Grid Connected Wind Power System Research Articles

Power Quality Improvement in Hybrid Power System using STATCOM :

Meeting the escalating electricity demands posed by population growth and industrial expansion presents a significant challenge. Utilizing renewable energy sources like wind, biomass, and hydro co-generation has become imperative to satisfy energy requirements. In this proposed framework, a model featuring a grid-integrated wind energy generation system and nonlinear load is developed using MATLAB/Simulink. Integrating wind energy into the power grid impacts electricity quality, notably manifesting in voltage fluctuations, harmonics, flicker, and poor power factor at the source. The efficacy of a wind turbine and, consequently, electricity quality are assessed. To enhance power quality, the project advocates for the implementation of a STATCOM control strategy in grid-connected wind power systems. A bang-bang controller, based on hysteresis current control, is devised for STATCOM. Integrating STATCOM with the Point of Common Coupling (PCC) mitigates power quality issues. In this envisioned scheme, the FACTS device STATCOM is linked with battery power storage (BESS) at the PCC to alleviate power quality concerns. Incorporating Battery Energy Storage Systems aids in stabilizing the real power source during wind power fluctuations and facilitates the rapid injection of reactive power at the PCC. Keywords: Wind energy, Solar Energy, STATCOM, Electric grid, IGBT, PWM.) etc.

Backstepping Control of an AC/DC/AC Converter in a Grid Connected Wind Power System

The contribution of this paper is to study a nonlinear control approach known as the backstepping control method to manage reactive and active power using new parametric values for the grid connected wind power generation system. Specifically, the research focuses on a system containing a wind turbine system, a permanent magnet synchronous generator (PMSG), and a grid connected via AC/DC/AC converter. A comprehensive mathematical model for both the wind turbine system, PMSG, and the grid connected via AC/DC/AC converter was developed for this purpose. The Simulation results of the grid-connected wind power generation system are presented and analyzed to show the performance of the nonlinear backstepping control method. The characteristics of the response to variations in generator speed and the power injected into the grid show the highlight of the performance of the backstepping method, under varying wind conditions.

Investigating Small Disturbance Stability in Wind Farm Grid-Connected Systems: A Data-Driven Approach

The presence of unknown synchronization characteristics, unclear instability mechanism, and various fault mode evolution laws, lacking corresponding theoretical support and analysis methods and instability criteria, are defined with clear physical concepts. It is still impossible to systematically understand the transient synchronization mechanism of the wind power grid-connected system from the perspective of the whole fault stage. Therefore, this study uniformly reveals its temporary synchronous stability problem and proposes a large/small disturbance adaptive synchronous stability control method, which improves the dynamic characteristics of the wind turbine through the control of the inverter itself to improve the system stability—using different scenarios, such as single doubly-fed wind turbines. The experimental results show that the small disturbance on the AC side significantly impacts the system characteristics, followed by a bit of annoyance on the DC side. The DC side fault will cause a change in system frequency characteristics, especially at the receiving end. However, compared with the Voltage Source Converters-High Voltage Direct Current (VSC-HVDC)system, Modular Multilevel Converters-High Voltage Direct Current (MMC-HVDC) systems operate at a much higher frequency and produce less low-frequency harmonics. This makes them less likely to induce subsynchronous oscillations in the system.

Stability enhancement control strategy for grid-connected wind power system based on composite feedforward damping

The stability of grid-connected wind power system (GCWPS) is prone to deteriorate due to the impedance interaction between wind turbines and the weak grid. For purpose of finding out the cause of power oscillation and effectively improving the stability of GCWPS under weak grid, firstly of all, a frequency coupling impedance model (FCIM) for GCWPS is established. Through analyzing the impedance characteristic of GCWPS, a significant coupling effect between GCWPS impedance and grid impedance in the middle-low frequency region under weak grid is observed, which is easy to cause power oscillation. For purpose of restraining the power oscillation of GCWPS under weak grid, this paper proposes an oscillation suppression strategy based on composite feedforward damping. Virtual damping is incorporated into the feedforward loop to rectify the impedance characteristic curve of GCWPS. Then, a FCIM of GCWPS that adopts the proposed oscillation suppression strategy is established, and the stability analysis demonstrates that the proposed strategy effectively enhances the GCWPS stability under weak grid. Additionally, compared with conventional control strategy, GCWPS exhibits enhanced adaptability to the increased output power and phase-locked loop (PLL) bandwidth under weak grid. Finally, experiments are undertaken to evidence the feasibility of the proposed oscillation suppression strategy.

