PURE AC-COUPLING – THE CONCEPT FOR SIMPLIFIED DESIGN OF SCALABLE PV-HYBRID SYSTEMS USING VOLTAGE/FREQUENCY STATICS CONTROLLED BATTERY INVERTERS

摘要

Pure AC-coupling describes a concept for Hybrid Power System design, where all components are operating independently and equitably on a common AC bus. A comparison of mixed AC- and DC-coupled system and "Pure AC-coupled" systems shows that "Pure AC-coupled" systems have numerous advantages such as standardized coupling of different components, off-the-shelf grid components can be used, simplified design and operation of island grids, compatibility with existing grids, reduction of system costs, increased reliability of electrical power supply as well as expandability. In order to be able to utilize all these advantages new control algorithms for battery inverters (V/f-statics or droopmode control) were developed and successfully implemented in the Sunny Island? battery inverter by ISET e.V and SMA. Comparable to the control of a pool of conventional power plants the concept of droop-mode-control is based on active power/frequency-statics and reactive power/voltage-statics. Furthermore the paper introduces the new battery inverters Sunny Island? 4248 and Sunny Island?4248 xx. These new inverters benefit from know-how gained in two areas. On one hand the cost reduction know-how and manufacturing processes developed for batch production of robust and reliable grid-tied PV inverters (Sunny Boy?). On the other hand the off-grid know-how in particular droop-mode control for "Pure AC-coupling", AC-coupled PV, battery management for longest battery life and system management for efficient and considerate use of (renewable) resources available at off-grid sites. Details on technical data are available at www.sma.de.