Photovoltaic grid-connected inverter current control method based on positive and negative sequence component separation

Abstract

The invention provides a photovoltaic grid-connected inverter current control method based on positive and negative sequence component separation aiming at the problem that in the first step abc-alpha beta of the prior SVPWM (Space Vector Pulse Width Modulation) coordinate transformation, the sum of default three-phase voltage vectors is zero constantly, so that when the three-phase unbalanced grid voltage is subjected to SVPWM transformation, the information distortion is caused, so that a voltage waveform can not be accurately reduced in the SVPWM inverse transformation. The photovoltaic grid-connected inverter current control method has the beneficial effects that through decomposing the unbalanced grid voltage into respective balanced standard positive sequence components U+d and U+q and respective balanced standard negative sequence components U-d and U-q, due to the respective balance of the positive and negative sequence grid voltage components, the voltage waveform inverted by utilizing a component space vector method can be better simulated, so that a more ideal grid-connected current waveform is obtained under the unbalanced power grid voltage.

Description

technical field [0001] The invention belongs to the technical field of photovoltaic inverter grid-connected power generation systems, and more specifically relates to a method for controlling the grid-connected current of a photovoltaic inverter based on the separation of positive and negative sequences. Background technique [0002] The solar photovoltaic inverter grid-connected power generation system has attracted more and more countries' attention recently, and the photovoltaic inverter, as the core device of the photovoltaic inverter grid-connected power generation system, has also achieved considerable development. [0003] figure 1 It is the basic structure diagram of photovoltaic inverter grid-connected power generation system. [0004] Such as figure 1 As shown, the three-phase photovoltaic inverter grid-connected power generation system is composed of solar panel arrays and photovoltaic inverters. The photovoltaic inverter further includes a Maximum Power Point ...

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Problems solved by technology

However, the foundation and premise of SVPWM transformation lies in the absolute balance of the three-phase power grid by default. For a three-phase power grid with unbalanced amplitude or phase, when the SVPWM transformation is directly performed on it, the real information of the power grid voltage will be lost, resulting in the photovoltaic inverter. The inverter cannot follow the grid voltage well, causing the waveform distortion of the grid-connected current and the increase of the total harmonic distortion (Thd) of the current, thereby causing harmonic pollution to the three-phase grid and affecting the power supply quality of the grid

[0011] In order to eliminate the influence of the inherent defects of the SVPWM algorithm on the grid-connected current waveform under unbalanced power grids, many new algorithms have been developed in recent years, such as the coordinate transformation method based on the symmetrical component method for the separation of positive and negative sequences of the three-phase grid voltage, and the power grid based on the least squares method. Algorithms for fast detection of voltage positive and negative sequence components have been proposed. These methods can indeed play a role in quickly and accurately separating the positive and negative sequence voltages of the power grid in theoretical research. However, for engineering practice, considering the research and development costs and the existing The limitation of the computing power of the embedded processor cannot be well applied in engineering

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