Specifications

Doc Number: VIS-ANA-VER-01001-9002
Date: 27 May 2004
Issue: 5.0
Page: 24 of 80
Author: J. Delgadillo
Controls Preliminary Design Report Issue 5.doc
The motor controllers are matched to, and thus ideally compensated to the brushless DC
motors that they drive. The current loop bandwidth of the motor controllers has been
measured to be around 800 Hz, which would easily satisfy the demanding outer axis rate
loops.
Resistive Regenerative units are connected to the motor controller power supply busses to
dissipate the generated excess energy when the motors are being decelerated or back driven.
4.2.4.3 AZ/ALT PDU Lube System
The Azimuth bearing lube pump is energized from the AZ/ALT PDU. A pressure switch will
detect and report a low-pressure fault. An overflow condition will be sensed by a level
switch, which will report the fault. Both faults will be Disabling Faults of the Azimuth axis,
but not of the lube pump motor power since the lube system has been designed to be ON at
all times. Protection to the lube pump motor is provided via a thermal overload protection
switch.
4.2.4.4 AZ/ALT PDU Status Board
The Status board provides extensive status and motor disabling capability. It interfaces to the
AZ and ALT Rate Loop Boards, to the CCU Control Board and the motor controllers.
4.2.4.5 AZ/ALT Rate Loop Boards
The Rate Loop boards receive rate demands from the Status board and rate feedback from the
motor tachometers (AZ)/CCU Digital Signal Processor (ALT) to close the rate loop. The
Rate Loop boards generate current commands, torque bias (AZ only) and delta tach control
(AZ only). Torque bias is used by the Azimuth axis to remove any backlash in the gear train
by counter-torquing two motors against the other two (refer to Figure 4.2.2.1.C for the
preload scheme plot). It can be seen that the preload type is a constant differential preload up
until saturation level. The preload level will be approximately 25% of motor rated torque.
Delta tach circuitry ensures that motors run at the same speed, which results in load sharing.
The rate loop compensation is similar to that of the MCU Position Loop. However, the Rate
Loop compensation will be set-up as a Type II Loop. The following break frequencies will
be the starting point for the VISTA system.
Lag1 0.26 Hz
Lead 1.59 Hz
Lag2 19.03 Hz