Grid-connected Generation System Research Articles

Short-term wind power output prediction using hybrid-enhanced seagull optimization algorithm and support vector machine: A high-precision method

ABSTRACT Affected by the uncertainty of external environmental factors, wind power generation has significant characteristics of randomness and non-stationarity. Accurately predicting wind power is a necessary technical means to improve the efficiency of wind energy utilization and reduce wind abandonment. Integrating large-scale wind power into the grid has put higher requirements for wind power prediction accuracy. Hence, this study proposes a combined prediction model based on wavelet denoising (WD), hybrid enhanced seagull optimization algorithm (HESOA) and support vector machine (SVM) to predict short-term wind power. The WD technology obtains effective signals from original wind power data, providing a reasonable basis for prediction research. The HESOA is proposed by introducing the Tent mapping, individual self-learning factor and Gaussian population strategy into the original seagull optimization algorithm to optimize SVM’s prediction ability. The case study results reflect that the prediction method is feasible and universal in suppressing wind power generation volatility in spring and winter. The RMSE of short-term wind power prediction is controlled below 65 kW, and the value of R2 is above 98%. This study improves the accuracy of wind power prediction and helps to strengthen the renewable energy consumption level and reliability of wind power grid-connected generation systems.

Design of sustainable offshore hybrid energy systems for improved wave energy dispatchability

Wave energy is a renewable energy source having a highly exploitable potential in several locations worldwide. In the framework of energy transition, the exploitation of wave energy combined with end-of-life offshore stranded gas reservoirs may lead to two positive impacts: the stabilization of the energy supplied to the grid and a better penetration of renewable energy in areas where the grid is not able to compensate the fluctuations associated to renewable energy production. Moreover, in order to guarantee the dispatched energy schedule, wave energy needs to be coupled with back-up systems aimed at valley filling. In the present study, an innovative approach to the conceptual design of hybrid energy systems based on wave energy is developed, entailing an operation strategy that complies with the dispatching needs of grid-connected generation systems. The probability of correct dispatching that the producer assures to the Transmission System Operator is used as a parameter to optimize the design of a Gas to Power back-up system used for valley filling. The approach supports the preliminary design of offshore hybrid energy systems based on wave energy, starting from historical wave data up to the definition of an optimal back-up system valorizing residual reservoir fuels and its operation strategy. The proposed design is evaluated through a Multi-Criteria Decision Analysis, including the technological, economic, environmental and safety aspects, which allows the assessment of the overall sustainability performance of the hybrid system, considering the fluctuations associated to wave power generation during a typical operation period. The methodology was applied to two test-cases in different offshore operating theaters (North and Adriatic seas), in order to test its potentiality. The results highlighted that, in both sites, similar design choices are suggested for the hybrid system. However, the annual energy production resulted 6.5 times higher in the North Sea test-case. The low energy generation in the Adriatic Sea test site caused a levelized cost of energy of 3960 EUR/MWh, much higher than the value obtained for the North Sea case (610 EUR/MWh). In both cases, the gas turbine park impacts negatively on the cost of energy production, but is critical in meeting the design value of the probability of correct dispatching.

Sliding Mode Resonant Controlled Step up Coupled Inductor fed DC-DC converter with Gallium Oxide Semiconductor Material

Resonant controlled step up coupled inductor fed DC-DC converter has received a lot of consideration in gridconnected generation systems using fuel cells or photovoltaics. The main subjects of this work are Open loop and closed loop design, modelling, and simulation on a resonant controlled step up coupled inductor fed DC-DC converter with a proportional integral (PI) controller and sliding mode controller (SMC).The findings are compared and analyzed using time domain aspects. The intention of this work is to enhance the net power with better performance of using semiconductor material such as Beta type of gallium Oxide utilized in different types of power generation, electric vehicles and other fields and also to reduce the steady state error. The results of this work represents the grander enactment of closed loop SM Resonant controlled DC-DC converter fed with step-up coupled inductor.

Design of a Three Phase Z-Source Inverter for Photovoltaic Systems

Due to the danger of extinction of fossil energy resources and their harmful effects on the environment, interest in renewable energy sources has increased today. Furthermore, the photovoltaic energy, which is among renewable energy sources, has started to gain importance day by day. Especially, grid-connected Photovoltaic (PV) power generation systems have begun to be installed and used widely. In the grid-connected power generation systems, variable environmental conditions cause the DC voltage obtained from the PV systems to vary continuously. In the applications where traditional inverters are used, additional DC/DC converters are required to obtain an output at the desired frequency and amplitude. On the other hand, Z-source inverters which are a new concept can perform this raising and lowering process without the need for any intermediate circuit elements, thanks to the impedance network in their structures. For this reason, in this paper, Z-source inverter is designed for the PV systems. Z-source inverter modeling with impedance network is realized by using a simple boost switching method, and the modulation index and duty cycle parameters are adjusted to increase the DC voltage applied to its input. It is observed from the simulation results that using of the Z-source inverter is proper and efficient in the PV power generation systems.

