Increasing Wind Power Generation Research Articles

Stability Domain Analysis and Enhancement of Squirrel Cage Induction Generator Wind Turbines in Weak Grids

There are significant concerns regarding the stability of increased wind power generation in weak power grids. This paper investigates and improves the stability of Wind Turbine Squirrel Cage Induction Generators (WT-SCIGs) with series compensation and weak interconnections to the power grid. Detailed time-domain and state-space modeling have revealed new bifurcations and oscillatory modes for a WT-SCIG connected radially to a weak grid through a series compensated line. The stability domain analyses are carried out by computing bifurcations in the system by analyzing eigenvalues of the linearized system. The analyses demonstrate for the first time how the degree of compensation at which the Hopf bifurcation occurs depends on the X/R ratio of the line, operating slip of the induction generator, and voltage regulator parameters as well as the time delays in measurements. A new damping controller is proposed, which greatly improves the dynamic stability of the WT-SCIG and eliminates destructive Hopf bifurcations in weak grids for a wide range of series compensation. This allows for a much larger percentage of series compensation than what is usually possible, while avoiding instabilities, thereby maximizing the power transfer capability.

A Modified Reynolds-Averaged Navier–Stokes-Based Wind Turbine Wake Model Considering Correction Modules

Increasing wind power generation has been introduced into power systems to meet the renewable energy targets in power generation. The output efficiency and output power stability are of great importance for wind turbines to be integrated into power systems. The wake effect influences the power generation efficiency and stability of wind turbines. However, few studies consider comprehensive corrections in an aerodynamic model and a turbulence model, which challenges the calculation accuracy of the velocity field and turbulence field in the wind turbine wake model, thus affecting wind power integration into power systems. To tackle this challenge, this paper proposes a modified Reynolds-averaged Navier–Stokes (MRANS)-based wind turbine wake model to simulate the wake effects. Our main aim is to add correction modules in a 3D aerodynamic model and a shear-stress transport (SST) k-ω turbulence model, which are converted into a volume source term and a Reynolds stress term for the MRANS-based wake model, respectively. A correction module including blade tip loss, hub loss, and attack angle deviation is considered in the 3D aerodynamic model, which is established by blade element momentum aerodynamic theory and an improved Cauchy fuzzy distribution. Meanwhile, another correction module, including a hold source term, regulating parameters and reducing the dissipation term, is added into the SST k-ω turbulence model. Furthermore, a structured hexahedron mesh with variable size is developed to significantly improve computational efficiency and make results smoother. Simulation results of the velocity field and turbulent field with the proposed approach are consistent with the data of real wind turbines, which verifies the effectiveness of the proposed approach. The variation law of the expansion effect and the double-hump effect are also given.

IMPROVING THE REACTIVE POWER CAPABILITY OF GRID CONNECTED DOUBLY FED INDUCTION GENERATOR

Due to increasing wind power generation in the electric power system, the reactive power generation by the wind farms is a major concern during both steady state and faulty conditions. This work, first, presents the reactive power capability (RPC) curve of doubly-fed induction generator (DFIG) considering three limitations (rotor voltage, rotor current and stator current) for reactive power production/consumption, for the complete operating range which is obtained by optimal rotor speed employing maximum power point tracking (MPPT) algorithm. It is established that the total reactive power generation is limited by rotor voltage at low speeds and by rotor current at higher speed. However, the total reactive power consumption is limited by stator current, for entire operating region. Selection of partial rated converter rating is crucial in terms of cost, efficiency, operating speed range and reactive power capability. The effect of converters rating on the enhancement of RPC of doubly fed induction generation is analyzed. Complete capability curves of DFIG for different stator voltages are developed considering grid-side converter (GSC) contribution towards reactive power capability.

