Power-sharing Research Articles

In Defense of (Limited) Oligarchy

Abstract In democracies around the world, the rich exercise a disproportionate share of political power. Democratic theorists universally condemn this. The current paper brings balance to this conversation by mustering a defense of limited oligarchy. I have two goals. First, I shall argue that we need not be overly despondent about the wealthy's outsized influence, for overrepresentation of the wealthy performs some good for us—good which might not be entirely obvious at first glance. Second, I hope to temper reform efforts that seek to limit the wealthy's influence. While the people should have a greater say than they currently do, the wealthy's influence should still be greater than what their numbers suggest. I ultimately embrace oligarchic bicameralism, an old idea that proposes ordinary persons be represented in the lower chamber of the legislature, and property be represented in the upper. This is accomplished through a combination of sortition and elections.

Distributed Self-Triggered Control for Frequency Restoration and Active Power Sharing in Islanded Microgrids

Distributed event-triggered secondary control in microgrids have been widely investigated to improve system efficiency. But most of them are based on consecutive triggering condition monitor, which would in turn increase the computation burden of the system. To this end, this paper presents distributed self-triggered algorithmic solutions to the frequency restoration control and active power sharing control of islanded microgrids. Different from event-triggered control schemes, in our self-triggered solutions, each distributed generator is equipped with a local algorithm that enables it to pre-compute the next triggering time instant according to the states at previous one. Our starting point is to design an triggering condition with a novel estimate error. Then, the next triggering time instant is determined by solving a quadratic equation established based on the triggering condition, rather than monitoring the triggering condition consecutively. Theoretical analysis and simulation results show that the proposed distributed self-triggered secondary controllers can highly reduce the communication and computation cost simultaneously.

An Analysis of The Effect of Heterogeneously Distributed Inertia Constant in Generation Mix Power System by Using the Graph Theory and Dijkstra’s Algorithm

A modern power system with a generation mix of conventional and renewable energy sources (RES) creates stability issues. This requires a detailed analysis of the system with an exact share of active power through the generating sources according to nature, location, and control. The interconnected network with a large number of rotating machines at the generation side works coherently with each other. As the share of RES increases, it leads to reduce rotational inertia in the power system. The most important factor affected by inertia is the rate of change of frequency (RoCoF). The higher RoCoF leads the system more vulnerable to small disturbances in the power system. In a large power system network with numerous generating sources and transmission lines, it is difficult to determine the availability of inertia in the system. This paper incorporates the concept of graph theory in the IEEE 30 bus system to analyze the impact of heterogenous inertia distribution on frequency stability. The graph theory network gives the idea about the distance between the nodes and it is helpful to find the share of power from the generating sources. In this paper, we calculate the shortest path between the nodes or substations by using Dijkstra's algorithm. The betweenness centrality of the node detects the vulnerable nodes in the system from the frequency response point of view.

Low pressure influence on a direct fuel cell battery hybrid system for aviation

Fuel-cell-based, hydrogen-driven aircraft can significantly reduce the climate impact of aviation but the low ambient pressures at high altitude negatively affect the performance of fuel cells. The influence of low pressures on the behavior of a direct hybrid-system that connects a fuel cell and a battery without a DC/DC converter, is examined and compared to a fuel-cell-only system. Low ambient pressure leads to a reduced fuel cell voltage and power output. The voltage change between maximum voltage and the voltage level at the operational power increases with a decreasing air pressure for both the hybrid-system and the fuel-cell-only system. However, in a direct hybrid, the battery stabilizes the system voltage level and the voltage decrease is significantly smaller for the hybrid-system than for the fuel-cell-only system. At an ambient pressure of 300 mbar, the voltage variation of a 4 kW system is 96% lower for a hybrid-system compared to a fuel-cell-only system. The lower pressure also reduces the power output of the fuel cell. In the direct hybrid the battery contributes a demand related share of power and the contribution from the fuel cell decreases with air pressure as the contribution of the battery rises.

