Tong Chaonan

The efficiency analysis for three-level grid-connected photovoltaic inverters

The grid-connected photovoltaic (PV) systems are an important part of renewable energy sources and their effect is getting more and more extensive. To improve the efficiency, small volume, and low prices of the PV systems, many kinds of new inverter topologies have been proposed to avoid using a grid isolation transformer, and the traditional three-level neutral-point-clamped (NPC) topology structure and T topology structure are presented and in-depth analyzed in this paper. Relative to conventional NPC topology, the T topology with fewer switching devices than before when producing the same number of output levels, which simplifies circuit and saves costs. Efficiency analysis results show that T topology have high efficiency, lower leakage current and EMI.

A new interleaved three-level Boost converter and neutral-point potential balancing

Due to a voltage imbalance of the divided capacitors in the output side of three-level Boost photovoltaic grid-connected inverter, a new topology of interleaved three-level Boost converters is presented. The proposed topology can balance the voltage of the divided capacitors through adjusting the duty cycle of the power switches. The operational principle is detailed and the work modes are analyzed. The neutral point drift problem of the inverter has been solved within the first level three-level Boost converter. The prototype has been verified both by a PSPICE simulation and a new topology inverter platform. Simulation and experimental results show that the current ripple of the converter equals to 1/8 of the traditional Boost converter current ripple, and the converter can well solve the neutral point drift problem of the inverter with voltage divided capacitors to obtain good dynamic and steady-state performance.

Energy consumption optimization of air conditioning based on building monitoring system

This paper proposes building monitoring system and optimization scheme about energy consumption of air conditioning. At first, building monitoring system is introduced in detail, which consists of node group, concentrator and upper computer. Large amounts of data including environmental parameters and air conditioning energy consumption data are collected, transmitted, stored, and displayed through the proposed system in real time. According to it, optimal performance index of air conditioning is defined. Optimization scheme of air conditioning is put forward based on this index, under which the use pattern of air conditioning is adjusted by the system. The reduction of air conditioning energy consumption is demonstrated its effectiveness through a case study.

The coupling model and robust controller design of vertical system in rolling mills

The mathematical model of electromechanical-hydraulic coupling system in rolling mills, which includes the servo hydraulic system, the mill housing system and rolls system, is established with the consideration of influence on dynamic behavior by nonlinearity and parameter uncertainties. Then the closed-loop gauge control system in frequency form is obtained. The robust controller design is introduced by using quantitative feedback theory, based on several system performance indexes. The influence on system stability by the performance of hydraulic automatic gauge control system is discussed, the reference signal tracking behavior and control performance comparison with PI controller is made via simulation case study, to show the advantage of the proposed control algorithm.

Stability analysis of nonlinear self-excited vibration in cold rolling main drive system

A nonlinear self-excited vibration model of main drive system in cold rolling is established. The mechanism of torsional vibration in main drive system stability is discussed within multiple scale method as well as Hopf bifurcation theorem. Then, the periodic solutions and condition of Hopf bifurcation are derived and the influence by subcritical/supercritical bifurcation is analyzed. Based on the simulation experiments with actual industrial data, the previous theoretical analysis and nonlinear model have been testified.

The Computer System of High Precision Reversible Cold Rolling Mill

Abstract The high precision Four-high reversible cold rolling mill was successfully completed in Shanghai in 1989, all the work of the project, including design, manufacture, installing and test, was done with the cooperation of Shanghai Metallurgic Equipment General Factory and the University of Science and Technology Beijing. The cold rolling mill is used to produce high precise cold strip, so it is necessary that the function and precision of control system are powerful. In this paper, the function of computer control system is introduced, the software function is also described. The ideas of the control units that affects thickness precision seriously are introduced emphatically, the control result is given at last.