Increasing Wind Power Penetration Research Articles

Hybrid model-data-driven dynamic VAR planning for wind-penetrated power system using spectral surrogate techniques

The increasing wind power penetration and proliferation of induction motor loads, of which dynamic impact cannot be revealed through steady-state analysis, bring challenges to the short-term voltage stability of modern power systems. This study proposes a hybrid model-data-driven approach for dynamic VAR source planning to enhance the short-term voltage stability of wind-penetrated power systems to reduce the computation burden of electro-mechanical transient models. Firstly, the theoretical background of Stochastic Spectral Embedding (SSE) is introduced. Then, a surrogate model for the electromechanical transient model is established using SSE following efficient expansion coefficient calculation and a designed partition strategy for the studied problem. Furthermore, a hybrid model-data-driven VAR deployment optimization model is established with 3 objectives, which is solved by a dual-population-based evolutionary algorithm (DPEA). The accuracy and effectiveness of the model are verified on a modified New England 39-bus system. Simulation results prove that the computational cost is reduced significantly in comparison with conventional model-based method without a compromise in accuracy and the proposed method is also more accurate than methods based on other surrogate models. The proposed SSE-based model can be applied to other power system analysis with electro-mechanical transient models to alleviate the computational cost.

Sub-Synchronous Oscillation Constrained Communication-Free Grid Frequency Control of Offshore Wind Farm Linked HVDC System

This paper proposes a frequency control method of a voltage source converter (VSC) high-voltage direct current (HVDC) system for large-scale offshore wind farms (OWFs) integration into an AC grid. Without frequency control, power output of OWFs varies with the wind velocity and it causes a grid frequency fluctuation. This fluctuation on the AC grid is becoming more severe as the level of wind power penetration increases. The previously suggested communication-free controls are vulnerable to continuously changing frequency fluctuations owing to concerns about its excessive energy releases. Therefore, our proposed control enables OWFs with HVDC to participate in grid frequency regulation continuously by considering its energy state when AC grid frequency fluctuates. In addition, there is a concern about sub-synchronous oscillation (SSO) instability owing to its cascading frequency control structure. A simplified small-signal model is developed to reveal out the existence of these SSO problems and its main factors in the frequency control scheme. Using developed model, overall system stability is comprehensively investigated. Also, a damping controller to mitigate SSO instability is also suggested and validated through simulation. To demonstrate the effectiveness of overall proposed frequency control, time-domain simulations were also carried out utilizing PSCAD/EMTDC under varying wind velocity condition.

Operation optimization of ventilated floor heating system in nearly-zero-energy building

As the share of renewable energy sources increases and building energy systems become more complex, optimizing system operation is necessary to fully improve economic, environmental, renewable penetration and thermal comfort performance. Most current studies focus on single-objective or multi-objective optimization of building systems, but the impact of different objectives and their combinations on operation is unclear. In this study, optimal schedules for a ventilated heating floor in a nearly-zero-energy building were determined using an improved particle swarm optimization algorithm coupled with prior knowledge-based search accelerating strategy. System performance was investigated under different combinations of optimization objectives, including reducing operational costs and carbon emissions, increasing wind power penetration, and improving thermal comfort. The results show that under the influence of prior knowledge, stochastic algorithm converges quickly with reasonable results even when the solution space is large. The performance of some single-objective optimization cases is unsatisfactory due to the exclusion of some control variables. In contrast, multi-objective optimization yields optimization problems better, which finds better dynamic operation status and leads to better system performance. Specifically, co-optimization of operational cost, wind power penetration and environmental cost together produces the most reasonable solution.

