+ Post New Thread
Results 1 to 8 of 8

5th January 2018, 19:59 #1
 Join Date
 Apr 2013
 Posts
 18
 Helped
 0 / 0
 Points
 980
 Level
 7
Orcad Capture Simulation of Voltage Controlled Mode Buck converter

5th January 2018, 19:59

6th January 2018, 00:14 #2
 Join Date
 Jan 2008
 Location
 Bochum, Germany
 Posts
 41,500
 Helped
 12663 / 12663
 Points
 239,549
 Level
 100
Re: Orcad Capture Simulation of Voltage Controlled Mode Buck converter
LM741 isn't suited for single supply operation and not specified for 5V supply at all. Redesign with reasonable parameters.
I also won't expect useful output from a PI controller without closing the feedback loop.
1 members found this post helpful.

6th January 2018, 00:14

14th January 2018, 06:45 #3
 Join Date
 Apr 2013
 Posts
 18
 Helped
 0 / 0
 Points
 980
 Level
 7
Problem in Simulation of Voltage Mode Control
Hello all,
This is my second post. I am new to all topics in Power Electronics. I have simulated a Voltage Mode controlled Buck Chopper.
Unfortunately the controller only seems able to handle changes in output current but not changes in input voltage. This is seen in the next image.
Could anyone please tell me what I am doing wrong.
Thankyou.
Shomik CLast edited by BradtheRad; 14th January 2018 at 08:25. Reason: Condensed two similar posts

14th January 2018, 06:45

14th January 2018, 09:58 #4
 Join Date
 Jan 2008
 Location
 Bochum, Germany
 Posts
 41,500
 Helped
 12663 / 12663
 Points
 239,549
 Level
 100
Re: Problem in Simulation of Voltage Mode Control
I don't understand how you arrived at the strange controller design. What's the reason behind dividing the process value and set point to a low mV voltage? How do you expect a stable output voltage without an integral term in the transfer function?

14th January 2018, 10:12 #5
 Join Date
 Apr 2013
 Posts
 18
 Helped
 0 / 0
 Points
 980
 Level
 7
Re: Problem in Simulation of Voltage Mode Control
Dear Sir,
Dear Sir, Thankyou for the reply.
Please forgive me on my ignorance. As I am completely new and working on my own I am facing problem with basic issues which experienced persons might assume to be just common sense.
I thought that dividing the reference value to a low mV input for error amplifier will lead to low mV output of the error amplifier which is then the input for the compensator amplifier which has the positive terminal grounded. And from books I read that the op amp to work in linear range with amplification the difference between the two inputs has to be very small.
Also I thought having a capacitance of 100pF will give me the integral term.
Thankyou.

14th January 2018, 11:15 #6
 Join Date
 Apr 2013
 Posts
 18
 Helped
 0 / 0
 Points
 980
 Level
 7
Re: Problem in Simulation of Voltage Mode Control
Sir,
Thank you.
As soon as I put the capacitance in series with the resistor the output of the opamp of the controller goes into saturation.
And also input voltage perturbation with my circuit shown is not handled only load current variations seem to be handled properly.
Thank you.

14th January 2018, 11:15

14th January 2018, 11:36 #7
 Join Date
 Jan 2008
 Location
 Bochum, Germany
 Posts
 41,500
 Helped
 12663 / 12663
 Points
 239,549
 Level
 100
Re: Problem in Simulation of Voltage Mode Control
A typical error amplifier + compensator is implemented with a single OP, look at popular PWM controller ICs or text book schematics.
The main disadvantage of voltage downscaling is the increasing error due to OP offset voltage. Apart form this point, it should work. Having a controller transfer function with integral term is however mandatory to avoid a stationary error. A popular PI transfer function is generated by putting the integrator capacitor in series with a resistor. Proportional and integral gain can be adjusted separately by changing both values.
Now you have a pure P controller with an additional low pass corner at 230 kHz, far beyond feasible control loop bandwidth.
   Updated   
And also input voltage perturbation with my circuit shown is not handled only load current variations seem to be handled properly.
As a first step, you may want to reduce the inverting amplifier gain from 150 to below 1 so that the integrator output range doesn't exceed the linear pwm range by a huge factor. Or more generally, design controller parameters by calculation instead of choosing it arbitrarily.

14th January 2018, 12:01 #8
 Join Date
 Apr 2013
 Posts
 18
 Helped
 0 / 0
 Points
 980
 Level
 7
Re: Problem in Simulation of Voltage Mode Control
Ok Sir,
Thank you. I will try that. Your input has been very helpful.
+ Post New Thread
Please login