Zhu Chunyi

Steganalysis of Compressed Speech

Based on the analyzing of the redundancy of coded parameters in G.723.1, a novel approach to detect hiding information is proposed in this paper. By using the statistical value of increaser entropy, this scheme can not only detect hidden messages embedded in compressed speech, but also estimate the embedded message length accurately .The experimental results show that the proposed scheme is effective.

Investigation on the control strategy of high power NPC/H-bridge inverter

Large power electronic converters are widely used in the oil and gas transportation, pumped storage and other fields. In order to achieve higher voltage and power, NPC/H-bridge multi-level topology is the most common solution. In this paper, the topology and control strategies of NPC/H-Bridge converter are investigated in details. Finally the PSIM simulation results validate that the control strategy of 3-segment switching pattern has a better performance.

Investigation on the switching property of IGCT used in large power voltage source inverter

The integrated gate commutated thyristors (IGCTs) have the features of high current, high voltage, high reliability, compact structure and low loss. They have been widely used in large power voltage source inverter systems now, and they have extensive application prospect. In the paper, the performance of IGCT and diode is introduced. With the function models of IGCT and diode, the switching property of IGCT used in large power voltage source inverter is investigated. And part of the simulation results are verified with experiment results. During the turn-on process of IGCT, over current through it will appears for the reverse recovery of the fly-wheel diode. During the turn-off process of IGCT, over voltage over it will appear for the existence of the stray inductance and the clamp inductance. The property of the snubber diode and the parameters of the circuit will also influence the turn-off process of the IGCT. In order to ensure the performance reliability, the parameters of the diode and the circuit should be carefully chosen.

Study on large power converter system for rolling mills

The performance of the large power converter system for rolling mills should meet the need of production technology and adapt to the requirement of the electric network. In the paper, the cycloconverter system is introduced. With the development of large power electronics, application of the large power converter using the self-controllable devices such as IGCT and IGBT becomes the trend. The three-level AC-DC-AC converter system with IGCTs whose rated power is 7.5MVA has been developed and put into use. And it is estimated that the AC-DC-AC converter system will be used in the drive for rolling mills in the near future.

Investigation on the 30MVA IGCT-based voltage source converter

The high power AC-DC-AC converters are widely used in various industrial fields. The integrated gate commutated thyristor (IGCT) is applied in medium and high voltage converter on a large scale due to its excellent characteristics. In this paper the investigation on the 30MVA IGCT-based high power voltage source converter is presented. The 30MVA converter is composed of two 15MVA IGCT-based five-level converters and the outputs of the two converters are in parallel connection. Each phase of the 15MVA five-level converter is composed of two IGCT-based three-level neutral point clamped (NPC) legs in an H-bridge form. The detailed topology design of the 30MVA large power converter is introduced in this paper. The modularization design is adopted in the converter to reduce its size and improve its power density. The power module of IGCT-based three-level NPC leg has been developed. The switching characteristics of IGCT are investigated and the influences of snubber circuit are simulated. The experiment of turn off process of IGCT is carried out. One type of carrier-based modified in-phase disposition (IPD) modulation scheme is researched and simulated.

The development of IGCT-based large capacity three-level dual-PWM converter

In media and high voltage large capacity converter systems the Integrated Gate Commutated Thyristor (IGCT) take the place of Gate Turn Off Thyristor (GTO) duo to its outstanding performance. And IGCT-based large capacity three-level converters are widely used in industrial motor-driving field. In this paper the development of a set of IGCT-based large capacity three-level dual-PWM converter is introduced. The converter includes PWM rectifier, DC capacitors, PWM inverter. The topology of the converter is given. The close-loop control strategy and SVPWM algorithm of PWM rectifier is presented in this paper. The control strategy and algorithm of the PWM inverter is also presented. The experiments were performed and the results show that the converter reaches the design requirement and has excellent performance.

A high-performance synchronous motor field-oriented control system

The paper introduces a damper flux-oriented control method of synchronous machines, and develops a mathematical model of a synchronous motor with damper flux-oriented control. It is proved through theoretical analysis and experiments that a damper flux-oriented drive system has the same steady performance as that achieved with airgap flux-oriented control; moreover the damper flux is not sensitive to the harmonics of the stator currents, and by using the feedback value, the dynamic performances of the drive system can be improved. A 2500 kW 12/6 Hz cycloconverter synchronous motor drive system with damper flux-oriented control has been manufactured and applied in rolling mills in China. The cycloconverter consists of three sets of antiparallel six-pulse bridge rectifiers without circulating current.<<ETX>>

Research on rectifier system in high power IGCT three-level PWM converters

The Integrated Gate Commutated Thyristor (IGCT) is mostly applied in medium and high voltage high power converter systems due to its outstanding performance. And IGCT-based high power three-level converters are widely used in motor-driving field. In this paper, based on the high power three-level IGCT back-to-back system, the rectifier system is analyzed. Four phase locking methods are proposed, and the last two methods are used for the case of unbalanced power grid. Improvements are made for the problems of midpoint voltage balance and harmonics in the traditional space vector PWM (SVPWM).

The simulation of three phase cycloconverter loaded by RL

This paper presents a digital simulation technique to study a three phase cycloconverter loaded by RL, which is proven to be more flexible. The output voltage, current and their harmonics can be computed easily by this technique. The mathematical models of this system are discussed in detail. Finally this paper gives some simulation results.<<ETX>>