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Homework Help: Power Electronics Rectifier Firing Angle and Overlap Angle

  1. Dec 30, 2017 #1
    1. The problem statement, all variables and given/known data
    upload_2017-12-30_11-53-18.png

    2. Relevant equations
    Since question says the current is always continous, so overlap is always there. So option B is incorrect.
    Also since firing angle is increased from 0 to 45, the overlap angle will reduce. So it'll be less than 45. So option A is incorrect.

    3. The attempt at a solution
    I don't know how to eliminate either C or D.
    Book says answer is C.
    But how?
     
  2. jcsd
  3. Dec 30, 2017 #2
    I have not been studying this, but I believe I know how to solve it based on this document: https://subjects.ee.unsw.edu.au/elec4614/Lecture 10 - Overlap in 1-phase circuits.pdf

    See page 4, equation 10.3:

    [itex]\cos(\alpha+\mu) = \cos \alpha - \underbrace{\frac{\omega L_s}{V_{max}}I_d}_{\text{constant}} \tag {10.3} [/itex]
    We want to find the overlap angle [itex]\mu[/itex].
    First we calculate the constant in the equation above, using [itex]\mu = 45^{\circ}[/itex] and [itex]\alpha = 0^{\circ}[/itex].
    When we have obtained the value of the constant term, we use the same equation and solve for [itex]\mu[/itex] with [itex]\alpha = 45^{\circ}[/itex]
    In my case this gave me [itex]\mu = 20.53^{\circ}[/itex].

    As I said I have not been studying this, so it would be nice if someone could verify this.

    Also, I would recommend you to understand how equation 10.3 is derived and not only insert numbers and use it.
     
    Last edited by a moderator: Dec 30, 2017
  4. Dec 30, 2017 #3
    How do I remember all these formula for the exam? There single phase, three phase, half wave, full wave, semi converter and full converter. Then there's same single and three phase for inverters.
     
  5. Dec 30, 2017 #4
    You should try to understand how the expressions are derived and be able to derive them yourself. By drawing figures (circuit, waveforms etc.) relevant for your problem you should be able to derive expressions using basic tools such as Ohm's law etc.

    During my first years at university I just tried to memorize the equations for the exams, but you do not really learn anything doing it that way, atleast I dont.
    Later, when I realised I had to understand how the equations etc. are derived from the basics we already know (basic physics, math, electrical circuits etc.) things went so much better...
     
  6. Dec 30, 2017 #5
    Thanks. Am practicing derivations now.
     
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