PID tuning of hydraulic drives with high inertia
Hi there.
I have a question about the tuning of a PID (PI)controller in hydraulic drive trains with high inertia. I have a system with a100kW hydraulic motor with an installed on its shaft encoder. That is how I amgetting feedback from it. Not surprisingly I have a controller for acquisitionand control of the hydraulic system (there are a few valves in the circuit).The last time when I was trying to tune the PID in the system (in thecontroller’s software), but I failed miserably. I did everything according tothe standard tuning procedure(https://robotics.stackexchange.com/q...-pid-loopslike here for instance) increase the proportional gain to reach steadyoscillations and so on. At the end of the day the controller works, but tooslow. And since it is a big hydraulic system that spins quite fast, I’vedecided not to go too crazy with the parameters and stopped there.
I read that it is quite challenging to tune PID controllersin hydraulic systems. The funniest thing is that I have a mathematical model ofthe system in Matlab/Simulink. So, in theory, I can easily derive the PIDparameters. I did it once, and it did not work out either. So could you pleaseadvise any best practice for PID (PI) tuning when it comes to fairly bighydraulic drive trains? Thank you in advance.
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Re: PID tuning of hydraulic drives with high inertia
Are you using a servo drive and proportional hydraulic valve, properly sized and matched to each other? I've tuned a few hydraulic servo systems without problems, but they were a matched system. I think the valve has to meet your motor's flow requirements and meet the requirements of the drive. Then you should be able to get the performance you're looking for.
Re: PID tuning of hydraulic drives with high inertia
@greggv,Originally Posted by greggv
Probably here I should mention a little bit about the test that I was doing. Fairly simple system, we set up (in the controller) a reference speed and then accelerating the motor (by opening the control valve in the circuit). When the motor's velocity exceeds the reference, the controller should decrease the control voltage input to the valve, hence decelerate the motor and bring it down to the reference speed. My first approach for achieving this was a gradually decreased voltage method (with two voltage decrements), to decelerate the motor. The response was good, let's say almost 1 s (from 2100 RPM to 2000RPM). And we are talking about the flow rate up to 200LPM (53GPM). With regards to the valve, I was testing it before (was designing its math model), so the valve won't be a bottle neck as well.
When I tried to do the same process with the PID...the same process took me almost half a minute (and it was the best time). So I reckon it is because of the PID parameters, rather than the controller. It is a fairly powerful controller from National Instruments (NI), and it is capable of doing these kind of tasks. Plus after I finished the test with with the voltage decrease method, I know that the output modules and the motor are capable of doing the task as well.
I mean at least I expect from the PID controller the same response time, or maybe bigger but with good reference control (but definitely not a dozen times slower). Autotuning of the PID is possible with the use of NI software, but when a big motor spins at 2000RPM, I would rather tune the PID manually, to be sure that nothing goes wrong.
Just wondering how big were your hydraulic systems? What about their inertia, flow rates? The motor in my system accelerates from 0 to 2000RPM within 2 - 2.5s, so it is a fairly big system.
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