Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Simulation Buck Converter

Oranje

Newbie level 4
Joined
May 8, 2019
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
77
Greetings Experts! I am trying to solve a homework problem on the subject of Power Electronics (DC-DC Converters--Buck Converter). The following problem statement has been provided:

1. Ideal source battery = 100Vdc

2. Load = Series combination of resistor (0.25 ohm), inductor (1mH), battery (10Vdc)

3. The total period (control time) of the chopper is 2.5ms and the ON time is 1ms.

My question is how to properly set-up this circuit in Pspice because my waveforms look incorrect. I have provided the link to the Pspice files and the image of the desired waveforms from the book. I believe my problem is in the Vpulse parameters, however, I do not have enough experience to understand what exactly to change. Please help.

View attachment buck.zip

IMG_1788.jpg

2019-07-14_031813.jpg
 

Easy peasy

Advanced Member level 5
Joined
Aug 15, 2015
Messages
2,429
Helped
894
Reputation
1,788
Reaction score
882
Trophy points
113
Location
Melbourne
Activity points
13,781
you can't turn an SCR off once fired - so your ckt needs a xtor or mosfet - which you can turn off

the SCR will stay on forever once triggered ...
 

Akanimo

Advanced Member level 2
Joined
Aug 30, 2016
Messages
608
Helped
109
Reputation
218
Reaction score
106
Trophy points
43
Activity points
4,258
Also look at the switching frequency. It's about 400Hz and I believe that's too low.

When you change your main switch to MOSFET, ensure you have sufficient gate drive voltage.

You mentioned that the 1mH inductance is part of your load. This suggests that it cannot be changed. But really, 1mH inductance as part of a battery is...

Well, ignoring the 1mH-load connection, by visual inspection 1mH seems to me a high value already for your spec. Umm, you may need to back calculate for switching frequency.

This is a charger so you have to give info on the charging voltage (and current).

Also, I'd recommend you change your rectifier diode to transistor too.

With these, i believe we can start from here.
 
Last edited:

Easy peasy

Advanced Member level 5
Joined
Aug 15, 2015
Messages
2,429
Helped
894
Reputation
1,788
Reaction score
882
Trophy points
113
Location
Melbourne
Activity points
13,781
a good idea to leave the diode as it is - keep things simple initially, it is fairly obvious the 1mH choke is part of the buck ckt.
 

Oranje

Newbie level 4
Joined
May 8, 2019
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
77
Greetings. I have replaced the SCR with an NMOS. The 1mH inductor is part of the 'motor' armature which is represented by resistor, inductor, and back-emf (10Vdc) combined. Correct me if I'm wrong, but the back emf is only applicable during steady-state operation of a motor, such that it has gained its rated rpm. At start-up, back-emf is very small. So, this analysis is for a motor which is in steady-state operation?
Can anyone provide the correct settings because the waveforms are still incorrect with swapping the SCR with an NMOS.

2019-07-16_223330.jpg
 

Easy peasy

Advanced Member level 5
Joined
Aug 15, 2015
Messages
2,429
Helped
894
Reputation
1,788
Reaction score
882
Trophy points
113
Location
Melbourne
Activity points
13,781
for 1mH and say 25% ripple the required sw freq can be found from: V/L = di/dt let us assume you want 5A ave into the batt, so +/- 1.25A peak ripple ( 25% peak )

We know the duty cycle will settle at 10V/100 = 10-12% hence Ton = 12%, Toff = 88%, (100-10)V / 0.001H = 2.5 / dt therefore Ton = 28uS ( 12% say )

and therefore Toff = 205uS ( 88%) Tperiod = 205+28 = 233uS, thus F = 4.291kHz for the assumed ripple current

At higher freq's the ripple current will be less but the duty cycle will stay largely unchanged for the required Vout ( for 100VDC in )
 

Akanimo

Advanced Member level 2
Joined
Aug 30, 2016
Messages
608
Helped
109
Reputation
218
Reaction score
106
Trophy points
43
Activity points
4,258
Greetings. I have replaced the SCR with an NMOS. The 1mH inductor is part of the 'motor' armature which is represented by resistor, inductor, and back-emf (10Vdc)
Can anyone provide the correct settings because the waveforms are still incorrect with swapping the SCR with an NMOS.

