Study on DC-Voltage Rising of Blocked Port in High-Frequency-Link Converters

High-frequency-link converters (HFLC) are the core part of multi-port power electric transformers. Some of the ports might be blocked during standby while other ports are kept running. Sometimes the blocked ports show significant rises of their dc voltages, which potentially makes these ports be unblocked unsafely and even triggers overvoltage protections. The mechanism of dc voltage rising is studied based on dual active bridges. The transient process excited by the running port is divided into three successive stages and the equivalent circuits and equations are established. The analyses reveal that junction capacitors, dc-link capacitors and leakage inductors play main roles in these transients. To avoid the voltage rising, dual phase-shifting modulation method is adopted, taking the place of single phase-shifting method, to keep power from being injected into the blocked ports during their standby. Simulations are carried out to validate the analyses and the proposed solution.