A Single-Objective Modulated Model Predictive Control for a Multilevel Flying Capacitor Converter in a DC Microgrid

Abstract

This paper presents a single-objective modulated model predictive control for a bi-directional DC-DC flying capacitor (FC) converter in a microgrid. The presence of FC facilitates the converter to integrate a low-voltage battery to a high-voltage DC bus at reduced voltage stress on its power switches. The converter in such a configuration demands a multi-objective controller to accomplish DC bus and FC voltage regulations, and bi-directional power flow. The proposed controller realizes these multiple control objectives by determining optimum duty ratio for the power switches using a single-objective cost function based on battery current. In doing so, the converter realizes its multiple control objectives without weighting factors in the cost function and operates its power switches at a fixed switching frequency. The proposed controller also eliminates an additional control loop by utilizing an improved dynamic reference model to generate appropriate battery current reference for the DC bus voltage regulation and bi-directional power flow. Finally, the proposed system is validated experimentally under step-response of DC bus voltage, load, PV power, and system parameter variations, and compared with a finite control set model predictive control to prove its effectiveness.