Are conventional energy megaprojects competitive? Suboptimal decisions related to cost overruns in Brazil

Cost minimization is arguably the most important criterion governing decisions about energy sector infrastructure construction. Usually, a winning project is picked among similar alternatives based on lowest levelized cost of energy, because, ceteris paribus, economies of scale drive down the unit cost of energy delivered. As such, megaprojects – here defined as costing more than a benchmark US$ 1 billion – are perceived as more competitive than smaller-scale options. However, megaprojects are prone to construction cost overruns and delays that, if included ex ante, may change the optimality of decision for a given project. We hypothesize that optimistic assumptions on techno-economic performance of megaprojects favor their inclusion in the solution of integrated assessment models (IAMs), preventing higher shares of non-hydro renewables, energy efficiency and other low-carbon options. To test this hypothesis, we ran the COPPE-MSB energy system cost-optimization model for infrastructure expansion. We estimate a factor (named Z factor, for zillions) to determine cost differences both within Brazil and vis-à-vis international parity and adjust the model's parameters for CAPEX and construction times of projects qualifying as megaprojects. Results show decreased coal and increased wind power generation, and a reduction in the number of new refineries leading to higher imports of diesel and gasoline.

Enhancing flexibility of power systems by exploiting operational controllability of large‐scale wind farms

Even though increasing wind power generation significantly benefits the greening of power system generation, the intrinsic uncertainty and variability associated with large‐scale wind generation greatly challenge the current power system operation, such as unit commitment (UC) and economic dispatch. So far, major wind farms are straightforwardly integrated into the existing UC framework as negative loads and operated with a wind‐in‐priority mode. With the prompt development of the control techniques of wind generators, such as switching on/off or fast pitching control, this manner of operation may underestimate the controllability of wind farms and result in the lack of operational flexibility of the power system. This paper addresses the issue by exploiting the controllability of wind farms in UC decision while considering its inherent uncertain nature. First, the wind generation controllability is modeled as an adjustable scenario set associated with prediction errors. And then a modified two‐stage stochastic UC model is formulated to incorporate the operational controllability of wind farms. A modified IEEE 39‐bus system is employed to demonstrate the proposed methodology. Simulation results show that the utilization of wind generation controllability can considerably benefit the economy, reliability, and flexibility of power system dispatch. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Aggregating the Demand Flexibility Related to Electric Hot Water Heating Under Endogenous Day-Ahead Prices

Residential sector has a large underutilized potential for demand response in its electricity consumption optimization. In this study residential electric hot water heaters (EHWH) are considered as distributed energy storage providing demand response in electricity markets. Heating optimization is conducted with a dynamic optimization model describing the water heating characteristics in Finland. Cost and CO2 emissions minimizing optimal heating controls are solved for an individual household and for a pool of EHWHs controlled by an aggregator. Water heating costs under fully dynamic and static electricity pricing contracts are compared. Our main contribution is to provide important insights of complex market dynamics related to the demand response resource aggregation, different electricity pricing contracts and increasing wind power generation. There are three main results. First, households benefit from adopting dynamic electricity pricing and allowing load control in terms of heating cost savings. Secondly, the optimal number of controlled EHWHs depend on the viewpoint. Lastly, cost minimization yields relatively good solution from environmental perspective when compared with the emissions minimization target.

Effects of Increased Wind Power Generation on Mid-Norway’s Energy Balance under Climate Change: A Market Based Approach

Thanks to its huge water storage capacity, Norway has an excess of energy generation at annual scale, although significant regional disparity exists. On average, the Mid-Norway region has an energy deficit and needs to import more electricity than it exports. We show that this energy deficit can be reduced with an increase in wind generation and transmission line capacity, even in future climate scenarios where both mean annual temperature and precipitation are changed. For the considered scenarios, the deficit observed in winter disappears, i.e., when electricity consumption and prices are high. At the annual scale, the deficit behaviour depends more on future changes in precipitation. Another consequence of changes in wind production and transmission capacity is the modification of electricity exchanges with neighbouring regions which are also modified both in terms of average, variability and seasonality.

Voltage quality assessment considering low voltage ride‐through requirement for wind turbines

This study proposes an effective method for voltage quality assessment considering low voltage ride-through (LVRT) requirement for wind turbines. With increasing wind power generation, there is a strong need for system connection requirements of wind turbines, for stable system operation even under fault conditions. The LVRT requirements specify acceptable voltage magnitude and duration for maintaining the connection to power systems under voltage sags. In general, different grid connection points of wind farms have different voltage quality performance. Therefore, LVRT requirements can be severe for certain connecting points and wind turbines. The proposed method can efficiently assess voltage sag performance at grid connection points, and vulnerable connection points that can be expected to incur more severe voltage sags causing wind turbine disconnections can be identified.

