Operation Mode Of Microgrid Research Articles

Operation characteristics analysis and optimal dispatch of solar thermal-photovoltaic hybrid microgrid for building

The optimal dispatch for hybrid microgrids is the crucial approach to decrease maintenance costs and enhance operational reliability. This paper aims to provide a feasible solution for the optimal dispatch of a solar thermal-photovoltaic hybrid microgrid. A distributed energy system of a building is established and the power load is analyzed. Operation parameters are optimized for hybrid microgrid in isolated operation mode and grid-connected operation mode. The operation performance with adequate and inadequate solar irradiation is evaluated by using fixed dispatch and optimal dispatch strategy. In addition, the performance of hybrid microgrid under power selling and purchasing conditions are analyzed. Results show that the operation mode of building hybrid microgrid can be adjusted to isolated/grid-connection modes based on actual power requirements. The optimal dispatch strategy shows great advantages on both solar adequate and inadequate conditions under isolated operation mode for hybrid microgrid, at most 14.3 % lower for maintenance than that of fixed strategy. In addition, the power selling to the external power grid can significantly improve the profit of the hybrid microgrid and generate earnings of $6102.1 per year under optimal dispatch. The research can offer an analysis approach for hybrid microgrid, and further increase clean energy utilization efficiency.

Smooth Transition Control Strategy for Operation Modes of Optical Storage Microgrid based on VSG

Addressing the challenge of suppressing voltage and frequency oscillations during mode transitions and achieving smooth transitions between grid-connected and islanded operation modes in peer-to-peer structured optical storage microgrids, is an urgent technical issue. This paper proposes a control strategy for smooth mode transitions based on numerical soft starters, focusing on the dynamic characteristics of voltage and frequency in optical storage microgrids during grid-connected and islanded operation modes. The numerical soft starter smoothens the input reference value of the current inner loop, reducing the impact of transient surge current on the current inner loop during transitions, thus ensuring the oscillations of bus voltage and frequency during microgrid mode transitions. In islanded operation mode, a VSG control strategy is introduced by constructing a small signal model to analyze the frequency response characteristics of the system under different inertia and damping characteristics, setting appropriate control parameters to provide strong frequency support for the system during islanded operation. Finally, an optical storage microgrid system is established using Matlab/Simulink to conduct simulation experiments under conditions such as grid-connected/islanded mode transitions, load fluctuations, and sudden changes in photovoltaic output power, validating the effectiveness of the proposed smoothing strategy.

A ground fault location algorithm in double‐circuit transmission lines with T‐off connection to an industrial microgrid by using current and voltage phasors information of a single terminal

AbstractThe paper presents a ground fault location algorithm (GFLA) in double‐circuit transmission lines (DCTL) with a T‐off connection to an industrial microgrid (IMG) containing electric arc furnaces (EAF), renewable distributed generations (RDG), and static VAR compensator (SVC). The design presented utilizes the information on the current and voltage phasors of one side of the transmission lines (TL) during the fault period, and there is no need for the availability of information on the type of faulty phase(s) and even the faulty section. To find the exact location of the fault in this design, the voltage phasor equations governing the fault point in positive, negative, and zero‐sequence (PNZS) domains, the zero‐sequence current (ZSC) equation of the fault point, and the boundary condition equation of the fault point have been used. The simulation system is implemented in Simulink/MATLAB using accurate modelling of all network components. The algorithm has been tested and evaluated in different fault conditions, including various locations, phase types, phase‐to‐ground connection resistance, occurrence time, and microgrid (MG) operation modes. The successful results of various tests of the proposed design as well as the analysis of various sensitivities confirm the satisfying performance of the suggested algorithm.

Distributed optimal operation of PV-storage-load micro-grid considering renewable and load uncertainties

Micro-grid is one of the important carriers for renewable energy integration. Optimizing the operation mode of micro-grid can improve economic benefits and reduce risks brought by uncertainties. To maximize the economic benefits of photovoltaic-storage-load micro-grid, a chance-constrained optimal operation model considering renewable and load uncertainties is proposed in this paper. Firstly, the photovoltaic (PV) power and load forecast error distribution function based on fitting method is obtained. Then, a probabilistic power balance constraint based on chance constrained theory is established to reflect risks brought by uncertainties. To protect the information privacy of different entities, the alternating direction multiplier method (ADMM) with self-adaptive parameters is used to the proposed optimal model in a distributed way. Case study demonstrates that the proposed model can achieve a profit and risk balance of micro-grid scheduling by setting different confidence levels, and the information privacy of micro-grid operator and users is well protected.

