Blar i NTNU Open på forfatter "Cai, Xu"
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A Modified Sequence-Domain Impedance Definition and Its Equivalence to the dq-Domain Impedance Definition for the Stability Analysis of AC Power Electronic Systems
Rygg, Atle; Molinas Cabrera, Maria Marta; Cai, Xu; Chen, Zhang (Peer reviewed; Journal article, 2016)Representation of ac power systems by frequency-dependent impedance equivalents is an emerging technique in the dynamic analysis of power systems including power electronic converters. The technique has been applied for ... -
Accurate aggregated modelling of wind farm systems in modified sequence domain for stability analysis
Zong, Haoxiang; Lyu, Jing; Cai, Xu; Zhang, Chen; Molinas Cabrera, Maria Marta; Rao, Fangquan (Peer reviewed; Journal article, 2019)With the wind power penetration rate continuously rising, a suitable wind farm model considering both accuracy and simplicity is required for power system stability analysis. To accomplish this goal, an accurate aggregated ... -
Autonomous Synchronizing and Frequency Response Control of Multi-terminal DC Systems with Wind Farm Integration
Yang, Renxin; Shi, Gang; Cai, Xu; Zhang, Chen; Li, Gen; Liang, Jun (Journal article; Peer reviewed, 2020)Recent analyses have shown that the grid-integration of offshore wind farms through MTDC systems has brought low inertia and small-signal stability issues, in which the dynamics of phase-locked-loop (PLL) play a crucial ... -
Control of a Type-IV Wind Turbine with the Capability of Robust Grid-Synchronization and Inertial Response for Weak Grid Stable Operation
Sang, Shun; Zhang, Chen; Cai, Xu; Molinas Cabrera, Maria Marta; Zhang, Jianwen; Rao, Fangquan (Journal article; Peer reviewed, 2019)With the increasing penetration of wind power, the effective inertia of the power system reduces. Besides, a series of interactive instability issues including sub-synchronous oscillations and harmonic oscillations were ... -
Frequency Domain Modelling and Stability Analysis of a DFIG-based Wind Energy Conversion System Under None-compensated AC Grids: Impedance Modelling Effects and Consequences on Stability
Zhang, Chen; Molinas Cabrera, Maria Marta; Rygg, Atle; Cai, Xu (Journal article; Peer reviewed, 2019)Impedance-based frequency domain method is an effective tool for the stability assessment of a doubly-fed induction generator (DFIG) system. Several impedance models have been proposed recently, however, these models are ... -
Frequency Domain Stability Analysis of MMC-Based HVdc for Wind Farm Integration
Lyu, Jing; Cai, Xu; Molinas Cabrera, Maria Marta (Journal article; Peer reviewed, 2016)This paper investigates the stability of offshore wind farms integration through a modular multilevel converter-based high-voltage dc (MMC-HVdc) transmission system. Resonances or instability phenomena have been reported ... -
Frequency-dependent source and load impedances in power systems based on power electronic converters
Rygg, Atle; Molinas Cabrera, Maria Marta; Cai, Xu; Chen, Zhang (Conference object; Peer reviewed, 2016)Representations of power systems by frequency dependent impedance equivalents is an emerging technique in dynamic analyses of power systems including power electronic converters. The technique has been applied for decades ... -
Harmonic State-Space Based Small-Signal Impedance Modeling of a Modular Multilevel Converter With Consideration of Internal Harmonic Dynamics
Jing, Lyu; Xin, Zhang; Cai, Xu; Molinas Cabrera, Maria Marta (Journal article; Peer reviewed, 2019)The small-signal impedance modeling of a modular multilevel converter (MMC) is the key for analyzing resonance and stability of MMC-based power electronic systems. The MMC is a power converter with a multifrequency response ... -
Harmonic State-Space Based Small-Signal Impedance Modeling of Modular Multilevel Converter with Consideration of Internal Harmonic Dynamics
Lyu, Jing; Zhang, Xin; Cai, Xu; Molinas Cabrera, Maria Marta (Journal article; Peer reviewed, 2018)The small-signal impedance modeling of a modular multilevel converter (MMC) is the key for analyzing resonance and stability of MMC-based power electronic systems. The MMC is a power converter with a multifrequency response ... -
Harmonic Transfer-function-based Impedance Modelling of a Three-phase VSC for Asymmetric AC Grids Stability Analysis
