Toshiba G7 Motor Characteristics

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 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 res ponse 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.

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 vibrat ion when operated

by an ASD, rather than directly from co mmercial power.

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 decr ea se 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 m otor (designed for use in conjunction with an ASD) is rec om mended. 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).

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 fo r the overload detectio n circuit is set to the max imum rated current of th e ASD at the

factory. This setting will have to be adj usted 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.