A hybrid butterfly algorithm in the optimal economic operation of microgrids.

With the increasing capacity of renewable energy generators, microgrid (MG) systems have experienced rapid development, and the optimal economic operation is one of the most important and challenging issues in the MG field. To reduce the overall generation cost of microgrids, a hybrid butterfly algorithm (HBOA) is proposed to address the optimal economic operation problem in MG systems. This algorithm uses adaptive switching thresholds to balance the global exploration capability and local exploitation capability of the algorithm. It introduces a diversity learning mechanism to enhance information exchange among populations to improve the algorithm's accuracy and proposes an elite-guided guidance strategy to accelerate the convergence speed of the algorithm. Numerical simulation experiments on 10 standard test functions validate that the HBOA algorithm has higher optimization accuracy and faster convergence speed. Simulation experiments are conducted on two operation modes of microgrids: Islanded and grid-connected, and compared with other algorithms. In islanded and grid-connected modes, HBOA can reduce operating costs by up to 11.7% and 17.7%, respectively. The experimental results confirm the applicability and superiority of the proposed algorithm for solving the optimal economic operation problem in microgrids.

Seamless Transition Between Microgrid Operation Modes Using ADRC Without an Islanding Detection Algorithm nor PLL

Seamless Transition Between Microgrid Operation Modes Using ADRC Without an Islanding Detection Algorithm nor PLL

Modelling the operation modes of local MicroGrid networks with mobile wind and solar power plants

The basis for the development of the global energy sector is the introduction of alternative energy and, accordingly, a complete change in approaches to the structural reorganisation of energy systems. An analysis of the state of electric power networks in Ukraine shows their almost complete depreciation, low reliability and structural obsolescence, which makes further development and expansion difficult to ensure the rapid growth of electricity consumption. Therefore, a trendy solution to the problem of modernising electric power networks while increasing their capacity and reliability is the use of MicroGrid systems, which are structural elements of the Smart Grid concept based on the intellectualisation of the management of the full cycle of electricity generation, use and storage. The miniaturisation and localisation of smart electric networks makes it possible to minimise power losses and ensure full control over their operating modes. A MicroGrid provides management of distributed energy resources and is essentially a hybrid, as it includes renewable energy sources alongside traditional ones. Regulation of MicroGrid operation modes and power flows in it is the key to increasing the sustainability of the operation processes. The article proposes the use of mobile wind-solar power plants as sources of distributed generation in the MicroGrid system, which is a new technical solution for improving the structural scheme of its implementation and optimising the management of operating modes. The structure of MicroGrid is substantiated and developed, and mathematical modelling of autonomous and hybrid modes of operation of the system with mobile renewable energy power plants is performed. The obtained results show the feasibility and energy efficiency of the developed MicroGrid system. Conclusions are drawn regarding the prospects for further development of MicroGrid with mobile power plants.

Microgrid source-network-load-storage master-slave game optimization method considering the energy storage overcharge/overdischarge risk

--This paper selects the whole microgrid system as the master and renewable energy, energy storage, and load as the game's slave. It builds a master-slave game optimization model for coordinating the microgrid's source-network-load-storage. The master's goal in the microgrid game is to minimize the overall operation cost. The slave in the renewable energy game aims to minimize the operation cost of renewable energy while considering penalties for wind and PV curtailment. The slave in the energy storage game focuses on optimizing energy storage regulation performance and considers overcharge/discharge risks. Meanwhile, in the load game, the slave aims for the highest power quality and improves load power quality as much as possible while preserving demand response capability to enhance system flexibility. The case analysis shows after 45 games, all game participants can achieve Stackelberg equilibrium, effectively balancing multi-party benefits and improving safety and regulation capabilities of energy storage operations. The microgrid operation scheme based on this method maintains the existing microgrid operation mode and ensures safe and stable system operation.

