Requirements of Battery Energy Storage Systems (BESS)
The area of application of BESS covers a very broad range of requirements and performance. This includes energy storage for short-term consumption for the stabilization of wind power and PV solar systems with network malfunctions, the balancing of short-term generation deficits and the storage of large amounts of energy. The latter is required for the stabilization of a supply network as soon as variable power generators such as wind and solar are integrated. SEMIKRON supplies optimized power modules for each of these applications that reliably meet the requirements at low cost.
The single-stage topology of a Battery Energy Storage System (BESS) on an AC energy network comprises only a network-side active front end converter.
The advantage of this topology is that the small number of power semiconductors yields both a low cost and relatively high degree of efficiency. The disadvantage, however, is that the battery voltage must be greater than the rectified network voltage.
By means of a buck-boost converter located between the network rectifier output and the storage batteries, a two-stage BESS is created in which the battery voltage can be significantly less than the rectified network voltage.
Two-stage topology based on SEMISTACK RE
Minimally modified active front end converters, such as the SEMISTACK RE from SEMIKRON, are used for the charging and discharging of storage batteries on the energy network. In this application, low power ripple is required when the battery is at minimum load. For this purpose, the three phases of the battery-side inverter are operated as an interleaved buck-boost converter. In doing so, the switching frequency on the battery is tripled and the filter cost is relatively low. The line-side active front end IGBT converter allows for bi-directional energy transfer.
To couple BESS with medium-voltage energy networks, IGBT modules with voltages from 3300 V upwards can be used in connection with multilevel topologies, e.g. with 3-level NPC circuitry.
Also in low voltage applications 3-level topologies allow the use of lower cost semiconductors, reduced harmonic content and reduced line filter requirements.