Modeling and Bifurcation Analysis for Photovoltaic Single-Sourced Trinary Inverter With Auxiliary Floating Capacitors Controlled by Finite-Control-Set Model Predictive Control

Asymmetric cascaded H-bridge (ACHB) trinary inverter has several advantages, such as high efficiency due to high power main H-bridge modulated under a fundamental low frequency, optimal modulation due to nonredundant output voltage levels, and reduction in output filter sizes due to high-quality staircase output waveform. However, ACHB inverter requires prestage isolated dc sources for the individual H-bridges and has inherent control issues of nonregenerative operation, being incompatible with photovoltaic source. This article proposes a single-stage, single-sourced ACHB trinary inverter topology without presources. Then, a control strategy using unity horizon length finite-control-set model predictive control (FCS-MPC) is proposed to modulate the ACHB inverter. Conventional unity horizon length FCS-MPC has presence of undesirable harmonics and chaos in its variable frequency switching waveform due to the minimum achievable error. Therefore, an exact discrete-time modeling for FCS-MPC is newly derived to show the nonlinear effects of power stage and control parameters in the closed-loop dynamics. And then, a bifurcation analysis-based design is proposed to eliminate the undesirable harmonics and chaos operation in the FCS-MPC closed-loop operation. The proposed topology and FCS-MPC controller design is implemented and verified in hardware by using a 2-kW prototype for standalone and grid-connected operation.