Multimode Control for Power Quality Improvement in an Electronically Coupled Distributed Generation Unit Under Grid Connected and Autonomous Modes

This paper develops a new multimode control strategy for power quality (PQ) improvement in distributed generation (DG) units that employs a voltage source converter (VSC) as the electronic interface medium. The devised control strategy seamlessly operates for both the grid connected (GC) and autonomous/stand-alone (SA) modes of microgrid (MG). A novel computationally efficient comb-filter driven discrete time oscillator is developed for current reference generation (CRG) under GC operation. It constitutes a cluster of zeros to introduce notch peaks at integer multiples of the fundamental frequency thereby ensuring improved harmonic rejection capability. Consequently, it ensures unconditionally balanced and sinusoidal grid currents with improved PQ to comply with grid interconnection codes prescribed in the IEEE std-519 and std-1547 even under electrical anomalies. In the SA mode, the CRG scheme is developed in a stationary reference frame with an improved vector proportional integral (VPI) compensator. Despite the uncertainty of load parameters, the proposed VPI guarantees zero steady-state error and superior transient response. A finite state machine-based synchronization framework is proposed to ensure secure and seamless transfer of MG between GC and SA even under disturbances. The practical viability of the proposed multimode control has been demonstrated by applying various switching rules in both GC and SA modes of MG operation.

Power quality enhancement of solar–wind grid connected system employing genetic-based ANFIS controller

Abstract The demand for electricity globally has led to the search for renewable energy resources for power generation and attaining it in an eco-friendly manner. The solar photovoltaic systems and wind-based generators of power are regarded as primary resources of renewable energy and are called Distributed Generation units as they are scattered in nature. These are operated with bidirectional converters by providing auxiliary services at grid side and load side in either mode of microgrid operation. Besides, the DC power generation units’ integration gets converted into AC system by means of inverters. These types of systems not only increase voltage and current harmonics and power frequency deviations but also drive the distribution system to risky operating zone. This emphasizes the stipulation of advanced control schemes for microgrid architecture. Consequently, power electronic converters introduce harmonics in the system and affect system performance. To report these expanded issues, the authors recognized an advanced custom power device entitled Distributed Power Flow Controller (DPFC). In this study, the proposed system on solar–wind-based hybrid energy approach has been examined primarily through the strategy of DPFC mechanism. Later, the system has been examined with Genetic Algorithm (GA)-based fuzzy logic controller and GA-based adaptive neuro fuzzy inference system controller for shunt control of context built with DPFC mechanism. Furthermore, the validated results are verified using MATLAB/Simulink software.

A Novel High Impedance Fault Detection Strategy for Microgrid Based on Differential Energy Signal of Current Signatures and Entropy Estimation

The non-linearly deterministic fault current characteristics with low current magnitude of high impedance fault (HIF) have thrown an inevitable challenge to the microgrid protection system. Moreover, differentiating HIF from non-fault events is also a challenging task under different operating scenarios of the microgrid. In order to address this, a simple and fast protection algorithm, based on Empirical Mode Decomposition (EMD) in conjugation with Teager-Kaiser Energy Operator (TKEO) is proposed in this article. This scheme process the current signals retrieved from both ends of the line through EMD, and subsequently, the current signal energy is extracted by TKEO. The incidence of a fault is affirmed by measuring the energy difference signal and estimation of entropy. By employing the second layer algorithm using entropy analysis, the non-fault disturbances, such as capacitor and load switching, temporary overloading, and DG outage, have been effectively distinguished from HIFs. The proposed technique is tested for grid-tied and autonomous microgrid operation modes with several HIF and non-fault cases. It is inferred that the proposed technique can detect and differentiate HIFs from other system perturbations seamlessly in less time. Compared to other methods, this scheme has procured excellent accuracy and reliability, and is also not affected by the dynamic current behavior of the microgrid. The PSCAD-EMTDC software is used to build and simulate the test system, and the MATLAB programming interface is utilized to develop and test the suggested method.

Protection coordination of DOCRs for different modes of microgrid operation

The present study is focussed on solving the relay coordination problem. Protection of microgrids is performed through the placement of directional overcurrent relays (DOCR). The efficacy of microgrid protection depends on coordination of all the DOCRs placed in the system. For this purpose, a number of optimization techniques have been employed by the power system researcher. In this paper, Grey Wolf Optimizer (GWO) is proposed for the protection coordination of DOCRs for different modes of microgrid operation. The proposed method is tested and validated on a 7-bus mesh system and a 9-bus radial test system. The proposed method has been compared with other meta-heuristic optimization approaches, namely Genetic Algorithm (GA), Artificial Bee Colony (ABC), Gravitational Search Algorithm (GSA), and Hybrid Particle Swarm Optimization Gravitational Search Algorithm (PSOGSA). Based on the obtained results, the GWO-based approach is very efficient in mitigating the problem of relay coordination as compared to other optimization techniques.

