Modeling and Control of Modern Electrical Energy Systems

6Single-Phase Alternating-Current (ac) DERs

In a single-phase ac distributed energy resource (DER) application, the power electronic converter is used to exchange the power between a dc side (either originally dc, e.g. in a PV system, or rectified to dc, e.g. in a wind energy system) and an ac side. The ac side can be a load, a grid, or a microgrid. This chapter studies the control system objectives and challenges pertaining to such a system. Various scenarios are treated while more and more of control objectives are taken into consideration and addressed.

(i) The power control via a current feedback loop (CFL) – also called the grid-following control – is presented. The CFL is properly structured to allow application of an optimal control approach. The CFL is invariably used in most applications due to the need for current limiting. (ii) The phase-locked loop (PLL) concept is discussed. Particularly, the single-phase enhanced phase-locked loop (ePLL) is studied and its analysis and design are presented. (iii) Subsequently, the concept of “grid support” is studied and is added to the power control to derive the virtual synchronous machine (VSM). It provides grid support functions as well as a “grid-forming” property. (iv) The dc voltage control and support is also presented. Particularly, obtaining inertia from the dc link capacitor is studied. (v) The ac load voltage control is discussed. It is shown how the VSM and grid-forming controller can be derived from the load voltage ...