Wind Power Penetration Rate Research Articles

Accurate aggregated modelling of wind farm systems in modified sequence domain for stability analysis

With the wind power penetration rate continuously rising, a suitable wind farm model considering both accuracy and simplicity is required for power system stability analysis. To accomplish this goal, an accurate aggregated modified sequence impedance model of the wind farm is established in this paper. The modified sequence impedance model of wind turbine generator is established, which considers the coupling between the positive- and negative-sequence impedances. The modified sequence impedances of the ac collection system, transformers, and ac grid are also derived. In this way, the impedance network of the entire wind farm system can be formed and simplified to acquire the accurate aggregated modified sequence impedance. Furthermore, the proposed model is compared with the traditional single-machine aggregated model which shows the necessity of establishing the accurate aggregated model. It is worth noting that the differences among each wind turbine generator’s operation points can be included in the proposed model. Compared with the results of impedance measurements of a target wind farm, the accuracy of the proposed aggregated sequence impedance model of the wind farm is verified in frequency domain. The application of the proposed model in the stability analysis of a grid-connected wind farm is also presented with consideration of the ac grid strength. What is more, the effect of the inertial controller on the wind farm system stability is also analyzed to make the impact of this study much more appealing and up to date.

Wind speed prediction research with EMD-BP based on Lorenz disturbance

Abstract Wind power, as a new energy generation technology, has been applying widely and growing rapidly, which make it become the main force of renewable energy. However, wind speed sequence has its own character of the intermittent and uncertainty, which brings a great challenge to the safety and stability of the power grid, one of the valid ways solving the problem is improving the wind speed predicting accuracy. Therefore, given atmospheric disturbances, we firstly used empirical mode decomposition (EMD) to deal with the non-linear wind speed sequence, and combined with strong adaptive and self-learning ability of BP neural network, then, a wind speed prediction model, EMD-BP neural network based on Lorenz disturbance, was proposed. Finally, it was to made use of actual wind speed data to take a simulation experiment and explored the improvement effect of the preliminary forecasting sequence of wind speed influenced by Lorenz equation in the transient chaos and chaos. The results show that, the improved model weakened the random fluctuation of wind speed sequence, effectively corrected the wind speed sequences initial prediction values, and made a great improvement for the short-term wind speed prediction precision. This research work will help the power system dispatching department adjust the dispatching plan in time, formulate the wind farm control strategy reasonably, reduce the impact brought by wind power grid connection, increase the wind power penetration rate, and then promote the global energy power market innovation.

Development of a genetic algorithm for maximizing wind power integration rate into the electric grid

In this paper, a new method was proposed with the objective of maximizing the rate of wind power integration into the electric grid. This method was based on the optimization of the parameters of the turbine governors (TGs) by means of a genetic algorithm. The tuning of TGs' parameters was formulated relying on an objective function aiming at reaching the maximum wind power penetration rate. The dynamic grid modeling consisted of synchronous machines, regulators, and wind turbines. The IEEE 14-bus modified test system was adopted to test the grid using the Power System Analysis Toolbox. The simulation results revealed that, with the optimized TGs' parameters, the rate of wind power integration improved considerably.

Improved VSM control of PMSG-based wind farms for transient stability enhancement

This paper analyzes the optimal control strategy of PMSG-based wind farms during faults in order to improve the transient stability of a power system with a high penetration rate of wind power. The investigated control strategies are the unity power factor (UPF), reactive power control (RPC), and particularly the concept of virtual synchronous machine (VSM). The transient stability level is assessed using the critical clearing time index, which was calculated based on trajectory sensitivity analysis. In light of the obtained results, it was found that RPC gives the best transient stability level, followed by the classical VSM control. Hence, an improved VSM control was proposed based on the transient model of a synchronous generator. The improved VSM has shown a behavior similar to a real synchronous generator, which results in better transient stability performances.

