Control of Independent-Input, Parallel-Output DC/DC Converters for Modular Battery Building Blocks

Abstract

Modular battery packs are desirable energy storage elements in applications such as DC microgrids and electric vehicles (EVs). Modular battery packs utilize DC/DC converters that are connected in series for high output voltage or connected in parallel for high output currents. An active battery management system (BMS) utilizes the cell state of charge (SOC) to control the cell current. The individual control to input current transfer functions vary with the number of converters in parallel. This paper presents a small-signal model for the parallel converters as a multi-input, multi-output (MIMO) system that shows the interactions among the input current transfer functions. The small-signal model is utilized to design the feedback loop. The paper uses hybrid feedforward control to reduce the interactions between the coupled input-current regulation loops; which simplifies the implementation, increases modularity, and eliminates the need for a central controller. that is generally employed in MIMO systems. The analysis is verified by simulations and by experiments. A 300 W module consisting of three parallel output 100 W boost converters for a cell active balancing management system is used for hardware validation.