According to Mitsubishi's drives manager, Chris Cusick, active filters
are the way ahead in fighting mains corruption and meeting the harmonic
distortion levels demanded by the electricity suppliers. Their
performance/cast ratio is unrivalled by competing technologies, he says,
and users are adopting them so rapidly that they will become the
dominant type within a few years.
Twelve-pulse bridge filters typically cancel out 80-90% of all harmonics,
but are very bulky. The switched bridge harmonic controller may be the
'Rolls-Royce' of filters, achieving greater than 95% correction, but it
is beyond the reach of most automation budgets. Active filters often
match switched bridge controllers for performance, but at a fraction of
the cost. In operation they absorb incoming harmonic currents, invert
them and feed them back to the mains to 'neutralise' further currents.
They also respond quickly to load changes - an area where all other
technologies struggle to maintain performance.
Mitsubishi recently established a supplier agreement with a leading
manufacturer of active filter systems, AIM Europe, and has been fitting
AIM filters to its portfolio of drives products. The company will
initially be introducing the technology to the water industry, which has
some issues regarding harmonics that it has not been able to address
adequately with existing technologies.