A Quantitatively Optimized Space Vector Modulation Method for Cascaded Inverters

Abstract

The invention discloses a quantitatively optimized cascaded inverter space vector modulation method. The DC power supply of each unit of the cascaded inverter can be a photovoltaic cell or an energy storage element. Firstly, in the one-dimensional space of inverter output vectors, all vectors are divided into several vector sets according to their level values, and the vectors corresponding to the two level values ​​closest to the output voltage command value and their respective vectors are found. vector set; then apply the least squares method to construct a vector selection function, calculate the vector selection function value of each switch vector in the two vector sets, and use the vector with the smallest calculated value in each set as the switch vector of the next switch cycle; finally calculate the Empty ratio. This modulation method applies the quantitatively optimized space vector modulation method to cascaded inverters of photovoltaic power generation systems, energy storage systems or hybrid energy storage systems, replacing the part of the unit DC voltage equalization control in the controller algorithm, simplifying the controller structure while ensuring the quality of the output waveform.

Description

technical field [0001] The invention belongs to the technical field of new energy power generation and energy storage control, and in particular relates to a quantitatively optimized cascaded inverter space vector modulation method. Background technique [0002] In photovoltaic power generation, energy storage devices or other hybrid energy storage systems, inverters are required to convert DC power into AC power. The cascaded inverter can meet the capacity and output voltage expansion requirements of this type of system. In a cascaded inverter, each photovoltaic cell (or energy storage element) and the single-phase inverter connected to it are called a unit. The energy storage element may be an element capable of storing electric energy such as a storage battery or a supercapacitor. [0003] The power generation of photovoltaic cells is closely related to factors such as light intensity, temperature, surface shading, and the dispersion of photovoltaic cell parameters. If...

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Problems solved by technology

[0007] (1) It is only qualitatively judging the effect of the switch vector on the rise or fall of the supercapacitor voltage. There is no quantitative comparison of the magnitude of the capacitor voltage change caused by each vector, and it is impossible to truly select the vector combination that best meets the DC voltage control objectives of all units. Therefore, the unit DC The voltage control effect is limited

[0008] (2) Only according to the rising and falling trend of the capacitor voltage, delete the vectors that do not meet the requirements on the one-dimensional coordinate axis, and there may be no optional vectors on the left or right of the output voltage reference value

[0009] (3) The quality of the output waveform is not considered

After deleting the unqualified vectors on the one-dimensional coordinate axis, there may be a large difference in the output levels of the left and right vectors of the remaining adjacent output voltage reference value, increasing dv / dt, resulting in the distortion rate of the output voltage waveform raised

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