ABSTRACT
The direct or indirect benefit of a power electronics controller is system efficiency improvement. Figure 1.1 is a simple example in a process heat control, which can be achieved two ways: (a) by inserting a control resistance (rheostat) or (b) by a control switch that is repetitively turned on for duration Ton and off for duration Toff. In the rheostat control, the average power going in the load is fraction RL ÷ (RL + Rc) of that coming out of the source, and the remaining power is wasted in Rc, giving the energy efficiency of RL ÷ (RL + Rc). In switch control with an ideal switch, all energy coming from the source goes to the load, and the energy efficiency is 100%, although the average power going in the load is lower by the duty ratio D = Ton ÷ (Ton + Toff). Thus, the power electronics switch controls the load power without wasting energy in the control (dummy) resistor.
