Performance characteristics of open-cycle linearly-diverging diagonal type single- and multiple-load generators

First, a new quasi-two-dimensional theory is proposed in order to analyse the whole electrical and gasdynamical performances of a diagonal type generator. Next, the performances of a large scale linearly-diverging diagonal type generator with thermal input of about 2000 MW driven by combustion gas of heavy oil fuel are evaluated. From numerical calculation results of single-load generators, it is made clear that the distributions of electrical and gasdynamical quantities in the inlet and exit regions of the generator channel obtained by the quasi-two-dimensional theory fairly differ from the ones obtained by the conventional quasi-one-dimensional theory. The generator output power obtained from the quasi-one-dimensional calculation shows 10–20% larger values compared to the results of the quasi-two-dimensional calculation. Choking phenomenon is apt to occur in the channel of small diverging angle. The diagonal angle and load current have great influence on the generator performances. The best angle is about 30° and the best value of load current 4 × 10⁴ A. A multiple-load generator can give considerably larger output power than the single-load one by suitably sharing the load current with several loads.     

An improved method to estimate the equivalent circuit parameters in DSSCs

In this report, an improved method to estimate the equivalent circuit parameters in the dye-sensitized solar cells (DSSCs) is introduced. It is founded that, several different groups of values of equivalent circuit parameters can fit well to the same experiment-measured I-V curve. Furthermore, the gap between some parameter values in those different groups is so large that it reaches up to several orders of magnitude. To eliminate this uncertainty of parameter estimation, an improved method, which based on both the extention of measured range and the computer simulation of current-voltage (I-V) characteristic curves, is proposed to ensure uniquely the values of DSSCs equivalent circuit parameters. A series of I-V curves which derived from the estimated parameters by this improved method fit well to the corresponding experiment-measured I-V curves. The results indicate that, there exclusively exists one group of parameter values for a special DSSCs equivalent circuit, thus demonstrating the validity of the improved method proposed in this work.     

Novel equivalent circuit model and statistical analysis in parameters identification

Parameter fitting based on the classical equivalent circuit model does not always reach reasonable solutions. It often gave negative series resistance and exaggerated diode ideality factor. Three problems were identified. The first problem was illuminated I–V is not a simple voltage shift by lumped series resistance. The second problem was rounded I–V curves in concentrator cells. The third problem was statistical instability in data fitting algorithm. A new model was proposed to describe the second problem. It was also effective to partly solve the first and the third problems.     

Estimation of equivalent circuit parameters of PV module and its application to optimal operation of PV system

A method to estimate the equivalent circuit parameters of a PV (photovoltaic) module is presented. The parameters are calculated using a least-squares fitting of the equivalent model current–voltage characteristic with the measured one. For applications of the equivalent circuit model parameters, a quantitative diagnostic method of the PV modules by evaluating the parameters is introduced and examined by simulation. A new maximum peak power tracking (MPPT) method using the model parameters, a solar insolation, and a cell temperature is also shown. Its performance is compared with other MPPT control algorithms by simulations. The performance of the proposed method was better than other MPPT methods.     

Quasi-three-dimensional analysis of a combustion MHD generator

A quasi-three dimensional code is developed for an MHD generator. Turbulent compressible steady state boundary layer equations near the electrode and insulator wall along with core region are explicitly solved for a seeded combustion plasma. Effects of leakage currents in the boundary layers and imperfect channel walls are included in the analysis. Accuracy and validity of the model is verified with experimental data. Effect of wall temperature, leakage currents and other parameters are analysed.     

Modelling a PEM fuel cell stack with a nonlinear equivalent circuit

A nonlinear circuit model of a polymer electrolyte membrane (PEM) fuel cell stack is presented. The model allows the simulation of both steady-state and dynamic behaviour of the stack on condition that the values of some of its parameters are changed in the two operating conditions. The circuit parameters can be obtained by means of simple experimental tests and calculations. A commercial PEM fuel cell stack is modelled as seen from the power conditioning system side, without requiring parameters necessary for complex mathematical models and not easily obtainable by the majority of users. A procedure of parameter determination is developed and a comparison between the simulated and experimental results for both steady-state and dynamic behaviour of the PEM stack is shown.     

