Feasibility studies of a converter-free grid-connected offshore hydrostatic wind turbine

Owing to the increasing penetration of renewable power generation, the modern power system faces great challenges in frequency regulations and reduced system inertia. Hence, renewable energy is expected to take over part of the frequency regulation responsibilities from the gas or hydro plants and contribute to the system inertia. In this article, we investigate the feasibility of frequency regulation by the offshore hydrostatic wind turbine (HWT). The simulation model is transformed from NREL (National Renewable Energy Laboratory) 5-MW gearbox-equipped wind turbine model within FAST (fatigue, aerodynamics, structures, and turbulence) code. With proposed coordinated control scheme and the hydrostatic transmission configuration of the HWT, the `continuously variable gearbox ratio' in turbulent wind conditions can be realised to maintain the constant generator speed, so that the HWT can be connected to the grid without power converters in-between. To test the performances of the control scheme, the HWT is connected to a 5-bus grid model and operates with different frequency events. The simulation results indicate that the proposed control scheme is a promising solution for offshore HWT to participated in frequency response in the modern power system

A novel synthesis and characterization of fluorescein isothiocyanate labeled poly(styrenesulfonate sodium salt)

The diffusion of polyelectrolytes in low-salt or salt-free aqueous solutions is a controversial question. It has been intensively discussed since it was discovered in 1978. Most previous experimental data were obtained from dynamic light scattering (DLS), whose precision, however, was reduced by stringent sample preparation and weak scattering of polyelectrolyte in low-salt solution. For the most commonly studied polyelectrolyte, poly(styrenesulfonate sodium salt) (NaPSS), the harsh polymerization condition and the manufacturing procedure lead to hydrophobic defects and aggregations, which also block a correct insight about the diffusion of polyelectrolyte. In contrast to DLS, fluorescence photobleaching recovery (FPR) directly looks on the optical trace of the self-diffusion of labeled molecule and is relatively insensitive to the thermodynamic interactions among the polymer. In this work, an efficient synthesis of fluorescein isothiocyanate (FITC) labeled poly(styrenesulfonate sodium salt) (NaPSS) under mild conditions is presented. This fluorescent polyelectrolyte, with 100% degree of sulfonation and no hydrophobic defects, was directly synthesized from monomer. The product was characterized by mass spectrometry, GPC/MALLS, 1H NMR, and fluorimetry. Twelve fractions with various molecular weights were obtained by injecting the sample solution into an analytical-scale GPC. The self-diffusion of some fractions was measured with FPR. The dependence of the diffusion coefficient on molecular weight is in agreement with the power-law. The partial specific volume of NaPSS in aqueous solution and salt solution were also determined by examining the densities of these solutions

Power generation control of a monopile hydrostatic wind turbine using an H∞ loop-shaping torque controller and an LPV pitch controller

We transform the NREL (National Renewable Energy Laboratory) 5-MW geared equipped monopile wind turbine model into a hydrostatic wind turbine (HWT) by replacing its drivetrain with a hydrostatic transmission drivetrain. Then we design an H∞ loop-shaping torque controller (to regulate the motor displacement) and a linear parameter varying (LPV) blade pitch controller for the HWT. To enhance performances of the pitch control system during the transition region around the rated wind speed, we add an anti-windup (AW) compensator to the LPV controller, which would otherwise have had undesirable system responses due to pitch saturation. The LPV AW pitch controller uses the steady rotor effective wind speed as the scheduling parameter which is estimated by LIDAR (Light Detection and Ranging) preview. The simulations based on the transformed NREL 5-MW HWT model show that our torque controller achieves very good tracking behaviour while our pitch controller (no matter with or without AW) gets much improved overall performances over a gain-scheduled PI pitch controller

Load reduction of a monopile wind turbine tower using optimal tuned mass dampers

We investigate to apply tuned mass dampers (TMDs) (one in the fore–aft direction, one in the side– side direction) to suppress the vibration of a monopile wind turbine tower. Using the spectral element method, we derive a finite-dimensional state-space model d from an infinite-dimensional model d of a monopile wind turbine tower stabilised by a TMD located in the nacelle. and d can be used to represent the dynamics of the tower and TMD in either the fore–aft direction or the side– side direction. The wind turbine tower subsystem of is modelled as a non-uniform SCOLE (NASA Spacecraft Control Laboratory Experiment) system consisting of an Euler–Bernoulli beam equation describing the dynamics of the flexible tower and the Newton–Euler rigid body equations describing the dynamics of the heavy rotor-nacelle assembly (RNA) by neglecting any coupling with blade motions. d can be used for fast and accurate simulation for the dynamics of the wind turbine tower as well as for optimal TMD designs. We show that d agrees very well with the FAST (fatigue, aerodynamics, structures and turbulence) simulation of the NREL 5-MW wind turbine model. We optimise the parameters of the TMD by minimising the frequency-limited H2-norm of the transfer function matrix of d which has input of force and torque acting on the RNA, and output of tower-top displacement. The performances of the optimal TMDs in the fore–aft and side–side directions are tested through FAST simulations, which achieve substantial fatigue load reductions. This research also demonstrates how to optimally tune TMDs to reduce vibrations of flexible structures described by partial differential equations

