Commutation Failure Factors Analysis In HVDC Transmission System

Commutation failure is one of the most common faults in HVDC transmission system, which is affected by many factors. This paper analyzes the effects of some major factors, such as voltage of commutation bus, DC current, advance firing angle, short circuit impedance and ratio of converter transformer, on the commutation failure in the inverter in HVDC transmission system. The obtained general rule of commutation failure in the inverter in HVDC transmission system is helpful to practical operation.     

Rapid Prototype Control of Hydraulic Automatic Transmission System Based on dSPACE

dSPACE is a prototype development and real-time control testing platform which is based on MATLAB/Simulink software. By establishing mathematic model of hydraulic automatic transmission system, the shift rules are achieved. A testing platform for hydraulic automatic transmission system is developed whose control software is programmed by simulink and using the dSPACE as the centre controller. The experiment of electric throttle control and power performance matching control of hydraulic automatic transmission system is carried out. the result shows that well matching performance of hydraulic automatic transmission system can be realizedby using the control strategy proposed in this paper, it provides a fast and efficient approach for researching and developing the hydraulic automatic transmission system.     

Integrated Control Strategy of Hydraulic-mechanical Automatic Transmission

Through the analysis of hydraulic-mechanical transmission and the modeling of torque converter, the traction performance of an automatic transmission car between hydraulic transmission and mechanical transmission under different throttle angle and different gears is discussed, and the control rule among dynamic gear-shifting, economic gear-shifting and mixed gear-shifting is made. Furthermore, the control strategy of engagement, disengagement and slip-control of lock-up clutch is set down. Simulation of integrated control of hydraulic-mechanical transmission which applies slip-control under multi-load-condition is carried out, and the result shows that the fuel economy of such type of the car gets an increase by 2.36%.     

Shift Control for Automated Mechanical Transmission

The gearshift of an automated mechanical transmission is performed by cutting off the power.The key to the gearshift of AMT is shift quality.Theinfluence of the control stategy during shifting processon shift quality is analysed.While resuming the power,the derivative of the speed differencebetween the clutch active disc and the clutch slave disc time instant is in direct proportion tothe discontinuity of the vehicle acceleration at the lock-up time instant.The large discontinuity of the vehicle acceleration will result in the jerk and the oscillation of vehicle that make passengers uncomfortable.A control stategy is proposed,that make small the derivative of the speed differencebetween the clutch active disc and the clutch slave disc by the integrated control of engine and clutch.The road test shows that the control stategy improves the shift quality.     

Voltage Stability Control of Local Power System

In this paper,the conception of bus voltage stability control area of local powersystem is presented,based on the practical criterion for voltage stability calculated by the real-timeinformation and the quasi-real time information form the power system.The method is test6d onIEEE-30-bus test system and results are satisfactory.     

FDTD Method''s Application in the Research of Television Interference From High Voltage Transmission Line

The mechanism of television interference is discussed from High voltage transmission line. Then the computational model is established, and scattering fields are calculated with the finite-difference time-domain(FDTD) method, and the results are visualized. The scattering effects of High voltage transmission lines on horizontal polarization waves (corresponding to TM mode) are greater than on vertical polarization waves (corresponding to TE mode).     

Synthetic Control Strategy for a Car With Hydro-mechanical Continuously Variable Transmission System at Standing Start

Continuously variable transmission (CVT) is the ideal transmission for automobile, it is also one of the most important research items of researchers and automobile companies all over the world. The dynamic simulation model is established and integrated control strategy of standing start is proposed for dual mode CVT vehicle, aiming at automatic vehicle with torque converter as a starter and metal pushing belt as a higher transmission equipment (Dual mode CVT vehicle), on the base of engine and torque converter performance experiment. Simulation result shows that vehicle performance can be improved by using the control strategy proposed. The research results provide the theory method of analyzing and designing for CVT vehicle.     

Simulation and Analysis of the Dual-Clutch Transmission Starting Control

With unique configuration characteristic,dual-clutch transmission(DCT)overcomes the shortcoming of power interruption when shifting in traditional AMT,which results in good power performance,fuel economy and driving comfort,and recently it becomes a new development trend in the field of transmission.Basing on the analysis of starting control principle of DCT,control principle and method that both the dual clutch engaged in the starting process simultaneously with engine constant speed are proposed.And the starting characteristic of the dry dual-clutch transmission is simulated and analyzed,providing theory foundation for the development and research of the dual-clutch transmission.     

An Analysis of PWM Switched-Mode Voltage Regulation System with the Cross Double-Fed Control

The dynamical modelling of the new converter with the cross double-fed control system is set by using the averaging techniques. The dynamical quality and the stability of the new system are analyzed with the modelling,and compared with the ordinary converter. The results show that the dynamical quality and the stability of the new converter are much better than those of the ordinary one.     

General Phasor Diagram and Power-angle Characteristic Equations of Extra High Voltage Long Distance Transmission Line

Installing compensation equipments is a good manner to improve line transmission capacity and maintain power system stability in the extra high voltage(EHV) long distance transmission line.It is of benefit to analysis and control by describing the effect of compensation equipment correctly.At present,for predigesting analysis or increasing real-time calculating speed,concentrated parameter circuit model is widely used to analyze 500 kV EHV long distance transmission line which may cause bigger error.So it is necessary to get a more reasonable model.On the basic of voltage and current distributed equations of even distributed long distance line,this paper deduces phasor diagram and power-angle character equations of uncompensated long line.Then the authors analyze the effect of compensators and define two characteristic parameters,namely,equivalent impedance x_(eq) and voltage coefficient K_V.Any compensating states of EHV long distance transmission line,example installing the compensators in the line or not or which type of compensators,is described by the general phasor diagram and power-angle characteristic equations.Furthermore,increment calculation(equations) of two characteristic parameters is presented by the compensator parameters which may make the concepts clear and predigests analysis easily.     

