Adaptive distributed ANN-based event-triggered consensus algorithm of a DC microgrid cluster

This paper proposes a distributed hierarchical control framework for energy storage systems (ESSs) in DC microgrid clusters, which achieves voltage regulation and current sharing for ESSs in each microgrid as well as the whole microgrid cluster. The primary control stage adopts a droop controller which only requires local information while the secondary control stage provides correction terms for ESSs within microgrids. The tertiary control stage samples the pinned ESSs in different microgrids with low sampling rate to provide the voltage setpoint, which ensures global current sharing among microgrid cluster. The corresponding multilayered event-triggered consensus algorithm for clusters is proposed to reduce the communication cost generated by operation of the distributed controller. Both the control framework and the consensus algorithm can be extended for satisfying higher dimensional regulation needs. The controller is validated in a DC microgrid cluster through simulation under different scenarios, and the results illustrate the effectiveness of the proposed controller.

DC microgrid (DCMG) clusters represent interconnections of multiple DCMGs to enable flexible power flow, and hence advantages of high resilience, economic dispatch, loss minimization, and optimal load response with microgrid-based distributed generations can fully be taken. However, small-scale DCMGs are known to be weak in nature due to low inertia and high grid impedance. Meanwhile, dynamic analyses of DCMG clusters have been plagued by their high order dynamic nonlinear system models since numerous state variables are involved. This article proposes large signal stability analysis of DCMG clusters based on Takagi-Sugeno multimodeling approach. With the proposed method, the large signal Lyapunov stability of the DCMG cluster is reduced to the computation of a series of linear matrix inequalities, which will significantly simplify the analysis. The influences of circuit parameters, power flows, and topological change on large signal stability of the DCMG cluster are revealed, and asymptotic stability regions of the network are estimated as well. In addition to simulation verification, a laboratory prototype of a ring topology DCMG cluster with three 48 V DCMGs interconnected is also built to validate the analysis by experimental results.

This paper presents the resilient operation of interconnected DC microgrid (MG) clusters with heterogeneous sources, under consensus based economical dispatch. The cyber physical structure of microgrids has been implemented to attain global economical operation of the energy storage devices in coupled MG clusters, which are dispatchable in nature. In practice, DC microgrids will also possess renewable energy sources which are intermittent and non-dispatchable. As such, we have considered a photovoltaic (PV) source along-with the batteries in every MG cluster. We have investigated the effect of cyber intrusions in the exchanged voltage information, on the operation of the interconnected clusters. Mitigation and detection technique has been proposed to detect the presence of cyber adversary and also, to maintain the economical operation of the DC MG clusters. The topology of the interconnected clusters, control strategy and the mitigation is developed in a real time platform using the real time digital simulators (RTDS). Extensive real-time simulations are done to validate the proposed detection and mitigation technique.

A new DC fault current limiter (FCL)-based circuit breaker (CB) for DC microgrid (MG) clusters is proposed in this paper. The analytical expressions of the DC fault current of a bidirectional interlink DC/DC converter in the interconnection line of two nearby DC MGs are analyzed in detail. Meanwhile, a DC fault clearing solution (based on using a DC FCL in series with a DC circuit breaker) is proposed. This structure offers low complexity, cost, and power losses. To assess the performance of the proposed method, time-domain simulation studies are carried out on a test DC MG cluster in a MATLAB/Simulink environment. The results of the proposed analytical expressions are compared with simulation results. The obtained results verify the analytical expression of the fault current and prove the effectiveness of the proposed DC fault current limiting and clearing strategy.

Energy router is one of the key elements for power electronic-based DC micro-grid (DCMG) cluster system. Traditional ac/dc converter and solid-state transformer can act as an energy router, but their functions and interfaces are restricted. In this paper, a novel modular-based energy router (MBER) for DCMG cluster has been proposed to extend the functions of energy router. Each module of MBER is composed of an ac/dc converter and an isolated dual-active-bridge converter with high-frequency transformers. The power multidirectional exchange mechanism between ac grid and DCMG cluster is shown. Then, the operation mechanism and the operation modes of MBER are analyzed. Considering the operation range of MBER is limited by the operation modes and the dc voltage of each module, a dc voltage adjustment strategy and the control method have been proposed to expand the operation range of MBER. Finally, the simulation and experimental results are presented to validate the proposed topology and control methods.

