| A novel speed-sensorless method based on motor power transition is studied in this thesis. A DSP of TI inc.-TMS320F240 is used as control core to form fully digital speed-sensorless variable frequency system.Speed closed-loop with speed sensor has the limitation of high cost, difficult installation, high bulk, low reliability and high dependency of working condition. Speed-sensorless variable frequency system avoids the defects that speed sensor system has and can meet the need of high performance of AC motor driving. Considering of its advantages, people put more attention on the study of Speed-sensorless variable frequency system in recent years. The current methods of estimating and controlling speed have one or more of these serious disadvantage: complicated structure, difficulty to realize or high dependency of the parameter of motor which will result in the inaccuracy if the motor runs for a long time.In this thesis, in order to retain magnetism constant, the author compensates the volt of motor stator resistance using two sampling current. With this provision, this thesis educes a novel method to estimate the slip speed by studying the power transition and power consumption of motor. Using the sampling current and volt based on V/F profilecalculates the motor input power. Apart the relating wasting power from input power, the author can get the electromagnetism power, and then can get the slip speed based on the relationship between electromagnetism power and slip speed. Form frequency compensating based on the study above. This method is simple and facile, moreover, it dose not depend on the motor parameter badly.Following analyzing the theoretic, the thesis workouts the control program using the assembly language and realizes the speed-sensorless variable frequency system based on F240 development board. The system controls a 1.1 KW asynchronous motor under V/F control with volt compensation and voltage space-vector (SVPWM). |
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