Interface Converters for Residential Battery Energy Storage Systems: Practices, Difficulties and Prospects

Abstract

Recent trends in building energy systems such as local renewable energy generation have created a distinct demand for energy storage systems to reduce the influence and dependency on the electric power grid. Under the current market conditions, a range of commercially available residential energy storage systems with batteries has been produced. This paper addresses the area of energy storage systems from multiple directions to provide a broader view on the state-of-the-art developments and trends in the field. Present standards and associated limitations of storage implementation are briefly described, followed by the analysis of parameters and features of commercial battery systems for residential applications. Further, the power electronic converters are reviewed in detail, with the focus on existing and perspective non-isolated solutions. The analysis covers well-known standard topologies, including buck-boost and bridge, as well as emerging solutions based on the unfolding inverter and fractional/partial power converters. Finally, trends and future prospects of the residential battery storage technologies are evaluated.

Considerations on Combining Unfolding Inverters with Partial Power Regulators in Battery–Grid Interface Converters

“…In the case of the unfolding frontend, the grid current in each half-period constantly flows through the couple of the frontend switches. For this reason, the frontend produces only conduction losses that can still be calculated with (9) as ∆P FE3,c = 7.8 W while ∆P FE3,sw = 0 W.…”

“…The operation of modern batteries occurs in conjunction with dedicated electronic converters controlling the charge and discharge of the batteries. The overviews of BESS usually emphasize two kinds of converters integrated into BESS: isolated and non-isolated [8,9]. The isolated converters are distinguished from the non-isolated ones by the absence/presence of the full power transformer in the converter.…”

“…At the same time, this definition of safety is rather vague. Reference [9] contains a brief analysis of the regulations applicable to BESSs. It has been concluded that these regulations define the constraints for various grid-tied electrical equipment but do not explicitly limit the voltage of batteries.…”

“…While the chargers have quite high AC limitations (for example, 250VAC in [11]), more accessible batteries have much lower DC limitations; ref [10] defines the dangerous level at 60 V while [11] defines it at and 36 V (for lead-acid batteries), and [12] at 50 V (for Li-ion batteries). As a consequence, according to Section 3 of [9], the market-available BESSs typically include a "safe" 48-60 V battery or a battery linked to the ratified grid voltage (300-400 V) or supplied in two configurations with low or high-voltage battery.…”

“…Introducing a pre-regulator compensates for the floating of battery voltage and stabilizes the DC voltage of the frontend at the level optimal for its operation. This makes the operation of the frontend more efficient for a wider range of SoC, but it also reduces the efficiency at the best operation point [8,9] due to the extra losses in the pre-regulator.…”