# PSPICE Simulation for a PI Control circuit

Status
Not open for further replies.

##### Newbie level 6
pi controller circuit

Hi all, I wanted to check the stability of a PI control loop as in attachment. In circuit, I used the simplest model of OP-AMP, which has rails of +5V and ground, and the open loop voltage gain is 1e+6. It is an idealized OP-AMP model as an accessory in ORCAD, since I am insterested in the general concept of the control loop rather than some specific performance of a type of chip.

I used V2 as a signal source to verify step response. During simulation, I met nonconvergence problems. If the components values are chosen in order to make control loop in oscillation, simulation can't be finished with error message like "Convergence problem in transient analysis at Time = .012 Time step = 9.537E-12, minimum allowable step size = 10.00E-12".

The amazing thing is accidentally I found if the gain of OP-AMP U32 was decreased to 1e+5, then the simulation could be went through. Can anybody familiar with PSPICE explain this phenomenon? Roughly I impute the failure to the accuracy caused by the high gain, since much higher gain needs much higher voltage accuracy on the input port of OP-AMP.

#### LvW

pi controller

Hi steadyj, there is one point I don´t understand in your schematic:

Both nodes "output" (which the program should consider as connected) exhibit different bias voltages (295mvolts resp. 500 mvolts). Can you explain this ?

More than that, as you are going to work with single supplies, I cannot follow your biasing scheme. And what is the purpose of the last amplifier ? I understand that the RC element models the opamp corner frequency, but it should be inside the opamp model. In your circuitry, the output impedance is not low and detrmined by the RC divider.

op amp pi loop

Deleted.

sasimillinium

### sasimillinium

Points: 2

##### Newbie level 6
pi control

Hi LvW, thanks for your reply. You are right that the DC bias value doesn't make sense. I uploaded a wrong file and now I have corrected it.

Yes It is just a PI controller with negative feedback. In a project I must use PI controller. And I use the RC-OPAMP combination to set up a two order model. And I want to know the PI controller performance for different parameters.

#### LvW

opamp pi controller

OK, good success.

sasimillinium

### sasimillinium

Points: 2

#### sasimillinium

##### Newbie level 3
Re: pi controller circuit

can u send correct circuit for pi controller in pspice schemstic

#### sasimillinium

##### Newbie level 3
Re: pi controller circuit

can u send correct pi controller circuit for pspice schematic

Status
Not open for further replies.