losses and other in power electronic circuit

Thread Starter


Joined Jan 4, 2012
Hello everyone,

It is me, again. I posted a question yesterday about an exam question that i have to answer. But i received a second question and i can choose which one i want to answer. It is also very long and difficult (for me) and again, any idea or start of answer will be appreciated and thanked :). For your information it is a question of the exam of "electric traction" in 1st year of Master of electromechanical engineering at "Université Libre de Bruxelles".

Here is the question:

Consider the chopper based traction system on board of the M5 underground system used by the company MIVB in Brussels (circuit diagram 3R900673, pages 2 and 3).
Calculate and draw the essential waveforms of voltages and currents that occur in the power electronic circuit (4p).
Calculate the average losses in the power semiconductor devices involved with traction (main GTO devices (77.01 and 77.02), freewheeling diode 76.05). Evaluate the losses versus motor voltage, motor current, supply voltage (4p).
Specify the requirements for the thermal resistance for the cooling system so that the chopper can operate up to an ambient temperature of 40 ºC at full power (4p).
Calculate the average losses in the snubber networks resistors (70.25 and R111). Evaluate these losses versus the motor voltage, the motor current and the supply voltage (4p).
Evaluate the stability of the current control system during braking with energy recovery to the third rail supply system (4p).
Additional data:
Maximum motor current: 1200 A;
Maximum supply current (from third rail): 850 A;
Rated motor voltage (two motors series connected): 2 * 350 V = 700 V;
Maximum supply voltage: 1150 V;
Minimum supply voltage: 360 V;
Chopper frequencies:
Rated chopping frequency: 538.2 Hz;
Chopper frequency switches from 538.2 Hz to 269.1 Hz if
δ > 0.88 or δ < 0.07;
Chopper frequency switches from 269.1 Hz to 538.2 Hz if
δ < 0.85 or δ > 0.10;
Chopper frequency switches from 269.1 Hz to 134.6 Hz if
δ > 0.95 or δ < 0.05;
Chopper frequency switches from 134.6 Hz to 269.1 Hz if
δ < 0.92 of δ > 0.08.
The GTO device (77.01) or (77.02) are turned on, on a rotating basis, so that only one of both is conducting at the same time. So, they switch at half the chopping frequency.
10.01: differentieel protection relay;
31.01: switchgear forward-reverse;
31.301: switchgear to select between third rail power supply or from workshop plug;
33.301: Power circuit breaker with automatic overcurrent protection (1500 A);
35.309 en 70.309: precharge circuit;
51.901: motor armature winding;
65.04: smoothing coil;
65.301: input circuit smoothing coil;
66.901: motor field windings;
68.01-02: DC link capactior;
68.09, 76.23, 70.25: snubbernetwork;
70.01, 70.02, 70.03: braking resistors;
70.05, 70.06: field windings - shunting resistors;
70.07: current limiting resistors, used during braking;
71.01: third rail current measurement shunt;
71.02: motor current measurement shunt ;
76.05: freewheeeling diode (D1170 S 25);
76.09: traction-diode;
76.11: braking-diode;
77.01, 77.02: main thyristors (GTO) (DG856BW25);
77.05, 77.06: braking thyristors (GTO);
77.13: braking – thyristor;
77.15: traction – thyristor;
77.17, 77.18, 77.19: thyristors to shunt van 70.07;
81.01: motor armature current measuring device;
81.02: chopper supply current measuring device;
81.302: DC link voltage measuring device.

Here is the link to dowload the figures useful to the questions (i don't know how put a folder in a message on a forum, sorry
you just have to click on "telecharger le fichier".

Again, thank you in advance for your answers.


Joined Mar 6, 2009
I really think you are expecting too much from forum members. The zipped download alone is ~28MB.

This is rather too complex a question and you have failed to comply with the essential requirement of posting homework - to show some of your work first.

Presumably this is an assignment worth a significant percentage of your final subject score. You must demonstrate some knowledge and diligence first.


Joined Nov 25, 2009

Ok, this is an educational site. We do have professionals in our ranks, but the information we can provide for any given subject is rather general.

If you take the time to explain a bit more thoroughly, maybe, just maybe, you might get someone to take interest to it, and get him involved to your question.