Turbine Inertia Research Articles

Performance Evaluation of Small Wind Turbines Under Variable Winds of Cities: Case Study Applied to an Ayanz Wind Turbine with Screw Blades

Small wind turbines placed at city locations are affected by variable-speed winds that frequently change direction. Architectural constructions, buildings of different heights and abrupt orography of Cities make the winds that occur at City locations more variable than in flat lands or at sea. However, the performance of Small-wind turbines under this type of variable wind has not been deeply studied in the specialised literature. Therefore, this article analyses the behaviour of small wind turbines under variable and gusty winds of cities, also considering three types of power electronics conversion configurations: the generally used Maximum Power Point Tracking (MPPT) configuration, the simple only-rectifier configuration and an intermediate configuration in terms of complexity called pseudo-MPPT. This general-purpose analysis is applied to a specific type of wind turbine, i.e., the Ayanz wind turbine with screw blades, which presents adequate characteristics for city locations such as; safety, reduced visual and acoustic impacts and bird casualties avoidance. Thus, a wide simulation and experimental tests-based analysis are carried out, identifying the main factors affecting the maximisation of energy production of small wind turbines in general and the Ayanz turbine in particular. It is concluded that the mechanical inertia of the wind turbine, often not even considered in the energy production analysis, is a key factor that can produce decrements of up to 25% in energy production. Then, it was also found that electric factors related to the power electronics conversion system can strongly influence energy production. Thus, it is found that an adequate design of a simple pseudo-MPPT power conversion system could extract even 5% more energy than more complex MPPT configurations, especially in quickly varying winds of cities.

Modeling the Coupling of Rotor Speed, primary Frequency Reserve and Virtual Inertia of Wind Turbines in Frequency Constrained Look-Ahead Dispatch

Modeling the Coupling of Rotor Speed, primary Frequency Reserve and Virtual Inertia of Wind Turbines in Frequency Constrained Look-Ahead Dispatch

Virtual inertia control to active support of the variable-speed wind turbine in variable frequency limit time

Constraining the virtual inertia of variable-speed wind turbines within the variable frequency limit time will be the key to improving the wind power’s reliability in actively supporting the system frequency. First, this paper analyzes the controllable characteristics and evaluation methods of the virtual inertia of the wind turbine. Second, it quantifies the variable frequency limit time of the grid with high-proportion wind power and considers the wind turbine speed and power margin to restrict the virtual inertia of the wind turbine during the period of frequency drop or increase to provide reliable inertia support to ensure the safety of the system frequency. On this basis, the inertia demand under the frequency safety of the system was analyzed, and the virtual inertia control strategy of the variable-speed wind turbine in the variable frequency limit time was proposed using the speed tracking performance of the wind turbine. Finally, the grid with a high-proportion wind power simulation system is built to verify that the variable-speed wind turbine can reliably satisfy the inertia demand of system frequency modulation under the proposed control strategy and significantly improve its active support performance to the power grid.

Deviation of Frequency and Inertia with penetration of Renewable

Inertia response is a function of bulky synchronous generators with large rotating rotor masses that cover the instantaneous difference between supply and grid demand, typically in power grids. The rotor rotation frequency helps speed up or slow down the rotor rotation due to the lack of adequate gap between the power supply and the electrical power demand. When demand increases or a fault occurs, or load fluctuations exceed the balance of supply and demand, grid inertia is always induced at this stage. This helps the automatic grid operator rebalance the system to avoid speed drifts, resulting in a relatively small change in AC frequency over the system's frequency range. But the system consists of a system with low or zero inertia, like the wind, it lacks the effect of inertia and could not gain equilibrium. So, to balance and to reach the target frequency; the frequency deviation of the system due to the lack of inertia of the wind turbine is improved by the droop control technique in this research because the wind system reduced the total inertia of the system. Droop rate control mode for AC generator techniques was used to control the frequency fluctuations due to the lack of inertia of the renewable energy system. A synchronous generator connected to the mains was used as the governor control mode. It works by controlling power generation using the mains frequency of the prime mover. This mode allows synchronous generators to run in parallel and share the loads with the same drooping technique in proportion to their rated output. Injected grid inertia increased generator inertia on large power grids.

