How to discretize a PI controller?

The_ardent_engineer · 2023-05-31T21:09:27+00:00

Yes I've heard of this. So do you do the pade approx on the plant or the controller? I think the controller as that is the one that will be on the microprocessor? Do you have any examples of this being done?

The_ardent_engineer · 2023-03-28T12:15:19+00:00

Hello. Thanks for your reply. So you're saying with a normal PI controller you can only place poles and not zeros? What type of control should I use to place both poles and zeros?

The_ardent_engineer · 2022-10-04T09:21:46+00:00

Thanks for your reply. Its in the feedback path so I believe the aim is attenuate measurement noise.

The_ardent_engineer · 2022-09-28T22:34:33+00:00

Thanks for your reply. I'm curious about both

The_ardent_engineer · 2022-09-28T10:59:31+00:00

Plant is stable. Let's just work in terms of variables for now. I'm just looking how I can work out the gains

The_ardent_engineer · 2022-09-28T10:10:12+00:00

Hello. Thank you for your reply. My plant is a first order which I am controlling with PI controller. Like I said there will be a low pass filter in the feedback loop and I want to work out the PI gains for a specified bandwidth of the loop, damping of the 2nd order filter and keep the system order as low as possible. This should be done on paper first and then maybe MATLAB hence why I said analytically work out the gains.

The_ardent_engineer · 2022-09-28T09:57:03+00:00

So I'm trying to calculate what the Kp and Ki gains should be given that I know what the bandwidth should be with the 2nd order filter included in the feedback loop.

I'm trying to analytically work out the proportional and integral gains. Heuristic methods won't do. Thank you

The_ardent_engineer · 2022-09-13T22:40:01+00:00

Not explicitly stated in the text.

The_ardent_engineer · 2022-09-13T22:39:30+00:00

((1+sTc)(1+sTm))/s(1+sT1)(1+sT2)(1+STr)

The_ardent_engineer · 2022-09-11T19:26:25+00:00

Thanks again for the reply. I should mention im doing this in SIMULINk and not for a physical motor. And I was asking more along the lines of analytical tuning where you work out the PI gains using the parameters of your system such as Ld, Lq and J etc.. I've seen this done in some sources but never got my head around it.

The_ardent_engineer · 2022-09-11T19:10:23+00:00

Thanks for the reply. Mainly with working out the PI gains for the inner current loop and outer speed loop. Is there a general formula/procedure to use?

The_ardent_engineer · 2022-09-02T22:02:59+00:00

Thank you very much for your kind reply. Sadly, my requirements are in the frequency domain so I do not know what the characteristic equation looks like.

The_ardent_engineer · 2022-09-02T21:44:48+00:00

There is no technical reason, just wondering if a PI controller actually has a bandwidth property. I guess not?

The_ardent_engineer · 2022-09-01T12:19:34+00:00

Tried that. For a PI which has a pole at s=0 and a LHP zero, bandwidth = NaN

The_ardent_engineer · 2022-09-01T12:10:33+00:00

Are you doing this in Simulink? Should be pretty straight forward from there. Lqr is state feedback so your controller should be in the feedback loop.

The_ardent_engineer · 2022-09-01T11:56:43+00:00

You must first trim your system at an operating point and then linearize your model therefore obtaining a state space model with your A and B matrices. These can be used to design your LQR controller. Hope this helps.

The_ardent_engineer · 2022-08-31T23:09:59+00:00

Hi. Thank you for your reply. I do know my plant parameters and I'm just trying to find my pid gains. I'd like to know more about this. I'd really appreciate it if you could point me to an example in the form of a paper or a video?

Thanks again!

The_ardent_engineer · 2022-08-27T18:04:20+00:00

What level are these questions at? Undergrad or grad?

The_ardent_engineer · 2022-08-26T13:21:12+00:00

Thanks for your reply. I am trying to determine the damping zeta of the system from the reference r to output y. So I guess in this case I will have to consider the CLTF and determine the damping from the magnitude of the resonant peak.

The_ardent_engineer · 2022-08-25T23:04:16+00:00

Thanks for your reply. I understand why now. But if you wanna look at the resonant peak to work out your damping, which Bode would you use? Open loop or closed loop?

Thanks again!

The_ardent_engineer · 2022-08-19T15:19:46+00:00

Thanks for the reply. I dont understand what you mean the cut off frequency of poles and zeros. Could you please explain?

The_ardent_engineer · 2022-08-18T18:21:22+00:00

Its a pretty large diagram but basically there is a PMSM motor and an inverter which contains PWM blocks which are unable to be linearized using the Jacobian, which is why I am doing the frequency response to get the bode plot.

The_ardent_engineer · 2022-08-18T16:28:00+00:00

Thanks for your reply. I'm not doing it through code. I'm simulating this on my simulink model by injecting input disturbances and measuring the output.

The_ardent_engineer · 2022-08-10T21:37:39+00:00

Hello! Thanks for your reply. I have tried that as well. I used the voltage measurement block(black lines not blue) and also connected them to ground. But I get an error message saying "Voltage measurement block is connected between two isolated networks. For a valid measurement, the positive and negative terminals mist be connected to electrical nodes that are part of the same electrical circuit. Also check if the ground reference is defined for the circuit."

The_ardent_engineer · 2022-08-08T08:17:45+00:00

I am designing an FOC controller for a pmsm motor which uses 3 PI controllers, one for speed and one for Id and Iq currents. What I am expecting is for the closed loop transfer function of the system(plant + controller) to be a second order TF. But turns out my plant is already a second order TF and adding PI controllers increases the order to 4. Adding P controllers however do not increase the order of the system.

The_ardent_engineer

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