Control of power electronic interfaces in distributed generation microgrids

Microgrid is an interconnection of renewable energy sources, loads, power electronic interfaces and energy storage devices. Renewable energy sources are intermittent in nature, and therefore, there is a need for energy storage devices to ensure continuous power supply to the load. Power electronic converters are required to interface the DC bus with energy storage devices. In this work, a bidirectional interleaved switched capacitor DC–DC converter is proposed as a power electronic interface for microgrids. The renewable energy source supplies energy to the load and charges the energy storage device when it is available. The stored energy in the energy storage device supplies energy to the load when the renewable energy source is not available. This is achieved by the proposed converter as it operates bidirectionally. The interleaving technique is carried out at the input side of the converter which reduces the input current ripples. The proposed converter has the following advantages: (i) reduction of ripple current, (ii) reduced voltage stress and (iii) extensive voltage gain and efficiency. It operates in both boost (step-up) and buck (step-down) mode. A 3 kW solar-powered microgrid with bidirectional interleaved switched capacitor DC–DC converter is designed and simulated in MATLAB. The simulation results are associated with the theoretical results obtained from MATLAB.

A resilience-oriented optimal planning of energy storage systems in high renewable energy penetrated systems

Grid-connected voltage-source inverters (VSIs) have evolved over the past years for the interconnection of renewable energy sources with the grid to satisfy the increased electrical load demand and utilize clean carbon-free energy. However, VSIs suffer a significant drawback of switching harmonics caused by the inverter switches. To reduce the amount of current distortion injected into the utility grid and meet harmonic constraints as defined by power quality standards, an LCL filter is often used. Although extensive literature describes assorted design procedures for an LCL filter, all these methods cannot guarantee an optimal solution, because no direct mathematical function between the LCL filter parameters and the total harmonic distortion (THD) exists. Presented in this paper is the application of an evolutionary annealing–simplex method to select the inductance values in the LCL filter. This method is compared to other methods previously presented in the literature: a systematic method and an inductance grid-search method based on a calculated distribution of total harmonic distortion for various inductance values. The goal is to select the smallest overall inductance values to ensure lower manufacturing costs while maintaining the filter performance. Simulation and experimental results verify that at least a 40% reduction in overall inductance can be achieved with the proposed method while simultaneously guaranteeing the filtering performance.

Recently, demands on MVDC distribution system is being significantly increased due to interconnection of renewable energy sources, expansion of DC load and high quality and reliability of the power supply system etc., while commercialization of facilities for MVDC is yet in early stage. Accordingly, demonstration projects on applying existing AC devices and cables to MVDC distribution system are being carried out. However, the protection on high-cost facilities such as converters and cables may not be reliable in the event of fault, and then operation method of protection coordination for MV-LVDC micro grid(MG) system is being required. For the purpose of stable operation of the 5kV MV-LVDC micro-grid, this paper proposes operation methods of protection devices depending on scenarios, such as faults on the MVDC line, LVDC line, or customer load. And also, a modeling of 5kV MV-LVDC MG system, which is composed of PV system, ESS, MVDC cable, DC/DC converter, DC/AC inverter, protection devices etc., is performed using PSCAD/EMTDC S/W. From the simulation results based on the proposed modeling and operation method of protection devices, it is confirmed that this paper is useful tool to perform the proper protection coordination.

DC line faults raise significant concerns in multiterminal high voltage direct current (MTDC) networks. The fault current ascends rapidly with a sharp peak, but isolating the entire faulty part is a non-sustainable solution for this matter. Therefore, rapid detection and classification of faults with high accuracy is indispensable. In this paper, a protection scheme is presented to protect MTDC networks based on voltage source converter (VSC) for interconnection of renewable energy sources, which incorporates main protection and post fault analysis. The main protection uses the Successive Data Window Technique (SDWT) as a fault detector, later on verifying it with the harmonics of the system voltage so as to prevent maloperation of the breakers, while the post fault analysis makes use of the voltage drop to classify the nature of fault, in addition to providing a backup in case the prior fails. The simulations results validate the protection scheme, which precisely identifies the fault and classifies its nature effectively. The performance of the proposed scheme is evaluated in PSCAD for MTDC networks. Matlab also verifies the results making this scheme a promising one.

