| HVDC breaker is one of the key equipment to ensure safty and stablility of DC power grid.The technology situation and research status of mechanical HVDC breaker,full-solid HVDC breaker and hybrid HVDC breaker at home and abroad are detailed introduced.It is comparatively analyzed that hybrid HVDC breaker combines the advantages of mechanical switches and power electronics.It also owes fast action time,low on-state loss,high work stability which has important research significance.A kind of hybrid HVDC breaker topology which is based on full-controlled power electronics is put forward.The topology includes current-limiting inductance,main flow branch,main breaking branch,absorbing branch and AC breaker.This topology is designed with symmetrical structure which can not only make current flow in two ways but also save numbers of device and cost of equipment.The main flow branch is made of mechanical switch and IGBTs in series,which has advantages of strong flowing capacity and low onstate loss.Short circuit breaking principle and sequential action of DC breaker are analyzed.The characteristic parameters of short circuit current is deduced and put forward the parameter design principle of current limiting inductance,main breaking branch and surge arresters.The balancing techniques of series or parallel connected IGBTs included in the main breaking branch ard studied.The reasons why voltage and current of IGBTs are unbalanced are analyzed.Based on the characteristics of the low frequency switching state of main breaking branch,snubber circuit of RCD is raised.For turn-off time and capacitance of RCD snubber circuit are contradictory,an improved RCD snubber circuit is proposed.For the question that current of IGBTs in parallel is unbalanced gate resistance compensation method is presented.In the software simulation models are built to verify the feasibility of the measures.The equivalent model of two-terminal HVDC transmission system with hybrid HVDC breaker is built.The influence that different parameters of current limiting inductance and surge arresters can make to the DC breaker is analyzed.The action process and current transferring process of DC breaker on short circuit condition are simulated to verify previous theory.In the laboratory,a low power DC breaker prototype is built and experimented in the condition of low voltage and low current to verify the current transferring and energy absorption principle.Simulation and experimental results show that the proposed hybrid HVDC breaker can not only effectively remove the short circuit fault,but also reduce the number of devices,save costs and reduce the device size. |
