Precor GEN06 Series Service Manual page 137

AC Drive Motor Controller
The AC drive system controls the three phase AC drive motor. In an AC motor, speed is con-
trolled by frequency independent of voltage or current, torque is controlled by the voltage/-
current applied to the motor 3 phase windings. The windings (stator) and rotor core of the
motor are designed to spin at a specific speed at the design frequency. The lower control mod-
ule generates the correct frequency to drive the motor at the command speed. Since the
speed of an AC motor is controlled by frequency, there is no need for a speed sensor.
The 3 phase AC motor generates enough torque to provide continuous duty run time. The 3
phase voltage amplitude of all three input AC sine waves is the same at any given time which
allows the torque to be applied smoothly throughout the rotation of the motor. Increasing the
input voltage/current amplitude increases the torque and decreasing the input amplitude
decreases the torque.
The lower electronics module (IFT drive) is responsible for sending the proper frequency to
control speed and the amplitude (same on all 3 phases) to control torque. The motor must then
be balanced both mechanically and electrically in order to translate the frequency and amp-
litude into fluid motion. Mechanical balance is achieved by balancing the weight of the fly-
wheel, and electrical balance is achieved by having the same winding resistance on all 3
phase windings.
Other AC drive motor controller features include "Dynamic Braking" and "Power Factor Cor-
rection". Dynamic Braking addresses an issue where an over-speed condition could occur. If a
Contact Precor Customer Support at support@precor.com or 800.786.8404 with
any questions.
9 Theory of Operation
Treadmill Base Operation
Page 130