Modular Bidirectional Differential Converter With Series Parallel Connected Output for Ultra-Wide-Voltage Applications: Control, Module Shedding, and Fail-Safe Operation

In this article, a modular output series-parallel series resonant converter (SRC) differential buck converter is analyzed for high-power, ultra-wide-voltage applications such as battery formation systems and bench-type power supplies where a zero voltage discharging function is required. An independent control method in one module is proposed to increase the efficiency of the converter compared to the conventional complementary control method. In the modular output-series connection, higher efficiency can be achieved by shedding needless modules in the low voltage range. Module shedding and activating techniques are proposed to eliminate current and voltage transients during a mode change under any load condition without the use of additional bypass switches. In addition, when a fault occurs in one module, its effect on the other module is analyzed. A practical solution involving turn-
off
processes for fail-safe operation is proposed, which reduces current stress and voltage spikes on devices and effect among modules without depending on the external signal from the central controller and the communication delay. A prototype of a modular series-parallel SRC- differential buck converter is implemented to verify the proposed concept.