With energy costs on the rise, it's no surprise users of
large motors have started to ask for big, fast variable frequency drives that
can help them cut their power costs. Siemens
Energy & Automation
has responded with a VFD that sets a new benchmark in combined size and speed.
The company has introduced an 8-MW Robicon
Perfect Harmony VFD that
operates with an output frequency of 500 Hz. According to Mark Harshman,
engineering director for Siemens large drive applications, it's the world's
largest high-speed VFD. "There are some big drives out there with outputs in
the 180 to 240 Hz range, but we've eclipsed them," he says.
The leap to
even faster VFD output frequencies is significant because it lets users deploy
smaller, faster motors without giving up power. Harshman estimates some
heavy-duty industrial applications could get by with motors that are about
one-third the size of what they would be with lower-frequency VFDs. Significant
energy savings would result from the motor downsizing.
Siemens had previously produced large drives with outputs in the
315 to 400 Hz range, but a control algorithm redesign bumped the output up to
500 Hz. "We won't be able to achieve the next step through software alone. The
hardware will have to change too,"
Harshman says.
In testing,
the new 8-MW drive was able to operate the motor in encoderless vector control
with 920 Hz IGBT switching frequency, resulting in an effective switching
frequency of 9.2 kHz and a sample frequency of 9.2 kHz.
This new
breed of VFDs can drive the efficient permanent-magnet motors that are increasingly
attractive in oil, gas and transportation applications – particularly those
requiring high-speed compression.
Harshman predicts the output frequencies will continue to rise with
subsequent generations of VFDs. "It's all being driven by the motor vendors and
users," he says. "We're just keeping up."
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