coopdegrace
Member
Hi All,
I have a PID control application that I would like to get your opinions on. As I am reality new to PID loops I am struggling somewhat... I am a huge fan of the forum and would appreciate any feedback.
We have a Chiller Unit here on site that needs to maintain a setpoint temperature. The unit consists of three fans with one connected to a VSD, the other two are DOL.
Currently the temperature is controlled by turning off a fan when temperature gets too low and turns on a fan when the temperature gets too high. Obviously this ON/OFF controller has issues with oscillation and over/undershooting setpoint.
What I would like to do is use the VSD controlled fan to "smooth" out the control of the system.
Say we have all three fans on and the temperature begins to fall below setpoint the VSD will ramp down to maintain the temperature. If the VSD drops to 0% then I would like to turn off one of the DOL fans and restart the VSD at 100% and continue to ramp it down until the temperature is stable.
On the flip side if two DOL fans are running and the temperature creeps up I want the VSD to start from 0% and ramp up until the temperature is again stable.
On my first attempt I am having issues when the temperature is high and one of the DOL fans turns off. Because we loose one of the DOL fans and the VSD controlled fan is essentially at 0% the temperature ramps up very quickly to a level that is not acceptable. I have played with the PID tuning settings to improve the loop response time but this is not enough and this also creates overshooting and oscillating issues.
My solution is to have the PID loop start back up again at 100% to mimic the DOL fan that has been turned off and ramp back down to stabilise the temperature. However I am not sure how to setup the PID function block to do this if it is at all possible??
I am wondering if this is the right way to approach the problem and if it is how is the PID block configured to control this way?
I have a PID control application that I would like to get your opinions on. As I am reality new to PID loops I am struggling somewhat... I am a huge fan of the forum and would appreciate any feedback.
We have a Chiller Unit here on site that needs to maintain a setpoint temperature. The unit consists of three fans with one connected to a VSD, the other two are DOL.
Currently the temperature is controlled by turning off a fan when temperature gets too low and turns on a fan when the temperature gets too high. Obviously this ON/OFF controller has issues with oscillation and over/undershooting setpoint.
What I would like to do is use the VSD controlled fan to "smooth" out the control of the system.
Say we have all three fans on and the temperature begins to fall below setpoint the VSD will ramp down to maintain the temperature. If the VSD drops to 0% then I would like to turn off one of the DOL fans and restart the VSD at 100% and continue to ramp it down until the temperature is stable.
On the flip side if two DOL fans are running and the temperature creeps up I want the VSD to start from 0% and ramp up until the temperature is again stable.
On my first attempt I am having issues when the temperature is high and one of the DOL fans turns off. Because we loose one of the DOL fans and the VSD controlled fan is essentially at 0% the temperature ramps up very quickly to a level that is not acceptable. I have played with the PID tuning settings to improve the loop response time but this is not enough and this also creates overshooting and oscillating issues.
My solution is to have the PID loop start back up again at 100% to mimic the DOL fan that has been turned off and ramp back down to stabilise the temperature. However I am not sure how to setup the PID function block to do this if it is at all possible??
I am wondering if this is the right way to approach the problem and if it is how is the PID block configured to control this way?