Optimized Active Power Dispatching Strategy Considering Fatigue Load of Wind Turbines During De-Loading Operation

With the increase of wind power penetration rate in the power grid, power dispatching including wind curtailment often happens to guarantee the safety of the power system. Considering the fatigue load of wind turbines during de-loading operation, how to optimally dispatch them along with the required power instructions becomes a hot issue. Under this background, this paper mainly studies the active power dispatching based on fatigue load optimization. In order to reduce the calculation complexity of the fatigue load, this paper proposes a simplified active power dispatching model for wind turbines via a look-up table. Subsequently, the ultra-short-term wind speed prediction is performed using the least squares support vector machine for the dynamic’s prediction of wind turbines, which will be applied in fatigue load pre-calculation. Moreover, in order to fast solve the optimal dispatching problem, the accelerated particle swarm optimization algorithm is adopted. Under different de-loading scenes, the simulation experiments show that the fatigue load of the wind turbines has certain regularity while different de-loading strategies yield different effects on the fatigue load. Finally, based on the evaluation of damage equivalent load (DEL), the proposed optimal dispatching strategy in this paper is proved to be effective to meet the external dispatching from the power grid while reducing the total fatigue load level of wind farm via optimizing the power instruction to each wind turbine.

Mechanism Research on the Influence of Large Scale Wind Power Integration on Power System Angle Stability

Base on the equivalent external characteristics of doubly-fed induction generator (DFIG) during the period of the fault and the power characteristic equation of delivery system, a novel method of eliminating equivalent mutual impedance is proposed to research the influence mechanism of different wind power penetration rate, the SG dispatch pattern and siting of wind farms on system transient power angle stability (TPAS) under fault condition are researched. The results show that system power angle characteristics are improved with the increase of the wind power scale. However, when the wind power scale reaches a certain level, the power angle stability promptly deteriorates. The distance of wind farms siting away from a SG group with leading power angle, as well as the generation reduction of the SG group, plays an important role in the improvement of TPAS. The effectiveness of the proposed method is verified by the numerical simulations of the two-machine power system.

Short term wind power scenarios forecast based on multivariate normal distribution

According to the fact that the increase of wind power penetration rate causes the influence of wind power’s randomness and fluctuation on the power grid, the single short-term wind power point prediction often cannot meet the needs of power grid risk assessment and decision-making. In this paper, we first calculate the theoretical probability model of each wind power forecast box by the end function in MATLAB, and then use the exponential covariance function expression to determine the best covariance matrix corresponding to the dynamic scenarios, and determine the multivariate normal distribution model of wind farm output obedience at multiple connected moments; For each predicted moment of the wind power point prediction value of the wind belongs to the prediction box, we direct sample random vector which obey multivariate normal distribution to form the wind power dynamic scenario. After a simulation experiment on a real wind farm, the results show that the scenario set considering wind power fluctuation at different time scales can cover the measured wind power curve and the reliability of the method is proved.

A capacity-investment model of wind power with uncertain supply-price under high penetration rate

Abstract With the rapid development of renewable energy, the proportion of wind power in power supply has grown significantly. Also, it influences the power price fluctuation. Since the marginal cost of wind power is almost zero, the growth of wind power's penetration rate has led to a crowding-out effect and challenged traditional power generation technology, substantially reducing the power price in the market. In perfect competition market, the real-time balance between supply and demand of power is regulated by the real-time power price fluctuation. So this paper models the intermittence of wind power as uncertain supply, and develops a capacity-investment model under the uncertainties of both supply and demand. We introduce priority dispatch elasticity to describe the crowding-out effect and take the power price to be endogenous in order to model the situation of high penetration rate. We compare the optimal wind power capacity decision under the strategy of priority grid connection and abandoned power management. Our results show that optimal capacity investment is inversely related to priority dispatch elasticity under both strategies. However, the profit from power generation is always higher when adopting the abandoned power management strategy.

Statistical analysis of wind energy characteristics in Santiago island, Cape Verde