Analysis of Factors Affecting Sub-Synchronous Oscillation in Doubly-Fed Wind Power Grid-Connected System Based on Impedance Sensitivity and Research on Suppression Strategy

Aiming at the matter of sub-synchronous oscillation (SSO) of the doubly-fed induction generator (DFIG) series compensation capacitors grid connection, a SSO suppression strategy based on adding damping controllers in rotor-side converter (RSC) is put forwarded. Considering the control parameters of power and current control loops of RSC, the equivalent impedance model of DFIG series compensation grid connection (SCGC) is established, and then combined with the equivalent RLC resonant circuit of the system, the mechanism and factors of SSO are analyzed by impedance method. Calculating the impedance sensitivity of the system impedance to parameters by sensitivity analysis method, so as to identify the leading factor affecting the SSO characteristics of wind power system. Combined with the stability criterion of system impedance characteristics, the parameters are adjusted to meliorate system stability. Based on the leading factor affecting the SSO and the mechanism of the SSO, the damping controllers are added in the RSC to supply positive damping for the system to eliminate the negative damping brought by the RSC and rotor resistance, thus suppressing the SSO of the system. The validity of the put forwarded suppression strategy is proved through PSCAD/EMTDC simulation.

Research on improving low-frequency oscillation characteristics of wind power grid-connected power system with doubly-fed wind generator based on virtual impedance power system stabilizer

Research on improving low-frequency oscillation characteristics of wind power grid-connected power system with doubly-fed wind generator based on virtual impedance power system stabilizer

Stochastic performance evaluation method of wind power DC bus voltage control system

The stochastic fluctuation of DC bus voltage of wind power grid-connected system is related to the safe and stable of power system, and the stochastic performance evaluation is an important means for early warning system. In order to evaluate stochastic performance of control system, this paper proposes a stochastic performance evaluation method based on minimum variance theory. A dual closed loop control model of wind power grid-connected converter DC bus voltage is established, the stochastic performance evaluation indicator is derived by time-series analysis and Diophantine decomposition, and the method to solve the indicator through operation data is given. The effectiveness of the proposed method is verified by FAST-MATLAB co-simulation platform. And the results show that the stochastic performance of the system can be improved by optimizing the parameters of the controller and the DC bus voltage.

Nonlinear rotor kinetic energy control strategy of DFIG-based wind turbine participating in grid frequency regulation

Large-scale wind power integration reduces the level of inertia in power systems, significantly deteriorating their frequency stability. To address this issue, a nonlinear rotor kinetic release control strategy is designed for wind power grid-connected systems based on an extended state observer (ESO) and nonlinear feedforward state feedback transformation (NFSFT) theories. First, the affine nonlinear system of a DFIG-based wind turbine participating in grid frequency regulation is established. The system is transformed into a basic equivalent linear system based on the NFSFT theory, and a nonlinear control law is obtained. Second, the ESO is used to observe the generalized disturbance composed of the complex parameter operation required by the nonlinear control law, which circumvents the huge computational burden of the nonlinear control law and the unknown uncertainty of the system. Finally, a limiting link and speed control link are added to prevent excessive release of the kinetic energy of the wind turbine rotor and complete the wind turbine speed recovery. A wind power grid-connected system is built using MATLAB / SIMULINK for simulation verification. The results show that the proposed strategy exhibits a better frequency regulation effect than other strategies.

A combination predicting methodology based on T-LSTNet_Markov for short-term wind power prediction

ABSTRACT Wind power has been valued by countries for its renewability and cleanness and has become most of the focus of energy development in all countries. However, due to the uncertainty and volatility of wind power generation, making the grid-connected wind power system presents some serious challenges. Improving the accuracy of wind power prediction has become the focus of current research. Therefore, this paper proposes a combined short-term wind power prediction model based on T-LSTNet_markov to improve prediction accuracy. First, perform data cleaning and data preprocessing operations on the original data. Second, forecast using T-LSTNet model in original wind power data. Finally, calculate the error between the forecast value and the actual value. The k-means++ method and Weighted Markov process are used to correct errors and to get the result of the final prediction. The data that are collected from a wind farm in Inner Mongolia Autonomous Region, China, are selected as a case study to demonstrate the effectiveness of the proposed combined models. The empirical results show that the prediction accuracy is further improved after correcting errors.

