Power Sharing Strategy Research Articles

A Real-Time Power Sharing Strategy for a Multi-Energy System While Considering Individual System Dynamics

For a sustainable and resilient energy supply, multi-energy systems (MES) are becoming more prominent. Real-time efficient power-sharing in an MES consisting of different generation sources, uncontrollable loads, multiple storage options, and Power-to-X technologies is a challenging task. The challenge arises due to constantly fluctuating generation and load, as well as the different system dynamics of each element in the setup. Optimizing the power-sharing among the various controllable elements in an MES could be broken down into a two-level process. The top-level process, commonly known as super-ordinate control, defines the power-sharing over a longer timeframe based on load and generation forecasts and multiple other factors. The lower-level process, commonly known as sub-ordinate control, based on the inputs from the super-ordinate control and live sensor data refines the control signals of the individual elements. This work focuses on developing a control framework for the sub-ordinate control process while considering the individual element dynamics such as dead time and rise time to a control signal. This is important as not considering differences in the system dynamics results in sub-optimal control, causing dynamic mismatches. This work proposes a simple rule-based power-splitting method backed up with individual PID regulators and Smith Predictor for each element in the MES, which are further coupled to each other for more precise and efficient control. The proposed method induces a cooperative behavior among the MES elements and improves the reaction time to a control signal while also improving the target tracking by 3-8%.

Optimal transient power sharing method for shipboard MVDC System based on segmented variable step dynamic programming

Supplying power for large pulsed power load with shipboard medium voltage direct current integrated power system has continued to be a challenge. The energy storage device configured in the system can effectively mitigate the power impact on grid and gas turbine gensets, but it also complicates the system operation, requiring advanced power sharing and control strategies for support. In this paper, the control framework of system configured with hybrid energy storage is presented, the objective function to quantify transient power disturbance on gas turbine genset is established, and the segmented variable step dynamic programming method for system transient power sharing is innovatively proposed and employed to derive the optimal transient power-sharing scheme for the rectangular and triangular large pulsed power load conditions. Compared with the conventional approach through MATLAB/Simulink simulation, the scheme derived from segmented variable step dynamic programming demonstrates enhanced utilization of the transient power compensation capability of hybrid energy storage, and leads to a reduction in the power regulation pressure on gas turbine gensets. In the assumption of two typical operating processes, as the results of the power impacts，the transient regulation rate of the genset rotor is reduced from 10.4 % to 9.9 % and from 13.7 % to 8.6 %, respectively, the fatigue damage of shaft system is decreased by 53 % and 94.4 %, respectively, and the maximum inlet relative temperature of gas generator turbine is reduced by 0.015 and 0.139, respectively.

Enhancing Power Sharing Strategy for Consistent Decarbonized Energy Sources in DC Residential Microgrids

A key issue in the transition to decarbonized energy sources with constant power sources is inaccurate current sharing and voltage quality. The main reason which causes these issues is the inevitable system impedance mismatches. This study addresses this issue by proposing an enhanced power‐sharing strategy that regulates adjustable resistance and compensates for voltage drops across the line impedance at the output of distributed generation converters. The control approach involves analyzing the mathematical relationship between system impedance mismatches and voltage drops in DC residential systems. Utilizing low‐computation proportional‐integral controllers, the secondary current sharing and load voltage controllers regulate converter outputs to compensate for mismatched resistance and voltage, ensuring proper current sharing and load voltage quality across various load conditions. Through the implementation of the proposed scheme incorporating adjustable resistance and voltage shifting terms, both the current‐sharing error and load voltage deviation are gradually reduced to negligible values, while maintaining stable performance in steady‐state conditions, without the need for prior knowledge of system parameters. Simulations and experimental studies are both conducted to demonstrate the effectiveness of the proposed control scheme. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Authoritarian multiparty governments

ABSTRACT In 2020, almost 50% of dictatorships included multiple parties in their government. Existing research has not studied this systematically, and generally considers granting outsiders access to ministerial cabinets a risky and costly strategy. This article provides evidence of authoritarian multiparty governments (AMGs) being a global and increasingly common phenomena. We argue that AMGs are a power-sharing strategy whereby autocrats co-opt outsiders through cabinet appointments to divide the opposition and consolidate their rule. Using individual-level data on ministers' partisan affiliation in autocracies worldwide, we show that AMGs positively correlate with ethnic divides, civil war, and “democratic” institutions, and we use new measures of power sharing to demonstrate that coalition partners often exert a real influence through their ministerial mandates. Our findings suggest that AMG is an overlooked survival strategy for autocrats and highlight the need to focus more on the organization and composition of the political executive in autocracies.

