Active Power Sharing Research Articles

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

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.

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 Novel Control Method for Active Power Sharing in Renewable-Energy-Based Micro Distribution Networks

The microgrid is an emerging trend in modern power systems. Microgrids consist of controllable power sources, storage, and loads. An elaborate control infrastructure is established to regulate and synchronize the interaction of these components. The control scheme is divided into a hierarchy of several layers, where each layer is composed of multi-agents performing their dedicated functions and arriving at a consensus of corrective values. Lateral and horizontal interaction of such multi-agents forms a comprehensive hierarchical control structure that regulates the microgrid operation to achieve a compendium of objectives, including power sharing, voltage, and frequency regulation. The success of a multi-agent-based control scheme is dependent on the health of the communication media that is used to relay measurements and control signals. Delays in the transmission of control signals result in an overall deterioration of the control performance and non-convergence. This paper proposes novel multi-agent moving average estimators to mitigate the effect of latent communication links and establishes a hierarchical control scheme incorporating these average estimators to accurately arrive at system values during communication delays. Mathematical models are established for the complete microgrid system to test the stability of the proposed method against conventional consensus-based methods. Case-wise simulation studies and lab-scale experimental verification further establish the efficacy and superiority of the proposed control scheme in comparison with other conventionally used control methods.

Active Power Sharing Method for Microgrids With Multiple Dispatchable Generation Units Using Modified FFC and IFC Mode Controller

Active Power Sharing Method for Microgrids With Multiple Dispatchable Generation Units Using Modified FFC and IFC Mode Controller

Active Power Sharing Control Strategy of Photovoltaic Microgrid Based on Adaptive Droop

An error of active power distribution will occur with a traditional resistive droop control, due to the difference of the output line impedance of parallel inverters, during the operation of island photovoltaic microgrid. Aiming to this issue, a control strategy for regulating the droop coefficient automatically is proposed. The active power and reactive power output by inverters as the feedback values are lead into the droop control equation in the strategy, and the active power is employed into the reactive frequency equation; the small disturbances will be produced in reactive power, and it can be employed to compute the sharing error of the active power, the process of clearing up reactive power disturbance, which is equal to the process of regulating the droop coefficient automatically, which can greatly improve the accuracy of active power sharing. Simulation and experiment results show that, by using the proposed strategy, the precision of active power sharing can be improved and the circulating currents between inverters are suppressed.

Distributed Dynamic Event-Triggered Control for Accurate Active and Harmonic Power Sharing in Modular On-Line UPS Systems

Due to the mismatched line resistance in the modular online uninterruptible power supply (UPS) systems, accurate active power and harmonic power sharing is an arduous work. To tackle this issue, this article proposes a distributed dynamic event-triggered control for the power sharing to accurately compensate the effect of mismatch among the line resistances. Benefiting from the proposed control strategy, the UPS modules adaptively regulate the virtual resistance at the fundamental and harmonic frequencies, and hence, the accurate active power and harmonic power sharing are achieved. In addition, the suggested technique allows the UPS modules to exchange information at only the event-triggered times, which greatly reduces the number of communication among the neighboring units. Furthermore, the system's stability is analyzed using a Lyapunov function. Finally, experimental case studies are provided to evaluate the performance of the proposed control strategy, showing its effectiveness in achieving the accurate power sharing, and plug-and-play capability.

Distributed secure sampled-data control for distributed generators and energy storage systems in microgrids under abnormal deception attacks

In this work, we investigate the active power sharing (APS) and energy balancing (EB) issues between distributed generators (DGs) and energy storage systems (ESSs) in microgrids with abnormal deception attacks. Firstly, the mathematical model of APS and EB issues under abnormal deception attacks is established, in which attack signals can tamper with the transmitted information and change appropriately with the system’s current state. Next, a distributed secure memory sampled-data controller is designed for APS and EB problems, and the corresponding solving algorithm is given. Furthermore, in order to reduce the conservatism of the results, an improved delay-dependent looped Lyapunov–Krasovskii functional is introduced by adding the combination term of time delay and free matrix. Meanwhile, the high dimensional linear matrix inequality (LMI) in the proposed control algorithm is decomposed into several low dimensional LMIs based on the decoupled method. Finally, a simulation experiment in microgrids is employed to demonstrate the effectiveness of the designed control scheme.

