Virtual synchronous control method for cascaded inverter based on unit active power standby

Abstract

The invention relates to a virtual synchronous control method of a cascade inverter based on unit active power standby, aims at solving the problems that a cascade H-bridge photovoltaic inverter doesnot have the characteristic of a synchronous motor, cannot participate in the frequency modulation of a power grid and can cause the over-modulation of an H-bridge unit due to sudden change of illumination. The method comprises the following steps: controlling direct current side voltage; controlling virtual synchronous, namely superposing frequency modulation power on the output power of a standby H bridge unit, and operating the rest of H bridge units at a maximum power point to obtain command values of grid-connected active power and grid-connected reactive power; controlling the current ona grid side; and controlling third harmonic injection, namely injecting reverse third harmonic into the initial modulation signals of the standby H bridge units, and injecting forward third harmonicinto the initial modulation signals of the rest of the H bridge units to reduce the modulation degree of the H bridge units. The virtual synchronous control method of the cascade inverter based on unit active power standby can realize that a single-phase cascade H-bridge photovoltaic inverter has the characteristics of the synchronous motor, participates in the frequency modulation of the power grid, reduces the modulation degree of the H-bridge unit and prevents over-modulation, and is simple in algorithm and easy in engineering realization.

Description

technical field [0001] The invention relates to a cascaded inverter virtual synchronous control method based on unit active power backup, and belongs to the technical field of cascaded inverter virtual synchronous control. Background technique [0002] Photovoltaic grid-connected power generation has attracted much attention because it provides clean energy and is environmentally friendly. In the face of how to improve the efficiency of photovoltaic systems and reduce power generation costs, cascaded H-bridge multilevel inverters have become a research hotspot due to their advantages such as modularization, easy expansion, high system efficiency, and low total harmonic distortion of grid-connected current. . [0003] Each DC-side photovoltaic array of a traditional cascaded photovoltaic inverter adopts an independent maximum power tracking control to achieve the maximum efficiency of the photovoltaic array. However, since the grid-connected inverter does not have moment of...

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Problems solved by technology

[0011] The problem to be solved by the present invention is to overcome the limitations of the above-mentioned solutions. Aiming at the problem that the single-phase cascaded H-bridge photovoltaic inverter does not have the characteristics of a synchronous motor, and at the same time, the H-bridge unit is prone to overmodulation, a method based on unit active power backup is proposed. Virtual synchronous control method for cascaded inverters

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