Drives and Controls Magazine
Next-generation drives ‘deliver 12% extra energy savings’
Published:  23 September, 2015

Mitsubishi Electric has announced a new generation of variable-speed drives which, it claims, can deliver an extra 12% of energy savings over standard variable torque curve operation. The FR-F800 drives are also said to offer other benefits including optimised speed control, simple start-ups, auto-detection of faults, enhanced communications, high reliability, and auto-tuning of induction or permanent magnet motors.

The F800 is designed primarily to control fan and pump motors, but can also be used for compressors and other applications. Initially there are six models, three in ratings from 0.75–110kW for 200–240V operation , and three in ratings from 0.75–630kW, for 380–500V supplies. They are said to be 98% efficient.

The inverters incorporate a “unique” function, called Advanced Optimum Excitation Control (AOEC), that adjusts the motor current constantly to achieve high torque levels at the same time as high efficiency. According to Matt Handley, Mitsubishi’s product manager for drives in the UK, previous systems have required a compromise by optimising either for performance or efficiency.

Another unusual aspect of the VSD is that it can auto-detect pump operating curves using a series of speed and torque points, unlike other systems that rely on a single point to activate trips. The drive can detect the torque curve of an attached pump or fan and react appropriately, eliminating nuisance trips caused by unusual, but not critical, load variations. It can sense both pump overloads (caused by blockages, for example) and under-loads (caused by broken belts or impellers).

The drive has an on-board PLC and two PID (proportional integral derivative) loops. The 6,000-step PLC (based on Mitsubishi’s L series) supports IEC 61131 programming and expandable I/O (via three option slots).

The dual PID capability allows the inverter to control a motor and other external equipment at the same time, avoiding the need for an external controller. The PID functions include a pump-priming function, upper and lower limit pre-warnings, and protection against burst pipe bursts, dry running and water hammer.

The drive can control several pumps, allowing variable-speed control to be applied to some of them, while the others are running effectively direct on-line (DOL). It can run pump-cleaning cycles automatically, to a schedule, or on demand.

Mitsubishi's new-generation variable-speed drives initially span ratings from 0.75–630kW

When controlling fans, the drive can detect broken belts and the built-up of material on their blades. It can ensure a smooth restart after a power failure by auto-detecting the fan speed and “catching” it automatically.

To minimise energy consumption, all unnecessary circuits are shut down during standby. The drive’s “intelligent” cooling fans activate only when a set-point temperature has been reached.

In the event of an emergency, a fire override mode will keep extraction fans and water pumps running – even to the point of the F800’s total destruction.