Research On Interrupting Characteristics Of New Type Of Capacitance Buffering Hybrid DC Circuit Breaker

Reliable connection of new energy sources such as wind power,photovoltaic power generation base can be implemented through flexible dc power grid,which can maximize the new energy power consumption.For many countries,flexible dc power grid becomes the core content to boost energy transformation and important paths to deal with climate change.The key equipment for developing the flexible dc power grid is the dc circuit breaker.Developing reliable and practical medium and high voltage dc circuit breaker has already become the main technical bottlenecks to build flexible dc power grid.In various kinds of dc circuit breaker schemes,capacitance buffering hybrid dc circuit breaker has the characteristics of simple structure and convenient control.This paper,which is based on the basic topological structure of capacitance buffering hybrid dc circuit breaker,proposes a new type of operating principle.DC current interrupting experiment is designed,the experiment successfully verifies the new type of operating principle and proves the superiority of traditional interrupting without arc.But further analysis of the results shows that,current conversion speed di/dt during commutation transient process and IGBT voltage spike will affect the breaking reliability of new type of capacitance buffering hybrid DC circuit breaker.Influencing factors of interrupting reliability is analyzed through simulation by PSCAD/EMTDC software.Simulation results show that,uncontrollable parasitic capacitance and stray inductance will result in commutation speed di/dt up to several kA/us,and that IGBT voltage spikes exceeds system rated voltage.In addition,the buffer capacitor value determines the recovery voltage rise rate du/dt.The above factors affect the mechanical switch arc and safety work of IGBT.In the process of the partial pressure after the conversion,if dielectric insulation recovery speed of mechanical switch is slower than rising velocity du/dt of system recovery voltage,initial recovery voltage will all be undertake by IGBT and will be not conducive to reducing the on-state loss.Aiming at the problems and influencing factors of the breaking characteristics,an improvement measure is put forward.That is,RC circuit is added in parallel with IGBT,the inductance of converter branch should be reasonable designed at the same time.The simulation and experiment study shows that,the optimized scheme can be able to control current conversion speed di/dt and recovery voltage rising velocity du/dt in a safe range.In addition,IGBT voltage spike will be significantly reduced.Eventually,this paper carries out circuit analysis of conversion process and formula derivation,then gets the approximate expressions of current conversion speed di/dt,IGBT voltage spike and recovery voltage rising velocity du/dt.A common key parameter matching principle is formed,and the overall parameter design flow of the DC circuit breaker is given.Based on the above general parameter matching principle and design flow,taking Shenzhen 10kV/1kA flexible DC power distribution system demonstration project as an example,a 10 kV DC circuit breaker prototype is designed and successfully developed to meet engineering needs.Through to the research and optimization on interrupting characteristics of new type of capacitance buffering hybrid dc circuit breaker,the current interrupting environment has been greatly improved,interrupting reliability is ensured.Meanwhile,parameter matching method with a good generality is obtained by circuit analyzing.It provides a theoretical guidance for prototype parameters design of capacitance buffering hybrid dc circuit breaker applying for different dc system.