By the brushless dc motor speed control principle, the square wave of brushless dc motor stator current and rotor position with strict corresponding relation, motor, under the control of the rotor magnetic pole position detection signal. Now in figures 1 three-phase inverter control circuit of brushless dc motor as an example to explain change and the distribution of the PWM signal.
first determine control system adopted by the winding commutation way (If use three three phase or two in two equal), according to the winding commutation way find out three magnetic steel rotor position sensor signal relative phase sequence and its relationship with the actual rotor position, yuntai motor, further deduced them with 6 power tube conduction, the relationship between the and then by the control unit for the generation of PWM waveform and distribution.
the system adopts two two phase winding. Using a hall type rotor position detector position signal, the output for the three mutually sent 120 & deg; Electric Angle, width 180 & deg; Electrical Angle of rectangular wave, as shown in figure 2. PA, PB, PC for three way the rotor position signal, the position signal processing unit is available after the inverter power switch can make the signal, as shown in figure 2.
forward electric system relevant waveform
figure 2 forward electric system relevant waveform
because the motor's running condition is different, can make the signal of power tube is different also. Therefore, must pass a running state (Positive and reverse, electrical, brake)Criterion, and then through the control logic unit to enable signal and PWM signal is assigned to each power tube, after enabling signal and PWM facies, output to the driving circuit, the control of power tube conduction and shut off.