Fault detection is essential in microgrid control and operation, as it enables the system to perform fast fault isolation and recovery. The adoption of inverter-interfaced distributed generation in microgrids makes traditional fault detection schemes inappropriate due to their dependence on significant fault currents. In this paper, we devise an intelligent fault detection scheme for microgrid based on wavelet transform and deep neural networks. The proposed scheme aims to provide fast fault type, phase, and location information for microgrid protection and service recovery. In the scheme, branch current measurements sampled by protective relays are pre-processed by discrete wavelet transform to extract statistical features. Then all available data is input into deep neural networks to develop fault information. Compared with previous work, the proposed scheme can provide significantly better fault type classification accuracy. Moreover, the scheme can also detect the locations of faults, which are unavailable in previous work. To evaluate the performance of the proposed fault detection scheme, we conduct a comprehensive evaluation study on the CERTS microgrid and IEEE 34-bus system. The simulation results demonstrate the efficacy of the proposed scheme in terms of detection accuracy, computation time, and robustness against measurement uncertainty.

Microgrids have benefited energy systems by getting rid of the abundant use of traditional energy resources, replacing them with distributed generations (DGs). The use of DGs in microgrids not only provides clean and green energy but also reduces the gigantic losses in transmission and distribution lines. Widespread adoption of renewable energy in microgrids saves customers from high fuel prices and provides a sustainable replacement for future fossil fuel depletion. Microgrids have proven to be the latest and most advanced power systems due to their new capabilities to operate in both grid-connected and isolated modes. Microgrids use multiple energy sources simultaneously, which can offset the intermittent behavior of renewable energy sources. In this study, we planned and optimized an industrial microgrid with an annual increase in load, which contains dispatchable generation, non-dispatched generation, and energy storage. In addition, to test the different behavior of a microgrid operating independently or in grid-tied mode, four typical days were selected to show the load demand and solar and wind energy forecast data for the entire year. The power output curves for each typical day were analyzed for every year in both stand-alone and grid-connected modes. Furthermore, to validate the feasibility of the microgrid, the investment and operations costs were also calculated in the paper.

The microgrid concept provides a flexible power supply to the utility where the conventional grid is unable to supply. The microgrid structure is based on renewable energy sources known as distributed generators (DGs) and the power network. Nevertheless, the power quality (PQ) is a great challenge in the microgrid concept. Particularly the inclusion of renewable energy sources into the conventional grids increases the problems in the quality of power, like voltage sag/swell, oscillatory transient, voltage flickering, and voltage notching which reduces the quality and reliability of the power supply. In this paper, a microgrid is considered which consists of PV cells as DG, battery energy storage system (BESS), and a novel control strategy known as the nonlinear autoregressive exogenous model (NARX). The proposed controller is an improved artificial neural network (ANN). The various case studies like sag/swell, unbalanced condition, and voltage deviation have been simulated with the model. The comprehensive simulation results are compared with the proportional-integral (PI) controller. Hence in this paper, the robustness of the proposed controller has been studied through different situations.

This paper introduces the setup of a Distributed Generation Microgrid (DGM) focused onto research on monitoring (electrical and environmental), controling and operating microgrids. This network is located at the Polytech Center Campus of the Federal University of Parana (UFPR), in Curitiba, Brazil. It consists of nine 13.8 kV feeders, three Distributed Generation (DG) sources and is connected to the main utility through a 69 kV distribution substation of the state electricity company named as Copel DIS. In addition to the electrical configuration, all components of the microgrid are presented, such as power generation, electrical and environmental meters, $\mu \mathrm{PMU}$ and the system monitoring computing environment.

This paper expands the conventional concept of microgrids — predetermined groups of loads and generators electrically connected to each other and possibly to the main power grid — into a new concept of dynamic microgrids (DMs) which allows different groupings of these resources based on actual real time supply and demand conditions in the network. Under the DM paradigm, the distribution network is continuously partitioned into dynamically changing microgrid cells which can be leveraged to improve the operational performance of distribution networks. The paper describes algorithms to define DMs based on real time conditions and also proposes a DM-based operational strategy wherein DMs operate in tandem during normal operations and can function as islands during faults to minimize customer interruptions. Simulations on standard test systems are used to demonstrate how such a strategy can be leveraged to minimize the impact of disturbances on customers, maximize the deployment of renewable generation and improve asset utilization.

