Intelligent Islanding Classification with MLPNN for Hybrid Distributed Energy Generations in Microgrid System

This paper presents ancillary voltage control for a distribution feeder by using energy storage system (ESS) in microgrid. The microgrid consists of photovoltaic, wind power, and distribution generator. The active and reactive power control, voltage and frequency droop control for the power converter of ESS are proposed to reduce microgrid impact on the distribution feeder. The voltage variation along the feeder due to change of renewable power generation is derived by executing power flow analysis. The actual voltage fluctuation on the microgrid is measured, which is used to control active and reactive power output of the power converter via energy management system in the microgrid SCADA platform. Three operation scenarios of the microgrid with ESS are tested to verify the effectiveness of the proposed control method. It is found that the power output of ESS can be well regulated to reduce voltage fluctuation on the microgid, which is complied with grid connect code to achieve better voltage control performance for the distribution feeder.

Improved particle swarm optimization for photovoltaic system connected to the grid with low voltage ride through capability

A microgrid (MG) is a discrete energy system consisting of an interconnection of distributed energy sources and loads capable of operating in parallel with or independently from the main power grid. The microgrid concept integrated with renewable energy generation and energy storage systems has gained significant interest recently, triggered by increasing demand for clean, efficient, secure, reliable and sustainable heat and electricity. However, the concept of efficient integration of energy storage systems faces many challenges (e.g., charging, discharging, safety, size, cost, reliability and overall management). Additionally, proper implementation and justification of these technologies in MGs cannot be done without energy management systems, which control various aspects of power management and operation of energy storage systems in microgrids. This review discusses different energy storage technologies that can have high penetration and integration in microgrids. Moreover, their working operations and characteristics are discussed. An overview of the controls of energy management systems for microgrids with distributed energy storage systems is also included in the scope of this review.

The rapid expansion of offshore wind energy and its integration into weak power grids have introduced significant challenges to system stability, particularly under fault conditions that cause voltage sags. Ensuring adequate Low Voltage Ride Through has become essential for maintaining grid reliability and preventing large-scale disconnections of wind farms.To address voltage sags caused by short-circuit faults during the grid integration of large-capacity offshore wind farms via weak networks, this paper establishes a simulation model of a permanent magnet synchronous generator (PMSG)-based offshore wind farm in the PSAT platform. Taking the Critical Clearing Time (CCT) as the core evaluation index, the Low Voltage Ride-Through (LVRT) capability is systematically assessed. By simulating short-circuit disturbances, the transient voltage response at the point of common coupling is analyzed, followed by a comparative evaluation of the voltage support effects of three dynamic reactive power compensation devices: Static Var Compensator (SVC), Static Synchronous Compensator (STATCOM), and Unified Power Flow Controller (UPFC). Results indicate that the rational configuration of dynamic reactive power compensation effectively mitigates voltage drops, significantly extends the CCT, and enhances transient stability margins. The distinct response characteristics and support efficacies of different devices are clarified, providing a theoretical foundation for optimizing LVRT strategies and selecting compensation equipment in offshore wind integration.

In this paper, a comprehensive review of several strategies applied to improve the Low Voltage Ride-Through (LVRT) capability is presented for grid-connected wind-turbine-driven Doubly Fed Induction Generator (DFIG). Usually, themost proposed LVRT solutions in the literature based on: hardware solutions, which increase the system costs and software solutions, which increase the control system complexity. Therefore, the main objective of this study is to take into account grid requirements over LVRT performance under grid fault conditions using software solution based on Higher Order-Sliding Mode Control (HOSMC). Effectively, this control strategy is proposed to overcome the chattering problem and the injected stator current harmonics into the grid of the classical First Order Sliding Mode (FOSMC). Furthermore, the resultant HOSMC methodology is relatively simple; where, the online computational cost and time are considerably reduced. The LVRT capacity and effectiveness of the proposed control method, compared to the conventional FOSMC, are validated by time-domain simulation studies under Matlab on a 1.5MW wind-turbine-driven DFIG.

