Tracking mirror beam sunlighting for deep interior spaces

A scheme is proposed for indirect natural illumination of deep office spaces based upon a tracking mirror mechanism. Computer simulation indicates that it can provide acceptable workplane illuminances in 10 m deep spaces for 8 hr per day under clear-sky conditions. The circumstances under which this scheme would be cost-effective are examined.     

Minimum time current controller design for two-interleaved bidirectional converter: Application to hybrid fuel cell/supercapacitor vehicles

In fuel cell hybrid vehicles (FCHV) with a supercapacitor (SC) used as auxiliary source of hybridization, classical SC converters limit the current tracking performance due to the presence of a large input inductance. A hardware solution to this issue consists in using an interleaved converter topology that enables considerably reducing the input inductance. To optimize interleaved converters usage, an intelligent control scheme that maximizes closed-loop performance in current tracking must be designed. For that purpose, we design two controllers: a transient-state controller and a steady-state one. The first controller is a bang-bang one that guaranties a fast transition from the initial condition to some closed region around the reference. The second controller ensures the local asymptotic stabilization of a certain desired limit cycle and is based on switching surfaces design. The proposed control scheme performances and robustness are evaluated through simulations with piece-wise constant source and reference current. Performances are also evaluated on a battery-like supercapacitor vehicle using an urban driving cycle.     

Determination of Battery Storage Capacity in Energy Buffer for Wind Farm

Design of a battery energy storage system (BESS) in a buffer scheme is examined for the purpose of attenuating the effects of unsteady input power from wind farms. The design problem is formulated as maximization of an objective function that measures the economic benefit obtainable from the dispatched power from the wind farm against the cost of the BESS. Solution to the problem results in the determination of the capacity of the BESS to ensure constant dispatched power to the connected grid, while the voltage level across the dc-link of the buffer is kept within preset limits. A computational procedure to determine the BESS capacity and the evaluation of the dc voltage is shown. Illustrative examples using the proposed design method are included.      

Development of constant-power driving control for light-emitting-diode (LED) luminaire

The illumination of an LED may be affected by operating temperature even under constant-current condition. A constant-power driving technique is proposed in the present study for LED luminaire. A linear system dynamics model of LED luminaire is first derived and used in the design of the feedback control system. The PI controller was designed and tuned taking into account the control accuracy and robust properties with respect to plant uncertainty and variation of operating conditions. The control system was implemented on a microprocessor and used to control a 150W LED luminaire. The test result shows that the feedback system accurately controls the input power of LED luminaire to within 1.3 per cent error. As the ambient temperature changes from 0 to 40 °C, the LED illumination varies slightly (?1.7%) for constant-power driving, as compared to that of constant-current driving (?12%) and constant-voltage driving (+50%). The constant-power driving has revealed advantage in stabilizing the illumination of LED under large temperature variation.     

An utility interactive power electronics interface foralternate/renewable energy systems

The foreseeable shortages in conventional sources of electric power has increased the emphasis on the research and development of alternate sources of energy. In order to make a noteworthy impact, the alternate sources of energy need to be utility interactive by means of a power electronic interface (a DC to AC converter). The inherent assumption in the control of DC to AC converters is, that the DC voltage available at the input of the converter is constant. However, when the input is an unregulated DC source such as a battery, fuel cell, photovoltaic cells or any other form of alternate source, maintenance of the constant DC voltage at the input of the converter is often impossible. A modified inverter switching technique is proposed for the interface with the utility grid such that the AC output of the inverter becomes immune to fluctuations in the unregulated input DC obtained from alternate energy sources     

Correction schemes for solar sensors with multiple time constants

A numerical scheme to correct for the delayed response of thermal solar radiation sensors is discussed. The proposed scheme employs only information that can be obtained from the response to a step input and does not require any auxiliary measurements. Furthermore, the scheme is applicable to instruments with any number of time constants and avoids the need for high order numerical derivatives. The development of such a scheme is motivated by a study of the Eppley Normal Incidence Pyrheliometer, which cannot be described accurately by a two-exponential model.     

