A Common Mode Voltage Suppression System for Photovoltaic Grid-connected Inverters

Abstract

The invention discloses a common-mode voltage suppression system for photovoltaic grid-connected inverters. In the system, a common-mode filter inductance is connected in series on the loop between the differential-mode filter inductance and the midpoint capacitance of the pull-back busbar. The common-mode filter inductance is an enhanced For a common-mode filter unit, the magnetic flux formed by the differential-mode current in the magnetic core cancels each other, so the differential-mode current will not affect the inductance of the common-mode filter unit. The present invention reduces the attenuation effect of the strong common-mode voltage on the differential-mode inductance, reduces the filtering pressure of the ordinary common-mode inductance in the rear stage, and most of the common-mode voltages are all dropped to the second common-mode filter inductance, with low The cost suppresses the strong common-mode voltage, effectively reduces the impact of the common-mode voltage on the grid side, and optimizes the EMC status of the whole machine.

Description

technical field [0001] The invention relates to the technical field of photovoltaic power generation, in particular to a common-mode voltage suppression system for photovoltaic grid-connected inverters. Background technique [0002] Photovoltaic grid-connected inverter is a power generation device that converts the DC power of photovoltaic panels into AC power. As an important member of the new energy team, solar energy has attracted widespread attention from all over the world in recent years. Distributed photovoltaic power generation brings this clean energy into thousands of households, so that everyone can enjoy the convenience brought by green energy to life. The grid-connected mode of distributed photovoltaic inverters often chooses to directly integrate the inverter into the low-voltage power grid of the end user, and the low-voltage power grid has the characteristics of a wide variety of load equipment, uneven anti-interference capabilities, and high requirements for...

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Problems solved by technology

In the second method, the differential-mode filter inductor is used to cooperate with the capacitor pulled back to the midpoint of the bus capacitor to suppress the common-mode voltage on the differential-mode filter inductor, which can effectively solve the problem of common-mode current flowing to the terminal power grid, but for direct parallel For the string inverters connected to the terminal low-voltage power grid, due to factors such as overall volume and efficiency, the switching frequency is relatively high. Magnetic materials with better high-frequency characteristics, such magnetic materials have low loss under high-frequency current, but the attenuation of the inductance value under the action of current is relatively serious. If the common-mode voltage is all borne by the differential-mode filter inductor, it will inevitably further Reduce the inductance, affect the effect of differential mode filtering, and then affect the output index of the whole machine

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