Flying capacitor voltage control method for three-phase five-level active neutral-point-clamped converter

Abstract

The invention discloses a flying capacitor voltage control method for a three-phase five-level active neutral-point-clamped converter. A kth-phase output load current ik, kth-phase flying capacitor voltage VkCf and DC bus total voltage 2Vdc of the converter are firstly sampled; the flying capacitor charging current i'kCf needed by the kth phase is obtained through a pure proportional controller; needed zero-sequence per unit voltage V0pu is obtained according to a decoupling constraint condition for the flying capacitor voltage and neutral point level control; modulated wave upper offset deltamk2 and modulated wave lower offset deltamk3 overlapped on the kth-phase modulated wave mk1 are thus calculated; according to mk2=mk1+deltamk2 and mk3=mk1-deltamk3, modulated waves mk2 for a switch transistor S5 and a switch transistor S6 and modulated waves mk3 for a switch transistor S7 and a switch transistor S8 are obtained; the charging and discharging process of the flying capacitor is then controlled through a carrier phase shift modulation mode; and finally, the purpose of flexibly controlling the flying capacitor voltage without influencing the neutral point level balance and output current of the three-phase converter are achieved, good decoupling effects for flying capacitor voltage control and neutral point level control are realized, and the operation reliability of the converter is ensured.

Description

technical field [0001] The invention relates to the technical field of inverters for grid-connected power generation, in particular to a method for controlling the flying capacitor voltage of a three-phase five-level active midpoint clamp inverter. Background technique [0002] In the field of high-voltage and large-capacity conversion, the application of multi-level inverters is favored. The five-level inverter further improves the output voltage level of the inverter and further reduces the harmonic content of the output voltage. Compared with other five-level topologies, the five-level active neutral point clamp inverter has the advantages of simple neutral point potential balance control, the least number of flying capacitors, improved stability, and more redundant control voltages for switch states. Balancing issues, reduced complexity of controlling multiple capacitor voltages in other topologies, and many more. [0003] Based on many excellent characteristics of the ...

AI Technical Summary

Problems solved by technology

[0009] The technical problem to be solved by the present invention is that the modulation algorithm of the three-phase five-level active neutral point clamp inverter in the prior art is complex and inconvenient for practical application, and the control process of the flying capacitor voltage will affect the inverter There is a coupling problem in the normal output of the inverter, the flying capacitor voltage and the neutral point current control. It provides a method that can flexibly control the flying capacitor voltage without affecting the neutral point potential balance and output current of the inverter, so as to improve the efficiency of the inverter. Flying capacitor voltage control method based on carrier phase-shift modulation for local and overall reliability of inverter operation

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