Improved Power Sharing Strategy for Parallel Connected Inverters in Standalone Micro-grid

The primary goal of integrating alternative energy systems such as solar and wind turbines into the power grid using power electronic devices is to meet the growing energy demands. Connecting inverters in parallel effectively enhance power capacity, reliability, and overall system efficiency. However, an uneven power distribution among the inverters is a significant limitation in these parallel connected inverters (PCI). This study focuses on a distributed generation (DG) unit comprising a solar photovoltaic system (SPV) and a battery energy storage system (BESS) connected to voltage source inverters (VSI) 1 and 2. The proposed approach aims to achieve uniform load/power distribution among the inverters with power management, maintaining a constant DC link voltage despite variations in solar irradiation and temperature. Additionally, the strategy targets the reduction of total harmonic distortion (THD) in the load current. The conventional droop control method is restricted in its ability to achieve accurate and uniform power distribution during load changes. An enhanced P-f and Q-E-based droop control technique (EDCT) and a fuzzy logic controller (FLC) have been proposed to address these challenges. Performance analysis using MATLAB/Simulink was conducted with two test cases, and a comparative assessment was carried out with a conventional controller, such as a Proportional Integral Controller (PIC) and Sliding Mode Controller (SMC), to showcase the effectiveness of the developed control technique. The proposed control method ensures equal sharing of active power of 2.5 and 4kW, 2.5 and 7.5kW and reactive powers of 2.5 and 4Vars, 2.5 and 7.5Vars among the inverters for the two cases even during the load change at t=0.5seconds. The settling time for DC link voltage and THD is effectively diminished to 0.03 and 0.25 seconds and 1.18% and 2.87% for the two test case studies of the proposed method, which are much lower than those of existing methods available in the literature.

Active Power Sharing Scheme in a PV Integrated DC Microgrid With Composite Energy Storage Devices

Active Power Sharing Scheme in a PV Integrated DC Microgrid With Composite Energy Storage Devices

Reactive power control of micro-grids using FOSMC for grid code compliance during asymmetrical voltage sags

Application of micro-grids (MGs) as a solution for future energy systems are significantly increasing in recent years. On the other hand, more stringent requirements are added to grid codes (GCs) of low-voltage distribution networks. Accordingly, this paper proposes a low-voltage ride-through (LVRT) control scheme for four-wire multi-source MGs. The novel strategy is composed of two layers for controlling each phase of the grid-connected sources independently. The primary layer contains a reverse-droop function for each phase and fractional-order sliding-mode-control (FOSMC). The secondary layer determines the total requested reactive power for each phase during symmetrical and asymmetrical voltage drops. Then, the mentioned power is shared among the phases of each inverter based on the reactive power-sharing strategy and GC requirements. Based on the proposed grid-following controller, the voltage of faulty phases is compensated by reactive power injection. In addition, power quality indexes are kept in acceptable ranges during abnormalities, and the FOSMC performs better than the conventional methods. The effectiveness of the proposed scheme is verified through offline simulations in MATLAB/Simulink as well as validation by real-time results.