In DC microgrid (MG) clusters, the interconnection between energy storage systems can further improve the reliability of the interconnected system. This paper pproposes an SOC-featured distributed tertiary control method to distribute the power in each DC MG's energy storage system automatically. When all the ESUs have the same capacity, the SOC and the output currents of ESUs in different MGs reach a consensus rapidly in both charging and discharging mode by adjusting the reference voltage. The distributed tertiary control also features in power balancing when ESUs have different capacities. We then discuss the adjustment factor γ on the convergent rate and choose a suitable value for a faster convergence. Simulation and experimental results are then presented to verify the effectiveness of the proposed control scheme.

A cluster of dc microgrids consisting of multiple interconnected dc microgrids has great potential for improving the reliability and reducing the cost of power generation. In this paper, a distributed coordination control strategy is proposed to overcome a series of problems of centralized control. This control strategy which adopts a hierarchical structure is based on the droop control method, then a modified control formula which achieves multi-objective is introduced to the voltage control and power generation cost control. Besides, a finite-time consensus algorithm is applied to obtain the average value obtained in finite steps. Meanwhile, an estimated connected topology is proposed for better utilisation of the finite-time consensus algorithm and acceleration of the convergence speed. This proposed topology ensures all this control method is a fully distributed one, which does not require the global information previously and has high reliability. By using the MATLAB/Simulink simulation platform, this proposed control strategy is verified in one dc microgrid and a cluster of those containing 4 dc microgrids. The simulation results under different scenarios all indicate the effectiveness of the proposed methods.

In this paper, the authors have attempted to address the problem of power sharing in networked hybrid AC/DC micro-grid clusters by utilising back-to-back converter. The hierarchical distributed cooperative control strategy is employed for both the AC and DC microgrid clusters (intra-microgrid control) and an inter-microgrid control strategy employing back-to-back converter for enabling power sharing among the clusters according to the required needs. The distributed secondary control for both the AC and DC MGs aid to reprimand the voltage drops due to presence of cable resistance and droop characteristics. It thus helps to achieve a regulated voltage at both the AC and DC PCC. Particularly in AC MG, it enhances the voltage and power quality. Further, it is worth noting that most of the consensus algorithms are asymptotically convergent and hence in order to achieve finite-time convergence, a modified consensus approach is used for the DC microgrid cluster. This is done to achieve faster consensus irrespective of the unforeseen disturbance / transients that may occur in the AC microgrid clusters. The distributed dynamic averaging consensus algorithm based on PI controllers (DAC-PI) is also investigated for robustness against physical and communication failures. With the proposed inter and intra-microgrid cluster control mechanism, power balance between three phase AC MGs and DC MG is illustrated in this work. This could be utilised as practical applications in stand-alone microgrids, marine power systems, more electric aircraft power systems and can be equipped with mode selection algorithms to enable connection to the utility thereby endowing flexibility and reliability to the network of microgrid clusters. Extensive simulations of test-cases are provided with MATLAB/Simpowersystems platform to elucidate the performance of the proposed control strategy and the hybrid infrastructure.

The cluster of DC microgrids consisting of multiple interconnected DC microgrids has great potential for improving the reliability and reducing the cost of power generation. Coordinated control is a common method often used to achieve this potential. This paper proposes a distributed coordination control strategy that overcomes a series of problems of centralized control to ensure stable and economical operation of DC microgrids. In this control strategy, based on the hierarchical structure, voltage secondary control and global generation cost control are introduced on the basis of original droop control. Each power generation unit only interacts with neighboring communication units through a finite-time consensus algorithm. The ultimate goal is to achieve multiple control goals including voltage stability and minimum global generation costs. This control method has high reliability, which does not require a central controller and only implements the strategy based on information exchange between neighbor units. At the same time, the finite-time consensus algorithm and communication sequence used in this paper are effective to speed up the calculation and reduce the control time. The proposed control strategy is verified in a system containing four DC microgrids. By using the Matlab/Simulink simulation platform, the corresponding simulation cases are performed for different scenarios such as plug-and-play and load fluctuation.

The hierarchical control framework including primary, secondary, and tertiary levels has become a standard solution for control of microgrids (MGs), where the tertiary is responsible for power flow management among clusters of microgrids. This paper presents a predictive function controller (PFC) design in tertiary level for DC microgrid (DCMG) clusters. The loading mismatch among neighbor microgrids is used in an updating policy to adjust voltage set points of the DC microgrids to facilitate the power flow and thus mitigate such mismatch. The design procedure of the PFC controller is detailed, and the simulation model with two interconnected DC microgrids is built in MATLAB/Simulink environment to verify the controller performance.