Cooperative control of time-delay wind power grid-connected unit under actuator saturation based on Hamiltonian method

In large-scale wind power generation, wide area control is often employed to overcome power oscillation, but this can result in the appearance of time-delayed voltage, which is transmitted to the wind power grid-connected system as an input signal. Additionally, ensuring the security of multi-grid parallel connection requires limiting the amplitude of the input signal. To address these challenges, this paper investigates the cooperative control problem for time-delayed wind power grid-connected unit under actuator saturation constraints. A novel control strategy that combines passive control with synchronous control is proposed. The system is transformed into a Hamiltonian structure, and a passive controller is designed using the principle of interconnection and damping assignment passivity-based (IDA-PB) to ensure stability. Based on this, an output feedback synchronous controller is proposed to account for saturation when multiple grids are connected in parallel. Stability criteria are provided to ensure the asymptotic stability of each closed-loop system and synchronous stabilization of all systems. Finally, simulation results verify the effectiveness of the proposed control strategy.

Frequency prediction after disturbance of grid-connected wind power systems based on WOA and Attention-LSTM

Under the guidance of the goal of the “carbon peaking and carbon neutrality”, due to the high proportion of renewable energy and the high proportion of power electronic equipment, the power system will bring strong randomness, low inertia and other characteristics, causing a large number of frequency stability problems. In order to solve the problems of traditional power system frequency prediction methods, such as difficulty in modeling and poor prediction accuracy, and to determine whether the frequency stability problem will occur after the wind power grid-connected system is disturbed, the Lasso algorithm is first used to reduce the dimension of the input data, and then the attention mechanism based long and short memory (attention LSTM) neural network is used to predict the output frequency curve, The network parameters are optimized by the global search algorithm Whale Optimization Algorithm (WOA). Finally, the accuracy of the algorithm is verified by taking the improved wind power grid-connected 39 bus as an example. The results show that this method has a good guiding significance for evaluating the frequency stability of the wind power grid-connected system after interference, and can effectively predict the frequency curve of the system after interference, and evaluate the frequency stability of the system after topology change.

Sub-synchronous oscillation suppression in MMC-HVDC grid-connected systems under wind farm fluctuation scenarios

In order to solve the problem of sub-synchronous oscillation (SSO) of wind power grid-connected system with modular multilevel converter based on high voltage direct current transmission (MMC-HVDC), which is characterized by frequency drift due to the fluctuation of wind power output and the dynamic interaction of MMC. By considering the coupling characteristics of wind power volatility and the internal harmonic dynamics of MMC, we establish a small-signal model of the interconnection system between the equivalent wind farm and MMC-HVDC, study the dominant factors triggering the system oscillation, and use model predictive control (MPC). The results show that the wind farm output, wind farm terminal voltage and terminal current are the dominant factors leading to SSO frequency drift. It is also verified that the MPC-SSDC control not only effectively suppresses SSOs with single frequency drift, but is also effective when multiple SSOs with different frequencies exist simultaneously. It is shown that MPC-SSDC can self-adapt to the multi-oscillation scenario of wind power grid-connected system to provide frequency and damping support for the system.

Research on simplified modeling of large-scale wind farms based on equivalent transfer function and aggregate equivalent

Introduction: In grid-connected research of large-scale wind farms, the problem of long simulation time exists in the research based on detailed model. In order to realize the fast simulation and grid-connected transient research of wind farm, this paper presents a simplified equivalent model of wind farm based on equivalent transfer function and improved capacity weighting method.Methods: This paper analyzes the mathematical model of wind turbine, corresponding to the strategy of design simplification, and the simplified model is built according to the equivalent transfer function. In addition, this paper considers the equivalent line loss model of collector line, classifies and aggregates the simplified wind turbines, and calculates the equivalent value of the converged wind turbines by using the improved capacity weighting method, the grid-connected simplified modeling of large-scale wind farm is realized.Results: A model of wind farm-MMC-HVDC flexible grid-connected wind power system is built. The simulation results show that the simplified equivalent model improves the simulation speed greatly while guaranteeing the dynamic characteristics.Discussion: The simplified equivalent strategy of wind farm can keep the same dynamic performance with the detailed model, and improve the simulation speed, and realize the fast simulation and grid-connected transient research of wind farm.

