The Research On Permanent Magnet Brushless DC Motor With DSP

The Brushless DC Motor(BLDCM) has been widely used for many years because of its excellent performance,easy control and high cost effectiveness.An investigation in hardware and software for the sensorless control over permanent BLDCMs using DSP and a sensorless control strategy of back electromagnetic force(Bemf) for permanent BLDCM have been put forward in this paper.First,the development and tendency of AC motors are described at home and abroad in this paper. An brief introduction to control strategy and structure principle of permanent BLDCMs,as well as the structure and characteristics of TMS320F240,are showed then.An analysis about the disadvantage and advantage of sensorless control over BLDCMs are followed.Based on that,a detail way of sensorless control is put forward by the advent of TMS320F240 with the digital control function.TMS320F240DSP has been designed as the main micro-controllor during hardware design.Minimum system,which includes power management,expanded RAM and ROM,keyboard/displaying and DSP etc.The invert bridge consists of six transistors.drived by speedy light-sensitive components.Circuits for signal collection have been given to measure the stator terminal voltage and current value.The entire structure is integrated well.When designing the software,the main two functions,startup of the motor and speed closed loop sensorless control,are complete.Using DSP,the PWM signal,the measurement of voltage and current signals and phase shifting are successively presented here.Some conclusions from this paper are gotten as follows:(1) Because the abundant inboard and outboard resource and high efficiency manipulation capacity of TMS320F240DSP,the software filter is used instead of the additional hardware filter while measuring the voltage.The zero-crossing point of Bemf and shifting of 30 degree later are decided by software,which considerably simplify the hardware structures that were made up of complex circuits in old days.(2) The sensorless control with Bemf is simply but versatile,but there are some disadvantage.Some advances are given to avoid the problems brought by the Bemf measurement.(3) Take advantage of the high-speed calculation capability of DSP. Without any additional speed-measuring circuit,calculating the running speed. ,then modulating PWM can be easily made to control the speed of the motor.