A Modulation Strategy to Suppress Leakage Current in Non-isolated Photovoltaic Systems

Abstract

The invention relates to a modulation strategy for suppressing non-isolated photovoltaic system leakage current. The technical characteristics are that the modulation strategy comprises the following steps that an H-bridge cascaded photovoltaic system is divided into a first-half period working mode and a second-half period working mode. Inverter output voltage is 0, -Vpv and -2Vpv under the first-half period working mode, the lower level switch state is maintained to be unchanged, a switch S21 and a switch S24 are turned off, and a switch S23 and a switch S22 are turned on. Inverter output voltage is 0, +Vpv and +2Vpv under the second-half period working mode, the upper level switch state is maintained to be unchanged, a switch S11 and a switch S14 are turned on, and a switch S13 and a switch S12 are turned off. An H-bridge cascaded multilevel inverter acts as the base, and half of the number of the required carriers is reduced in comparison with that of a conventional modulation strategy starting from the modulation strategy without changing the system structure or increasing system cost so that calculation amount is greatly reduced. Besides, common-mode voltage is controlled within a certain range so that an effect of suppressing leakage current is achieved.

Description

technical field [0001] The invention belongs to the technical field of photovoltaic power generation, in particular to a modulation strategy for suppressing the leakage current of a non-isolated photovoltaic system. Background technique [0002] Due to the high cost of the photovoltaic power generation system, the total power generation of photovoltaics is relatively small compared with other common energy resources. Reducing the cost of photovoltaic systems and improving efficiency is the key. One of the ways to reduce costs is not to use transformers. Since non-isolated photovoltaic inverters are not electrically isolated from the grid, a leakage current loop path with low impedance will be formed, resulting in Leakage current will not only cause problems such as electromagnetic interference and grid-connected current distortion, but also cause harm to equipment and personal safety. At home and abroad, there are two main methods to solve the problem of output common mode ...

AI Technical Summary

Problems solved by technology

The hardware method filters out the common-mode voltage by adding a filter at the output of the inverter, or adopts an improved topology. The disadvantages of this method are: adding hardware increases the size and weight of the inverter, and the control system design is complicated. At the same time It is necessary to redesign the parameters of the filter or transformer used, which reduces the reliability of the system

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