Precor TRM 811.v2, Service Manual

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Drive Motor Operation
AC Drive Motor Controller
Treadmills use an AC drive system to control a three phase AC drive motor. In an AC motor, speed
is controlled by frequency independent of voltage or current and torque is controlled by the
voltage/current applied to the 3 windings. The windings (stator) and rotor core of the motor are
designed to spin at a specific speed at the design frequency. This is by design of the motor itself.
By changing the frequency of the drive current, we can change the speed. The lower control
module generates the correct frequency to drive the motor at the desired speed. Since the speed of
an AC motor is controlled by frequency, there is no need for a speed sensor.
Figure 9: AC Drive Motor Controller