Study Of Low Speed Control Strategy On Induction Motor Speed Sensorless

With the development of power electronics and control technology, speed control by variable frequency has played an increasingly important role in AC motor. With the outstanding speed control, braking performance, high efficiency, high power factor and energy-saving effect, speed control by variable frequency has become the best way of energy-saving, transformation of traditional industries, improving process, improving the automation level of the production process and improving technological advancement. It has a wide range of applications, such as fans, pumps, textile machinery and machine tools. In the variable frequency control system, it always need speed loop by speed generator or encoder to achieve high dynamic and high-precision speed performance. However, in practical applications it has some new problems: increase system cost, lower the anti-EMI ability of system, and the speed sensor is easy to be the source of fault, etc. To eliminate the problems by using speed sensor, the speed sensorless of direct field oriented method is studied in this paper from the AC induction motor speed control principle, and the DSP-controller system of induction motor speed sensorless direct field oriented control is designed.Also, to the problems of low speed accuracy and torque ripple using VVVF and traditional vector control methods when the AC motor speed control system is at low speed, the combination way of current model flux observer and EMF is proposed to estimate the rotor flux amplitude and phase. Speed feedback loop formed by current model is used to estimate the rotor speed, which improve vector control in low-speed control section, achieve satisfactory test results.On the basis of theory, the hardware platform of induction motor control system is completed by using TI's TMS320F2808 DSP controller which is ASIC of motor control. This paper details the working principle and circuit design of DSP clock generator, JTAG interface, rectifier and filter, three-phase inverter bridges, protection circuits and switching power supply, etc. The design of frequency control system is adapted to different types of induction motors within power. It also has protections of under voltage, over voltage, over temperature, over current and overload, etc.