Pioneering `drive-on-a-plate` opens up OEM applications

The Welsh drives-maker Invertek has unveiled a pair of developments which, it believes, could give it technological leads over its larger rivals. They are a low-cost, rugged inverter built onto a steel plate, which can be incorporated into equipment such as pumps and washing machines, and an open-loop AC drive which, the company claims, achieves the Holy Grail of full torque at 0.0Hz.

The drives made their debuts at the Hannover Fair in April, where the open-loop drive was demonstrated suspending a 10kg weight without any mechanical assistance.

The steel-plate drive (below) uses technologies originally developed for the automotive industry to print circuits and components onto a stainless steel plate which acts as a heat sink. The result is a compact, robust drive suitable for applications usually considered too arduous for conventional drives.

The Compact Optidrive`s electrical interconnections and laser-trimmed resistors are printed directly onto the steel plate. Other components, including the power semiconductor die, are surface-mounted onto it. The die is connected to the circuit using a wire bonding technology, thus eliminating the extra packaging normally needed for these components.

The low-profile components are resistant to vibration and the whole assembly can be encapsulated to give it an IP21 level of protection. No physical connections are needed to program the drives because they use Invertek`s infra-red based Optiwand technology.

Invertek has signed an exclusive five-year contract with a sub-contractor which developed the technology for automotive applications. Initially the drive will be available in ratings up to 1.5kW, but Rhydian Weslon, Invertek`s sales and marketing director, says that the aim is to extend the range up to 4kW. At first, the drives will cost about 30% less than a conventional inverter, but Weslon hope to boost that figure to 50% "when volumes start coming through".

Invertek has already taken its first orders for the technology from Europe and the US for OEM applications including cranes and heating and ventilation equipment. For large orders, the shape of the plates can be tailored to the application. For smaller orders, there will be standard designs.

Another possibility is to use the steel-plate drives as the basis for integrated motor-inverters and, according to Weslon, Invertek is already talking to motor manufacturers about this possibility.

Invertek`s second new development is a range of drives that it says will deliver their full rated torque at zero speed, without overheating the motor or needing any form of feedback device. In its Hannover demonstration, the drive was controlling a motor holding a 10kg weight in a steady position without using an encoder.

To perform this feat, the drive measures voltage and current very precisely and performs continuous real-time tuning of the motor parameters, explains David Jones, Invertek`s R&D director (shown in the photo, above). "The difficulty is the temperature, which increases as the motor holds steady, and this affects the resistance," he adds.

The Optidrive Plus is not designed to hold the full torque at zero speed indefinitely. It typical applications, 10—20 minutes should be the maximum, says Jones.

The Optidrive Plus is based on Invertek`s existing technology which it will replace at a similar price. Weslon stresses that it is a standard inverter, not a systems drive, which is also suitable for demanding applications such as hoists and elevators. It will span ratings from 0.37--160kW.

Other characteristics of the new drive include: eight preset speeds; built-in PI control; continuous real-time tuning of motor parameters; simple set-up using the motor`s nameplate data; and programmable S-ramps.

A third new arrival on Invertek`s Hannover stand was a low-cost Optidrive, costing about 30% less than standard models. Called the Optidrive E, the entry-level range covers ratings from 0.37—2.2kW and dispenses with the infra-red communications of other Optidrives. Weslon says that it will help Invertek to compete at the bottom end of the drives market.

Finally, Invertek was demonstrating a new version of its Optistore parameter editing and storage software which now supports satellite communications, allowing users to monitor and log Optidrive data from a PC anywhere in the world.