Pspice Buck Converter Simulation

[OrangeArav]

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 image of the desired waveforms from the book and my Pspice circuit. I believe my problem is in the Vpulse parameters, however, I do not have enough experience to understand what exactly to change. Please help.

 

[Harald Kapp]

A typical DC-DC converter doesn't use thyristors. A thyristor is hard to turn off once it has ben turned on. Use a MOSFET instead.

 

[WHONOES]

A typical DC-DC converter doesn't use thyristors. A thyristor is hard to turn off once it has ben turned on. Use a MOSFET instead.

Correct about thyristors. All of them have what is termed a "latch current". This a current level that when exceeded, causes the thyristor to latch or stay on irrespective of what is happening to the gate. The only things that will then turn the thyristor off are if the anode goes negative with respect to the cathode causing the device to become reverse biased or the current flow in the device is reduced below the "latch" threshold. It should be noted that the latch current is generally a small percentage of the devices rated current.

 

[OrangeArav]

Good Day,

I have changed the thyristor to a MOSFET and I'm trying to set-up the parameters. Please specify how I should set-up the parameters for this circuit. I believe the 10Vdc which serves as a back-emf of a motor should be changed to some other Pspice model. Also, what should we do with Vpulse parameters. Any suggestions?
Another question I have: In the problem statement (attached) it mentions that back-emf is 10Vdc but in reality back-emf varies with rpm of motor. So, is this problem describing when the motor has reached its rated rpm and the back-emf is at its max? Confirm on this, please.

 

[WHONOES]

The negative part of your gate drive needs to be connected to the circuit ground. Then you need to add a 90V offset to it.

 

[Harald Kapp]

The negative part of your gate drive needs to be connected to the circuit ground. Then you need to add a 90V offset to it.

In reality: yes. A so called high-side driver will be required.
For the purpose of simulation the gate drive by V2 as connected will work.

The parameters of V2 are not clearly visible, they are partly obscured by the mouse cursor and the pink selection. Post the values or a better picture, please.
From what i can glimpse it looks like you are setting up a period of PER = 233µs and a pulse width of PW=1ms. That is incompatible. Pulse width needs to be less than period. See e.g. this tutorial on setting up quare wave sources in Pspice.

Another question I have: In the problem statement (attached) it mentions that back-emf is 10Vdc but in reality back-emf varies with rpm of motor.

There is no motor mentioned in the problem statement. The load is an ideal battery. Who knows (sorry for the pun) what this battery stands for.

Also: the problem statement asks for calculating the various results. Simulation results may not be accepted as valid solutions. All values can be calculated manually assuming an ideal switch instead of a MOSFET (and other components also assumed as ideal). How to do this should have been the content of the preceding class hours. That way you eliminate the parameters of the MOSFET from your calculations assuming ideal on and off states of the switch.

 

[OrangeArav]

Greetings,
Here is the list of the settings for Vpulse, V2:
V1=1
V2=10
TD=0
TR=1n
TF=1n
PW=1m
PER=2.5m
Please make suggestions.

 

[WHONOES]

Which spice platform are you using?