Motor Characteristics
Listed below are some variable speed AC motor control concepts with which the user of the W7 Adjustable Speed Drive should become familiar.
Pulse Width Modulation Operation
The W7 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.
Overload Protection Adjustment
The W7 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. 70.
Power Factor Correction
DO NOT connect a power factor correction capacitor or surge absorber to the output of the ASD.
If the ASD is used with a motor that is equipped with a capacitor for power factor correction, remove the capacitor from the motor.
Connecting either of these devices to the output of the ASD may cause the ASD to malfunction and trip, or the output device may cause an
Light Load Conditions
When a motor is operated under a continuous light load (i.e., at a load of less than 50% of its rated capacity) or it drives a load which produces a very small amount of inertia, it may become unstable and produce abnormal vibration or trips because of an
frequency may be lowered to compensate for this undesirable condition (see Program | Special | |
Control | PWM Carrier Frequency). |
|
Note: | For proper operation, the carrier frequency must be 2.2 kHz or above except when | |
| operating in the Constant Torque or Variable Torque modes. |
|
W7 ASD Installation and⇒Operation Manual | ⇒ | 11 |
Load-produced Negative Torque
When the ASD is used with a load that produces negative torque (an overhauling load), the
To minimize the undesirable effects of negative torque the dynamic braking system may be used. The dynamic braking system converts the regenerated energy into heat that is dissipated using a braking