Optimal Power Capture Research Articles

Research on Decoupling Duty Cycle Optimization Control Method of a Multiport Converter for Dual-Port Direct Drive Wave Power Generation System

Dual-port direct drive wave energy power generation systems (DP-DDWEPGS) have received widespread attention due to their smooth and zero-free output power, compared to single-port direct drive wave energy power generation systems (SP-DDWEPGS) which have the disadvantage of large out-put power fluctuations. To further enhance the performance of the DP-DDWEPGS, optimal power capture control is proposed to achieve maximum power point tracking. Meanwhile, a multiport converter is applied to the DP-DDWEPGS to solve the problem caused by an excessive number of switching devices in the overall system converter. The multiport converter fulfills all the functional requirements of the DP-DDWEPGS while reducing the number of switching devices. However, switch multiplexing of the multiport converter also introduces coupling relationships between each port and the wave force exhibits time-varying characteristics, necessitating advanced control methods with superior fast-tracking capability. Therefore, in this paper, a decoupling duty cycle optimization model predictive control for DP-DDWEPGS is proposed. Based on the characteristics of switching multiplexing, NSC finite control set model predictive control (FCS-MPC) decouples the current prediction and the cost function, reduces the number of candidate voltage vectors in each operation, and shortens the operation time by 70%. To address the issues of high ripple value and increased error due to decoupling in FCS-MPC, duty cycle optimization control is added, greatly reducing the fluctuations in electromagnetic force and power of the permanent magnet linear generator (PMLG). Based on the established simulation model, the feasibility and superiority of the multiport converter and decoupling duty cycle optimization model predictive current control method are verified.

Integrating Wind and Solar Energy: Performance Evaluation of Hybrid Systems with Advanced Control

Abstract–This study focuses on the integration of wind and solar energy sources to create hybrid power systems, with an emphasis on evaluating their performance through advanced control techniques. The increasing demand for sustainable energy solutions has driven the need for efficient utilization of renewable resources. Wind and solar energies, being prominent among these resources, offer substantial potential for power generation. The paper investigates the performance of hybrid systems that combine both wind and solar energy generation. These systems are designed to seamlessly switch between the two sources based on availability and prevailing environmental conditions. The integration is facilitated by advanced control mechanisms that ensure optimal power capture and distribution. The evaluation encompasses various aspects of performance, including efficiency, reliability, and grid adaptability. The hybrid system's ability to handle fluctuating conditions and its response to grid perturbations are studied comprehensively. Furthermore, the influence of different control strategies on overall system performance is analyzed.

Comprehensive wave-to-wire model and control strategy design for wave energy conversion system

Considering the practical application of wave energy generation, a comprehensive wave-to-wire (W2W) model is proposed in this paper. A novel wave energy conversion (WEC) system with a center of gravity adjustment mechanism is proposed. The proposed W2W model involves the coupling modeling between the absorber and the center of gravity adjustment mechanism as well as the coupling modeling between the absorber and the power take-off (PTO) system. Based on the coupling relationship between the absorber and the center of gravity adjustment mechanism, a resonance control strategy is proposed. In addition, based on the coupling relationship between the absorber and the PTO system, an impedance-matching control strategy is proposed. Combined with the above two control strategies, the two conditions of optimal power capture can be met at the same time, so the WEC system can realize the maximum power point tracking (MPPT). In addition, in order to ensure the safe operation of the WEC system under extreme wave conditions, a power constraint control strategy is proposed to constrain the absorbed power. Finally, the feasibility of the W2W model and the accuracy of the proposed control strategies are verified under the regular and irregular waves.

Wave energy converter optimization based on differential evolution algorithm

A parameter optimization method for an oscillating buoy-type wave energy converter (WEC) is presented from the perspective of submerged buoy volume; which affects both the power production and cost investment. The effects of submerged buoy volume on the optimal power capture are studied using the differential evolution algorithm and linear potential flow theory. The cost indictor V/P (V and P representing submerged buoy volume and power capture, respectively) is introduced to measure the cost-effectiveness of the WECs. The power capture and cost performance of the optimized WECs in regular and irregular waves are discussed. The results show that the WEC with the large power take-off (PTO) damping has good adaptability to a range of wave frequencies; however, the optimal submerged buoy volume is not cost-efficient due to the consequent relatively large cost indicators. The best choice of WEC in terms of cost-effectiveness is one designed with a large PTO damping and a buoy of slightly small non-optimal submerged volume.

