Search

Series-cascaded microgrids (SCMGs) indeed provide control flexibility and high-voltage synthesis capabilities. However, the power distribution in SCMGs based on distributed generation (DG) sources stays understudied. This paper proposes an SCMG topology using non-dispatchable DG sources and battery energy storage, with an integrated power-routing control. The objective is to address power distribution limitations and stabilize SCMG output voltages under varying conditions. A case study validates the control methodology, considering zero irradiation levels for photovoltaic (PV) and maximum power sharing. The battery modules play a crucial role by providing power, voltage support, and maintaining capacitor voltage at a reference value of a PV-integrated module. This is achieved through a third harmonic current injection in the fundamental frequency current, coupled with proportional power distribution using a third harmonic power signal. The effectiveness of the proposed SCMG topology and control is demonstrated through MATLAB/Simulink and hardware-in-loop analyses (Typhoon HIL). The results present an extended power distribution between series-cascaded DG sources-based units while ensuring stable SCMG output voltages, even in adverse conditions like PV module intermittency. Future work aims to extend the proposed topology to a ring/delta-connection SCMG, where third harmonic current aids power distribution among SCMG legs and between series-cascaded DG sources-based units. [ABSTRACT FROM AUTHOR]

Microgrids (MG) are a new and innovative concept in modern distribution networks. Several challenges are associated with the operation and control of MG networks. Active and reactive power sharing among energy resources interfaced through power electronic conversion stages is a major challenge. Although active power sharing can be achieved under varying scenarios, sharing of reactive power between distributed generation units is difficult to achieve. This paper presents a novel and innovative control scheme to ensure sharing of reactive power between Distributed generation units within an autonomous, islanded AC microgrid. A framework composed of novel multiagent moving average estimators is proposed to make the participating nodes share active and reactive power among themselves. Detailed case studies are carried out in MATLAB and Simulink environment to verify the efficacy of the proposed control scheme. Furthermore, a lab scale MG set up is implemented to verify the operation of the control scheme in an MG environment. [ABSTRACT FROM AUTHOR]

This paper presents the idea of a smart load that can adjust the input power flow based on the intermittent power available from RESs (Renewable Energy Resources) to regulate the line voltage, and draw a constant power from the grid. To this effect, an innovative power flow controller is presented based on a Resistive ES (Electric Spring) in combination with a PEAT (Power Electronics based Adjustable Transformer), which can effectively shape the load power flow at the subnetwork level. With a PEAT incorporated in the step down transformer at the grid side, the proposed controller can supply non-critical loads through local RESs, and the critical loads can draw a relatively constant power from the grid. If there is an abundance of power produced by the RESs, the controller can supply both non-critical loads and critical loads through the RES, which significantly reduces the power demand from the grid. The principle, practicality, stability analysis, and controller design are presented. In addition, simulation results show that the power flow controller performs well in shaping the load power flow at the subnetwork level, which decreases the power demand on the grid. Experimental results are also provided to show that the controller can be realized. [ABSTRACT FROM AUTHOR]

• A control synthesis is proposed to damp capacitor current resonance for LCL-filtered GCI. • The stability and performance characteristics are analyzed and compared with methods from the literature. • Intuitive design, wider stable damping region, better dynamic performance, and higher parametric robustness are the potential benefits of the proposed control synthesis. In distributed power generation systems, the inherent resonance phenomena of LCL -filtered grid-connected inverter is one of the major challenges faced by the integration of renewable energy resources with the electric power grid. In this context, the capacitor current based multi-loop active damping method is employed due to lossless resonance damping and flexible control design. However, the damping loop with the feedback compensation design suffers from relatively higher parameters sensitivity unless employed with the reduced digital delays. The filter parameters fluctuation causes a shift in resonance frequency, which leads to ineffective damping at the critical resonance frequency and may risk the control loop stability. Therefore, an alternative linear control synthesis is proposed to design the capacitor current damping loop in order to reduce the filter parameters sensitivity. The proposed design realizes the equivalent virtual impedance in an alternative manner to suppress the resonance peak and enhanced the stability characteristics of the grid-connected inverter. A detailed stability and performance analysis have been done to show the widened stable damping region and high parametric robustness of the suggested design as compared to the literature method. Simulations and experimental results are presented to confirm the theoretical findings. [Display omitted] [ABSTRACT FROM AUTHOR]

