Research Of The Controllable Exciting Flux-Switching Motor For MW-Class Semi-direct Driven Wind Power Generation System

The stator excited machines,whose armature windings,excitation windings and permanent magnets(PMs)are all placed on the stator while the rotor is only composed of low cost iron,has simple structure and high reliability.Hence,they are widely concerned and more and more used in wind power generation system(WPGS).Among them,the electrically excited flux-switching(EEFS)machines and hybrid excited flux-switching(HEFS)machines have good application prospects in WPGS because of their advantages of sinusoidal back-EMF and adjustable magnetic field.Based on the requirement of the generators used in MW-class semi-direct driven WPGS,a 48/28 poles EEFS machine is proposed firstly.Its air-gap magnetic field characteristics are analyzed,and its electromagnetic characteristics and output characteristics are studied by finite element analysis(FEA).The results show that when used in WPGS,this machine can maintain constant output power and voltage and high output efficiency by changing the winding connection mode and the magnitude of excitation current.However,it has the problem of insufficient overload capacity.Secondly,based on the size and structure of MW-class EEFS machine,a traditional HEFS motor is designed.The effects of the PM length as well as the iron-bridge thickness on the electromagnetic characteristics and efficiency of the HEFS machine are studied.Besides,the advantages and disadvantages of this machine in WPGS are compared with those of EEFS machine.The comparison results show that the overload capacity of HEFS machine is much higher than that of EEFS machine.However,due to the contradiction between PM magnetic circuit and excitation magnetic circuit,the efficiency of this machine can not be better than that of EEFS machine.To solve this problem,a new type of HEFS machine is proposed based on the traditional HEFS machine,and the electromagnetic characteristics as well as output characteristics of the aforementioned three types of machines are compared.It can be concluded that the new HEFS machine not only possess higher overload capacity and efficiency than the EEFS machine,but also has much higher magnetic regulation capacity and efficiency than the traditional HEFS machine with the same PM consumption.Finally,a high-power EEFS machine and a low-power improved HEFS machine are prototyped,and the no-load and load performances are measured.The experiments results and the simulation results show a good agreement.