Research On The Key Techniques Of Digital Controlled Ups With Parallel Operation

With the demands of important electrical equipments for high quality power supply, UPS (Uninterruptible Power Supply) has been widely used. The developments of full-controlled power electronic devices, high performance DSP and advanced control technology promote UPS to develop toward green, digitizing, intelligentizing and parallel operation etc. The paralleled operation of UPS makes power supply system enlarge its capability expediently and realize redundancy, which enhances system reliability. Therefore, study on digital paralleled UPS is being taken more and more attention. This dissertation research deeply on Digital controlled UPS and Parallel Operation. Through theoretical analysis, software and hardware design, a large number of experiments, we developed a prototype successfully and summarize some useful theoretical results and practical experience.Base on the cooperative project"Digitized High Power UPS And Its Paralleled Control"which is created by South China University of Technology, School of Electronic and Information Engineering and Guangdong ChuangDian Electric Power Co., Ltd. What this dissertation researching on deeply include digital control for low power single-phase SPWM invertor, three-phase invertor which powering unbaland load, digital phase-lock-loop and the paralleled control for three-phase UPS, and so on, which generally includes as follows:1. Introduced the traditional SPWM invertor style single-phase UPS, and ananlysize the model from the perspective of average state space. A triansient output voltage RMS PI control strategy has been proposed. Experimental results for 10KVA single-phase UPS prototype verify validity and reliability of this control method.2. Analyze the mechanism of asymmetry three-phase output voltage, and deduce the negative sequence output voltage is the main reason for the output voltage asymmetry. In the dq coordinates, the positive and negative sequence voltage which decomposited from the fundamental component of output voltage has been controlled under the synchronous frame and the asymmetry of output voltage has been suppressed. The compensataor for harmonic component was also designed which suppress the distortation of output voltage. Simulation and prototype experimental results verify the effectiveness of this method3. Make a description on the three control strategy principles of UPS parallel operation which includes master-salve, distributed and non interconnection line mode, analysize the model, circulating current and its power characteristics of the three phase UPS parallel system, and then a parallel control scheme has been proposed. Two level phase-lock-loops is used in the UPS output voltage synchronuous control; and the current-sharing control is base on the comparision between each UPS's output current RMS in the parallel system to regualate its ouput voltage RMS. Finally, high-power UPS 30KVA prototype experiments were carried out to verify the feasibility and effectiveness of parallel control method.