Improved power circuits save motor energy

Improved power circuits are coupled with the advanced processing power in variable speed drives for electric motors that set new benchmarks for energy saving.

Mitsubishi Electric has launched a new series of variable speed drives for electric motors that will set new benchmarks for energy saving.

Improved power circuits are coupled with the advanced processing power of the latest generation of electronics to provide enhanced power control strategies for the drive.

The FR-F700 features both optimum excitation control, for improved motor efficiency during constant speed operation and acceleration periods, and optimum torque patterns which accurately match the power delivered to that required at any instant.

The speed of optimisation is effectively instant, so the drive is always giving maximum performance and efficiency to the load; previous generations of technology could only effectively optimise for energy efficiency under steady load or speed conditions.

"The F700 will reset the benchmark for energy efficiency," says Guy Kennet, Mitsubishi's Drive Development Manager.

"The ease of commissioning, its predictive maintenance monitor and connectivity to control systems will make it a leader with field engineers, while production managers will love its tripless reliability." Aimed primarily at pump and fan drives, where most energy saving potential is found, the F700 has the intelligence to optimise energy usage for every possible load profile.

For instance some materials, such as batter, can change their viscosity when being mixed and the F700 can instantly detect this and constantly re-optimise its settings to follow the changing conditions.

Additionally, a basic flux vector operation is available for applications requiring high levels of dynamic control.

Excitation control has been a feature of previous generations of Mitsubishi drives, but the new version developed for the F700 performs significantly better across the entire speed range.

The enhanced energy savings at lower speeds can provide up to 12 per cent extra savings against standard V/F performance.

This is particularly significant as many pumps and fans have to be rated to cope with occasional peak conditions, leading to oversizing of the motor and drive system.

Therefore they run for the vast majority of their operating lives with low or very low load conditions, only ramping up to full performance at times of peak loading.

The energy being saved can easily be confirmed using the operating panel on the front face of the drive.

Parameter selection will instantly display current power savings in kilowatts or as a percentage ratio against set criteria, or cumulative energy saving (kWh), energy cost savings in local currency, and various averages over given time periods.

This information can, naturally, be downloaded via the communication network to a central location.

The control panel is detachable and a flying lead allows it to be mounted remotely from the drive, on say the door of a control cabinet.

Parameter setting is via a user-friendly rotary potentiometer and a digital lock can be deployed to prevent unauthorised resetting.

The F700 has many other features designed to save the user money, either directly or indirectly.

One such is the removable terminal block, which means that if a unit has to be exchanged, say during a system reconfiguration project, time-consuming rewiring is not necessary: instead the terminal block is simply removed from the old drive and inserted into the new one.

Significantly the terminal block is compatible with Mitsubishi's previous generation inverters, the 500 series.

The on-board EMC filter is to a new design that ensures compliance with European EMC legislation for industrial environments.

The cooling fan has been especially developed for the F700, using larger than normal bearings for an operating life expectancy in excess of 10 years.

This is further enhanced because the fan is switched off when not required.

To further lengthen operating life while reducing cost of ownership, the F700 also monitors its own key components, such as capacitors and protection circuits, and flags up if/when they are coming towards the end of their operational life.

Similarly a timer will highlight when specified maintenance procedures are due, reducing unplanned downtime.

An RS 485 communication port is fitted as standard and connection to all the major networks and protocols is covered, including CC-Link, DeviceNet, Profibus, Modbus and, for HVAC and building automation, LONWorks.

A USB interface is shortly to be available.

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