Abstract: Considering the new requirements for sensorless permanent magnet brushless DC motor in a liquid floated gyro, a new phaselocked loop steadyspeed control system is presented based on complex programmable logic device (CPLD) and ML4411.The back electromotive force (backEMF) detection, commutation and power drive are realized by the chip ML4411. The zerospeed start control is realized by a CPLD chip, so does the generation of the speed reference. The control accuracy is greatly improved via the application of the twolevel phaselocked loop (PLL) technique. The requirements for the performance of the gyro are satisfied with the proposed control system in a motor speed test, which provides an effective method to improve the performance of the gyro.

Key words: liquid floated gyro； phaselocked loop, steadyspeed control