Reduced Order Generalized Integrator Based Modular Multilevel Converter Loop Current Suppression Strategy under Unbalanced Conditions in Distribution Networks

Qiang Wang, Xipeng Zeng () and Xiangliu Song
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Qiang Wang: Hubei Provincial Engineering Research Center of Intelligent Energy Technology, Yichang 443002, China
Xipeng Zeng: College of Electrical and New Energy, China Three Gorges University, Yichang 443002, China
Xiangliu Song: College of Electrical and New Energy, China Three Gorges University, Yichang 443002, China

Energies, 2024, vol. 17, issue 17, 1-18

Abstract: Under the condition of grid voltage imbalance, the circulation of the bridge arm inside the modular multilevel converter (MMC) increases significantly, which leads to the aggravation of the distortion of the bridge arm current, and, thus, increases the system loss and reduces the power quality. To address this problem, this paper analyzes the mechanism of circulating current generation and proposes a circulating current suppression strategy based on a reduced-order generalized integrator (ROGI), which firstly uses the ROGI system to separate the second-harmonic positive- and negative-sequence components in the circulating current from the DC, and then converts the rotating coordinates of the circulating current’s second octave component into the DC to be fed into the proportional–integral quasi-resonance (PIR) controller for suppression. A simulation model of a 23-level MMC inverter is built in MATLAB/Simulink, and the control strategy proposed in this paper is compared with the classical proportional–integral (PI) control in simulation experiments. The simulation results show that the amplitude of the circulating current fluctuation of the classical PI control is reduced from 90 A to 22 A, and the harmonic distortion rate of the bridge arm current is reduced from 32.56% to 5.57%; the amplitude of the circulating current fluctuation of the control strategy proposed in this paper is reduced from 90 A to 5.7 A, and the harmonic distortion rate of the bridge arm current is reduced from 20.2% to 1.13%, which verifies the effectiveness of the pro-posed control strategy.

Keywords: modular multilevel converter; circulation suppression; reduced-order generalized integrator; proportional–integral resonance controller (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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