Nonlinear Internal Model Control of Wind Farm Power Optimization under Wake Effect

This paper is dealing with the efficiency of wind power under the wake effect. In our previous work, the efficiency is shown to be first depending on the wind turbine's applied control strategy, besides the influence of the environment topology. It is also widely demonstrated that the wind turbine performance decreases under sudden wind profile variations. Therefore, the first main control objective was to perform an optimal wind power capture, particularly below-rated wind speed, while avoiding substantial loads on the drive train shafts. Herein, the focus is on the wake effect in wind farms. Indeed, a wind farm is often subject to wake effect in addition to wind disturbance, in consequence, the wind turbines may fail in respecting the optimal power production as expected. The second main objective is then to maximize the power extraction under the wake effect. So, as an extension of our previous work, this present one aims to apply nonlinear internal model control to each turbine within a small wind farm and to point out that, it is indeed essential to consider the wake phenomenon to determine the real performance of a wind farm power production. Validation results using a wind farm simulator are provided to illustrate the theoretical developments applied on a single turbine in comparison with our previous work performed without wake effect, as well as using a small windfarm comprising 5 machines.

Adaptive Multi-objective Sliding Mode Control of a Wind Energy Conversion System Involving Doubly Fed Induction Generator for Power Capture Optimization

Adaptive Multi-objective Sliding Mode Control of a Wind Energy Conversion System Involving Doubly Fed Induction Generator for Power Capture Optimization

Application of real‐time nonlinear model predictive control for wave energy conversion

This article presents an approach to implement a Nonlinear Model Predictive Controller (NMPC) in real-time with a non-standard cost index. The proposed technique's applications are presented to maximize the energy produced by a Wave Energy Converter (WEC) when the cost index is a non-quadratic piecewise discontinuous functional of some design variables. The presented framework is based on pseudo-quadratisation and weight scheduling, which is implemented using the ACADO toolkit for MATLAB/Simulink. The proposed strategy features code generation and deployment on the real-time target machines for industrial applications. The simulations and experiments confirm the success of the proposed approach in achieving the feasible operation of the NMPC and an optimal power capture by the wave energy converters.

Adaptive Control of Wind Turbine Generators for Power Capture Optimization by Using Integral Backstepping Approach During Partial-Load Operation

The paper proposes an effective nonlinear integral backstepping approach strategy (IBS) through the use of a new adaptive power control algorithm for variable-speed wind turbine generators (VS-WTGs) to optimize the power extracted from the WTGs. The suggested approach is applied to one of the most frequently used maximum power control methods called as tip speed ratio (TSR) during partial-load operation considering the effects of the variations in wind velocity profile and unmodeled system dynamics such as external disturbances. The proposed method of control is known to scale-back the mechanical stress at the level of the GT shafts (generator and turbine). Furthermore, the IBS approach is relatively simple, which significantly reduces the online computational time and cost. Some numerical simulation results prove, under different wind speed models, that the proposed AC-TSR-IBS method works well on the level of the improved efficiency and the rapid system response compared to conventional TSR-PI method.

A Novel Model Predictive Voltage Control of Brushless Cascade Doubly-Fed Induction Generator in Stand-Alone Power Generation System

The aim of this paper is to present a model predictive voltage control (MPVC) strategy for stabilizing the amplitude and frequency of the output voltages in a Brushless Cascade Doubly-Fed Induction Generator (BCDFIG) under load changing and variable speed of generator shaft in stand-alone mode. BCDFIGs are a particular model of BDFIGs that consist of two induction machines called the control machine and the power machine, so that their rotors are electrically and mechanically coupled together. In this paper, unlike previous studies, which the BCDFIG rotor was integrated, the generator rotor is analyzed as a complex of two rotors of two separate induction machines. Also, the output voltages of generator are predicted and regulated in different operating conditions by using model predictive voltage control. In order to stabilize the amplitude and frequency of BCDFIG output voltages, the appropriate voltage vector is determined to apply to the stator of control machine. This generation system is simulated and simulation results prove the accuracy of proposed method. Experimental results on prototype BCDFIG are provided to validate the proposed methods. Finally, the effectiveness of the proposed controller brings better power capture optimization under variable speed wind turbine.