Stability Modeling and Analysis of Grid Connected Doubly Fed Wind Energy Generation Based on Small Signal Model

Stable wind power generation can ensure the quality of power transmitted by the grid. The application of large-scale grid-connected wind power systems will induce problems such as grid oscillation and frequency instability. In order to solve the problem of abnormal power system interaction caused by large-scale wind power access and improve the stability of grid-connected doubly-fed wind power generation, this paper proposes a stability modeling analysis of grid-connected doubly-fed wind power generation based on small signal model. First, the operating conditions of the grid-connected DFIG are analyzed, and the vector diagrams of the three operating conditions are given. When the grid-connected DFIG is in the super-synchronous working state, the sub-synchronous working state and the synchronous working state. According to the operating conditions of the grid-connected doubly-fed generators, the grid-connected doubly-fed wind power generation system is linearized. According to the relationship between the actual speed and the synchronous speed of the doubly-fed generator, the operating conditions of the doubly-fed generator are analyzed. By introducing the small-signal model, we analyze the small-signal of the grid-connected doubly-fed wind power generation system. The indirect current control circuit is used to perform reactive power compensation for grid-connected doubly-fed wind turbines. By calculating the reactive power loss of the grid-connected DFIG and the reactive power loss of the transmission line, the compensation capacity of the grid-connected DFIG is calculated. The transient voltage of the wind turbine is controlled by the rotor-side frequency converter, combined with the pitch angle control model. So far, this paper has realized the modeling analysis of grid-connected doubly-fed wind power generation stability. The simulation results show that the modeling analysis in this paper is reasonable for the small-signal analysis results of the stability of grid-connected doubly-fed wind power generation. In the rotor voltage simulation test, after the oscillation occurs for 1 s, the model starts to simulate and eliminate the fault. During the simulation period of 0.7 s∼1.0 s, the output voltage of the converter decreased to 168 V, and the voltage waveform did not fluctuate greatly after 1.0 s. The experimental results show that this method can improve the stability of grid-connected doubly-fed wind power generation.

Research on Control Strategy of Grid-connected Brushless Doubly-fed Wind Power System Based on Virtual Synchronous Generator Control

The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid, which leads to the decline of grid stability. Therefore, a control strategy of brushless doubly-fed reluctance generator (BDFRG) based on virtual synchronous generator (VSG) control is proposed to solve the problem in this paper. The output characteristics of BDFRG based on VSG are similar to a synchronous generator (SG), which can support the grid frequency and increase the system ‘inertia’. According to the mathematical model of BDFRG, the inner loop voltage source control of BDFRG is derived. In addition, the specific structure and parameter selection principle of outer loop VSG control are expounded. The voltage source control inner loop of BDFRG is combined with the VSG control outer loop to establish the overall architecture of BDFRG-VSG control strategy. Finally, the effectiveness and feasibility of the proposed strategy are verified in the simulation.

Control Strategy and Corresponding Parameter Analysis of a Virtual Synchronous Generator Considering Frequency Stability of Wind Power Grid-Connected System

The doubly-fed induction generator (DFIG) based on the control strategy of constant parameter virtual synchronous generator (VSG) can cause problems of sharp frequency variations in the grid-connected system, long adjustment times, and large overshoot of the active power output from the DFIG. Aiming at dealing with the above-mentioned problems, a VSG control strategy with an independent flexible link (IFLVSG) is proposed in this paper without changing the parameters and structure of the VSG, so that the moment of inertia and damping coefficient can be flexibly adjusted according to the change of the system frequency, so as to improve the system frequency stability. To form a complete selection scheme for control parameters in IFL, the state space equation including IFLVSG control is established, and the advantages of exponential IFL are highlighted by using the sensitivity calculation method. At the same time, in order to improve the analysis efficiency, the main control parameters affecting the frequency stability of the system are selected according to the sensitivity value. Finally, the root locus analysis method is used to reveal the influence law of the main control parameters on the frequency stability of the system. The formed scheme provides a theoretical basis for the selection of control parameters.

