Power unbalance control method of common DC bus cascaded photovoltaic inverters

Abstract

The invention discloses a power unbalance control method for a cascade-connected photovoltaic inverter of a common DC bus, belonging to the photovoltaic power generation technical field in the field of electrical engineering. The purpose is to solve the power imbalance problem of the common DC bus cascaded photovoltaic inverters. The steps are as follows: control the voltage of each DC bus in the three-phase cascaded H-bridge inverter, so that the photovoltaic array corresponding to each common DC bus works at the maximum power point, and obtain the reference value of the active component of the grid-connected current according to the reference value of the active component. Perform grid-connected current control with the reference value of reactive power components; perform third harmonic compensation according to the three-phase modulation voltage obtained in the previous step, and calculate the working mode of each H-bridge converter according to the modulation voltage after compensating for the third harmonic. Compared with the prior art, the linear modulation range of the common DC bus cascaded photovoltaic inverter is further expanded, and the ability of the common DC bus cascaded photovoltaic inverter to cope with power imbalance is improved.

Description

technical field [0001] The invention belongs to the photovoltaic power generation technology in the field of electrical engineering, and in particular relates to a power unbalance control method of a common DC bus cascading photovoltaic inverter. Background technique [0002] Due to the limitation of semiconductor switching devices, it is difficult for traditional centralized inverters to further increase the rated power in high-voltage and high-power photovoltaic systems. At the same time, in order to realize the medium voltage grid connection, the traditional centralized inverter needs a bulky power frequency transformer, which increases the volume of the inverter. The cascading photovoltaic inverter adopts a modular design, which can achieve high-voltage output through the cascade of many modules, and realize high-voltage grid connection without the need for a power frequency transformer; at the same time, the isolated DC in the cascading inverter The / DC circuit enables...

AI Technical Summary

Problems solved by technology

[0009] 1) The improved MPPT algorithm can effectively solve the problem of H-bridge power imbalance, but it will greatly reduce the efficiency of the inverter

[0010] 2) The reactive power compensation strategy can deal with severe power imbalance, but this method will reduce the system power factor

[0011] 3) The third harmonic compensation strategy improves the linear modulation range of the H-bridge converter to 1.155, but its ability to deal with power imbalance is still weak and cannot deal with more serious power imbalance situations

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