Low frequency oscillation restraint in power systems that include asynchronized turbogenerators

Yangtze River is abundant of water and can provide enough water as cooling and heating source for water source heat pumps (WSHP). A pair of contrast experiments with open loop system and close loop system of WSHP were finished in order to get the heat pump's COP, the system's COP and the distribution of water temperature in the heat exchanger etc. This paper compared the characteristic and the COP of these two kinds of system. The heat pump's COP of the open loop system and close loop System are 3.08 and 3.77 respectively, and the system's COP are 2.83 and 2.80 respectively. At last, applications of open loop system and close loop System of WSHP at Yangtze River were analyzed and the key problem for attention was pointed out in the paper.      

Power Flow Analysis of System with UPFC

This paper first analyzes the working mechanism of the UPFC,and a practical method of power flow simulation is presented.The method can bring controlling of UPFC to accord with power flow simulation in the best,and can calculate the power flow with several UPFC.IEEE 5 nodes system and IEEE 30 nodes system are tested.     

Modelling and Analysis of Multi-terminal Unified Power Flow Controller

To control the complex powers emanating from a bus in power system, there are two solutions. The obvious solution is to equip each of the n lines radiating from the node with its own UPFC. The next evolution of the idea is to equip with a multi-terminal UPFC. First, the configuration and the principle of the Two-terminal UPFC (when n=2) are presented. In consideration of the existing shortages of output model-constructing method and topological model-constructing method for T-UPFC, a switching function mathematical model of this device is constructed by introducing the concept of switching function. It has more generality than the output and the topological model with the consideration of the internal switching character and the physical course of the T-UPFC.     

Influence of Steam Turbine System on Low Frequency Oscillation

Low frequency oscillation of electric power system is a problem which electric workers always care about. The influences of prime mover characteristics were ignored in the past research. The paper introduces the models of steam turbine system and each part of electric power system, and calculates the corresponding eigenvalues, then analyzes the influences of steam turbine system on low frequency oscillation.     

Analysis of Loosely Coupled Inductive Power Transfer System

In LCIPT system, the selection of system operation frequency has a relationshi Pwith the cost and power transfer capability of the power supply. Due to the development of Power device and system efficiency requirement , it is restricted to increase the system operation frequency . This paper presentes a topology which transfers power through LC oscillation. When the voltage of the capacitor is less than reference voltage, the switch is turned off and the capacitor is charged, which makes the switching frequency far less than the syntonic frequency. Thus the system efficiency is improved, and the system cost is reduced. This is verified by the time domain and frequency domain simulations of Saber. This topology not only can be used in LCIPT, but also in other convertors.     

Optimal Control System for UPFC

This paper first analyzes the internal dynamic process of the UPFC,then a five order differential equation is presented to describe dynamic behavior of UPFC. In term of this,a optimal control system is designed.Dynamic simulation of a transmission system demonstrates the effectiveness.     

DIGITAL POWER SYSTEM STABILIZER ( DPSS )

A digital power system stabilizer ( DPSS ) and its design method are presented in this paper. The mathematical model of a single machine infinite bus power system is obtained using off-line parameter identifications, and on the base of the identified model the control system is synthesized by generalized minimum variance control principles. Through feedback combination of several signals this control system has double functions of damping low frequency oscillation and automatic voltage regulating. In order to avoid static errors the very effective way is to combine discrete generalized minimum variance control with continuous integral control. Besides the proposed control strategy is very simple in structures and very easy to realize. Simulation results under several cases have shown the correctness and effectiveness of the proposed control strategy.     

海上大风延伸期预报研究进展

海上大风是海洋产业的重大灾害性天气,而延伸期预报是世界性难题。目前,延伸期预报主要分成动力延伸、低频振荡、经验波传播、数理统计、气候扰动分解和集合预报等6种方法,以动力延伸中的数值模式和低频振荡中的MJO监测诊断最为流行。随着大数据时代的到来,基于大数据分析,以数值预报产品为基础的集合预报成为未来业务发展的重点方向。这6种方法都可以用于海上大风等重大灾害性天气预报,许多学者尝试较多的是气候扰动分解、低频振荡中的低频天气图等方法中的溯源技术,通过找到源头,实现重大灾害性天气的延伸期预报。     

