Brushless DC motor without position sensor control method 2
5. Inductive method
Inductance methods come in two forms: one for salient-pole permanent magnet brushless DC motors and the other for permanent magnet brushless DC motors with embedded magnetic steel structures. The first type of inductance method mainly determines the change of inductance by applying a detection voltage to the motor winding during starting. In a salient pole motor, the self-inductance of the winding can be expressed as an even cosine function of the angle between the winding axis and the straight axis of the rotor. By detecting the change in the self-inductance of the winding, the approximate position of the rotor axis can be judged, and then the saturation of the core is determined. The trend of change determines its polarity, which ultimately leads to the correct position signal. This method is difficult and can only be applied to salient pole motors, so it is less used now. Compared with the first method, the second method is the true inductance method. In the in-line permanent magnet brushless DC motor, the winding inductance will change accordingly due to the change of the rotor position. By detecting these changes, after a certain calculation, the rotor position signal can be obtained. In this method, uninterrupted real-time detection of the winding inductance is required, which increases the difficulty of implementation, and the application is not very extensive.
6. State Observer Method
The basic idea of the "state observer method" is to take the parameters such as the motor speed, rotor position angle and current as the state variables, establish a mathematical model for the motor based on the defined state variables, and obtain the discrete state variables by digital filtering. Value to achieve control of the motor. The "state observer method" solves the problem that the motor is difficult to control under high speed and heavy load conditions, and its good anti-interference ability makes it more suitable for a harsh working environment. The huge amount of computation of the "state observer method" limits its application to some extent. This method generally uses a digital signal processor (DSP) to undertake a large amount of computation, thereby increasing the system cost, which is rare in practical applications.
The driving method of the brushless straight motor can be divided into a plurality of driving modes according to different categories, and each has its own characteristics.
Press the drive waveform:
1. Square wave drive, this drive mode is easy to implement, and it is easy to realize motor position sensorless control;
2. Sinusoidal drive, this driving method can improve the running effect of the motor and make the output torque uniform, but the implementation process is relatively complicated. At the same time, this method has two modes: SPWM and SVPWM (space vector PWM). The effect of SVPWM is better than SPWM.
