Research On Three-level Inverter Control Technology And Short-circuit Current Limiting

Neutral-Point Clamped three-level inverter is a topology extensively used in the field of high-voltage high-power applications,but this circuit is complex,difficult to control,and become a hot research at home and abroad.NPC three-level inverter modulation technology and the mid-point voltage balance are two important issues,this paper has been studied in these two aspects,and analysis the method of short-circuit current limiting control.This paper first analyzes the working principle of NPC three-level inverter,establishes the inverter mathematical model,introduces the space vector modulation technology,and focuses on a simplified SVPWM algorithm based on 60 degree coordinate system.The algorithm can make the three level modulation equivalent to the two level modulation,so it is easy to understand and easy to implement.The neutral voltage fluctuation is an unavoidable problem in the operation of NPC type inverter.In this paper,the causes of neutral voltage fluctuation are analyzed,and the law of neutral voltage fluctuation under various load conditions is introduced.The neutral potential hysteresis control strategy is introduced and the controller design,simulation and experiment both demonstrate the effectiveness of this scheme.This paper also studies the current limiting control strategy of the three-phase symmetrical short-circuit fault on the load side of the NPC three-level inverter.The current loop can quickly limit the short-circuit current while ensuring a good current waveform,which is validated by simulation and experiment.However,there is a control delay in the digital control.This paper further analyzes the problem of instantaneous transient rise in the short circuit fault during the delay period,and proposes a method to quickly limit the transient current by using the DSP power interrupt without increasing hardware circuit,which can facilitate the transition to the current loop control.