Generating a virtual physical model through measurement data and reverse engineering: Applying a performance prediction model for an industrial gas turbine during start-up

The gas turbine virtual physical model can be applied to various fields such as performance optimization, diagnostics, and prognostics. For this purpose, it is important to increase the accuracy of the physical model. However, in order to generate such a model, the design information and off-design performance characteristics of its components are required, yet it is difficult to obtain this information because manufacturers do not generally release it. This study proposes a method for the generation of a virtual physical model to predict gas turbine system performance through reverse engineering, based on operational data but without information on component performance or design information; its effectiveness is discussed. There have been many studies to correct an initial gas turbine’s physical model using operational data. In the existing studies, detailed component performance and design information was required, to generate an initial physical model. It is normally difficult to obtain component performances and design information. Therefore, a method is proposed to generate a physical model at a reference point, using operating data and assumed information, and to create a final physical model through component performance map correction. An initial physical model is constructed based on the information and performance characteristics used for general gas turbine components, not design information of the target engine. The component blocks consisting of the gas turbine are simplified by combining them at each region. In addition, a method of estimating the moment of inertia of a gas turbine’s rotating parts, using operating data, was proposed. The target engine is a single-shaft industrial gas turbine consisting of a compressor, combustor, and turbine. A virtual physical model was created using one of the three datasets measured in the start-up operation; the accuracy of the generated model was verified using the other two datasets. Shaft speed, fuel mass flow rate, compressor exit temperature, compressor total pressure ratio, and exhaust gas temperature measurement data were used. As a result, it was confirmed that, for both the data used to generate the model and the data that were not, the model predicted the measured variables well. It is expected that the proposed method can be used to create a virtual physical model for use in operation optimization and diagnostics from the operator's point of view, where it is difficult to obtain component performance and design information.

Aggregated SFR model for VSC HVDC interconnected power systems with high penetration of wind power

This letter proposes a novel aggregated system frequency response (ASFR) model, which can fully capture the frequency characteristics of the voltage source converter-based high voltage direct current (VSCHVDC) interconnected power system with high penetration of wind power. First, a multi-machine SFR model is presented, considering the inertia and frequency control processes of VSCHVDC and wind turbines (WTs). Then, a novel aggregation approach is proposed to transform the multi-machine SFR model into a single-machine SFR model on the basis of different control modes of the VSCHVDCs and WTs. Finally, simulation studies are conducted to validate the performance of the proposed ASFR model and its application in frequency response analysis.

Optimizing the integration of photovoltaic and wind energy systems for enhanced efficiency

This paper presents a novel integration scheme of solar Photovoltaic (PV) with a large-capacity Doubly Excited Induction Generator (DFIG)-based wind energy system. The proposed scheme leverages both the grid and rotor-side power converters of the DFIG to inject PV power into the grid, eliminating the need for a dedicated converter for PV power processing and offering a cost-effective PV-grid integration solution. The system effectively delivers a substantial amount of PV power to the grid when compared to an equivalent rating inverter used in conventional PV-grid systems. Moreover, the proposed scheme prevents circulating power during sub-synchronous operation in the presence of solar radiation, enhancing overall system efficiency. Additionally, the system's stability benefits from turbine inertia, allowing for higher PV penetration into the power grid. The intermittent complementary nature of solar PV and wind energy sources significantly improves the utilization of the converters. Furthermore, the proposed scheme minimally impacts Maximum Power Point Tracking (MPPT) for PV and wind sources, except in rare environmental glitches, which the PV power control algorithm is adept at handling. The study provides a comprehensive system model used to design the control strategy, supported by analysis, simulations, and experiments conducted on a laboratory prototype.

