Temperature Rise Loss Suppression Of Brushless DC Motor For Helicopter Rescue Hoist At Multi-elevations

The main factors for the heating of the airborne rescue hoist are stator & rotor losses of hoist motor and the regenerative energy consumed by brake resistors.The atmospheric characteristics of multi-elevations reduce the convective heat dissipation efficiency,make the motor temperature rise higher,and affect the reliability of permanent magnet,Hall sensors,and insulation.Based on the electromagnetic & temperature field,key technical issues such as stator loss & rotor loss suppression,control algorithms and regenerative energy management have been studied in depth,to solve temperature rise due to the hoist BLDCM running at multielevations.The main research contents and contribution of the thesis are as follows:1.Aiming at the issue of high temperature rise and rise rate of hoist motor in high altitude environment,the coupling FEM field model of electromagnetic and temperature is established,and the temperature rise sensitivity factor of hoist motor is studied.Based on the analysis of the influence of multi-elevations on heat distribution and heat gradient of hoist motor,the thesis proposes a comprehensive method based on motor design,control algorithm and regenerative energy management to improve the temperature rise of hoist motor,which provides theoretical support and research framework for the following chapters.2.To improve the problem of rotor heat concentration caused by the continuous eddy current loss of hoist motor,a method for surface rotor structure of a hoist motor to weaken the rotor eddy current loss with the third harmonic back-EMF maintained is proposed.By adjusting the polar arc coefficient,the embedded depth and the ratio of thickness of permanent magnet to the length of air gap,which leads to reduce the phase current harmonics distribution and decrease the rotor eddy current loss.The harmonic distribution of the air gap magnetic field is corrected and the back-EMF with a spcefic third harmonic can be obtained.Compared with the conventional hoist motor rotor structure,it has higher third-harmonic signal-to-noise ratio and lower rotor eddy current loss,which provides a prerequisite for reducing rotor temperature rise and estimation of rotor position sensorlessly.A rotor position estimation algorithm consists of flux linkage fundamental and thirdharmonic assistance(F-THA)for the hoist motor is proposed.The algorithm uses the flux fundamental to locate the rotor position at the first time,and uses the third harmonic which is not affected by the parameter changes such as resistance to perform a second accurate positioning,which improves the zero-crossing drift issue due to the integral calculation of flux.The dynamic detection error of rotor position with F-THA is reduced by improving the key nodes of the hoist S-type speed model and the time lagging/leading compensation measures during commutation.F-THA is used as backup for Hall sensors of the hoist motor,also the algorithm is able to use in the general sensorless control.3.A minimum continuous current algorithm with the switching of back-EMF waveforms based on the minimum copper loss model(MCCES)is proposed.Based on the extreme value model of stator copper loss with the constraint condition of average electromagnetic torque,the algorithm obtains the optimized three-phase current expressions.The ideal back EMF with linear segmentation causes copper loss and torque ripple in the given current calculation of the algorithm.The slide mode observer is used to estimate the back EMF on-line,the Sigmoid function is used as the switching function to reduce chattering,also the resistor and inductance parameter adaptation rate are designed to avoid influence on observation accuracy by stator temperature rise.MCCES not only reduces the temperature rise of the stator winding,but also improves the instantaneous resonance of the hoist and the rotor by greatly weakening the torque ripple of the motor.The rotor temperature rise is improved by the shortened heat transfer process from stator to rotor,due to the decreased stator copper loss.4.According to the operation mode and speed sensitivity characteristics of the airborne hoist,a regenerative power & losses model which does not depend on the height is established to accurately describe the grid-connected energy.An improved regenerative energy average power feedback method(REAF)is proposed.The recovery of the hoist regenerative energy can solve the heating problem during the braking operation,but it is necessary to quantitatively describe the grid-side energy.The operating height of rescue hoist is determined by the hovering altitude of helicopter,therefor the conventional energy flow modeling method cannot be used to construct the regenerative energy.The proposed modeling method focuses on system speed and load disturbances,accurately calculating the instantaneous power of regenerative energy at any height;accounting for the loss term also helps to reduce the volumetric weight of the forestage converter and the energy storage device.Simulation and experiment show that the feedback method can effectively suppress the power fluctuation during the regenerative energy feeding back,and stabilize the DC bus voltage.From the perspective of reducing the heat generation and reliability of the airborne hoist,the dissertation studies the suppression method of major losses and the residual rotor position detection method of the hoist motor.The theories and algorithms proposed in the dissertation are verified by simulation and experiments.