Comparison of single particle and equivalent circuit analog models for a lithium-ion cell

The physics-based single particle (SP) model was compared to the semi-empirical equivalent circuit analog (ECA) model to predict the cell voltage under constant current charge and discharge for different sets of Li-ion cell data. The parameters of the models were estimated for each set of data using nonlinear least squares regression. In order to enhance the probability of finding the global optima, a combination of the trust region method with a genetic algorithm was applied to minimize the objective function (the sum of squared residuals). Several statistical quantities such as sum of the squared errors, adjusted R², root mean squared error, confidence intervals of the parameters, and prediction bounds were included to compare the models. A significance test (t test) on the parameters and the analysis of the variances (F and χ² tests) were also performed to discriminate between the goodness of the fit obtained from the two models. The statistical results indicate that the SP model superiorly predicts all sets of data compared to the ECA model, while the computation times of both models are on the same order of magnitude.     

The variable analysis of an MHD generator with electrical output of 10 kW for application to bi-plant method electricity generation

Magnetohydrodynamic (MHD) generators can be used to increase the total efficiencies of fossil power plants by adopting a bi-plant design, in which electricity is generated using both a turbine and the MHD generator. An MHD generator with an electric output of 10 kW is numerically analyzed herein for application to bi-plant method electricity generation. An electrically conductive plasma flue gas, with a high temperature of approximately 3000 K from the power plant, was considered for the generation of electricity from its flow in the magnetic field, where electricity was produced directly without the turbine facility from the MHD generator. Velocity profiles were calculated using an ANSYS code simulation. Then, using the magnetic flux density, the electrical output was calculated to design the MHD generator. The magnetic flux density, velocity, and geometrical variables affected the power output of the MHD generator. The power was proportional to the square of magnetic flux density, whereas velocity and power density were constant.     

Analysis of multicrystalline silicon solar cells by modified 3-diode equivalent circuit model taking leakage current through periphery into consideration

We proposed a modified 3-diode equivalent circuit model for analysis of multicrystalline silicon (Mc-Si) solar cells. By using this equivalent circuit model, we can precisely evaluate the characteristics of Mc-Si solar cells taking the influence of grain boundaries and large leakage current through the peripheries into consideration and extract electrical properties. The calculated value of current-voltage characteristics for small size (3 mm×3 mm) Mc-Si solar cells using this model completely agreed with the measured value at various cell temperatures. Moreover, the calculated open-circuit voltage (V_oc) obtained by extracted parameters and measured V_oc agreed well.     

不同工况下3.3MW永磁直驱风力发电机电磁场仿真分析及损耗修正

文章设计了一台3.3 MW外转子表贴式永磁直驱风力发电机,并对其电磁性能及短路故障情况进行了有限元仿真分析。首先,得出了这台电机在额定工况下的转矩和磁密分布等结果,以及在相间绕组短路和三相绕组短路两种情况下电机转矩、电压和电流等曲线的变化情况;然后,通过三维静磁场仿真,探究了电机定子的径向通风道结构对二维有限元仿真的影响程度,并对铁耗进行了修正;最后,通过电磁场-温度场的耦合迭代仿真,考虑了温度场影响下的电机内部材料特性的变化对电机损耗结果的影响。     

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.     

Effect of hydrofoil flexibility on the power extraction of a flapping tidal generator via two- and three-dimensional flow simulations

In this study, we investigate the effect of hydrofoil flexibility on the power extraction of a flapping tidal stream generator with hydrofoils down-scaled for a water channel in an experiment with a typical Strouhal number and frequency. The described deformations in the chord and spanwise directions are imposed onto the surfaces of the hydrofoil to analyze the flexibility effect. In a two-dimensional (2D) simulation, parameter studies of the chordwise flexure are conducted and a 30% improvement in the rate of the power-extraction efficiency is then achieved when the chordwise flexure is 20% of the chord length. In a three-dimensional (3D) simulation, the chordwise flexure of 20% achieves a 15% improvement in the rate of the power-extraction efficiency for the hydrofoil with an aspect ratio (AR) of 5, which is less than that in the 2D simulation due to 3D effects such as tip loss and a spanwise vortex. Meanwhile, the effect of the spanwise flexure on the power extraction is minor as compared to that of the chordwise flexure. It was also found throughout the parametric study of the AR variation that the 3D effect of the chordwise flexible hydrofoil is slightly stronger than that of the rigid hydrofoil.     