Synchronverter-based frequency control technique applied in wind energy conversion systems based on the doubly-fed induction generator

• A novel synchronverter-based approach for frequency support is proposed. • A comprehensive analysis of three frequency control techniques is presented. • A modified IEEE 14-bus test system is used to assess a wind farm. The increasing penetration of wind energy conversion systems (WECSs) based on the doubly-fed induction generator (DFIG) has raised serious concerns about the stability of modern power systems. One important issue is the frequency control of interconnected networks, which may become more complex owing to the low inertia of wind turbines. In this context, this work presents a novel frequency control approach that associates the grid-side converter (GSC) with a synchronverter. To assess the performance of the proposed solution, a thorough comparison with other well-known frequency control techniques is presented, that is, pitch angle control and switching angle controller (SAC). Simulation tests of the IEEE 14-bus modified test system are carried out in PSCAD/EMTDC® software to assess the behavior of a 165 MW wind farm (WF) when frequency variations occur. The results show that the classical control approaches can restore the system frequency within a time interval up to 63% shorter and a frequency dip lower than 13% when compared with WECSs that cannot provide frequency support. In turn, the synchronverter-based technique presents improved performance while attenuating a frequency dip by 45.7% and 56.9% when compared with the aforementioned strategies and WECSs without frequency support, respectively.

An Improved Adaptive Load Shedding Control Strategy for Primary Frequency Regulation of Wind Power Generation System

With the continuous improvement of the proportion of wind power generation, the volatility and uncertainty of wind power pose a serious threat to the stable operation of the power system. However, the traditional primary frequency regulation strategy does not fully consider the influence of wind turbine inertia. In addition, it may cause the secondary frequency drop if the instantaneous power of the wind turbine drops too much during the speed recovery. To solve this problem, this paper proposes an adaptive primary frequency regulation strategy for the mobile load shedding power tracking curve. Under this strategy, by controlling the output active power reference value, the kinetic energy stored in the rotor is fully released to support the grid frequency for a short time. Then, in the process of rotor speed recovery, the frequency secondary drop can be alleviated by moving the load-shedding power tracking curve. Finally, the simulation results in MATLAB/Simulink verify the rationality of the proposed adaptive load-shedding control strategy.

Extended Simplified Electro-Mechanical Model of a Variable-Speed Wind Turbine for Grid Integration Studies: Emulation and Validation on a Microgrid Lab

The energy transition towards renewable energies is crucial for the sustainable development of a society based on hydrocarbons. The current level of penetration and growth of wind energy in electric power systems is evident and many researchers have presented new methods for simulating and representing the electrical and mechanical characteristics of variable-speed wind turbines. However, complete mathematical models developed and implemented, for example, in MATLAB/Simulink® software, require significant computational efforts that could make grid studies impractical when its scale tends to increase. To contribute to facing this issue, this paper proposes an extended simplified model for a variable-speed wind turbine that considers the dynamic behavior of its mechanical system and includes an approximate representation of the power electronic converter. This approach broadens the scope of studies related to grid frequency control and power quality (fast-frequency response, primary frequency control, and voltage control, among others), considerably reducing the computational burden. Several validations of the proposed simplified model are presented, including comparisons with a doubly fed induction generator-based wind turbine model (phasor type) from the MATLAB/Simulink® library, and laboratory experiments under controlled conditions. The results show a good fit of the proposed simplified model to the MATLAB/Simulink® model, with minimal delays about 3% of the wind turbine inertia constant. Moreover, with the proposal, the computational time is reduced by up to 80% compared to a detailed model. This time reduction is achieved without penalizing the numerical accuracy and the estimation quality of the real behavior of the variable-speed wind turbine.