Superimposed current based differential protection scheme for AC microgrid feeders

Legacy protection schemes face numerous challenges with the emergence of microgrids. Due to the complex controls, the fault responses in microgrids differ from conventional behaviour and vary with the operation mode. In this paper, a differential protection scheme based on fundamental frequency superimposed current phasors is proposed for microgrid feeders. The phasors are extracted using dq components instead of conventional Fourier algorithms. The performance of proposed method is tested for different fault scenarios by carrying out simulations in MATLAB/SIMULINK software. The results confirm that internal faults are detected in a few milliseconds. At the same time, the scheme remains insensitive to external faults with CT saturation and other system disturbances. The proposed scheme is unaffected by the microgrid mode of operation, direction of power flow and DG type.

Distributed power flow controller based on fuzzy-logic controller for solar-wind energy hybrid system

The demand of electricity globally led to the concept of renewable energy resources for power generation that are eco-friendly and freely available from nature. The solar photovoltaic systems and wind-based power generators are considered as primary renewable resources and are called as Distributed Generation units as they are scattered in nature. These are operated with bidirectional converters by providing auxiliary services at grid side and load side in either mode of microgrid operation. Besides, the DC power generation units’ integration gets converted into AC system by means of inverters. These types of systems not only increase voltage and current harmonics, power frequency deviations but also drive the distribution system to risky operating zone. This emphasizes the stipulation of advanced control schemes for microgrid architecture. Consequently, power electronic converters introduce harmonics in the system and affect the system performance. To report these expanded issues, the authors recognized an advanced custom power device entitled distributed power flow controller. The proposed hybrid solar-wind energy system is first studied with a distributed power-flow controller. Later the system is examined by replacing proportional integral controller with fuzzy logic controller (FLC) for shunt control of distributed power-flow controller. To validate the investigations, MATLAB/Simulink software is used.

Boost-converter reliability assessment for renewable-energy generation systems in a low-voltage DC microgrid

Renewable-energy-based generating systems like photovoltaic (PV) systems, and energy storage devices like batteries are mostly considered as two types of main generation sources for the islanded operation mode of a low-voltage DC microgrid (LV-DC MG). Dynamic characteristics of the off-grid LV-DC MG, for instance, fluctuation in load power or frequent changes in the PV-system output power; as well as transient characteristics such as DC faults, and switching actions of power devices may reduce the converters’ reliability. To explicate the viewpoints mentioned, this paper will evaluate the reliability of DC-DC step-up converters used for renewable energy-based generation systems, typically for the PV systems of the LV-DC MG from different dynamic and fault conditions. To perform the reliability analysis, the dynamic-voltage-dependent (DVD) failure rate (FR) and fault-current-dependent (FCD) failure rate of the PV-system step-up converter will be formularized. More clearly, the assessment of step-up converter reliability and its discrete components is based on a new combination of the used-time-dependent (UTD) failure rate, FCD-FR, and DVD-FR and the use of a Markov-state transition diagram. Experimental results illustrate that the output capacitor of the boost converter is greatly influenced by the transient and dynamic characteristics of the PV-generating system. The DVD-FR of the boost converter is quite small when compared to its FCD-FR. Moreover, the PV-system boost converter’s reliability is most rapidly decreased by multiple repeated dynamic cases when the LV-DC MG is in the islanded mode. In addition, when considering both dynamic and transient characteristics of the LV-DC MG, two indices, namely, mean-time-to-failure (MTTF), and mean-time-between-failures (MTBF) of the PV-system boost converter could also be quickly reduced.