Internal illumination prediction based on a simplified radiosity algorithm

This paper describes a new model for predicting natural interior illumination in the urban context. A simplified radiosity algorithm is used to define the external luminous environment and this model structure is used to predict internal illumination from sky and external obstructions for the range of sky conditions. This illumination is predicted with comparable accuracy to the ray tracing program RADIANCE, but at a computational cost several orders of magnitude lower. A standard diffusing sphere approximation (the BRS split flux equation) is currently used to solve internally reflected light. Comparisons suggest that the accuracy of this approach is adequate for the purpose of predicting the energy implications of photoresponsive lighting control. The model is in a form readily amenable for inclusion into other programs that require internal illuminance as an input, to improve the accuracy of their predictions without recourse to external simulation programs.     

Power quality investigation of a solar PV transformer-less grid-connected system fed DVR

This paper presents a single stage transformer-less grid-connected solar photovoltaic (PV) system with an active and reactive power control. In the absence of active input power, the grid-tied voltage source converter (VSC) is operated in a reactive power generation mode, which powers the control circuitry, and maintains a regulated DC voltage to the VSC. A data-based maximum power point tracking (MPPT) control scheme which performs power quality control at a maximum power by reducing the total harmonic distortion (THD) in grid injected current as per IEEE-519/1547 standards is implemented. A proportional-integral (PI) controller based dynamic voltage restorer (DVR) control scheme is implemented which controls the grid side converter during single-phase to ground fault. The analysis includes the grid current THD along with the corresponding variation of the active and reactive power during the fault condition. The MPPT tracks the actual variable DC link voltage while deriving the maximum power from the solar PV array, and maintains the DC link voltage constant by changing the modulation index of the VSC. Simulation results using Matlab/Simulink are presented to demonstrate the feasibility and validations of the proposed novel MPPT and DVR control systems under different environmental conditions.     

基于PR控制的海上风电场并网VSC-HVDC系统

提出了一种新的适用于海上风电场并网的新型高压直流输电(Voltage Source Converter based HVDC,VSC-HVDC)系统的比例谐振(Proportional Resonant,PR)控制策略。该方法充分利用PR控制器能够在αβ坐标系下对交流输入信号无静差控制的特点,将矢量控制策略下的有功电流和无功电流分量转换到αβ坐标系下进行调节,实现风电场和电网侧换流器维持直流电压稳定以及有功、无功功率的解耦控制。与常用的双闭环PI控制相比,该策略无需多次坐标变换和前馈解耦控制,且易于实现对系统谐波电流的补偿,降低了实现难度,提高了系统的鲁棒性和并网电能质量,为海上风电场并网VSC-HVDC系统提供了一种优化的控制方案。     

压气机级间喷水燃气轮机的实验研究

文中给出了在SIA－02燃机上进行压气机级间喷水的实验方案，并给出按等功率及等涡轮出口温度运行条件下，发动机各主要性能参数在不同工况下随喷水量的变化规律。依据实验，总结出压气机级间喷水对燃机性能影响的结论。     

Advanced PID type fuzzy logic power system stabilizer

An advanced fuzzy logic control scheme has been proposed for a microcomputer based power system stabilizer to enhance the overall stability of power systems. The proposed control scheme utilizes the PID information of the generator speed. The input signal to the stabilizer is the real power output of a study unit. Simulations show the effectiveness of the advanced fuzzy logic control scheme     

DSP based inverter control for alternate energy systems

This paper presents a DSP based algorithm to control inverters used in interfacing alternate energy systems with the electric utility. Since a constant and ripple free dc bus voltage is not ensured at the output of alternate energy sources, the main aim of the proposed algorithm is to make the output of the inverter immune to the fluctuations in the dc input voltage. In this paper a modified space vector pulse width modulation (SVPWM) technique is proposed which will maintain the quality of the ac output of the inverter, regardless of the ripple present at the inverter input. The principle is explained qualitatively and extensive experiments have been carried out to verify and validate the proposed algorithm. A 16-bit fixed-point C2000 family DSP from Texas Instruments was used as the controller to implement the proposed control algorithm.     

