Simulation model for wind turbine with asynchronous generator interconnected to the electric network

This paper presents the study of a structure composed of a wind turbine, a speed multiplier and an asynchronous generator coupled to the infinite power network through a line of energy transfer electric modelled by an R–L circuit. After modelling of the global system, the behaviour of the proposed structure in steady states and in transient regimes is studied. The problem of the electric energy transfer to the network was studied. On the other hand, if the wind speed changes too much variation, this will cause a violent variation of power and result in step out operation of the generator from the power system. This paper proposes a control strategy to reduce the power variations by introducing feed forward control combined with conventional feedback control.     

Performance of laboratory polymer electrolyte membrane hydrogen generator with sputtered iridium oxide anode

The continuous improvement of the anode materials constitutes a major challenge for the future commercial use of polymer electrolyte membranes (PEM) electrolyzers for hydrogen production. In accordance to this direction, iridium/titanium films deposited directly on carbon substrates via magnetron sputtering are operated as electrodes for the oxygen evolution reaction interfaced with Nafion 115 electrolyte in a laboratory single cell PEM hydrogen generator. The anode with 0.2 mg cm⁻² Ir catalyst loading was electrochemically activated by cycling its potential value between 0 and 1.2 V (vs. RHE). The water electrolysis cell was operated at 90 °C with current density 1 A cm⁻² at 1.51 V without the ohmic contribution. The corresponding current density per mgr of Ir catalyst is 5 A mg⁻¹. The achieved high efficiency is combined with sufficient electrode stability since the oxidation of the carbon substrate during the anodic polarization is almost negligible.     

A numerical model for thermoelectric generator with the parallel-plate heat exchanger

This paper presents a numerical model to predict the performance of thermoelectric generator with the parallel-plate heat exchanger. The model is based on an elemental approach and exhibits its feature in analyzing the temperature change in a thermoelectric generator and concomitantly its performance under operation conditions. The numerical simulated examples are demonstrated for the thermoelectric generator of parallel flow type and counter flow type in this paper. Simulation results show that the variations in temperature of the fluids in the thermoelectric generator are linear. The numerical model developed in this paper may be also applied to further optimization study for thermoelectric generator.     

Freely Customized virtual generator model for grid-forming converter with hydrogen energy storage

Currently, there is a large-scale penetration of renewable energy sources (RES) in power systems around the world, most of which are based on the power converter technology. The result of such penetration is the emergence of frequency and voltage regulation problems in power systems with RESs. An effective way to solve the mentioned problems is the use of energy storage systems (ESS), among which hydrogen ESSs are promising. However, the quality of such solution mainly depends on the approach to the power converters control. One of the most effective is a grid-forming power converter control strategy. Within this strategy, many scientific groups have proposed the concept of a virtual synchronous generator (VSG). However, the existing VSG models use a series structure with a stiff direction of signals, which completely mimics conventional synchronous generators. In this regard, the fundamental problems inherent in such a structure arise, e.g., a coupling between active and reactive power control. This paper describes a freely configurable VSG model (FC-VSG), in which the structural control blocks can be transferred from one level to another, and the levels themselves can be installed not only in series, but also in parallel. The case studies carried out made it possible to identify the configuration of the FC-VSG, which excludes the fundamental problems inherent in the conventional VSG structures. At the same time, the most efficient and reliable frequency and voltage regulation is provided, which has been proved by qualitative and quantitative comparison, including with the conventional VSG structure.     

Aggregated dynamic model for wind farms with doubly fed induction generator wind turbines

As a result of increasing wind farms penetration in power systems, the wind farms begin to influence power system, and thus the modelling of wind farms has become an interesting research topic. Nowadays, doubly fed induction generator based on wind turbine is the most widely used technology for wind farms due to its main advantages such as high-energy efficiency and controllability, and improved power quality. When the impact of a wind farm on power systems is studied, the behavior of the wind farm at the point common coupling to grid can be represented by an equivalent model derived from the aggregation of wind turbines into an equivalent wind turbine, instead of the complete model including the modelling of all the wind turbines. In this paper, a new equivalent model of wind farms with doubly fed induction generator wind turbines is proposed to represent the collective response of the wind farm by one single equivalent wind turbine, even although the aggregated wind turbines operate receiving different incoming winds. The effectiveness of the equivalent model to represent the collective response of the wind farm is demonstrated by comparing the simulation results of equivalent and complete models both during normal operation and grid disturbances.     