Maximum power generation control of a hybrid wind turbine transmission system based on H∞ loop-shaping approach

The paper presents the design, modelling and optimal power generation control of a large hybrid wind turbine transmission system that seamless integrates planetary/parallel gear sets with a hydraulic transmission to improve the turbine’s reliability and efficiency. The hybrid wind turbine has power splitting flows including both mechanical and hydraulic power transmissions. The turbine transmission ratio can be controlled to continuously vary for the maximum wind power extraction and grid integration. Dynamics of the hybrid wind turbine is modeled as an incremental disturbed state space model based on the dynamic equations of each mechanical/hydraulic element. To achieve good tracking and robustness performance, an optimal H∞ loop-shaping pressure controller is designed, which accurately tracks the optimal load pressure in the hydraulic transmission for maximizing wind power generations. The validations of the proposed hybrid wind turbine and the H∞ loop-shaping pressure controller are performed based on a detailed aero-hydro-servo-elastic hybrid type wind turbine simulation platform with both mechanical geared transmission and hydraulic transmission, which is adapted from the NREL (National Renewable Energy Laboratory) 5 MW monopile wind turbine model within FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. The validation results demonstrate that the hybrid wind turbine achieves better performance in both the maximum wind power extraction and power quality than the hydrostatic wind turbine. In addition, the proposed H∞ loop-shaping pressure controller has better tracking performance than the traditional proportional integral (PI) controller

Current situation and research prospect of home monitoring technology for cardiovascular system

Cardiovascular disease has become the leading cause of death in China. Home medical monitoring of cardiovascular circulatory system (cardiovascular system for short) is of great significance for the early detection, diagnosis and treatment of cardiovascular diseases. Physiological parameters of the cardiovascular system mainly include blood pressure, cardiac output, blood glucose content, blood oxygen saturation, ECG, respiration, etc. These physiological parameters need long-term daily monitoring to find the abnormalities and changes of the system. Therefore, home medical monitoring is necessary. This paper reviews the current situation of home monitoring technology for the main parameters of cardiovascular system in recent years, and prospects its future research trend

Vibration and power regulation control of a floating wind turbine with hydrostatic transmission

We design a blade pitch controller employing linear parameter-varying (LPV) synthesis techniques for a floating hydrostatic wind turbine (HWT) with a barge platform, which is based on the LIDAR (Light Detection and Ranging) preview on the wind speed. The developed control system can simultaneously reduce barge pitch motions and regulate the power in Region 3. These two functions would normally disturb each other if designed separately. The state space model is not affinely dependent on the wind speed thus the LPV controller is obtained by satisfying multiple LMIs evaluated at a set of gridded points within the wind speed range in Region 3. An anti-windup compensation scheme is then used to improve the LPV controller’s performance when the pitch undergoes saturation around the rated wind speed. The simulations based on a high-fidelity barge HWT model show that our pitch controller significantly reduces barge pitch motions, loads on blade bearings & tower, and generator power fluctuations, compared with a gain-scheduled PI pitch controller

All that Glitters is not Gold: Understanding the Impacts of Platform Recommendation Algorithm Changes on Complementors in the Sharing Economy

Sharing platforms often leverage recommendation algorithms to reduce matching costs and improve buyer satisfaction. However, the economic impacts of different recommendation algorithms on the business operations of complementors remains unclear. This study uses natural quasi-experiments and proprietary data from a home-cooked food-sharing platform with two recommendation algorithms: word-of-mouth recommendation (WMR) and botler personalization recommendation (BPR). Results show the WMR negatively affects revenue while BPR has a positive effect. The contrast revenue effects have been attributed to capacity constraints for complementors and matching frictions for consumers. WMR encourages sellers to specialize in high-quality products but limits new product development. BPR promotes innovation to suit diverse customer tastes but may reduce quality. This reflects the exploration-exploitation trade-off: WMR exploits existing competences, while BPR explores new products to satisfy personal preferences. The authors discuss implications for how to utilize recommendation algorithms and artificial intelligence for the prosperity of sharing economy platforms