Control Engineering: Model parameter estimation for a motor which will be under various loads
Usually control loops are tuned under around the operational conditions. But the PID loops are usually robust enough to take care of some deviations (especially with the right tuned integral part. The Proportional only won't handle it.). If you want to increase the robustness, use several nested loops (for position control, for example, you might want to implement an internal velocity loop. For the velocity loop - internal torque/current loop).

The idea is, to make the outer position loop not to care about the underlying physical system (well, to some extent), it is done with the inner loop. The inner loop will (given it is velocity loop) will take velocity reference as input from the position PID controller, assuming the velocity loop is perfect (or modelled with some transfer function for better results). The same can be done with the velocity loop, by implementing the inner torque-regulating loop. So only the innermost loop will have to take in consideration the actual physical system parameters. The parameters for the outer loop plants will be the artificial ones, derived from the inner ones.







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