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%

• 6 diodes, bridge connected

• Rated current 200 A

• Output inductor: 10 mH, 100 A;

• DC-link capacitor: 15000 μF

• 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

• 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

• 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.

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**• DC-link capacitor: 15000 μF

• 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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