STATE VARIABLE METHOD FOR DYNAMIC SIMULATION OF HVDC SYSTEMS

A flexible mathematical model used for dynamic simulation studies of HVDC systems which is based on the stale variable method is presented, and the correspongding computer program has been implemented. Generality, easy to use, and suitable to run on microcomputers are the main features of the model and the computer program. Therefore the model is easy to be extended for application. An example is given in the paper to verily the coneclness of the model and the program.     

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.     

Testing Study on Hydraulic Torque Converter for Car

A test bed with computer control for hydraulic torque converter test is built up. The structure and principle of the test bed are introduced. The performance characteristic of torque converter for a CVT car is studied, and the mathematic model of the torque converter is established based on test results, which lays a foundation for the exploitation of automatic transmission car with hydraulic torque converter.     

Study of the Digital Measurement Tachnique and Apparatus for Impulse High-Voltage

A digital measurement apparatus is developed for Impulse high voltage. Ine ap paratus composes of a high speed A/D converter(20 MHz),a single-chip computer interface and some other high speed analog intergrated circuits with excellent function,It is characteristic of flxing transient waveforms,storing,processing and analysing waveform data measuring maxi-mum value of impulse high voltage.     

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.     

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.     

A FAST ALGORITHM FOR DIGITAL SIMULATTON OF HVDC SYSTEMS

After considering the features of the differential equations which have described the dynamic behaviours of HVDC systems, a fast algori -thm is presented for these equations. Compared with the fourth Runge-Kutta Method,this method has less amount of calculation with the same precision, numerical stability and other properties. Therefore, the use of the method has greatly increased the speed of the digital simulation of HVDC systems.In this paper an example of calculation is given, and the results obtained hv using this example are compared with the results obtained by calculating with the fourth Runge-Kutta Method. The speed of simulation by using this method is about 1.8 timss as fast as that by using the fourth Runge-Kutta Method.     

Overview on Control Strategies of High Voltage Direct Current Transmission System

Recent research progresses are summarized about the High Voltage Direct Current(HVDC) transmission system in control methods and modulation of HVDC transmission system,coordinated control of multi-infeed HVDC transmission system and AC-DC system.Some outsanding problems in current research are pointed out on such sides as system modeling,studying object,aim of coordinated control and engineering application.Based on the requirements of real systems and some latest research achievements on control technology and measure methods,some new research thoughts about HVDC transmission system for some problems of assessment and optimal combination of current control strategies,application of intelligent control methods and enhancement of coordinated control are proposed.     

TRANSIENT STABILITY ANALYSIS OF PARALLEL AC/DC SYSTEMS

In this paper the particular problems in transient stability study of parallel ac/dc systems are analyzed, a mathematical model together with the relevent algorithms for transient stability evaluation is proposed, and an illustrative example is given to show the effects of dc adjustment and the correctness of the model and algorithms.     

A SFG METHOD FOR RELIABILITY EVALUATION OF HVDC SYSTEMS

Steady-state probability, frequency and duration are the three main indices in reliability evaluation of the HVDC systems. Generally, they are solved by numerical methods. Their topolgical formulaes are derived by using the basic theory of ccates graph and considering conditions for some particularity of state-space in this paper. A set of generalised formulaes can be applied to obtain these indices expression about reliability parameters of components. Finally,an example is given to illustrate and verify this method.     

Theoretical Analysis for the Performance of HVDC Grounds Electrodes and the Mathematical Modal

The performance of HVDC ground electrodes is analyzed in detail.On the basis of electromagnetic field theories and its assumptions,the mathematical model is built,the ground resistance,the distribution of potential and temperature are computed with the current field distributions of HVDC ground electrodes.     