A novel current source PWM drive topology with specific harmonic elimination switching patterns

This letter presents a novel current source PWM rectifier/inverter topology which has low input current harmonics and high input displacement factor, for high-power induction motor drive applications. A suitable PWM specific harmonic elimination (PWM-SHE) switching pattern is developed in order to just eliminate the 11th and 13th harmonics, required by the proposed topology. A genetic algorithm and the conjugate gradient descent method are combined to solve the nonlinear transcendental functions for PWM-SHE. This scheme converges quickly.     

Fuzzy logic based DSP controlled servo position control for ultrasonic motor

In this paper, position control of an ultrasonic motor was implemented on the basis of fuzzy reasoning. A digitally controllable two phase serial resonant inverter was developed to drive the ultrasonic motor by using a TMS320F243 digital signal processor. The driving frequency was used as a control input in the position control loop. The position characteristics obtained from the proposed drive and control system were demonstrated and evaluated by experiments. The experimental results verify that the developed position control scheme is highly effective, reliable and applicable for the ultrasonic motor.     

Optimal control in the power management of fuel cell hybrid vehicles

Several types of power management strategies have been developed to improve the fuel economy of fuel cell hybrid vehicles (FCHVs). Optimal control based on the Minimum Principle provides the necessary optimality conditions which minimize fuel consumption and optimize the power distribution between power sources while the vehicle is being driven. In the optimal control scheme, the costate is an equivalent parameter between fuel usage and electric usage. The optimal trajectory of the costate can be derived from one of the necessary conditions. In this paper, an optimal control scheme based on the Minimum Principle is proposed for cases without a state constraint and for those with a state constraint. The conditions in which a variable costate can be replaced with a constant costate are presented. The simulation results with constant costates are compared to those with variable costates in order to prove that variable costates can be replaced with constant costates when using the proposed optimal control scheme.     

A Statistical Approach to the Design of a Dispatchable Wind Power-Battery Energy Storage System

A scheme that allows the dispatch of steady and controllable level of power from a wind power generating station is proposed in this paper. The scheme utilizes two battery energy storage systems (BESSs) in which the generated wind power is used to charge one BESS, while the second BESS is used to discharge constant power into grid. The role of the two BESS interchanges when the discharging BESS reaches specified operating limit. With this scheme in mind and based on given wind speed statistics, charging characteristics of the BESS are studied, and a method to determine the expected charging time of the BESS to reach stipulated battery state of charge is developed. The expected BESS charging time, in turn, dictates the constant power level that can be dispatched to the grid through the discharging BESS. The corresponding discharge time is also determined using the developed method, the accuracy of which is validated experimentally. The proposed design procedure is then used to determine the minimum BESS capacity based on the expected wind power. Statistical likelihood of dispatchable power delivery achievable from the scheme is also obtained.      

太阳电池最大功率及其跟踪模式

根据太阳电池电流方程及输出功率极值条件,在温度保持不变时,可建立最大功率方程,由此可在伏安特性坐标系内绘制大范围光照变化时最大功率的轨迹线,发现其呈现为S形状。据此提出三种最大功率的跟踪模式:(1)恒载跟踪;(2)恒压跟踪;(3)计算跟踪。其中恒载跟踪适用极低光照和极强光照,恒压跟踪适合于中等光照,计算跟踪适合于恒压跟踪向恒载跟踪的过渡光强。计算跟踪是本文给出的一种最大功率电压联立求解的计算方法。     

