Frequency Converter And Motor Applications; Torque Limit, Current Limit, And Unstable Motor Operation; Overvoltage Trips - Trane TR150 Service Manual

Frequency Converter and Mot...

5 Frequency Converter and Motor Applications

5.1 Torque Limit, Current Limit, and
Unstable Motor Operation
Excessive loading of the frequency converter can result in
warning or tripping on torque limit, overcurrent, or inverter
overload. Avoid this situation by sizing the frequency
converter properly for the application. Ensure that
intermittent load conditions cause anticipated operation in
torque limit or an occasional trip. Pay attention to the
following parameters when matching the frequency
converter to the motor for optimum operation.
Parameters 1-20 to 1-25 configure the frequency converter
for the connected motor.
These parameters set:
•
Motor power.
•
Voltage.
•
Frequency.
•
Current.
•
Nominal motor speed.
It is important to set these parameters accurately. Enter the
motor data required as listed on the motor nameplate. The
frequency converter relies on this information for accurate
motor control in dynamic loading applications.
Parameter 1-29 Automatic Motor Adaption (AMA) activates
the automatic motor adaptation (AMA) function. When
AMA is performed, the frequency converter measures the
electrical characteristics of the motor and sets various
frequency converter parameters based on the findings. This
function sets the following parameter values:
•
Parameter 1-30 Stator Resistance (Rs)
•
Parameter 1-35 Main Reactance (Xh)
•
Parameter 1-37 d-axis Inductance (Ld)
If motor operation is unstable, perform AMA if this
operation has not already been performed. AMA can only
be performed on single-motor applications within the
programming range of the frequency converter. Refer to
the operating guide/quick guide for more information on
this function.
Set parameter 1-30 Stator Resistance (Rs) and
parameter 1-35 Main Reactance (Xh) parameters for the
AMA function. Use factory default values, or values that are
supplied by the motor manufacturer.
BAS-SVM04B-EN
TR150 and TR170 Service Manual
NOTICE
Never adjust these parameters to random values even
though it seems to improve operation. Such adjustments
can result in unpredictable operation under changing
conditions.

5.1.1 Overvoltage Trips

Overvoltage trip occurs when the DC-link voltage reaches
its DC link alarm voltage high (see chapter 1.9.1 Short
Circuit and Overcurrent Trips). Before tripping, the frequency
converter shows a high-voltage warning. Mostly, fast
deceleration ramps concerning load inertia causes an
overvoltage condition. During deceleration of the load,
inertia of the system acts to sustain the running speed.
Once the motor frequency drops below the running speed,
the load begins overhauling the motor. The motor then
becomes a generator and starts returning energy to the
frequency converter. This is called regenerative energy.
Regeneration occurs when the speed of the load is greater
than the commanded speed. The diodes in the IGBT
modules rectify this return and raises the DC link. If the
amount of returned energy is too high, the DC voltage
increases, causing the frequency converter to trip.
There are a few ways to overcome this situation. One
method is to reduce the deceleration rate so it takes
longer for the frequency converter to decelerate. A rule of
thumb is that the frequency converter can only decelerate
the load slightly faster than it would take for the load to
naturally coast to a stop. A second method is to allow the
overvoltage control function (parameter 2-17 Over-voltage
Control) to take care of the deceleration ramp. When
enabled, the overvoltage control function regulates
deceleration at a rate that maintains the DC-link voltage at
an acceptable level. One caution with overvoltage control
is that it does not make corrections to unrealistic ramp
rates.
For example, the deceleration ramp has to be 100 s due to
the inertia, and the ramp rate is set at 3 s. Overvoltage
control initially engages, then disengages and allows the
frequency converter to trip. This is purposely done so the
unit's operation is not misinterpreted.
The frequency converter has an AC brake function, which
increases magnetization current to increase loss in motor
and reduce DC-link voltage. If the DC-link voltage exceeds
a certain voltage, the overvoltage control changes the
frequency.
02/2017 All rights reserved.
5
5
39