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.     

Mechanics Characteristis Andlysis and Improvement of Film Dynamie Sthess Modulaten

The kinematical principle and mechanical characteristic of the cell membrane stress modulator are analyzed, which is a key equipment of the external cell bringing up experimental system. A designing project of the experimental system is put forward based on position measurement and controlling modulating region. It validates that the design can improve the mechanical characteristic of the device. At the same time, the device can work smoothly, the life time of its correlative parts can be increased, and the power waste of the system can be reduced.     

A PRACTICAL PWM CONTROL METHOD OF CURRENT SOURCE GTR INVERTER

According to the principle that the orbit of stator current vector in complerplane should be as close to a circle as possible, the PWM control pattern is derived and determined. The control method is realized by using a micro-computer.     

A NEW PWM METHOD-AVERAGE VALUE PWM

In this paper, a new PWM method-average value PWM is presented. This method has been compared with other PWM methods and realized by using a micro - processor-controlled GTR inverter. Some experimental results and discussions for them have been given.     

Improvement and simulation on direct torque control system of permanent magnet synchronous motor

To solve the problems of large flux, torque ripple and inconstant inverter switching frequency in conventional direct torque control (DTC), a space vector modulation (SVM) technique is introduced to the conventional PMSM-DTC system and analyzed thoroughly based on the mathematical model. This novel control method which enjoys the advantages of VC and DTC has only one easy adjustable PI regulator and is easy to realize. The simulation verifies that this control system is capable of effectively improving the steady state performance and keeping the excellent dynamic performance of the PMSM-DTC system simultaneously and remain the switching frequency constant.     

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.     

Electromagnetic torque ripple control of induction motor fed by dual frequency inverter

Direct torque control(DTC)of space vector modulation fed by dual frequency inverter is studied in order to solve the problems of large torque,big flux ripples and inconstant switching frequency of conventional DTC in large power occasions. On the basis of conventional DTC,factors affecting flux and torque ripples are analyzed and the space voltage vector mathematical model of induction motor is deduced,which is implemented by S-function. Based on dual frequency theory,the system is supplied by cascaded inverters to decrease losses. The high frequency unit is in charge of improving the dynamic performance of the system,whose switching current is relatively low;while the low frequency unit is in charge of energy delivery,whose switching frequency is far lower than that of the high frequency unit. The simulation results illustrate that by using this program,the system has a better performance in both dynamic and static performance,and the electromagnetic torque ripple,flux ripple and switching losses are significantly reduced. Thus the system efficiency is improved and suitable for medium and large power occasions.     

A Review on Class D Audio Power Amplifier Control Techniques

Although class D amplifier has high efficiency, its distortion is larger than linear counterparts due to switching behaviour of power transistors. It is the hotspot of power electronics and audio power amplifier that researching new control technique to improve fidelity of class D amplifier. In this paper, a few novel control techniques in class D audio power amplifier are reviewed.     

THE EXPERIMENTAL STUDY ON REAL-TIME HOLOGRAPHIC THREE WAVEFRONT INTERFEROMETER

Real-time holographic three wavefront interferometer combineing wavefront interference with holography has been proposed in this paper. The apparatus can be used for a number of pratical applications including the measurement of flatness for an optical flat. Thickness for transmissive or refective films. It has peculiar character comparing with other interferometers.     

Suggestion for Moment Modulation of Prestressed Concrete Continuous Beams

Based on the information from China and overseas,a design suggestion for moment modulation of post-tensioned prestressed concrete continuous beams with bond has been put forth in this paper. The result calculated by the suggestion is consistent with the result of varying rigidity method.     

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.     

Two quadrant Current Chopper Control for Brushless DC Motor

In order to decrease the current ripple and improve the operating performances of the rare earth permanent magnetic brushless DC motor system,a two quadrant current chopper is used in the system and its operating principles are analyzed in this paper.The results of digital simulation and system experiment are presented and confirm that the system based on the two quadrant current chopper has attractive performances.     

SIMULATION STUDY OF ACTIVE POWER DISTORTION COMPENSATOR

In this paper, the effectes of modulation index, modulation frequency, modulation method and LPF parameters on current-fed active compensator arc studied by using digital simulation and the performances of voltage-fed active compensator are compared with those of the current-fed active compensator.     

Realization of Flash Stimulation with PWM in the Extraction of Visual Evoked Potential

Evoked EEG signal can be obtained by flash stimulation in the extraction of flash visual evoked potential(FVEP).Experiments show that the width,frequency and flash times of flash pulses will play key role for extracting FVEP.Aims at the feature of VEP extraction and its correlation factors,the flash stimulation method with pulse width modulation(PWM) technology has been discussed,and the realization methods based on hardware and software are studied,then the output of precise PWM with special integrated circuit is realized.So the parameters of flash stimulation can be adjusted based on the material conditions of FVEP extraction,then VEP can be extracted effectively.Experiments show that it is of better effectiveness for FVEP extraction by using the method based on the output of precise PWM to control the flashing stimulation.     

Digital modulation mode recognition based on multi-classclassification of support vector machine

To solve the overfitting, underfitting and local minimum existing in neural networks, a digital modulation mode recognition method based on support vector machine (SVM) is proposed. Seven characteristic parameters are extracted from instantaneous amplitude, instantaneous phase, instantaneous frequency, frequency spectrum, and changes in characteristics of the envelope to train support vector machine. Compared with the existing algorithms, using binary tree theory to design multi-class classifier has the features of simple, high-speed, high-precision. The simulation results indicate that the scheme can achieve 97% recognition accuracy when the signal to noise ratio (SNR) is above 15 dB with the AWGN channel.     

Analysis of the Modulation Phenomenon of Complex Vibration in Gearbox Fault Diagnosis

This paper presents a modulation phenomenon of complex vibration which occured when gear teeth broke or shaft seriously bent in gearbox. Based on the mechanism of gear vibration and modulation sideband,the peper analyzes this complex modulation phenomenon.     

Modulation Transfer Function of Image Monitoring System for Bridge''s Deformation

The principles of image monitoring system for bridge's deformation is proposed. Based on linear system theory, the whole system comprises linear shift-invariant system composed of atmosphere, optical sub-system and camera. The modulation transfer function of each component is analyzed, especially for the atmosphere. For a special system, modulation transfer functions on different weather condition such as sunny, cloudy, rainy and fogy weather are analyzed.     

Improve the Hardware of Watt-hour Meter Reading Figure in Machinery to Achieve to Long-range Reading

It is a time-consuming job that reading electricity meter from door to door every month. So, improving the hardware of traditional watt-hour meter will change the machinery digit into electricity digit, and read electricity meter in long-rang with wireless carrier. Aautomatic collection, transfer and handling are applied to electricity energe manage system. It overcomes the weakness of traditional mannered reading model. The feature is that simple change the circuit to get the effect in low cost.