| This dissertation is supported by the Ministry of Education under the project "Research on System Theory and Key Technology for Distributed Energy System" (No. 306004), it focus on the research of parallel inverter applied to Distributed Generation System.The Distributed Generation System (DGS), which is composed of various energy sources by parallel connection, is the one of way to dramatically develop renewable energy resource, improve the reliability and expand the capacity of power supply system. The power supply of Distributed Energy System can be made up of various energy sources which are converted to electric power to form microgrid. Its units disperse separately, and connect to AC mains in parallel. To small scale DGS, its power supply units are parallel inverter commonly. Many parallel connection solutions, especially the wireless parallel control technique, fit to the DGS with many dispersed inverters. A perfect DGS includes parallel inverter module, output line impedance, AC mains, and the load connected to AC mains. Among the parts above, the inverter is the key component, which is in charge of converting the distributed energy to electric power and forming microgrid with proper techniques such as inverting and current sharing.The system control strategy is demonstrated comprehensively, and the main circuit topology, the output characteristics and power control, the composing and tracking of inverter voltage are also researched as well. Besides modeling and simulating the parallel control strategy of inverter, a set of DSP controlled wireless parallel inverter is also designed. What's more, the instrument achieved satisfying experimental results. The main aspects of this dissertation are summarized as follows:1. Using the main circuit model of single inverter, the open-loop and closed-loop characteristics of this system are analyzed, and the double closed-loop voltage adjuster of inverter, which can be applied to practice, are designed in detail, Moreover the parameter design method and principle of output filter inductor in parallel inverter units are proposed as well.2. An adaptive pre-synchronization scheme is put forward to solve the starting phase error of the wireless parallel inverter system. The digital phase locked technology is adopted in this system;it can not only fix the phase and frequency of output voltage, but also enhance the system capability to anti-jamming effectively.3. According to the math model of droop parallel control, the power droop characteristics, the power decoupling control, the performance of output power, and so on have been analyzed and discussed. At the same time, in order to provide references for system design, it expounded the effects on system performance of each control variable in power control loop with bode diagrams.4. By analyzing the limitation of droop parallel theory, a parallel scheme of virtual impedance auto-revise is presented in this paper, which is based on inductor current feedback control. And the satisfied control effects of output active power, reactive power and harmonic power have been achieved by means of adjusting the equivalent output impedance of parallel units.5. Aiming at the frequency characteristic of output load for common wireless parallel system, the dynamic coefficient droop method of active power is introduced to eliminate the system steady error of output frequency. Furthermore, the simulation verifies the theory analysis successfully.6. With establishing and analyzing the simulation model of single wireless parallel inverter system by MATLAB, both dynamic and steady performances of the system, which controlled by the parallel scheme of virtual impedance auto-revise, have been improved.7. Developing the wireless parallel inverter prototype. The advanced DSP and the reasonable logical flow have been used to ensure the system functions. The experimental results show that the parallel effect is rather good in the system. |
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