Research Of Two Kinds Of Control Schemes For Brushless DC Machine And Its Relevant Issues

As a kind of Mechatronic System, Brushless DC Motor(BLDC) is widely used in various industrial fields because of its characteristics of high power density,excellent speed controlling performance and high reliability of structure. With the ever-growing demands of BLDC drive system’s performance, it’s very important to perfect all kinds of control schemes of BLDC.Since it’s hard to expend speed by weakening field on the method of traditional square wave current control for BLDC,the applied range of BLDC is under restrictions naturally. Two kinds of control schemes for BLDC are studied to obtain the practical schemes of field-weakening from the perspective of vector control in this paper, which are respectively vector control on 120 degree-conduction and vector control on 180 conduction type.Unlike sinusoidal permanent magnet synchronous motor, considering trapezoidal wave distribution of BLDC’s Back EMF, the mathematical model of BLDC based on Back EMF vector orientation is established,which laid the theoretical foundations for the further study on the two kinds of control schemes.For the vector control on 120 degree conduction, a new type of current vector control scheme is proposed from the perspective of basic stator current vector. This scheme is not only suitable for the constant torque area which is under the based speed but also very effective for constant power area which is above the based speed, which makes the vector control on 120 conduction extended to the field-weakening area. Considering the exact rotor position is required in this new comprehensive current vector control scheme, therefore, the rotor position estimator is designed on the basis of rotor position information gained by three hall position sensors. This srotor position estimator has certain robustness for the installation location of hall position sensors. For vector control scheme on 180 degree conduction, a vector control scheme suitable for he trapezoidal wave BLDC based on Back EMF vector orientation is established in this paper, which is referred to the vector control scheme of sinusoidal permanent magnet synchronous motor based on rotor flux orientation This control scheme make the drive system rotate on the field-weakening area reliably by combining over modulation and the restraint of voltage limit circle. This paper makes a simulation research on the effectiveness of above-mentioned two kinds of control schemes, and respective characteristics and properties of these two schemes are compared.