(1990). ENERGY FUNCTION ANALYSIS FOR POWER SYSTEM STABILITY. Electric Machines & Power Systems: Vol. 18, No. 2, pp. 209-210.

Energy function analysis for power system stability

IEEE transactions on computer-aided design of integrated circuits and systems : a publication of the IEEE Circuits and Systems Society

The electric power system is currently undergoing a period of unprecedented changes. Environmental and sustainability concerns lead to replacement of a significant share of conventional fossil fuel-based power plants with renewable energy resources. This transition involves the major challenge of substituting synchronous machines and their well-known dynamics and controllers with power electronics-interfaced generation whose regulation and interaction with the rest of the system is yet to be fully understood. In this article, we review the challenges of such low-inertia power systems, and survey the solutions that have been put forward thus far. We strive to concisely summarize the laid-out scientific foundations as well as the practical experiences of industrial and academic demonstration projects. We touch upon the topics of power system stability, modeling, and control, and we particularly focus on the role of frequency, inertia, as well as control of power converters and from the demand-side.

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Foundations and Challenges of Low-Inertia Systems (Invited Paper)

The inertia of today׳s power system decreases as more and more converter connected generation units and load are integrated in the power system. This results in a power system which behaves differently from before which causes concerns for many grid operators. Therefore, a detailed study is needed to investigate the relevance of this inertia in the operation, control and stability of the system. Moreover, a new definition of the term system inertia is necessary since is it expected that in the future also the renewable electricity generation units will deliver the so-called virtual (synthetic) inertia. In this paper a review of the research related to inertia in a power system is given. Both the challenges as the solutions from an operator point of view to control a system with low inertia are discussed. Also a new definition of inertia is proposed to incorporate the different forms of inertia which are each described in more detail. From recent studies, it can be concluded that the influence of reduced inertia on frequency stability is generally considered as the main challenge for system operators, but with the additional measures listed in this paper, this impact can be mitigated.

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The relevance of inertia in power systems

The modern power system is progressing from a synchronous machine-based system towards an inverter-dominated system, with large-scale penetration of renewable energy sources (RESs) like wind and photovoltaics. RES units today represent a major share of the generation, and the traditional approach of integrating them as grid following units can lead to frequency instability. Many researchers have pointed towards using inverters with virtual inertia control algorithms so that they appear as synchronous generators to the grid, maintaining and enhancing system stability. This paper presents a literature review of the current state-of-the-art of virtual inertia implementation techniques, and explores potential research directions and challenges. The major virtual inertia topologies are compared and classified. Through literature review and simulations of some selected topologies it has been shown that similar inertial response can be achieved by relating the parameters of these topologies through time constants and inertia constants, although the exact frequency dynamics may vary slightly. The suitability of a topology depends on system control architecture and desired level of detail in replication of the dynamics of synchronous generators. A discussion on the challenges and research directions points out several research needs, especially for systems level integration of virtual inertia systems.

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Virtual Inertia: Current Trends and Future Directions

A novel procedure for estimating the total inertia of the Great Britain (GB) power system is presented. Following an instantaneous in-feed loss, regional variations in the estimate of inertia are obtained from measured frequency transients using installed synchronised phasor measurement units (PMUs). A method is proposed to first detect a suitable event for analysis, and then filter the measured transients in order to obtain a reliable estimate of inertia for a given region of the GB network. The total inertia for the whole system is then calculated as a summation, with an estimate also provided as to the contribution to inertia from residual sources, namely synchronously connected demand and embedded generation. The approach is first demonstrated on the full dynamic model of the GB transmission system, before results are presented from analyzing the impact of a number of instantaneous transmission in-feed loss events using phase-angle data provided by PMUs from the GB transmission network and also devices installed at the domestic supply at 4 GB universities.

Inertia Estimation of the GB Power System Using Synchrophasor Measurements

Increasing levels of wind power integration pose a challenge in system operation, owing to the uncertainty and non-dispatchability of wind generation. The probabilistic nature of wind speed inputs dictates that in an optimization of the system, all output variables will themselves be probabilistic. In order to determine the distributions resulting from system optimization, a probabilistic optimal power flow (POPF) method may be applied. While Monte Carlo (MC) techniques are a traditional approach, recent research into point estimate methods (PEMs) has displayed their capabilities to obtain output distributions while reducing computational burden. Unfortunately both spatial and temporal correlation amongst the input wind speed random variables complicates the application of PEM for solving the POPF. Further complications may arise due to the large number of random input variables present when performing a multi-period POPF. In this paper, a solution is proposed which addresses the correlation amongst input random variables, as well as an input variable truncation approach for addressing the large number of random input variables, such that a PEM can be effectively used to obtain POPF output distributions.

Point Estimate Method Addressing Correlated Wind Power for Probabilistic Optimal Power Flow

A novel procedure for estimating the total inertia of the Great Britain (GB) power system is presented Following an instantaneous in-feed loss, regional variations in the estimate of inertia are obtained from measured frequency transients using installed synchronised phasor measurement units (PMUs) A method is proposed to first detect a suitable event for analysis, and then filter the measured transients in order to obtain a reliable estimate of inertia for a given region of the GB network The total inertia for the whole system is then calculated as a summation, with an estimate also provided as to the contribution to inertia from residual sources, namely synchronously connected demand and embedded generation The approach is first demonstrated on the full dynamic model of the GB transmission system, before results are presented from analyzing the impact of a number of instantaneous transmission in-feed loss events using phase-angle data provided by PMUs from the GB transmission network and also devices installed at the domestic supply at 4 GB universities

Inertia estimation of the GB power system using synchrophasor measurements

The traditional electrical grid is transitioning into the smart grid. New equipment is being installed to simplify the process of monitoring and managing the grid, making the system more transparent to use but also introducing new security problems. Smart meters are replacing the traditional electrical utility meters, offering new functionalities such as remote reading, automatic error reporting, and the possibility for remote shutoff. This last feature is studied in this paper through two scenarios where the effects are outlined, both on a theoretical level and through a simulation. In the first scenario, the frequency property of the grid is the target to possibly cause a blackout. In the second scenario, the voltage is driven out of bounds by the adversary.

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Christopher S. Saunders

Papers

Inertia Estimation of the GB Power System Using Synchrophasor Measurements

Point Estimate Method Addressing Correlated Wind Power for Probabilistic Optimal Power Flow

Inertia estimation of the GB power system using synchrophasor measurements

Remote Control of Smart Meters: Friend or Foe?

Remote Control of Smart Meters: Friend or Foe?