| Summary: | 碩士 === 中原大學 === 機械工程研究所 === 93 === Abstract
The Brushless DC (BLDC) motor is provided with some advantages, such as high efficiency, high power density and high rotational speed range. But the position sensor such as the encoder or the Hall sensor tends to be affected under the condition of high temperature or other rigorous environments, thus the drivers that have not position sensor be the potential driver techniques. And we can pay low cost and bring the efficiency of BLDC by this way.
Among the technique of sensorless drive, the terminal voltage sensing is the most common one. However, its disadvantage is that the back emf is small under low rotating speed. The communication of the phase of motor is not exact because back emf too small as the phase change signal will be interfered by the noise. As a result, it is restricted to use at not low rotational speed. And the traditional sensorless of the motor driver needs extra assistance by hardware; it will increase the cost of manufacture and maintenance.
The paper proposes a new way to solve the erroneous judgment of the change phase signal in the lower rotating speed for the end voltage detection method with BLDC motor sensorless control. We try to use a digital filter with changeable gain to replace the traditional analog filter. The purpose is to solve the back emf voltage too slow in low speed for the end voltage detection method. Furthermore the phase lag in FIR filter is linear, that is, we can compensate the phase lag when rotating in high-speed range to the phase commutation signal and to finish the speed control in close loop system.
We catch the real signal of motor to a digital signal by the I/O card and analysis the signal by the software of Matlab. From the time signal and the frequence signal by the Fast Fourier Transform (FFT), this method can reduce the erroneous judgment in the lower rotating speed and we can drive the motor by sensorless control method to 2Hz.
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