| Brushless DC motor(BLDCM) is widely used in various areas such as commerce, industry, and aerospace, because of their simple structure, low maintenance, good controllability and high efficiency. Sensorless control, diagnosis method for inverter open-circuit faults of driver system and applications of BLDCM in electric bicycles are studied in this paper. The main research results are as follows:(1) This paper proposes a method to estimate the initial rotor position of sensorless BLDCM. The changing rules of current, voltage, and inductance are analyzed when voltage vectors are applied to the stator windings. The relationship between the changing trends of the floating phase terminal voltages and the initial rotor position is established through the inductance ratio of the conducting phase windings. Based on the relationship, a novel method is presented to estimate the initial rotor position. In the proposed method, three voltage vectors are applied to the stator windings, and then, the changing trend of each floating phase terminal voltage is detected one by one. As a result, the 60 electrical degree resolution can be achieved. When the rotor is located in the critical sector, the movement of the rotor is considered to estimate the sector. The experiment results have verified the effectiveness of the proposed method.(2) Focusing on the problem that the starting performance of sensorless BLDCM is sensitive to the loads, this paper proposed a novel closed-loop starting method based on the direct back electromotive force(back-EMF). The principle of the commutation points extracted from the floating phase terminal voltages in accelerating process is analyzed, and the method of getting the floating phase terminal threshold voltages is presented also. In the accelerating process, the commutation points are determined by comparing the floating phase terminal voltages and the setting threshold voltages, while in running process, the commutation points are delayed by 30 electrical degree from the back-EMF zero-crossing points. The motor can be started reliably either on light loads or heavy loads because of the closed-loop starting strategy. The experiment results have verified the effectiveness of the proposed method.(3) This paper presents a novel online diagnosis method for the inverter open-circuit fault of BLDCM driver systems in high side pulse width modulation-low side on(H_PWM-L_ON) modulation mode and in high side on-low side pulse width modulation(H_ON-L_PWM) mode. By analyzing the line voltages of conducting phase windings in normal and fault modes, the difference of line voltages during the PWM_ON and PWM_OFF time is considered as the fault feature to detect the open-circuit fault, and in the next working mode of the inverter, the faulty switch could be identified. The difference of line voltages is estimated inexpensively by the terminal voltages using the time division multiplexing strategy. The maximum diagnosis time is no less than one electrical period. This method has the features of a simple circuit, convenient implement, high reliability, low cost, and is immune to closed-loop or open-loop control strategies. The experiment results verified the effectiveness of the proposed method.(4) The application of BLDCM in the electric bicycle is studied. In order to improve the performance of sensorless control, reduce torque ripple, and improve operational reliability of the electric vehicle, dual-mode electric vehicle control system is developped. Two position sensorless control methods based on comparator and AD sampling, a dual-mode automatic switching method, a control strategy of commutation torque ripple reduction based on the bus current, a intelligent recognition method of the relationship between the Hall position sensor signal and the winding are designed in this paper. |
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