Wind Power Penetration Level Research Articles

A Two-stage Stochastic Programming Model for Optimal Reactive Power Dispatch with High Penetration Level of Wind Generation

The increasing of wind power penetration level presents challenges in classical optimal reactive power dispatch (ORPD) which is usually formulated as a deterministic optimization problem. This paper proposes a two-stage stochastic programming model for ORPD by considering the uncertainties of wind speed and load in a specified time interval. To avoid the excessive operation, the schedule of compensators will be determined in the first-stage while accounting for the costs of adjusting the compensators (CACs). Under uncertainty effects, on-load tap changer (OLTC) and generator in the second-stage will compensate the mismatch caused by the first-stage decision. The objective of the proposed model is to minimize the sum of CACs and the expected energy loss. The stochastic behavior is formulated by three-point estimate method (TPEM) to convert the stochastic programming into equivalent deterministic problem. A hybrid Genetic Algorithm-Interior Point Method is utilized to solve this large-scale mixed-integer nonlinear stochastic problem. Two case studies on IEEE 14-bus and IEEE 118-bus system are provided to illustrate the effectiveness of the proposed method.

Probabilistic forecast for aggregated wind power outputs based on regional NWP data

With the high level of wind power penetration, the big users in power systems, like system operators and market traders, demand the aggregated wind power forecasts for a specific region. A method searching for the similar wind characteristics in the numerical weather predictions (NWP) data is proposed here. The similarity is defined by a weighted Euclidean distance, and the dimensionality is reduced by means of principal component analysis. The probabilistic forecasting results are constructed by the selected samples with the proposed distance-weighted kernel density estimation method. A case study of 28 wind farms in the East China is provided to evaluate the performance. The proposed method is easy to apply and performs well in practice.

Probabilistic wind power forecasting using a novel hybrid intelligent method

As a consequence of increasing wind power penetration level, it will be a big challenge to control and operate the power system because of the inherent uncertainty of the wind energy. One of the ways to deal with the wind power variability is to predict it accurately and reliably. The traditional point forecasting-based technique cannot notably solve the uncertainty in power system operation. In order to compute the probabilistic forecasting, which yields information on the uncertainty of wind power, a novel hybrid intelligent method that incorporates the wavelet transform, neural network (NN), and improved krill herd optimization algorithm (IKHOA), is used in this paper. Also, the extreme learning machine is exerted to train NN and calculates point forecasts, and IKHOA is applied to forecast the noise variance. The robust method called bootstrap is regarded to create prediction intervals and calculate the model uncertainty. The efficiency of proposed forecasting engine is evaluated by usage of wind power data from the Alberta, Canada.

Low voltage ride-through enhancement of DFIG-based wind turbine using DC link switchable resistive type fault current limiter

Doubly-fed induction generator (DFIG)-based wind turbines utilise small-scale voltage sourced converters with a limited overcurrent withstand capability, which makes the DFIG-based wind turbines very vulnerable to grid faults. Often, modern DFIG systems employ a crowbar protection at the rotor circuit to protect the rotor side converter (RSC) during grid faults. This method converts the DFIG to a squirrel cage induction generator, which does not comply with the new grid codes. The recent grid codes need wind turbines to stay connected to the utility grid during and after power system faults, especially in high penetration level of wind power. Furthermore, the crowbar switch is expensive. This paper proposes a novel DC-link switchable resistive-type fault current limiter (SRFCL) to improve the LVRT capability of the DFIG. The proposed SRFCL is employed in the DC side of the RSC. The SRFCL solves crowbar protection activation problems and eliminates subsequent complications in the DFIG system. The proposed SRFCL does not have any significant impact on the overall performance of the DFIG during normal operation. Whenever the fault, whether symmetrical or asymmetrical, occurs, the SRFCL not only limits rotor over-currents but also prevents rotor speed acceleration and restricts high torque oscillations even during zero grid voltage, as recommended by some grid codes. To prove the effective operation of the SRFCL on the RSC fault current limitation, analytical analysis is performed in each switching interval. The proposed approach is compared with the crowbar-based protection method. Simulation studies are carried out in PSCAD/EMTDC software. In addition, a prototype is provided to demonstrate the main concept of the proposed approach.

