Matrix converters, an alternative to standard AC inverter drives,
aren't exactly new. Academic and corporate researchers have been fiddling with
the matrix concept, which eliminates the need for DC electronics, for about ten
years now. Yaskawa
Electric,
however, has announced plans to bring commercial versions of these
groundbreaking drives to North America.
"So far, they've been available mostly in Japan," says Rafi
Wilkinson, a senior product manager for Yaskawa Electric USA. Starting later
this year, the company will offer its line of AC 7 Matrix Converters, which span a range from 7.5 to 60 HP, on our shores.
Unlike
standard drives, Yaskawa's Matrix Converters don't need a DC bus when converting
AC input voltages to variable-frequency AC output voltages. "The matrix converter
directly converts the voltages. There's no intermediate stage at all," says
Wilkinson.
To perform
that direct conversion, the matrix converter relies on control algorithms and
an array of nine bi-directional, IGBT-based switches that sit between
three-phase incoming power source and the three motor leads. Wilkinson says the converter creates a "virtual DC bus" by monitoring the three
incoming voltages and using them to create a reference voltage for PWM control.
The converter's control algorithms trip whatever combination of switches is
needed to achieve the desired output voltage. (Check out the slideshow below for a
more detailed look at the circuitry and principles of operation).
According
to Wilkinson, the voltage drop associated with the switch-based converter
averages 7 percent, not enough to make a difference in most applications. On
the plus side, it offers a three-level output, which can lower surge voltages
and bearing currents.
What's
more, the elimination of DC electronics promises other advantages for end users.
One big one is a reduction in power supply distortion. Wilkinson says the drive
brings harmonic distortion down to 7 percent, compared to about 28 percent or
more for standard AC drives. Another advantage is line regeneration. "The
bi-directional nature of the switches provides an inherent line regenerative
capability by allowing us to direct excess drive energy back to the grid," he
says.
Yaskawa is positioning the AC 7 Matrix Converter as an
alternative to standard drives with external line regeneration module. With its
built-in line regeneration capabilities, the matrix converter takes up less
room and has fewer components than a drive with a separate module. As for cost,
"you would pay about what you would pay for a classic drive with line regen on
the side," Wilkinson says.
Applications
for the matrix converter include materials handling systems, converting machines,
elevators, test stands and HVAC applications. "Pretty much any of the classical
applications with frequent starts and stops," Wilkinson says.
Tweet This
7 
