Novel modularized photovoltaic grid-connected system based on three-port power channel and control method

Abstract

The invention discloses a novel modularized photovoltaic grid-connected system based on a three-port power channel and a control method. The system comprises a front-stage three-port isolation type DC / DC photovoltaic converter, a rear-stage three-phase half-bridge cascade MMC and a combination thereof. The front-stage three-port DC / DC converter adopts a three-winding high-frequency transformer for isolation, an input port is connected with a photovoltaic array, and two output ports are respectively connected to two sub-modules of upper and lower bridge arms of each phase unit of the MMC. The half-bridge cascade structure of the MMC enables the output voltage to be the superposition of the output voltage of each sub-module, and the output current harmonic wave is greatly reduced through carrier phase-shifting modulation, so that the MMC can be directly connected with a medium-voltage AC power grid and a medium-voltage DC power grid. According to the topology, through power decoupling control, the capacity of a power decoupling capacitor can be reduced by dozens of times, and the size of a system is greatly reduced. In addition, the photovoltaic power among the topological phase units is balanced in the form of direct-current circulating current through a direct-current link, so that the problem of mismatch of the photovoltaic power is well solved.

Description

technical field [0001] The invention relates to a novel modular topology based on a three-port power channel, in particular to a cascaded modular multilevel converter (MMC) DC side for a three-phase photovoltaic grid-connected power generation system A photovoltaic power generation system for voltage fluctuation suppression and photovoltaic power balance between bridge arms belongs to the technical field of power electronic power conversion. Background technique [0002] As a renewable and clean energy, solar energy is attracting more and more attention. Photovoltaic power stations are developing towards large-scale and grid-connected. The traditional centralized photovoltaic array tends to cause the maximum power point tracking (Maximum PowerPoint Tracking, MPPT) to fall into the local maximum power point, resulting in low photovoltaic utilization. And with the increase of voltage and power level, traditional two-level and three-level voltage source inverters can no longer...

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Problems solved by technology

[0007] To sum up, the main problems of the existing technology are: MMC systems usually need to use large-capacity electrolytic capacitors for power decoupling, which affects the life and reliability of photovoltaic power generation systems; it is difficult to avoid the occurrence of modular photovoltaic inverters. Power mismatch problem, the existing topological power mismatch elimination strategy has small balance ability and poor balance effect, which greatly limits the practical application of this structure

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