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This study proposes a new sensorless speed control system for a micro-permanent magnet synchronous motor. Owing to the special characteristics of the micro-permanent magnet synchronous motor, a new rotor position estimator is proposed here. First, by detecting the three-phase zero-current crossing points, a low-resolution of the current position can be detected. Next, by using a Proportional Integral (PI) state estimator, the resolution of the current position can be obviously improved. After that, the deviation voltage between the ideal d-axis voltage and the estimated d-axis voltage is computed to compensate the estimated rotor position. By using the estimated rotor position, the proposed sensorless closed-loop control system, which has good performance including fast transient responses, good load disturbance responses and good tracking responses, can be realised. A digital signal processor, TMS320F28335, is used as a control centre to execute the rotor position estimating algorithm and control algorithm. Experimental results show that the sensorless micro-permanent magnet synchronous motor control system can provide a wide adjustable speed range from 5 to 40 000 r min with satisfactory performance, which is better than the micro-permanent magnet synchronous motor using an attached 64 pulses revolution encoder.