Enter Varispeed G7 - The Motor-Friendly Inverter .
01 July 2002
Enter Varispeed G7 - the motor-friendly inverter
Yaskawa is claiming a few technology breakthroughs with the launch of its
Varispeed G7 inverter drive (0.4-300kW), which was shown for the first
time in the UK at the Drives & Controls show. The most significant is
'Three Level Control', which has the effect of reducing the PWM waveform
dv/dt by 50% and thus halving the output voltage to the motor.
This has some important advantages in terms of motor protection, not
least being big reductions in potentially damaging bearing currents,
audible noise, RFI, EMI and reflected voltage waves. As a result,
Varispeed G7 can be used in conjunction with old or existing motors,
without having to install output chokes - even on cable runs of 300m or
A new open loop flux vector control method has been introduced, which is
claimed to achieve the performance of a closed loop system with encoder
feedback, effectively doubling the open loop speed control range from
100:1 to 200:1. Open loop torque control is also improved to 150% or more
of the motor's full load torque at 0.3Hz.
All this development work is, however, reflected in the price. The G7
costs around 50% more than equivalently sized drives, but Yaskawa
believes the performance bonuses and the reduction in additional EMC
hardware requirements more than make up for the difference!
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