Zhang, Chen; Molinas Cabrera, Maria Marta; Rygg, Atle; Lyu, Jing; Cai, Xu (Journal article; Peer reviewed, 2019)Impedance modeling and stability analysis of a grid-VSC system under symmetric ac grids have been extensively discussed in the literature, where the dq domain impedances are usually adopted. As for asymmetric ac grids, ... -
Impact of power flow direction on the stability of VSC-HVDC seen from the impedance nyquist plot
Amin, Mohammad; Molinas Cabrera, Maria Marta; Lyu, Jing; Cai, Xu (Journal article, 2017)The high-voltage dc (HVDC) systems are appearing more and more, and it is becoming a requirement that the HVDC voltage-source converters (VSCs) operate both as an inverter and a rectifier without changing the controls to ... -
Impact of Power Flow Direction on the Stability of VSC-HVDC Seen from the Impedances Nyquist Plot
Amin, Mohammad; Molinas Cabrera, Maria Marta; Lyu, Jing; Cai, Xu (Journal article; Peer reviewed, 2016)The high-voltage dc (HVDC) systems are appearing more and more, and it is becoming a requirement that the HVDC voltage-source converters (VSCs) operate both as an inverter and a rectifier without changing the controls to ... -
Impedance-based Analysis of Interconnected Power Electronics Systems: Impedance Network Modeling and Comparative Studies of Stability Criteria
Zhang, Chen; Molinas Cabrera, Maria Marta; Rygg, Atle; Cai, Xu (Journal article; Peer reviewed, 2019)Impedance is an intuitive and effective way for dynamical representation of power electronics devices (e.g. VSCs). One of its strengths towards others is the natural association with circuits. However, impedances of VSCs ... -
Mimo impedance based stability analysis of DFIG-based wind farm with MMC-HVDC in modifed sequence domain
Zong, Haoxiang; Lyu, Jing; Zhang, Chen; Cai, Xu; Molinas Cabrera, Maria Marta; Rao, Fangquan (Chapter, 2019)The modular multilevel converter (MMC) based high-voltage direct current (HVDC) transmission is widely applied for the large-scale wind farm integration making its interaction stability analysis especially significant. ... -
Modeling and analysis of grid-synchronizing stability of a Type-IV wind turbine under grid faults
Zhang, Chen; Cai, Xu; Rygg, Atle; Molinas Cabrera, Maria Marta (Peer reviewed; Journal article, 2020)Transient behavior and response of wind turbines have been extensively studied in the context of the low-voltage-ride-through (LVRT) for many years, in which the identified transients are mostly associated with circuit ... -
Modified sequence domain impedance modelling of the modular multilevel converter
Zong, Haoxiang; Lyu, Jing; Zhang, Chen; Molinas Cabrera, Maria Marta; Cai, Xu; Rao, Fangquan (Chapter, 2019)The accurate sequence impedance model of the modular multilevel converter (MMC) is essential for the precise stability analysis of various MMC-based interconnected systems. This paper presents a modified sequence impedance ... -
On the Equivalence and Impact on Stability of Impedance Modeling of Power Electronic Converters in Different Domains
Rygg, Atle; Molinas Cabrera, Maria Marta; Chen, Zhang; Cai, Xu (Journal article, 2017)Small-signal analysis of power electronic converters and systems is often carried out by impedance-based methods. At the core of these methods lies the impedance modeling, which can either be obtained through analytical ... -
On the Impedance Modeling and Equivalence of AC/DC Side Stability Analysis of a Grid-tied Type-IV Wind Turbine System
Zhang, Chen; Molinas Cabrera, Maria Marta; Rygg, Atle; Cai, Xu (Journal article; Peer reviewed, 2018)Impedance modeling of a Type-IV wind turbine is usually associated with model reductions, e.g. the grid-side converter (GSC) is modeled in detail, whereas the machine-side converter (MSC) is simplified as a constant power ... -
Optimal Design of Controller Parameters for Improving the Stability of MMC-HVDC for Wind Farm Integration
Lyu, Jing; Cai, Xu; Molinas Cabrera, Maria Marta (Journal article, 2017)A subsynchronous oscillation (SSO) phenomenon has been observed in a modular multilevel converter-based high-voltage DC (MMC-HVDC) transmission system for wind farm integration in the real world, which is independent of ... -
Properties and Physical Interpretation of the Dynamic Interactions between Voltage Source Converters and Grid: Electrical Oscillation and Its Stability Control
Zhang, Chen; Molinas Cabrera, Maria Marta; Rygg, Atle; Li, Zheng; Cai, Xu (Journal article; Peer reviewed, 2017)Voltage source converters (VSCs) play an important role in the power conversion of renewable power generation (RPG) systems. Conventional power systems are considerably affected by power electronic devices in systems with ...