Wu Xiaojie

An improved neutral-point-potential balance control strategy for three-level PWM rectifier

Neutral point potential balance control is very important to three-level neutral-point-clamped (NPC) rectifiers. In this paper, the balance control strategy is studied with three-level space vector pulse width modulation (SVPWM) algorithm based on reference voltage decomposition. An improved neutral-point potential balance control strategy based on balance factor is proposed and the principle is analyzed. Simulation and experimental results verify the validity of the control strategy.

Control of electrical excited synchronous machine at low switching frequency

The operation of the PWM converter should be kept at low switching frequency so as to restrain the dynamic losses of the three-level converter and improve its output power. However, traditional control methods are no longer suitable for this condition with the resulting increasing output harmonic distortion and reduction of dynamic performance. To overcome the above problems, a novel complex matrix model of the electrically excited synchronous machine combining the complex vector and matrix was established in this paper. And then, a hybrid observer was proposed to identify the instantaneous fundamental component of the stator current. With the consideration of the delay introduced by the switching device and the time-discrete sampling, a novel current control system was designed based on the control theory. MATLAB simulation and DSP experimental results verify the effectiveness of the proposed control method.

A novel control scheme of 230kA DC power source using thyristor, Phase-shifting rectifier transformer and On-load tap changer

This 230 kA DC power source is composed of four set separated DC power in parallel operation. There are +3.75deg, -3.75deg, +11.25deg, -11.25deg phase shifting between each rectifier transformer and original source. Each set device mainly contains on-load tap changer, phase-shifting rectifier transformer and con-phase counter parallel rectifier. In this paper, a current control scheme is realized based on SIEMENS corp. product. According to the required function, the hardware is chose and described, and the software is designed and realized. The design control system is organized by current control level, logic control level and human level. The relation between these levels is determined. The system is validated by electrolytic aluminum plant. From the measured data, the current control precision can reach 0.1% in dynamic process. The rectifier efficiency is more than 97.5%. The whole control devices realized zero current changing on-load tap changer. This developed DC power source can utilize for electrochemical, electro winning, plasma torches etc