Wave power extraction from a tubular structure integrated oscillating water column

Integrating wave energy converters with marine structures such as breakwaters, piles, and offshore wind turbines offers benefits in terms of wave power extraction, construction costs, and survivability. In this paper, the integration of an oscillating water column(OWC) into a vertical tubular structure is considered. The OWC chamber is enclosed by the tubular-structure with its submerged side partially open to the sea. As ocean waves propagate through the device, an air turbine installed at the top of the chamber can be driven to extract wave power. An analytical model based on potential flow theory and the eigen-function matching method is developed to solve the wave scattering and radiation problems of the device in finite water depths. Wave excitation volume flux, hydrodynamic coefficients, optimal turbine damping and power capture factor are evaluated. Upon successful validation, the model is applied to investigate the effect of the radius and finite wall thickness of the tubular-structure, the size and position of the opening on wave power extraction. We find that a thinner chamber wall thickness offers benefits to wave power extraction in terms of a broader primary band of power capture factor response, and that a broader and higher capture factor band can be achieved by increasing the height of the vertical opening.

Mechanical behaviour of wind turbines operating above design conditions

Improving production of electric power from renewable sources is fundamental in order to decrease the use of fossil fuels. A crucial aspect for future development of renewable sources is to guarantee competitive prices to end users and profitably economic returns to those who invest in these technologies. This can be reached by constantly surveying plants performances, optimizing the operative conditions and evaluating the possibility to implement upgrades. For what concerns wind turbines, there are many possibilities to increase power production. This study is focused on analyzing the HWRT (High Wind Ride Throughout) cut-out strategy: it is a method that allows extending the power curve of a wind turbine above the cut-out wind speed (25 m/s, typically) at which the wind turbine is abruptly shut down for structural integrity issues. The HWRT instead is a particular generator and pitch control strategy that maintains the turbine productive for higher wind speeds (up to at least 30 m/s) through a soft cut-out strategy. Starting with a reverse engineering approach, this study aims at creating a mathematical model of a real wind turbine operating with the HWRT control, and then evaluating the effects of this control strategy on stresses and structural vibrations. The point of view of this study fills a lack in the way this kind of issues is commonly approached in the wind energy practitioners community: actually, wind turbine power capture optimization strategies are typically assessed mainly by the point of view of the energy balance and insufficient attention is devoted to the mechanical aspects and the possible consequences on the wind turbine remaining useful lifetime. The research is structured in the following steps. At first, the wind turbine model is constructed and the characteristic dimensions, blade shapes and natural frequencies are found. Subsequently, with this information, aeroelastic simulations through the FAST (Fatigue, Aerodynamics, Structures and Turbulence) software are implemented and validated against operation data. Finally, conclusions are drawn about the impact of the soft cut-out strategy on structural health and fatigue.

Hydrodynamic performance and power absorption of a multi-freedom buoy wave energy device

Hydrodynamic performance and power absorption of an oscillating buoy wave energy converter (WEC) with 3 degrees of freedom (DOFs) are studied. The DOFs are surge, heave and pitch. Linear potential theory is utilized. Optimal PTO damping coefficient is selected. Optimal PTO power output and capture width ratios are calculated and compared. Influences of the buoy's radius, draft and geometry are investigated. The geometries are cylinder, hemisphere-bottom cylinder, cone-bottom cylinder, linear-chamfered cylinder and circular-chamfered cylinder. Results show that only surge and pitch interact with each other. The interaction is intensified on the resonant frequency of pitch, and is significant with special radius and draft. Power absorption of 3-DOF WEC increases significantly (at least 46.6% here) than unidirectional WEC and the power absorption band is wider. Heave is the main power capture DOF. Pitch gets the biggest power absorption at the resonant wave frequency. Increasing radius benefits the power capture efficiency at low wave frequencies and is harmful at high wave frequencies, except for pitch motion. Increasing draft benefits the power capture efficiency in surge and heave, but is harmful in pitch. For surge, heave and 3-DOF motion, cylinder is the best shape. For pitch, the hemisphere is the best shape.

