AC to DC Design

You are really out of your depth with this and I feel that the help you need at this stage is "face to face".The current form shown for your RL circuit is a concern and there is no consideration of resonance and other possible outcomes.

Your MATLAB results seem to indicate that you've modelled "ideal" diodes with no forward voltage losses (as one example of why you need face to face support.). Your input current waveform also seems odd, as you have high delta "i" exactly corresponding to your Vin zero crossing even though the load is not resistive.

how can i have face to face support ? :)

How about talking to your course tutor, Mildred?

Not sure what your constraints are for the application however it appears you are forgetting to add capacitance into the equation which is a very critical part of DC waveform filtering.

Keep in mind that capacitance is the inverse of inductance and will decrease/improve circuitry impedance.

Every circuit design has some nominal low capacitance value which normally must be factored in when using a modeling program.

If you assume zero circuit capacitance it will have a negative affect on the waveform shape and increase circuit total impedance.

A strictly inductive circuit presents very high impedance values which can increase the size of the rectifier physical footprint and significantly add to the overall cost.

To minimize output ripple you must add a RLC network filter across the rectifier output terminals as part of the design.

You should be able to plug the design variables into MATLAB, observe the output waveform components then determine the needed filter component values.

Most likely you will have to develop a table of calculated filter component values then plug them in one at a time to observe and fine tune the rectifier output waveform to acceptable design limits.

Good luck!

Homework?

please if you can help me , give links or show me a way.

just very basic question

1) when i decrease the R in the load (suppose my output current increase)but why also my input current increase ?

2) the power rate of the load is 5kw , P= v.i => I out should be around 16.667

because i =p/v= 5000/300= 16.667 . is it ok?

3) also Z= V/i so Z= 300/16.6667 = 18 so R^2 +(wL)^2 = 18 if like this i calculate and assume R to find L or assume L to find R. i get different current output. High current or high ripple. or i should ignore this part and just focus in No.2 ?

tq

) when i decrease the R in the load (suppose my output current increase)but why also my input current increase ? Power In - Power Losses = Power Out - The software is maintaining this basic law of physics.

2) the power rate of the load is 5kw , P= v.i => I out should be around 16.667

because i =p/v= 5000/300= 16.667 . is it ok? Yes the value fits in the equation.

3) also Z= V/i so Z= 300/16.6667 = 18 so R^2 +(wL)^2 = 18 if like this i calculate and assume R to find L or assume L to find R. i get different current output. High current or high ripple. or i should ignore this part and just focus in No.2 ? It depends on if this is an abstract problem or a "real world" design application. How finite are the design constraints? What are the design tolerances? You must know these requirements then do the math in the correct formulation in order to solve the issues.

Why do with computers that is difficult to understand when you can do the same thing with a few Schade's curves that are much easier to understand? Ask your professor if she or he even knows that Schade's Curves exist. You might get extra credit for this one.

You want to get a copy of the paper titled, "Analysis of Rectifier Operation" by O.H. Schade. It was published in 1943. Yes, 72 years ago. Mr. Schade put a lot of work into those curves. Don't waste his efforts by ignoring them.

Put away the computer, read a few papers and get into the lab. That is the only way you will learn anything. You can scale your experiments down to get a first order solution that can be verified using reasonably common lab equipment. I find that with computers, students like to use them as a crutch, thinking that the computer will think for them and fail to learn about real life. Don't fall into that trap.

Here is an excerpt from the paper with a figure discussing regulation of a full-wave rectifier driving an RL load.

Good luck with your quest.

I was going to mention Schade curves but Brave Sir Robin beat me to it. As manufacturers of transformers and dc power supplies they are the most useful set of formulas and curves and apply equally to silicon diodes as they do to vacuum tube rectifiers. I once had a customer who insisted we make the transformer he had calculated so we did that and also made him one as calculated with Schade curves. We were within 1% while his design was about 30% out.

Well worth getting these curves and understanding the influence of all the circuit components from the input of your transformer to rectifiers, capacitors, inductor and the details of the DC load. Also don't forget the RF suppression capacitors across the rectifier and the main filter capacitors.