TechArchive

Original article date: October 1999

Is it possible to have an efficient drive that provides multiple control modes? It seems so, as Tommy Miller has been finding out

System developers often want one unit that will do many tasks. This can reduce the time it takes to get up the learning curve as well as reducing stock holding. Meiden is now launching the VT230S, which is a five-in-one vector drive that can provide an effective means control for a very wide range of applications. It also enables motors to run much quieter.

The five operating modes are as follows:

1. Variable frequency control for variable torque loads with ‘advanced torque control’. This mode uses auto tuning to give voltage vector control in open loop.

2. Variable frequency control for constant torque loads with advanced torque control. This mode again uses auto tuning to give voltage vector control in open loop but, in this case, withoutthe higher constant current rating associated with the above type.

3. Sensorless vector control. In Meiden’s case, this refers strictly to flux vector control without use of an encoder. Becaus ethere are two current loops – to control the magnetising and driving currents independently – it is possible to achive torque at zero speed, which is claimed to be an industry first.

4. Closed loop vector control, where an encoder is required. However, if the encoder signal is lost, the drive will switch automatically to sensorless vector control and will also send an alarm output.

5 Permanent magnet motor control. Although Meiden has provided this facility in the VT230S architecture, the company has not yet launched its range of dedicated permanent magnet motors.

It can be seen that the range of applications for which the VT230S will be suitable is far greater than would be the case for a conventional drive – whatever its operating mode.

Quieter motors

Apart from the VT230S being very versatile, its other notable feature is how much more quietly it makes motors run. The characteristic whine of an AC motor under inverter control can be effectivley reduced by means of the ‘soft sound’ technology which randomly changes the VT230S drive’s switching frequencies.

Following tests, the development team found that there was no single set of frequncies through which the inverter could be switched randomly to have a satisfactory effect on all motors. This is due to the root cause of the noise: resonances in the motor laminations, whcih will be different for every motor. It is therefore necessary for the commissioning enginer to alter certain parameters to reduce the noise levels. However, this is relatively simple because adjustments can be made with the motor running, which allows the results to be heard immediately.

• Meiden

October 1999