ABB 2032-04-16-06 The Integrated Gate Commutated Thyristor

ABB 2032-04-16-06 The Integrated Gate Commutated  Thyristor

DESCRIPTION

The outstanding feature of the IGCT - leading to its name and its  main advantages - is not only the silicon wafer itself, but the way  it is driven by the gate - the electrical and mechanical gate-drive  design. The «hard- drive» concept at the heart of IGCT operation  requires the mechanical integration of gate driver and semiconductor into one single unit with low circuit inductance. It also  implies a number of new converter features, which make IGCT  converters different from GTO or IGBT converters. It is the scope  of this application note to make designers familiar with the data  sheets and the use of IGCTs in their main application areas.

The following features are important to remember:

• no turn-off snubber is needed in applications without series  connection; where turn-off snubbers are used, they are  considerably smaller than those of GTOs 

• the customer control interface is reduced to a power supply,  an optical control input and an optical status feedback output 

• gate drive geometry is an important parameter in mechanical  stack design.

Data sheet user’s guide

This section is a detailed guide to the correct understanding  of an IGCT data sheet. Parameters and ratings will be defined  and illustrated by figures where appropriate, while following the  sequence in which parameters appear in the data sheet. For  explanation purposes, data and diagrams associated with IGCT  type 5SHY 55L4500 have been used, but because all IGCTs  have similar data sheets, this guide is applicable to all IGCTs.  Additionally a 5SHX 26L4520 data sheet is used to explain the  diode parameters of reverse-conducting devices. The data sheets distinguish between maximum rated values and  characteristic values. Maximum rated values indicate limits  beyond which damage to the device may occur. Characteristic  values are parameters defined under typical application  conditions.

Key features

·High snubberless turn-off rating
·Optimized for medium frequency
·High electromagnetic immunity
·Simple control interface with status feedback
·Ac or Dc supply voltage
·Option for series connection (contact factory)

Thermal data

In addition to the thermal data of the IGCT, the data sheets of  reverse conducting IGCTs have thermal data for the diode part.  The data is documented in the same way as in section 2.6. Rth and Zth are specified without heat flow between the GCT-part  and diode-part.

IGCTs in Voltage Source Inverters (VSI)

Reverse conducting IGCTs (RC-IGCT), asymmetric IGCTs  (AS-IGCT) and their corresponding diodes are qualified and tested  in test circuits built according to the circuit diagram below. It is  an equivalent circuit for the switching events occurring in a VSI  circuit, be it of 2-level or 3-level topology.

Determining the value of the di/dt limiting inductor

In a VSI, as in most power electronic circuits, a diode turn-off  is caused by an IGCT turn-on and the diode’s turn-off di/dt  capability is, in most cases, lower than the turn-on di/dt  capability of the IGCT. This is especially true in common applications without a turn-off snubber. Hence the di/dt choke LI  must be  large enough to allow operation within the di/dt range of the diode  even at the highest DC-link voltages. Typical values for  ABB diodes are between 200 and 1000 A/µs depending on  diode wafer size and switching voltage. Diode switching losses and surge currents are also dependent  on the choke size and these considerations may require a larger  inductance value. This, however, will come at the cost of a slower  clamp circuit transient (tdyn) and longer switching dead times.