Toshiba G7 manual Motor Characteristics, Motor Autotuning, Pulse Width Modulation Operation

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.

G7 ASD Operation Manual 13