Abstract
For the high-frequency resonant accident of modular multilevel converter (MMC) in real engineering, in this paper, the 10th order state-space model of MMC is established based on the dynamic phasor method. The state-space model of MMC controller for power control is established according to the practical engineering. Then the time delay of input and output is considered in the controller, and the Pade fitting in state-space model applicable to the eigenvalue method is introduced to the complete state space model of MMC. Based on the proposed model, the MMC high-frequency resonance phenomenon is analyzed by the eigenvalue method, and the accuracy of the model is verified by simulation results. Besides, it is demonstrated that high time delay causes high-frequency resonance in the MMC system based on the participation factor and the system eigenvalue trajectory. Then, the coupling relationship between the input and output time delay inside the controller and the d-q axis time delay is investigated, and a new time delay compensation method to suppress high-frequency resonance is proposed based on Pade fitting, which can be used jointly with the traditional method with good effect.
Highlights
Given the wide application of Modular multilevel converter (MMC) in high voltage direct current (HVDC) projects, the time delay in MMC controller inevitably leads to stability problems in practical projects [1], such as 550Hz oscillation at DC side of Xiamen (Fujian, China) project, 1270Hz oscillation in Luxi (Yunnan, China) project and 700Hz and 1.8kHz in Yue HVDC project (Hubei, China) [1], [2]
HIGH ORDER dynamic phasor (DP) MODEL OF MMC When DP is applied to MMC [16], the three-phase time-varying variables in MMC system are directly expressed in the form of nonlinear multiplication terms in the d-q axis rotating at the fundamental frequency and the d2-q2 axis rotating at the second harmonic frequency
In this paper, the state-space model of MMC is established based on the dynamic phasor method
Summary
Given the wide application of Modular multilevel converter (MMC) in high voltage direct current (HVDC) projects, the time delay in MMC controller inevitably leads to stability problems in practical projects [1], such as 550Hz oscillation at DC side of Xiamen (Fujian, China) project, 1270Hz oscillation in Luxi (Yunnan, China) project and 700Hz and 1.8kHz in Yue HVDC project (Hubei, China) [1], [2]. F. Wang et al.: High-Frequency Resonance Analysis and Stabilization Control Strategy of MMC Based on Eigenvalue Method the modeling of MMC is more complex than that of two-level converter. Based on the issue above, multi-harmonic linearization method and harmonic state space (HSS) method are further developed and utilized in MMC modeling within high-frequency bandwidth [3], [9], [10]. Given that the essence of high-frequency oscillations, the time delay in the controller, is not considered in the existing literature, this paper proposes a time delay compensation control method based on the Pade fitting model.
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