A Decentralized Nonlinear Harmonic Power Sharing Scheme Considering Harmonic Residual Capacity and Working Conditions of Fundamental Load

A Decentralized Nonlinear Harmonic Power Sharing Scheme Considering Harmonic Residual Capacity and Working Conditions of Fundamental Load

Adaptive power-sharing strategy in hybrid AC/DC microgrid for enhancing voltage and frequency regulation

This paper introduces a new adaptive control strategy for power-sharing in a hybrid AC/DC microgrid (HMG). The existing interlink converter (ILC) control methods exhibit limitations under heavy load and contingency conditions. To overcome this limitation, a bidirectional control strategy is proposed for the ILC, which effectively coordinates battery energy storage systems (BESSs) in both sub-grids while mitigating stress on the ILC and BESSs. The control strategy utilises the state of charge (SoC) and instantaneous power of the BESSs to stabilise frequency and DC voltage on the AC and DC sub-grids, respectively, enabling autonomous operation and plug-and-play capability. Stability analysis employing root locus and a stress level relaxation index for BESSs are presented. Performance evaluation based on the moving mean square error criterion validates the effectiveness of the control strategy. Simulation results using MATLAB/SIMULINK demonstrate the superior performance of the proposed strategy in regulating both voltage and frequency within the system over the existing control approaches. Furthermore, the proposed approach significantly reduces stress levels on the BESSs in different operation conditions.

SoC-Adaptive Power Sharing Strategy Applied to DC Microgrids Supplied by Multiple Energy Storage Systems

A non-linear <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$SoC$</tex-math></inline-formula> -adaptive management and control scheme is applied to DC microgrids (MGs) supplied by energy storage systems (ESSs) and connected to the grid. The management and control strategy are performed via decentralized methodologies, allowing power sharing between the battery banks with or without a low-speed communication link, while their limits of operation for charging and discharging are not exceeded. Additionally, the aforementioned technique is based on the sigmoidal function where the solution shows two degrees of freedom as the DC-link voltage error and the state-of-charge <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$(SoC)$</tex-math></inline-formula> in the outer loop (DC-link voltage control), and classical proportional-integral <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$(PI)$</tex-math></inline-formula> controllers regulating the current flow through the DC/DC power converters in the inner loop. To analyze the system stability, the DC MG model was calculated to evaluate the poles movement, frequency and step responses at different scenarios. Finally, the authors rely on a set of results in the Typhoon <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\text{\text{®}}}$</tex-math></inline-formula> 602+ hardware to demonstrate the effectiveness of the proposed solution as well as, a comparison between it and the classical droop controller.

Design of an Improved Hybrid Lithium-Ion-Ultracapacitor Energy Storage System for Transport Vehicles

Lead-acid batteries (LABs) are mostly used in internal combustion engine (ICE) vehicles for starting lightning ignition (SLI). With the increased in load demand for transport vehicles (TVs), LABs are experiencing performance failure. LABs are not able to meet the load demand, which results in deep discharge, and shorten their lifespan. Therefore, this research study seeks to design a hybrid lithium-ion-ultracapacitor energy storage system (ESS) that will have a high storage capacity and longer lifespan at a reduced weight compared to a single LAB ESS. Power-sharing strategy is used as the technical solution to improve the battery performance. Two bidirectional DC–DC buck-boost converters and two level fuzzy logic control (FLC) will make up the full-active topology of the energy management system. The FLC 1 will provide the total reference power to start the ICE and to charge the energy storages based on the power demand, while ensuring that the state of charge is within the minimum and the maximum range of the battery, protects the battery from overcharging and deep discharging. To monitor the bidirectional buck and boost converters during the charging and discharging of the HESS, the FLC 2 is responsible for allocating complete control and managing the reference power of the energy storage (LIB and UP). The suggested method is expected to limit the power drawn from the battery and increase battery lifespan without changing the batteries current chemical composition. The simulation will be carried out utilizing the MATLAB/Simulink tool.

Efficient and Reliable Power-Conditioning Stage for Fuel Cell-Based High-Power Applications

