590 Series DC Digital Drive Programming
D-59
FIELD CONTROL
This function block contains all the parameters for the field operating mode.
It controls the drive's full wave, single phase, motor field thyristor bridge circuit.
The FIELD CONTROL function block is viewed in three sub-menus on the MMI: FLD
VOLTAGE VARS, FLD CURRENT VARS and FLD WEAK VARS.
In the FIELD CONTROL menu, you select the field operating mode: open loop voltage
control or closed loop current control.
The inputs to the FIELD CONTROL block come from FLD VOLTAGE VARS and FLD
CURRENT VARS.
FIELD ENABLE controls the field thyristor bridge and is set to DISABLED in permanent
field motor applications. Disabling the field automatically overrides the field fail alarm. If
FIELD ENABLE is enabled, you can select between voltage and current control using the
FLD CTRL MODE parameter. The default is VOLTAGE CONTROL.
The diagnostic DRIVE ENABLE (Tag 84) is also used by the FLD. QUENCH DELAY to
delay disabling the field when Run is removed.
FLD VOLTAGE VARS : MMI Sub-Menu
Contains the parameter for the open loop VOLTAGE CONTROL mode.
In VOLTAGE CONTROL mode, set the value of FLD.VOLTS RATIO to provide the correct
field voltage. This control mode provides open-loop phase angle control of the thyristor
bridge. To calculate FLD.VOLTS RATIO, divide the desired DC field voltage by the line-
to-line RMS AC input voltage and multiply by 100. Note that supply voltage variations are
not compensated for in the field supply when in this mode of operation.
FLD CURRENT VARS : MMI Sub-Menu
Contains the parameters for the closed loop current control mode.
CURRENT CONTROL mode uses actual field current feedback for closed-loop control giving accurate motor field control independent of motor
temperature. This mode makes use of a simple PI controller and is a pre-requisite for field weakening.
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