Coupled-dc Module Based Photovoltaic System with Power Mismatch Tolerated Modulation

This paper presents a coupled-dc power module based cascaded multilevel converter integrating utility-scale photovoltaic generations (CDPM-PV). CDPM-PV inherits merits like modular structure, distributed maximum power point tracking (MPPT), direct distribution grid access, from cascaded H-bridge based PV system (CHB-PV). But, it supplies more flexible power routes than CHB-PV, through coupling different dc-links. Power routes are intended for enlarging the entire operating range including conditions of active power mismatch arising from non-ideal elements like partial shading and parameter variations. The system construction with its self-balancing principle is firstly introduced. Switching states for different operating regions are then derived based on the principle of easing implementation. Based on these, a modulation strategy including initial switching pattern selection and coordinated power routing is proposed to allow module-mismatches. Operating ranges are also analyzed and compared with conventional CHB-PV. Simulation results of a 3MW/13.8kV system developed in Matlab/Simulink platform, and experiment results based on a 2.4kW/311V setup are presented and have demonstrated that the CDPM-PV topology with proposed modulation strategy can not only ride through a larger range of module mismatches, but also improve solar power utilization and system efficiency owing to non-compromised MPPT.