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Tampere University of Technology 1842-2076
Electrical Engineering DEE-34016 Modeling and Control of Electric Drives
Jenni Rekola Programmable calculator allowed 5 guestions/ä 6 p

Answers in English or in Finnish allowed
1. Control of separately excited DC machine

a) Draw control block diagram of separately exited DC machine operating in four guadrants with
speed control and shortly explain the figure.

b) The open-loop freguency response of separately excited DC machine is presented in Fig. 1. Are
the control parameters well chosen? Why?

c) What means the anti-windup of the integrator in the control system? What might happen without
the anti-windup?

d) How the anti-windup of the integrator can be realized?

e) How the discretization of the control system might affect to the control?

£) How the un-idealities of the real-world motor drive and its control might differ from the ideal
system?

 

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Freguency (rad/s)
Fig. 1. Open-loop freguency response of separately excited DC machine

2. Control of an induction motor

a) Explain briefly the operation principle of scalar control method (Volts/Hz-control, U/f-
control)?

b) What measurements are reguired in scalar control method?

€) What means IR-compensation and why it is used?

d) How the control changes depending on the operation region (constant voltage region or field
weakening region)?

e) Why the vector control (field oriented control) or DTC are used instead of scalar control?

f) How the reguired magnetizing current of the induction machine varies depending on the
operating method of the motor (motor mode or generator mode)?

10)
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Tampere University of Technology

19.12. 2016
48-422016-

Electrical Engineering DFE-34016 Modeling and Control of Electric Drives

Jenni Rekola

Programmable calculator allowed 5 guestions/ & 6 p
Answers in English or in Finnish allowed

3. Control of an induction machine

9)

D)
o)
K)
o)
d

Draw the control block diagram of direct vector control (field oriented control) of an
induction machine and explain it briefly.

What reference frame is used in direct vector control (field oriented control) and why?

Why the flux model is needed in the control system?

What measurements are reguired in direct vector control (field oriented control)?

What measurements are reguired in direct torgue control (DTC)?

The switching freguency of the IGBTs in the motor inverter is not constant if DTC is used.
Mention some advantages/disadvantages caused by non-constant switching freguency.

4. Compare the following control methods: scalar control (Volts/Hz control, U/f-control), vector
control (field oriented control), direct torgue control (DTC)

 

a) Which method produces fastest torgue control?

b) Which method enables accurate control during transients?

c) Which method enables accurate control without speed sensor?
d) Which method reguires stator current measurement circuit?

e) Which method is suitable to pump and fan applications?

£) Which method is reguired in cranes and elevators?

Multiple control methods might be a correct answer to one guestion. In this case, mention all of them.
5. Model Predictive Control

a) Explain briefly the basic idea of model predictive control method (2p)

b) Mention the main differences between model predictive control and basic linear control based on
PI-controllers

c) Mention pros and cons of model predictive control method (2p)

d) What kind of system can be controlled by model predictive control method? Are there some
limitations?

20)