Development of a Modular Reconfigurable Battery System with Asymmetric Module Voltages
This paper presents a technology to operate heterogeneous, mixed batteries, i.e., batteries with different voltages in a modular cascaded double H bridge circuit allowing multilevel series/parallel output. It proposes a novel solution that can establish parallel connectivity across modules with different voltages exploiting a parasitic buck/boost dc-dc stage that adjacent modules form if already small inductance is added. The paper will particularly use a differential-mode inductance that does not affect the load current but only the inter-module current to balance and control the circulating current. The solution requires minimal sensors for voltage and current control. We demonstrate precise control of energy transfer between modules, ensuring a constant circulating current even with such different, asymmetrical module voltages. In consequence, the system can operate heterogeneous batteries with different voltages with both dynamical series and parallel connections. Beyond dynamically reconfigurable batteries, this development has also implications on conventional energy conversion with modular multilevel converters, where it allows expanding the parallel mode to cases with very different module voltages and even boosting the voltage internally to practically any level.