Impact of Battery Energy System Integration in Frequency Control of an Electrical Grid with Wind Power

The rapid increase in the integration of renewable energy sources into the electrical grid is posing new challenges for the dynamic responses due to the global inertia reduction. In this regard, the impact on frequency stability of such reduction and the potential support from wind power have been investigated lately. However, it is well-known that the variability of wind power and its reduced inertia may not be enough to handle the power unbalance. Energy storage systems (e.g., batteries) may provide the required additional flexibility to ensure proper response. In this paper, an analysis of how the different control loops for frequency support on wind power and batteries interact and perform is presented. To gain insights from the different impacts, a sensitivity analysis comparison for frequency regulation through (i) inertia and droop control of a variable speed wind turbine and (ii) battery is performed. The analysis was carried out through simulations using the well-known 4 generator 2-area model adapted to include a wind farm. From a battery perspective, its ramping capabilities were varied to provide frequency regulation. The paper shows how, depending on the control parameters and battery size, the frequency response may even become unstable due to interactions of the various pieces of technology. Thus, it shows that coordinated actions, control optimization and grid status among different actors on the grid (as battery and wind) is required for stable operation.

Increasing the stability of hydrogen production in the wind energy-hydrogen system through the use of synthetic inertia of the wind turbine

One of the trends in the development of the electric power industry in the world is the use of renewable resources. In recent years, the development of hydrogen energy has been widely discussed, which, when combined with renewable energy sources, makes it possible to obtain “green” hydrogen. One of the promising solutions for obtaining green hydrogen is the development of wind energy-hydrogen systems. However, one of the limiting factors, in addition to economic aspects, are technical limitations. Sustainable hydrogen production is complicated by the variability of wind energy. In addition, energy systems with a predominant share of wind power units have a low total inertia value. Consequently, such systems become more sensitive to changes in load modes in the grid and become less stable in emergency modes. Together, these facts reduce the reliability of wind energy-hydrogen system. The paper proposes to increase the stability of wind energy-hydrogen system and power system as a whole to apply synthetic inertia for wind power plants. It is shown that by adjusting the parameters of synthetic inertia can provide not only the required inertial response, but also increase the dynamic stability of the power system and as a consequence wind energy-hydrogen system. The influence of the measurement window time and calculation of the frequency change rate, which is important in certain modes, is also investigated.

Closed-Form Solution of Fundamental Frequency of Steel-Concrete Hybrid Wind Turbine Tower

With the development of wind power energy, the steel-concrete hybrid tower has been gradually popularized as the onshore tall wind turbine tower. To avoid the resonant response that brings violent damage to the wind turbine tower, the fundamental frequency of the hybrid tower must be carefully analyzed. This study develops a closed-form solution of the fundamental frequency of the hybrid tower, where the abrupt changes of cross-section and material properties, the effect of prestressing, and the mass and rotary inertia of the wind turbine are taken into account. It provides an effective way to obtain the fundamental frequency in the preliminary design of the hybrid tower. The effectiveness of the proposed solution is validated by comparing it with the results of finite element analysis, showing good agreement. By using the proposed solution, a parametric analysis is conducted to investigate the variation rules of the fundamental frequency to the design parameters. It indicates that with the variation of the proportion of the concrete/steel segments, the correlations between the fundamental frequency and the design parameters also change significantly. The parametric analysis conducted herein may provide instructive guidelines to adjust the parameters in the preliminary design of the hybrid tower.

Comparison of primary frequency control methods for wind turbines based on the doubly fed induction generator

The penetration of large levels of wind energy leads to technical problems affecting the frequency stability of the power system. Naturally, a wind power plant does not provide an inertial response nor does it regulate the system frequency in case of generation-demand imbalance due to the decoupling between the rotor speed and the grid frequency through the electronic converter (AC/DC/AC). This paper reviews, analysis and compares the performance of four control methods based on the modification of the electromagnetic torque set point and one of the mechanical torque. These methods allow that activation of the wind turbine inertia when a frequency deviation occurs, contributing to the regulation of the system frequency similarly to a conventional synchronous generator. However, wind turbines only change their operating point for a limited time and not permanently.