Mainstream power-conditioning devices such as boost converters are frequently utilized for developing a compatible interface between a fuel cell, electrical storage, and high power loads. The conventional power stage comprising a unique boost converter suffers from low efficiency and poor reliability due to excessive power losses, particularly in high-power applications. Additionally, the presence of high ripple contents can reduce the lifespan of the fuel cell itself. With this background, this paper proposes and experimentally validates a physical components-assisted equivalent power-sharing strategy between parallel-coupled boost converters (PCCs) that is subjected to a wide spectrum of low-voltage–high-power conditions. The operation of PCCs is bottlenecked by several practical limitations, such as the presence of inner circulating currents (ICCs) and stability issues associated with the equivalent sharing of power. To overcome these limitations, a module of reverse blocking diodes is suggested to avoid ICCs between the PCCs. Further, an equalization filter is properly placed to improve the equivalent power-sharing capability. The proposed strategy is theoretically assessed in a MATLAB/Simulink environment with a 6 kW proton exchange membrane fuel cell (PEMFC) as the main power source. A scaled-down laboratory setup consisting of an 810 W PEMFC stack, an electronic load, three boost converters, and a filter circuit is then designed and critically evaluated. A consistent agreement is observed between the experimental findings and the simulation results under realistic operating conditions.

An Imbalance-Status-Enabled Autonomous Global Power-Sharing Scheme for Solid-State Transformer Interconnected Hybrid AC/DC Microgrids

This paper proposes a novel imbalance-status (IS)-enabled autonomous global power-sharing scheme for a solid-state transformer (SST) interconnected hybrid AC / DC microgrid system. Firstly, the proposed scheme globally estimates instantaneous active power imbalances according to the existing droop regulation characteristics of each sub-microgrid, and normalizes these imbalances by introducing the definition of IS. Next, three novel IS-enabled controllers are designed for the SST’s three core converters, to autonomously share the power imbalances in the entire system. Then, the control parameters of the proposed scheme are optimized through small-signal analysis. The control effectiveness and flexibility of the proposed scheme in realizing global power-sharing function are verified by controller hardware-in-loop experiments in RT-LAB platform.

Correction to “Distributed Optimal Power Sharing Strategy in an Islanded Hybrid AC/DC Microgrid to Improve Efficiency” [Feb 23 724-737

In [1], the incorrect version of Fig. 18 was published. The following are the correct figures. Fig. 18. Results of Case III; (a) fpu and $V_{pu}^{dc}$; active power of (b) ICs and (c) DGs.

Accurate Reactive Power Sharing Strategy for Droop-Based Islanded AC Microgrids

In islanded ac microgrids, the mismatched impedances of the interfacing feeders between the inverters and the load bus cause poor reactive power sharing when the conventional frequency and voltage droop control technique is employed. Such operation endangers the whole microgrid reliability as it may lead to overloading certain inverters and, consequently, triggering protection relays and causing cascaded failure. Thus, this article proposes an accurate reactive power sharing strategy that considers the mismatched feeder impedances in islanded ac microgrids. It is based on the optimal tuning of the virtual complex impedance for each inverter. The proposed strategy has several advantages. First, it has a physical meaning as it establishes an explicit relationship between the mismatched values of the actual resistive–inductive feeders and the assigned values for the proposed virtual complex impedance to each inverter. Hence, further degradations in the microgrid voltages are prevented. Second, there is no need for prior knowledge about the actual feeder impedances in the design stage as they are estimated online from the available measurements. Finally, the proposed control is reliable and fault-tolerant as it copes with unexpected failures such as failure of (or sudden switching <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> ) some inverters and communication disruptions/delays. It ensures accurate power sharing even under the primary controllers after losing communication links with the secondary controller. The simulation and experimental verification results are presented to validate the performance of the proposed technique.

Combined Provision of Economic Dispatch and Frequency Regulation by Aggregated EVs Considering Electricity Market Interaction

A combined delivery of economic dispatch and frequency regulation (FR) services from electric vehicles (EVs) is proposed to exploit the dynamic flexibility of EV charging load and its revenue opportunities in the electricity markets. The economic feasibility is assessed with the combined operation model of EVs for optimal bidding in the day-ahead energy market and FR market. The proposed optimization adopts the hierarchical control framework with EV aggregator (EVA) as the intermediate control unit to interact with the power system operator. As EVs are paid for FR based on their actual performance, a dynamic control strategy for charging EVs in response to regulation signals is developed to validate the technical feasibility of combined operation. The autonomous control of EVA modulates the charging of each EV to ensure the optimal charging schedules and real-time frequency control. A case study reveals that the profitability of EV charging control can be significantly increased by energy cost reduction and additional regulation revenue. The proposed dynamic control with a novel power-sharing strategy of EVA provides effective frequency support based on the optimal charging schedule and capacity bids without violating charging demand and availability constraints of each individual EV.

