Multi-terminal Heterogeneous Generalized Impedance Modeling and Analysis of MMC-MTDC Transmission Systems

doi:10.11930/j.issn.1004-9649.202405012

Abstract

Abstract:

The prominent risks of broadband oscillation among renewable energy, modular multilevel converter-based multi-terminal high voltage direct current (MMC-MTDC) and AC grid severely constrain the safe and stable operation and efficient accommodation of renewable energy. The control strategies of different converter stations of MMC-MTDC are various such as constant AC voltage, constant DC voltage and constant power control, and there is a strong nonlinear coupling between the multi-terminal converter stations, which brings challenges to the modeling and analysis of the system oscillation. Therefore, a modular modeling method of MMC-MTDC control system considering positive- sequence and negative-sequence control is firstly proposed in this paper. And then, aiming to the complex AC and DC grid structures, a generalized impedance model of different sections of MMC-MTDC is established with the multi-terminal nonlinear coupling considered. Finally, taking the three-terminal MMC-MTDC ring network as an example, simulation is conducted to verify the accuracy and validity of the generalized impedance model. The coupling effects of the multi-terminal interconnection system and the positive-sequence control and negative-sequence control on the impedance characteristics are analyzed, which will provide a basis for the oscillation analysis of renewable energy base connected into MMC-MTDC interconnection system.

Key words: MMC-MTDC, generalized impedance model, broadband oscillation, positive- and negative- sequence control, multi-terminal coupling

Guoliang ZHOU, Liping GAO, Yanqiao LIANG, Wenjin LI, Xin WANG. Multi-terminal Heterogeneous Generalized Impedance Modeling and Analysis of MMC-MTDC Transmission Systems[J]. Electric Power, 2025, 58(3): 73-85.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202405012

https://www.electricpower.com.cn/EN/Y2025/V58/I3/73

Figures/Tables 20

Fig.1 MMC-MTDC interconnection system topology

Fig.2 Positive- and negative-sequence separation control block diagram based on delayed signal cancellation

Fig.3 Block diagram of synchronous rotation angle generation

Fig.4 AC voltage control diagram in V/f control mode

Fig.5 PQ control diagram

Fig.6 DC voltage control diagram

Fig.7 AC current control diagram

Fig.8 Circulating current control diagram

Fig.9 Arm modulation signal generation diagram

Fig.10 Node admittance network

Fig.11 The structure of AC impedance of MMC in islanded renewable energy system

Fig.12 Three-terminal MMC-MTDC ring system

Fig.13 Influence of 2# renewable energy system on the AC impedance of 1# islanded converter station

Fig.14 Influence of grid strength of grid-connected station on AC impedance of 1# islanded converter station

Fig.15 Comparison of AC impedance of 1# islanded converter station before and after adopting positive and negative control

Fig.16 Influence of positive- and negative-sequence control of grid-connected station on AC impedance of 1# islanded converter station

Fig.17 Bode diagram of MMC DC impedance model verification

Fig.18 Impedance verification Bode diagram of DC system connected to 1# station

Fig.19 AC impedance verification Bode diagram of 1# islanded converter station

Fig.20 AC impedance verification Bode diagram of grid-connected converter station

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