Power output of segmented MHD Faraday generators with hall voltage compensation

Hall voltage causes a deterioration of the performance of a segmented MHD Faraday generator, and methods of compensation for this effect are studied. A simple network analogue is developed and used to analyze current flow through the generator and the effect of compensating voltages.Practical segmentation ratios are found to be <0.2. This limit is shown to be well below that required to minimize Hall effects due to electrode length. Smaller segmentation ratios, as used in larger designs therefore, are used mainly to cover inter-electrode breakdown caused by Hall voltages.Hall effect compensation is found to produce a significant increase in generator power only at the expense of a large recirculation of power and internal losses.     

Transient-boundary voltage method for measurement of equivalent circuit components of rechargeable batteries

A method is presented for measuring the equivalent circuit components of rechargeable batteries. The temporal discharge-rest-charge-rest sequence of a rechargeable battery is described, using the principles of transient circuit analysis, to derive equations for the battery voltage as a function of time during voltage transients and at the boundaries at transitions between transient phases. The equations lead to a new measurement method for battery characterization. The equivalent circuit of the battery is described as an ideal voltage source in series with a resistor and the parallel combination of a resistor and a capacitor. The battery model uses different values of resistance and capacitance, in the parallel combination, during the different phases of the discharge-rest-charge-rest sequence. The method is used to measure the circuit parameters of a nickel-cadmium battery.     

适合于变速恒频双馈感应发电机的Crowbar对比分析

电网运行新规则要求变速恒频双馈感应发电机在电网电压跌落的情况下仍与电网相连接，为做到这一点需要安装低压旁路系统。综合分析了低压带来的负面影响以及低压旁路的具体实现方法；对比了多种Crowbar电路各自的优缺点；最后介绍了变速恒频双馈发电机相关保护控制策略和新型旁路系统。     

Parameterization of a synchronous generator to represent a full‐scale converter generator for fault studies

This paper addresses the representation of the full‐scale converter generator technology by equivalent operational impedances 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. The industry standard employs software packages where generators are represented by their equivalent synchronous generator operational impedances, calculated according to standards or for electromagnetic simulation models, when studying fault currents and protection settings for wind power plant installations. Hence, it is of importance to represent non‐synchronous wind generators also by an equivalent synchronous generator. The effectiveness of the proposed method has been validated by simulation and site measurements. Copyright © 2013 John Wiley & Sons, Ltd.     

Multiresponse optimization of exhaust thermoelectric generator using Taguchi-based gray relation analysis

The best operating condition of the exhaust thermoelectric generator (ETEG) provides more power output and low-pressure drop (low-PD). So it is required to optimize the operating condition of the ETEG. In the present work, Taguchi's L₁₈(6¹ 3³) orthogonal array was chosen to find the optimal parameters. Analysis of variance was used to determine the percent contribution of the control factors such as engine loads (ELs), different types of heat exchangers (HEs) with and without inserts, water flow rate (WFR), and external load resistance (ELR) on the thermoelectric power output and PD in the HE. The confirmation test was carried out at optimum levels for the regression equations and Taguchi method. Gray relational analysis was performed to find the optimum value of the power output and PD. It is observed that the optimal operating condition is EL₆ HE₁ WFR₃ ELR₂ (EL₆ = 10 kg, HE₁ = G-type test section, WFR₃ = 0.08 kg/s, and ELR₂ = 40 Ω).     

Time stepping finite element analysis of a variable speed synchronous generator with rectifier

Several applications for renewable energy conversion make use of variable speed generators. A conversion from variable frequency to grid frequency is therefore essential. One part of the converter is a rectifier. A rectifier model is presented, which is integrated in a time stepping finite element simulation environment where the generator and circuit equations are solved simultaneously. The model handles bidirectional alternator speeds as the application is a linear generator for ocean wave energy conversion. The rectifier model is extended with a load model, consisting of R, L and E, and simulations show what impact the rectifier has on the generator’s behaviour.     

热环应用于喷雾干燥装置的技术经济分析

针对喷雾干燥排气余热原有回收装置存在的不足，提出了用热环来回收排气余热以预热新鲜空气，并进行了技术经济分析。通过计算实例表明，该技术的设备投资回收期一般在6个半月左右。     

300 MW QFS2型汽轮发电机组轴系稳定性分析

通过对现役类似匹配汽轮发电机组轴系振动状况的调研和测试,结合有关理论分析与计算结果,对300MWQFS2型双水内冷汽轮发电机与东方汽轮机厂300MW汽轮机匹配轴系的稳定性、振动特性作了分析。结果表明,新匹配的轴系能稳定运行,振动特性良好,能确保新机组的成功匹配和安全运行。