# about my power electronic exam

Discussion in 'Homework Help' started by ron8861, Jun 17, 2012.

1. ### ron8861 Thread Starter New Member

Jun 17, 2012
4
0
IN the pdf file i have three question about power electronic

in the first question inverter feed to the inductive load,S1 and S2 switches working half period(S1 open half period after S2 open half period)they are not open at the same time.you can see given values
in a)plotting el,is1 and id1 graphs changing with time.
in b)and calculate average currents on switch and diode.

in second question buck converter;C has very big value,the switch open at 400microsec and closed at 400microsec too.with an ideal circuit elements a)plotting to the is,il and ic current graph

and last question 3 phase rectifier Ll has infinity value.with an angle a=0 value Vd=300V.For an Id=120A calculate a and commutation angle u

please help me about this questions.in the first question the output current in the inverters io going to the rght but in this il going to the left.how can be the el graph in the second question i think ic current always become zero for an open circuit.D=1/2 and on the 2.5 ohm resistor we have 125V and how can be the il graph with this values.
thanks from now for your helps.20 june will be last time.

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2. ### WBahn Moderator

Mar 31, 2012
18,087
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I can't read whatever language this is in, but the indications are that this is a Final Exam for this course, not a review sheet or such. If so, then are your sure asking for help on it is allowed?

3. ### ron8861 Thread Starter New Member

Jun 17, 2012
4
0
this is not actually a final exam questions teacher gave this questions and we will make them at home after one week we will deliver it to the teacher.i explain what means on the questions.it is not english!!

4. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
I know it's not English. What language is it, Norwegian?

Thanks for the partial clarification. What are the ground rules for this assignment? It now sounds like a take-home final. Here, in general, take-home exams are expected to be solved without assistance from any source other than the instructor. What is the expectation there, for this particular assignment?

5. ### ron8861 Thread Starter New Member

Jun 17, 2012
4
0
hmm there is no restriction in this exam.teacher said solve this problem and bring me..if he want to see how i solve them he said 'u must choose them alone and without any helping'..i just want to take some suggestions about these questions.i had some idea about these questions

6. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
The the first problem: It sounds like we are assuming ideal and instantaneous switching. Assume the system starts out with zero current and both switched open.

Q1) Now start the thing working and close S1 for 50µs. How much current is flowing in the different branches of the circuit at that time?

Q2) Now open S1 and close S2 and apply the continuity conditions for an inductor. How much current is flowing in the different branches of the circuit at that time?

Q3) Now wait 50µs. How much current is flowing in the different branches of the circuit at that time?

Q4) Now open S2 and close S3 and apply the continuity conditions for an inductor. How much current is flowing in the different branches of the circuit at that time?

Q5) Does the answer to Q4 match the initial conditions? If not, then the system is not in steady state. If it does, then calculate the requested averages.

Q6) Now repeat the exercise only close S2 first. Do you end up getting the same averages as Q5? If not, then the answers may depend on initial conditions.

7. ### ron8861 Thread Starter New Member

Jun 17, 2012
4
0
what kind of formulas that i used in this current calculations.in ned mohans book there is nothing explaining about half bridge inverters i write google about half bridge inverters and i found different kind of things.just mentioned about with and instant voltage changing inductor current doesnt change instantaneously

8. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
Don't go looking for a bunch of formulas that apply to this specific circuit. Apply the fundamental circuit analysis skills that should have been the whole point of several classes leading into this course. Part of those fundamentals should have discussed what can and what can't changed instantly with regards to different components.

9. ### MrChips Moderator

Oct 2, 2009
12,635
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Turkish

GEBZE HIGHER INSTITUTE OF TECHNOLOGY
Electronics Engineering

SCIENCE 629 Advanced Topics in power electronics

Q-1: a figure of pure-phase inverter
feeds the inductive load L. each
switch S1 and S2, respectively, each half-peryotta
açılmaktadırlar shuts down (or off at the same time
not clear). E = 10 V, L = 100μH, and f = 10kHz
According to that;
a-eL, voltage and currents IS1 and ID1
depending on the time to draw graphs.
b-flowing through the switch and diode
Calculate the average values ​​of currents.

Q-2: The following step-down (lowering) DC-DC converter that is very large capacitor C
Let's face. 400 μsec when the switch is open and closed. Ideally, the use of circuit elements according to
a-iS, iL, and iC grfiklerini depending on the time of the draw.