Zero-Inertia Offshore Grids: N-1 Security and Active Power Sharing

With Denmark dedicated to maintaining its leading position in the integration of massive shares of wind energy, the construction of new offshore energy islands has been recently approved by the Danish government. These new islands will be zero-inertia systems, meaning that no synchronous generation will be installed in the island and that power imbalances will be shared only among converters. To this end, this paper proposes a methodology to calculate and update the frequency droops gains of the offshore converters in compliance with the N-1 security criterion in case of converter outage. The frequency droop gains are calculated solving an optimization problem which takes into consideration the power limitations of the converters as well as the stability of the system. As a consequence, the proposed controller ensures safe operation of off-shore systems in the event of any power imbalance and allows for greater loadability at pre-fault state, as confirmed by the simulation results.

Active Power Sharing in a Micro-Grid with Multiple Grid Connections

This paper presents a mechanism for active power sharing among multiple dispatchable and distributed generation units within a micro grid comprising one or multiple interconnections with the main grid. Ideally, a micro grid should act as a constant load or a constant voltage source when connected to the main grid. However, to achieve ideal operation, natural load variations and the intermittency of renewable energy sources within the microgrid need to be adequately and timely compensated for by dispatchable power sources. While several control algorithms have been reported in the literature to achieve ideal microgrid operation, the majority of the proposed methods assumed a micro grid with a single interconnection to the main grid. In the real world, micro grids may have to maintain multiple live links with the main grid for several technical and operational reasons such as reliability, power-dispatch restriction, and operational limitations requirements. Therefore, a new method of active power sharing is proposed in this paper, which is equally effective for micro grids with one or multiple grid connections. The robustness of the proposed method is examined under different microgrid operating conditions. The results reveal the flexibility of the proposed method to adapt under various real-world operating conditions.

Distributed fixed-time secondary control of an islanded microgrid via distributed event-triggered mechanism

The fixed-time secondary control problem for an islanded microgrid (MG) through an event-triggered communication mechanism is investigated in this paper. A distributed event-triggered fixed-time control strategy is proposed to achieve frequency and voltage secondary restoration. And a proportional active power-sharing is also achieved through an undirected topology. The given control protocol using frequency, voltage magnitude and active power measurement values of neighboring distributed generations only when the predefined event-triggered condition is satisfied. In comparison with the periodic communication way, the presented method exhibits excellent performance in alleviating communication burden and promoting control efficiency. Moreover, compared with conventional asymptotic control algorithms, the objectives of islanded MG secondary control are obtained within a fixed settling time by using the presented fixed-time control approach. The estimation of settling time is unrelated to any initial states. Several simulation experiments are conducted to demonstrate the effectiveness of the proposed control scheme.

Decentralized secondary control for frequency regulation based on fuzzy logic control in islanded microgrid

This paper presents a fuzzy-based decentralized secondary control for frequency restoration and active power-sharing in an islanded microgrid, this controller uses the local frequency error to generate an extra term for compensating the deviation and maintaining accurate active power-sharing. No communication infrastructures are needed, event detection, time dependent-protocols, and state estimation are not required. Its design and implementation are straightforward, also, it offers quick dynamic frequency recovery with accurate active power-sharing. To verify the validity of the proposed controller, several tests have been carried out: frequency restoration and active power-sharing during load disturbances, synchronization with plug and play (PnP) ability, as well the communication latency impact. Moreover, the effect of data drop-out and interferences were analyzed in real-time simulation using Truetime. The results have shown the high capability and the fast response of frequency restoration while maintaining the active power-sharing, no oscillations and ripples were presented in steady-state response, likewise, a smooth dynamic response during PnP test is observed. The communication latency and interferences have no impact on the proposed controller that showing a significant improvement in settling time 50% without frequency packet losses and 81%, 90% in the presence of 30% and 70% of frequency packet losses respectively.