Nonlinear predictive control of a DFIG-based wind turbine for power capture optimization

A nonlinear predictive controller is proposed for a variable speed wind turbine. The objective is power capture optimization and transient loads reduction. The controller acts only on low wind speed area. It consists of a doubly fed induction generator controller coupled with a model predictive aeroturbine controller. Unlike the majority of existing work on DFIG, the nonlinear controller deals directly with the generator model without any simplifying assumptions. This makes it possible to remove some assumptions on the DFIG model. The nonlinear DFIG controller achieves asymptotic torque and flux tracking. For the aeroturbine part, the model predictive controller uses predictions of the output to compute the optimal control sequence. It makes a compromise between power capture optimization and loads reduction. The controllers design procedure is detailed. The global controller is tested with the parameters of a real experimental variable speed wind turbine. It is compared with PID and LQG controllers. The simulations show satisfactory results in comparison with these schemes. The proposed controller achieves better power capture optimization and load reduction. It therefore allows a good achievement of the design objectives.

Intelligent control of a DFIG wind turbine using a PSO evolutionary algorithm

This paper presents an intelligent proportional integral sliding mode controller (iPI-SMC) for power capture optimization of a doubly fed induction generator (DFIG) based wind turbine system. The designed method is based on a combination of proportional integral (PI) control, swarm optimization and sliding mode control (SMC). For this approach, the PI action is included in the sliding surface in order to improve the performances of standard SMC. Thus, the proposed controlling method is associated to particle swarm optimization (PSO) based evolutionary algorithm to improve the controller performances by optimizing PI and SMC gains. The stability of the system using the proposed controller is investigated by Lyapunov theory. The simulation results of the investigated PSO based PI-SMC method are compared with integral sliding mode control (ISMC) as well as conventional SMC. The results reveal that the proposed controller presents low tracking error and less chattering. In addition, the proposed method shows more robustness to uncertainties and faster transient response compared to the others methods control (i.e. ISMC and SMC).

Nonlinear Modeling and Verification of a Heaving Point Absorber for Wave Energy Conversion

Although the heaving point absorber (PA) concept is well known in wave energy conversion research, few studies focus on appropriate modeling of nonlinear fluid viscous and mechanical friction dynamics. Even though these concepts are known to have nonlinear effects on the hydrodynamic system, most research studies consider linearity as a starting point and in doing so have a weak approach toward modeling the true dynamic behavior, particularly close to resonance. The sole use of linear modeling leads to limited ability to develop control strategies capable of true power capture optimization and suitable device operation. Based on a 1/50 scale cylindrical heaving PA, this research focuses on a strategy for hydrodynamic model development and experimental verification. In this study, nonlinear dynamics are considered, including the lumped effect of the fluid viscous and mechanical friction forces. The excellent correspondence between the derived nonlinear model and wave tank tested PA behaviors provides a strong background for wave energy tuning and control system design.

A method for comparing wave energy converter conceptual designs based on potential power capture

The design space for ocean wave energy converters is notable for its divergence. To facilitate convergence, and thereby support commercialization, we present a new simple method for analysis and comparison of alternative device architectures at an early stage of the design process. Using Thévenin's theorem, Falnes crafted an ingenious solution for the monochromatic optimal power capture of heaving point absorber devices by forming a mechanical impedance matching problem between the device and the power take-off. However, his solutions are limited by device architecture complexity. In this paper, we use the mechanical circuit framework to extend Falnes' method to form and solve the impedance matching problem and calculate the optimal power capture for converter architectures of arbitrary complexity. The new technique is first applied to reprove Falnes' findings and then to assess a complex converter architecture, proposed by Korde. This work also provides insight into a master-slave relationship between the geometry and power take-off force control problems that are inherent to converter design, and it reveals a hierarchy of distinct design objectives unbeknownst to Korde for his device. Finally, we show how application of the master-slave principle leads to the reduction in the dimensionality of the associated design space.

Power maximization of variable-speed variable-pitch wind turbines using passive adaptive neural fault tolerant control

Power maximization has always been a practical consideration in wind turbines. The question of how to address optimal power capture, especially when the system dynamics are nonlinear and the actuators are subject to unknown faults, is significant. This paper studies the control methodology for variable-speed variable-pitch wind turbines including the effects of uncertain nonlinear dynamics, system fault uncertainties, and unknown external disturbances. The nonlinear model of the wind turbine is presented, and the problem of maximizing extracted energy is formulated by designing the optimal desired states. With the known system, a model-based nonlinear controller is designed; then, to handle uncertainties, the unknown nonlinearities of the wind turbine are estimated by utilizing radial basis function neural networks. The adaptive neural fault tolerant control is designed passively to be robust on model uncertainties, disturbances including wind speed and model noises, and completely unknown actuator faults including generator torque and pitch actuator torque. The Lyapunov direct method is employed to prove that the closed-loop system is uniformly bounded. Simulation studies are performed to verify the effectiveness of the proposed method.

