G7 ASD Operation Manual
13
Motor Characteristics
Listed below are some variable speed AC motor control concepts with which the user of the
G7 Adjustable Speed Drive should become familiar.
Motor Autotuning
Motor production methods may cause minor differences in the motor operation. The negative effects of
these differences may be minimized by using the Autotune feature of the G7 ASD. Autotuning is a
function of the G7 that measures several parameters of the connected motor and places these readings in a
stored table. The software uses the information in the table to help optimize the response of the ASD to
application-specific load and operational requirements. The Autotuning function may be enabled for
automatic tuning, configured manually at
F400
, or disabled.
The measured parameters include the rotor resistance, the stator resistance, the required excitation
inductance, rotational inertia values, and leakage inductance values.
The G7 ASD is also equipped with a factory-loaded table of motor parameters that fit several different
types of motors. To use this function, disable Autotune and select a motor type at
F413
.
Pulse Width Modulation Operation
The G7 ASD uses a sinusoidal Pulse Width Modulation (PWM) control system. The output current
waveform generated by the ASD approaches that of a perfect sine wave; however, the output waveform is
slightly distorted. For this reason, the motor may produce more heat, noise, and vibration when operated
by an ASD, rather than directly from commercial power.
Low Speed Operation
Operating a general-purpose motor at lower speeds may cause a decrease in the cooling ability of the
motor. Reducing the torque requirement of the motor at lower speeds will decrease the generated heat at
lower speeds.
When the motor is to be operated at low speed (less than 50% of full speed) and at the rated torque
continuously, a Toshiba VF motor (designed for use in conjunction with an ASD) is recommended. When
the ASD is used with a VF motor, the VF Motor overload protection setting must be enabled (see
Program
⇒
Protection Parameters
⇒
Overload
⇒
V/f Motor Enable/Disable
).
Overload Protection Adjustment
The G7 ASD software monitors the output current of the system and determines when an overload
condition occurs. The overload current level is a percentage of the rating of the motor. This function
protects the motor from overload.
The default setting for the overload detection circuit is set to the maximum rated current of the ASD at the
factory. This setting will have to be adjusted to match the rating of the motor with which the ASD is to be
used. To change the overload reference level, see
Electronic Thermal Protection #1 on pg. 154
.
