350 kVA Multi-Function Converters for DC-Microgrid Applications

In a dc-microgrid, ac is harmonized with dc, and therefore, a multi-function converter is required to transfer power between ac and dc grids. This paper presents design and implementation of converters with multiple functions that include grid-connection (GC) mode, uninterruptible power supply (UPS) mode, and mode transition. Control laws for the GC and UPS modes based on a direct digital control with division-summation (D- Σ) processes are presented in detail. During operation, mode transition between the two modes is discussed. Experimental and simulated results from two 350 kVA multi-function converters with circulating power test are used to verify the analyses, designs and discussions.