Distributed Robust Frequency Restoration and Active Power Sharing for Autonomous Microgrids With Event-Triggered Strategy

In real-word applications, distributed generators (DGs) cooperate to accomplish the objectives of frequency restoration and active power sharing with time restrictions plays a crucial role in improving power quality of AC islanded microgrids. To address this issue, two novel distributed robust secondary control protocols, namely finite-time and fixed-time consensus algorithms, which subject to unknown external bounded disturbances are put forward. The main features of the proposed algorithms are distributed implementation, discrete control, asynchronous communication, and local computation. Take the event-triggered strategy into consideration, the developed algorithms have faster convergence speeds as long as the event-triggered parameters are limited in a certain range. Through Lyapunov synthesis, the conditions of maximum/off-line settling time for finite/fixed-time frequency restoration and active power sharing algorithms are first established. In addition, the detailed implementation process of distributed robust event-triggered control approach is provided. At the end of this paper, considerable amount of various simulations under the unified wide-time-scale framework are conducted to illustrate the performance of the proposed algorithms.

Power Quality Improvement Using an Active Power Sharing Scheme in More Electric Aircraft

This article proposed a harmonic suppression scheme that used a dc-dc converter as an active harmonic injector to cancel voltage harmonics on the HVdc bus within a hybrid power generation centre (HPGC). A permanent magnet synchronous generator and a battery are considered to supply power to a common HVdc bus through their dedicated ac-dc and dc-dc converters respectively within the HPGC. We proposed simplified mathematical models of harmonics from the ac-dc and dc-dc converters. Thereafter, an active power sharing scheme between the PMSG and the battery is developed to control the magnitudes of targeted harmonics to be the same. The targeted harmonics on the HVdc bus can thus be cancelled by properly tuning the carrier signal phase angles within ac-dc and dc-dc converters. A closed-loop control scheme has been developed and this scheme is with no extra hardware cost. To demonstrate the effectiveness of the proposed scheme, we selected the first-band harmonic ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f_c</i> − 3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f₀</i> ) as the targeted harmonic component. The harmonic cancellation scheme for this component has been developed and validated using experimental results. It has been demonstrated that the proposed method can achieve over 90% reduction of this specific harmonic component on the HVdc bus within this HPGC using one dc-dc converter.

A new approach for integrating wave energy to the grid by an efficient control system for maximum power based on different optimization techniques

In this paper, a Wave Energy Conversion (WEC) model consisting of a Savonius type wave turbine plus DC generator, Battery Energy Storage System (BESS), inverter, and Inductance-Capacitance-Inductance (LCL) filter is designed. In this study, the optimization techniques are used to maximize Savonius type wave turbine self-efficiency considering different factors such as the height, depth, length, and time period of the wave. Four meta‐heuristic optimizations are competing in this article for obtaining the optimum parameter design based on the output electrical power of the wave. These are Whale Optimization Algorithm (WOA), Artificial Immune System (AIS), Bat Algorithm (BA), and Particle Swarm Optimization (PSO) algorithm. The comparative results verify the reliability of WOA in maximizing the overall electrical output power from the wave turbine while confining with the constraints. Moreover, an efficient control system is designed to operate in Islanded Mode (IM) and Grid-Connected (GC) operations according to the matching between the maximum estimated output power from the WEC system and the system load. A proposed control scheme is performed for adjusting the system frequency and voltage in islanded mode operation and ensuring active power-sharing in grid-connected mode. The islanded control scheme consists of three levels; droop control, inner voltage, and current control, outer control based on model predictive control (MPC) to maintain the system frequency and voltage to their nominal values. WOA is also proposed to improve the performance index by optimally evaluate the control signal and tracking error weighted parameters. The GC control scheme is based on the Active/Reactive Power (P/Q) controller to ensure active power-sharing. The effectiveness of the proposed controller has been verified by considering system parameters uncertainties.

Enhanced Active and Reactive Power Sharing in Islanded Microgrids

The intermittency of renewable energy makes the control of islanded microgrids more difficult than that of the grid-connected mode. In conventional methods, the controller is designed to regulate the system frequency and voltage only based on the droop control theory. Consequently, the system frequency and voltage regulation are mostly provided by the fast response distributed generators (DGs), e.g., energy storage systems. This controller design will reduce the availability of DGs with lower droop gains for future dispatches. The main novelty of this article relies on proposing an intelligent power sharing (IPS) approach to regulate the system frequency and voltage based on DGs' operating power capabilities and their droop control gains. The communication infrastructure is involved in the proposed IPS to diminish the dependence on fast response DGs. Moreover, the IPS is equipped with an adaptive virtual impedance to reduce the impact of coupling between the active and reactive power on the voltage regulation. The performance of the controller is evaluated through different simulation studies based on a 14-bus CIGRE test system. Time-domain simulations prove the effectiveness of the IPS approach in achieving acceptable frequency and voltage regulation along with high-power sharing accuracy. Also, a small-perturbation stability analysis is developed to study the IPS control robustness under different scenarios.