Problem of frequency regulation in an AC system is a major challenge in modern power system. Recently due to considerable growth of renewable energy sources and distributed generations, the concept of microgrid is gradually more being used. But, renewable energy sources (RESs), forming a MG, are by nature having unpredictable variations of their power output. The system disturbances occurs either from generation side or from load side causes uncertainties in power output which make it difficult for the conventional controllers to provide good dynamic performance over an extensive variety of working environment. This paper addresses the microgrid system with respect to load disturbances and proposes a fuzzy gain schedule proportional-integral-derivative (FGSPID) controller and for relative investigation, the traditional PID controller is additionally executed on the same microgrid framework. Simulation response validates that the frequency response of the microgrid system has enhanced significantly with the application of FGSPID controller as compared to conventional controller.

The concept of microgrid is invented to harmonize local electricity production and consumption. The increasing interest on microgrids is caused by the considerable growth of renewable energy sources (RES) and distributed generation (DG). In a large geographical region, there can exist multiple microgrids. Many academic articles have reported the technicalities of microgrids operating in islanded mode, and few have analyzed their aggregated technical/economic impacts or benefits on the network in a larger region. Deregulation encourages RES to participate in energy markets to facilitate competition among different energy providers. Apart from participating in energy markets, an alternative way of making use of and making profit out of multiple microgrids is to take part in the ancillary-service market. This paper investigates the technical aspects of providing frequency control reserves (FCRs) and the potential economic profitability of participating in FCR markets based on a setup of multiple microgrids. In particular, it has a focus on the communication aspects under different market scenarios, i.e., decentralized or centralized coordination approach, for FCRs with the assumption of the possible aggregation of reserve provision from multiple microgrids (microsources and flexible loads).

The concept of microgrid (MG) in the field of power engineering rapidly adapted for the rapid improvement in power electronics technology. Due to the benefit of such a distribution system with direct current (DC) minimum losses and simple to integrate with an electrical energy storage system DC MG have attracted more attention these days. DC MG is a hot research topic consists of various sources due to the expansion of distributed generation. The critical issue is to dispense regulated voltage support and accurate power-sharing capability in such a multisource DC MGs. Since the control scheme plays an essential role in establishing premier power quality and high efficiency of MG, a thorough review of trending control methodology in DC MGs is required. This paper explains the primary control methodology within the hierarchical control architecture for DC MGs.

With the growing need for energy, the concept of Microgrids (MG) with notable benefits for both production and demand sides was introduced. An MG consists of distributed generation units (DG), Energy Storage Systems (ESSs), and loads. It can operate either connected to the grid or in islanded mode. In the case of a fault or a disturbance, MG can be isolated from the main grid. Then, due to the imbalance between production and consumption, the MG frequency will deviate from the standard value. This makes the MG frequency will deviate from the standard value. The most important issue in the transition from connected to disconnected mode is to fix the disconnected MG frequency. This frequency deviation and its attenuation rate are of high importance for the demand side. To improve MG performance, MGs can be connected through a back-to-back (BTB) converter and form a multi-MG (MMG). Local DC resources are connected to their MG through an inverter, while other AC generations are directly connected to the MG. This article investigates the effects of MMG operation on each MG performance. It also examines the role of each MG in maintaining the balance between production and consumption in the MMG structure. It is assumed that each MG has at least one Micro-Turbine (MT) containing excitation control for its voltage regulation. Simulations are carried out in MATLAB Simulink environment to study frequency fluctuations. It is shown that the cooperation of the MGs can improve the performance of the MMG system.

ABSTRACTIn recent years, the concept of micro-grid has appeared as an appropriate way for the integration of Distributed Energy Resources (DERs) in the distribution networks. However, micro-grids have encountered a number of challenges from control and protection aspects. One of the main issues relevant to the protection of micro-grids is to develop a suitable protection technique which is effective in both grid-connected and stand-alone operation modes. This article presents a new micro-grid protection strategy based on positive-sequence impedance using Pha-sor Measurement Units (PMUs) and a designed Microprocessor-Based Relay (MBR) along with a narrowband communication system (only to exchange digital information, not electrical power). The main attribution of the proposed scheme is that it has the ability to protect micro-grids containing either radial or looped feeders; additionally, the capabilities of automatic updating of pick-up threshold value and single-phase tripping have been considered in the...