Heavy duty load sharing application tips for FR-A700 from Mitsubishi UK
A load-sharing application is one where there are two or more motors mechanically connected to drive the same load. In this application a Mitsubishi FR-A700 sensorless vector drive is controlling a long conveyor belt.
In theory, if there are multiple motors that are all supplied by the same frequency, they will all output the same shaft speed and, since they are physically connected, they will all share the load evenly.
In the Mitsubishi configuration a speed reference signal is sent to the Master Drives, and a torque reference from the Master Drive is read into the PLC. The PLC then uses its PID algorithm to create torque reference which is sent simultaneously to each slave drive
Differences in loading, friction, tension and other factors mean that some motors will always pull harder and others will be dragged along by the mechanical linkage. As well as affecting the operation of the system, this leads to nuisance tripping and excessive bearing loads at different points and a tendency to stretch a conveyor belt in some places and bunch it up in other places.
Load sharing applications exist primarily in heavy industries where large loads need to be transported long distances. Example applications include:
• Long Conveyor runs – aggregates, mining, and tunnel boring
• Chain conveyors
The advantages of a Mitsubishi Electric UK solution using
FR-A700 variable speed drives with real sensorless vector (RSV) technology
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