FCS-MPC for four-switch three-phase AC-DC converters with DC-link capacitor voltage balancing

Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability reduction.In order to solve these problems,a finite control set model predictive control(FCS-MPC)for FSTP AC-DC converters with DC-link capacitor voltage balancing is proposed.In this strategy,in order to facilitate calculation,theαβcoordinate system model is established and all voltage vectors are evaluated by establishing a cost function.During the whole process,phase locked loop(PLL)and complex modulation strategy are not required.In the new established cost function,the additional objective term of suppressing capacitor voltage fluctuation is to eliminate effectively the capacitor voltages oscillations and deviations and improve the system reliability.The simulation results show that the proposed strategy can keep the capacitor voltage balancing and has good dynamic and static performance.

Design Consideration for High Power Density GaN Buck-Rectifier in ISOP-IPOS Converter based dc Distribution, System

GaN （gallium nitride） buck-rectifier has been proposed to realize high power density ISOP （input series and output parallel）-IPOS （input parallel and output series） converter-based dc distribution system. The ultra-low loss bi-directional switch can be developed by the GaN power device because of the low on-resistance, the high-speed switching behavior and its own device structure. The buck-rectifier using the GaN bi-directional switches has the potential to achieve higher power density than the commonly utilized boost-rectifier. Availability of the GaN-HEMT （high electron mobility transistor） for the buck rectifier has been verified taking the theoretical limit of the on-resistance and the switching loss energy into account. Design consideration for a high power density buck-rectifier has been also conducted and the application effect of the GaN bidirectional switches has been evaluated quantitatively. The ISOP-IPOS converter-based dc （direct current） distribution system takes full advantage of the buck-rectifier and the rectifier using GaN devices contributes to realizing higher power density dc distribution system.