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Configuring the Inverter for Multiple Motors

Configuring the Inverter for Multiple Motors

Simultaneous Connections

For some applications, you may need to connect two or more motors (wired in parallel) to a single inverter’s output. For example, this is common in conveyor applications where two separate conveyors need to have approximately the same speed. The use of two motors may be less expensive than making the mechanical link for one motor to drive multiple conveyors.

Some of the requirements when using multiple motors with one drive are:

U/T1

V/T2

Inverter Motor 1 W/T3

Motor 2

to Nth motor

Operations and Monitoring

Inverter Configuration for Multiple Motor Types

•Use only V/F (variable-frequency) control; do not use SLV (sensorless vector control).

•The inverter output must be rated to handle the sum of the currents from the motors.

•You must use separate thermal protection switches or devices to protect each motor. Locate the device for each motor inside the motor housing or as close to it as possible.

•The wiring for the motors must be permanently connected in parallel (do not remove one motor from the circuit during operation).

NOTE: The motor speeds are identical only in theory. That is because slight differences in their loads will cause one motor to slip a little more than another, even if the motors are identi- cal. Therefore, do not use this technique for multi-axis machinery that must maintain a fixed position reference between its axes.

Some equipment manufacturers may have a single type of machine that has to support three different motor types—and only one motor will be connected at a time. For example, an OEM may sell basically the same machine to the US market and the European market. Some reasons why the OEM needs two motor profiles are:

•The inverter power input voltage is different for these markets.

•The required motor type is also different for each destination.

In other cases, the inverter needs two profiles because the machine characteristics vary according to these situations:

•Sometimes the motor load is very light and can move fast. Other times the motor load is heavy and must move slower. Using two profiles allows the motor speed, acceleration and deceleration to be optimal for the load and avoid inverter trip (fault) events.

•Sometimes the slower version of the machine does not have special braking options, but a higher performance version does have braking features.

Having multiple motor profiles lets you store several “personalities” for motors in one inverter’s memory. The inverter allows the final selection between the three motor types to be made in the field through the use of intelligent input terminal functions [SET] and [SET3]. This provides an extra level of flexibility needed in particular situations. See the following page.