Reliable Electric Power Supply Based On Large Capacity Power Electronic Technology

Higher power system reliability which the electricity providers are pursuing is also the objective requirement of the consumers. Power grid develops more and more large and complex. Especially the increasing proportion of industrial sensitive loads, as well as mi-crogrids contain a large number of distributed, power sources connected to the grid, etc., challenge the power system reliability.With the development of power electronics technology, the device capacity is growing and all aspects of the technology becomes more and more mature. Therefore power elec-tronic technology is more widely used in power systems. And it provides an effective tech-nical way to improve the power system reliability. The main content of this paper is the use of high-power electronics technology to improve power system reliability on power supply and power generation, including the following aspects:Firstly, a reliable power supply system based on energy storage and diesel generator is fully studied in this paper. The mathematical model and control strategy of the all parts of the system are analyzed. System operation principles, operation status transfer, transfer control strategy, and coordination control, etc., are studied. Simulation results show that the proposed system works very well in all working state and during the transfer process. So, the system can provide a reliable power supply to the industrial sensitive loads.Then, the medium and low voltage transfer switch system are study in this paper. Transfer switch is a very important part in the dual or multiple power supply system for large industrial sensitive loads. This paper presents a400V/1000kVA hybrid automatic transfer switch. Operation principle and switching control strategies are introduced and proved to be correct through field experiments. The prototype the paper developed greatly reduces the transfer time compared to the previous mechanical switch. So, it effectively improves the power supply reliability of the application site sensitive loads. This paper also studies the10kV static transfer switch with transformer load. The reason why transfer in-rush current occurred is analyzed. And a transfer strategy which can eliminate the inrush current is proposed. Simulation and experiments are carried out. And results proved the ef-fectiveness of the proposed transfer strategy. Inrush current is eliminated and transfer fail-ure is avoided. So, power supply reliability is improved on the lOkV distribution network level. Then, some power supply reliability issues in microgrids are studied in this paper. One is the grid-tied/grid-off transfer strategy of the energy storage and its grid interactive in-verter. A hysteresis current control based off grid transfer stategy is proposed to cut off the transfer time. So voltage sag duration is shortened during the transfer process. Simulation and experiments are carried out to proved the effectiveness of the proposed transfer strategy. Another issue is the fault characteristics of the inverter interfaced distributed generators and micro protection. A power variation based protection method is proposed. Simulation re-sults show the method can isolate the fault into the smallest area, which helps to improve the microgrid power supply reliability index.Finally, in order to improve power system dynamic reliability, a energy storage based VSC excitation system is studied. Linear model of the single machine infinite bus with energy storage based VSC excitation system is established in this paper. A phase com-pensation based active and reactive power injection controller is designed. Damping effects, advantages, and disadvantages of some damping measures are comparativelly analyzed. Simulation shows that the storage based VSC excitation can provide greater damping than traditional thyristor and VSC excitation without energy storage. And storage based VSC excitation can improve the angle stability under small and large disturbance. A test bench of VSC excitation without energy storage is established in the dynamic simulation laboratory, and preliminary validation experiments are carried out, which laid the foundation for the subsequent industrial prototype development.