Control method for expanding operation range of three-phase cascaded H-bridge inverter

Abstract

The invention discloses a control method for expanding the operation range of a three-phase cascaded H-bridge inverter, and aims to solve the problem of power imbalance of the three-phase cascaded H-bridge inverter. The method mainly comprises the following steps: (1) controlling the voltage of each direct-current bus in the three-phase cascaded H-bridge inverter to enable a photovoltaic array corresponding to each common direct-current bus to work at a maximum power point, and obtaining an active power value transmitted by the corresponding common direct-current bus; (2) calculating a grid-connected current reactive component reference value; (3) calculating a grid-connected current active component reference value and controlling the grid-connected current in combination with the grid-connected current reactive component reference value obtained in the previous step; and (4) distributing the three-phase total active modulation voltage and the three-phase total reactive modulation voltage obtained in the previous step, calculating the total modulation degree of each H-bridge converter, and injecting third harmonics to obtain the modulation wave of each H-bridge converter. Comparedwith the prior art, the linear modulation range of the three-phase cascaded H-bridge inverter is further expanded, and the capacity of the three-phase cascaded H-bridge inverter for coping with powerimbalance is improved.

Description

technical field [0001] The invention belongs to the photovoltaic power generation technology in the field of electrical engineering, and particularly relates to a control method for expanding the operating range of a three-phase cascaded H-bridge inverter. Background technique [0002] In high-voltage and high-power photovoltaic systems, traditional centralized inverters are limited by semiconductor switching devices, and it is difficult to further increase the rated power. 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. To solve these problems, one of the methods is to use a three-phase cascaded H-bridge inverter. The modular structure design can use common low-voltage switching devices to achieve higher output voltage, improve the power level of the inverter, and avoid the use of power frequency transformers. High-frequency...

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Problems solved by technology

[0010] 1) Hybrid modulation can expand the linear modulation range of the H-bridge converter to 4 / π, but it will increase the voltage fluctuation of the DC side capacitor of the H-bridge converter and affect the efficiency of MPPT

[0011] 3) The third harmonic compensation strategy will not aggravate the voltage fluctuation of the DC side capacitor of the H-bridge converter, and improve 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 cope with more severe power imbalance

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