Research On Key Techniques Of High Speed Switched Reluctance Motor

With the rapid development of science and technonlgy,researchers have paid more attention on high speed and super high-speed motor at home and abroad.High-speed motors have the advantages of small volume,high power density and connecting with the high-speed load or prime motor without variable speed device,which overcomes the traditional motor with large volume,needing gearbox and difficulty of maintenance,which won wide application in the field of high-speed directly drive.Switched reluctance motor(SRM)has simple structure,wide speed range,high reliability advantages,particularly suited to high speed operation,in aviation,flywheel energy storage,high speed centrifugal fan,air compressor,and many other high speed directly drive field has a unique advantage.When the SRM with conventional structure and materials running with high speed and high frequency,the core loss increases significantly leading to reducing motor efficiency,severe temperature rising,and even burning down the motor.For this reason,this paper focus on the design and key technology of high speed high power SRM(HSHP-SRM)used in direct-drive high-speed centrifugal blower and a series of work have been launched,mainly including the following contents:(1)In order to solve the problem of severe rotor temperature rising of high speed SRM,the 6-stator slots and 2-rotor poles is adopt that reduces the alternating magnetic field frequency of rotor core.The “torque dead-zone” of conventional 6/2 SRM was studied and the self-starting problem was solved by adopting the rotor shape with double air gap or gradual air gap.The principle of extending single-phase torque was analyzed.For the half-period conduction condition,there is a multi-phase conduciton interval.This paper proposes a multi-phase excitation method to solve the problem that the single-phase torque superposition method cannot consider the influence of phase coupling and stator yoke saturation on the resultant torque.The winding connection type will affect the phase sharing magnetic circuit to influence the resultant torque.This paper studies the influence of two different winding connection types on the starting resultant torque.(2)Loss is an important factor that causing the temperature rise of high-speed motor,and it has always been the key difficulty of high-speed motor.In this paper,the AC copper loss,iron loss and wind resistance loss of high-speed high power SRM are analyzed.For the winding copper loss,the analytical models with the consideration of skin effect,proximity effect and the magnetic field through the conductor is developed.Based on them,the influence of different parameters on winding loss has been studied.Due to the notch is wide,the main magnetic flux may go through part of the winding,which causes severe hot for the conductors near the notch.In this paper,several shcemes have been proposed to reduce the winding loss and their advantages and disadvantages have been analyzed.For iron consumption,based on the orthogonal decomposition iron consumption model,this paper analyzes the influence of high harmonics and the influence of DC bias on iron consumption.The influence of different winding connection type to iron loss have been analyzed,which shown that comparing with1N1 S the winding connection type of 3N3 S can reduce 31.8% total iron loss.For the wind resistance loss,based on the computational fluid dynamics(CFD)technique,the fractional and differential pressure resisting moments of the SRM salient pole rotor have been ayalyzed,which shown that the differential pressure resisting moment takes up 78% of the total wind loss.Finally,caps are added to the rotor end to reduce the wind loss.(3)Based on the calculation losses,the temperature rise of HSHP-SRM is analyzed,and the unidirectional fluid-solid coupling model is established.The temperature field of motor parts are shown with forced air-cooling.Then based on the salient rotor pole structure,an oblique pole structure is proposed to obtain the fored air cooling effect.The simulation shown that the double oblique pole structure does not reduce the output torque of the SRM but can effectively reduce rotor temperature rise.(4)Rotor mechanical strength analysis and dynamics analysis have been the key issues of high-speed motors.In this paper,the equivalent thin-wall cylinder model is used to analyze the rotor stress of SRM motor and the stress concentration of the SRM rotor is analyzed by finite element method(FEM).Considering bearing stiffness and damping with the shaft speed changing conditions,the high-speed motor using sliding bearing of the critical speed,unbalance response and stability problems are analyized.Compared with the constant stiffness and damping analysis method,this method has higher calculation accuracy.Moreover,the analysis show that this shaft structure scheme can be stable operation.(5)To verify the influence of winding connection types on start-up torque and iron loss,the effect of double oblique pole structure,an HPHS-SRM with rated speed 1 8000 r/min and rated power 160 k W was manufactured and the current waveforms under different operating conditions,temperature rise and vibration data have been measured.Results show that the motor performance can meet the design requirements.