PID Manul-Automatic control Example (P controller)

[m7amdiii]

Dear NI Community,

I'm trying the "Automatic-Manual PID control" example, but I'm facing a problem. When I put the values of Ki and Kd to be zero and try to change the Kc value the system never overshoots. This case always happens even after changing the type (series, parallel and academic) and the gain units (bandwidth and Kc).

Thanks in advance.

[GerdW]

Hi m7,

---

@m7amdiii wrote:

I'm facing a problem. When I put the values of Ki and Kd to be zero and try to change the Kc value the system never overshoots.

---

So the problem is "the pure P control doesn't overshoot"?

Why is this a problem?

[m7amdiii]

Thanks for the reply,
Yes exactly that’s the problem. 
It’s a problem because the system should become unstable at some point by increasing the P value.

There’s another example for controlling a motor velocity and it behaves normally, the overshoot increase as the P increases and when the values increases a lot the system becomes unstable.

[GerdW · Accepted solution]

Hi m7,

the example shows "unstable" outputs when I increase the P gain to >50. (Example: Use a fixed load of 15 and a P gain of 100!)

The P gain only acts on the error…

[m7amdiii]

Thank you for your response.

[m7amdiii]

Good morning/evening everyone,

I'm currently trying to simulate the PID response of the parallel form in the Manual-automatic PID Example.

It behaves like the table when i adjust the units to be secs and bandwidth, but when I use P controller only while the other 2 gains are zero, it behaves opposite to the table.

So, does anyone has a solution to this case?

Thanks in advance.

[GerdW]

Hi m,

---

@m7amdiii wrote:

So, does anyone has a solution to this case?

---

Simple solution: the table is only valid for a PID control. It is not valid for a pure P control...

[m7amdiii]

Firstly thanks for your reply,

Secondly, that’s not the case in Simulink.

I simulated the system there and tried different gains and parameters (P, PI, PD, PID) and it behaved accordingly to the table.

[GerdW]

Hi m7,

---

@m7amdiii wrote:

I simulated the system there and tried different gains and parameters (P, PI, PD, PID) and it behaved accordingly to the table.

---

I also tried the example VI with different P gains (and zero I&D gain) and it behaved like described by your table.

• With growing P gain (in the range of 10…30) the steady state error got smaller.
• With even more growing P gain (>= 40) there are more overshoots…

I don't understand your problem…

[m7amdiii]

Hello GerdW,

My problem is:

- When setting the gain unit to be bandwidth, the system behaves similar to Simulink when using PI, PD, and PID but the P response is inversed. But when setting the unit to Kc gain, the behavior reverses too, which is logical because the unit changed. Yet, I'm trying make it similar too Simulink. So, I was searching for the correct combination.

Thanks for your replies.

Best regards,