Inertia Optimization Control and Transient Stability Analysis of Wind Power Grid-Connected System

The virtual inertia control effectively makes up for the insufficient inertia caused by the high penetration wind power grid connection. However, it has an impact on the mechanical part of the wind turbine and greatly increases the difficulty of the dynamic stability analysis of the system, resulting in limited engineering practicability. Therefore, the state equation of the wind power grid-connected system is established in this paper, and the influence of virtual inertia control on wind turbine shafting oscillation is analyzed based on the small-signal theory. Secondly, the nonlinear extended disturbance observer is designed as the compensation signal of inertia control to improve its dynamic stability supportability. Based on the integral manifold method, the shafting model of the wind turbine is reduced, and the transient energy function of shafting is established, which provided the basis for the design of the shafting stability controller. Finally, a grid-connected wind power system with high permeability is installed, and the results demonstrate that under the proposed control strategy, the swing stability of power angle is significantly improved, and the wind turbine shafting oscillation is suppressed.

Coordinated Control of Wind turbine and Energy storage system for Microgrid Stability

In recent decades, the development of renewable energy has accelerated significantly due to several factors such as changing energy needs, the problem of global warming, and the depletion of fossil fuels. Wind energy is one of the renewable generation sources that can be used to achieve the EU's 2030 targets at a lower cost. However, its intermittent and stochastic nature could significantly impact the reliability and stability of the electricity system. Therefore, there is a clear necessity to mitigate power fluctuations to make the most of wind energy. To fill this gap, this paper presents a centralized control strategy based on a droop controller and a storage-integrated controller for a grid-connected variable speed wind power system (permanent magnet synchronous generator) (PMSG) to manage and stabilize the power output during intermittency periods. The main objective is to provide a stable U/f when a fluctuation event occurs. A grid failure scenario was tested to see how the control system behaves in the event of an unexpected fluctuation and its role in the stability of the power system under varying wind speed and load conditions. The effectiveness of the proposed control method was tested using MATLAB/Simulink on a small power system. The simulation results demonstrate the control system’s performance in the stability of the U/f during grid interruption.

Quantitative Analysis of the Interactive Influence for Harmonic Emission in Wind Farms

In the process of integrating large-scale wind farms into the power system, the harmonic interaction among wind farms causes potential safe and stable operation threats to the power grid. To effectively control the harmonics of the wind power grid-connected system, quantitative analysis of the harmonic interaction is very necessary and meaningful. Therefore, this paper firstly explains the harmonic interaction among wind farms from the perspective of the primary and secondary emission. We use the concept of harmonic impedance to analyze the mechanism of harmonic interaction and proposed a calculation method for quantitative analysis of the harmonic interaction. Using the calculation method, the influence caused by the wind farm self-impedance, the contact impedance, and Static Var Generator to the harmonic interaction are quantitatively analyzed. Finally, taking multiple wind farms in actual operation as a case, the effectiveness of the method is verified by time domain simulation.

DC Bus Voltage Control of Wind Power Inverter Based on First-Order LADRC

The wind power grid-connected inverter system has the characteristics of non-linearity, strong coupling, and susceptibility to grid voltage fluctuations and non-linear loads. To obtain the ideal control effect, the improved linear active disturbance rejection controller (LADRC) controls the voltage outer loop. Firstly, the mathematical model of the wind power grid-connected inverter is analyzed, on this basis, a linear active disturbance rejection control based on the reduced-order linear extended state observer is designed, reduce the phase lag of the observer, improve the system’s disturbance observation accuracy; reference lead correction lag correction method, the observer gain is improved and connected in series to the total disturbance channel to reduce the noise amplification effect of the observer; through frequency domain response characteristic analysis, the results show that the improved LADRC has better disturbance rejection performance. The simulation results of various working conditions show that the improved method has better rapidity and immunity compared with traditional LADRC.