Current PIλ Control of the Single-Phase Grid Inverter

In a grid-connected power generation system, the grid-connected current of the inverter is sensitive to nonlinear factors such as periodic disturbance of grid voltage, which results in grid-connected current waveform distortion. By establishing a single-phase photovoltaic grid-connected inverter control system model, designing an inverse current fractional-order PI (PIλ or FO-PI) controller and the dynamic and steady-state performance, antidisturbance and grid connection inversion characteristics of the system are simulated and compared under the action of the integer-order PI controller and fractional-order PI controller. The quality of the inverter grid-connected current is analyzed by using the fast Fourier transform (FFT). The simulation results show that the fractional-order control system can reduce the total harmonic distortion (THD) of the grid-connected current and dynamic performance and antidisturbance ability of the improving system while satisfying the steady-state performance indexes.

Advancing Grid-Connected Renewable Generation Systems

If we look at the history of renewable energy sources (RESs), how it all began, and how rapidly they continue to develop, it can be argued that one of the main reasons is due to the rapid improvements in power electronics technology in interfacing the renewable source to the grid [...]

Application of Improved Droop Control Based on Grid Impedance in Photovoltaic Grid-Connected Power Generation system

When the power grid impedance mutates, the output power of the grid-connected photovoltaic power generation system controlled by drooping will become very unstable. To solve this problem, an improved droop control algorithm based on network impedance detection is proposed. Taking photovoltaic grid-connected power generation system as the research object, the influence of power grid impedance on traditional droop control is firstly expounded by introducing power grid impedance value into traditional droop control. Then the method of real-time network impedance extraction is introduced. Furthermore, according to the bandwidth and phase angle constraints of the equivalent output impedance phase frequency characteristics of the photovoltaic grid-connected inverter, the controller parameters are updated in real time to achieve the purpose of adaptive network impedance mutation. Finally, the proposed method is tested and verified by real-time simulation in the loop respectively. The results show that the proposed method is correct.

Formula omitted] control for switched IT2 fuzzy nonlinear systems with multiple time delays applied in hybrid grid‐connected generation

The paper concentrates on H∞ control problem of switched IT2 fuzzy nonlinear systems with multiple time delays and disturbance. The problem exists extensively in hybrid grid-connected generation converter system, which can be felicitously described through switched interval type-2 (IT2) fuzzy model for bifurcation behavior, electromagnetic interference. The application of IT2 fuzzy switched descriptor in hybrid grid-connected generation is proposed for the first time avoiding bifurcation behavior effectively and successfully coordinates the individual components of the hybrid grid-connected generation system leading to operating in a dynamically stable way subordinating to the given patterns. To ensure the system stable subjecting to disturbance, methods of LMI and free-weighting matrices are employed to design the controller. Availability and validity are verified through a numerical simulation.

Frequency Adaptive Circle Tracing Observer-Based Control Algorithm for Ride-Through Operation of Grid-Connected SECS

This article deals with a ride-through strategy for a three-phase grid-tied solar photovoltaic array system. Unlike the conventional control algorithms, this control algorithm does not tradeoff with power quality melioration features while permitting ride-through dynamics of the solar energy conversion system (SECS). As per the revised IEEE-1547 standard, the distributed energy resources have to provide a full range of services even under voltage disturbances caused by faults like existing power plants. In this article, the grid-connected solar power generation system follows the grid code even under ride-through operation with the presence of reactive local load, unlike the traditional algorithms. In order to map future challenges, the low-voltage ride-through features of three-phase SECS at symmetrical/asymmetrical faults, are explored here. This control strategy is capable to operate SECS at various modes. To operate the voltage source converter within a safe limit, a constraint is incorporated on the active power of SECS to avoid overcurrent and energy aggregation in the dc-link capacitor, which reduces the life-time of the dc-link capacitor. Simulated results demonstrate the effectiveness of the control strategy for various operating conditions. The comparative performances of the presented control strategy are analyzed to demonstrate the effectiveness under the presence of distorted grid voltages and non-Gaussian noises in sensed measurements. Test results manifest the dynamics of SECS at various operating conditions.