View attachment 154441
Please provide your simulation waveform along with the schematic. That way it can be seen quickly what's happening. There's really not much time to simulate your circuit.
 
Last edited:

Oranje

Newbie level 4
Joined
May 8, 2019
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
77
Easy peasy,
Please provide the definition of sw frequency, what does it mean, and its purpose. Also, what is the source of ripple current? I know that when converting AC to DC there is a small ac component which is desired to be small and that is why a smoothing capacitor is used for such purpose; however, where does ripple come from in case of DC to DC conversion? Also, what exactly do you mean by dury cycle will settle at 10V/100V, why you divide these numbers? Duty cycle is defined as ton/T. Please explain my confusions.
I will post my simulation images after work today.
 

Oranje

Newbie level 4
Joined
May 8, 2019
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
77
Greetings Pspice Experts,

I am attaching the results of simulation. The results do not look anything like that of the book. The way I set the Vpulse model is by double-clicking on each of the properties and setting the value. Please confirm if this is correct. What values should I be setting these properties to? Please make any suggestions to resolve my current situation. Thank you.

2019-07-17_184441.jpg
2019-07-17_184405.jpg
 

Easy peasy

Advanced Member level 5
Joined
Aug 15, 2015
Messages
2,429
Helped
894
Reputation
1,788
Reaction score
882
Trophy points
113
Location
Melbourne
Activity points
13,781
A 10V source will always read 10V regardless of the current in or out of it - you need to read up more on the sim program
 

Oranje

Newbie level 4
Joined
May 8, 2019
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
77
Easy peasy,

Well, if I knew the software I wouldn't post questions here. So, please provide constructive guidance and/or suggestions, otherwise don't post anything. Tell me exactly what I need to change about the circuit. :)

Also, I would like to add that the 10Vdc is the back-emf of the motor.
 

Easy peasy

Advanced Member level 5
Joined
Aug 15, 2015
Messages
2,429
Helped
894
Reputation
1,788
Reaction score
882
Trophy points
113
Location
Melbourne
Activity points
13,781
It's very hard to advise when you don't know the level the OP is at, if you look at a 10V source you will see 10V regardless of all else, this is what you seem to have done - again hard to tell as information supplied is limited - you need to look at the gate drive and the output side of the mosfet ( volts ) and the amps in the choke.

then you can increase the pulse voltage to the gate to say 12V for ON, and see the mosfet turn on....

regards, EP.
 

Oranje

Newbie level 4
Joined
May 8, 2019
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
77
Easy peasy,

All I know is what was included in the problem statement (attached). All else I cannot provide because I do not have enough experience in whatever you are talking about. I know that the waveforms provided as a solution look like the ones attached. My question is how can we model the circuit, such that we get similar waveforms?
As I know you are very experienced and this takes time on your end, we can discuss mentoring in private (write me in private) with an incentive from my side.

IMG_1799.jpg
IMG_1800.jpg
IMG_1788.jpg
 

BradtheRad

Super Moderator
Staff member
Joined
Apr 1, 2011
Messages
13,440
Helped
2,656
Reputation
5,306
Reaction score
2,561
Trophy points
1,393
Location
Minneapolis, Minnesota, USA
Activity points
100,501
For a tutorial, here is a simulation containing the chief components of a buck converter. It is animated and user-interactive (you press the momentary switch to operate the converter).

Electron flow (or rather current bundle flow) is portrayed according to direction and intensity. Scope traces tell the story.

It takes a minute of experimentation, to find the right tempo of switch-clicking, so that you create waveforms that are similar to your diagrams. You'll see how duty cycle affect output voltage. Below the diode waveform you might spot a frequency readout.

By clicking the link below:

1) Navigates to website falstad.com/circuit

2) Loads the schematic.

3) Runs it on your computer.

tinyurl.com/y5xp27vj

It takes a minute of experimentation, to find the right tempo of switch-clicking, so that you create waveforms that are similar to your diagrams.

You can save the schematic to your computer.

You can edit it, change values, add components, etc.
 
Toggle Sidebar

Part and Inventory Search


Welcome to EDABoard.com

Sponsor

Sponsor

Design Fast


×
Top