Search

Because the single-phase brushless fan motor presents an inductive load, the winding current will lag the back-electromotive force (EMF) an unequal phase based on the different motor speed. In order to improve the efficiency and torque performance, adjusting the commutation angle to keep the optimizing commutation at different speed is necessary. In this paper, the new structure with low cost to achieve the optimizing commutation is accomplished by the concept of phase-locked loop (PLL) to synchronize the winding current and back EMF. The PLL IC CD4046 is adopted to develop a feedback circuit and performs the function of phase advance. The purpose is to force the winding current to be synchronized with the back-EMF. Finally, the related experimental results are used to confirm the feasibility and effectiveness of the proposed driving method.

One of the methods to improve efficiency and torque performance of the single-phase brushless DC (BLDC) motor is to find out the optimum commutation angle at each different speed. We used the finite-element method (FEM) to simulate the back-EMF voltage and the coil current for the single-phase BLDC motor, and then adjust the conduction time of switches by detecting the waveform of coil current. The motor can improve its efficiency, noise, and vibration when it obtains the optimal shift angle of each speed. We used PSPICE to verify the exactness of FEM simulation results of the single-phase BLDC motor. We adopted Microchip's dsPIC30F4011 digital signal processor (DSP) to process the Hall signal and the driving signals of switches of the driving system prototype of the single-phase BLDC fan motor. Finally, we used the related experimental results to confirm the feasibility and effectiveness of the proposed driver.

For improved efficiency and torque performance, brushless DC (BLDC) motors require a phase advance circuit. In a conventional phase advance circuit, the induced voltage of the Hall sensor is assumed to be a sinusoidal wave. But the actual induced voltage of the Hall sensor includes other harmonic components which influence the real phase advance angle. Performance curves of phase advance angle versus frequency for a conventional circuit do not work well when the harmonic components are considered. We therefore propose an improved circuit in which the phase advance angle is more accurate than that of a conventional circuit when the harmonic components are considered. Furthermore, the proposed circuit provides better performance. We present experimental results to verify the related theoretical analysis.

A single-phase brushless dc motor requires an asymmetric air gap to eliminate the dead point where the excitation net torque is zero. In this paper, we use the finite-element method (FEM) to analyze the properties of cogging torque, starting torque, and electrical circuits. Others have discussed the influences of various asymmetric air gaps on these properties. However, the optimum asymmetric air-gap condition is very difficult to find. Here, we describe an optimum asymmetric air-gap structure that not only produces an optimum starting torque but also reduces the cogging torque to a tolerable range. We compare simulation results with the measurement results to illustrate the accuracy of the FEM model.