• An enhanced resilient control strategy for multi-feeder islanded AC microgrids that shares reactive power proportionally and restore load feeder voltages, simultaneously. • One of the important aspects of the proposed control scheme is that, only the voltage magnitude information is required to transfer at each inverter's controller to achieve the two-fold objectives, simultaneously. For this, quadratic optimal problem is formulated based on phasor impedances of all the load feeders in the network, which computes optimal voltage commands. • A novel load estimation scheme to dynamically estimate phasor impedance at each load feeder associated with the voltage and current of that feeder. • Approximation of microgrid system with multiple load feeders to solitary feeder system. The salient property of this approach is to reduce the computationally expensive and communication intensive MG networks into small, sparse, and efficient alternatives, increasing the feasibility of MG network deployment. • Modeling and analysis of microgrid is verified through stability analysis using system wide mathematical small signal model. • Detailed analysis and comparison of the proposed control structure is presented under the effect of load and transmission line impedance variation at different points for the multi-feeder and approximated models of the MG system. In multi-feeder microgrid systems, accurate power sharing and voltage regulation at each load feeder is more challenging than the conventional single-feeder microgrids. This paper presents an enhanced resilient control strategy for multi-feeder micro-network systems by considering the load feeder voltage regulation and power balancing as a quadratic optimization problem. The proposed control strategy is composed of impedance estimator and optimal controller. However, the impedance estimator obtains each load feeder impedance while optimal controller computes the voltage commands for each distributed generator. One of the important aspects of the proposed control scheme is that only the voltage magnitude information is required to transfer at each inverter's controller, with primary aim to achieve the two-fold objectives. This control strategy is also extended to approximate the whole network impedance into solitary load feeder for micro-networks with extensive number of load feeders. This makes the system computationally less burdening. The MATLAB/Simulink and experimental results are obtained under varying load conditions and line parameter uncertainties for radial type multi-feeder microgrid configuration that reflects the effectiveness of the proposed scheme. The verification outcomes prove the proposed method capability of accurate reactive power sharing, regulation of load feeder voltages, and frequency restoration. [ABSTRACT FROM AUTHOR]

• Distributed FIR based control of renewable based DC microgrids. • Improvements in secondary control. • Resilient to communication link failures and latencies. Recent advancements in renewable energy have made it possible to meet the load demand on the grid by utilizing smaller distributed renewable energy resources. However, advanced control techniques are required to eliminate the potential of instabilities caused due to load demand variation, as well as the power generation fluctuations by these renewable sources. Due to intermittent nature of renewable sources, a distributed average-based control is presented with a communication network within small-scale distributed grids with improved DC microgrid (MG) control resilience. Global reference set point is achieved using an average-based estimated correction term by utilizing the communication network structure to converge all the agent nodes to a common agreement. Any link failure or latencies in the communication network may disturb the load balance within generating and load agent nodes of the DC MG. The proposed distributed FIR based filter secondary control aims to improve the resilience of the DC MG control by achieving load sharing and voltage regulation, keeping the main conventional control system unaffected by communication link islanding. The effectiveness of the proposed control scheme is substantiated through a detailed study comparing it with existing conventional techniques by presenting mathematical model and experimental simulation results using MATLAB/Simpower tool. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• A hierarchical distributed microgrid control structure replacing centralized monitoring and control. • A novel distributed averaging approach for estimation of system values. • A comprehensive small signal model analysis of the MG system. • Analysis of the proposed methodology under communication latencies. • Comparative study of the proposed methodology with conventional consensus-based methods. Autonomous, self-governing micro energy networks are a smart energy solution that satisfy the energy needs of isolated communities. Such smart micro networks usually comprise of several distributed semi-controllable power resources, storages and loads. Usually, the power generation sources draw their energy from renewable energy resources. Power electronics converters suitably condition the power to be transmitted and utilized. A sensory, control and communication layer ensures the integration of several network components to achieve stable network operation. Distributed power-sharing methods function at local processing and decision-making nodes across the energy network. The complete control scheme is a hierarchical structure divided into four control levels. Faults and latencies experienced at the communication network layer adversely affect the performance of the control scheme. This paper proposes a new and improved hierarchical, multi-agents-based control strategy for efficient power-sharing, voltage and frequency regulation between nodes during communication link latencies. A novel distributed averaging estimator is proposed to estimate power injected in the system at various nodes and thereby mitigate the effect of relayed information delays. The effectiveness of the proposed strategy is established comprehensively through mathematical modeling, analytical proofs, discrete-time small signal stability analysis, and MATLAB case study simulations. [ABSTRACT FROM AUTHOR]