Prediction of Horizontal Axis Wind Turbine Acoustics

Wind power industry has been a growing market and maturing technology for several decades. Increasing wind power generation necessitates closer installation of wind turbines to people and their residences. For that reason, wind turbine noise becomes a serious and controversial phenomenon and it is anticipated to become more stringent issue while wind power generation is increased recently. The aim of this study was to propose a methodology to predict the wind turbine blade noise by using two dimensional blade section flows and noise analysis/simulation and combining the noise sources to evaluate the total blade noise with reasonable accuracy. Within the scope of this work, the purpose was to perform a two dimensional flow and noise simulation for the two bladed NREL Phase VI wind turbine with the aid of a commercially available Computational Fluid Dynamics (CFD) software ANSYS-FLUENT by using User Defined Functions after applying some corrections under certain assumptions. Analysis results were compared with the 12% scaled model of NREL Phase VI wind turbine acoustic noise measurements conducted in In Korea Aerospace Research Institute (KARI) at the low speed wind tunnel. Blade noise of the measurements were compared with the analysis results at different wind speeds of 5.4 m/s, 7.4 m/s, 12.3 m/s, and 13.3 m/s. For the tip region and inboard area of the blade, reasonable agreement was achieved at certain wind speeds. Additionally, the summation of the contribution from the each blade section was used to predict the total noise emission.

Impact of increased wind power generation on subsynchronous resonance of turbine-generator units

With more and more wind power generation integrated into power grids to replace the conventional turbine-generator (T-G) units, how the subsynchronous resonance (SSR) of conventional T-G units is affected becomes an important technical issue. In this paper, a group of T-G units are interconnected with a series compensated transmission line, and some units are substituted by a nearby DFIG-based wind farm (WF). Under such circumstances, the SSR of power systems would change accordingly. This paper establishes the mathematical model to analyze the torsional interaction (TI) and the induction generator effect of the T-G units. Both eigenvalue analysis and time domain simulations demonstrate the impact of DFIG-based WF on SSR of power systems and how the control parameters of wind farms can affect the SSR.

Analyzing the Impacts of Wind Generation on Distribution System Performance

Increasing wind power generation affects performance of existing power system in terms of power losses, voltage regulation and short circuit levels. Jhimpir wind generation having 49.5 MW capacity is connected to 132kV network of Hyderabd Electric Supply Company (HESCO) to meet its energy demand. Distribution network of HESCO is modelled and simulated using Power system Simulator – Siemens Network Calculator (PSS SINCAL) as simulation platform. Simulation results are compared to observe impacts of wind integration to existing power system network. Simulation results indicate reduction of power losses from 15.26 to 14.79MW as a result of wind integration to existing HESCO network. Reduction in power losses is mainly caused by changed current flows in lines. Reduction in current also reduce line drops resulting in improved bus voltages. Short circuit level is slightly increased for all buses due to network modification. Increase in short circuit level is highest near the wind generation as Zorlu grid shows 13.02% increase. 66kV network shows small increase in short circuit level due to its long distance from wind generation facility. Use of real network data for this research work identifies possible protection issues alongwith the reduction in power losses and voltage drop. Each system network has separate network parameters and will have different response to any network change. Hence a simulation analysis is important to ensure maximum benefits from renewable energy sources and their integration with existing power system network

풍력발전과 전기자동차가 전력계통의 신뢰도에 미치는 영향 평가

An increasing number of electric vehicles (EVs) in power system affects its reliability in various aspects. Especially under high EV penetration level, new generating units are required to satisfy system’s adequacy criterion. Wind power generation is expected to take the major portion of the new units due to environmental and economic issues. In this paper, the system reliability is analyzed using Loss of Load Expectation (LOLE) and Expected Energy Not Served (EENS) under each and both cases of increasing wind power generation and EVs. A probabilistic multi-state modeling method of wind turbine generator under various power output for adequate reliability evaluation is presented as well. EVs are modeled as loads under charging algorithm with Time-Of-Use (TOU) rates in order to incorporate EVs into hour-to-hour yearly load curve. With the expected load curve, the impact of EVs on the system adequacy is analyzed. Simulations show the reliability evaluation of increasing wind power capacity and number of EVs. With this method, system operator becomes capable of measuring appropriate wind power capacity to meet system reliability standard.

