Model Predictive Control of Capacitor Voltage Balancing for Cascaded Modular DC–DC Converters

Input-series output-series (ISOS) modular dc-dc converters are suitable for applications involving high input and output voltages. Input voltage sharing (IVS) and output voltage sharing (OVS) of the constituent modules must be guaranteed for an ISOS system. A duty cycle-based model predictive control (DC-MPC) scheme is proposed in this paper to achieve IVS and OVS for an ISOS system. The employed switching frequency in the DC-MPC scheme is fixed; duty cycles are optimized and then determined by minimizing a cost function, which is derived from an ISOS system aimed at achieving IVS and OVS. IVS and OVS can, therefore, be obtained by employing the optimized duty cycle within each sampling period. In addition, challenges and disadvantages of directly using traditional MPC to achieve IVS and OVS is briefly discussed, while the proposed DC-MPC can effectively avoid them. Compared with the existing proportional integral-based schemes in the literature, the proposed DC-MPC is better for IVS and OVS because it is a very simple and intuitive approach with lower cost and higher overall dynamic performance. Simulation and experiments are conducted to verify that the proposed DC-MPC scheme works well during both steady and transient states.