An Isolated Four-Port Voltage Self-Balancing Converter for Bipolar DC Microgrids

Voltage balance is a fundamental but crucial requirement for bipolar dc microgrids. Issues such as asymmetric loads, power mismatches from dc sources, and inconsistent device specifications can cause voltage imbalance, reducing efficiency, and potentially triggering protection mechanisms. To address these challenges, an isolated four-port voltage self-balancing converter (VSBC) based on dual active bridge (DAB) is proposed, integrating voltage balancing and power conversion into a unified design. VSBC extends the zero voltage switching range and minimizes the grid voltage ripple by consistent current regulation between the positive and negative poles. Compared to the voltage balance converter that uses dual LC branches, VSBC eliminates two voltage regulation capacitors and an inductor, significantly reducing its size. Furthermore, LC branches are susceptible to oscillations between the positive and negative poles under load variations and fault conditions. The VSBC’s transformer offers effective galvanic isolation, enhancing safety and eliminating oscillations by removing capacitors from the design. The effectiveness is validated by a down-scaled experimental prototype.