Tertiary control is the highest level in hierarchical control of microgrids to perform power exchange between the microgrid and external networks. In this Letter, a tertiary control strategy based on predictive function control (PFC) is proposed to manage power flow in DC microgrid (DCMG) clusters. Unlike linear PI control suitable for single‐input and single‐output systems, the PFC strategy is a nonlinear control method and capable of multiple input and multiple output control tasks with multiple objectives optimisation on‐line. By solving the cost function in the finite receding horizon, voltage set points are computed in real‐time to create bus voltage difference for power transfer between interconnected DCMGs. The PFC‐based tertiary control for the DCMG cluster is verified through simulations.

Multibus dc microgrids, which combine renewable energy sources, energy storage systems, and loads, have voltage stability requirement, which solicits increasing research attention in practice. Potentially complex architectures of the multibus dc microgrids make it difficult to evaluate the stability using the conventional stability criteria. In this article, some constraints related to the conventional stability criteria, such as right-half-plane (RHP) poles or zeros in the subsystems are discussed. Further, an impedance-based stability criterion is proposed in the light of generalized bode plots for multibus dc microgrids. The configuration of the multibus dc microgrid is simplified by adopting generalized voltage source, generalized current source, and two-port model. Then, impedances or admittances for each bus port can be derived, which are helpful for assessing the stability of the system. Using the proposed stability criterion, the stability of each bus port in the multibus dc microgrid can be evaluated separately. The proposed stability method considers the number of RHP pole of the open-loop transfer function for the system so the stability of the system consists of subsystems with RHP pole and zero can be analyzed correctly. Moreover, the intermittent bus converter connected with neighboring dc microgrid can be regarded as an extension unit. Then, the proposed method can be easily extended and is acting as a generalized approach for different configurations, i.e., single-bus dc mirogrid or a cluster of dc microgrids. Experiments are done to validate the effectiveness of the proposed criterion.

This work accentuates on using unified interphase power controller (UIPC) to control power flow between clusters of multiple microgrids in a hybrid microgrid. The clusters of microgrids are interconnected through the UIPC, which is able to provide bidirectional power flow between the clusters. A new optimal fractional order-based control strategy is described for UIPC control. Simulation results are provided for power exchange control performance between clusters of AC and DC microgrids as well as with the main power grid.

With the rising popularity of DC microgrids, clusters of such grids are beginning to emerge as a practical and economical option. Short circuit problems in a DC microgrid clusters can cause overcurrent damage to power electronic devices. Protecting DC lines from large fault currents is essential. This paper presents a novel localized fault detection and classification technique for the protection of DC microgrid clusters. In this paper, a variational mode decomposition (VMD) and artificial neural network (ANN) based technique is proposed for accurate and effective fault detection and classification. This research aims to train an ANN that can detect and classify faults in DC microgrid clusters with multiple sources and loads by applying VMD to extract features of current signals. Different types of short circuit faults such as Pole to Pole and Pole to ground faults are considered under various grid operating conditions. The proposed method is capable of real-time fault detection and diagnosis, which can help prevent system failures and minimize downtime. The results indicate that the proposed approach is efficient and effective in detecting/classifying faults in DC microgrid clusters improving the reliability and system safety. The performance evaluation is carried out through rigorous case studies in MATLAB/Simulink environment to prove the efficacy of the proposed method. The VMD-ANN approach is shown to outperform other traditional signal processing techniques in terms of accuracy and robustness. Moreover, the proposed method is applicable to a wide range of DC microgrid clusters, making it a versatile and valuable tool for future research and development.

A detailed and real-time implementation of the cyber and physical layer of the DC microgrid (MG) clusters are presented in this work. The physical layer is implemented using a real time digital simulator (RTDS) and the communication layer is implemented in Mininet. The objective of the work is to study the interaction of the communication, power electronics devices and other microgrid components to analyze effect of cyber adversaries and intrusions on the control mechanisms. Especially, the accurate modeling of the communication networks is a challenging task and has been attempted in this paper for the global control of interconnected DC MGs. Global control structures facilitate interconnection of neighboring MG clusters for better utilisation of distributed energy resources (DERS) and enable inter and intra power exchange in MGs. The global physical network is implemented in RTDS and Mininet is employed for understanding the cyber-physical systems (CPS) interactions. Real-time simulations are provided for the validation of the implemented system.