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1. 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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2. Microgrid Control Strategy Based on Battery Energy Storage System-Virtual Synchronous Generator (BESS-VSG)

   https://doi.org/10.1109/KPEC47870.2020.9167653  

   Gao, Wei (July 2020, 2020 IEEE Kansas Power and Energy Conference (KPEC))

   null (Ed.)

   With more and more renewable energy resources integrated into the power grid, the system is losing inertia because power electronics-based generators do not provide natural inertia. The low inertia will cause the microgrid to be more sensitive to disturbance and thus a small load change may result in a severe deviation in frequency. Based on the basic VSG algorithm, which is to mimic the characteristic of the traditional synchronous generator, the frequency can be controlled to a stable value faster and more smoothly when there is a fluctuation in the PV power generation and/or load change. However, characteristic of the VSG depends on the system structure in consideration of multiple generations, such as Synchronous Generator (SG), PV and Battery Energy Storage System (BESS), which greatly increases the complexity of applying VSG in practical power system. Furthermore, with BESS-VSG, Maximum Power Point (MPP) operation of PV is guaranteed. In addition, an adaptive VSG method is developed for a microgrid system, and the corresponding simulation in Matlab/Simulink shows the effectiveness of the adaptive VSG method. 

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3. Frequency Response Improvement of PMSG Wind Turbines Using a Washout Filter

   https://doi.org/10.3390/en13184797  

   Shabestari, Parisa M.; Mehrizi-Sani, Ali (September 2020, Energies)

   null (Ed.)

   High integration of renewable energy resources, such as wind turbines, to the power grid decreases the power system inertia. To improve the frequency response of a low-inertia system, virtual inertia approach can be used. This letter proposes a control method to decrease the frequency transients and restore frequency to its nominal value. A wind turbine usually works based on maximum power point tracking (MPPT) curves to achieve the maximum power. In this letter, the proposed controller uses a non-MPPT method to leave power for frequency regulation during transients. Moreover, it uses a washout filter-based method to remove the steady-state error in the frequency. Simulation results in the PSCAD environment validate the improved performance of the proposed method during load changes by comparing it with the MPPT and non-MPPT methods. 

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4. Frequency Regulation in Hybrid Power Dynamics with Variable and Low Inertia due to Renewable Energy

   https://doi.org/10.1109/CDC.2018.8619580  

   Hidalgo-Gonzalez, Patricia; Callaway, Duncan S.; Dobbe, Roel; Henriquez-Auba, Rodrigo; Tomlin, Claire J. (December 2018, Frequency Regulation in Hybrid Power Dynamics with Variable and Low Inertia due to Renewable Energy)

   As more non-synchronous renewable energy sources (RES) participate in power systems, the system's inertia decreases and becomes time dependent, challenging the ability of existing control schemes to maintain frequency stability. System operators, research laboratories, and academic institutes have expressed the importance to adapt to this new power system paradigm. As one of the potential solutions, virtual inertia has become an active research area. However, power dynamics have been modeled as time-invariant, by not modeling the variability in the system's inertia. To address this, we propose a new modeling framework for power system dynamics to simulate a time-varying evolution of rotational inertia coefficients in a network. We model power dynamics as a hybrid system with discrete modes representing different rotational inertia regimes of the network. We test the performance of two classical controllers from the literature in this new hybrid modeling framework: optimal closed-loop Model Predictive Control (MPC) and virtual inertia placement. Results show that the optimal closed-loop MPC controller (Linear MPC) performs the best in terms of cost; it is 82 percent less expensive than virtual inertia placement. It is also more efficient in terms of energy injected/absorbed to control frequency. To address the lower performance of virtual inertia placement, we then propose a new Dynamic Inertia Placement scheme and we find that it is more efficient in terms of cost (74 percent cheaper) and energy usage, compared to classical inertia placement schemes from the literature. 

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5. Frequency Regulation using Data-Driven Controllers in Power Grids with Variable Inertia due to Renewable Energy

   https://doi.org/10.1109/PESGM40551.2019.8973437  

   Hidalgo-Gonzalez, Patricia; Henriquez-Auba, Rodrigo; Callaway, Duncan S.; Tomlin, Claire J. (August 2019, 2019 IEEE Power & Energy Society General Meeting (PESGM))

   With the increasing penetration of non-synchronous variable renewable energy sources (RES) in power grids, the system's inertia decreases and varies over time, affecting the capability of current control schemes to handle frequency regulation. Providing virtual inertia to power systems has become an interesting topic of research, since it may provide a reasonable solution to address this new issue. However, power dynamics are usually modeled as time-invariant, without including the effect of varying inertia due to the presence of RES. This paper presents a framework to design a fixed learned controller based on datasets of optimal time-varying LQR controllers. In our scheme, we model power dynamics as a hybrid system with discrete modes representing different rotational inertia regimes of the grid. We test the performance of our controller in a twelve-bus system using different fixed inertia modes. We also study our learned controller as the inertia changes over time. By adding virtual inertia we can guarantee stability of high-renewable (low-inertia) modes. The novelty of our work is to propose a design framework for a stable controller with fixed gains for time-varying power dynamics. This is relevant because it would be simpler to implement a proportional controller with fixed gains compared to a time-varying control. 

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