Research On Distributed Control And Structure Of The Power Converters

As one of the most widely used technologies for 21st century, power electronics gets a rapid progress along with its stepped-up role in the national economy. Reliability and systematic performance requirement are thus demanded more and more. In this dissertation, the topology-related distributed control within the power converter is researched. This work provides a new way to construct the converter and realize the control function, which is valuable for realization of new converter, simplifying the converters' structure and enhancing the system reliability. It can be well applied to the complex power electronics system.In the first chapter, the conventional centralized control method in power converters has been summarized and classified for the purpose of contrast. In the same chapter, the research background of this work is introduced, including the more and more wide applications of digital control technology in the power electronics and the rapid development of the power electronics integration technology. Based on the two aspects, the conclusion can be drawn that the distributed converter structure has a promising prospect.In the second chapter, the basic concept and the characteristics of the distributed converter structure have been clarified. According to the view of the bionics, the distributed power electronics system and the human body system have the same characteristics of hierarchical architecture and autonomous decentralized control. Also the two systems have the similar advantages such as simplified system structure, enhanced reliability, convenient implemention of fault-tolerant technology, convenient modularization and online maintenance. Based on the characteristics of the distributed structure power electronics system, the general software architecture is proposed and two typical hardware structures are illustrated too. In chapter two, the power integration module named power electronics cell has been proposed which can be applied in the distributed converter structure. There control structures of the distributed converter are also proposed. The laboratory prototype of power electronics cell has been realized by using discrete components, which provides the hardware basis for the further study.In the third chapter, as a typical distributed converter structure a single phase full-bridge inverter with dual-loop feedback control, which is composed of two power electronics cells, has been studied. Four inverter control structures including the synchronization mode, hierarchical mode, master-slave mode and fully decentralized autonomous mode are presented by dividing the control loop in different ways. Basedon the small-signal averaging model, the characteristics of the new structures are discussed and the effects of the parameter dispersivity, the multi-rate sampling, the communication, and the synchronization error of reference and carrier signals in the new structures are analyzed. It can be concluded that for the studied inverter, only the dispersivity of the voltage feedback coefficient in the synchronization mode affects the output greatly and other parameters dispersivity has little effects on the output performance. At the same time, the output waveform will be distorted because of the different startup time of the two cells in the synchronization mode. Compared with other three modes, the synchronization mode has more drawbacks. Conclusion is also made that the effects of the other nonideal factors can be eliminated by well-designed system and control loop. Because of its special structure and characteristics, the proposed fully decentralized autonomous mode has been discussed in detail. The simulation and experimental results included in the dissertation verified the theoretical analysis. The research on distributed inverter structure not only provides the new way to form new type inverters, but also provides the guideline for the other types of distributed converter structures.In the fourth chapter, the distributed multilevel converter structures have been researched. Based on the idea of forming multilevel converter topologies from the basic cells, the division mode of the multilevel converter topologies has been further investigated. Three kinds of division modes have been proposed according to the topologies' features. The advanced basic cells proposed in this paper are more suitable for the multilevel converters because it can be applied to most multilevel converter topologies and at the same time, two complementary switches are included in the same cell. The distributed five-level inverter prototypes for generalized topology and cascaded topology have been built. The prototypes show the distributed control within the complex converter has many advantages such as the simple structure, the shortened interconnection wires and the enhanced reliability. The theoretical analysis shows that the lower-order harmonic contents increase if there is a synchronization error among the cells, but the synchronization method proposed can obtain high accuracy and can avoid its side effects on output performance. So the distributed multilevel converter structures, which have many advantages, can achieve the same output performances as the conventional centralized ones. The research of distributed multilevel converters is valuable for applying multilevel technologies into industry more widely.In the fifth chapter, the fault-tolerant technology is researched. In the multilevelconverters, the mass components and complex structure lead to low reliability, so the fault-tolerant technology is important. By analyzing the typical multilevel topologies and the existing fault-tolerant method, we find a principle of the fault-tolerant technologies, which is contained in the distributed multilevel converters constructed by the advanced basic cells. The principle is that in the fault-tolerant methods, the two switches in the same cell should be dealt with simultaneously. So the realization of the fault-tolerance in multilevel converters gets the benefits from the distributed control. The quick detection and protection can be obtained in the damaged cell and that prevents the whole system breakdown. The concept of the control signal reconfiguration has been proposed to deal with the fault situations in the multilevel converters, which have the switching states redundancy, such as the flying-capacitor topology, cascaded topology and generalized topology. The fault-tolerant method for carrier-modulated cascaded five-level converter has been proposed. With the proposed method, when the fault occurs in the three-phase multilevel inverters, the normal line-to-line voltage can be achieved. At the same time, the structure of the topology is identical to the normal one and the voltage stress and current stress of the components are not changed. The principle discovered in the dissertation gives the guide for systematic researching on fault-tolerant technology and designing new fault-tolerant methods. And the proposed fault-tolerant method has many advantages and can be easily implemented in the multilevel inverters.Summaries are given in the last chapter, and the consequent research anticipation included.