Multilevel LVDC Distribution System with Voltage Unbalancing and Disturbance Rejection Control Topology

With the emergence of power electronic technology and advancements in highly efficient electric power converters, DC-DC converters play a significant role in DC networks and DC distribution systems. Not being fully understood, nevertheless, the stability, protection and safety of DC systems present an open challenge for the research community. In this study, a high quality low voltage DC distribution system has been proposed, which provides a constant power in the event of voltage disturbance (sag), fluctuations, and fault. A three wire line system is adopted: +375 V line, neutral and -375 V line. Furthermore, the required DC power is transformed from DC or AC voltages by using load side converters, and these power converters do not need any transformers to adopt the proper DC voltage. In this research work double-closed-loop control strategy, the outer voltage control loop and inner current loop (decoupled without the exact value of boost inductance) are proposed. If short circuit or any fault occurs on the load side, the proposed strategy prevents the effect of remaining load. Also, the grid reconnection and disconnection is very smooth. Furthermore, a voltage balancer is proposed near to low voltage side. To confirm the effectiveness of the suggested control topology, simulations are performed in Matlab/Simulink and PSCAD software. The results obtained from simulation show that the suggested control system topology can provide excellent power in various conditions.