Inverters get more energy efficient

Using inverters to control and optimise pumps and fans can help companies significantly reduce their energy bills. Dean Palmer compares two recently-launched drives Two new inverters have been launched recently - one that will help companies cut their energy bills and the other to help machine designers develop more compact designs. Starting with the energy efficient inverter, Mitsubishi Electric has developed the FR-F700, a new range of variable speed drives for electric motors that have increased processor speed and optimum excitation control, improving motor efficiency during constant speed operation and acceleration periods. Optimum torque patterns on the F700 also help accurately match the power delivered to the level required at any instant. The speed of optimisation is effectively instant, so the drive is always giving maximum performance and efficiency to the load. According to Roger Payne, divisional manager automation systems at Mitsubishi UK, "previous generations of technology could only effectively optimise for energy efficiency under steady load or speed conditions." Aimed primarily at pump and fan drives where most of the energy saving potential is, the F700 is smart enough to optimise energy usage for every possible load profile. For example, the drive can instantly detect a change in viscosity of a material or liquid and constantly re-optimise its settings to follow the changing conditions. Guy Kennet, Mitsubishi's drive development manager commented: "The F700 is the start of a new generation of drives by the company. The F700 performs significantly better across the entire speed range. These energy savings at lower speeds can provide users with up to 12% extra savings against standard V/F performance." He added that many fans and pumps have to be rated to cope with occasional peak load conditions and so end up having an oversized motor and drive system. The F700 has a detachable control panel, a flying lead to allow it to be mounted remotely from the drive. Parameter setting is done via a rotary potentiometer and a digital lock can be deployed to prevent unauthorised re-setting. There is also a removable terminal block to save users on re-wiring costs, and it is compatible with Mitsubishi's previous generation inverters, the 500 series. A new EMC filter is included which ensures compliance with European EMC legislation for industrial environments and there's also a new cooling fan which, because it uses new, larger bearings and the fan is switched off when it is not required, has a life expectancy of 10 years. Oh, and for the environmentally aware end users, the black coloured enclosure on the F700 is manufactured from a durable, recyclable plastic. The other new inverter is the new miniature Jaguar 'Cub' developed by IMO Precision & Controls. This should appeal to design engineers or machine builders in applications where space and performance are at a premium. The drive, which is small enough to fit in the palm of a hand, delivers a higher motor starting torque using STV technology, a simplified version of IMO Jaguar's torque-vector control system for consistent, powerful operation. Running at 5Hz and using an advanced magnetic flux estimator and motor slip compensation with auto-boost, starting torque can be as much as 150% or more. By keeping motor loss to a minimum, the Jaguar Cub saves electrical power in fan or pump applications. At 1Hz, IMO claims the STV technology "improves voltage control performance and reduces motor instability at low speed to about half or less than that of a conventional inverter." The inverter comes with timer operation, input and output phase loss protection, loss-of-load protection and thermostatically-operated long life cooling fans designed to last for seven years at 40°C. And, like Mitsubishi's F700, to reduce noise and save more energy, the Cub's cooling fan can be turned off when not required. A DC reactor can be connected to the Cub in order to limit mains supply circuit harmonics and the unit is fitted with a PTC thermistor input and PID control. There's also condition monitoring software and alerts available and enhanced network connectivity one would expect these days. And like my new Hyundai car, the warranty is five years! Pointers * Inverters are being developed that are smaller and more energy efficient for fan and pump applications * On Mitsubishi's new F700 inverter, the speed of optimisation is instantaneous, ensuring the drive always gives maximum performance and efficiency to any given load * IMO's Jaguar Cub miniature inverter sits in the palm of the hand and will appeal to machine designers in applications where space is at a premium