Civil War Settlements, Perceived Agreement Fairness, and Trust in Political Authorities: Investigating the Influence of Power Sharing on Public Opinion in Divided Societies

Little is known about civil war settlements' effects on public opinion in countries emerging from conflict, cases in which beliefs in agreement fairness and trust in political authorities may influence acceptance of the peace process. We posit that settlements designed to redistribute power and resources will be perceived as fairer and produce larger improvements in trust in the national government for individuals from marginalized groups than for those from dominant groups. Employing original survey data collected in the Philippines, we test these propositions with reference to the country’s 2014 peace agreement. We find that marginalized Muslim groups perceive a fairer peace agreement and report improved trust in comparison to the dominant Christian community. Using a survey experiment to analyze the influence of power-redistributing settlement measures, we find that trust in the government is not significantly affected by information regarding power sharing, a result that holds for members of both communities.

An Adaptive Inertia and Damping Control Strategy Based on Enhanced Virtual Synchronous Generator Model

In modern converter-dominated power systems, total inertia is very variable and depends on the share of power generated by renewable-based converter-interfaced generation (CIG) at each specific moment. As a result, the limits required by the grid codes on the rate of change of frequency and its nadir or zenith during disturbances become challenging to achieve with conventional control approaches. Therefore, the transition to a novel control strategy of CIG with a grid-forming power converter is relevant. For this purpose, a control algorithm based on a virtual synchronous generator (VSG) is used, which simulates the properties and capabilities of a conventional synchronous generation. However, due to continuously changing operating conditions in converter-dominated power systems, the virtual inertia formed by VSG must be adaptive. At the same time, the efficiency of adaptive algorithms strongly depends on the used VSG structure. In this connection, this paper proposes an enhanced VSG structure for which the transfer function of the active power control loop was formed. With the help of it, the advantages over the conventional VSG structure were proven, which are necessary for the effective adaptive control of the VSG parameters. Then, the analysis of the impact of the VSG parameters on the dynamic response using the transient characteristics in the time domain was performed. Based on the results obtained, adaptive algorithms for independent control of the virtual inertia and the parameters of the VSG damper winding were developed. The performed mathematical modeling confirmed the reliable and effective operation of the developed adaptive control algorithms and the enhanced VSG structure. The theoretical and experimental results obtained in this paper indicate the need for simultaneous development and improvement of both adaptive control algorithms and VSG structures used for this purpose.

Evaluating Power Sharing Performance of Distributed Generators in Microgrids With Hybrid Sources and Mixed Tie-Lines

Proportional output power sharing amongst distributed sources in islanded microgrids is necessary to maintain a good voltage profile, avoid tripping of sources and avoid circulating current flows. Underground (UG) cables are popular in densely populated areas and military applications. However, researchers typically consider microgrid networks with overhead lines (OHL) in their studies. This paper examines the power sharing performance among droop controlled inverters and virtual synchronous generators in a system with mixed tie-line configurations i.e., network sections with both OHL and UG cable tie-lines. Furthermore, two proposed control strategies to vary the virtual impedance linearly as a function of the DG output currents are examined for their effectiveness to improve the proportional power sharing. The studies are performed considering a system with four inverter based sources operated with the popularly used <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$RL$</tex-math></inline-formula> droop controllers through detailed simulations in MATLAB/Simulink. The enhancement of power sharing is verified for both uniform and non-uniform inverter controls, different R/X ratios of the OHL and UG cables, and in a meshed network configuration with different loading conditions. Controller hardware in the loop (CHIL) based experiment validation is carried out in Typhoon HIL with linear, non-linear and induction motor load, showing that proposed control strategy results in enhanced power sharing in addition to damping oscillations due to dynamic loads.

Conflict Resolution through Communication: Habermasian Study of Pinter’s The Homecoming

In his Communicative Action Theory, Habermas argues that it is possible to achieve an innovative rationality which has the ability to resolve social conflicts and reach consensus and mutual understanding through communicative action. This ‘communicative rationality’ rests on intersubjective recognition of Habrmasian three ‘validity claims’: Truth, Rightness, and Truthfulness. Based on this classification and drawing on critical-qualitative research into Pinter’s The Homecoming, this paper examines the speech acts of the characters in this play to see if they are able to redeem their criticisable validity claims discursively in their familial context. The conclusion which is drawn here is that ‘emancipation’ can be achieved through ‘communicative rationality’ only if all the members of family and, on a larger scale, all members of society have an equal share of power; and, ‘communicative action’ can be possible even through silence, monologues, and deformed dialogues which are Pinter’s unique style in composing theatrical dialogues. Keywords: Habermas, Pinter, The Homecoming, Communicative rationality, Communicative action.

