# electric traction system

#### audric

Joined Jan 4, 2012
3
Hello everyone,
I'm a student in electromechanical engineering and i received a difficult question for my exam and i need to answer it. But i don't know how to start and which steps follow to answer. So i decided to ask your help. I know the question is long so i will understand if anyone doesn't want to answer. But all idea or solutions will be appreciated and thanked.
Here is the question and the given data's:

In electric traction systems with power electronic converters measures are needed to avoid DC link voltage instability, associated with large supply line current fluctuations. This can be analysed on lab scale with the model described below.
The DC power supply, including overhead line, is simulated by means of a transformer fed diode rectifier and a 10 mH reactance. The traction system itself is modelled by a DC-link capacitor (15000 μF), a power transistor and a freewheeling diode connected to compose a chopper. The traction system input reactance is simulated as part of the previously mentioned 10 mH reactance. The traction motor is simulated by means of a DC motor with series connected field windings, loaded with a DC generator.
Analyse by means of simulation the control measures that have to be taken to damp the fluctuations, with minimal loss of torque control dynamic performance, which is needed for anti-skid control by the traction system.

Evaluation criteria are as follows: Quality of the mathematical models and the simulation models; Quality of transfer functions used for the control analysis. Quality of the proposed solutions (8);
Adequacy of the proposed control systems (4);
Quality of the simulations, in particular taking into account the non-linear behaviour (4);
Quality of the controls, in particular with respect to the damping of the fluctuations and preservation of the control dynamics (4).

Power supply network three phases 380 V, SC power: 30 MVA
Three phase transformer
• 380V/220V
• Y-D connection
• Rated power: 20 kVA
• Short circuit voltage 2%

Diode rectifier
6 diodes, bridge connected
• Rated current 200 A
• Output inductor: 10 mH, 100 A;
Chopper
• Semiconductor devices voltage rating: 600 V
• Semiconductor devices current rating: 200 A
• Switching frequency: 1 kHz
• Output inductor: 5 mH, 100 A, 0.08
Ω
DC motor
Field inductor: 12 mH, armature inductivity: 5 mH
• Armature resistivity: 0.16
Ω, Field inductor resistivity: 0.05 Ω
Inertia (inclusive load machine): 0.85 kg m2
• Rated armature voltage: 220 V
• Rated armature current: 100 A
• Rated rotation speed: 1000 rpm
• Rated power: 19 kW
Control system
PI current control system tuned to have maximum bandwidth and step response overshoot of 10%.
• The current measurement is done with a hall probe compensated current transformer.
• The load machine is controlled to simulate the vehicle dynamic behaviour.

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#### t_n_k

Joined Mar 6, 2009
5,455
Are you allowed to use simulation software in achieving your solution?

This looks rather more like an extensive work assignment rather than an exam question.

#### thatoneguy

Joined Feb 19, 2009
6,359
Are they asking for coefficients for a PID controller without the D?

An entire schematic for a control system?

This is a rather large problem.

#### strantor

Joined Oct 3, 2010
6,690
Are they asking for coefficients for a PID controller without the D?
PI control is out there; i have run into it a few times, as well as PD control. It works ok for systems that don't need the precision of PID. It's a heck of a lot easier to tune as well.

#### thatoneguy

Joined Feb 19, 2009
6,359
PI control is out there; i have run into it a few times, as well as PD control. It works ok for systems that don't need the precision of PID. It's a heck of a lot easier to tune as well.
I understand that, I'm just not sure what the question is asking for, if that makes sense.

#### strantor

Joined Oct 3, 2010
6,690
I understand that, I'm just not sure what the question is asking for, if that makes sense.
ah, ok. sorry.

#### audric

Joined Jan 4, 2012
3
Are you allowed to use simulation software in achieving your solution?

This looks rather more like an extensive work assignment rather than an exam question.

I'm agree. It looks like very difficult. Yes i suppose i can use any software i want for it.

#### t_n_k

Joined Mar 6, 2009
5,455
Have you drawn up the block diagram for the system?

#### GetDeviceInfo

Joined Jun 7, 2009
2,174
Several years ago I wrote my Electrical TQ, where several questions involved long sequential calculations. It was relatively easy as the concepts where 'top of mind', thanks to the fact that I had just spent 3 months in school studying those specific concepts. I couldn't do those calculations today without substantial review.

The point is, your best resources for assistance will likely be a paid professional working in the field, or one of your classmates that has the subject 'top of mind'.