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As concern about limited energy is gradually growing and wind energy is regarded as one of the best solutions, research on the wind turbine system has been vigorously accomplished. The commercial tools to simulate the non-linear dynamic characteristics of the wind turbine system are various, but the tools take a significant amount of time to simulate the control algorithm and require many input variables. In this paper, the procedures to simulate and examine the controller of wind turbines at the initial design stage are proposed by a 4 degrees of freedom mathematical model of wind turbine, and methodology to make the turbine model is also proposed by effective mass and stiffness defined in the modal domain. The proposed method in this paper is simpler than other methods. The simulations by the three kinds of models for the 2-MW wind turbine are accomplished to discuss the simulation results: a 2 degrees of freedom wind turbine model without considering tower and blade behavior, a 4 degrees of freedom model considering tower and blade behavior modeled by mode shape function, and a 4 degrees of freedom model by the suggested method.

A short overview of different piezoelectric structures and devices for generating renewable electricity under mechanical actions is presented. A vibrating piezoelectric device differs from a typical electrical power source in that it has capacitive rather than inductive source impedance, and may be driven by mechanical vibrations of varying amplitude. Several techniques have been developed to extract energy from the environment. Generally, “vibration energy” could be converted into electrical energy by three techniques: electrostatic charge, magnetic fields and piezoelectric. Mechanical resonance frequency of piezoelectric bimorph transducers depends on geometric size (length, width, and thickness of each layer), and the piezoelectric coefficients of the piezoelectric material. Manufacturing processes and intended applications of several energy harvesting devices are presented.

Water hammer phenomena caused by a sudden valve closure investigated in one-component two-phase flows. The phenomena in one-component two-phase flows are more complicated than those in two-component two-phase flows because of the presence of mass transfer between liquid and vapor. Basic partial differential equations based on a one-dimensional homogeneous flow model are solved analytically by linearization and iterated Laplace transformation. The profiles of the pressure transients at the closing valve are given. It is shown that the mass transfer between the two phases has a great influence on the profile of the pressure transients, and that the magnitude of the influence depends on the relaxation time τM of the interphase mass transfer.

The fuel economy of wheel loaders is deeply affected by the efficiency of their propelling transmissions, however, the torque converter (TC) in existing propelling transmissions is a low-efficiency component and leads to excessive energy consumption. Accordingly, this paper replaces the TC with a hydrodynamic mechanical power split transmission (HMPST) for improving the fuel economy of wheel loader. Based on probability similarity theory, the typical operating mode for the vehicles is constructed, which is used to evaluate the energy consumption performance of the selected solutions. The four reasonable solutions, which can be initially applied to wheel loaders, are selected from among the HMPSTs using the lever diagram. Furthermore, the comparisons on efficiency and loading characteristics between these four solutions and a prototype TC are conducted. The design optimization for all the four solutions is implemented, in order to find the optimal fuel saving solution relative to the prototype TC, and only one solution with pure power split can meet the constraints. Finally, a simulation model of the wheel loader powertrain is established for validating the effectiveness of this optimal solution. The results show that the optimized solution can effectively improve the fuel economy of wheel loaders compared to the prototype TC and provides a novel substitute for current technology.

In the paper the three-dimensional case of heat transfer and air flow is presented for indoor space cooling during the summer in Rijeka, Croatia, with an A/C unit mounted on the wall. Numerical modelling is used to analyse the effect of different air flow angles of the A/C unit on the temperature and air velocity distribution under standard conditions with and without direct solar radiation source. As a parameter of thermal comfort conditions, the airflow velocities, indoor temperatures with its gradients and the mean radiant temperature are analysed. Physical processes are modelled using the computational fluid dynamics software FLUENT. Calculations are carried out for an empty room without internal heat sources. When direct solar radiation through the window for extreme case of summer solstice is included in calculation, considerable deviations from thermal comfort conditions are observed yielding the conclusion that solar radiation must be included in numerical simulations to properly predict heat balance and thermal comfort parameters in enclosed spaces.

Implementation of a new electricity trading arrangement is imminent in the UK. It aims to improve power industry efficiency and economy, but its dynamic nature is also associated with more uncertainties. The flexible ac transmission systems (FACTS) concept is particularly applicable to a dynamically changing transmission system. Advantages of FACTS could be compromised by interactions in a transmission system, however, in particular where multiple power flow control devices are used. This paper addresses the coordination of power flow control in a large power system, managing transmission constraints to meet the security standards against the background of this open market structure.

AbstractAs wind farms become larger, there is scope for improved operation via wind farm control. Further development of wind farm control would be facilitated by more flexible operation of wind farms and so by more flexible operation of wind turbines. A novel approach to wind farm control is proposed that provides full flexibility of both. It consists of a wind farm controller architecture and an interface to individual turbines. The design of a specific realisation of the interface, the Power Adjusting Controller, is presented that requires little information on the turbine dynamics or controller and does not compromise the operation of the wind turbine controller or the turbine's safety. Results from a DNV Bladed simulation of a 5MW wind turbine are presented to illustrate the behaviour of the Power Adjusting Controller and to confirm that it meets the requirements to enable fully flexible operation of wind turbines and, so of wind farms.

We study the stability of a Markovian model of electricity production and consumption that incorporates production volatility due to renewables and uncertainty about actual demand versus planned production. We assume that the energy producer targets a fixed energy reserve, subject to ramp-up and ramp-down constraints, and that appliances are subject to demand-response signals and adjust their consumption to the available production by delaying their demand. When a constant fraction of the delayed demand vanishes over time, we show that the general state Markov chain characterizing the system is positive Harris and ergodic (i.e., delayed demand is bounded with high probability). However, when delayed demand increases by a constant fraction over time, we show that the Markov chain is non-positive (i.e., there exists a non-zero probability that delayed demand becomes unbounded). We exhibit Lyapunov functions to prove our claims. In addition, we provide examples of heating appliances that, when delayed, have energy requirements corresponding to the two considered cases.