Novel three-level NPC current converter modulation and midpoint level control strategy

Abstract

The invention discloses a novel three-level NPC current converter modulation and midpoint level control strategy comprising the steps of 1, firstly acquiring an upward modulating wave U*p and a downward modulating wave U*n; 2, decomposing the upward modulating wave U*p into U*p1 and U*p2, decomposing the downward modulating wave U*n into U*n1 and U*n2, and thus acquiring an analytic expression ofthe downward modulating waves under different modulating degrees m; 3, using a model prediction control method, and predicting the midpoint voltage of a (k+1) moment and a (k+2) moment; and 4, comparing the midpoint voltage of the (k+1) moment and the (k+2) moment with a reference voltage Uref, and then deciding whether to switch the modulating wave; then outputting a final PWM pulse to the three-level NPC current converter after the modulating wave is compared with a carrier wave. The control strategy provided by the invention selects the modulating wave through predicting the midpoint voltage values of two future moments to serve as a criterion; and provided is the three-level NPC current converter modulation and midpoint level control strategy which achieves balanced midpoint voltage, small switching loss and high efficiency under full modulating degrees and full power factors.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a modulation and midpoint potential control strategy of a novel three-level NPC converter. Background technique [0002] In recent years, with the wide application of three-level neutral point clamped (NPC) converters in photovoltaic grid-connected systems, the technology of three-level NPC converters has become increasingly mature, but its inherent neutral point potential balance problem Still needs to be perfected. [0003] At present, the modulation methods of the three-level NPC converter mainly include the carrier PWM method and the space vector PWM (spacevector PWM, SVPWM) method. [0004] Space vector PWM (SVPWM) has been widely welcomed due to its high voltage utilization rate and flexible vector selection, but this method has complex algorithms and a large amount of calculation. On the contrary, the basic carrier PWM has the advantages of simple a...

AI Technical Summary

Problems solved by technology

[0009] The purpose of the present invention is to provide a novel three-level NPC converter modulation and midpoint potential control strategy, which solves the problems of high switching frequency, high switching loss and low efficiency in the application of existing dual-modulated wave carrier PWM

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