System Power Quality Analysis under Wind–Hydro Complementary Generation Mode

The highly random and characteristics of wind power generation challenge the power quality of the wind–hydro complementary generation system (WHCGS). Herein, the transient characteristics of power quality under the complementary generating mode are studied. First, a nonlinear hydropower system (HPS) model is innovatively established considering the dynamic characteristics of hydrounits under part load operation, and then a wind power system model including wind speed model, wind turbine and its controller, generator and converter is established. Finally, the applicability of WHCGS model in power quality evaluation is established and verified by IEEE‐9 node model. Combined with active power, frequency, and voltage power quality indicators, the effects of wind–hydro capacity ratio and voltage sag on the system are quantified. The results show that the increase in wind power penetration will deteriorate the power quality of WHCGS. Moreover, when the wind power capacity reaches 60 MW, it will damage the voltage and frequency stability of HPS. Besides, the larger the voltage sag amplitude, the worse the power quality of WHCGS. The longer the voltage sag lasts, the higher the risk of WHCGS instability. This article provides a technical reference for the safe and stable operation of WHCGS.

Frequency‐trajectory‐oriented control strategy for primary frequency regulation of wind farms

AbstractWith the rapid increase of wind power penetration, the frequency indicators of power system, encompassing frequency deviation and rate of change of frequency (RoCoF), are prone to exceed the pertinent relay thresholds, thus leading to serious power outages. Wind farms can participate in primary frequency regulation (PFR) to alleviate the above problem. However, wind farms reserve capacity (WFRC) presented by overspeed control and pitch angle control is the important factor for frequency safety especially when large disturbance occurs, and it varies obviously in different conditions. Thus, WFRC should be utilized optimally to avoid insufficient or excessive response of wind farms in PFR. To overcome the challenge, this paper proposes frequency‐trajectory‐oriented control (FTOC) for wind farms based on a two‐fold optimization framework, seeking to obtain the best frequency control performances in PFR through realizing the optimal compromise between frequency results and the consumption of WFRC. First, when the frequency indicators deviate significantly from the normal values, the optimal frequency trajectory is planned periodically according to the local standards and operation conditions, thereby minimizing the total consumption of WFRC on the premise of frequency safety. Second, based on model predictive control and a real‐time power system parameters estimator, the total reference power of wind farms, which helps the frequency track the latest planned trajectory, is optimally distributed among wind generators according to their reserve capacity. In this case, through the optimal frequency trajectory planning and tracking, the new method in this paper not only effectively prevents the frequency results from exceeding the local standards under diverse conditions, but also finds the optimal balance among frequency indicators safety, frequency trajectory smoothness, and the reserve capacity consumption of wind power generators. Finally, the simulation results prove the effectiveness and advancement of FTOC.

Cooperative Primary Frequency Regulation Strategy of Wind Storage System Based on Variable Inertia Coefficient

Direct-drive permanent magnet synchronous wind turbine-generator (PMSG) is connected to the grid through the rotor side and grid side converter. The rotor speed is decoupled from the grid frequency, so PMSG output power cannot respond to the change in system frequency. However, with the gradual increase of wind power penetration, the static stability of system frequency is weakened, so the new grid-connected wind farm should have the ability of active frequency support. This paper proposes a cooperative primary frequency regulation (PFR) strategy for wind storage systems based on variable inertia coefficient. PMSG provides inertia based on the distribution of rotational kinetic energy and modifies the polarity of the inertia coefficient at the frequency recovery stage to speed up the frequency recovery. Droop control is realized by energy storage and variable power tracking control (VPPT). Energy storage and VPPT respectively suppress the frequency decrease/increase and only participate in the down/up single-side PFR, which can reduce the energy storage configuration capacity. And a safety discharge coefficient considering the state of charge (SOC) is introduced to prevent over-discharge of energy storage devices when outputting energy. Finally, the PFR capability of PMSG under the proposed control strategy is verified by simulation results.