Research on frequency modulation control of photovoltaic power generation system based on VSG

Abstract In order to improve the friendliness of the grid connection of new energy power generation, the new energy photovoltaic (PV) unit is equivalent to a synchronous generator in the power system and a virtual synchronous generator (VSG)-controlled PV energy storage complementary grid-connected power generation system model is established and studied to analyze the VSG. When power is supplied to the load together with the power grid, the energy storage unit inside the VSG will release and store the electrical energy according to the fluctuation of the PV output, which plays the role of the adjustment of the prime mover; in the case of load power fluctuations, and power grid assume the corresponding active power regulation according to their capacity. The amount of active power adjustment to jointly and maintain the power balance inside the system under the condition of fluctuating load power. The overall system architecture and control strategy of PV grid-connected inverter based on VSG algorithm are proposed. The PV-VSG proposed here not only takes into account the maximum power point tracking control but also has independent participation in the power supply. A series of characteristics of synchronous generators, such as network frequency modulation voltage regulation and inertia damping, can effectively improve the new energy PV power generation system and promote the new energy consumption. The results of system simulation and field demonstration operation fully show the effectiveness and correctness of the proposed control strategy based on VSG algorithm.

Set-Membership Global Estimation of Networked Systems.

This article is concerned with set-membership global estimation for a networked system under unknown-but-bounded process and measurement noises. First, a group of local set-membership estimators is deployed to obtain the local ellipsoidal estimate of the true system state. Each estimator is capable of communicating with its neighbors within its communication range. Second, a global estimation approach is proposed which generates a trace-maximal ellipsoid within the intersection of all the local estimation sets with an aim to improve the difference of the local estimate at each time instant. Sufficient conditions for providing a global estimate under both complete and incomplete measurement transmissions are derived. Third, as an application, a modified distributed photovoltaic grid-connected generation system is provided to verify the effectiveness of the developed set-membership global estimation approach. Furthermore, an islanding fault detection scheme is derived based on the calculated global ellipsoidal estimate. Finally, simulation verification of the obtained theoretical results on the distributed generation system is presented.

Simulation research on the grid connected generation system of solar thermal power generation

Objective: To improve the efficiency and stability of the solar thermal power generation system, and promote the optimization and development of solar thermal power generation grid connection. Methods: The working principle of the heat exchanger in the heat storage system is analyzed. Combined with the technological requirements of the system, the mathematical model of the heat exchanger is established by the mechanism modelling method. According to the inherent characteristics and control requirements of the heat storage system, the control schemes are proposed. The control strategies of different control algorithms, such as single-loop control, Smith predictive compensation control, cascade-Smith control, and feedforward-cascade-Smith control, are designed and adopted. The simulation model is established to obtain step response waveforms of different control systems. The advantages and disadvantages of different control strategies are comprehensively analyzed and compared. Results: After introducing the superheated steam mass-flow disturbance, the error of the single-loop control system increases. After adjusting the system to restore the oscillation state, the system error is high (10.24%). Smith predictive compensation control system fluctuates, with a peak time of 548 seconds

Research on Topology of the High Step-Up Boost Converter With Coupled Inductor

High step-up boost converters with coupled inductor have attracted much attention in the fuel cell or photovoltaic grid-connected generation system, however, there are few literatures elaborated on the construction ideas and derivation methods of them. Accordingly, in order to obtain a clear roadmap on the derivation and inner connection of these converters, a comprehensive review and analysis are presented in this paper. First, the basic boost converter with coupled inductor is regarded as the basic topology, and its merits and demerits are analyzed in detail. Then, in order to address these demerits, various step-up techniques are introduced, such as the rectifier circuit, the active-clamped circuit, the multi-winding coupled inductor, and the voltage doubler rectifier; and numerous new topologies are continuously proposed by combinations and equivalent simplifications. In addition to a detailed synthesis of each topology, a comparative and quantitative analysis among some important converters is presented, and the optimal one is chosen to build a 250 W prototype. Finally, based on comparisons and analysis, the main characteristics and inner connections of these high step-up boost converters with coupled inductor are identified and clarified.

Distributed Event-Triggered Estimation Over Sensor Networks: A Survey.

An event-triggered mechanism is of great efficiency in reducing unnecessary sensor samplings/transmissions and, thus, resource consumption such as sensor power and network bandwidth, which makes distributed event-triggered estimation a promising resource-aware solution for sensor network-based monitoring systems. This paper provides a survey of recent advances in distributed event-triggered estimation for dynamical systems operating over resource-constrained sensor networks. Local estimates of an unavailable state signal are calculated in a distributed and collaborative fashion based on only invoked sensor data. First, several fundamental issues associated with the design of distributed estimators are discussed in detail, such as estimator structures, communication constraints, and design methods. Second, an emphasis is laid on recent developments of distributed event-triggered estimation that has received considerable attention in the past few years. Then, the principle of an event-triggered mechanism is outlined and recent results in this subject are sorted out in accordance with different event-triggering conditions. Third, applications of distributed event-triggered estimation in practical sensor network-based monitoring systems including distributed grid-connected generation systems and target tracking systems are provided. Finally, several challenging issues worthy of further research are envisioned.

