Steve Bailey
Lifetime Supporting Member + Moderator
Anybody have any experience with the Frenic Mega VFD's PID feature?
Today I was trying to modify a customer's setup with less than spectacular results. The drive is controlling a fan and has been functioning OK for several months under control of its own PID with the setpoint coming from the drive's keypad. The control loop is modulating the frequency reference to achieve a current setpoint.
The customer wants to be able to establish the setpoints from the HMI in the control room rather than from the drive keypad. They also want to operate in a additional mode where they enter a speed setpoint instead of a current setpoint. They have an unsuccessful attempt to achieve the second mode of operation. Their attempt was a selector switch wired to two of the drive's discrete inputs. One of those inputs was programmed to be a preset speed selection, the other programmed with a value corresponding to something called "Cancel PID Control". For those who know the drive the parameter was E06 which controls the interpretation of the signal on the X6 terminal and the value of the parameter is 20.
The "Cancel PID Control" command does not do what they expected it to do. It appears to still be reacting to an unstable PID loop. Instead of operating at the preset speed it will slowly ramp down to around 10 Hz (the preset setpoint is 25 Hz) and then jump up to 60 Hz and ramp down again.
The manual seems to indicate that asserting this command should disable the PID controller and permit preset speed control, but experience is otherwise. Does anyone know if the "Cancel PID Control" was added at a specific firmware level?
To get it to work the way they want I had to change the value in parameter J0 which enables/disables the PID function. That parameter can't be changed while the drive is running nor does the customer have the means to change it from the control room.
Today I was trying to modify a customer's setup with less than spectacular results. The drive is controlling a fan and has been functioning OK for several months under control of its own PID with the setpoint coming from the drive's keypad. The control loop is modulating the frequency reference to achieve a current setpoint.
The customer wants to be able to establish the setpoints from the HMI in the control room rather than from the drive keypad. They also want to operate in a additional mode where they enter a speed setpoint instead of a current setpoint. They have an unsuccessful attempt to achieve the second mode of operation. Their attempt was a selector switch wired to two of the drive's discrete inputs. One of those inputs was programmed to be a preset speed selection, the other programmed with a value corresponding to something called "Cancel PID Control". For those who know the drive the parameter was E06 which controls the interpretation of the signal on the X6 terminal and the value of the parameter is 20.
The "Cancel PID Control" command does not do what they expected it to do. It appears to still be reacting to an unstable PID loop. Instead of operating at the preset speed it will slowly ramp down to around 10 Hz (the preset setpoint is 25 Hz) and then jump up to 60 Hz and ramp down again.
The manual seems to indicate that asserting this command should disable the PID controller and permit preset speed control, but experience is otherwise. Does anyone know if the "Cancel PID Control" was added at a specific firmware level?
To get it to work the way they want I had to change the value in parameter J0 which enables/disables the PID function. That parameter can't be changed while the drive is running nor does the customer have the means to change it from the control room.