Dual mode AC DC AC converter for contactless power transfer system

A new type AC DC AC converter which can work in Buck or Boost mode is proposed in order to overcome the deficiencies of the primary circuit of the traditional contactless power transfer system. Through switching this two modes and turning the duty cycles of the switches, not only the resonant current amplitude of the primary resonant current can be controlled to be constant against a wide range variation of input voltage, but also the problems, such as surge current, high cost, complex control etc., caused by the DC filter and DC/DC converter in a traditional CPT system are effectively eliminated. The topology and operation principle of the proposed converter have been analyzed. The corresponding control strategy has been presented and verified by simulation results.     

重组减蛋综合征病毒KnobS干酪乳杆菌的构建与表达

以干酪乳杆菌为传递载体,以开发食品级安全的减蛋综合征病毒疫苗为目标,构建了一个温度敏感型自杀型质粒系统p ORZP-UKD。将该质粒电转化到干酪乳杆菌L.casei中,经过2次升温处理和5-氟尿嘧啶抗性筛选,挑选阳性克隆,采用PCR和SDS-PAGE方法进行鉴定。KnobS基因整合到干酪乳酸杆菌基因组内,并实现融合蛋白KnobS的分泌表达。表明得到了一株具有无任何选择性标记、携带有KnobS表达盒元件的基因组整合的重组干酪乳酸杆菌KnobSΔupp L.casei,且整合的外源基因能够随着细菌的复制而进行表达,为减蛋综合征病毒免疫保护性抗原KnobS疫苗的进一步研制提供了试验数据。     

OPTIMAL ACTIVE POWER ADJUSTMEMT OF LARGE HYBRID AC/DC SYSTEMS AFTER OUTAGE CONTINGENCIES WITH THE APPLICATION IN RELIABILITY EVALUATION

An optimal active power adjustment model is deve in this paper for hybrid AC/DC systems after outage contingencies. The objective of the model is to minimize the rejection of load when some elements are out of service, with adjustment strategy approaching practical system operation. A large number of outage contingencies are simulated when the Monte-Carlo Method is emyloyed to evaluate the system reliability, requiring fast calculation of each simulation. The model and computer method proposed in this paper satisfy such a requirment because of the application of concentric relaxation, recursive branch constraint treatment in linear programming and a direct method for B-1 matrix modification. This paper is concerned with the simplified steady state conditions of the system based on DC load-flow, which implies the reliability indices calculated are the measures about static loss of load. The results for a 14-bus hybrid AC/DC system are given.     

DIGITAL SIMULATION OF HIGH VOLTAGE AC/DC PARALLEL SYSTEMS

The method of companion model is applied to the digital simulation of high voltage hybrid AC/DC systems for the first trme in this thesis.The mathematical model of the digital simulation of hybrid AC/DC systems is represented. This method can model the normal states, faults and games of faults of any hybrid AC/DC systems. The method has a series of advantages : saving the computation and the amounts of memory, high precision and fast calculation and it can be used with convenience. The simulation results of a hybrid AC/DC system arc in consistent with that of theoretical analysis. It shows that the mathematical model, the simulation method and the program in this thesis are correct.     

Novel Image-adaptive Watermarking Algorithm

Digital watermarking is an effective method to provide copyright protection for digital media. A blind image- adaptive watermarking algorithm based on DCT domain is presented. The algorithm selects adaptively the step size of quantization to embed the watermark bits by modifying DC components via the human visual system model and local characteristics of image; at the same time some AC components of the blocks with less perceptual capacity are also modified to embed the same watermark bits by using quantization. Thus the relation between robustness and imperceptibility can be well balanced. The algorithm recovers the watermark without any reference to the original image. Compared with the similar algorithm reported in the literature, this method can give better image quality and is better robust against noise and commonly used image processing techniques.     

A SELF-TUNING CONTROL FOR A PARALLEL AC/DC POWER SYSTEM

Based on a non-linear system model, an adaptive control methodology is presented for a parallel AC/DC power system by means of on-line recursive parameter identifications. Taking the advantage of rapid power regulatiing ability of the DC power system and combining with the generalized minimum variance self-tuning control principles, the dynamic qualities of the controlled system has been greatly improved. Using SISO form makes the control system very simple to implement. Through the design, simulation and analysis of the self-tuning control system for a practical example, it shows that the self-tuning control strategy is very promising for AC/DC power systems.     

