>-- Original Message -- >Date: Mon, 12 Jul 2004 12:09:04 +1200 >From: Birger Brunswiek >To: FlightGear developers discussions <[EMAIL PROTECTED]> >Subject: Re: [Flightgear-devel] Autopilot >Reply-To: FlightGear developers discussions <[EMAIL PROTECTED]> > >ver these books which I'm going to get from the library: (name and ISBN)
PID controllers / by Karl J. ?str?m and Tore H?gglund. 1556175167 Adaptive Control (2nd Edition) 0201558661 Control Theory : Multivaria le & Nonlinear Methods 0748408789 The >Control Handbook 0849385709 Handbook of PI and PID controller tuning rules / Aidan O'Dwyer. 1860943500 Digital Control of Dynamic Systems (3rd Edition) 0201820544 Advanced Control Unleashed: Plant Performance Management for Optimum Benefit 1556178 >58 Control Systems Engineering 0471445770 I'll add one of the textbooks that I used in my education: Process dynamics and control 0471863890 Isn't it more apropriate to have a multidimentional PID c ntroller rather than multipl > 1 dimentional PID controllers? Or is that just the same? I'm not sure what you mean by multidimentional PID controller, but I believe that that it would be the same as multiple one dimentional PID controllers. If we look at multivariable control, where we have multiple inputs and multiple outputs, we still use one PID controller for for each input-output pair. Consider an autopilot that is supposed to control the ailerons and the rudder. We know from experie ce (and probably from theory) that an aileron deflection will result in a roll, and that a rudder deflection result in a yaw, but also in a roll. Aileron deflection also result in a yaw, but I guess not as much as rudder deflection. So we have tw inputs: aileron and rudder, and two outputs: roll and yaw. Theese variables are not independent, the aileron does not only control roll, and the rudder does not only control yaw. They both interact. Of course the aileron controls roll much more tha it controls yaw and the rudder controls yaw more than it controls roll. So our two PID controllers would be: one with roll as input and aileron as output, and one with yaw as input and rudder as output. This might seem obvious, but still one should know the theory behind and note that it also makes sense in theory. When it comes to tuning the two PID controllers, one has to keep in mind that they interact. In general more conservative controller settings must be used, but I guess you'll fin more on multivariable controller tuning in one of the books :-) >What is the benefit of cascading PID controllers? Lets look at an autopilot that is supposed to steer the aircraft towards the heading bug. Suppose that the only thing we can man pulate is the aileron. Obviously we need a PID controller with aileron as its output. We choose roll angle as input. Now we can set the reference to say 20 degrees, and a properly tuned PID controller will hold a 20 degree roll angle. But how do e get it to steer towards the heading but? One solution is for the pilot to set the reference roll angle apropriately so that the aircraft steers toward the heading bug. Another is to let another PID controller set the reference roll angle. The outp t of this controller is then connected to the reference of the first controller. This is what we call a cascade configuration. For this example the benefit is that, well without cascading we wouldn't be able to do what we wanted (steer towards the h ading bug). For situations where cascading is not required, it can still be used and might give a more robust or smoother control loop. -- Roy Vegard Ovesen -- Roy Vegard Ovesen _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
