Speed control system of a universal motor

A speed control system of a universal motor being electrically connected with a universal motor and comprising:

• a speed detecting unit provided in said universal motor;
• and
• a controller electrically connected with both said universal motor and said speed detecting unit, said controller have formed with a slow start unit, a speed control unit and a stopping-protecting unit, said slow start unit comprising a start flag initial module and a start flag clearing module, said start flag initial module comprising a start flag and an independent acceleration weight, said start flag clearing module clearing said start flag when the rotating speed of said universal motor rises up to a set reference value, said speed control unit provided with a rotating speed command input module, a computing module and a compensation module, said computing module calculating actual rotating speed of said universal motor according to feedback signal frequency of said speed detecting unit, said computing module further calculating speed difference by having the actual rotating speed subtracting said rotating speed command for judging correction needed by a conduction angle, said compensation module compensating a numerical value of correction, said stopping-protecting unit electrically connected with both said speed detecting unit and said electromagnetic switch, said stopping-protecting unit calculating that the actual rotating speed of said universal motor is low or stops in accordance with feedback signal frequency of said speed detecting unit, said stopping-protecting unit sending out a protection signal for cutting off the power source of said universal motor via said electromagnetic switch.