Distributed Optimal Power Sharing Strategy in an Islanded Hybrid AC/DC Microgrid to Improve Efficiency

In an islanded hybrid ac/dc microgrid (IHMG), ac and dc subgrids are connected via interlinking converters (ICs). For reliable operation of an IHMG, achieving distributed generators’ power sharing (DGPS) throughout the entire IHMG and ICs’ power sharing (IPS) is the main objective in an IHMG. To improve efficiency of an IHMG, minimizing operating costs of DGs is required and thus cost-minimized DGPS needs to be achieved. Similarly, when multiple ICs operate in an IHMG, efficiency-maximized IPS can further improve the efficiency of an IHMG, as total loss of ICs can vary by the IPS ratios. Thus, this paper proposes a distributed power sharing strategy to achieve cost-minimized DGPS and efficiency-maximized IPS simultaneously, without any communication lines for DGs. Incremental cost-based droop controlled DGs and distributed controlled ICs are coordinated for cost-minimized DGPS and a distributed optimal power sharing method of ICs is proposed to achieve efficiency-maximized IPS. The proposed strategy secures both cost-minimized DGPS and efficiency-maximized IPS, with only sparse communication lines among ICs, thus resulting in a significant improvement in IHMG efficiency and reliability.

A neural network-based adaptive power-sharing strategy for hybrid frame inverters in a microgrid

The capacitive-coupling inverter (CCI) is more cost-effective in reactive power conditioning and enhanced reactive power regulation ability when compared with the inductive-coupling inverter (ICI). As power conditioning capability is vital for a microgrid (MG) system, a new MG frame with hybrid parallel-connected ICIs and CCIs was proposed in this paper. With lower DC-link voltage for the CCI, an adaptive power sharing method was proposed for reducing total rated power and losses. A power-sharing control layer based on a back-propagation neural network that guarantees rapid and accurate sharing ratio computation was investigated as well. The results of simulations and experiments were used to verify the effectiveness of the proposed method.

Exploring teacher agency to address controversial issues in religious education – a forum theatre and action research approach

ABSTRACT Dealing with controversy is highlighted in policy documents as a cornerstone of democracy and education. However, previous research points to several challenges for teachers when dealing with controversial issues (CI) in class. In this article, we apply an ecological conceptualisation of teacher agency and explore the ways in which forum theatre (FT) and action research (AR) can provide conditions for developing religious education (RE) teachers’ agency to address CI. Our main findings indicate a shift in teachers’ orientations from short-term goals of exercising power and control to avoid causing conflict in class towards a process orientation in which an ‘avoidance strategy’ transformed gradually into some combination of a ‘deliberation and embodiment strategy’ and a ‘trust and power-sharing strategy’. We conclude with a reflection on whether this new approach to addressing CI has the potential to become substantiable and hence contribute to the educational goal of promoting democratic education.

Local energy communities modelling and optimisation considering storage, demand configuration and sharing strategies: A case study in Valencia (Spain)

Local energy communities require tools to select their most fitting community members, power-sharing strategy and technologies for their goals. This work aims to develop a model and a methodology to optimise local energy communities. We evaluate the presence of a battery energy storage system with different capacities and ownership options. Besides, we test two different sharing strategies like static and variable coefficients. Finally, we characterise local energy communities’ demand by comparing residential and commercial loads and varying the number of consumption points. We apply the method to a case study consisting of a 100 kWp photovoltaic installation in Valencia simulated with an hourly resolution for a whole year. We use real consumption data from households and commercial buildings and the current administrative requirements, obtaining the flows and status of each component within the local energy community at every moment. We assess each alternative’s economic performance, autarchy degree, and the amount of avoided greenhouse gasses emissions. Results indicate that a local energy community well optimised can fulfil economic, environmental or self-consumption goals. Results only advise installing a storage to increase the degree of self-consumption. Moreover, we obtain the best financial and environmental results in large communities with a 75% residential consumption.