Research On Multi-closed-loop Active Voltage Control Drive In IGBT Series

Insulated Gate Bipolar Transistor(IGBT)has the advantages of high voltage,high current,high switching frequency and simple control.IGBT has been widely used in medium and high voltage industrial occasions,especially in high voltage direct current transmission.Due to the continuous increase of DC bus voltage in the power grid,the voltage tolerance level of single IGBT cannot be satisfied,so IGBT series is used to improve the voltage tolerance.However,the voltage unbalance in IGBT series is very easy to occur between devices.At present,a variety of methods for controlling the voltage unbalance in IGBT series have been proposed domestic and overseas.In this paper,the problem of voltage unbalance in IGBT series is solved by studying the active voltage control technology.This paper focus on IGBT and control system modeling,the reasons of voltage balance in IGBT series,multi-closed loop control design,reference voltage waveform setting and loss optimization,self energy auxiliary power supply design and so on.First,the basic structure of IGBT is introduced,and the working principle and working characteristics of IGBT in various states are analyzed.The function fitting method of dynamic characteristic is given.On the basis of introducing Hefner model which is widely used in simulation software,this paper gives the specific steps and methods to establish IGBT model in simulation software,and gives a method to verify the accuracy of IGBT model.Next,on the basis of IGBT model,this paper analyzes the causes of voltage unbalance in IGBT series from the two parts of working principle and simulation analysis,and proposes a parallel resistance calculation method suitable for static voltage balance.The voltage unbalance under dynamic condition is studied emphatically as the research foundation of the subsequent control method design.Then,this paper introduces the principle of active voltage control,and the multi-loop control is added in this methd.Through the study of the small signal model of control system and IGBT,its transfer function is derived,And based on the bode plots of the transfer function,we can choose the control parameters,and use the stability and gain margin of bode plots to prove the necessity of the multi-loop control.At the same time,the working principle of reference voltage waveform in output characteristic is given.A design of optimized reference voltage waveform for IGBT dynamic characteristics function fitting is proposed to illustrate the importance of the optimization design from the loss of device.Combined with the establishment of model and design parameters,and it is verifiedthat multi-loop active voltage control can control the collector-emitter voltage following the reference voltage waveform better and complete voltage balance.The influence of optimized reference voltage waveform on device loss and control effect is studied by simulation.Finally,an IGBT drive module in series including multi-closed-loop control circuit,full analog reference voltage waveform generation circuit,drive protection circuit,fault processing circuit and self energy auxiliary power supply is built.The output waveform of the reference waveform generation circuit is given in the experimental results,and then the reliability of multi-closed-loop active voltage control system in single IGBT control is verified.Its voltage balance effect and loss optimization result are verified in IGBT series experiment.At the same time,the design scheme of the self energy dual flyback auxiliary power supply is given in detail,and it is verified that the auxiliary power supply can supply the IGBT driver module with stable output under the condition of high voltage and wide input range.