rdrast
Lifetime Supporting Member
Well, that is actually over complicating things. Getting down to the absolute basics, pull out a block diagram of an old (but not ERC Old) analog DC drive.
Closest to the motor (control wise, not SCR wise), is always a current regulator, which takes a setpoint and feedback. True, for winder applications, or tension control, I'll often just inject my command signal to the setpoint channel of the current regulator. In a typical drive, the next outer loop is the actual speed regulator, which again has a setpoint and a feedback. The output of the speed regulator directly becomes the command input to the current regulator (ignoring current limit controls for now).
On a DC drive and motor, with a fixed field, armature current is directly proportional to torque, which is why it generally works so well for winders and such, since the speed loop is normally much slower then the current loop. Even more generally, each time you add another outer loop, you introduce more lag into the system, as each outer loop must be slower then the loop it's feeding for stability.
Modern AC drives, with intelligent vector control, or ABB's direct torque control perform wonderfully when directly controlling the motor torque. Of course, that didn't work so well in the 6 step drive days
Dan, don't you ever sleep?
Closest to the motor (control wise, not SCR wise), is always a current regulator, which takes a setpoint and feedback. True, for winder applications, or tension control, I'll often just inject my command signal to the setpoint channel of the current regulator. In a typical drive, the next outer loop is the actual speed regulator, which again has a setpoint and a feedback. The output of the speed regulator directly becomes the command input to the current regulator (ignoring current limit controls for now).
On a DC drive and motor, with a fixed field, armature current is directly proportional to torque, which is why it generally works so well for winders and such, since the speed loop is normally much slower then the current loop. Even more generally, each time you add another outer loop, you introduce more lag into the system, as each outer loop must be slower then the loop it's feeding for stability.
Modern AC drives, with intelligent vector control, or ABB's direct torque control perform wonderfully when directly controlling the motor torque. Of course, that didn't work so well in the 6 step drive days
Dan, don't you ever sleep?