Distributed Privacy-Preserving Active Power Sharing and Frequency Regulation in Microgrids

To avoid potential privacy threats and associated cyber-security issues in microgrids, this letter presents a distributed active power sharing and frequency regulation method with preserved privacy of local information. In the proposed approach, the transmitted data including the active power outputs and capacities are protected by adding noise to the original ones. Theoretical analysis and verification studies are performed to illustrate the advantages of the proposed method.

Robust Distributed Disturbance-Resilient $H_\infty$-Based Control of Off-Grid Microgrids With Uncertain Communications

In this article, a novel robust distributed cooperative control (RDCC) scheme is proposed to be used in the secondary layer of off-grid (autonomous) ac microgrids (MG). The MG, including heterogeneous units such as distributed generation and battery energy storage systems. Most of the reported studies have assumed the ideal conditions to communicate among units. They have not considered any uncertainties or disturbances in the network, whereas the communications are already subjected to uncertainties or disturbances. To tackle these concerns, we give an RDCC scheme based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$H_\infty$</tex-math></inline-formula> control theory for MGs in the present external disturbances and uncertain communication links. The proposed method is extended for a time-varying topology network (that can be considered as an unreliable network which makes the problem more challenging). The theoretical concepts of the proposed control strategy, including the mathematical modeling of MG, graph theory, fundamental lemma, and controller design procedure, are outlined. Sufficient conditions are also derived by using the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$H_\infty$</tex-math></inline-formula> control theory, which leads to a set of linear matrix inequalities. Finally, to evaluate the performance of the proposed control strategy, offline digital time-domain simulation studies are carried out on a test MG system in MATLAB/Simulink environment. The results are compared with several previously reported methods. Simulation results and comparison with previous works reveal the effectiveness, efficiency, authenticity, and accuracy of the proposed method in regulating MG voltage and frequency, state of charge (SoC) balancing, and providing accurate proportional active power-sharing.

Adaptive Droop-Based Control for Active Power Sharing in Autonomous Microgrid for Improved Transient Performance

This article presents a decentralized adaptive droop-based control for active power sharing between the parallel inverters in autonomous microgrids. This article is focused on improving the transient performance of the system proposing a robust controller. The analysis does not require load current measurement where the Lyapunov analysis-based control takes load current as a disturbance to the system. The mathematical analysis takes a more practical form of LC filter configuration where the dynamics due to resistances across the LC is also considered. Controller gain conditions are considered by employing a detailed Lyapunov analysis. A comparative study of the conventional droop control with the proposed adaptive droop control is included in this article. MATLAB has been employed as the Simulink platform for the comparative study. In addition, for experimental verification, an FPGA-based hardware setup has been developed and the related results are presented to verify the real-time operation of the proposed adaptive control.

Resilient cooperative control of AC microgrids considering relative state‐dependent noises and communication time‐delays

In this study, a resilient distributed control algorithm is proposed for the secondary voltage and frequency restoration of an autonomous inverter-based microgrid considering simultaneous relative state-dependent noises and communication time-delays (CTDs). The proposed algorithm is robust against potential time-varying stochastic noises and CTDs, which corrupt the data exchanges in the secondary control layer. Additionally, this study considers the contribution of both distributed generation and distributed energy storage (DES) units in islanded AC microgrids. The presence of DES creates the need for an extra control algorithm to provide state-of-charge (SoC) balancing for these units and having precise active power-sharing. The theoretical concepts of the proposed control algorithm, including the mathematical modelling of microgrid, basic lemma, and controller design procedure, are outlined. The performance assessment of the presented control algorithm is evaluated through simulations on a test microgrid in MATLAB/Simulink software. Then, some previously-reported algorithms are selected to compare the proposed control algorithm with them. The obtained results show the effectiveness and robustness of the presented algorithm in regulating the voltage and frequency, matching SoCs, and as a result, having precise active power-sharing.