Novel power capture optimization based sensorless maximum power point tracking strategy and internal model controller for wind turbines systems driven SCIG

Under the trends to using renewable energy sources as alternatives to the traditional ones, it is important to contribute to the fast growing development of these sources by using powerful soft computing methods. In this context, this paper introduces a novel structure to optimize and control the energy produced from a variable speed wind turbine which is based on a squirrel cage induction generator (SCIG) and connected to the grid. The optimization strategy of the harvested power from the wind is realized by a maximum power point tracking (MPPT) algorithm based on fuzzy logic, and the control strategy of the generator is implemented by means of an internal model (IM) controller. Three IM controllers are incorporated in the vector control technique, as an alternative to the proportional integral (PI) controller, to implement the proposed optimization strategy. The MPPT in conjunction with the IM controller is proposed as an alternative to the traditional tip speed ratio (TSR) technique, to avoid any disturbance such as wind speed measurement and wind turbine (WT) characteristic uncertainties. Based on the simulation results of a six KW-WECS model in Matlab/Simulink, the presented control system topology is reliable and keeps the system operation around the desired response.

Performance investigation of a two-raft-type wave energy converter with hydraulic power take-off unit

Raft-type wave energy converter (WEC) is a multi-mode wave energy conversion device, using the relative pitch motion to drive its hydraulic power take-off (PTO) units for capturing energy from the ocean waves. The hydraulic PTO unit as its energy conversion module plays a significant role in storing large qualities of energy and making the output power smooth. However, most of the previous investigations on the raft-type WECs treat the hydraulic PTO unit as a linear PTO unit and do not consider the dynamics of the hydraulic circuit and components in their investigations. This paper is related to a two-raft-type WEC consisting of two hinged rafts and a hydraulic PTO unit. The aim of this paper is to make an understanding of the dynamics of the hydraulic PTO unit and how these affect the performance of the two-raft-type WEC. Therefore, a combined hydrodynamic and hydraulic PTO unit model is proposed to investigate and optimize the performance of the two-raft-type WEC; and based on the simulation of the combined model, the relationships between the optimal power capture ability, the optimal magnitude of the hydraulic PTO force and the wave states are numerically revealed. Results show that an approximately square wave type hydraulic PTO force is produced by the hydraulic PTO unit, which causes the performance of the two-raft-type WEC not to be sinusoidal and the energy capturing manner different from that of the device using a linear PTO unit; moreover, there is an optimal magnitude of the hydraulic PTO force for obtaining an optimal power capture ability, which can be achieved by adjusting the parameters of the hydraulic PTO unit; in regular waves, the optimal power capture ability as well as the optimal magnitude of the hydraulic PTO force normalized by the wave height presents little relationship with the wave height, mainly depends on the wave period; in irregular waves, the trends of the optimal power capture ability and the normalized optimal magnitude of the hydraulic PTO force against the peak wave periods at different significant wave heights are generally identical and show a good correlation. All means that the hydraulic PTO unit of the two-raft-type WEC can be tuned to the wave states, and these would provide a valuable guidance for the optimal design of its hydraulic PTO unit.

Nonlinear control of wind turbine with optimal power capture and load mitigation

The main control objectives associated with the variable speed wind turbine is to extract maximum power at below rated wind speed (region 2) and to regulate the power at above rated wind speed (region 3). This paper proposes a nonlinear framework to achieve the above two control objectives. The paper discusses about the application of an integral sliding mode control (ISMC) in region 2 and a fuzzy based proportional integral (PI) control in region 3. Same ISMC is adopted for the stable switching between operating regions (transition region 2.5) and the control input maintains the continuity at the instant of switching. Lyapunov stability criterion is used to prove the stability of ISMC. The controllers are tested for different wind speed profiles with different turbulence component. Finally the performances of the proposed controllers are tested with nonlinear Fatigue, Aerodynamics, Structures, and Turbulence WT model and the results are compared with the existing baseline + PI controllers.