Modeling method for uneven capacitor voltage of npc cascaded inverters with pulse hopping

Abstract

The invention discloses a method for modeling the uneven capacitor voltage of NPC cascaded inverters with pulse jumping. The mechanism of the uneven capacitor voltage analyzes the equivalent circuit when different vectors act, and clarifies the influencing factors of the uneven capacitor voltage. Including capacitor size, switching frequency, modulation ratio, load impedance, and power factor, the expression of capacitor voltage uneven current is obtained. Using the method of combining component superposition and two-port equivalent circuit, the capacitor voltage uneven switching function and capacitor voltage uneven The first-order ordinary differential equation model of capacitor voltage inhomogeneity is established from the angle of average current, and the unknown parameters of the model are solved in combination with the actual working conditions of the inverter. The multi-factor capacitance voltage uneven mathematical model established, the capacitance value, switching frequency, modulation ratio, load impedance, power factor and other factors are modeled in a unified manner, and a six-dimensional space model of capacitance voltage unevenness is constructed, which can analyze multiple variables The uneven change of capacitor voltage when acting at the same time.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a modeling method for uneven capacitor voltage of NPC cascaded inverters with pulse jumping. Background technique [0002] In recent years, with the development of power electronics technology, single-phase multilevel inverters have been widely used in various applications. The single-phase CHB-NPC inverter has the advantages of low output voltage harmonic content, large output power, and low electromagnetic interference. It has obvious application advantages in the fields of rail transportation, electromagnetic emission, and new energy power generation. [0003] Uneven DC side capacitor voltage is an inherent problem of single-phase CHB-NPC inverters, which will lead to poor quality of inverter output voltage. Many studies mainly control the DC side capacitor voltage equalization effect by optimizing the modulation algorithm. Although a good voltage equali...

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Problems solved by technology

However, there is no quantitative modeling of capacitor voltage unevenness in the analysis process, and the vector balance domain analysis method is not suitable for single-phase CHB-NPC inverters

Liu Zhan and others established the capacitor voltage uneven formula in "Research on Bus Midpoint Voltage Balance of Active Midpoint Clamped Five-Level Inverter Based on Space Voltage Vector" (Proceedings of the Chinese Society for Electrical Engineering) and obtained The balance domain curve of the midpoint potential with respect to the modulation ratio and power factor, but there is a lack of modeling research on the mechanism of voltage unevenness

In "Analysis of Capacitor Voltage Balance Control of Three-level NPC Inverter Based on Midpoint Current" (Proceedings of the Chinese Society for Electrical Engineering), Chen Zhong et al. analyzed the voltage balance characteristics of three-phase NPC inverters, and gave The balance domain of power factor and modulation ratio in different modulation ranges, but no unified model of capacitor voltage influenced by multiple factors

In "Modeling and Control of Midpoint Balance of T-type Three-level Inverter" (Power Engineering Technology), Li Yong and others analyzed the mechanism of midpoint potential unevenness of T-type three-level inverter, and established the capacitor voltage The uneven transfer function model analyzes the influence of current and power factor on the uneven capacitor voltage, but does not further study the influence of other factors such as switching frequency

[0005] The above technology does not establish a unified mathematical model of capacitor voltage unevenness due to multiple factors such as capacitor size, switching frequency, power factor, modulation ratio, and load impedance. When the device works under different working conditions, the key factors affecting the uneven voltage of the capacitor

Although the specific value of the capacitor voltage unevenness can be determined through software simulation, the obtained capacitor voltage uneven value is only a set of data points of the inverter operating under specific working conditions, and it cannot theoretically explain the influence of various influencing factors on the capacitor voltage unevenness. The extent of the role of the capacitor voltage can not be analyzed, nor can it provide theoretical guidance for the parameter design of the inverter.

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