88 Frequency Converters and Motors 3.4.2 Reversing The direction of rotation of asynchronous and many synchronous motors is determined by the phase sequence of the supply voltage. If two phases are swapped, the direction of rotation of the motor changes (the motor reverses). Fig. 3.6 The rotation direction of the motor reverses when the phase sequence is changed A FC can reverse the motor by electronically changing the phase sequence. Reversing is accomplished by either using a negative speed reference or a digital input signal. If the motor must have a specifi c direction of rotation when fi rst put into service, it is important to know the factory default setting of the FC.
Since a FC limits the motor current to the rated value, a motor controlled by a FC can be reversed more frequently than a motor connected directly to the mains. N Fig. 3.7 Braking torque of the frequency converter during reversing