Brushless DC motor is a kind of motor whose power supply is DC without commutator. The shell can be packaged with high-quality galvanized steel or high-quality thermosetting plastic. The positive pole of motor power supply voltage is represented by the symbol vs, or VM; the negative pole is represented by GND; the control circuit power supply voltage is represented by the symbol VCC; the speed control voltage is represented by the symbol VSP; the speed feedback signal is represented by the symbol VFG (or FG).

　　At present, the brushless DC motor is PWM speed regulating motor with built-in drive circuit

　　The motor speed can be controlled by adjusting the speed control voltage VSP,

　　The motor feeds back 12 pulses per revolution.

　　In order to meet the normal operation of air conditioning; achieve the balance of refrigeration and heating capacity; so it is necessary to ensure that the speed of indoor and outdoor fans meet the requirements of the system; and keep the speed stable. In order to achieve the above purpose, the method of PWM voltage regulation and speed regulation can be used to adjust the fan speed, and the actual speed can be obtained according to the speed feedback signal, and then the PWM duty cycle can be adjusted according to certain rules, so as to keep the speed stable