Modeling, control and simulation of a photovoltaic /hydrogen/ supercapacitor hybrid power generation system for grid-connected applications

Hybrid renewable energy systems (HRES) should be designed appropriately with an adequate combination of different renewable sources and various energy storage methods to overcome the problem of intermittency of renewable energy resources. Focusing on the inevitable impact on the grid caused by strong randomicity and apparent intermittency of photovoltaic (PV) generation system, modeling and control strategy of pure green and grid-friendly hybrid power generation system based on hydrogen energy storage and supercapacitor (SC) is proposed in this paper. Aiming at smoothing grid-connected power fluctuations of PV and meeting load demand, the alkaline electrolyzer (AE) and proton exchange membrane fuel cell (PEMFC) and SC are connected to DC bus of photovoltaic grid-connected generation system. Through coordinated control and power management of PV, AE, PEMFC and SC, hybrid power generation system friendliness and active grid-connection are realized. The validity and correctness of modeling and control strategies referred in this paper are verified through simulation results based on PSCAD/EMTDC software platform.

Improved QPR Power Controller With Harmonic Compensator For Wind Grid-Connected Inverter

The grid-connected inverter plays an important role in wind turbine grid-connected power generation system. The performance of inverter control strategy directly affects the grid-connected current quality. For quasi-proportional resonant(QPR) control, the output signal step of controller exists owing to the input signal step, and the grid current will be distorted by the low-frequency noise in the input signal. In order to solve these problems, the performance of quasi-PR control should be improved, so a method of constructing quasi-PR controller with two degrees of freedom is adopted, by which the improved controller can effectively suppress the influence of the step and low-frequency noise in the input signal on the grid-connected current. The improved controller is simulated on MATLAB, and the results show that the applied method can effectively improve the property of the existing problems of quasi-QPR controller and the quality of grid-connected current. Keywords: Grid-connected inverter, Harmonic compensator, Matlab/Simulation, 2-DOF,QPR. DOI: 10.7176/CTI/8-05

Research on remote test data access method of new energy grid-connected generation based on cloud platform

In view of the trend of the development of power grid information and the characteristics and application requirements of the current new energy grid-connected characteristic test system, the cloud computing service is applied to the remote testing system. The remote testing cloud data platform for new energy grid-connected power generation is designed and constructed. On the basis of this platform, a design scheme of real-time/historical data access and wireless secure transmission is proposed. The feasibility of the high efficient storage of the platform and the reliability and security of the data transmission access are proved by the test of the remote testing system of new energy grid-connected power generation. To some extent, the platform solves the problem of data access in the existing platform. It gives full play to the role of cloud platform data center. The platform provides data support for operation characteristics analysis and grid-connected monitoring and diagnostics of new energy grid-connected generation system.

Design and Simulation of Power Generation System Based on Photovoltaic Cells

Based on the volt-ampere characteristics and internal structure of photovoltaic (PV) cells, this paper uses Simulink to construct PV cells simulation model, maximum power point control simulation model, control circuit dq algorithm simulation model, SVPWM modulation algorithm simulation model, grid-connected PV power generation system simulation model, and it performs simulation studies on the maximum power tracking control of the PV power generation system. The simulation results show that the method of grid-connected inverter control can maximize the maximum power point tracking of the PV power generation system, which is of high practical values.

Modelling autonomous hybrid photovoltaic-wind energy systems under a new reliability approach

Hybrid photovoltaic-wind energy systems are being designed and implemented as stand-alone or grid connected generation systems, due to the need to use local, environmental friendly and low cost energy sources. In this study, a novel methodology to optimize the size of an autonomous hybrid photovoltaic-wind power system with battery storage is presented. A multi-objective optimization problem is considered with two objective functions, the total net present cost and a new reliability indicator called maximum expected energy not supplied, which is calculated using a probabilistic approach. The non-dominated sorting genetic algorithm-II was utilized to find the model solution. The results obtained with the presented methodology were compared with those from traditional methodologies, with the proposed methodology generating a set of feasible solutions, with respect to the system economy and reliability, which maximizes the use of renewable sources and reduces the size of the system backup.

Special Issue on Advancing Grid-Connected Renewable Generation Systems

Renewables are heavily involved in power generation, as an essential component for today’s energy paradigm. Energy structure—both national and international—has been undergoing significant changes over the past few decades.[...]