System and method for using and controlling permanent magnet AC motor in place of triac-controlled PSC motor

摘要

A system and method for controlling a speed of a permanent magnet AC motor (38) based on a delay angle of a triac-controlled AC voltage signal (66) from a triac (34). A simulated load (54) connected to the triac (34) enables a load current and creates the signal (66). A first detector (48) detects a zero-crossing point of the AC voltage signal, and a second detector (50) detects a subsequent turn-on instance of the triac (34). A speed command generator (52) measures an interval between the zero-crossing point and the subsequent turn-on instance, and converts the delay angle to a speed command for controlling the speed of the motor (38). The simulated load (54) may include resistors (70) having a resistance which causes the load current to be below a holding current rating of the triac (34), thereby causing the triac (34) to turn off after the interval has been measured.