航空三级式无刷同步电机单相交流励磁特性研究OA

The single-phase AC excitation method is one of the leading solutions to the excitation problem during the starting process of the wound rotor synchronous starter/generator(WRSSG).It does not need to change the structure of the main exciter(ME),has low requirements for the excitation power supply,and is easy to implement.The single-phase AC excitation method transfers energy to the rotor side through a pulsating magnetic field.Due to the presence of nonlinear components in the ME rotor circuit,the operating mechanism of the circuit is complex.After analyzing the basic principles and working characteristics of single-phase AC excitation methods,this paper proposes starting excitation strategies. Firstly,the performance requirements for ME in the starting mode are proposed,and the parameters of the 12 kV·A WRSSG are introduced.Then,similar to a single-phase asynchronous motor,the ideal mathematical model of a single-phase ME is established,and the ME's no-load rotor EMF is derived. The brushless excitation system,composed of the ME,rotating rectifier(RR),and main generator(MG)field winding,is a nonlinear,multivariable,and strongly coupled system.To accurately calculate the performance of the single-phase ME brushless excitation system,a field-circuit coupling simulation model is established.ME is modeled using the finite element(FE)method,while RR and MG field windings use a circuit model.Through parameterized simulation,the influence of the excitation voltage Uef and the excitation frequency f1 on the performance characteristics of the single-phase AC excitation method is explored. Simulation results show that the higher the excitation voltage Uef,the higher the ME excitation current Ief and ME output current IF.The excitation efficiency η slightly increases as Uef increases.Moreover,Uef does not influence the variation trend of the ME output current IF with the machine speed n.The excitation frequency f1 has a significant influence on the characteristics of the single-phase AC excitation method.When the excitation frequency is low,the IF-n curve of ME is close to that of DC excitation,and IF increases with the increase of n.When the excitation frequency is high enough,the ME output current almost does not vary with speed changes,a characteristic known as an approximate"constant current source".In this condition,the electromagnetic torque of ME is minimal,close to 0,but the output current and excitation efficiency are not high.Accordingly,two single-phase AC excitation strategies are proposed:(1)Using the"constant voltage and constant frequency"strategy throughout the whole starting process.(2)Using the"constant voltage and constant frequency"AC excitation in the low-speed stage,and using the"variable voltage and constant frequency"AC excitation in the high-speed stage to achieve online flux weakening. Finally,a 12 kV·A WRSSG prototype is manufactured.The experiments involving different speeds,excitation voltages,and excitation frequencies are carried out.The results align well with the simulation results,proving the accuracy of the established FE field-circuit coupling simulation model. The following conclusions can be drawn.(1)When f1 is greater than 0.5fm,the ME has the characteristics of an approximate"constant current source",without the need for real-time adjustment of the external excitation power supply.(2)When f1 is greater than 0.5fm,the drag torque generated by ME is small,which reduces the burden of MG during the starting process.(3)The output current and excitation efficiency of the ME are not high,and the excitation efficiency is about 0.1 to 0.3.