Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - Classic Control - Manual (Page 25)

1-8 Overview of Drive
7000-UM150I-EN-P – June 2013 7000 “B” Frame
SGCT Features and Benefits
An SGCT is a Symmetrical Gate Commutated Thyristor with an
integrated gate drive. Positioning the gate drive close to the SGCT as
shown in Figure 1.6, creates a low inductance path that provides
more efficient and uniform gating of the device. As a result, the
device is better suited than a conventional GTO to handle the
fluctuating levels of voltage and current while it is switching on and
off during gating.
An SGCT has similar characteristics to an IGCT (used on some VSI
drives), including low conduction and switching losses, low failure
rate, and double sided cooling for low thermal stress. However, the
SGCT achieves voltage blocking capability in both forward and
reverse directions up to 6500 volts by a NPT (Non-Punch-Through)
structure and nearly symmetrical pnp transistor in the wafer, while
the current is unidirectional.
The IGCT only blocks voltage in one direction and allows current
flow in both forward and reverse direction, thus needs a built-in anti-
parallel diode.
Implementing SGCTs in the PowerFlex 7000 results in significant
advantages including:
1. Simplification of the snubber design and a reduction in the size
of the snubber capacitor by a factor of 10.
2. Operation at a higher switching frequency (420-540 Hz), hence
reducing the size of passive components (DC link inductor and
motor filter cap) by 50%.
3. Improving performance of the drive.
4. Reduction of component count, hence improving reliability, cost,
and size of the drive.
5. Fail safe failure mode (non-rupture).
Figure 1.6 – SGCT with integrated gate drive (left) and unit cell structure (right)