As a volcanic archipelago, the Republic of Cape Verde relies dominantly on diesel to power its electricity supply. Recognizing the financial and environmental burden of diesel generation and risk of energy security, the government of Cape Verde has launched an ambitious goal of 50% electricity from renewables by 2020, since the country is endowed with high potential of renewable energy resources such as wind and solar. Although the annual average penetration rate of wind power has reached 24% of total electricity production generated in Cape Verde, raising the wind energy penetration level in future will pose numerous challenges for the operation and control of the power system because of wind's inherent intermittency and unpredictability. In this study, a statistical analysis of the wind characteristics in Santiago island, is presented by using historical wind speed and power data of the Santiago wind farm in 2014. A two-parameter Weibull distribution is first applied to model the wind speeds on various timescales and to determine wind energy potential in Santiago island, Cape Verde. The annual average wind speed was 8.57 m/s with a standard deviation close to 3.29 m/s. The monthly Weibull scale parameters varied from 5.64 m/s to 13.7 m/s, while the monthly Weibull shape parameters varied from 1.97 to 9.13. Although the monthly mean power density of the rainy season from August to September was low, the annual mean power density shows that Santiago has good wind potential. Then, an approach to modeling the equivalent power curve based on available wind speed and power output data from the wind farm is proposed. By utilizing the estimated power curve, the uncertainty set of wind power generation, resulted from the uncertainty of wind speed forecast, can be obtained to quantify the power system reserve requirements. A statistical analysis of wind power ramp is also given for estimating the power capacity requirement of the energy storage system that can be considered as a reasonable way to mitigate the wind intermittency and minimize curtailment of wind. Results of this study contribute to assess the wind energy potential of Cape Verde for investors, and can be used to quantify the uncertainties of wind power generation for the power system operator.

ELCC Approach for Calculating Capacity Credit of Wind Power in Korea

The share of wind power generation in domestic renewable energy is expected to increase significantly due to nationwide effort to reduce greenhouse gas emission and to enlarge the portion of renewable energy in electricity generation mix. In this study, the capacity credit, which is the most important factor for evaluating the effective capacity of domestic wind power, is calculated by using the ELCC (Effective Load Carrying Capability) methodology. The ELCC method is known to have the most sophisticated rationale among the various capacity credit estimation methods. We used the single-year data (2014) for the reference system, power demand and wind utilization. CC has been calculated to be about 0.3091 when the wind power penetration rate is less than 1%, and CC has a tendency of decreasing steadily with increasing penetration rate. According to the survey, there is no previous research on national level CC for domestic wind power generation.

A Case Study of Wind-PV-Thermal-Bundled AC/DC Power Transmission from a Weak AC Network

Wind power generation and photovoltaic (PV) power generation bundled with the support by conventional thermal generation enables the generation controllable and more suitable for being sent over to remote load centre which are beneficial for the stability of weak sending end systems. Meanwhile, HVDC for long-distance power transmission is of many significant technique advantages. Hence the effects of wind-PV-thermal-bundled power transmission by AC/DC on power system have become an actively pursued research subject recently. Firstly, this paper introduces the technical merits and difficulties of wind-photovoltaic-thermal bundled power transmission by AC/DC systems in terms of meeting the requirement of large-scale renewable power transmission. Secondly, a system model which contains a weak wind-PV-thermal-bundled sending end system and a receiving end system in together with a parallel AC/DC interconnection transmission system is established. Finally, the significant impacts of several factors which includes the power transmission ratio between the DC and AC line, the distance between the sending end system and receiving end system, the penetration rate of wind power and the sending end system structure on system stability are studied.

Study of the Maximum Penetration Rate of Wind Power in an Island Network

The Penghu islands have abundant wind resources; the capacity factor of local wind farms exceeds 47% and these wind farms are slated for expansion. However, wind turbine power output is unstable and excessive turbine installation may negatively affect system stability. This paper seeks to determine an upper limit of the wind power penetration in the Penghu region power system to minimize waste and optimize system safety.

Co-optimizing generation and transmission expansion with wind power in large-scale power grids—Implementation in the US Eastern Interconnection

This paper studies the generation and transmission expansion co-optimization problem with a high wind power penetration rate in large-scale power grids. In this paper, generation and transmission expansion co-optimization is modelled as a mixed-integer programming (MIP) problem. A scenario creation method is proposed to capture the variation and correlation of both load and wind power across regions for large-scale power grids. Obtained scenarios that represent load and wind uncertainties can be easily introduced into the MIP problem and then solved to obtain the co-optimized generation and transmission expansion plan. Simulation results show that the proposed planning model and the scenario creation method can improve the expansion result significantly through modelling more detailed information of wind and load variation among regions in the US EI system. The improved expansion plan that combines generation and transmission will aid system planners and policy makers to maximize the social welfare in large-scale power grids.