ANTICIPATED FAIIURE ANALYSIS OF HVAC/DC HYBRID SYSTEMS

A method of anticipated failure analysis(AFA)in HV AC/DC hybrid systems is presented in this paper for the first time. In this method node-injection-power is used to simulate outage states of AC/DC branch circuits, linked with the fast decoupled load flow, to obtain the load flow solutions after the anticipated failures. An example for calculation in this paper shows the effectiveness and correctness of this method and computer programs.     

Modeling and Simulation of the Doubly Fed Generatorwith the Matrix AC-AC Converter as an Exciter

According to the space vector modulation method of the AC DC AC converter,the switch control scheme of the matrix AC AC converter is deduced,and the model of a three phase matrix AC AC converter is constructed. According to the mathematic model of the doubly fed generator and the excitation control principle based on dynamical synchronous reference frame,the simulation model of the generator and excitation controller are established,then the modeling and simulation of the doubly fed generator system with the matrix AC AC converter as an exciter are implemented.The steady state and transient characteristics of the system are simulated,the harmonics of the EMF and stator?rotor current are researched.     

Influence of HVDC System on the Shaft of Hydro-generator Unit

Widely concerns of the influence of the HVDC system on the Three Gorges power station have been shown so far. Based on the understanding of the mechanism of the non-characteristic harmonics introduced by HVDC system, the influence of interharmonics on the shaft of hydro-generator unit is studied. A MATLAB simulation model for the Three Gorges hybrid AC and DC transmission system with considering the effect of generator-unit shaft is established. Through time-domain simulation, the influence of the minor-associated component of interharmonics on the generator-unit shaft is analyzed, which arise from the asynchronous operation of the HVDC system. Also, the complex torque coefficient method in frequency-domain is used to analyze this problem. Same conclusions can be drawn from the results of timedomain and frequency-domain analyses.     

A NEW DISCONTINUOUS CURRENT MODEL FOR SCR DC MOTOR SPEED CONTROL SYSTEM AND CURRENT ADAPTIVE CONTROL

The paper presents a new approximative model suitable to discontinuous current and continuons current in the three-phase controlled bridge rectifier DC motor control system. This model offers a new approach for discontinuous current adaptive control.As an example of application of the model, digital simulation results of discontinuous current adaptive control in a double-closed-loop control system are presented.     

日本农产品区域品牌保护制度及其启示

随着农业领域国际竞争的日益激烈,作为增强农业综合竞争力的重要因素,世界各国越来越重视农产品区域品牌保护。近年来,日本根据本国国情和国际农业形势的发展变化,积极制定农产品区域品牌的保护制度以激励和保护本国农业的发展。本文通过对日本农产品区域品牌的保护制度进行分析和评价,从而得出其对我国的启示作用和借鉴意义。以日本为鉴,我国也应该从本国国情出发,完善区域品牌的相关法律、法规,发挥政府的职能,发展产品保护行业协会,强化安全质量标准体系的监控并大力开展市场推广与广告宣传。     

Alleviating Bus Voltage Stress in Single Stage Power Factor Correction Converters

High DC bus voltage stress is an important issue for the single stage PFC converters in practical application. This paper analyzes the inherent reason of the high bus voltage stress of single-stage power-factor-correction (PFC) AC/DC converters. Four possible resolving schemes are analyzed and discussed, and some of practical implementation circuits topologies are also given. Theoretical analysis and simulation results show that the both series-charging, parallel-discharging capacitors (SCPDC) scheme and bus-voltage-feedback (BVF) method are deemed to be more viable than the other two methods.     

Analysis on the Effect of Harmonic on the Instruments with Average Value Principle

The application of non-linear load produces a mass of harmonics. The AC voltage meter and the AC current meter used in power system are usually rectifying instruments, which adopt principle of responding to the average value of voltage and current and get the virtual value by using of the proportion between the average value and it. Because they are designed based on the 50 Hz standard sinuous wave, the principle error will occur when the voltageof power system and the current of loads include harmonic. Based on their working principle, this kind of error is analyzed quantificationally. And the result shows that it can not be neglected. The voltage and current meters with real virtual value are proposed.     

