Single-phase cascaded H-bridge photovoltaic inverter control strategy based on trapezoidal wave modulation

Abstract

The invention discloses a single-phase cascaded H-bridge photovoltaic inverter control strategy based on trapezoidal wave modulation, and belongs to a photovoltaic power generation technology in the field of electrical engineering. The invention provides a single-phase cascaded H-bridge photovoltaic inverter control strategy based on trapezoidal wave modulation, aiming at the problem of overmodulation of partial units caused by uneven power of photovoltaic modules of H-bridge units of a single-phase cascaded H-bridge photovoltaic inverter, and mainly comprises the following steps: (1) sampling related voltage and current; (2) controlling the direct-current bus voltage of all H-bridge units, and enabling each photovoltaic module to operate at the maximum power point; (3) controlling the grid-connected current; and (4) when the H-bridge unit is over-modulated, the over-modulation unit adopts trapezoidal wave modulation, and other unit modulation waves compensate reverse harmonics. Compared with the prior art, the cascaded H-bridge photovoltaic inverter has the advantages that the linear modulation range of the H-bridge unit in the cascaded H-bridge photovoltaic inverter is expanded to 1.273, and the capacity of the cascaded H-bridge photovoltaic inverter for coping with photovoltaic power imbalance is further improved.

Description

technical field [0001] The invention belongs to photovoltaic power generation technology in the field of electrical engineering, and in particular relates to a single-phase cascaded H-bridge photovoltaic inverter control strategy based on trapezoidal wave modulation. Background technique [0002] With the development of the household photovoltaic industry, the cascaded H-bridge photovoltaic inverter can realize module-level shutdown and module-level MPPT due to its multi-level output. It has obvious advantages in household applications and has very important research value. . However, due to the unitized structure of the cascaded H-bridge photovoltaic inverter, each H-bridge unit is independently connected to a photovoltaic module on the DC side. When the light intensity of each module is different, the generated power is also different. If the power balance control strategy is not adopted, each H-bridge unit will distribute the total modulation wave according to the power ...

AI Technical Summary

Problems solved by technology

[0007] 1) Adopting a hybrid modulation strategy will aggravate the fluctuation of the DC bus voltage, which is not conducive to the stable operation of the system;

[0008] 2) When the reactive power compensation control strategy is adopted, it is difficult to work at the unit power factor, which does not meet the requirements of grid connection;

[0009] 3) Using the third harmonic compensation method, the linear modulation range of the H-bridge unit is limited to 1.155, and it will not be able to cope with the further expansion of the photovoltaic power imbalance

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