The Analysis of Abnormal State for Power Distribution Network Based on MATLAB

Along with the extensive use of power cable lines in power distribution system, the probability of fundamental frequency resonance has greatly increased. It may endanger the security operation and power supply reliability of the power system. On the basis of theoretical analysis and numerical calculations using MATLAB language combined with a real instance, it is indicated that the improper electrical parameter coordination caused by the abundance of power cable lines result in fundamental frequency current resonance, in addition, the countermeasures based on SVC to solve the problem are put forward. Further more, digital simulations have been carried out in detail based on the dynamic simulation model developed by the application of MATLAB/Simulink and its power system simulation software. Simulation results proves the effectiveness and practicability of the scheme presented.     

Filtering Method for the Decomposition of Heart Rate Variability Power Spectral

Heart rate variability is a convenient tool to study the autonomic nervous system of human body. It is a focus of studying cardiovascular disease in clinic. The main spectral components are distinguished in the heart rate variability spectrum: ultra low frequency(ULF),very low frequency(VLF), low frequency(LF), high frequency(HF) components .While different part has different physiological meaning. This paper discusses the design of an effective digital filter for heart rate variability power spectral analysis,which provides a scientific measure of heart rate variability power spectral analysis in further studies and clinical applications.     

Application of Power Spectral Density Analysis in STM

The tunneling-current signals which acquired by STM,include both the sample's molecular structure and the dynamic characteristics of STM system.The Short Time Fourier Transform(STFT) is utilized to estimate the power spectral density(PSD)of the tunneling-current signals and the data's feature vector was extracted in the frequency space.The results obtained by PSD estimation reveal that spectral-space-based feature vector can distinguish the interference from power line(50 Hz),and it can explain and analyze the dynamic characteristics of STM efficiently by using a damped harmonic oscillator model.Meanwhile,the recognition is helpful in the control of the practice scanning condition of STM and the 3-D recreation for the images of STM.     

Single-end Flyback High-frequency High-voltage Switching Power Supplies

Based on the research of a practical project of high frequency high voltage switching power supplies,the system design and experimental investigation of a single end flyback high frequency high voltage switching power supply are presented. In order to solve the problem of durable voltage of power MOSFETs that are used in the single end flyback high voltage switching power supply,an effective approach that adopts dual MOSFETs in series connected is proposed.The procedure of the designing and the parameter of each device is given in detail.A prototype of 220 Volt input and 2000V/3mA output is developed, and the validity of the scheme is demonstrated by the experiment.     

A New Method of Extracting Fault Components Under Power System Swing

To solve the problem that the existing method of extracting fault components is easily affected by power system swing,a new methed has been proposed in this paper,which can be used in high speed protection of transmission lines. This proped method ean greatly decrease unbal-ance outputs under power swing condilions without frequency tracking circuits,therefore it can make the protection using fault compnents operate correctly.     

Research on a Novel Inverter of VSC

In order to improve waveform performance of light HVDC system, a lot of switches which operate in high frequency are used, which causes large switching losses and results high cost. A new Buck type voltage source converter(BVSC) is proposed. The new BVSC comprises a dual-buck converter and a three-phase inverter operating in grid frequency. Only two high frequency switches are used, which results good output waveform performance. In order to reduce the high frequency switching losses, a novel improved double-frequency Buck type voltage source converter(DBVSC) is also proposed. An additional dual-Buck converter is added to the BVSC, the added dual-Buck converter deals with the fundamental power that operates in low frequency, and BVSC only deals with harmonic power that operates in high frequency. The output waveform is enhanced and the switching losses are reduced in DBVSC, and the power rating is also increased. The DBVSC is very suitable for large power rating application. The one cycle control theory is adopted to control the proposed DBVSC with analog circuit, which is very simple. The proposed DBVSC and control method are verified by simulation.     

