Optimized low switching frequency modulation with neutral point voltage control for three‐level converters

Bo Guan; Chuanchuan Luo; Xiaoliang Zhen

Optimized low switching frequency modulation with neutral point voltage control for three‐level converters

Bo Guan

Chuanchuan Luo

Xiaoliang Zhen

Vol. 24, No. 7, pp. 1035-1046, Jul. 2024

10.1007/s43236-024-00783-8

Multilevel converter

Neutral point voltage

Pulse width modulation

Switching frequency

Abstract

The use of three-level converters with low switching frequency (SF) modulation is urgently needed for medium voltage high power applications. However, since it is not possible to frequently adjust the injected zero-sequence voltage and duty time of redundant vectors, the neutral point (NP) voltage problem of three-level converters becomes a tricky issue under low SFs. In this paper, an optimized low SF modulation with NP voltage control is proposed, which is based on half-wave symmetry selective harmonic elimination pulse width modulation. The proposed modulation specifically addresses the low-frequency NP voltage fluctuation of three-level converters, using the amplitude and phase of the 3n-order harmonics as degrees of freedoms (DOFs). In addition, it actively optimizes the control problem into constraint equations. By revealing the relationship between these new DOFs and low-frequency NP voltage fluctuation, and obtaining the optimum settings for the new DOFs, the newly established constraint equations can naturally suppress the low-frequency NP voltage fluctuation, without the need for real-time switching angle adjustments. It fits very well with the feature that switching angles can only be calculated offline and used via a table online. Experimental results show the validity and feasibility of the proposed modulation strategy.

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Cite this article

[IEEE Style]

B. Guan, C. Luo, X. Zhen, "Optimized low switching frequency modulation with neutral point voltage control for three‐level converters," Journal of Power Electronics, vol. 24, no. 7, pp. 1035-1046, 2024. DOI: 10.1007/s43236-024-00783-8.

[ACM Style]

Bo Guan, Chuanchuan Luo, and Xiaoliang Zhen. 2024. Optimized low switching frequency modulation with neutral point voltage control for three‐level converters. Journal of Power Electronics, 24, 7, (2024), 1035-1046. DOI: 10.1007/s43236-024-00783-8.