Inertia Support During Variable Wind Conditions

Wind variations are important to consider while designing inertia support strategies. A model has been evaluated but the findings should reflect issues with several control strategies utilizing a fixed inertia support pattern. Wind variability of 0.5 m/s from second to second is observed in real wind data. However, drastic changes in wind speed can occur within the duration of inertia support. An improved inertia control algorithm has been presented allowing a stable delivery of inertia support from variable speed wind turbines (VSWT) subjected to realistic wind conditions. The controller improves the previously presented inertia algorithm and smoothly transitions from a locked operation window to MPPT-operation. The impact of the utilized wind speed filter is described and its impact on the simulation found to be of great importance

Provision of Virtual Inertia Support Using Battery Energy Storage System

The paper presents the importance of the grid inertia constant for the frequency stability of the future high-res low-inertia power systems. Since more and more renewable energy sources (RES) are being connected to the power system via inverters, the grid inertia constant is reduced. This issue can be mitigated by applying appropriate control mechanisms through which RES can provide virtual inertia and provide rotating reserves for primary frequency control. The concept of a virtual inertia provision using battery energy storage system (BESS) is elaborated in the paper. By applying a virtual inertia concept, RES can provide support for frequency control during disturbances almost like conventional synchronous generators. The influence of virtual inertia on the stability of the part of Croatian power system was analyzed using BESSwith a control mechanism that enables its participation in frequency control

Virtual Inertia Scheduling (VIS) for Real-Time Economic Dispatch of IBRs-Penetrated Power Systems

A New Concept Called Virtual Inertia Scheduling (VIS) is Proposed to Efficiently Handle the Increasing Penetration of Inverter-Based Resources (IBRs) in Power Systems. VIS is an Inertia Management Framework that Targets Security-Constrained and Economy-Oriented Inertia Scheduling and Generation Dispatch with a Large Scale of Renewable Generations. Specifically, It Determines the Appropriate Power Setting Points and Reserved Capacities of Synchronous Generators and IBRs, as Well as the Control Modes and Control Parameters of IBRs to Provide Secure and Cost-Effective Inertia Support. First, a Uniform System Model is Employed to Quantify the Frequency Dynamics of the IBRs-Penetrated Power Systems after Disturbances. Leveraging This Model, the s-Domain and Time-Domain Analytical Responses of IBRs with Inertia Support Capability Are Derived. Then, VIS-Based Real-Time Economic Dispatch (VIS-RTED) is Formulated to Minimize Generation and Reserve Costs, with Full Consideration of Dynamic Frequency Constraints and Derived Inertia Support Reserve Constraints. the Virtual Inertia and Damping of IBRs Are Formulated as Decision Variables. a Deep Learning-Assisted Linearization Approach is Further Employed to Address the Non-Linearity of Dynamic Constraints. Finally, VIS-RTED is Demonstrated on a Two-Machine System and a Modified IEEE 39-Bus System. a Full-Order Time-Domain Simulation is Performed to Verify the Scheduling Results and Ensure their Feasibility

Enhancing grid-forming converters control in hybrid AC/DC microgrids using bidirectional virtual inertia support

This paper presents a new grid-forming strategy for hybrid AC/DC microgrids using bidirectional virtual inertia support designed to address weak grid conditions. The stability of hybrid AC/DC microgrids heavily relies on the AC mains frequency and the DC-link voltage, and deviations in these factors can lead to undesirable outcomes such as load curtailments and power system congestions and blackouts. This paper introduces a unique approach that leverages bidirectional virtual inertia support to enhance the stability and reliability of hybrid AC/DC microgrids under weak grid conditions. The proposed strategy employs virtual inertia as a buffer to mitigate rapid changes in DC-link voltage and AC frequency, thereby enhancing system stability margins. This strategy significantly contributes to a more stable and reliable grid operation by reducing voltage and frequency fluctuations. A standard hybrid AC/DC microgrid configuration is used to implement the bidirectional virtual inertia support, where a bidirectional interlinking converter control is adjusted to deliver inertia support to both the AC and DC subgrids. This converter utilizes the DC grid voltage and AC grid frequency as inputs, effectively managing active power balance and implementing auxiliary functions. Extensive simulations are conducted under weak grid conditions and standalone mode to validate the effectiveness of the proposed strategy. The simulation results demonstrate a remarkable improvement in frequency nadir, rate-of-change-of-frequency (RoCoF), and DC bus voltage deviation in the hybrid AC/DC microgrids. The bidirectional virtual inertia support substantially reduces voltage and frequency fluctuations, enhancing the microgrid stability and resilience. There is an improvement of over 45% and 25% in the frequency deviation and voltage deviation, respectively, achieved through implementing the proposed control strategy