Transient stability analysis of DFIG-based wind farm-integrated power system considering gearbox ratio and reactive power control

Nowadays, integration of large-scale wind farms (WFs) into power systems is experiencing rapid growth. As this rapid integration can affect transient stability significantly, employing doubly fed induction generator (DFIG)-based wind turbines, which have shown better behavior regarding system stability, has attracted much attention. This research contributes to the literature by investigating the transient stability of the power system with increasing penetration of DFIG-based WFs. In the proposed framework, the current-balance form is utilized for the network equations, and in this way, transient stability is performed using time-domain simulation. According to the simulation results, when the rate of wind power generation exceeds 0.7 per-unit, the increasing trend of the critical clearing time (CCT) is reversed and the CCT decreases greatly with the increased wind power penetration. In addition, the reactive power compensation by DFIG, the gearbox ratio, the power system strength, and DFIG parameters are comprehensively investigated as effective parameters on transient stability. Since the rated rotor speed of DFIG significantly impacts the electrical torque and machine currents, the reduction of the rated rotor speed due to the change of the gearbox ratio has been investigated as one of the effective factors to improve the transient stability. The simulation results demonstrate the effectiveness of the proposed approach in improving power system transient stability.

An efficient analytical approach for operational reliability evaluation of integrated electricity‐heat energy systems with variable wind power

AbstractThe increase in wind power penetration leads to the risk of energy supply interruption in integrated electricity‐heat energy systems (IHES). This paper presents an analytical‐based approach for the efficient operational reliability evaluation of the IHES. The wind power distribution characteristic model considering correlation is constructed based on Hidden Markov Model (HMM). To reduce computational complexity, a critical system state identification (CSSI) method is proposed that characterises both random device failures and wind power uncertainty. Under each critical system state, the analytical function relationship between the reliability index and the uncertainty factors is established based on the virtual stochastic response surface (VSRS) method. The analytical function can directly calculate the reliability index when the wind power output varies, avoiding a large number of repeated calculations of the optimal load‐shedding model of the system and reducing the time required for reliability assessment. This allows the operator to evaluate the operational reliability of the integrated energy system in real‐time. The numerical simulation of the test system combining the IEEE 33‐node distribution system and the existing 28‐node heating system proves the effectiveness of the proposed method.

A novel modeling and emergency control method of transient energy of DFIG-based wind turbine under grid fault

The anti-interference ability of the power system continues to decline with the increase of wind power penetration. Due to the limitation of the reduction of the synchronous generators proportion and the response speed, the emergency power controllability of the power system with large-scale wind power is insufficient, and the stability problems of the power system continue to highlight under the grid fault. At the same time, wind turbines can hardly provide emergency support for the power system due to the maximum power point tracking mode. Therefore, the transient energy of doubly fed induction generator based wind turbine (DFWT) during the grid fault is depicted, which is accumulated by the imbalance between the input mechanical power and output electromagnetic power. And a new idea of utilizing the fault transient energy of DFWT to provide emergency power support for the power system is proposed in this paper. Firstly, the expression of stator short-circuit current of DFWT in the crowbar input and reactive power support stage is derived. The dynamic model of the rotor speed of DFWT is established further, and the calculation method of fault transient energy of DFWT is proposed. Next, in order to maximize the utilization of the transient energy, the calculation method of control duration time and control reference value is proposed, and the transient energy emergency control (TEEC) method of DFWT is proposed. The case studies and experimental results show that the TEEC method can not only provide stable power support for the power system, but also alleviate the short-term power impulse of DFWT after the grid fault removal, and accelerate the recovery of the rotor speed of DFWT, which is conducive to the safe and stable operation of DFWT and the power system.

Flexibility-enhanced strategies of generations to improve the integration of renewable energy considering uncertainties

Power systems with a high proportion of renewable energy are confronted with immense challenges and a huge amount of renewable energy has been curtailed. To promote the integration of renewable energy, this paper focus on exploiting the generation flexibilities. For hydropower units, a high-resolution dynamic regulation model of reservoir volume is proposed, in which the real-time situation of inflow is considered. The reservoir’s flexibility which is hindered by the static flood water limit level (FLWL) is exploited by this method. For thermal units, a deep peak regulation of thermal is constructed to enhance the system’s flexibility. Furthermore, considering the uncertainties of renewable energy, a chance-constrained reservoir flexible model influenced by random reservoir inflow and a chance-constrained spinning reserve and power flow model influenced by the wind uncertainty are developed. Based on those models and their coordination, an optimal dispatching model considering generation flexibilities and uncertainties is proposed. Simulation results on the IEEE 30-bus system show that the proposed model with multiple flexible resources can increase wind power penetration by 10% and save half of the cost compared with the conventional dispatching methods. These results demonstrated the efficiency of the proposed method whether the integration of renewable energy or the saving of operation costs.

