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1. Exploring Dynamic P-Q Capability and Abnormal Operations Associated with PMSG Wind Turbines

   https://doi.org/10.3390/en16104116  

   Rahman, Shahinur; Li, Shuhui; Das, Himadry Shekhar; Fu, Xingang; Won, Hoyun; Hong, Yang-Ki (May 2023, Energies)

   With the proliferation of large-scale grid-connected wind farms, subsynchronous oscillation (SSO) incidents associated with Type-4 wind turbines (WTs) with a permanent magnet synchronous generator (PMSG) have occurred frequently. These incidents have caused severe reliability risks to the power grid. Conventionally, P-Q capability charts are utilized to ensure the safety operating region of a synchronous generator. However, a PMSG WT exhibits completely different and dynamic P-Q capability characteristics due to the difference in energy conversion technique and several critical factors related to the WT power converters. This paper presents a comprehensive dynamic P-Q capability study of a PMSG WT with sufficient and accurate considerations of the WT control and operation in the dq reference frame, its power converter constraints, and grid dynamics. Models of a PMSG WT are first developed based on its control principle in the dq reference frame. Then, algorithms for obtaining the P-Q capability charts of the WT are developed with the considerations of complete WT constraints in different aspects. The study analyzes the root cause of many abnormal operations of grid-connected PMSG WTs, reported in the literature, from the dynamic P-Q capability perspectives. The proposed study is verified via an electromagnetic transient (EMT) model of a grid-connected Type-4 WT. 

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2. A Comprehensive P-Q Capability Study for Grid Interconnection of Inverter Based Resources Plant

   https://doi.org/10.1109/IAS54024.2023.10406385  

   Rahman, Shahinur; Li, Shuhui; Das, Himadry Shekhar (October 2023, 2023 IEEE Industry Applications Society Annual Meeting (IAS))

   With the increased inverter-based resources (IBRs) connected to the grid, IBR P-Q capability charts are needed, proposed, and developed by the power industry to assure IBR operation efficiency and reliability. This paper presents a comprehensive P-Q capability evaluation for an IBR plant interconnected with the transmission grid. The proposed study considers the impact of different IBR grid-connected filters, IBR vector control implementation in the dq reference frame, and special interconnection nature of IBRs in a plant structure. The models and algorithms developed for the IBR P-Q capability analysis have considered specific IBR constraints that are different from those of a synchronous generator. The paper especially focuses on exploring the P-Q capability characteristics of IBRs and IBR plant at different interconnection points that are important for managing, designing, and controlling IBRs within an IBR plant, and for the development of international standards, such as IEEE P2800, for connecting IBRs to the transmission and distribution grids in a plant structure. 

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3. Implementing Inertial Control for PMSG-WTG in Region 2 using Virtual Synchronous Generator with Multiple Virtual Rotating Masses

   https://doi.org/10.1109/PESGM40551.2019.8973788  

   Yan, Weihang; Gao, Wei; Gao, Wenzhong; Gevorgian, Vahan (August 2019, 2019 IEEE Power & Energy Society General Meeting (PESGM))

   null (Ed.)

   With the increasing integration of renewable energy, the problems associated with deteriorating grid frequency profile and potential power system instability have become more significant. In this paper, the inertial control algorithm using Virtual Synchronous Generator (VSG) is implemented on type-4 Permanent Magnet Synchronous Generator (PMSG) - wind turbine generator (WTG). The overall nonlinear dynamic model and its small-signal linearization of PMSG-WTG using VSG is established and comprehensively analyzed. Inevitably, the direct application of VSG introduces large inertia which causes conflict between the fast-varying of available wind power and inverter control with slow dynamics, particularly in region 2 of wind turbine. Aiming to address such issue, VSG with multiple virtual rotating masses is proposed in order to improve the active power tracking performance as well as to boost inertial control of a VSG. The inertial responses are verified in a modified 10MVA IEEE 14 bus microgrid system. The assessment of the simulation results demonstrates the applicability of VSG on renewable energy generation units. 

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4. Grid Interconnection Modeling of Inverter Based Resources (IBR) Plant for Transient Analysis

   https://doi.org/10.3390/en16073211  

   Das, Himadry Shekhar; Li, Shuhui; Rahman, Shahinur (April 2023, Energies)

   The increase in penetration levels of inverter-based resources (IBRs) is changing the dynamic performance of power grids of different parts of the world. IBRs are now being more and more integrated into the grid at a single connection point as an IBR plant. Due to the complex nature and dynamicity of each inverter model, it is not realistic to build and analyze full complex models of each inverter in the IBR plant. Moreover, simulating a large plant including detailed models of all the IBRs would require high computing resources as well as a long simulation time. This has been the main issue addressed in the new IEEE Std 2800-2022. This paper proposes a novel approach to model an IBR plant, which can capture the transient nature at the plant level, detailed IBR control at the inverter level, interactions of multiple IBR groups in a plant structure, and a collector system connecting the IBRs to the grid. The IBRs in the plant use a voltage source inverter topology combined with a grid-connected filter. The control structure of the IBR includes a cascaded loop control where an inner current control and outer power control are designed in the dq-reference frame, and a closed-loop phase-locked loop is used for the grid synchronization. The mathematical study is conducted first to develop aggregated plant models considering different operating scenarios of active IBRs in an IBR plant. Then, an electromagnetic transient simulation (EMT) model of the plant is developed to investigate the plant’s dynamic performance under different operating scenarios. The performance of the aggregated plant model is compared with that of a detailed plant model to prove the effectiveness of the proposed strategy. The results show that the aggregated EMT simulation model provides almost the same result as the detailed model from the plant perspective while the running time/computation burden is much lower. 

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5. A State-Space Model of an Inverter-Based Microgrid for Multivariable Feedback Control Analysis and Design

   https://doi.org/10.3390/en13123279  

   Patarroyo-Montenegro, Juan F.; Vasquez-Plaza, Jesus D.; Andrade, Fabio (June 2020, Energies)

   In this work, a synchronous model for grid-connected and islanded microgrids is presented. The grid-connected model is based on the premise that the reference frame is synchronized with the AC bus. The quadrature component of the AC bus voltage can be cancelled, which allows to express output power as a linear equation for nominal values in the AC bus amplitude voltage. The model for the islanded microgrid is developed by integrating all the inverter dynamics using a state-space model for the load currents. This model is presented in a comprehensive way such that it could be scalable to any number of inverter-based generators using inductor–capacitor–inductor (LCL) output filters. The use of these models allows designers to assess microgrid stability and robustness using modern control methods such as eigenvalue analysis and singular value diagrams. Both models were tested and validated in an experimental setup to demonstrate their accuracy in describing microgrid dynamics. In addition, three scenarios are presented: non-controlled model, Linear-Quadratic Integrator (LQI) power control, and Power-Voltage (PQ/Vdq) droop–boost controller. Experimental results demonstrate the effectiveness of the control strategies and the accuracy of the models to describe microgrid dynamics. 

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