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5 Adjustable Frequency Drive and Motor Applica-

tions

5.1 Torque Limit, Current Limit, and Unstable Motor Op-

eration

Excessive loading of the adjustable frequency drive may result in warning or tripping on torque
limit, overcurrent, or inverter time. This is not a concern if the adjustable frequency drive is prop-
erly sized for the application and intermittent load conditions cause anticipated operation in torque
limit or an occasional trip. However, nuisance or unexplained occurrences may be the result of
improperly setting specific parameters. The following parameters are important in matching the
adjustable frequency drive to the motor for optimum operation. These setting need careful at-
tention.

Par. 1-03

Torque Characteristics

sets the mode in which the adjustable frequency drive

will operate.
Parameters 1-20 through 1-29 match the adjustable frequency drive to the motor and
adapt to the motor characteristics.
Parameters 4-17 and 14-25 set the torque control features of the adjustable frequency
drive for the application.

Par. 1-00

Configuration Mode

sets the adjustable frequency drive for open-loop or closed-loop

operation or torque mode operation. In a closed-loop configuration, a feedback signal controls the
adjustable frequency drive speed. The settings for the PID controller play a key role for stable
operation in closed-loop, as described in the Instruction Manual. In open-loop, the adjustable
frequency drive calculates the torque requirement based on current measurements of the motor.

Par. 1-03

Torque Characteristics

sets the adjustable frequency drive for constant or variable torque

operation. It is imperative that the correct torque characteristic is selected, based on the appli-
cation. If, for example, the load type is constant torque, such as a conveyor, and variable torque
is selected, the adjustable frequency drive may have great difficulty starting the load, if started
at all. Consult the factory if uncertain about the torque characteristics of an application.

Parameters 1-20 through 1-25 configure the adjustable frequency drive for the connected motor.
These are motor power, voltage, frequency, current, and rated motor speed. Accurate setting of
these parameters is very important. Enter the motor data required as listed on the motor name-
plate. For effective and efficient load control, the adjustable frequency drive relies on this
information for calculating the output waveform in response to the changing demands of the
application.

Par. 1-29

Automatic Motor Adaptation (AMA)

activates the automatic motor adaptation (AMA)

function. When AMA is performed, the adjustable frequency drive measures the electrical char-
acteristics of the motor and sets various adjustable frequency drive parameters based on the
findings. Two key parameter values set by this function are stator resistance and main reactance,
parameters 1-30 and 1-35. If unstable motor operation is experienced and AMA has not been
performed, it should be done. AMA can only be performed on single motor applications within the

High Power Service Manual for VLT

FC Series

Adjustable Frequency Drives

5 Adjustable Frequency Drive and Motor Ap-

plications

MG.90.L1.22 - VLT

is a registered Danfoss trademark

5-1