The microgrid represents a controllable electric entity that contains different loads into distributed energy resources. All typical microgrids use two or more sources by which electricity is generated, at least one of which is a renewable source. In this respect the main issues of the energy storage systems (ESS) are the enhancing of the stability of microgrid and power balance. Also the insertion of the energy storage systems is beneficial for both operation modes of microgrids, grid connected and islanded. This chapter begins with an overview of the current state of microgrids and ESS. The island operation mode of microgrids is based on the energy storage system. At the first level the control tasks during this mode of operation are to regulate the voltage and to maintain the frequency at the constant value. The power in each unit is shared among the storage units by secondary control of the energy storage system taking into account the energy level of each of them. Further, the authors present storage technologies of the electrical energy, i.e. converting it into mechanical, chemical, electrochemical, electromagnetic and thermal energy. The widespread mechanical energy storage technology is the pumped hydro (99% of the world total storage capacity) followed by the compressed air energy and flywheel. Afterwards, the fuel cell, biomass and fossil fuel compose the chemical storage domain. Batteries constitute the electrochemical storage technology. Electromagnetic and thermal energy storage technologies are represented by the super capacitors respectively the heat pumps. Both the features of the energy Storage technologies and the main properties will be presented. A comparison of the discharge time of the storage technologies by application is taken into account. The advantages and disadvantages of the storage technologies will be highlighted. The lack of the appropriate standards of interconnecting different kinds of energy sources and ESS to the microgrid is a disadvantage in technology developing. Thereby the IEC/ISO 62264 standards refers to wind turbine technology, while the IEEE 2000 standard refers to photovoltaic interconnection power systems. In order to reduce air pollution and mitigate climate change, in recent years the need to use renewable energy sources in microgrids has become important. In fact, technological development, public and political policies, availability of different renewable energy resources to be used in microgrids, are elements that create real perspectives in widespread development of renewable energies and their required ESS. The environmental impact and the costs of renewable energy resources have been estimated through the life cycle assessment (LCA) methodology, which determines whether the use of renewable sources and ESS is sustainable. A case study regarding a PV system with and without batteries used into a microgrid that supply a wastewater treatment plant situated in Romania will be presented. Life cycle assessment was used to quantify ecological sustainability and costs in both cases compared to a conventional supply of electricity from the grid. Conclusions and measures are drawn in order to increase the utilization of renewable sources and ESS in microgrids. Also the technically, economic and environmental benefits of inserting microgrids are discussed. The bibliographic references will be presented at the end of the chapter.

The low voltage ride-through (LVRT) capability of the doubly-fed induction generator (DFIG) significantly impacts upon the integration of wind power into the power grid. This paper develops a novel comprehensive control strategy to enhance the LVRT and reactive power support capacities of the DFIG by installing the energy storage system (ESS). The ESS is connected to the DC-link capacitor of the DFIG and used to regulate the DC-link voltage during normal or fault operations. The unbalanced power between the captured wind power and the power injected to the grid during the transient process is absorbed or compensated by the ESS. The rotor-side converter (RSC) is used to control the maximum power production and the grid-side converter (GSC) is used to control the reactive power before participating in the voltage support. When the supply voltage continues to drop, the rotor speed is increased by controlling the RSC to realize the LVRT capability and help the GSC further enhance the reactive power support capability. The capacity of the GSC is dedicated to injecting the reactive power to the grid. An auxiliary transient pitch angle controller is proposed to protect the generator’s over speed. Both RSC and GSC act as reactive power sources to further enhance the voltage support capability with serious voltage sags. Simulations based on a single-machine infinite-bus power system verify the effectiveness of the developed comprehensive control strategy.

Analyzing low voltage ride through capability of doubly fed induction generator based wind turbine

This study explores the management of a system of multiple interconnected microgrids in a loop configuration. To facilitate renewable integration and reduce the cost of operation, an economic dispatch model of the distributed energy resources (DER) with dynamic update of the states of the energy storage systems (ESS) to handle the forecasting error in the photovoltaic (PV) power output is developed. By simulating the economic dispatch of DER for various PV output profiles, the minimum size of ESS required in a microgrid can be determined. The sizing and placement of ESS in a loop configuration, be it one ESS for each individual microgrid or one ESS for the whole interconnected system, are also explored. The case study conducted found that the total capacity of the ESS for the interconnected microgrids in a loop configuration with a single shared ESS is smaller than that for the loop configuration with individual ESS, which is in turn smaller than that for the islanded mode.

CHP system with Energy saving, environmental protection, economic and other characteristics,have good prospects for the development and application value.This paper directe a micro grid system consisted by photovoltaic cells, wind turbines, fuel cells, microturbines, auxiliary boilers, thermal energy storage systems and batteries and heat load and electrical load.Considering various distributed power generation costs, environmental costs and micro-grid equipment maintenance costs,To meet the constraints of micro-grid operation, optimization of the different micro-grid distributed power and energy storage system power output, make the system's total operating costs are minimized.This paper analyzes the economic and environmental of micro-grid optimal operation characteristics, given a model of CHP micro-grid.For the cost of power generation and emissions of different weights, using bacterial foraging optimization(BFO) algorithm,through a numerical example verified the Correctness and effectiveness of mathematical model and optimization algorithm .

