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

초록

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 non-redundant output voltage levels, and reduction in output filter sizes due to high quality staircase output waveform. However, ACHB inverter requires pre-stage isolated DC sources for the individual H-bridges and has inherent control issues of non-regenerative operation, being incompatible with photovoltaic source. This paper proposes a single-stage, single-sourced ACHB trinary inverter topology without pre-sources. 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 2kW prototype for standalone and grid-connected operation. IEEE

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