Chapter 1 Background

The dominant waveforms in electric energy processing systems are engineered to be periodic because of the physics and materials of loads and sources and because of the need to exercise regular control actions at appropriate time scales. In utility and many other applications, sinusoidal AC waveforms are prevalent, due in part to historical reasons (e.g., the functionality, simplicity, and reliability offered by transformers and AC generators). While many sources (and often voltage sources) are designed to be nominally sinusoidal, the nonlinearities in energy systems, ranging from device geometries to materials to switching, tend to introduce harmonics in other key waveforms, such as currents. However, energy processing networks are engineered structures, so they are designed to have desirable properties such as being convergent systems. This particular property guarantees that periodic inputs will yield periodic steady-state responses throughout the system, as is, for example, commonly observed in utility power systems.