Does wind energy mitigate market power in deregulated electricity markets?

A rich body of literature suggests that there is an inverse relationship between wind power penetration rate into the electricity market and electricity prices, but it is unclear whether these observations can be generalized. Therefore, in this paper we seek to analytically characterize market conditions that give rise to this inverse relationship. For this purpose, we expand a recently developed theoretical framework to facilitate flexibility in modeling the structure of the electric industry with respect to the degree of market concentration and diversification in the ownership of wind power capacity. The analytical results and their attendant numerical illustrations indicate that the introduction of wind energy into the market does not always depress electricity prices. Such a drop in electricity prices is likely to occur when the number of firms is large enough or the ownership of wind energy is sufficiently diversified, or most often a combination of the two. Importantly, our study defines the circumstances in which the question of which type of firm invests in wind power capacity is crucial for market prices.

Priority Control Strategy of VSC-MTDC System for Integrating Wind Power

For the obvious advantages in integrating wind power, multiterminal HVDC transmission system (VSC-MTDC) is widely used. The priority control strategy is proposed in this paper considering the penetration rate of wind power for the AC grid. The strategy aims to solve the problems of power allocation and DC voltage control of the DC system. The main advantage of this strategy is that the demands for wind power of different areas can be satisfied and a power reference for the wind power trade can also be provided when wind farms transmit active power to several AC grids through the DC network. The objective is that power is well distributed according to the output power of wind farm with the demand of AC system and satisfactory control performance of DC voltage is obtained.

Study on the Coordination of Load Shedding and Under-Frequency Load Shedding (UFLS) in Small Weak Receiving Power System with Wind Power Penetration

Frequency influencing factors in small weak receiving power grid with wind power penetration during the disturbance of power shortage are analyzed in this paper, such as wind power penetration rate, wind turbine types, inertia control loop and wind power fluctuation. Based on the influencing factors above, in the light of the phenomenon of large dive depth and long duration of the frequency first swing after fault, the coordination scheme of load shedding and under-frequency load shedding based on the simulation system is proposed: load shedding time and load shedding ratio coordination scheme. Simulation results verify the correctness of the theoretical analysis and the rationality and feasibility of the coordination scheme proposed.

An Energy Storage System Sizing Method for Wind Power Integration

Combining an energy storage system (ESS) with a wind farm is an effective way to increase the penetration rate of wind power. ESS sizing is an important part in wind farm planning nowadays. In this paper, a basic method for determining the optimal capacity of an ESS integrated with a wind power generator to meet the requirements of grid integration is presented. With the proposed method, the necessary ESS capacity which can provide the best benefits between the regulation effects and energy storage size was calculated. The segmentation method and automatic segmentation method are proposed to improve the performance of the basic method. Further work on expanding the method to determine the necessary capacity of ESS for real-time control is studied. The time window method is used to enable the proposed method available under all working conditions. The simulation results verify the effectiveness of the proposed method.

A new hybrid pneumatic combustion engine to improve fuel consumption of wind–Diesel power system for non-interconnected areas

This paper presents an evaluation of an optimized Hybrid Pneumatic-Combustion Engine (HPCE) concept that permits reducing fuel consumption for electricity production in non-interconnected remote areas, originally equipped with hybrid Wind–Diesel System (WDS). Up to now, most of the studies on the pneumatic hybridization of Internal Combustion Engines (ICE) have dealt with two-stroke pure pneumatic mode. The few studies that have dealt with hybrid pneumatic-combustion four-stroke mode require adding a supplementary valve to charge compressed air in the combustion chamber. This modification means that a new cylinder head should be fabricated. Moreover, those studies focus on spark ignition engines and are not yet validated for Diesel engines. Present HPCE is capable of making a Diesel engine operate under two-stroke pneumatic motor mode, two-stroke pneumatic pump mode and four-stroke hybrid mode, without needing an additional valve in the combustion chamber. This fact constitutes this study’s strength and innovation. The evaluation of the concept is based on ideal thermodynamic cycle modeling. The optimized valve actuation timings for all modes lead to generic maps that are independent of the engine size. The fuel economy is calculated for a known site during a whole year, function of the air storage volume and the wind power penetration rate.