Research On The Energy Absorption And Topology Optimization Of HVDC Mechanical Circuit Breaker

Flexible DC transmission with the advantages of long transmission distance,low loss and large power is the efficient measure for energy to access the grid,and HVDC circuit breaker is one of the key equipments for building a reliable and flexible DC transmission grid.As the flexible DC transmission voltage level is continuously improved and developed,the fault current that the DC breaker needs to break in the event of a fault will also increase.After breaking the fault current,the arrester needs to absorb hundreds of megajoules of energy.This paper mainly studies the energy absorption of the arrester during breaking process of the DC circuit breaker and the optimized topology of the energy absorption.Firstly,the energy flow of the mechanical DC breaker during the breaking process is analyzed.It is concluded that the total energy that the arrester needs to absorb during the breaking process is the sum of the energy stored in the smoothing inductor and the energy provided by the DC voltage source.The simplified volt-ampere characteristic curve of the equivalent arrester is established,and the equivalent model of the arrester is combined with the breaking process of the DC breaker to obtain the relationship between the energy absorption of the arrester and the DC system.The simulation model is built and the result shows that: the energy absorption of the arrester decreases with the increase of the initial operating voltage coefficient of the arrester and the voltage ratio of the arrester,and with the increase of the the smoothing inductance and the current amplitude,the more energy is absorbed by the arrester.According to the analysis and simulation results,this paper proposes an optimized energy absorption topology that reduces the equivalent inductance.The structure of reducing the equivalent inductance optimization energy absorption topology is expounded,and the working principle is analyzed theoretically.The breaking simulation model is established.The theoretical analysis and simulation results show that the energy absorption resistance connected in parallel across the smoothing inductor absorbs part of energy in inductor,thereby reducing the inductive energy absorbed by the arrester;at the same time,by reducing the equivalent inductance during the line current drop,the time that line current drops to zero reduce the energy provided by the DC voltage source.The magnitude of the breaking current of the DC circuit breaker is also an important factor affecting the energy absorption of the arrester.Therefore,this paper proposes a topology for current-limiting optimized energy absorption.The topology connects the line inductance to the current limiting branch through the coupled reactor.The oscillating current through the low-side capacitor and the primary inductor of the coupled reactor will induces a current opposite to the fault current in the line inductance,thereby limiting current and reducing the energy absorption.The structure and breaking process of the current-limited optimized energy absorption topology are analyzed.The energy flow in the breaking process is theoretically analyzed,and the parameters of the current limiting topology are selected.The simulation model is built to verify the current-limiting optimization of the energy-absorbing topology and the effectiveness of reducing the energy absorption of the arrester.