Pathways for the degradation of organic photovoltaic P3HT:PCBM based devices

We report on studies of device degradation in organic photovoltaic devices based on blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). Since delamination, oxidation, and chemical interactions at the metal electrode/organic interface have long been posited as degradation pathways in organic electronic devices, we first investigated the stability of a variety of electrodes for devices stored in an inert, dark environment. Second, a set of experiments was designed to separate the effects at the metal/organic interface from the degradation of the active layer or the hole extraction interface. To do this, Ca/Al electrodes were deposited to complete half of a substrate's devices, and samples were left both under constant illumination and 10% illumination (10% duty cycle of 1 sun illumination) in a glovebox environment. After more than 200 h of measurement, additional electrodes were deposited and device performance of each set was compared. Third, to assess the degree of degradation caused by photo-induced processes, device stability in an inert atmosphere under constant illumination, and 10% illumination conditions was also investigated. Last, various degradation mitigation strategies in air under constant illumination were explored. The results showed that the active layer itself is not inherently unstable on the timescales studied here. Choosing the appropriate electrode (Ca/Al) reduced interfacial degradation, storing the active layer in an inert, dark environment did not cause significant degradation, and storing the active layer under constant illumination caused only a limited reduction in performance. Our results indicate that the metal/organic interface can be a significant source of degradation in the devices, and we discuss approaches that could reduce this instability.     

非反向Buck-Boost变换器的多模式定频双向ZVS控制策略

非反向Buck-Boost变换器在可再生能源发电系统、储能系统等电压变化范围较宽的场合得到广泛应用。传统四边形控制方法,能实现非反向Buck-Boost变换器各开关管的ZVS,但存在如下问题：1）大的电感电流引起的较大的导通损耗;2）各模式之间切换引起的输出电压波动;3）需要离线预先计算,使用多维查找表和线性插值法,无在线检测实时计算的闭环,整体控制复杂。该文提出的多模式定频双向ZVS充放电控制策略,解决了以上3个问题。首先,提出多模式定频ZVS恒压放电控制策略,不需要添加任何额外的有源或无源器件,通过将整个宽输入电压范围分成3个模式,并独立分析每个模式的特点,可增加控制条件以简化计算过程,同时实现各模式的在线实时恒压闭环和通态损耗最小ZVS。无需使用多维查找表和线性插值法,整体控制简单容易实现。其次,提出多模式平滑切换控制策略,可保证在模式切换时各开关管占空比跳变前后,闭环输出始终保持稳定。然后,提出多模式定频ZVS恒流充电控制策略,实现了非反向Buck-Boost变换器的双向ZVS充放电控制。最后,给出各模式区间划分的理论依据和电感参数的计算原理,并搭建500 W的实验样机验证了所提出方案的有效性。     

Study of an incrementally loaded multistage flash desalination system for optimum use of sensible waste heat from nuclear power plant

Existing practice of nuclear desalination cogeneration incurs loss of nuclear plant power generation because it competes for live steam with nuclear plant steam turbine. Such loss is completely avoided with the nuclear desalination plant design proposed in the present study. The plant called GTHTR300 is based on a high‐temperature gas reactor rated at 600 MWt. Gas turbine is used to replace steam turbine as power generator. The gas turbine converts about a half of the reactor's thermal power to electricity while rejecting the balance as sensible waste heat to be utilized in a multistage flash (MSF) plant for seawater desalination. A new MSF process scheme is proposed and optimized to efficiently match the sensible waste heat source. The new scheme increments the thermal load of the multistage heat recovery section in a number of steps as opposed to keeping it constant in the traditional MSF process. As the number of steps increases, more waste heat is utilized, and top brine temperature for peak water production is increased. Both tend to increase water yield. Operating with a similar number of stages, the new process is shown to produce 45% more water than the traditional process operating over the same temperature range. As a result, the GTHTR300 yields 56,000 m³/d water and generates 280 MWe power at constant efficiency with and without water cogeneration. Copyright © 2012 John Wiley & Sons, Ltd.