Socio-Economic conditions of Pourakarmikas – A Sociological Study in Mysore City Corporation

Untouchability is one of the worst features of the Hindu Society. In the process of evolution of caste on the principles of graded chathurvarna (four Varnas) such as Brahmana, Kshatriya, Vaisya and Shudra the vast body of people known as Panchama, exterior, Antyajas or scheduled castes fell outside the purview of chaturvarna. They were denied the rights enjoyed by Brahmin's, Kshatriya's. Vaishya's and Upanayana even they were prohibited to perorm upanayana to wear sacred thread, learning Vedas, doing trade and other clean occupations. They were forced to live on the outskirts of village, thus restricting their movement. In this way, they were segregated and become the Anthyajas or Untouchables. The untouchables (Panchamas or Avarnas) had no share in social, political and judiciary power.

Robust Volt-VAr Control Strategy for Improvement in Reactive Power Sharing in a Droop Based Islanded Microgrid

Robust Volt-VAr Control Strategy for Improvement in Reactive Power Sharing in a Droop Based Islanded Microgrid

Impartial Sequential Model Predictive Control of Parallel T-Type Rectifiers for Power Sharing and Circulating Current Elimination

A parallel T-type rectifier connection is often required to improve the system capacity and stability in high-power applications. However, the parallel rectifier faces the challenges of zero-sequence circulating current (ZSCC) elimination, neutral point (NP) voltage balance, DC voltage stability and power sharing. First, to solve the multi-objective optimization problem of two parallel three-level T-type rectifiers with LCL filters (LCL-3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Rs), a double closed-loop control scheme is adopted. In this scheme, an impartial sequential model predictive control (ISMPC) is proposed as the inner-loop controller for ZSCC elimination and NP voltage balance, and an adaptive droop control with voltage feedforward is designed as the outer-loop controller to achieve DC voltage stability and power sharing for each rectifier based on its capacity. Second, the main influencing factors of ZSCC in LCL-3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Rs are analyzed, and ZSCC elimination is considered as one control objective in ISMPC. Finally, ISMPC is proposed to solve the problem that sequential model predictive control (SMPC) could not select the optimal solution due to the fixed priority and the excessive process only controlled a single objective. The proposed method is tested on a prototype hardware platform of a 10-kW and a 5-kW parallel rectifier. Experiment results demonstrate the superiority of this method over existing methods under several typical scenarios.

Unit Combination Scheduling Method Considering System Frequency Dynamic Constraints under High Wind Power Share

Power systems with a high wind power share are characterized by low rotational inertia and weak frequency regulation, which can easily lead to frequency safety problems. Providing virtual inertia for large-scale wind turbines to participate in frequency regulation is a solution, but virtual inertia is related to wind power output prediction. Due to wind power prediction errors, the system inertia is reduced and there is even a risk of instability. In this regard, this article proposes a unit commitment model that takes into account the constraints of sharp changes in frequency caused by wind power prediction errors. First, the expressions of the equivalent inertia, adjustment coefficient, and other frequency influence parameters of the frequency aggregation model for a high proportion wind power system are derived, revealing the mechanism of the influence of wind power prediction power and synchronous machine start stop status on the frequency modulation characteristics of the system. Second, the time domain expression of the system frequency after the disturbance is calculated by the segment linearization method, and the linear expressions of “frequency drop speed and frequency nadir” constraints are derived to meet the demand of frequency regulation in each stage of the system. Finally, a two-stage robust optimization model based on a wind power fuzzy set is constructed by combining the effects of wind power errors on power fluctuation and frequency regulation capability. The proposed model is solved through affine decision rules to reduce its complexity. The simulation results show that the proposed model and method can effectively improve the frequency response characteristics and increase the operational reliability of high-share wind power systems.

