Modulation method of three-phase flying capacitor multilevel photovoltaic inverter

Abstract

The invention discloses a modulation method of a three-phase flying capacitor multilevel photovoltaic inverter, which is characterized in that firstly, line voltage signals vac<*>, vba<*> and vcb<*> are obtained from initial modulation waves va<*>, vb<*> and vc<*> and are respectively multiplied by a coefficient K, then a zero sequence signal v0 is obtained through a zero sequence signal calculation unit, the zero sequence signal is added with the Kvac<*>, Kvba<*> and Kvcb<*> to obtain final modulation waves va<**>, vb<**> and vc<**>, logic signals Sa, Sb and Sc are obtained from the modulation waves va<**>, vb<**> and vc<**> and a carrier wave through a comparator, and a switching signal is obtained from the logic signals Sa, Sb and Sc through a logic circuit of the modulation method. The modulation method has the beneficial effects that a switching signal generation circuit has a simple structure, and both an analog circuit and a digital circuit can be adopted for implementation; a single carrier modulation strategy is adopted in a system modulation mode, so that the problem of too complex implementation of the traditional multicarrier modulation strategy and space vector modulation strategy is solved; and additionally, the system common mode voltage is kept constant, thereby effectively suppressing system drain current.

Description

technical field [0001] The invention relates to the technical field of power electronic conversion, in particular to a modulation method for a three-phase flying capacitor multilevel photovoltaic inverter. Background technique [0002] There are three main types of multilevel inverters widely used at present: diode clamping type, flying capacitor type and cascade type. Generally speaking, the number of clamping devices in the flying capacitor type is half that of the diode clamping type, and it has the advantages of not requiring cascaded multi-channel isolated input power, and has been applied in photovoltaic power generation systems. Due to the parasitic capacitance between the photovoltaic system and the ground, improper control of the photovoltaic inverter will cause high-frequency components in the voltage across the parasitic capacitance, which will cause leakage current. Leakage current will lead to output current distortion of photovoltaic inverter, electromagnetic ...

AI Technical Summary

Problems solved by technology

For example, the space vector pulse width modulation method needs to determine the sector, calculate the vector action time and vector sequence distribution, etc., the calculation amount is large, and the implementation is relatively complicated

The multi-carrier modulation method also requires sector judgment, and then through multi-carrier modulation and other links, the implementation is also more complicated

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