Novel power equalization modulation strategy of cascaded H bridge

Abstract

The invention discloses a novel power balance modulation strategy suitable for a cascaded H-bridge multi-level converter, and belongs to the technical field of multi-level PWM converters. The method is based on the idea of carrier reconstruction and carrier degree-of-freedom recombination, and comprises the following steps: firstly, reconstructing three triangular carriers so that the three triangular carriers are uniformly distributed among different layers for periodic circulation; secondly, adjusting the vertical degree of freedom of the sinusoidal modulation wave; and comparing the modulated wave with a carrier wave to obtain an optimized PWM pulse signal. According to the method, power balance among the output units can be realized, so that direct-current voltage discharge is kept consistent, and the output voltage quality of the converter is improved; the time required for balancing is shortened to the maximum extent; and meanwhile, the consistency of the average switching frequency is also realized. In addition, the method can be expanded to n cascade units, so that the practicability of the converter is improved.

Description

technical field [0001] The invention belongs to the technical field of multi-level converter multi-carrier PWM, and specifically relates to a novel power balance modulation method suitable for symmetrically cascaded H-bridge multi-level inverters. Background technique [0002] In recent years, multi-level inverters have gradually replaced traditional two-level inverters in the field of high voltage and high power because of their advantages such as high output voltage level, low switching stress, small electromagnetic interference, and small voltage change rate (dv / dt). Transformer has become a research hotspot. Multilevel inverters can be divided into clamp type and cascade type. Clamped multilevel inverters can be further divided into three types: flying capacitor clamped (FC), diode clamped (neutral point clamped, NPC) and hybrid clamped. Among them, cascaded H-bridge (cascaded H-bridge, CHB) inverter does not need to consider the voltage equalization problem of the DC ...

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Problems solved by technology

[0005] The present invention is a novel modulation strategy for cascaded H-bridge multi-level inverters, under the traditional LS-PWM modulation strategy, the problem of unbalanced output power of each unit, and solves the problem of symmetrical cascaded H-bridge in traditional modulation The contradiction between the unbalanced output power and the optimization of the output phase voltage under the strategy, while shortening the power equalization time

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