This study is dedicated to establishing a comparative analysis of the performance of different local controllers on the cooperative control of DC microgrids. One of the elementary and challenging issues in DC microgrids is the assurance of fairness in proportional current sharing while accomplishing voltage regulation in parallelly connected distributed energy sources. In this work, structural improvements are proposed to enhance the system stability and control performance. A finite-gain controller was employed in the outer voltage control loop with a simple proportional (P) controller in the inner current control loop of a converter. Due to the finite-gain controller, droop-like power sharing was achieved without droop coefficient. In order to further enhance the power-sharing accuracy and DC voltage regulation, a different method was adopted in consensus-based cooperative control to estimate the average current and average voltage difference. Moreover, small signal analysis was used to scrutinize the stability and control performance of the local controller, while different communication delays and current disturbances were applied to examine the performance of the controller. Finally, a four-node-based DC microgrid setup was developed in MATLAB/Simulink environment, and simulation results of the proposed and existing techniques were scrutinized. The simulations results demonstrated the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

The monitoring and control of renewable energy sources (RESs) based on DC (Direct Current) microgrids (DC MG) are gaining much consideration at this time. In comparison with the isolated individual control of converters in a microgrid, DC microgrids provide better voltage regulation and harmonized energy generation/consumption. To address the inherent vulnerability of communication links, robust methods have been proposed that improve the resilience of communication-based control. However, the failure of the communication links in microgrid control layers remains a considerable issue that may lead to one or more nodes being disconnected and operating as a communication island. Such types of communication islanding may cause the unpredictable behavior of the system and further destabilization may lead to a cascaded failure. This paper proposes a fast algorithm to detect and evaluate network connectivity based on the information stored at every node in the form of a look-up table. The control structure has been modified under communication islanding, and a communication connectivity observer is used at every node to detect and address power flow issues under communication islanding. The proposed method has been verified through mathematical analysis, simulation, and experimental results. [ABSTRACT FROM AUTHOR]

Communication-based distributed secondary control is extensively used in DC microgrids. Compared to centralized control, it can provide better voltage regulation and load sharing in microgrids. A conventional secondary control technique that converges the system to a common operating point is improved by using the control methodology to detect the communication link failure and stabilize the system operation during communication islanding. Recently, more robust control schemes have been proposed to improve resilience, but communication islanding has not been addressed at the secondary level control for which the system requires additional tertiary control. However, link failure is a possibility in the microgrid, so this paper proposes a control scheme at the secondary level to detect communication islanding. Communication islanding may lead the system to unpredictable behavior, which may cause the system to become unstable and may further lead to a cascading failure. The proposed control scheme sustains the stability and operation of a DC microgrid. Voltage and current observer works in a parallel manner with the proposed secondary control to achieve a correction term for global operating points. The proposed control scheme has been verified through analysis and simulation. [ABSTRACT FROM AUTHOR]