Applied Mechanics and Materials Vols. 448-453

Abstract: Energy storage technology plays an important part in wind power generation system integrated with energy storage device. This paper researches on the control strategy of smoothing the output curve of wind power. Take advantage of high power density ultra-capacitor to achieve this objective according to a basic principle that the desired wind power approaches the average value of wind output in the previous period. Meanwhile in order to make the dispatch more flexible, SoC level of ultra-capacitor and fluctuation of wind power are considered to optimize the time constant in real time. The wind power generation system integrated with energy storage device is simulated in the PSCAD/EMTDC software. The simulation results demonstrate the efficacy of proposed control strategy.

Abstract: In the existing linear wake (cylindrical surface) model of horizontal axis wind turbines, the rotor was taken as the actuator-disc composed of infinite blades with infinitesimal chords. The distribution of variable circulation along blade was not taken into account and the span-wise (or radial) component of induced velocity is totally ignored. And assumed that the all trailing vortex filament shed from blade trailing edge would locate on their own cylindrical stream-surface. This aerodynamic model for determination of wake configuration is obviously different from that actually observed wake in wind tunnel experiment. Therefore, a "nonlinear" wake model was proposed, in this model the wake vortex system was divided into the central vortex along rotor axis, the bound vortex along blade axis, the wake vortex sheets shed from blade trailing edge and extent into infinity behind the rotor. Then, on the basis of potential theory in fluid mechanics a set of integral equations for evaluation of induced velocity in wake were derived with Biot-Savarts formula.

Abstract: The wind power generation has developed rapidly, but it brings a serious of problems. This paper analyzed the development situation of the waste of wind resource, declining using hours and profit. In addition, this paper analyzed the problems and the supporting policy, with put forward to some countermeasures and suggestions of the wind power generation. It is important for China to develop the wind power generation.

Abstract: Because mostly used variable speed wind turbines based on doubly fed induction generator (DFIG) do not provide with transient voltage support capability under fault conditions, the security and stability of grid is influenced by wind farms integration in the case of severe short circuit fault contingency occurred on the grid side. The modified power converter controller model with transient voltage support capability and pitch control model used for post-fault stability control are implemented in DIgSILENT/PowerFactory. The models validation and the contribution to transient voltage stability enhancement are verified by power system simulation containing large wind farms. From simulation results, it can be illustrated that modified power converter controller with transient voltage support capability can provide dynamic reactive power to support grid voltage recovery and the modified pitch control model can reduce mechanical power , preventing wind turbines from over-speeding and also providing more reactive power generation stability for the power converter controller in the duration of power system large disturbance. The conclusion is presented that the control strategy can effectively improve the transient voltage stability of the gird.

Abstract: Wind power generation is not stable and cannot supply constant electrical output, which challenges the attempt to integrate large scale wind power scheme into grids. Hybrid energy storage system (HESS) composed of super-capacitor and battery generally has strong complementarities on the technical performance, which can greatly improve the economic and technical performance of the system when it is used to smooth the volatility of the wind power. However, the main factor influencing the composite energy storage system efficiency is capacity configuration of the storage system. In order to get optimal capacity configuration of the HESS, this paper presents an optimization scheme to improve performance/cost ratio of the HESS while meeting the requirement of smoothing wind power fluctuations. In the optimization model, the power output average and maximum fluctuations in wind farm are taken as main constraints, and simulated annealing method is introduced into Stochastic Particle Swarm Optimization (SPSO) to improve its convergence, which creates an Improved Stochastic Particle Swarm Optimization (ISPSO) to seek the optimal ratio of super-capacitor and battery. Simulation comparison of ISPSO, SPSO and PSO verifies the feasibility and effectiveness of the model for capacity optimization. Meanwhile, it can provide decision-making reference for energy storage system design of wind farm.

Abstract: For enhancing low voltage ride though (LVRT) capability, this paper proposes a new protection scheme of series dynamic breaking resistor (SDBR) connected to the grid-side inverter (GSI) of directly driven permanent magnet synchronous generator (D-PMSG) wind power system, which has a lot of advantages such as possessing low cost, simple structure and high reliability. The structure, switching control strategy and matched resistance of SDBR are researched. The proposed scheme was then applied to uplift GSI voltage during a fault, maintain active power delivered to grid, inhibit DC-link overvoltage and GSI overcurrent. The simulation analysis shows that the SDBR can substantially improve the LVRT capacity of D-PMSG wind power system in PSCAD/EMTDC.

Abstract: Along with the increasing of wind power penetration in the grid, much attention has been paid to the high voltage ride through (HVRT) capability of double fed induction generator (DFIG) based wind parks. To regulate the reactive power dynamically, the distribution static synchronous compensator (D-STATCOM) has been considered to be a valid method. In this paper, the D-STATCOM device is applied to enhance the HVRT capability of DFIG during a symmetrical voltage swell at the grid side. The function, The configuration, operating principle and feed-forward decoupling control strategy is presented, finally the model of power system containing DFIG based wind farms and D-STATCOM is established in the environment of PSCAD/EMTDC, HVRT during symmetrical grid voltage swell is simulated. The validity of the proposed control strategy is verified by the simulation results.

Abstract: Vortex generators (VGs) are an effective way to control flow separation in wind turbine. To understand the mechanism of VGs controlling flow separation, the flow field around airfoil Du97W300 with VGs was simulated and analyzed with CFD tools, and this numerical method is validated through the comparison between the numerical results and the experimental results. Furthermore, the flow fields around airfoil equipped with four different types of VGs are calculated and analyzed. The results show that the helical vortex induced by counter-rotating VGs develop approximately along streamwise direction; these types of VGs can cause a delay in stall and enhance the maximum airfoil lift coefficient. However the helical induced vortex actuated by the co-rotating VGs develop nearly along vortex generator direction and cannot cause a delay in stall effectively. In the counter-rotating VGs, the Q integration (the character parameter of induced vortex) of rectangular is twice of the triangle, and the Q integration of the forward triangle is almost equal to the backward triangle VGs.

Abstract: Wind turbine generator (WTG), with a large inertia in the time-domain, has a significant restraint to the high-frequency fluctuations of the wind speed. When analyzing and modeling the wind turbines electrical and controlling processes, its needed to quantify or estimate this inhibition. To estimate the WTGs inertia parameters, a digital filter is introduced to approximate the inertia transfer model of WTGs blade, drive chain and the generators rotor, by analyzing the correlation of the filters output and the generators rotor speed, the time window with the best correlation probability is selected as the restraint performance indicator of the blade, drive chain and generators rotor. The proposed method is finally verified by the simulation using the SCADA data.

Abstract: Wind power short-term predicting technology has a great significance in process of wind power decision-making. Recent years, the technology had been studied extensively in industry. Markov chain model has strong adaptability, forecast accuracy higher and other else advantages, which is suitable for wind power short-term prediction. This paper have set up one step Markov prediction model and based on which predicting short-term wind power output, and taken the historical power data of an actual wind farm in Jilin Province as an example to simulate and analyze. The paper also have proposed and used RMSE, MXPE, MAPE error analysis indicators to analyze simulation results of different status spaces. The results showed that when the status space is 60 the prediction accuracy of the method is best.