Research on Current Situation and Trend of Control Strategies for Hybrid Electric Vehicles

The vehicle's driving performances is determined by the control strategies and constructions of hybrid electric vehicles (HEV). The constructions of HEV are classified according to the change of state of charge of battery pack, and a study on current situation and trend of control strategies for HEV is presented in this paper. The research indicated that the current control strategies for HEV are not perfect and need further optimization. The control strategies should realize the optimum match among engine, motor, battery and transmission according to the characteristics of each component and vehicle's driving conditions. Many aspects including the fuel economy, emission, the life of battery pack, drivability, the reliability of each component and HEV's manufacture cost should be considered in the control strategies. A study on the control strategies and its optimization that take account of the aspects mentioned above is a work emphasis in the future. This paper also points out the PHEV equipped with small motor, small engine and continuously variable transmission is an ideal system construction for getting optimal fuel economy, lower emissions, steady drivability, lower manufacture cost and HEV's mass.     

Direction analysis on Contactless Power Transmission System

After analysis on the direction relationship betueen primary side and secondary side of existing contactless power transmission system, a random rotatable pick-up is proposed. Two connecting modes of three orthogonal wound coils are studied. Based on analysis and mathematical calculation, instantaneous output voltage and its ratio to the maximal and minimal value when the pick-up rotate in three-dimensional space is given. All the calculation is verified by experiment results.     

Electric Vehicle of Direct Torque Control System Based on TMS320LF2407 Controller

A fully digitized electric vehicle direct torque control system with DSPTMS320LF2407 controller is described. The system hardware and software structures are presented. The performance of the direct torque control system is studied by simulation with MATLAB. Based on the simulation of the induction motor, waveform of current, speed, torque and flux are obtained. The testing results are also presented. Experimental results show that the design is feasible.     

Lightning Protection Performance of Transmission Line with High Tower and Great Span

This paper studies lightning protection performance of transmission line with high tower and great span, and puts forward the lightning shielding model of transmission line with high tower and great span. The model simulates the developing process of lightning downward leader, and take the effect of upward leader to downward leader into account. Moreover, the model consider backward lightning , that is even downward leader have developed lower than transmission line, Which will be occur lightning line. Aim at a certain sea transmission line with great span, its lightning performance is calculated with regular method, EGM and the model. The results have been analysed and compared. Because of thinking over backward lightning , the model can be used for calculating lightning shield performance of all kinds of transmission lines.     

Application of Fuzzy Control in Direct Torque Control of an Induction Motor

The key of motor control is to control motor's torque essentially.Direct torque control,which emerged after the field-oriented control,directly stresses the instantaneous torque control of induction machine,which avoids some problems existing in field-oriented control,thus,it gets more attention.In conventional direct torque control system,switch vector is selected directly by the errors of stator flux-linkage and torque,after introducing fuzzy logic,optimal selecting switch state is realized by various strategies by distinguishing the grade of the errors of stator flux-linkage and torque,the dynamic and steady state performances of induction motors are improved.This paper presents a design method of the fuzzy controller.Simulation results demonstrate that it is effective,the stator currents pulsation at start-up and the torque pulsation are decreased.     

Development of Car Continuously Variable Transmission on the Basis of Personal Computer

During the process of developing the Car Continuously Variable Transmission, the Control rule of the system is so complicated that we have to adjust and modificate the control parameters often. Direct debugging and empoldering by using singlechip system will result in long empoldering period and low efficiency. The present article presents an empolder scheme based on the control of Personal Computer. In the empoldering process we will predigest the Car Transmission Control Unit of the Continuously Variable Transmission into an extension which is only used for parameter tracking and measurement, while the matching control of the system and the parameter monitor is achieved with the host computer. Serial communication is carried out in the communication between the host computer and the extension. In addition, we have developed the corresponding monitoring and debugging software with Visual C++ 6.0 also. The practice shows that the system has successfully realized the empoldering of the TCU(Transmission Control Unit) with great efficiency.     

Reliability Evaluation Model of Composite Generation and Transmission System Incorporating FACTS Devices

The utilization of Flexible AC Transimssion System(FACTS)technology has significant impact on power system reliability performance.Series FACTS devices such as Thyristor Controlled Phase Shifting Transformers(TCPSTs) and Thyristor Controlled Series Compensators(TCSCs) can change the natural allocation of the power flow and effectively alleviate transmission congestion.Parallel FACTS devices such as Static Var Compensators(SVCs)can provide reactive power support and maintain voltage stability.So it is important to quantitatively evaluate their benefits to the power system reliability.The traditional models of the composite generation and transmission system reliability evaluation are mainly focused on conventional generation and transmission facilities.This paper researches the power flow model of TCPST and TCSC,and then presents the optimal load shedding model incorporating TCPSTs,TCSCs and SVCs and effectively incorporates them into the reliability evaluation model.The proposed method is tested on the RBTS and the obtained results show that the system reliability can be improved effectually by FACTS devices.     

企业内部控制存在问题及解决对策

企业内部控制是指企业为保护其经济资源的安全完整、防范管理漏洞、保证会计信息的真实可靠,利用企业内部分工而制定和实施的相互制约、相互联系的控制职能方式、措施及程序。强化企业内部控制作为完善公司治理、保障企业经营安全的重要手段,已愈益为我国企业认同与重视。从对企业内部控制的不同认识出发,深刻理解内部控制的内涵;通过分析研究目前我国企业内部控制存在的问题及其产生的原因,论述了建立和完善企业内部控制的紧迫性和必要性。我国多数企业还停留在建立内控制度的初级阶段,实际抵御风险的能力极其薄弱,企业的内部控制与风险管理亟待规范和改进。