Fast modeling of the motor broadband equivalent circuit model

This paper proposes a modeling method of the motor broadband equivalent circuit model. The impedance amplitude-frequency characteristics of the motor terminal through measuring are obtained. The impedance amplitude-frequency characteristics are devided into several regions based on its first resonant point information,and the motor broadband circuit topology is developed with each region equaling a resonance unit. The RLC parameters of resonance unit are extracted through frequency and corresponding impedance of the any non-resonant and resonant point in each unit. This proposed method is used to build DC and AC motor broadband equivalent circuit model. Their impedance amplitude-frequency characteristics are simulated by the Saber software. The measurement results and the simulation result of references are compared. The DC motor simulation results coincide with the measurement results in 0.1~50 MHz,and the AC motor is in 0.1~40 MHz. The results show that the motor broadband circuit model is reliable and feasible.     

A NEW ON LINE AND REAL TIME METHOD FOR DETERMINING HARMONIC AND REACTIVE CURRENTS

According to the basic idea of phasar analysis and by applying a special multiplier, a new on line and real time method is derived for determining harmonic current and reactive current of an electric network. This method has a good dynamic response characteristic and solves for the first time the determining problem for the compensation system in single phase system,which is also appliable to the three-phase system.     

A new control design for grid integration ofDFIG wind farm with VSC-HVDC

This paper proposes a control scheme for a doubly-fed induction generator (DFIG) wind farm with VSC-HVDC grid integration to ensure secure and reliable operation of power system with fluctuated wind power penetration. The whole system dynamic models are respectively described. Based on vector control system with a virtual voltage orientation, a steady-state voltage control block and a dynamic voltage control block with a cross-product term of d-q currents are separately designed for WFVSC to control the corresponding parts of the wind farm voltage. Meanwhile, with the consideration of AC and DC side parameter variation and external disturbance, an improved backstepping control scheme with Lyapunov stability provement is also proposed for the GSVSC. The combination of the two schemes makes up the new control design of this study. Besides, to verify the performance of the proposed new control design, three different cases are suggested which contain the AC and DC side parameter variation and external disturbance such as local load cut off-in, grid voltage harmonics. Finally, numerical simulations using MATLAB/Simulink are presented for a 200MW DFIG wind farm with VSC-HVDC grid integration to validate the proposed control scheme and demonstrate the improved system operation performance. Moreover, the corresponding discussions are also presented for further illustrations.     

PROBABILISTIC STABILITY EVALUATION OF AC/DC POWER SYSTEMS WITH PARALLEL MONTE CARLO METHOD

This paper presents a new method for the probabilistic stability evaluation of AC/DC power systems. The transient stability model is described and the stochastic factors having effects on the stability behaviors are analysed and modeled. A theorem governing the probabilistic relations among the occurences of different types of disturbances is derived. A method of parallel computation is oresented, which is based on Monte Carlo simulation. An illustrative example is also given to show the application of the concepts and method presented in this paper.     

基于DPSIR和云模型的宿鸭湖水库水环境安全评估

为了推动水库水环境安全工作的开展,强化水源区水质保护,以宿鸭湖水库为例,应用DPSIR模型建立了水库水环境安全评估的指标体系,通过熵值法确定了各指标的权重,采用云模型对其2015年的水环境安全进行了评估,结果表明：该水库水环境处于较安全等级,但存在安全隐患；由于上游工业废水、居民生活污水、餐饮业的废弃物随着降雨径流汇入水库,再加上水产养殖、观光旅游等人类活动的影响,使其TN、TP的浓度和入库量增加,水库水质难以达标,需引起水库管理部门的重视。结论：云模型可减少评估过程中的不确定性,实现水库水环境安全概念与其定量数值间的合理转换,使其评估结果与实际相符。     

强酸性电解水的杀菌机理与应用

电解水是一种新型机能水,为稀食盐水在电场作用下电解出的水溶液,根据电解方式及程度不同分为酸性电解水与碱性电解水。强酸性电解水具有低pH（2~3）、高氧化还原电位（900~1200mV）及一定的有效氯含量（10~160mg/L）,表现出较强的杀菌能力,而且与传统的杀菌剂相比具有广谱高效、操作简单、安全无害、环境友好等优点,近年来已被作为一种新型杀菌剂广泛应用于医疗、农业、食品加工等行业的杀菌消毒。笔者介绍了强酸性电解水的特性、生产原理、杀菌机理与杀菌效果,阐述了影响强酸性电解水杀菌效果的因素及其在农业中的应用,并展望了强酸性电解水的应用前景。