A frequency control scheme of a doubly-fed induction generator considering random wind speeds

The low inertia characteristic of the power system is increasingly prominent with the increase of wind power penetration. Therefore, the threat of random wind speeds and sudden frequency events to the frequency stability of a low inertia power system is further enhanced. It is necessary for wind power generators to provide frequency auxiliary service for the power system through appropriate control schemes. To address these issues, a frequency control scheme is proposed for a doubly-fed induction generator (DFIG) to support the frequency stability of the system in this paper, which can play a role in additional-loop-based frequency smooth control (FSC) and dynamic inertial control (DIC) by a smooth switcher. The objective of FSC is to smooth the frequency fluctuation caused by random wind speeds, load fluctuation, etc., while DIC aims at improving the frequency nadir (FN) and simultaneously preventing rotor speed over-deceleration during a large disturbance. In addition, a smooth switcher is proposed to coordinate the advantages of FSC and DIC. Note that the proposed approach can be automatically switched from FSC to DIC, while frequency deviation exceeds the given threshold due to a large disturbance. Finally, simulation results on the IEEE 14-bus system show the advantages of the proposed method in improving frequency stability under real complex situations while ensuring the stable operation of wind turbine generators.

Chaos Control of Doubly-Fed Induction Generator via Delayed Feedback Control

With the increasing wind power penetration, wind farms are directly influencing the power systems, so the need to improve the quality of the system is an open research topic. A Doubly-Fed Induction Generator (DFIG) is often used in wind power systems. However, DFIG has a complex structure and often works in harsh environments, so potential faults may occur. Faults can cause the system to fall into a chaotic working state, which is a harmful phenomenon for DFIG, since it makes the operating quality of the system worse, even leading to system destruction if not fixed on time. This study presents simulations of the chaotic phenomenon that occurs for a DFIG under specific working conditions based on Lyapunov’s exponents. The delay feedback controller is designed, and along with the selection of the appropriate controller parameters, the chaotic phenomenon is quickly eliminated, bringing the system back to stable operation.

Primary Frequency Regulation Strategy of PMSG-Based Wind Turbines Integrated Inertia Control

Direct-drive permanent magnet synchronous wind turbine-generator (PMSG) generally operates in maximum power point tracking (MPPT) mode. PMSG cannot provide additional active power support when the grid frequency fluctuates.The gradual increase of wind power penetration leads to greater frequency regulation pressure, which brings hidden dangers to the power grid. This paper focuses on the grid connection of direct-drive PMSG, proposing a primary frequency regulation strategy integrated with inertia control. The proposed strategy controls the rotor kinetic energy to simulate inertia of synchronous units by adding the support power of the response frequency variation. It concludes with variable power tracking control and energy storage system control. Compared with the traditional strategy retains active power, this proposed strategy increases wind energy utilization. Adopting variable power tracking control combined with energy storage can overcome secondary frequency drop and reduce energy storage configuration capacity.

An Advance Control of Grid Integrated Wind Turbine Driven DFIG-Battery System with Grid Power Shaping Under Gust Wind Variation