Evolution of primary frequency control requirements in Great Britain with increasing wind generation

Abstract With the increase of renewable generating capacity following the ambitious targets set by many governments for the next decades, there will be major changes in power generation and challenges for balancing transmission grids. In particular, primary frequency control requirements will be increased following a potential reduction of system inertia. An assessment of the frequency response reserve needed is made through use of a simple model of the Great Britain transmission grid for different loads and wind power penetration. This model analyses the effect of changing the system inertia and the effectiveness of standard frequency response as well as dynamic frequency control support. It is observed that an increased wind power generation requires substantial additional reserves for primary frequency control if the wind turbines do not contribute to the overall system inertia. However, it is also shown that these reserves can be dramatically reduced if the system is provided with fast acting response by dynamic frequency control support.

Impact of Increasing Wind Power Generation on the North-South Inter-Area Oscillation Mode in the European ENTSO-E System

After the enlargement of the European ENTSO-E power system towards Turkey at the end of 2010, the East-West Inter-Area Oscillation mode in the enlarged the European ENTSO-E power system has been identified in the frequency range of 0.15 Hz (TP = 7s) accompanied by insufficient damping. By the end of 2012, more than 107 GW of wind generation capacity had been installed across Europe, representing about 25% of the peak demand of ENTSO-E power system. In this paper, the impact of large scale wind power generation in the European ENTSO-E system on the North-South Inter-Area Oscillation mode using a detailed dynamic model of the European ENTSO-E system is investigated by gradually replacing the power generated by the synchronous generators in the system either Full Size Converter or Doubly Fed Induction Generator (DFIG) wind turbines. Because the whole system is extremely nonlinear, the analysis method in state space is senseless; therefore the damping behavior of Inter-Area-Oscillations of the whole system was analyzed in detail using the analysis method in time domain. The model was created using DIgSILENT software.

Impact of Wind Power Development on Transmission Planning at Midwest ISO

The Midwest Independent Transmission System Operator (MISO) has experienced significant amounts of wind power development within the last decade. The MISO footprint spans the majority of the upper Midwest region of the country, from the Dakotas to Indiana and as far east as Michigan. These areas have a rich wind energy resource. States in the MISO footprint have passed laws or set goals that require load serving entities to supply a portion of their load using renewable energy. In order to meet these requirements, significant investments are needed to build the transmission infrastructure necessary to deliver the power from these often remote wind energy resources to the load centers. This paper presents some of the transmission planning related work done at MISO which was largely influenced by current and future needs for increased wind power generation in the footprint. Specifically, topics covered are generator interconnection, long-term planning coordination, and cost-allocation for new transmission lines.

Improved Reactive Power Capability of Grid Connected Doubly-Fed Induction Generators

Due to increasing wind power generation in the electric power system, the reactive power generation by the wind farms is a major concern during both steady state and faulty conditions. This paper, first, presents the reactive power capability (RPC) curve of doubly-fed induction generator (DFIG) considering three limitations (rotor voltage, rotor current and stator current) for reactive power production/consumption, for the complete operating range which is obtained by optimal rotor speed employing maximum power point tracking (MPPT) algorithm. It is established that the total reactive power generation is limited by rotor voltage at low speeds and by rotor current at higher speed. However, the total reactive power consumption is limited by stator current, for entire operating region. Selection of partial rated converter rating is crucial in terms of cost, efficiency, operating speed range and reactive power capability. The effect of converters rating on the enhancement of RPC of doubly fed induction generation is analyzed. Complete capability curves of DFIG for different stator voltages are developed considering grid-side converter (GSC) contribution towards reactive power capability.

Dual Electric Power Supply with Increasing Wind Power Generation, Requirement for an Advanced Secondary Control Concept

Based on the example of the East German power system - being coupled to the European interconnected grid - there has been investigated for low load situations- up to which amount wind power generation can be fed in and transported through the high voltage transmission network as well as- up to which amount wind power can be overtaken by reducing as far as possibly the power generation of the normal power plant units.Based on this an advanced secondary control concept (tie line bias control) is introduced for a fair splitting up of the whole renewable power generation, which is fed into the interconnected power system, to the different grid partners.