Research

PhD defence by Weihua Zhou

Time

11.11.2020 kl. 13.00 - 16.00

Description

Weihua Zhou, Department of Energy Technology, will defend the thesis "Modeling, Analysis, and Stability Enhancement of Power Electronic-Dominated Power Systems"

TITLE

Modeling, Analysis, and Stability Enhancement of Power Electronic-Dominated Power Systems

PHD DEFENDANT

Weihua Zhou

SUPERVISOR

Professor Zhe Chen

CO-SUPERVISOR

Assistant Professor Yanbo Wang

MODERATOR

Associate Professor Yongheng Yang

OPPONENTS

Associate Professor Yongheng Yang, Dept. of Energy Technology, Aalborg University (Chairman)
Professor Antonello Monti, RWTH Aachen University
Professor Seddik Bacha, Grenoble Alpes University

ABSTRACT

Recently, renewable energies such as wind power and solar power have been increasingly explored. Due to the superior flexibility, full controllability, and high efficiency, power electronic converters are widely utilized as the interfaces to integrate these renewables into conventional power systems, which results in modern power electronic-dominated power systems (PEdPSs). However, the impedance interactions between the various control loops of the power electronic converters and the grid may cause wideband electromagnetic oscillatory instability phenomena. Modeling, analysis, and stability enhancement strategies are developed in this thesis to assess the system stability, identify the instability source, and improve system stability, respectively.

First, an impedance-decoupled modeling method of PEdPSs for stability assessment is presented. This presented impedance-decoupled concept can split the whole power plant into several sub-modules, based on which the (generalized) Nyquist criterion is performed simultaneously in all the submodules. If the (generalized) Nyquist criterion is not satisfied in some submodules, the whole system is assessed as unstable. The presented impedance-decoupled modeling method is able to efficiently assess system stability based on only terminal impedance frequency characteristics of individual components, where the RHP poles calculation can be avoided.

Second, a gray-box hierarchical oscillatory instability source identification method of the PEdPSs is presented. This presented instability source identification method is able to conduct system-level, component-level, and parameter-level stability analysis sequentially. In detail, if the power plant is assessed as globally stable, only system-level stability needs to be analyzed. Only terminal impedance frequency responses of individual components are required in the three steps, which enables instability source identification even if no internal information of the power electronic converters is known due to the business secrecy and intellectual property rights.

Third, the effect of reactive power output of the grid-connected inverter (GCI) under different control strategies is investigated using the complex space vector and complex transfer function theory. It’s found that although reactive power injection of the current-controlled GCI make little effect on the system stability, the negative reactive power injection of the power-controlled GCI can reshape the q-axis impedance component and improve the low-frequency stability under weak grid conditions.

Finally, two operating point-dependent stability enhancement strategies are presented for single-GCI-based and multiple-GCI-based power plants, respectively. Specifically, a grid voltage feed-forward control loop is introduced to mitigate the low-frequency instability phenomena of single GCI induced by the outer power control loop and phase-locked loop (PLL), of which the feed-forward coefficient is determined by power controller parameters, current controller parameters, operating point, and grid impedance. In addition, dispatch of the active and reactive power among multiple-paralleled GCIs is optimized to improve system low-frequency stability, where more/less active power and less/more reactive power are allocated to the GCIs with narrower/wider bandwidths of power control loops and PLLs.

The effectiveness of the presented modeling, analysis and stability enhancement strategies in this thesis is validated by theoretical analysis, time-domain simulation based on Matlab/Simulink platform, real-time verification based on OPAL-RT platform, and experimental verification in laboratory. Otherwise, component-level and parameter-level stability analysis is further performed to identify problematic component and parameter sequentially.

 

The defence will be in english - all are welcome

Streaming info tbd.

 

 

 

 

Host

Department of Energy Technology

Address

Pontoppidanstræde 101, Room 1.015

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