Rockwell Automation 1391 USER MNL/DIGITAL AC SERVO DR - Manual (Page 23)

Chapter 4
Description of Operation
4-2
Figure 4.1
PWM Waveform
300V DC
Bus
Time 0
Typical
400
µ
s
Typical
400
µ
s
Typical
400
µ
s
Typical
400
µ
s
The three-phase relationship between the reference signal and the timing
wave provide PWM pulses to the power transistor base drive. This base
drive switches the power transistors across the 300V DC bus, providing
current to the motor windings, thus causing the motor to turn. A resolver
attached to the motor provides a signal corresponding to the actual rotor
position of the motor. This signal is decoded to a signal representing rotor
position and is fed to the commutation logic along with the torque
command. In this way, the drive combines the desired position signal and
current reference with the decoded resolver signal to produce a reference
signal commanding the motor to speed up or slow down. See Figure 4.2.
Figure 4.2
Operation
Commutation
Logic & Current
Loop Integrator
PWM Generator
& Base Drive
Position Decoder
Motor
Resolver
Current
Reference
Timing Signal
Generator