P-HiL Evaluation of Virtual Inertia Support to the Nordic Power System by an HVDC Terminal

This paper provides an assessment of the effect from virtual inertia provided by an HVDC converter terminal on the Nordic power system. The analysis is based on results from Power-Hardware-in-the-Loop (P-HiL) tests with a laboratory-scale Modular Multilevel Converter (MMC) representing an HVDC terminal interfaced with a real-time phasor simulation of the Nordic grid. The applied control method for providing virtual inertia is utilizing the derivative of the locally measured grid frequency to adapt the power reference for the studied converter terminal. The power injection provided by the converter and the resulting impact on the frequency dynamics of the power system are investigated as a function of the emulated inertia constant and the frequency droop gain. The results demonstrate how the HVDC converter can effectively support the dynamic response of the power system when exposed to large load transients by improving the frequency nadir and reducing the Rate-of-Change-of-Frequency (ROCOF). Keywords: HVDC Transmission , Power-Hardware-in-the-Loop , Real-time Simulation , Virtual InertiaacceptedVersio

Feasibility studies of a converter-free grid-connected offshore hydrostatic wind turbine

Owing to the increasing penetration of renewable power generation, the modern power system faces great challenges in frequency regulations and reduced system inertia. Hence, renewable energy is expected to take over part of the frequency regulation responsibilities from the gas or hydro plants and contribute to the system inertia. In this article, we investigate the feasibility of frequency regulation by the offshore hydrostatic wind turbine (HWT). The simulation model is transformed from NREL (National Renewable Energy Laboratory) 5-MW gearbox-equipped wind turbine model within FAST (fatigue, aerodynamics, structures, and turbulence) code. With proposed coordinated control scheme and the hydrostatic transmission configuration of the HWT, the `continuously variable gearbox ratio' in turbulent wind conditions can be realised to maintain the constant generator speed, so that the HWT can be connected to the grid without power converters in-between. To test the performances of the control scheme, the HWT is connected to a 5-bus grid model and operates with different frequency events. The simulation results indicate that the proposed control scheme is a promising solution for offshore HWT to participated in frequency response in the modern power system

Internal energy based grid-forming control for MMC-HVDC systems with wind farm integration

The virtual synchronous control is regarded as an effective solution for grid-tied converters to operate under weak grid conditions and provide inertia support. However, for those grid-tied converters which control the DC voltage, e.g., the receiving end converter (REC) in modular multilevel converter based high-voltage direct-current (MMC-HVDC) transmission systems with wind farm integration, the application of virtual synchronous control is difficult due to the cascade control loops. The dynamic performance of DC voltage control may also be degraded. To address these issues, a novel grid-forming control strategy with real-time inertia support and fast DC voltage control is proposed for the REC. The cascade control loops of the virtual synchronous control are simplified by utilizing the internal energy stored in sub-module capacitors to emulate synchronous generator rotors. Moreover, the DC voltage is decoupled with the submodule capacitors voltage, thus being robust to sudden power change. Simulation results in PSCAD/EMTDC show that the proposed control realizes fast inertia support and desired dynamic control of the DC voltage, especially in weak grid operation

Novel Energy Management System for a DC MicroGrid

This paper presents a design and simulation of a rule based energy management system for a dc MicroGrid that considers a cost function to reflect the battery degradation and that relates to the actual battery parameters.The derivation of the battery cost function and the utilization of that to ensure an optimum utilization of the battery energy storage were presented. The detailed description of the algorithms used to implement the EMS was presented. Simulation on PSCAD/EMTDC software was used to demonstrate the operation of the EMS both under grid connected and islanded modes. Further, the inertia support provided by the super-capacitor to avoid the collapse of the dc link of the MicroGrid was demonstrated

Dual-loop Primary Frequency Regulation Controller for VSC-HVDC System

This paper presents a frequency control mechanism for an AC system through the active and reactive power loops of a VSC-HVDC system. The proposed scheme makes use of the reactive power loop for inertia support by exploiting the voltage-power sensitivity of loads, and active power droop control has been used to provide governor-like support following the large-disturbance. The performance of the presented controller is evaluated through various simulation case studies in DIgSILENT Power Factory including small-perturbation to demonstrate the effect of the frequency controller in system electromechanical mode damping. From the set of case studies it can be found that the proposed dual-loop control has favorable effects on the frequency behaviour and the inter-area mode damping of the system. © 2017 IEEE