Grid-Forming Inverter Control for Power Sharing in Microgrids Based on P/f and Q/V Droop Characteristics

Grid-forming inverters are anticipated to be integrated more into future smart microgrids commencing the function of traditional power generators. The grid-forming inverter can generate a reference frequency and voltage itself without assistance from the main grid. This paper comprehensively investigates grid-forming inverter modelling and control methodology. A decentralized method employing an active power versus frequency P − f droop and a reactive power versus voltage Q − V droop is exploited to drive the operation of the grid-forming inverter. This decentralized method ensures balancing the supply and demand beside the power-sharing task between two or more inverters. The performance of the grid-forming inverter is examined by monitoring the frequency and RMS voltage of the inverter bus for three different periods of a varying PQ load. In addition, the performance of the resultant droop is compared with the assumed droop to validate the effectiveness of the proposed method. Finally, two grid-forming inverters equipped with the same droop characteristics are connected to a single load to observe the power-sharing concept among them. All simulations are implemented and executed using Matlab/Simulink version R2014b.

Improved Power Sharing and Energy Management Platform in Microgrid Considering Stochastic Dynamic Behavior of the Electric Vehicles

In this study, an improved model of optimal power sharing and energy management as well as total harmonic distortion (THD) control in AC microgrids in order to control the voltage and frequency parameters by considering the random behavior of electric vehicles (EVs) is presented. The proposed model is developed based on the primary and secondary controller. The primary controller is planned with the purpose of optimal power-sharing, reduction of feeder's impedance mismatch and also THD reduction. The primary controller is modeled with the hybrid Event-Triggered approach and virtual impedance method. The secondary controller has been modeled using the particle swarm optimization (PSO) algorithm with the aim of reducing the power distribution error and optimizing the virtual impedance parameters, as well as considering the participation of EVs in the stochastic power flow equations. In addition to comparing the performance of the proposed model with conventional methods, it has also been compared with other meta-heuristic methods. The results of this have been verified in two software environments (MATLAB/Simulink) and experimental setup (dSPACE model 1202) in different scenarios and also the stability of the proposed model based on the Nyquist stability criterion, the Root Locus method and small signal analysis has been presented.

Parallel Power Sharing Control of Multi-Controllable Rectifiers in a High-Power DC Fast Charging Station

The increase in demand for the fast charging of electric vehicles (EVs) has promoted research and the application of high-power direct current (DC) fast charging stations, and research on the stability control of charging stations with a parallel structure of multi-controllable rectifier modules is of great significance. Taking into account the dynamic and steady-state performance, the parameters of the dual-loop controller based on virtual impedance control are designed to realize the power sharing of multi-controllable rectifier modules. The constant power load model of EV charging at a constant current is established, and the load capacity of the cascaded system of converters is studied by using the impedance analysis method. The experimental and simulation results verify the effectiveness and correctness of the power sharing control strategy and the cascaded system stability analysis.

Artificial Intelligence and Mathematical Models of Power Grids Driven by Renewable Energy Sources: A Survey

To face the impact of climate change in all dimensions of our society in the near future, the European Union (EU) has established an ambitious target. Until 2050, the share of renewable power shall increase up to 75% of all power injected into nowadays’ power grids. While being clean and having become significantly cheaper, renewable energy sources (RES) still present an important disadvantage compared to conventional sources. They show strong fluctuations, which introduce significant uncertainties when predicting the global power outcome and confound the causes and mechanisms underlying the phenomena in the grid, such as blackouts, extreme events, and amplitude death. To properly understand the nature of these fluctuations and model them is one of the key challenges in future energy research worldwide. This review collects some of the most important and recent approaches to model and assess the behavior of power grids driven by renewable energy sources. The goal of this survey is to draw a map to facilitate the different stakeholders and power grid researchers to navigate through some of the most recent advances in this field. We present some of the main research questions underlying power grid functioning and monitoring, as well as the main modeling approaches. These models can be classified as AI- or mathematically inspired models and include dynamical systems, Bayesian inference, stochastic differential equations, machine learning methods, deep learning, reinforcement learning, and reservoir computing. The content is aimed at the broad audience potentially interested in this topic, including academic researchers, engineers, public policy, and decision-makers. Additionally, we also provide an overview of the main repositories and open sources of power grid data and related data sets, including wind speed measurements and other geophysical data.