Fulfilment of Grid Code Obligations by Large Offshore Wind Farms Clusters Connected via HVDC Corridors

The foreseen high penetration levels of wind power will force the systems operators to apply restrictive constraints on wind power plants. The ability of offshore wind clusters, which are connected via HVDC, to fulfill the grid codes, especially those related to voltage stability is investigated. This came in the frame of a project to develop an integrated and practical tool to design offshore wind clusters (EERA-DTOC). The applied case studies examine the system stability during and after severe disturbances, and the compliance with the grid codes. Additionally, this paper explains the applied procedure to utilize the outcomes of Net-OP tool, which proposes an optimized topology to connect the wind power clusters to the interconnected power systems. The integrated simulation environment, namely, PSS/E, is used to implement a highly detailed and dynamic model based on the recommendations of Net-OP tool. The results confirm that wind farm clusters respond to faults and disturbances as desired by the grid codes.

Technical impacts of high penetration levels of wind power on power system stability

With increasing penetrations of wind generation, based on power‐electronic converters, power systems are transitioning away from well‐understood synchronous generator‐based systems, with growing implications for their stability. Issues of concern will vary with system size, wind penetration level, geographical distribution and turbine type, network topology, electricity market structure, unit commitment procedures, and other factors. However, variable‐speed wind turbines, both onshore and connected offshore through DC grids, offer many control opportunities to either replace or enhance existing capabilities. Achieving a complete understanding of future stability issues, and ensuring the effectiveness of new measures and policies, is an iterative procedure involving portfolio development and flexibility assessment, generation cost simulations, load flow, and security analysis, in addition to the stability analysis itself, while being supported by field demonstrations and real‐world model validation. WIREs Energy Environ 2017, 6:e216. doi: 10.1002/wene.216This article is categorized under: Wind Power > Systems and Infrastructure Energy Infrastructure > Systems and Infrastructure

Provision of enhanced ancillary services from wind power plants – Examples and challenges

Emphasis in this article is on the power system impact of wind power plants capability to provide enhanced ancillary services, i.e. temporary frequency response (TFR) and power oscillation damping (POD). The main objective of the article is to analyze and justify the challenges in the use of TFR and POD from wind power plants (WPPs). The study is conducted with an aggregated wind power plant model which is integrated into a generic power system model, specifically designed to assess the targeted ancillary services in a relatively simple, but still relevant environment. Various case studies with different wind power penetration levels are considered.The study shows that WPPs can provide additional control features such as TFR and POD to enhance the stability of power systems with large share of wind power. Nevertheless, the results illustrate that the power system stability can be potentially degraded without careful coordination between WPPs, simultaneously providing TFR or POD in power systems with large displacement of conventional power plants by WPPs. The article provides to TSO new insights into the need for service coordination between WPPs into future power systems.

Fast adaptive back‐stepping terminal sliding mode power control for both the rotor‐side as well as grid‐side converter of the doubly fed induction generator‐based wind farms

A fast adaptive back-stepping terminal sliding mode power control strategy for both the rotor-side converter and the grid-side converter of doubly fed induction generator (DFIG) is proposed in this study. The proposed control strategy for the DFIG converters utilises the active and reactive power components derived from the three-phase voltage and current without the use of phase-locked loops. For a multimachine power network, incorporating long-distance transmission lines, inter area oscillation has been a critical issue. Additionally the integration of wind farm to the existing power systems results in the variation of its operating point over time due to unpredictable wind speed variation and consequent fluctuation in the power outputs. Further the proposed control strategy for the DFIG-based wind farms has been tested on a two- area four-generator system in MATLAB/Editor and MATLAB/Simulink environment subjected to different levels of wind power penetration. The significance and effectiveness of the proposed control strategy to damp out inter area oscillations have been illustrated in the simulation and result section.