Parameterization of a synchronous generator to represent a doubly fed induction generator with chopper protection for fault studies

This paper addresses the representation of the wound rotor asynchronous generators by an equivalent synchronous generator, valid for short circuit current calculations. Modern wind power plants are required and designed to ride through faults in the network, subjected to fault clearing. Accurate knowledge of the wind turbine short circuit current contribution is needed for component sizing and protection relay settings during faults within the wind power plant collector system or in the external networks. When studying fault currents and protection settings for wind power installations, the industry standard is to employ software packages where generators are represented by their equivalent synchronous generator operational impedances. Hence, it is of importance to represent non‐synchronous wind generators by an equivalent synchronous generator. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical Flow Simulation in Turbine Mode of Counter-Rotating Type Pumping Unit to Cooperate with Wind Turbine

This serial research has proposed the hybrid power system combined the wind power unit with the counter-rotating type pump-turbine unit, to provide the constant output for the grid system, even at the suddenly fluctuating/turbulent wind circumstance. In this paper, the tandem impellers prepared for the counter-rotating type pumping unit were operated at the turbine mode, and the performances and the flow conditions were investigated numerically with accompanying the experimental results. Even though providing the pumping unit for the turbine mode, the maximum hydraulic efficiency is close to one of the counter-rotating type hydroelectric unit designed exclusively for the turbine mode. Besides, the runners/impellers of the unit work evidently so as to coincide the angular momentum change through the front runners/impellers with that through the rear runners/impellers, namely to take the axial flow at not only the inlet but also the outlet, without the guide vanes. From these results, it can be concluded that this type unit is effective to work at not only the pumping but also the turbine modes.     

An analytical approach to non‐linear dynamical model of a permanent magnet synchronous generator

This paper proposes an analytical approach to investigate the transitory dynamic regime of a low‐power permanent magnet synchronous generator that works in an actual wind power station. The governing non‐linear differential equations are solved by means of the optimal homotopy asymptotic method, and explicit analytical solutions are obtained. Four cases are analysed for different moments of inertia and electrical resistances specific to sudden short circuit produced at the generator terminals and sudden change of load. The proposed procedure is highly efficient and controls the convergence of the approximate solutions, ensuring a very fast convergence. Such analytical approach allows modeling and simulating turbine generator systems for real‐time computations, offline applications or stability problems. Numerical investigations are also performed in order to validate the analytical results. Copyright © 2014 John Wiley & Sons, Ltd.     

Numerical analysis of thermal response tests with a groundwater flow and heat transfer model

The Kelvin line-source equation, used to analyze thermal response tests, describes conductive heat transfer in a homogeneous medium with a constant temperature at infinite boundaries. The equation is based on assumptions that are valid for most ground-coupled heat pump environments with the exception of geological settings where there is significant groundwater flow, heterogeneous distribution of subsurface properties, a high geothermal gradient or significant atmospheric temperature variations. To address these specific cases, an alternative method to analyze thermal response tests was developed. The method consists in estimating parameters by reproducing the output temperature signal recorded during a test with a numerical groundwater flow and heat transfer model. The input temperature signal is specified at the entrance of the ground heat exchanger, where flow and heat transfer are computed in 2D planes representing piping and whose contributions are added to the 3D porous medium. Results obtained with this method are compared to those of the line-source model for a test performed under standard conditions. A second test conducted in waste rock at the South Dump of the Doyon Mine, where conditions deviate from the line-source assumptions, is analyzed with the numerical model. The numerical model improves the representation of the physical processes involved during a thermal response test compared to the line-source equation, without a significant increase in computational time.     

Numerical model of a thermoelectric generator with compact plate-fin heat exchanger for high temperature PEM fuel cell exhaust heat recovery

This paper presents a numerical model of an exhaust heat recovery system for a high temperature polymer electrolyte membrane fuel cell (HTPEMFC) stack. The system is designed as thermoelectric generators (TEGs) sandwiched in the walls of a compact plate-fin heat exchanger. Its model is based on a finite-element approach. On each discretized segment, fluid properties, heat transfer process and TEG performance are locally calculated for higher model precision. To benefit both the system design and fabrication, the way to model TEG modules is herein reconsidered; a database of commercialized compact plate-fin heat exchangers is adopted. Then the model is validated against experimental data and the main variables are identified by means of a sensitivity analysis. Finally, the system configuration is optimized for recovering heat from the exhaust gas. The results exhibit the crucial importance of the model accuracy and the optimization on system configuration. Future studies will concentrate on heat exchanger structures.     

火电机组凝汽器中加装自清洗强化换热装置可提高发电效率

在火电机组凝汽器中加装自清洗强化换热装置,可以明显改善火电机组凝汽器的换热效率,减少冷源损失;降低发电汽耗,从而降低发电煤耗;减少机组的耗水量;减少化学药剂的使用;机组的热经济性显著提高。同时也是减少环境污染、温室效应气体排放和降低水耗的重要途径,也是缓解煤炭供应日趋紧张的重要技术措施。     

冷却塔用超级比转速混流式水轮机的设计

基于冷却塔用水轮机工作环境的特点,对全流道进行三维定常数值模拟,对比分析了超低比转速混流式水轮机与常规发电用水轮机参数选择设计的不同,并通过合理选择参数和数值模拟优化,开发出一种高性能的超低比转速混流式水轮机。算例分析表明,该新型水轮机不仅节能,还可以达到带动风扇旋转散热的目的,为其他行业合理利用富余能源提供了借鉴。     

Matching of a DC motor to a photovoltaic generator using a step-upconverter with a current-locked loop

