Sensorless Brushless Dc Motor Speed Control System

This paper focused on the design and realization of speed control system of sensorless permanent magnet brushless DC motor (BLDC) based on digital signal processor (DSP). And a close-loop speed control solution based on DSP TMS320F240 and sensorless control method of Back-EMF zero-crossing for permanent magnet BLDC motors including stator current and rotor speed feedbacks was also presented. By investigating and analyzing the problems emerged during the system designing process, different solutions had been provided.(1) The fact that actual phase-delay angle a of low-pass filter may exceed 30° in high speed will conflict with the demand of the sensorless control method that α must be within 30° . As a result, a hardware solution based on two order LPF and sluggish voltage comparator was presented. After establishing the transfer function of this circuit, a group of desirable device parameters had been acquired by making circuit simulation and experimenting.(2) To fulfill the requirement of the power module in this system, this paper expatiated on the principle of switch-power used in this system as well as its realization with TOP223 switch-power IC. The selection method of device parameter was also given.(3) With the high reliability and real-time demand on system software, three running states of main program were designed. The way to switch between different states was also presented. And the basic timing of main program was provided by the PWM period interruption of TMS320F240.(4) To deal with the problems encountered in the BLDC open-loop starting stages, a rotor pre-orientation method combined with stator phase current measurement was presented. A rotor speedup program was designed by modifying the PWM output unit of TMS320F240 directly and changing the phase switch delay time with speed. After analyzing the switching stages between inner and outer synchronization, a program was designed to find the best switching time and thesoftware judgment method of switching time was also given.(5) In allusion to the key problems met in the realization of close-loop speed control including rotor speed and stator current feedbacks, A phase compensation method using PWM period interruption time as the benchmark time for compensation, as well as the conversion expressions between phase compensation angle β and delay time Td were presented. The calculation method of rotor speed using interval time between stator phase alternation was also given. By analyzing the connection between generatrix current of inverter and phase current in different PWM stages of BLDC motors, a stator current measurement solution using a single current sensor and its software realization were described. At last, to eliminate the differences between various data type, a generalized data conversion method and its formula were provided. Meanwhile, an incremental PI arithmetic including integral separating was introduced.In the experimental part of this paper, different waveforms of BLDC motors under different circumstances were given. The correctness of this system had been proved by analyzing the waveforms. The conclusion part of this paper presented the scarcity and limitation of the system and shows the direction for future research work.