Application of frequency shifting in truncating substructure low order normal modes

A method to cutoff substructure low order normal modes in component mode synthesis is proposed. Frequency shifting technique is introduced in substructure free vibration differential equation. Quasi-static constraint mode is taken into coordinate transformation and the contribution of substructure low order normal modes to system middle frequency modes is reduced,thus substructure low order normal modes truncation is achieved. This technique is used to compute dynamic characteristics of a body-in-white FEM mode in the frequency band of 160~190 Hz. The results show that compared with traditional component mode synthesis,which keeps 1 836 normal modes,this method only needs 297 normal modes and saves 27.7% calculation time. It means frequency shifting technique can improve the computational efficiency for middle frequency band dynamic characteristics of complex structure.     

Analysis of the Power System''s Voltage Stabilization by Modeling and Simulink

The simulink of the power system can help people to analyze the actual power system's various state.As an important instrument,the Matlab software gains the recognition because of its all-sided and professional features.But when it is used in the field of dynamic process of the power system,there exist some disadvantages such as the difficulty of the modeling.The state-space module can be used to set up the three rank compact model of the generator and the electrical machine.It makes the modeling more convenient and more easily jointed to the system's primary parameter such as voltage and frequency.The typical model of the power system is built including the generator,electrical wire,load and SVC by using the function of the Simulink.In order to make the model's physical conception,some necessary predigestion is made to the typical model.At last,some conclusions about the voltage stabilization are gained by using the simulink of the system's malfunction,testifing the correctness and feasibility of this compact modeling.     

Instantaneous Frequency Estimation of the Surface Myoelectric Signal Wigner-Ville Distribution Based Technique

The analysis of the surface myoelectric signal is a valuable and the signal is recorded while a muscle is performing a sustained contraction tool for assessing the progression of localized fatigue. Mean and median frequencies of an electromyogram power spectrum are often used as indicators of muscular fatigue during static contraction. To evaluate muscle fatigue during cyclic dynamic contraction, according to the features of surface myoelectric signal during dynamic contraction, an instantaneous frequency detection technique based on cross Wigner-Ville distribution is proposed. The estimation error of the algorithm by means of a simulated stochastic process with statistical properties similar to the those of surface myoelectric signal. The theoretical and experiment validates that the instantaneous frequency suites well to tracking spectral changes due to muscle fatigue with very low SNR.     

Voltage and Reactive Power Optimization of Main Electric Power Network in Chongqing

Based on the reactive surplus of Chongqing 220 kV main electric power network under low water and low load, and on state of higher system voltage, a thorough research is done on voltage and reactive power of the system power network by means of calculation,analysis and experiments. A main network calculating equivalence model of power network in Chongqing is constructed. And reactive power optimizing calculation is figured out on the Chongqing power network on condition that the loss minimum of the active power network is object function. Several optimizing compensatory schemes are put forward. Based on the calculation result and the analysis of all schemes, the most reasonable and feasible optimizing scheme could be achieved. Meanwhile, the feasibility that the system voltage could be adjusted when generator operating under excitation was demonstrated. According to the experience of under-excitation operation of the same type units , it decreases the system voltage, improves Chongqing power network running performance, and strengthens the coordination and stabilization of system.     

Power Train of a New Type of Hybrid Electric Vehicle

The powertrain of a new type of zero emission electric vehicle is researched, which powered primarily by air-breathing proton exchange membrane (PEM )fuel cells with gaseous hydrogen as fuel,and with Lead-acid battery as assistant power.The fuel cell system provides power for the vehicle while the vehicle travel at a cruising speed,and the exceed power will charge for battery.The fuel cell and the battery system will together provide power to the vehicle during periods of peak power demand such as vehicle acceleration or traveling at a high constant speed.At the same time, the powertrain parameter of this fuel cell vehicle are matched reasonably.At last, the dynamic of an electric vehicle is simulated, and the result shows that the dynamic performance perfectly meets the need of the design target.     

Low Voltage Power Line Communication Based on MSK

For that the characteristics of low voltage power line channel are complicated and variable, how to use low voltage power line to realize reliable and high speed communication has always been the hottest question in power line communication field. This article introduces how to apply MSK to the low voltage power line communication. It analyses the application elements of MSK and structures the model of low voltage power line communication based on MSK. simulation result indicates that MSK modulation technology can satisfy the characteristics that the bandwidth of power line communication channel is narrow and the attenuation to the amplitude of signal is time variable and frequency selected. Also, it makes better use of the spectrum.