Modeling And Simulation Of Novel Power Electronics HVDC Circuit Breaker

With the increasing demand for energy all over the world, oil, coal, natural gas and other traditional fossil fuels will be eventually consumed. For this reason, the development of wind, solar and other new energy sources will surely be the future development trend. However, the current development of new energy sources due to its incorporated large grid instability becomes bottleneck for development. To break through the bottleneck, the application of HVDC technology will be an effective solution because the effect on the stability and reliability of the power grid is relatively small when new energy is converted into direct current for convergence and network transmission. HVDC technology has the advantages of long-distance transmission interconnection between different grids, and optimizing the entire transmission network and so on. With the development of power electronics technology, HVDC technology is getting lower cost and better performance.As can be seen from the DC transmission, development of HVDC applicable breaker is critical because HVDC breaker has the ability to timely isolate faulty equipment, cables, branch, or the power unit, which is essential for maintaining safe and stable operation.However, compared with the AC power system, the DC system fault protection system failure protection is facing more severe challenges, mainly in the following points:(1) In the HVDC transmission system, there is no zero-crossing point in the short circuit voltage and current waves, which means that the fault current needed to be cut off is large, putting forward higher demands for these devices. The release of the remaining energy in the circuit is a very critical and urgent problem.(2) Because of the high HVDC power, if there is short circuit, the resistance of the circuit decrease to minimum value suddenly, thus the short-circuit current rises rapidly. The DC switch must be turned off before reaching the maximum fault current value (within several milliseconds). Thus the corresponding time of a mechanical breaker response time is too long (dozens of milliseconds), making it difficult to meet the protection requirements.With multiterminal HVDC technology and networking, in order to remain safe and reliable transmission, some fast HVDC circuit breakers are needed to develop. Because the short-circuit current can be effectively controlled and isolated within an acceptable peak range only if the fault is cut rapidly.In order to solve the problem of DC transmission Protection, based on the previous several HVDC circuit breakers topologies, some power electronics non-isolated high voltage DC breakers are developed. These circuit breakers have the characteristics of fast fault-clearing, low control cost and low loss. In this paper, high-voltage simulation analysis was carried out. By adopting the same control method, simulation for low-voltage circuit breakers and associated low voltage verified experiments are also conducted. Based on analysis of the experimental and simulation results, the superiority of these new proposed pure power electronics topology DC circuit breaker functions is verified. Superiority mainly are the integration of DC circuit breaker functions and DC transformer, and the ability of fast fault-clearing in a few milliseconds, which has very important significance for the stable and reliable operation of DC power transmission.This paper presents a new auxiliary control algorithm in HVDC circuit breaker to ensure quick and efficient removal of short-circuit failure. A simple control mode can achieve switch between boost and buck mode at the same power flow direction, and can also implement a circuit breaker function. This paper also implements six kinds of simpler HVDC circuit breakers based on pure semiconductor devices, which are more suitable for HVDC transmission system. Summary of main achievements are as follows:(1) A new improved control algorithm was proposed which can ensure that the system sudden short-circuit fault quickly be removed;(2) One HVDC breaker topology is proposed. And its working efficiency was analyzed. Compared with the existing topologies the proposed topologies reduced power consumption, cost and control difficulty. At the same power flow direction it can achieve switch between boost and buck mode, which provides a good platform for flexible and reliable DC power supply being more suitable for HVDC transmission systems;(3) The simulation of the proposed HVDC breaker topology in discontinuous inductor current state was carried out and the corresponding low-voltage high-voltage experiments were carried;(4) Based on the classical DC converters five additional power electronics HVDC circuit breakers topologies were proposed, which used one switch group, reducing the number of power switches, power consumption and equipment cost.