Pilot-Bus-Centered Automatic Voltage Control With High Penetration Level of Wind Generation

The increasing wind power penetration level affects the performance of automatic voltage control (AVC) on voltage regulation. Previous studies indicated that pilot-bus selection and the partitioning method have the potential to improve the performance of AVC in maintaining the desired voltage profile. However, due to the dynamic and intermittent nature of wind generation, it is necessary to establish systematic pilot-bus selection criteria to enhance the effectiveness of AVC under high penetration level of wind power. This paper proposes a new approach for pilot-bus selection that considers both the physical response of generators and the wind power fluctuation. A new pilot-bus-centered partitioning method is also developed based on the newly defined electrical distance reflecting the controllability of pilot buses to load buses. Case studies based on the New England 39-bus system are provided to illustrate the effectiveness of the proposed approaches.

Optimal planning and operation of energy storage systems in radial networks for wind power integration with reserve support

Though energy storage system (ESS) is a promising approach to alleviate the variability of non-dispatchable wind power and other forms of renewable energy sources, its high investment cost has impeded its wide deployment. Aiming at exploiting the arbitrage benefit of ESS in reserve market and raising revenue of shareholders, this study explores the optimal planning and operation of ESS in radial networks. Besides load balancing, ESS is used to provide three kinds of operating reserve services in presence of high wind power penetration, including spinning reserve, upward and downward regulation reserves. In light of the capacity limitation of ESS, the time duration of reserve provision has been taken into account. In the proposed model, unit commitment and AC optimal power flow (AC-OPF) are combined together over sequential time series to find the optimal location and size of ESSs. In order to reduce the computational complexity, the extended DistFlow model of AC-OPF is adopted to convert the problem into a mixed-integer second-order cone programming. Numerical studies on the IEEE 34-bus distribution test feeder are used to investigate the effects of ESS with respect to various penetration levels of wind power and load scales.

Quantifying operating reserves with wind power: towards probabilistic–dynamic approaches

In this study, the economic benefits of using a probabilistic-dynamic approach (PDA) in the quantification of operating reserves are investigated and compared with more traditional quantification rules in power systems with high penetration levels of wind power. To do this, a comprehensive methodology to quantify different operating reserves categories within the real-time system operation is proposed. The quantification is based on an iterative process where the total costs of the system are minimised, that is the sum of the operating costs (including the additional costs of partially loading generating units due to operating reserves) and the costs of the expected energy not supplied. The PDA considers conventional generation outages; load and wind forecast uncertainty on an hourly basis as well as load and wind variability in a 10 min time frame. The authors use the Chilean power system to demonstrate the efficiency and advantages of the proposed reserve quantification approach.

Australian National Electricity Market Model - Version 1.10

This working paper provides details of the Australian National Electricity Market (ANEM) model version 1.10 used in the research project titled: An investigation of the impacts of increased power supply to the national grid by wind generators on the Australian electricity industry. The paper provides a comprehensive reference of the ANEM model for the other project publications that use the ANEM model to analysis the sensitivity of four factors to increasing wind power penetration. The four factors include (1) transmission line congestion, (2) wholesale spot prices, (3) carbon dioxide emissions and (4) energy dispatch. The sensitivity of the four factors to wind power penetration is considered in conjunction with sensitivity to weather conditions, electricity demand growth and a major augmentation of the transmission grid of the Australian National Electricity Market (NEM) called NEMLink (AEMO 2010a, 2010b, 2011a, 2011b).The sensitivity analyses use 5 levels of wind power penetration from zero wind power penetration to enough wind power to meet the original 2020 41TWh Large-scale Renewable Energy Target. The sensitivity to weather is developed by using half hourly electricity demand profiles by node from three calendar years 2010, 2011 and 2012. The sensitivity to growth is developed by incrementing the nodal demand profiles over the projection years 2014 to 2025.Five inputs of the ANEM model are:(1) Half hourly electricity 'total demand' for 50 nodes in the NEM;(2) Parameter and constraint values for 68 transmission lines and 330 generators, albeit incorporating the de-commissioning of Generation plant occurring over the period 2007-2014;(3) Carbon price, which is assumed zero in this project;(4) Fossil fuel prices; and(5) Network topology of nodes, transmission lines and generators.Five outputs of the ANEM model are:(1) Wholesale spot price at each node (half hourly),(2) Energy generated by each generator (half hourly),(3) Energy dispatched (sent out) by each generator (half hourly),(4) Power flow on each transmission line (half hourly), and(5) Carbon dioxide emissions for each generator (daily).ANEM uses a Direct Current Optimal Power Flow (DC OPF) algorithm to determine optimal dispatch of generation plant, power flows on transmission branches and wholesale prices.