Intermittent power control in wind turbines integrated into a hybrid energy storage system based on a new state-of-charge management algorithm

Wind technology has developed sustainably in recent decades, becoming the primary source of renewable energy integrated into the power system. The high penetration levels of wind energy involve technical problems because of the intermittent power injected by wind turbines, caused by the variability of wind speed. This means a significant challenge in the operation of power grids reliably. This paper presents the intermittent power control in wind turbines based on direct-drive permanent magnet synchronous generator technology (DD-PMSG) integrating through the DC link a hybrid energy storage system (HESS) composed of lithium-ion electrochemical batteries (BESS) and supercapacitors (SESS), to convert a wind power plant into a dispatchable energy source. To ensure the stable operation of the wind turbine and HESS system, a new algorithm is developed to manage the state-of-charge (SOC) of the HESS to avoid its full charge/discharge. This is achieved by considering the mutual support between the batteries and the supercapacitors. The simulation results illustrate the power variation of the wind turbine integrated to the HESS, with different wind speed profiles and different initial state-of-charge for the BESS and SESS. Furthermore, it is shown how the algorithm manages the state-of-charge of the HESS under both normal and critical operation, demonstrating a good performance during the system operation. In this way, the power output of the wind turbine becomes stable and controllable, even in adverse situations, thanks to the control of the algorithm. Finally, new concepts related to wind turbine inertia and wind turbine rotational speed have been introduced from the point of view of the generator and the grid, which could be useful for electrical studies. The whole dynamic model has been developed in MATLAB/Simulink.

Some effects of turbine inertia on the starting performance of vertical-axis hydrokinetic turbine

Straight-bladed vertical-axis hydrokinetic turbines have a number of advantages for power extraction from river, tidal, and ocean currents. They are simple to construct, the generator does not need to be submerged, and they can have good power extraction efficiency. Among their potential disadvantages is that when the load is lost, or when they start with no load, they can reach high instantaneous blade speeds before returning to a “steady” runaway speed. These high speeds can cause high loads on the blades and must, therefore, be fully understood. This paper describes a computational investigation of the effect of inertia as a turbine starts from rest with no load and reaches runaway. Turbine inertia is modified by altering the blade density while the turbine geometry is not altered. At the minimum inertia, the added mass contributes significantly to the dynamics, and the highest overshoot occurs in blade speed. Increasing inertia damps the peak but slows the acceleration. The added mass depends on blade mass but is constant for the whole starting sequence and is independent of water speed. The results give guidance for the design of turbines to balance the minimization of the overshoot and starting time.

Transient analysis of H-type Vertical Axis Wind Turbines using CFD

In this study, the effect of various parameters on the start-up and transient behavior of Darrieus straight-bladed Vertical Axis Wind Turbine (VAWT) was analyzed. Airfoil profile, angle-of-attack, and chord length were varied, yielding two optimal turbines, one for transient and another for steady performance. This optimization revealed that the chord length (solidity) has the most significant impact on the performance of the turbine undergoing both transient and steady operations. An examination of the contribution of drag and lift forces to the startup of these two optimized turbines shows that the drag has a positive contribution to the performance of the transient optimized turbine especially at high TSRs. The performance of the optimized turbines when subject to four different wind profiles: a real wind profile, and three distinct sinusoidal profiles was also assessed. At low average wind speeds, a high frequency of the incoming wind is favorable for allowing both optimized turbines to produce more power. The rotor behavior under dynamic loads was also investigated, demonstrating that the transient optimized turbine is more responsive and therefore easier to control. In addition, minimizing the inertia of the steady-optimized turbine significantly improves its startup characteristics, making it superior to its steady-optimized counterpart.

Small Signal Stability Analysis and Optimize Control of Large-Scale Wind Power Collection System

