| Energy conservation and environmental protection are currently the world's universal concern, and the construction of a resource-saving and environment-friendly society in China is currently the main tasks and goals. In China's power system, about one-fifth of the total installed capacity is used for driving fans, pumps and so on which need to speed the load, causing a serious waste of energy. High-voltage VVVF technology is one of the most effective manner of Motor energy saving. And with rapid development of power electronic devices and technology, VVVF technology is maturing. However, with inverter widely used in power system, it also produced a number of problems. In this paper, some related problems in operation of the diode neutral point clamped (NPC) three-level inverter were studied.In this paper, first the background and development of high-voltage inverter and the meaning of its application in power system are introduced, and the trend of its development was also talked simply. Then it introduced possible failures in the process of running. In chapter 2, the structure of the diode clamp three-level inverter is focused on, including all parts of the composition and their working principle. And the features of several other structures are also introduced in this paper. In chapter 3 the performances and principles of ZnO are also analyzed, and a selection including parameters is determined for restraining over-voltage of the inverter. Chapter 4 main focuses on the over-voltage problems which may occur during the running process, and make the simulation of various failures processes with simulation model. Several typical over-voltage process are studied, including the emergency shutdown of acceleration and deceleration process, the three-phase short-circuit process, the single-phase ground short-circuit process, the neutral point drift process, and so on. The detailed over-voltage process are analyzed, and a simple equivalent circuit is established, through which the energy distribution process and the simulation of over-voltage waveform are detailed analyzed. Using zinc oxide non-linear resistance (ZnO) restrains the over-voltage process, and the simulation proves the effectiveness of its protection role. Finally the role and significance of water-cooling system are analyzed, and also its superiority. The method of heat loss calculation is discussed and the principles of the water cooling are studied, including the materials and nature of radiator and the problem need to pay attention to on the design of water cooling.
|
PDF Full Text Request