What is meaning of "classic" control in context of EE?

Question

As electrical engineers, we often come across the terms "classic control" & "modern control"

What does classic mean here? Is it meaning "old" or of "past time"?

Answer 1

This is from Linear Systems Control by Hendricks, Jannerup and Sørensen pp. 5-8: -

Classical Control

"The Classical Control period was characterized by a concentration on single loop, Single Input, Single Output feedback (SISO) systems designed with the theoretical tools developed during and just after the Second World War.

For the most part these could be applied only to linear time invariant systems. The main underlying concept is that closed loop characteristics of a system can be determined uniquely given the open loop properties of the system. This includes the important disturbance rejection and steady state error properties of the feedback system

The theoretical tools were those developed by Nyquist, Bode, Evans and Nichols earlier and the connection between these methods was clarified and extended. Performance was assessed in terms of bandwidth, gain and phase margin or rise time, percentage overshoot, steady state error, resonances and damping."

Modern Control

"The large number of states in MIMO state variable systems and the possibly large number of feedback loops which might exist in a closed loop system make it necessary to consider how decisions might be made about the feedback levels in the different loops. It has turned out that this is not a simple question and it is difficult to impossible in fact to make any reasonable, balanced statement about what might be required. (...)

In 1960 and 1961 a significant set of breakthroughs were made generally available with the publication of four papers by Rudolf Kalman and co-workers. These papers dealt with (1) the optimal control of discrete time systems, (2) the design equations for the Linear Quadratic Regulator (LQR), (3) optimal filtering and estimation theory for discrete time systems and (4) the continuous time Kalman filter."

Summary

Classical control is generally about designing controllers for single input - single output systems by pole/zero placements. You look at Bode Plots and Nyquist Plots, and investigate phase/gain margin, bandwidth, etc. and assess if you are "on the right track".

Modern control is generally used for multiple input - multiple output systems by eigenvalue placements. You create a linear model of your system, set up a state space equation and define controller gains (for a specific control architecture, optimal control for example) to make sure you are meeting certain requirements (rise time, overshoot etc.)