ABSTRACT There has been an increase in wind power penetration into the utility grid. The wind speed variations exhibit undesirable oscillations that influence power quality and system reliability. Therefore, the grid operation is challenging in this scenario. Battery energy storage system (BESS) smooths out wind power production and reduces fluctuations. However BESSs low power density and high capacity requirements to compensate for fluctuation limit its implementation for high-power applications. This paper introduces a wind energy conversion system (WECS) based on a doubly fed induction generator (DFIG) incorporating a vanadium redox flow battery (VRFB) in the DC-link, which supports grid power smoothing and power balance even under varying wind speed. Real-site wind data was used to develop a technique for designing the VRFB. The rotor side converter (RSC) employs an off-maximum power point tracking to keep the VRFB operation within the limit and deliver consistent power to the grid. An improved phase lock loop control is designed for DFIG that suppresses DC offset at the input and allows RSC and grid side converter (GSC) to perform appropriately even under grid disturbances. The GSC control is designed with an improved DC-link voltage control by adopting an anti-windup fractional-order proportional-integral (AWFOPI) controller, which can improve transient response. A sparrow search algorithm is adopted to tune the AWFOPI controller. Matlab Simulink is used to simulate the system. Test results show that the system performs well under various operating conditions and is satisfactory. It has also been tested on the OPAL-RT real-time simulator test bench.

Equivalent modeling and multi-parameter coupling optimization for DFIG-based wind farms considering SSO mode

As a low-carbon and environmentally friendly renewable energy source, wind power has been globally recognized as the best solution to achieve energy saving and emission reduction and promote low-carbon economic growth. With the increase of wind power penetration, wind power has a great impact on sub-synchronous state stability and dynamic characteristics of the grid-connected system. Aiming at the fact that the correlation between clustering indexes and sub-synchronous oscillation (SSO) mode and the difference of the contribution to the clustering results are seldom considered in the current equivalent modeling of doubly-fed induction generator (DFIG)-based wind farm, this paper proposes a clustering method based on the index dimension reduction and weighted fuzzy C-means (WFCM) clustering algorithm. Besides, for the SSO study of the grid-connected system without sufficiently considering the coupling effects between controller parameters, a multi-parameter coupling optimization design strategy combining orthogonal experiment method (OEM) and response surface method is proposed. Firstly, the dominant variables of SSO mode of the DFIG-based wind farm connected to weak grid by series compensation system are taken as the initial clustering indexes. After dimension reduction by principal component analysis, the WFCM algorithm is utilized to cluster the wind farm. Then, the proportional and integral coefficients of the grid-side controller, rotor-side controller and phase-locked loop are optimized to achieve the simultaneous optimization of the SSO characteristics and dynamic characteristics of the system. Finally, the interaction between control parameters and the influence degree and trend on the system performance are quantitatively evaluated, and the optimal parameter combination is obtained. The proposed strategy can mitigate SSO more effectively while improving anti-interference than the particle swarm optimization based on OEM.

Damping Torque Analysis of the PMSG-Based WT with Supplementary Damping Control for Mitigating Interarea Oscillations

This study presents a comprehensive analysis of the impact that a supplementary damping controller of the permanent magnet synchronous generator (PMSG)-based wind turbine (WT) has on low-frequency oscillation (LFO) damping. A reduced mathematical model of an interarea system is first established. Then, an auxiliary damping controller is designed using the PMSG active power control loop, enabling the WT to actively support the interarea LFO mitigation. Based on this, the damping torque analysis (DTA) method is applied to explore the contribution of the PMSG-based WT with an auxiliary damping controller to LFO damping enhancement, whose analytical expressions of the damping torque coefficients reveal the impacts of the control parameters and the operation conditions on the system damping characteristics. It is evident that the installation location of the wind power plant (WPP) plays a leading role in determining whether the damping provided by the PMSG controller is positive or negative. Also, the contribution of damping from the PMSG can be improved by tuning the droop coefficient of the PMSG controller properly. The results indicate that the proposed damping control is always helpful in improving the system damping when the wind power penetration increases. Accordingly, analytical conclusions can serve as guidelines for the control design. Case studies of a two-area test system integrated with a PMSG-based wind farm have been conducted to verify the theoretical analysis.

