| As a strategic choice for the development of China’s large power grid,DC transmission has a series of advantages compared with AC transmission,such as low transmission loss,high transmission capacity and good system stability.The high voltage DC circuit breaker is the vital equipment for establishing and developing HVDC and flexible DC transmission.The core component of DC circuit breaker is IGBT,so it is the basic job to recognize and cope with IGBT’s malfunction correctly.At present,the most commonly used condition monitoring parameter for fault detection is collector-emitter voltage.Since forward recovery occurs when the transfer branch IGBT is turned on,considering the accurately measured voltage waveform over the forward recovery period could be the guarantee for setting monitoring criterion aright.This paper focuses on the acquisition of the instantaneous voltage waveform of IGBT’s turn-on under the operating condition of transfer branch IGBT of hybrid DC circuit breaker.Using the combination of theoretical derivation and experimental fitting,a forward recovery behavior model suitable for the transfer branch IGBT is built.In this thesis,forward recovery process of IGBT is studied primarily.After analyzing and determining that the existing IGBT model cannot reflect the process,a construction idea of a behavioral model suitable for transfer branch IGBT of DC circuit breaker is proposed by formula derivation,in which a U-I curve graph corresponding to a cluster of known currents is obtained,and the voltage at that moment is determined by the intersection of the current waveform to be sought and the known current waveforms.The experiment of IGBT forward recovery characteristic with the trigger signal under lightning surge current is carried out.The current waveform is reconstructed by two-stage fitting,and the relationship between fitting coefficients of the U-I curve and the current waveform of each stage is analyzed sequentially,and then the U-I curves under all current waveforms are set up,thus the U-I curves of the known current group is completed.The validity of the model is verified through comparison between the results of simulation and experiment.It is illustrated that whether the model is universal by contrasting models with different driving voltages.Finally,a 500kV hybrid DC circuit breaker is taken as the research object,and the voltage waveform over the forward recovery term of the branch IGBT during the first conversion process is simulated.Specific guidance is proposed based on the implementation principle of the existing testing program. |