Application of Hydraulic Torque Converter Incorporated in Mechanical Continuously Variable Transmission

Continuously Variable Transmission which is the ideal transmission for automobile can improve dynamical and economical performance and reduce pollution emission effectively. Vehicle equipped with CVT where hydraulic torque converter is acted as start clutch have better acceleration performance and its starting control is very simple. Based on performance test of hydraulic torque converter and simulation on lock-up dynamic process of torque converter clutch, matching characteristic between engine and torque converter is evaluated , and the lock-up control rule of torque converter clutch and the control strategy of standing start of vehicle equipped with Continuously Variable Transmission with torque converter is proposed. By computer simulation on start process, vehicle equipped with CVT have better acceleration performance than equipped with five-speed MT.     

An Investigation on Power Distribution Model of Intelligent Building''s Computer Room

In this paper, some problems such as circuit jam, mutual disturbance of signals, bad operation reliability and so on were analyzed, which resulted from the deficiency of integral electric and computer systems design and installation. It discusses mainly such problems as power supply, separation of alternating and direct currents, ground connection, undisturbed signal lines and so on. Then it puts forward a reference model for computer room's synthetical power distribution.     

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.     

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.     

An asymmetric fault ride-through control method forPMSG wind turbine based onsuper-capacitors

With the rapid increasing interaction between wind turbines and power systems, wind turbines have to have the fault ride-through (FRT) capability to ensure the safe operation of power grid. In order to improve the asymmetric FRT capability of permanent magnet synchronous generator (PMSG) wind turbine, a novel control FRT method based on super-capacitors is proposed. In this method, super-capacitors are connected to the DC bus of AC-DC-AC converter via a bi-directional DC-DC converter, and the power processed by the super-capacitors is controlled to limit the increasing of the DC bus voltage of the AC-DC-AC converter in grid failure condition, and to reduce the 2nd order voltage ripple in the DC bus. Meanwhile, the proposed control method employs the grid voltage feed-forward approach to reduce the negative sequence current component in the grid side converter. According to the low voltage ride through (LVRT) standard, the selection of the super-capacitor capacity is also discussed, and then a mathematical model of the super-capacitor with the bi-directional DC-DC converter is established for designing the controller. Simulation results for a 1MW PMSG wind turbine by MATLAB show that the proposed control method reduces both the negative sequence current component in grid side converter and the 2nd order voltage ripple in DC link at the same time. The results also demonstrate that the asymmetric FRT capability of PMSG wind turbine is improved, which verifies the effectiveness of the proposed control method in this paper.     

Fuzzy Control and Simulation of Regulating System for Permanent Magnet Synchronous Motor

This paper researches the fuzzy control and simulation of regulating system for PMSM in electrical vehicle. The mathematics model is set up.The PMSM,the PMSM measures demux, dq to abc converter and the three phrase PWM converter models are set up in MATLAB/ Simulink. The fuzzy controller is designed with two dimension fuzzy design method, and take E and EC as input variable, U is the output variable. According to the controller and models, the fuzzy control model of regulating system for PMSM is created in matlab/simulink. At last, to test the accuracy of the control method with the simulation result.     

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.     

The modeling and simulation of a new USBCAN bus converter in Stateflow

The USBCAN bus converter is a connector of USB bus and CAN bus.It is difficult to judge whether the device works well or not and meets design requirement or not by ordinary ways.Regarded the Matlab/Simulink/Stateflow toolbox as the platform,the model of a USBCAN bus converter is established.The model of the bus converter is tested and verified in the Matlab/Simulink simulation environment.The results of the simulation analysis show the model is suitable for simulating the working state of the device.A new simulation and judging method for bus converters is proposed.     

A New Method of Piece-Wise Solution in Faulted Power Systems with Variable Configurations

A new model and its algorithm are presented in this paper to simulate calculating the electric values of short circuit fault in large-scale power systems with variable configurations. The method proposed herein reduces the computer storage requirements compared with the available approaches. And it completely avoids the modification computation of nodal impedance (or admittance) matrices of the original networks and the repeated calculations for each type of faults.