A new merit function to accommodate high wind power penetration of WGRs (wind generating resources)

In this paper, we propose a new merit function to provide practical information to find optimal wind farm locations and projects based on spatial wind farm output prediction, including correlation with other wind farms. Our approach can predict what will happen when a new wind farm is added at various locations. Spatial power prediction of geographically distributed wind farms and their statistics through the proposed prediction model based on Kriging techniques will be presented. Using the proposed prediction model of wind generating resources, the performance of the spatial merit function in the context of the McCamey areas of ERCOT (Electric Reliability Council of Texas) will be provided. A new merit function through the prediction of wind farm outputs can play a key role to accommodate high wind power penetration from spatially distributed wind farms in power system planning models. In addition, we also propose the Kriged Wind Farm-SMES (Superconducting Magnetic Energy Storage System) hybrid model to enhance the higher wind power penetration levels using a new merit function. The proposed merit function requires only the existing data of wind generating resources around the candidate wind farm sites in order to reduce the time and costs for the installation of an anemometry tower as a practical method of wind resource assessment study compared to MCP (Measure-Correlate-Predict).

Hybrid Reference Function for Stable Stepwise Inertial Control of a Doubly-Fed Induction Generator

Upon detecting a frequency event in a power system, the stepwise inertial control (SIC) of a wind turbine generator (WTG) instantly increases the power output for a preset period so as to arrest the frequency drop. Afterwards, SIC rapidly reduces the WTG output to avert over-deceleration (OD). However, such a rapid output reduction may act as a power deficit in the power system, and thereby cause a second frequency dip. In this paper, a hybrid reference function for the stable SIC of a doubly- fed induction generator is proposed to prevent OD while improving the frequency nadir (FN). To achieve this objective, a reference function is separately defined prior to and after the FN. In order to improve the FN when an event is detected, the reference is instantly increased by a constant and then maintained until the FN. This constant is determined by considering the power margin and available kinetic energy. To prevent OD, the reference decays with the rotor speed after the FN. The performance of the proposed scheme was validated under various wind speed conditions and wind power penetration levels using an EMTP-RV simulator. The results clearly demonstrate that the scheme successfully prevents OD while improving the FN at different wind conditions and wind power penetration levels. Furthermore, the scheme is adaptive to the size of a frequency event.

An Analysis of the Effects and Dependency of Wind Power Penetration on System Frequency Regulation

The integration of renewable energy sources into power systems has gathered significant momentum globally because of its unlimited supply and environmental benefits. Within the portfolio of renewable energy, wind power is expected to have a soaring growth rate in the coming years. Despite its well known benefits, wind power poses several challenges in grid integration. The inherent intermittent and non-dispatchable features of wind power not only inject additional fluctuations to the already variable nature of frequency deviation, they also decrease frequency stability by reducing the inertia and the regulation capability. This paper closely examines these effects as well as the effect on tie-line flows and area control error, which causes a larger and longer frequency deviation in the integrated system. Further, the effect of wind power on frequency regulation capability at different penetration levels is also examined. The analytical and simulation results presented here provide some guidance on determining maximum wind power penetration level given a frequency deviation limit.

