Resonant-Frequency Tracking Method for Medium-Frequency Inverters Based on RLS and DSOGI-PLL Methods

Jingyu Niu; Guowei Xu; Wei Liu; Hongqiang Sang

doi:10.46604/ijeti.2026.16723

Authors

Jingyu Niu School of Electrical Engineering, Tiangong University, Tianjin 300387, China
Guowei Xu School of Electrical Engineering; School of Mechanical Engineering, Tiangong University/ Advanced Mechatronics Equipment Technology Tianjin Area Major Laboratory, Tianjin 300387, China
Wei Liu School of Electrical Engineering; School of Mechanical Engineering, Tiangong University/ Advanced Mechatronics Equipment Technology Tianjin Area Major Laboratory, Tianjin 300387, China
Hongqiang Sang School of Mechanical Engineering, Tiangong University/ Advanced Mechatronics Equipment Technology Tianjin Area Major Laboratory, Tianjin 300387, China

DOI:

https://doi.org/10.46604/ijeti.2026.16723

Keywords:

medium-frequency inverter, resonant-frequency tracking, parameter identification, feedforward compensation

Abstract

This study aims to improve resonant-frequency tracking in medium-frequency inverters subjected to switching harmonics and load-parameter variations. The proposed method combines recursive least squares (RLS) feedforward estimation with dual second-order generalized integrator phase-locked loop (DSOGI-PLL) feedback. The RLS algorithm identifies the equivalent resistance and inductance online and calculates the resonant-frequency feedforward value from the estimated inductance. In parallel, two SOGIs extract the fundamental components of the total voltage of the resistor-inductor-capacitor (RLC) circuit and the resonant current, and a normalized cross-product phase detector generates the feedback correction. The method reduces frequency drift after a phase-shift step by approximately 93% and shortens the convergence time after an inductance step from 9.29 ms to 2.32 ms. These results demonstrate that the proposed method can improve resonant-frequency tracking accuracy and dynamic response under phase-shift modulation and load-parameter variations.

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