Papers by Keyword: Variable-Speed

Abstract: Dedicated to the disadvantage of variable-speed drive, the energy regulation based variable-speed electrohydraulic drive is proposed. It is a novel solution by adding an energy regulation device and a flow valve into the system. It combines the advantages of variable-speed drive, valve control and energy regulation. But it is a multiple-input multiple-output control system, coupled with strong nonlinear, volatility and uncertainty of some parameters, which make the control strategy complicated. The multiple-compound PID control strategy, as well as the parameter tuning rule, is proposed.

Abstract: The variable-speed electrohydraulic drive, which can achieve similar energy efficiency as volume drive system, has some good features. But the slow response and poor low-speed performance limit the development of the variable-speed electrohydraulic drive. The energy regulation based variable-speed electrohydraulic drive is a good solution to solve these problems by adding an energy regulation device and a throttling valve into the system. The sine simulations of energy regulation based electrohydraulic variable-speed drive are carried out. The simulation results have showed that the energy regulation system can not only achieve the goal of a good response, but also keep a good energy-saving performance.

Abstract: The purpose of this paper is to find the optimum design attack angle for fixed-pitch variable-speed wind turbine blade design, given the base-line wind turbine and the blade airfoil. Aerodynamic characteristics, i.e. lift and drag coefficients and lift to drag ratio, of the wind turbine, are analyzed. Two design attack angles along with the base-line attack angle (with maximum lift to drag ratio) are selected for the wind turbine blade design exercise. Blade design outcomes are analyzed and compared along with load performance and power performance. This paper is possibly the first attempt to determine the optimized design attack angle for maximizing annual energy production, given the base-line wind turbine and the blade airfoil.

Abstract: Wind power is a clean and renewable energy, and its exploitation is developing rapidly across the world. The Variable Speed Constant Frequency (VSCF) wind power generation system requires the doubly-fed wind generator (DFIG) to have high response as well as good robustness. DFIG will be affected both by internal disturbance of parametic variations and external disturbance of the load torque oscillation. The dynamics of the current response of the present PI controlled rotor may be in bad condition. In addition, the above disturbances reduce efficiency and stability of the wind turbine. Internal model control (IMC) is a kind of control strategy based on mathematical model to design the controller, it has advantages such as simply to design, robustness, convenient to research. Compared with PI control, IMC has a faster response, and is insensitive to the parameter variation and disturbances, but the IMC highly depends on accurate model of the controlled object. To solve this problem, combine the neural networ and IMC to design the neural network internal model controller .The simulation indicates that the dynamic performance and the anti-interference ability of DFIG are improved.

Abstract: In view of the high-order, nonlinear, strong coupling, multivariable and time varying character of wind energy conversion system, the fuzzy-logic control strategy is introduced in this paper. First, this thesis analyzes and establishes the mechanism model for each component element of the megawatt class variable-speed variable-pitch wind turbines as well as the wind speed model. Second, for the goal of maximum wind power extraction under rated wind and peak power output maintaining above rated speed wind, PID controllers as well as fuzzy-logic controllers are designed respectively by different wind velocity condition. The simulation results demonstrate that no matter for the following up performance or the anti-interference capability, the fuzzy controllers which are devised in the paper have a better control effect than PID controllers. The fuzzy controllers can reduce system’s overshoot and regulation time more effectively, offset the negative impacts of nonlinearity, and they have better robustness too.

Abstract: Comprehensive consideration the even teeth sintering machine’s pallet car and the smooth and continuous meshing of variable acceleration segment of the sprocket wheel’s tooth profile, puts forward a new type sprocket wheel’s tooth profile to make variable acceleration segment’s unified equation. According to the displacement, velocity and acceleration’s curves of the pallet car in the stage of variable acceleration, with the method of locus of the contact new tooth profile’s equation is deduced. The sprocket wheel which is derived by this method is stability in variable speed process, concise, easy to manufacture and analyze the characteristics equation of tooth profile.

Abstract: The non-stationary random responses of the moving tires induced by the road roughness in time domain were obtained, and then those non-stationary responses were treated as the non-stationary inputs to study the non-stationary vibration of a high-pier bridge under vehicles with variable speed. The effect of the two inputs on the mid-span deflections was compared with the measured responses under different parameters including vehicle acceleration and vehicle deceleration. The verified results showed that the proposed method can simulate accurately the vibration of bridge under vehicle moving with variable speeds.

Abstract: For an actual project of groundwater source heat pump air conditioning system in Yangli region, by the field investigation on energy usage status of the system operation, analyzes the causes of non-energy-saving operation such as water pumps energy consumption too much, presents an intelligent control strategy of the system energy saving operation for solving the problem, performs the program design of energy saving control based on Programmable Logic Controller (PLC) and variable frequency technique, finally predicts the system energy saving potential.

Abstract: The liquid-gas flow is proposed to accurately simulate the offshore environmental state. The aerodynamic feature is estimated using the three-dimensional model of horizontal-axis wind turbine with NRELS809 series aerofoil by means of the simulating software tool of FLUENT. The variable speed is implemented via the six different wind speeds. The calculated results show that the similarly evolutional tendency of velocity occurs in the wake region when operating at the six variable speeds. The stall speed is related to blade height and wind speed. The small blade height or large wind speed also leads to the serious stall phenomenon. The total force is conducted to estimate the potential capability for leeward and windward surface to capture wind power. The calculated results reveal that the larger wind speed facilitates generating the more magnitude of total force. However, the velocity and force feature for the wind turbine has the especially rapid change at the wind speed of 6 m/s, which perhaps results from the intrinsic geometry and configuration.