Assessing the effect of wind power peaking characteristics on the maximum penetration level of wind power

A probabilistic approach with considering the peaking characteristics of wind power is proposed to determine the maximum wind power penetration level (WPPL). To evaluate the effect wind peaking characteristics brought to the hosting capacity of systems, a detailed simulation of wind speed/load distributions over a long period is required. Thus, taking an hour as the time scale, the time-sharing peaking characteristics of wind power are discussed by describing the hourly distribution of wind output and load. Based on the chance constrained programming, a WPPL model is established in this study. The optimisation process is achieved using the improved particle swarm optimisation algorithm based on Monte–Carlo simulation. This proposed approach has been applied to an actual power system in central China. Simulation results show that the WPPL would be too optimistic without considering the anti-peaking characteristics of wind power. Besides various sensitivity analyses are performed to assess the effect of other parameters on the maximum penetration level.

Impact Study of PMSG-Based Wind Power Penetration on Power System Transient Stability Using EEAC Theory

Wind turbines with direct-driven permanent magnet synchronous generators (PMSGs) are widely used in wind power generation. According to the dynamic characteristics of PMSGs, an impact analysis of PMSG-based wind power penetration on the transient stability of multi-machine power systems is carried out in this paper based on the theory of extended equal area criterion (EEAC). Considering the most severe PMSG integration situation, the changes in the system’s equivalent power-angle relationships after integrating PMSGs are studied in detail. The system’s equivalent mechanical input power and the fault period electrical output power curves are found to be mainly affected. The analysis demonstrates that the integration of PMSGs can cause either detrimental or beneficial effects on the system transient stability. It is determined by several factors, including the selection of the synchronous generators used to balance wind power, the reactive power control mode of PMSGs and the wind power penetration level. Two different simulation systems are also adopted to verify the analysis results.

Performance analysis of energy storage system based on liquid carbon dioxide with different configurations

Due to the intermittence and fluctuation of wind resource, the increasing penetration level of wind power will bring huge challenges to maintain the stability of power system. In order to smooth the wind power output, additional controllable power from conventional power plant or energy storage system is required. In current paper, one basic scheme of liquid carbon dioxide storage system is proposed. The parametric analysis is conducted to examine the effect of some key thermodynamic parameters on the performance of this scheme. Subsequently, the basic scheme is improved according to the results. The mathematical models of two improved schemes are developed and the performance analyses are conducted. According to the results, the optimal scheme and configuration are determined. After optimization analysis and comparison analysis, compared to the other energy storage systems, the round trip efficiency of Scheme 3 is acceptable in consideration of the energy generated per unit volume of storage. As a conclusion, the optimal scheme has a good potential for storing wind power in large scale and offers an attractive solution to the challenges of the increasing penetration level of wind power.

Serving the Future: Advanced Wind Generation Technology Supports Ancillary Services

Grid integration of wind power plants is complicated by wind variability and the technical characteristics of wind generators. The generation mix is evolving in today?s power system as conventional coal plants reach the end of their useful lives and are being displaced by cleaner technology such as wind and gas. At high levels of wind power penetration, the need for ancillary services increases, while the traditional resources that provide those services may become less available or economically feasible. Developing wind plant controls that allow performance more like that of conventional generation presents the opportunity for wind plants to provide a full range of ancillary services.

Performance analysis of a novel energy storage system based on liquid carbon dioxide

Due to the intermittence and fluctuation of wind resource, the increasing penetration level of wind power will bring huge challenges to maintain the stability of power system. Integrating compressed air energy storage (CAES) system with wind farms can weaken this negative effect. However CAES system needs large caverns or mines to store compressed air, which is restricted in application. In this paper, a novel energy storage system based on liquid carbon dioxide is presented. The mathematical models of compressed liquid-carbon dioxide energy storage system are developed. The parametric analysis is conducted to examine the effect of some key thermodynamic parameters on the system performance. Compared with AA-CAES, the liquid carbon dioxide energy storage system has advantages such as a high energy density, high EVR. Moreover, the round trip efficiency of this system can reach about 56.64%, which is acceptable in consideration of the storage volume. Therefore, this proposed system has a good potential for storing wind power in large scale and offers an attractive solution to the challenges of the increasing penetration level of wind power.