How accurate control of permanent magnet brushless dc motor commutation after compensation current, namely how to precisely control PWM100 % duty cycle time is the key to silent controller design! This requires the MCU control system has the following features:
1)Soon A/D converting speed, can continuous rapid sampling after commutation;
2)In the PWM during the opening of the particular time trigger A/D sampling; Because in the PWM inverter with perceptual load control system, due to some parasitic parameters of the system of PWM during the open and shut off the motor phase line ringing (As shown in figure 4), the ringing is coupled to the A/D sampling circuit, so we should avoid in the process of PWM switch to A/D sampling. If we trigger current at the point of the PWM opened during sampling, we will be the average of the current, which will be conducive to our control of current compensation.
in fact, it's not difficult to find such a MCU, such as the special motor control chip XC866 infineon, on-chip programmable control chip CY8C24533 with CYPRESS, etc. XC866 A/D conversion speed can reach 2 within us, plus program execution time, an A/D conversion to the total time within the eight of us, at that time interval complete enough to determine whether the current compensation. CY8C24533 CYPRESS is specifically designed for motor control development with high speed A/D chip, within its SAR8 conversion speed can reach 3 us, combined with the automatic alignment trigger mode, A/D can be triggered at any time in the PWM current A/D sampling, it is also easy to realize the precise control of the current.
figure 2 b is the system that USES XC866 control chip after the optimization of measured in phase current waveforms, can be seen from figure 2 b, commutation current pulse basically eliminated, basic close to square wave phase current of the motor. In the control system of electric vehicle, the motor vibration to accelerate and runtime has been eliminated, ultra-quiet controller design is realized.
