Inertia

About: Inertia is a research topic. Over the lifetime, 12006 publications have been published within this topic receiving 164291 citations.

The role of inertia for grid flexibility under high penetration of variable renewables - A review of challenges and solutions

Abstract: Several studies show that grid-integrated renewable energy (RE) sources have the potential to replace conventional synchronous generators in the network. This means the grid will experience low conventional inertia that is currently provided by synchronous generators. Low, unpredictable and time-changing inertia in the power system, as a result of high penetration of non-synchronous RE sources, can cause rapid frequency oscillations. The rapid and unpredictable frequency oscillations are the major source of stability challenges in the power system. Therefore, this research presents a comprehensive literature survey on the role of inertia for grid flexibility under high penetration of non-synchronous RE sources to the power system. As inertia is becoming a time-changing quantity, inertia estimation techniques have been gaining popularity as solutions to stability challenges faced by the power system. Related to time-changing inertia, the following are discussed in this survey research. First, synthetic inertia provision in the network and the need for inertia estimation are intensively discussed. Second, the importance of prior knowledge of the system inertia, which will help operators to apply suitable control strategies to mitigate stability challenges, is also addressed. Third, the significance of co-existence, coordination and optimization of both conventional synchronous generator's inertia and synthetic inertia, as a key feature towards reliable and flexible grid in low inertia environment, are also emphasized. Finally, technical challenges, key issues, and further research needs are highlighted.

Effects of loading velocity, stiffness, and inertia on the dynamics of a single degree of freedom spring-slider system

Abstract: Numerical simulation of the nonlinear dynamics of a single degree of freedom spring-slider system can provide useful insight into the effects of loading velocity, friction environment, elastic stiffness, and inertia on the stress drop and dynamic behavior of earthquakes. In our numerical simulations using a rate- and state-dependent friction law, we varied the loading velocity by 7 orders of magnitude, the stiffness by 2 orders of magnitude, the mass by 5 orders of magnitude, and the velocity-weakening parameter (B-A) by a factor of 160. Four stability regimes were identified in the load point velocity-stiffness space when inertia was taken into account. For cyclic stick-slip instabilities, the stress drop amplitude increases with decreasing load point velocity, with decreasing stiffness, with increasing velocity weakening parameter B-A, and with decreasing mass. Simple scaling relations for the static stress drop, dynamic stress drop, “static” friction, and shear fracture energy with the natural logarithm of load point velocity were observed. Using the scaling relation for static stress drop, we infer the normalized velocity weakening parameter b-a (with respect to normal stress) to range from 0.0011 to 0.0039 for triaxial experiments on saw cut Westerly granite specimens sandwiched with a simulated gouge layer of ultrafine quartz at pressures from 10 MPa to 100 MPa. Unless we take b-a throughout the seismogenic layer to be much higher than experimental measurements, the effect of loading velocity by itself is not sufficient to account for the increase of stress drop with increasing earthquake recurrence time inferred from seismological data. To the extent that our simple system can be treated as an analog for earthquakes, our study shows that the velocity weakening parameter (B-A) controls the magnitude of the static stress drop far more than the loading velocity. If velocity weakening increases systematically with increasing healing time, then the coupled effect of loading velocity variation and change in friction environment can account for the seismological observations.

A Dual-Adaptivity Inertia Control Strategy for Virtual Synchronous Generator

Abstract: The virtual synchronous generator (VSG) improves the robustness of the inverter-interfaced distributed generator (IIDG) against instability by introducing a virtual inertia. However, the transient response of the active power and the angular frequency conflict with each other for the IIDG with fixed inertia control. It is necessary to adopt adaptive control to improve overall performances of power and frequency as the operating condition changes. This paper analyzes the impact of the inertia on power and angular frequency. A dual-adaptivity inertia control strategy is proposed to offer a responsive and stable frequency support and also achieve the balance between power regulation and frequency regulation according to different operating conditions. The principle of parameter design is given to obtain the range of adaptivity. Quantitative assessment considering the cumulative effect of the output deviation and its duration is also presented to evaluate the proposed strategy intuitively. The strategy is further verified based on PSCAD/EMTDC and a hardware-in-loop experiment platform based on RTDS. Results confirm that the proposed strategy not only achieves rapid frequency response with slight dynamic deviations under disturbances but also strikes a balance between the frequency and power and leads to improved overall control.

Generalized diffusion wave equation with inertial effects

Abstract: A generalized diffusion wave equation, which includes inertial effects, is derived on the basis of the linear analogs of the complete equations of continuity and motion of free-surface flow. Specializations of this equation lead to four types of diffusion wave models, depending on whether the inertia terms (local and convective) are excluded from or included in the formulation: (1) full inertial, (2) local inertial, (3) convective inertial, and (4) noninertial. Analysis of these diffusion wave models reveals substantial differences in their behavior, particularly with regard to the Froude number dependence of their hydraulic diffusivities. The full inertial and local inertial models have neutral Froude numbers, while the convective and noninertial models do not. In addition, the neutral Froude number of the full inertial model (wide channel with Chezy friction) simulates that of the complete equations (Fr = 2). For low Froude number flows the noninertial model is shown to be a good approximation to the full inertial model. The noninertial model is a better approximation to the full inertial model than either local or convective models.