Theory And Design Research Of Brushless Doubly-fed Machines Based On Magnetic Field Differential Modulation

Brushless doubly-fed machine(BDFM)is a new kind of multifunctional induction motor with good application prospect.The previous researches on the magnetic field modulated brushless doubly-fed machines are all based on additive modulation,that is,the equivalent pole pairs is equal to the sum of the power winding pole pairs p_p and the control winding pole pairs p_c.This makes the brushless doubly-fed machibe can only be applied to low speed occasions in the power frequency condition,and the range of speed adjustment is also limited.The differential modulation brushless doubly-fed machibe can achieve a lower equivalent pole pairs and a higher speed range because the equivalent pole pairs si equal to p_p and p_c minus.In addition,the power density will also increase with the increase of the speed.The key obstacle to the development of differential modulation brushless doubly-fed machines is the design of the rotor.It is impossible to design a differential modulated rotor with ideal performance by using the current mainstream additive modulated rotor design methods.Therefore,the purpose of this paper is to study the basic theory of the differential modulation brushless doubly-fed machines in depth,and find a new way to explore an effective rotor design scheme to realize the stable operation of the brushless doubly-fed machine in the differential modulation mode so as to improve its natural synchronization speed and speed range.Then expand the application field of brushless doubly-fed machine and promote its practical process.The research contents of this paper are summarized as follows:Firstly,the background of the topic is introduced,and the necessity of the research on the differential modulation brushless doubly-fed machine is expounded.The development history of brushless doubly-fed machine is summarized.The relevant domestic and foreign research status is summarized.Secondly,the basic principle of differential modulation is analyzed.The‘negative number’characteristic of differential modulation brushless doubly-fed machine is proposed,and the cascade asynchronous torque generation mechanism is analyzed.Based on the steady-state equivalent circuit model,the cascade asynchronous torque is calculated,the cause of the"negative poles"phenomenon is explained,and the influence of the steady-state circuit parameters on the asynchronous start-up performance is discussed,and the relevant suggestions are given.The power transmission characteristics of differential modulation brushless doubly-fed machine system under different speed and pole-pair number distribution conditions are analyzed.Then,the transient mathematical models of the differential modulation brushless doubly-fed machines in ABC stationary coordinate system and dq0 rotating coordinate system are derived.By using the deduced motion equation to build a Simulink simulation model,the correctness of the mathematical model is verified by the simulation results of different operating modes of the differential modulation brushless doubly-fed machine.Then,the selection principles of pole-pair number and slot number are discussed and the stator windings of 1/4 pole pairs and 3/2 pole pairs brushless doubly-fed machines are designed.And after a certain exploration attempt,two different new methods are used to design and optimize 1/4 pole pairs and 3/2 pole pairs differential modulation rotors respectively.Through the theoretical analysis of magnetomotive force harmonics,the two rotor windings designed by the new method meet the requirements of differential modulation.Finally,based on the stator and rotor schemes of 1/4 pole pairs and 3/2 pole pairs differential modulation brushless doubly-fed machine,the corresponding experimental prototypes were developed respectively,and the finite element models are established according to the design parameters.Combined with the analysis of finite element simulation results and experimental results,the feasibility of differential modulation operation mode and the effectiveness of the design scheme are verified.