machines is revealed.4.In-depth analysis of the mechanism of the three basic elements acting together is provided.The mechanism of the three basic elements in an electric machine acting separately and together is investigated based on the magnetic field modulation phenomenon in the airgap.The variation on the overall modulation effects influenced by the individual elements is illustrated by representative examples.The mutual coupling relations and constraints of the three elements,such as the local saturation in modulator caused by the source or filter,the torque components determined by the unequal-width and modular salient poles,and the principal pole pair number matching relation between source and filter are theoretically analyzed.The modulation functions considering local saturation and unequal-width/modular salient poles are improved,and corresponding modulation behaviors are introduced.The effective harmonic components of modulated airgap field with summation and differential modulations are listed.5.The optimization law of rotor salient pole reluctance modulator is summarized.The possibility to improve the modulated airgap fields,selectively increase the effective harmonic components,enhance the output torque capability and reduce the torque ripple for electric machines featuring salient pole reluctance modulator from the perspective of the general airgap field modulation theory by modifying the salient rotor pole is investigated.General modified rotor pole configuration advices for the typical magnetic field modulated machines are proposed based on the torque production mechanism,and the optimal modulator parameters are different with varying pole pair combination while the modified rotor pole configuration and scopes modulator parameters keep unchanged,saving finite element analysis computational cost and providing general initial design together with further optimization guidance.6.The design method for the asymmetric composite rotor modulator is proposed.The modulation behavior of the composite modulator is analyzed from the perspective of the magnetic field conversion mechanism based on the knowledge of the brushless doubly-fed machine general properties.The magnetic field modulation capability of the composite modulator is evaluated and the modulated airgap harmonic phase shift phenomenon caused by the short-circuited coil modulator is firstly verified in detail.Based on the theoretical investigation,a general method for the modified asymmetrical composite modulator is proposed,and the modulated airgap field distribution together with the torque character comparison of brushless doubly-fed machine is presented to show the effectiveness.