The frequency security problem of power system is highlighted as wind power penetration increases yearly, the eigenvalue analysis method based on the deterministic model is difficult to accurately evaluate the small signal stability of power system. The Weibull probability distribution is used to describe the uncertainty of wind speed. In this paper, the shape and scale parameters of the Weibull distribution are calculated by using the maximum likelihood approach and combining with the measured data, and the stability of small signal with large-scale wind power access is analyzed by the probability distribution method. Meanwhile, considering that the lack of inertia of the system caused by high-penetration wind power access can easily lead to the problem of frequency stability, it is proposed to take the maximum damping ratio of regional oscillation mode as optimization objective, virtual inertia and pitch angle control parameters as variables, and frequency stability as constraints, an small signal stability optimization model of wind power access to power system is established according to the proposed probabilistic small signal stability model. The sensitivity algorithm is used to obtain the optimal solution for the virtual inertia and pitch angle control parameters, and the validity of the proposed method and model is verified by two-area four-machine examples. Simulation results show that by optimizing the virtual inertia and pitch angle parameters of wind turbines, the small signal stability of the high-penetration wind power access system can be improved under the condition of ensuring sufficient inertia of the system, which provides a certain theoretical basis for the safe and reliable operation of wind power large-scale cluster access power system.

Dynamic Study of Load Detachment in Supercritical Carbon Dioxide Brayton Cycle

The supercritical carbon dioxide Brayton cycle has become the choice of a wide range of users because of its higher efficiency and smaller turbine size, and is often used in space vehicles, sodium cooled fast reactors, Marine power equipment and other energy storage and power generation applications. However, in the process of use, the detachment of the load is a common problem, if not well handled often cause the system to crash. In this paper, based on the software Simulink in MATLAB, the moment of inertia of turbine and generator is regarded as fixed value, the key parameter differential equations of Brayton cycle are derived, and the dynamic recompression and intercooling Brayton cycle models are established. The response parameters of the system after load disconnection and different time tie-back are studied. The responses of key parameters of the system after load detachment were obtained. It was found that the recompression model had higher stability under load detachment and tie-back conditions than the intercooling model, and the length of parameter variation after load detachment was linear. The earlier the tie-back was, the faster the system could restore stability.

Modelling and performance analysis of a recuperated gas turbine with low-Btu fuel

• A gas turbine model was estabilished considering recuperator, fuel, and generator. • The recuperator is the dominant component for thermal inertia of smallgas turbine. • 1-D heat soakage model was more proper for radial rotor than 0-D lumped model. • The thermal inertia and volume effect are good for gas turbine with sudden load change. • Overspeed in load shedding and surge in deceleration need to be studied case by case. Low-Btu fuels such as land fill gas and bio-gas are good alternatives to high priced natural gas. Due to the limited production of low-Btu fuel, small gas turbines are widely applied in such applications. For higher power efficiency at full and part load conditions, the small gas turbine is always equipped with a recuperator and a high-speed generator. Due to low shaft inertia, a small gas turbine’s speed response is quick. Therefore, for standard simple cycle gas turbine, control lags from instruments, actuators, thermal inertia, or volume effect may induce control instabilities during transient loading, and resulting in over speed, flow instabilities, and even mechanical failure. However, for recuperated engine burning low BTU fuel, other factors including the large volume of the combustor and recuperator, the thermal inertia of the rotor and recuperator, lags in the fuel valve lags, and efficiency changes caused by rectifiers of the high-speed generators could all induce visible changes and lags in the engine’s transient operations. This paper summarizes the influences of the gas turbine engine itself, the recuperator, and the high-speed generator in one model. It is believed that this is the first time that all these effects and interactions have been analysed together. Heat soakage, volume dynamics, recuperator transient characteristics, and the rectifier model were combined and tuned in detail to understand the separate effects. From the analysis of transient cases such as, load shedding and acceleration, conclusions are drawn made regarding overspeed and recovery time. The recuperator thermal inertia, low-Btu fuel, and combustor and recuperator volume effect interact with each other to produce more than three times larger overspeed or nearly five times more recovery time compared to a natural gas engine with recuperator. The fuel valve with a 0.02 s-time constant was found to be adequate even for the most severe case described in this paper. The recuperated gas turbine did not necessarily lead to lower compressor surge margin and should be investigated on a case-by-case basis. Rectifier system efficiency variation should be taken into account especially for the acceleration process. To convert a natural gas turbine engine into low-Btu gas turbine, the matching point of the gas turbine components needs to be carefully selected for efficiency, surge margin, and transient manoeuvre behaviour.