Accurate Active and Reactive Power Sharing Based on a Modified Droop Control Method for Islanded Microgrids.

When multiple paralleled distributed generation (DG) units operate in an islanded microgrid, accurate power sharing of each DG unit cannot be achieved with a conventional droop control strategy due to mismatched feeder impedance. In this paper, a small AC signal (SACS)-injection-based modified droop control method is presented for accurate active and reactive power sharing among DG units. The proposed control method adjusts the voltage amplitude of each DG unit by injecting small AC signals to form a reactive power control loop. This strategy does not need communication links or to specifically obtain the physical parameter of the feeder impedance and only requires the local information. Moreover, the parameter design procedure and stability analysis are given full consideration. Finally, simulation and experimental results verify the effectiveness of the proposed control scheme, and accurate active and reactive power sharing can be achieved.

A Distributed Scheme for Voltage and Frequency Control and Power Sharing in Inverter-Based Microgrids

Grid-forming inverter-based autonomous microgrids present new operational challenges as the stabilizing rotational inertia of synchronous machines is absent. The design of efficient control policies for grid-forming inverters is, however, a nontrivial problem where multiple performance objectives need to be satisfied, including voltage/frequency regulation, current limiting capabilities, and active power sharing and a scalable operation. We propose, in this article, a novel control architecture for frequency and voltage control, which allows current limitation via an inner loop, active power sharing via a distributed secondary control policy, and scalability by satisfying a passivity property. In particular, the frequency controller employs the inverter output current and angle to provide an angle droop-like policy, which improves its stability properties. This also allows us to incorporate a secondary control policy for which we provide an analytical stability result, which takes line conductances into account (in contrast to the lossless line assumptions in the literature). The distinctive feature of the voltage control scheme is that it has a double-loop structure that uses the dc voltage in the feedback control policy to implement a power-balancing strategy to improve performance. The performance of the control policy is illustrated via simulations with detailed nonlinear models in a realistic setting.

Explaining the decline of US wind output power density

US wind power generation has grown significantly over the last decades, in line with the number and average size of operating turbines. However, wind power density has declined, both measured in terms of wind power output per rotor swept area as well as per spacing area. To study this effect, we present a decomposition of US wind power generation data for the period 2001–2021 and examine how changes in input power density and system efficiency affected output power density. Here, input power density refers to the amount of wind available to turbines, system efficiency refers to the share of power in the wind flowing through rotor swept areas which is converted to electricity and output power density refers to the amount of wind power generated per rotor swept area. We show that, while power input available to turbines has increased in the period 2001–2021, system efficiency has decreased. In total, this has caused a decline in output power density in the last 10 years, explaining higher land-use requirements. The decrease in system efficiency is linked to the decrease in specific power, i.e. the ratio between the nameplate capacity of a turbine and its rotor swept area. Furthermore, we show that the wind available to turbines has increased substantially due to increases in the average hub height of turbines since 2001. However, site quality has slightly decreased in this period.

Power Sharing Control for a Microgrid with PV Power Plants, Batteries and Quasi-Z-source Cascaded H-bridge Multilevel Inverter

In recent years, Quasi-Z-source cascaded H-bridge multilevel inverters (qZS-CHBMLIs) have become an interesting solution for integrating renewable energy into the utility grid. The possibility of performing power conversion in a single stage, without an additional DC/DC converter, and a higher voltage gain, are their main advantages over traditional inverters. In addition, individual control of the maximum power point tracking (MPPT) can be achieved for each PV plant. Owing to the intermittent nature of PV power plants, battery energy storage systems (BESS) are commonly used to smooth out PV power fluctuations. This paper presents a control system for the active and reactive power delivered to the grid according to the system operator references and an EMS for an ES-qZS-CHBMLI. The BESS is coordinated through an energy management system (EMS) based on the state of charge (SOC) The system is evaluated under two different operation modes. One of them, where the PV power plants operate according to their MPP and the other in which the MPPT faults and thus, the PV power is decreased. A MATLAB-Simulink simulation is used to validate the proposed control system for a grid-connected single-phase configuration based on a qZSCHBMLI with three cascade qZSI, each connected to a 4.8 kW PV power plant and a BESS.