High-Efficiency Partial Power Converter for Integration of Second-Life Battery Energy Storage Systems in DC Microgrids
Authors: Naser Hassanpour; Andrii Chub; Neelesh Yadav; Andrei Blinov; Dmitri Vinnikov
Abstract:
Buildings around the world are being pushed toward zero-emission standards, especially in Europe, where new rules and the growth of solar power and other renewables are changing how we use energy. However, there is a big challenge that home battery energy storage systems (BESS) are still expensive, making it tough for many households to store solar energy for later use. A smart, promising, greener and cheaper solution is to reuse old electric vehicle (EV) batteries, particularly 2nd life lithium iron phosphate (LFP) batteries, which still hold most of their original capacity but cost much less than new 1st life batteries.
To make this work, however, it needs special electronics to connect them safely and efficiently to modern 350 V DC microgrids. Therefore, this research article introduces a high-efficiency partial power converter (PPC) that integrates the 2nd life battery to DC microgrid. The paper introduces a novel architecture of the PPC for integration of 2nd life battery in DC microgrid. Unlike conventional converters that manage the entire power flow, PPC handles only a small portion of the total power, easing the load on components and significantly improving efficiency. One of the main innovations is its ability to morph its topology and change its working mode and operate in different modes. It can also smoothly switch between buck, boost, and flyback-like modes, which means it can control the battery current accurately even when the battery and grid voltages are almost the same.
The design uses smart features like a regenerative snubber to protect components from voltage spikes, a solid-state circuit breaker for safe and smooth startup, and an optimized transformer system to keep everything running cool and stable. The PPC is controlled using a droop-based decentralized method, compatible with standards like NPR9090-2024 and Current/OS. This allows easy plug-and-play integration into DC microgrids without needing external communication for parallel operation or voltage control. The design was tested using a 4-kW laboratory prototype, which achieved a peak efficiency of 99.45% and maintained high performance across all expected operating conditions. The prototype showed stable thermal behavior, smooth switching in all modes, and reduced transformer voltage overshoot and inrush currents.
This article connects theoretical advances in partial power conversion with practical needs for building-integrated energy storage. By demonstrating a complete system that meets standards for reusing 2nd life EV battery packs in residential DC microgrids, it provides clear ways to lower storage costs, improve grid resilience, and support circular economy goals. The proposed converter design and concept benefit smart building manufacturers, battery repurposing companies, and zero-emission construction initiatives, while offering a solid experimental and technical foundation for further research and commercial use.
