Sizing three phase inverter's IGBT

Hi to everyone,
I'm working on a three phase sinewave converter project for a 3 kW squirrel cage motor (230/400 V AC). The converter's topology I have to realize is shown in the simplified scheme in the attachment. I've some doubts about the right selection of IGBT's current ratings.
Assuming for the motor a power factor cosφ = 0.8, I determine the motor's rated current as: I_m = 3000/(1.73*400*0.8) = 5.41 A (RMS).
The questions are the following:
1) In selecting IGBT's rated current, I have to consider the RMS or peak value of motor's rated current?
2) In the IGBT's datasheet are reported 2 values of rated current I_c: one referred to a lower case temperature (25 °C) and the other referred to an higher case temperature (typically 80°C). To rightly choose the IGBT I think that the motor's rated current should be lower than the IGBT's rated current at higher case temperature, which represent the worst operating condition. Is this correct?
3) Since at start-up the motors draws up to 7-10 times the rated current, this high current can damage the IGBTs chosen with reference to the rated motor's current (5.41 A)? Should I choose the IGBT by referring to the peak value of current during the start-up?

This is my first post in this forum and I have written in English only a few times, so I hope you understand me and my poor English!

Hi,
1. Need to consider RMS values. These values are also used for switching loss calculation; Peak values may be limited by control strategies and protective devices for faults.
2. After loss, and heatsink/cooling solution calculation, estimate IGBT temperature; if close to 80C, use this value. Anyway, using this value allow a headroom for lower temperatures.
3. Power converters have advantage that can be controlled, and this advantage is transfered to motor and load. 7-10 times current at stat-up is valid at direct connection to grid; when use a converter you can limit current at any value (theoreticaly), so no problem related to start-up; you can impose maxim allowed current at start-up to obtain maxim acceleration, depending of application.

iop95 said:

Hi,
1. Need to consider RMS values. These values are also used for switching loss calculation; Peak values may be limited by control strategies and protective devices for faults.
2. After loss, and heatsink/cooling solution calculation, estimate IGBT temperature; if close to 80C, use this value. Anyway, using this value allow a headroom for lower temperatures.
3. Power converters have advantage that can be controlled, and this advantage is transfered to motor and load. 7-10 times current at stat-up is valid at direct connection to grid; when use a converter you can limit current at any value (theoreticaly), so no problem related to start-up; you can impose maxim allowed current at start-up to obtain maxim acceleration, depending of application.

Click to expand...

Thanks for your useful answer. Do you know some book, paper, guide or something else which deal with the design of a motor's power converter explaining the choosing criteria of single devices, protections e whatever else? Also some project example.