Study On The Design And Control Technology Of The External-rotor Permanent Magnet Direct-drive Roller Used In Extrusion Food Machinery

The food extruder extrudes and processes the raw materials by the relative motions of the rollers. Traditional food extruder works with the help of the modality composed with asynchronous motor and gearing.The traditional food extruder’s working efficiency is low and the maintenance costs of the extruder is high.The rotor of the permanent magnet direct-drive motor which is designed in the thesis directly connects with the roller’s internal surface. The roller is directly drove to rotate by the rotor.This kind of transmission system’s working efficiency is high.What’s more, it can save the space and its maintenance costs is low.It will save the cost and increase production when it is practically applied.The thesis analyzes the design method of the external-rotor PMSM.Because of the motor’s external-rotor structure, the heat generated by motor’s windings is hard to dissipate. What’s more, because the roller which is drove by the motor extrudes and rubs the raw materials for the long time, the motor’s working temperature is high. It is about 90℃.So the thesis studies to select the motor’s size, heating load and permanent magnet suitably to reduce the motor’s temperature rise in the high working temperature. The thesis reduces the harmonic generated by the motor at low speed by reasonably selecting the number of the slots per pole per phase. Then the motor which is designed is simulated in two-dimensional electromagnetic field with the help of ANSOFT finite element software. From the simulation, the prototype’s flux density distribution, no-load back EMF and other results are obtained. They prove the feasibility of prototype’s electromagnetism scenario.The temperature field of the motor should be calculated. It can ensure that the temperature of every part of the motor is in a reasonable range. The thesis calculates the motor’s heat loss and heat extraction coefficient during steady-state operation. The core loss is calculated with the help of Bretotii formula. The heat extraction coefficient of water is calculated with a series of for formula derivation. Through the above calculations, analyzing the motor with the three-dimensional steady-state temperature field simulation, the food extruder’s three-dimensional steady-state temperature distribution for the further verification of scenario’s feasibility can be testified.The external-rotor PMSM is hard to be equipped with the encoder, so the required rotor position and instant speed for traditional vector control can’t be provided. The food extruder’s speed can’t be regulated in time when it is under abrupt change of load. It will produce a negative impact on the quality of the product. The thesis designs a sensor-less vector control system for the designed external-rotor prototype. It estimates the motor’s rotor position and speed with the help of the pulse vibration of high frequency voltage injection method, realizing the food extruder’s vector control. Then the motors sensor-less vector control system is simulated with the help of MATLAB. The vector control system’s dynamic property and anti-interference performance is proved by the simulations of changing the motor’s speed and adding sudden load. The simulations also prove the control system can realize the food extruder’s low-speed vector control instantaneously and steadily.