Blockchain Based Peer-To-Peer Energy Trading Between Wind Power Producer and Prosumers in Short-Term Market

With the increase of wind power penetration, the deviation caused by its volatility and intermittency poses a growing threat to the grid. Energy trading in short-term markets for wind power and backup storage helps compensate for the deviations. Furthermore, the introduction of peer-to-peer (P2P) energy trading can effectively reduce the risk of centralized market management. However, the higher cost of energy storage are not conducive to wind power producers (WPPs). And P2P trading also suffers from trust and efficiency problems. This paper provides a blockchain based short-term energy trading market, which resolves generation deviations through efficient and trusted real-time transactions between WPP and prosumers. The blockchain-based energy trading market is a trustless P2P structure, and the trading is triggered by smart contracts to ensure efficiency. Furthermore, a reputation mechanism is designed to incentivize WPP’s generation forecasts to be accurate and prosumers to participate in the market. A bilevel optimization method is designed to increase the revenue of WPP and reduce the costs of prosumers. The market can effectively balance the deviation of wind power generation, increase the revenue of WPP by 9.55%, and reduce the costs for consumers by 5.6%.

Frequency Trajectory Planning-based Frequency Regulation Strategy for Wind Turbines Equipped with Energy Storage System

The increase in wind power penetration has weakened the equivalent inertia of the power system, posing a significant challenge to frequency stability. In this paper, a frequency trajectory planning (FTP)-based frequency regulation (FR) strategy is proposed for permanent magnet synchronous generator-based wind turbines equipped with an energy storage system (ESS) on the DC link. The core idea is that the frequency index provided by the grid code is used to plan a safe frequency trajectory when the system frequency fluctuates. The FR power provided by the ESS is controlled by tracking the planned frequency trajectory to compensate for the unbalanced power in the system, provide inertia support, and ensure the frequency stability of the power grid. The proposed strategy can suppress the frequency fluctuation and optimize the FR power of the ESS. It also effectively circumvents the complex parameter design process of virtual inertia control. The simulation model is established in Matlab/Simulink to verify the effectiveness of the control strategy.

Voltage Stability Analysis of a Power System with Wind Power Based on the Thevenin Equivalent Analytical Method

The traditional black-box Thevenin equivalent method cannot analyze the influence mechanism of wind power integration on Thevenin equivalent parameters. With the increase in wind power penetration, it will be difficult to accurately assess the voltage stability of power systems with wind power. Therefore, a Thevenin equivalent analytical method is proposed to analyze the voltage stability of a power system with wind power. This method adopts the equivalent model of wind power integration based on the current source model. It establishes the Thevenin equivalent analytical model for power systems with wind power by dividing the node types. Then, the analytical expressions of the Thevenin equivalent parameters are derived based on two equivalent modes to characterize the mechanism of wind power integration on the Thevenin equivalent parameters. In addition, the calculation flow chart of the voltage stability criterion is formulated based on the analytical value of the Thevenin equivalent impedance under different load growth ratios and wind power penetrations. Finally, a case study is conducted on the improved IEEE 39 node system with wind power. The results demonstrate the feasibility and effectiveness of the proposed Thevenin equivalent analytical method, which can more accurately judge the voltage stability of the power system with wind power.

Data-Driven Model Predictive Control Method for Wind Farms to Provide Frequency Support

As the wind power penetration increases, wind farms are required by the grid codes to provide frequency regulation services. This article develops a fully data-driven model predictive control (DMPC) scheme for the wind farm to provide temporal frequency support. The main technical challenge is the complexity and the nonlinearity of wind turbine dynamics that make the DMPC intractable. Based on Koopman operator (KO) theory, a specialized dynamic mode decomposition (SDMD) algorithm is proposed, which fits a global linear dynamic model of the wind turbines. The performance of learning dynamics is powered through integrating the physical knowledge of the wind turbine into the specialized observables of KO. To stabilize the rotor speeds in frequency regulation, the active power contribution is optimally dispatched in a moving horizon fashion. Simulation results show that the DMPC can efficiently learn and predict the wind turbine dynamics. During the frequency response process, the proposed method can effectively track the frequency support order specified by the utility grid operator while significantly stabilizing the rotor speeds.