| Motor is an important electromechanical energy conversion device,which consumes the most of the electricity currently.AC motor,especially squirrel cage induction motor,is used widely because of the advantages of simple structure,strong durability,convenient manufacture and maintenance,low cost,etc.Nonetheless,the control of asynchronous motor is comparatively complicated due to the high order,nonlinear and strongly coupled multivariable system.However,its variable frequency speed regulation can be performed excellently with vector control or direct torque control,of which the vector control,especially rotor field oriented control,which can realize decoupling control of torque and flux linkage,is mostly used in the applications of variable frequency speed regulation of high performance.Under the base frequency(50Hz or 60Hz),constant torque control is usually used to keep the maximum output torque of the motor in the speed control.But when the frequency is above the base frequency,with the limit of the bus voltage,terminal voltage of the motor cannot continue to increase and therefore the maximum output torque of the motor will decline with the increase of the speed.This is especially obvious when electric vehicles and other equipment work at a higher speed,during which the air resistance is proportional to the square of driving speed and the result rise quickly accordingly.When the speed rises to a certain value,the air resistance will account for the main part of the total resistance,while the output torque of the drive system decrease,making it difficult to meet the requirements of large torque output in high speed operation.Therefore,it is important to study the technology and methods to extending the constant torque range,which is of great significance to improve the power density of the motor and meet the driving requirements of electric vehicles and other loads in higher-speed operation.A new method to extending the constant torque range,namely Y/? winding changeover technology,was presented and explored,in terms of present technology shortcomings,with an overview of the present technology and its characteristics from three aspects of PWM modulation,converter and motor.What's more,the analysis on the mathematical model of open-end stator winding asynchronous motor was presented here as well as the explanation of the amplitude and phase changes of all the basic voltage vector under different inverter switching states while the stator winding of the machine was under the condition of Y-connected or?-connected,together with the division of the sector.Moreover,according to the changes of the voltage in the Y/? transformation,the control logic of Y/?transformation was analyzed and embedded into the vector-control system so as to extend the constant torque range of the motor.The simulation model of the control system was established on the Matlab/Simulink,and the simulation results proved that the speed drop was extremely slight while the connected type of the stator winding is transformed and there was almost no effect on dynamic performance.The hardware system of the speed control system with TMS320F2812 as the control core was designed,including the current sampling circuit,voltage sampling circuit,IPM driving and protecting circuit,Y/? transforming circuit and speed setting circuit etc.Furthermore,C program for the drive system was programmed and debugged.Through the test of the prototype,a smooth transition was realized from Y-connected to ?-connected or vice versa.The constant torque range was extended by the times of ?3? significantly improving the motor power density and proving the effectiveness and excellence of new technology. |
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