A photovoltaic (PV) generator is a nonlinear device having insolation-dependent volt-ampere characteristics. Because of its relatively high cost, the system designer is interested in optimum matching of the motor and its mechanical load to the PV generator so that maximum power is obtained during the entire operating period. However, since the maximum-power point varies with solar insolation, it is difficult to achieve an optimum matching that is valid for all insolation levels. In this paper it is shown that for maximum power, the generator current must be directly proportional to insolation. This remarkable property is utilized to achieve insolation-independent optimum matching. A shunt DC motor driving a centrifugal water pump is supplied from a PV generator via a step-up converter whose duty ratio is controlled using a current-locked feedback loop     

Contribution to the improvement of voltage profile in electrical network with wind generator using SVC device

Wind energy is a growing renewable energy because of its several advantages; this has changed dramatically with more wind energy penetrating the conventional power network. The influence of wind generators on the power quality is becoming an important issue; non-uniform power production causes variations in system voltage and frequency, therefore, a wind farm requires high reactive power compensation. The advances in high power semiconductor devices have led to the development of Flexible AC Transmission System (FACTS). This paper presents the impact of wind energy integration on voltage stability and the goal of FACTS devices such as Static Var Compensator (SVC), which is a power electronic switch, to control the reactive power injection according to the thyristor firing angle, introduced as a state variable in power flow and combined with the nodal voltage magnitudes and angles of the power network for iterative solutions, thereby regulating the bus voltages.     

Transient stability analysis of a power system with one generator connected to an infinite bus system

This paper presents a novel method to identify the fault that would affect the transient stability of one machine to an infinite bus. Here, the swing equation of each machine is expressed in the form of a closed-loop transfer function in Laplace ss-domain. In the transfer function, the duration of the fault and the changes in maximum electrical power output of the machine during and after the fault are considered. Then, the real value of the dominant root of each machine's characteristic equation is identified on the real axis of the s-plane. In this method, the generator has been considered unstable based on the position of the real value of the dominant root in the left half or very close to the imaginary axis or in the right half of the s-plane. The results obtained by the proposed method are compared with those of the conventional step-by-step method on the basis of different fault clearing times, and good agreements have been demonstrated.     

含沙水流对水轮机过流部件焊缝的影响

含沙水流对水轮机过流部件焊缝有很强的磨蚀破坏力,其主要原因是焊缝材料的疲劳强度很低,在相同的磨蚀强度下,焊缝材料最先被磨蚀破坏。研究结果表明,在焊接过程中,采取适当的表面强化工艺,提高焊缝材料的抗疲劳特性．是提高水轮机过流部件焊缝表面抗磨蚀能力的有效途经。     

Wind tunnel tests of a hydrogen-fueled detonation ramjet model at approach air stream Mach numbers from 4 to 8

Experimental studies of an axisymmetric hydrogen-fueled detonation ramjet model 1.05-m long and 0.31 m in diameter with an expanding annular combustor were performed in a pulse wind tunnel under conditions of approaching air stream Mach number ranging from 4 to 8 with the total temperature of 290 K. In a supersonic air flow entering the combustor, continuous and longitudinally pulsating modes of hydrogen detonation with the corresponding characteristic frequencies of 1250 and 900 Hz were obtained. The maximum measured values of fuel-based specific impulse and total thrust were 3600 s and 2200 N.     

Dynamic model of wind energy conversion systems with variable speed synchronous generator and full-size power converter for large-scale power system stability studies

This paper presents a dynamic model for variable speed wind energy conversion systems, equipped with a variable pitch wind turbine, a synchronous electrical generator, and a full power converter, specially developed for its use in power system stability studies involving large networks, with a high number of buses and a high level of wind generation penetration. The validity of the necessary simplifications has been contrasted against a detailed model that allows a thorough insight into the mechanical and electrical behavior of the system, and its interaction with the grid. The developed dynamic model has been implemented in a widely used power system dynamics simulation software, PSS/E, and its performance has been tested in a well-documented test power network.     

Extraction of ultrapure hydrogen with V-alloy membranes: From laboratory studies to practical applications

The membranes of vanadium alloys can be substantially more productive and much cheaper than the palladium alloy membranes which are widely used for hydrogen separation. However, the insufficient workability of vanadium alloys makes difficult producing the membranes of any shape, except for small thick flat samples, suitable only for laboratory studies, while membranes in the form of thin-walled tubes are most preferable for practical use. Such seamless thin-walled self-maintained membranes of tubular shape, made of V-Pd and V-Fe alloys with a thin Pd-coating on their inner and outer sides and with welded joints to stainless steel on both ends, were fabricated and tested for their throughput, service life, mechanical stability, and capability of hydrogen recovering from WGS mixtures. In view of reliable and highly productive operation of tubular V-alloy membranes as well as of their absolute selectiveness, the assembly from 18 membranes was fabricated to use it in the multi-fuel processor feeding a 1 kW PEM FC and providing up to 16 slpm of ultrapure hydrogen by the steam conversion of light and heavy hydrocarbons including diesel “Euro 5”. A similar assembly made of V-Fe alloy membranes was estimated for hydrogen purification in MOCVD applications.