As the wind power penetration is increasing rapidly into the power grid, modern gird codes require the wind turbines (WTs) to possess the low voltage ride-through (LVRT) capability. In order to evaluate the performance of a WT under grid fault conditions, a voltage sag generator (VSG) is needed to simulate all kinds of grid faults. This paper investigates a three-phase programmable VSG based on a voltage source inverter (VSI). A novel dual-loop proportional integral resonant (PIR) controller with a zero sequence voltage compensation scheme is applied to control the VSI, so that the four kinds of possible grid voltage dips can be precisely simulated. The effectiveness of the proposed VSC is validated by the experimental results.

This paper investigates the control and operation of permanent magnet synchronous generator (PMSG)-based wind generation systems employing the full-scale frequency converter under network fault conditions. The factors inducing the oscillations of DC-link voltage of the full-scale frequency converter during grid voltage dips are analyzed. A novel control strategy is proposed to suppresses the DC-link voltage oscillations and enhance the low voltage ride-through (LVRT) capability of PMSG-based wind turbine. The generator-side converter is controlled to maintain a stable DC-link voltage, while the grid-side converter is controlled to provide a dynamic coordinated control for the active and reactive power output according to the grid voltage amplitude variations during grid faults. The simulation results implemented in Matlab/Simulink show that the proposed control strategy not only improves the stability of PMSG by means of suppressing the DC-link voltage oscillation, but also provides a dynamic reactive power support to restraint the disturbance of the grid voltage. (5 pages)

Low voltage ride-through (LVRT) capability curve describes the power grid requirements where generators must continue in operation through short time period of voltage depression and must not disconnect from the power grid unless the specified time has exceeded. This paper presents a conceptual design of the LVRT capability curve for a distributed generator (DG) by taking system relay coordination into consideration. Protective relay models have been incorporated into the transient stability analysis using the dynamic time-domain simulation. The benefits, gained from the LVRT capability imposed on the DG, in terms of dynamic voltage support, are illustrated using a practical small-scale hydro generator connected to a distribution grid.

This paper presents an overview of the state of the art control strategies specifically designed to coordinate distributed energy storage (ES) systems in microgrids. Power networks are undergoing a transition from the traditional model of centralised generation towards a smart decentralised network of renewable sources and ES systems, organised into autonomous microgrids. ES systems can provide a range of services, particularly when distributed throughout the power network. The introduction of distributed ES represents a fundamental change for power networks, increasing the network control problem dimensionality and adding long time-scale dynamics associated with the storage systems' state of charge levels. Managing microgrids with many small distributed ES systems requires new scalable control strategies that are robust to power network and communication network disturbances. This paper reviews the range of services distributed ES systems can provide, and the control challenges they introduce. The focus of this paper is a presentation of the latest decentralised, centralised and distributed multi-agent control strategies designed to coordinate distributed microgrid ES systems. Finally, multi-agent control with agents satisfying Wooldridge's definition of intelligence is proposed as a promising direction for future research.

The doubly-fed induction generator (DFIG) based wind energy conversion system (WECS) is a mature and promising renewable energy solution amid growing global energy demand. As supply reliability and system resiliency become increasingly important, low voltage ride-through (LVRT) capability has become mandatory for such systems. During a voltage dip at the AC bus, where the WECS delivers power, it must stay connected and aid voltage recovery by supplying reactive power, as per local grid standards. While ON-grid LVRT strategies have been extensively researched, OFF-grid LVRT operations have received little attention. For greater source reliability, WECSs should also operate in OFF-grid mode, where similar voltage dip issues can arise. This paper proposes a hybrid LVRT strategy for DFIG-WECS in OFF-grid mode. A battery energy storage system (BESS) maintains the DC bus voltage, while a grid-forming converter (GFC) holds the AC bus voltage with its limited current capacity. The DFIG rotor disconnects from the rotor side converter (RSC) and connects to a crowbar during the voltage fall and rise period. Between these two periods, the DFIGRSC provides reactive power. The method is validated using a MATLAB/SIMULINK model in an OPAL-RT real-time simulation, demonstrating that under different wind velocities, the OFF-grid DFIG-WECS withstands different levels of voltage dips while supporting voltage recovery. Keywords-battery energy storage system (BESS), doubly fed induction generator (DFIG), grid forming converter (GFC), low voltage ride through (LVRT), vector control (VC), wind energy conversion system (WECS)