The position detection method adopted by the sensorless brushless DC motor controller is the third harmonic detection method of back EMF. There are two signals input to the controller, one is the zero crossing signal of a opposite EMF, and the other is the zero crossing signal of the third harmonic of rotor flux, These two signals are used to control the permanent magnet synchronous motor to run in the self synchronous working state. Therefore, this control system is different from the traditional control system using 3-channel back EMF zero crossing signal in the back EMF fundamental wave method of thin strip (also known as terminal voltage method). Since the third harmonic detection method is quite sensitive and does not need to go through a low-pass filter with great attenuation rate in signal processing, the third harmonic detection can correctly detect the position of the rotor at low speed. Because the third harmonic signal can be processed by 90 ° integrator circuit which maintains stability in the whole frequency range, the detection accuracy is high. The direct effect is that the motor has high operation efficiency and large output torque. Therefore, this paper studies a controller suitable for the third harmonic detection method. The task of Brushless DC motor controller is to complete position closed-loop control, speed closed-loop control and start-up control. The position closed loop is to make the motor run in the self synchronous state, and the speed closed loop is to speed regulation. Because the third harmonic detection method can not detect the position of the motor rotor at zero speed, it also needs more complex starting control. 2.1 realization of position closed-loop: the position closed-loop is completed by interruption in this controller, and the three-phase synchronous signal sequence corresponding to three-phase 6 beats is pre compiled in the control program of the controller. Each jump of the third harmonic causes an interruption, and the controller outputs the next synchronous signal sequence. A. each jump edge of the opposite potential causes an interrupt, so that the controller points to the first synchronization signal sequence. The realization of position closed loop mainly consists of decoding circuit and third harmonic pulse generation circuit. The decoder circuit decodes the three-phase synchronous signal output by the microcomputer into the conduction signals of six inverter power devices. Its function is the same as that of the decoder used in the traditional terminal voltage method. The controller studied in this paper is completed by gal16v8 programmable logic device. When the brushless machine is running, each jump of the third harmonic position signal corresponds to a commutation time. 4. What is the background and process of the "new material support level improvement project"?, The only thing that can cause the microcomputer to produce an external interrupt is that the external signal has an upper jump edge, so it needs an edge pulse generation circuit. The control system can automatically follow the resonant frequency and convert the upper jump edge and lower jump edge of the input third harmonic signal into a narrow pulse width with upper jump edge. Using two rising edge monostable triggers may accomplish this function. The edge pulse generation circuit is shown in Fig. 1, in which the pulse width is determined by the RC delay network of the monostable trigger. This pulse width shall not be greater than the pulse width of the third harmonic position signal at the maximum speed, otherwise one commutation time will be missed in each cycle at the maximum speed, which will make the motor run in an unstable state! [endif] ! [ENDIF] 2.2 realization of speed closed loop the realization of speed closed loop includes the measurement of speed, the setting of control quantity and the adjustment of PWM wave duty cycle. Since the frequency of the third harmonic position signal is directly proportional to the speed of the motor, for the motor with P = 2, the third harmonic signal will jump 12 times for each revolution of the rotor. Therefore, the speed may be measured by measuring the third harmonic signal. Since the third harmonic frequency is relatively low, the frequency measurement method is used to measure the speed. If you want to measure the speed of the motor in a short time, the measured speed error is too large. Therefore, the controller adopts the cycle measurement method.
Copyright © 2011 JIN SHI