Control method for expanding the operating range of three-phase cascaded photovoltaic grid-connected inverters

Abstract

The invention discloses a control method for expanding the operation range of a three-phase cascade photovoltaic grid-connected inverter, which aims to solve a problem that the system cannot operate stably because of the grid-connected current distortion caused by unbalanced input power of a DC side photovoltaic panel of the three-phase cascade photovoltaic grid-connected inverter. The control method comprises the steps of (1) total DC side voltage control which is used for enabling the total DC side voltage of each H-bridge unit to track the total maximum power point voltage and obtaining anactive current instruction value of the system; (2) network side current control which can realize independent control for active current and reactive current and generate three phase inverter modulation wave signals at the same time; and (3) inter-phase power balance control in which the actual value of the total voltage of each phase is enabled to track the instruction voltage through an inter-phase voltage regulator, a regulation factor of the total voltage of each phase is obtained so as to modify the three phase inverter modulation wave signals, the H-bridge unit output mode is distributed according to the modified modulation wave signals, and thus the inter-phase power balance control is realized.

Description

technical field [0001] The invention relates to a control method for expanding the operating range of a three-phase cascaded photovoltaic grid-connected inverter, and belongs to the technical field of cascaded photovoltaic grid-connected inverter control. Background technique [0002] Photovoltaic grid-connected power generation has attracted much attention because it provides clean energy and is environmentally friendly. Faced with the problems of how to improve the efficiency of photovoltaic systems and reduce power generation costs, cascaded multilevel inverters have become a research topic due to their advantages such as modularization, easy expansion, high system efficiency, and low total harmonic distortion (THD) of grid-connected current. hotspots. In addition, each power unit of the cascaded multi-level inverter needs an independent DC power supply, which is just in line with the characteristics of photovoltaic module power generation, making MPPT control of a singl...

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Problems solved by technology

[0008] 1. The control method based on the zero-sequence injection of the fundamental wave can improve the phase-to-phase power imbalance of the three-phase cascaded photovoltaic grid-connected inverter to a certain extent, but the adjustment range is small. When the phases are seriously unbalanced, the system cannot Stable operation

[0009] 2. The control method based on the weighted maximum and minimum fundamental wave zero-sequence injection cannot inject accurate fundamental wave zero-sequence components, resulting in poor dynamic performance

[0010] 3. Although the phase-to-phase power balance method based on fundamental wave zero-sequence plus third harmonic injection can further expand the operating range of the system, when the output power of a certain H-bridge unit is too large so that its modulation degree is greater than 1.15, this method cannot achieve phase-to-phase power Balanced, unable to meet all working conditions of three-phase cascaded photovoltaic grid-connected inverters

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