A Step-Up Reconfigurable Multimode LLC Converter Module With Extended High-Efficiency Range for Wide Voltage Gain Application in Medium Voltage DC Grid Systems

In this article, a newmodular multimode reconfigurable step-up resonant converter that is capable of extending very high efficiency from full load to reduced load conditions is proposed for wide voltage gain application in medium voltage dc (MVdc) grid system. The proposed converter module is able to switch from a hybrid control scheme that consists of variable frequency and phase shift control to pulsewidth modulation (PWM) control in the auxiliary switch of the output voltage quadrupler (VQ). In addition, the input bridge can also be reconfigured to a half-bridge mode to suit high input voltage range while utilizing a hybrid control technique that consists of variable frequency and asymmetrical PWM control. With the proposed approach, the converter module is able to achieve constant output voltage regulation without requiring a wide spectrum of switching frequency or phase shift control. Hence, close-to resonance operation with very high efficiency can be maintained for a wide range of input voltage and loading conditions. Soft switching operations are always guaranteed for all the primary side switches, the output diodes and the auxiliary switch in the VQ. The steady-state and dynamic performance of the proposed modular multimode step-up converter are validated through simulation results on a silicon carbide (SiC) based 360 V–1 kV/16 kV, 80-kW system and experimental results on a proof-of-concept 150–400 V/6.6 kV, 10-kW SiC laboratory prototype. Results confirmed that the efficiency is maintained between 97.8% and 99.1% from full load to at least 20% load condition for the specified input voltage range.