Differential Protection Scheme for A Micro Grid with Inverter-Type Sources Based On Positive Sequence Fault Currents

The microgrid (MG) is a coordinated collection of different distributed generation (DG) typesthatsupply local demandthrough a distribution network. MG may operate in two different modes: grid-connected (GC), and islanded (IS)modes.The fault current valuevaries significantly between the GC and IS mode for a MG with inverter-based distributed generators(IBDGs). The fault currents are minimal in the IS mode owing to the power electronics equipment have a limited current carrying capacity. Therefore, the coordination of traditional overcurrent (OC) protection is difficult for these two operation modes. Therefore, a comprehensive MG protection scheme should be established to safeguard MG against all kinds of faults. The main protection strategy proposed in this paperis a positive sequence differential current protection scheme. The envisioned concept can overcome the protective device coordination problems, and all fault types can be detected during both operation modes of MG for radial andloop configurations. The validation of the proposed design is performed using PSCAD/EMTDC software. The results indicate that the maximum fault clearing time for the main protection in GC mode and IS modeisof 31.5 ms and 34 ms respectively. Compared with other schemes, the proposed scheme has a faster clearing time and is less expensive.

A NEW METHOD TO ENHANCE THE DIFFERENTIAL PROTECTION OF THE MICROGRID BY SELF-BACKUP PROTECTION

Although the differential protection schemes consider as one of the effective types to protect the microgrid, this method may result in inaccurate performance because of the loss of communication link connecting the two ends of the line or other reasons. Therefore, the use of backup protection can lead to more accurate results. In this paper, self-backup protection is presented to cover the mal-operation of main protection. In this scheme, a new R-ratio method is defined based on the summation of the three-phase currents and the minimum of the three-phase voltages to overcome the low fault current during the islanded microgrid. The proposed scheme can detect all fault types during both operation modes of microgrid, grid-connected and islanded for radial and loop configuration. The validation of the proposed scheme is performed using PSCAD/EMTDC software. The simulation results proved that the proposed scheme could provide adequate protection against various fault types in grid-connected and islanded operation modes for a radial and loop configuration.

Bridge-to-Bridge Independent Control Method for Dual-Active-Bridge Interlinking Converter

In dual-active-bridge (DAB) converters, the driving-synchronization signal is supposed to be required to be transmitted across the primary bridge and the secondary bridge to realize a phase shift for power flow. In this letter, a novel bridge-to-bridge independent (B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I) control method is proposed. In this control method, cross-bridge transmission of sampling/driving signals is not required. Thus, full modularity of each side in the DAB converter was realized. B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I control is suitable for high-voltage series low-voltage parallel (HSLP) modular DAB interlinking converter in medium-voltage dc applications because: first, the bridge-level modularity of B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I control benefits electromagnetic compatibility and insulation design with the HSLP connection; second, B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I control features series-side voltage sharing; and third, B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I control can adapt for various operation modes of microgrids.

Polymorphic Distributed Energy Management for Low-Carbon Port Microgrid With Carbon Capture and Carbon Storage Devices

In order to reduce the carbon emission of the port and build a green port, a polymorphic distributed energy management method for the low carbon port microgrid with carbon capture and carbon storage device is proposed. Firstly, this paper presents a low carbon port microgrid in a polymorphic network environment to realize the information interaction among energy subjects in different modes and improve network communication performance among port power generation device, main grid, carbon capture and carbon storage device. Secondly, the energy management model of low-carbon port microgrid is constructed considering the additional carbon capture device and carbon storage device in the port. Then, based on the multi-agent consensus algorithm, a distributed energy management method is proposed, which is respectively oriented to the grid-connected operation mode, island operation mode and switching operation mode of the port microgrid, so as to achieve the economic, low carbon and reliable operation of the port microgrid. Finally, the simulation results of Matlab verify the effectiveness of the proposed method.

Research on coordinated control strategy of isolated DC microgrid with PV/hybrid energy storage

During the operation of DC microgrid, energy storage system plays an important role in supplying the power difference between distributed generation unit and load and maintaining the voltage stability of DC bus, in recent years, hybrid energy storage technology has gradually attracted the attention of researchers. In this paper, a power distribution control strategy of hybrid energy storage system (HESS) is studied. The droop control based on virtual capacitor is used for the converter of supercapacitor (SC) to realize the power distribution in HESS, and the control strategy is improved to solve the problem that the deviation of bus voltage caused by droop control. Based on the control strategy of HESS, a coordinated control strategy of isolated DC microgrid is studied. By considering SOC of battery and the power demand of load, 3 operation modes of DC microgrid are set. DC microgrid can work in a designated mode under various conditions to achieve efficient and stable operation. Finally, the theory of the above control strategies is verified by the simulation work in RTDS and hardware-in-the-loop experiment based on DSP28335 and RTDS.