Rockwell Automation 1391 USER MNL/DIGITAL AC SERVO DR - Manual (Page 22)

Chapter
4-1
Description of Operation
Chapter Objectives Chapter 4 is intended to familiarize the reader with the circuitry of the
1391-DES in terms of function and operation.
General The intended use of the 1391-DES is to control the speed and torque of an
AC servomotor in a closed loop position system. A complete servo system
can be configured with a 1391-DES Servo Drive, 1326 AC Servomotor
and 1391 Isolation Transformer. Refer to the 1391-DES Block Diagram
presented in Figure 4.4 for general layout.
The 1391-DES PWM Servo Drive is made up of the following: 300V DC
power supply, power transistor output modules, shunt regulator circuit,
logic power supply, microprocessor based logic boards, isolated current
sensing, circuit breaker and line contactor.
300V DC Power Bus Supply The drive contains an integral, unregulated, 300V DC nominal, full load
power supply. It consists of the power transformer input (230V AC,
three-phase, 50 or 60 Hz), a three-phase input bridge rectifier and one
power supply filter capacitor (C1).
PWM Operation The 1391-DES incorporates a fixed timing wave (V
T
) of 2500 Hz. The
drive generates a three-phase sine wave by varying the width of the fixed
timing pulses (see Figure 4.1). This frequency corresponds to the velocity
command. The 0 to 10V DC velocity command is scaled to provide an
output frequency (dotted line) that varies from 0 to 200 Hz, depending on
the maximum velocity of the motor. This variable frequency output drives
a permanent magnet AC servomotor whose speed varies as a function of
the frequency.