Resesrch On The Key Technologies Of The Closed-Loop Active Current Source Gate Drive For High Power IGBTs

In order to deal with the energy crisis and environmental degradation,many countries around the world are vigorously developing emerging applications such as renewable energy generation technologies,new energy vehicles and high-voltage direct current transmission.These emerging applications promote the extensive use of high power converters.The reliability of high power converters is important for these applications and is heavily related to the key components,that is,the high power insulated gate bipolar transistors(IGBTs).The IGBT reliability is heavily related to the switching stresses and losses which are controlled by the gate drive.With the development of IGBT manufacturing technologies,the conventional gate drive(CGD)achieves poor performance of switching stress limitation.Considering the trade-off between switching stresses and switching losses,the CGD fails to meet the high requirements for the reliability of IGBTs.And the active gate drive methods have attracted much attention.This dissertation presents the research on an optimized active gate drive for high power IGBT modules.The switching stresses and losses during different IGBT switching transient stages are analyzed firstly to explore the optimized gate drive.Based on the analysis,a closed-loop active current source gate drive(ACSD)with fast feedback circuits is presented.The ACSD adopts current sources controlled by the gate drive signal to charge and discharge the IGBT gate,achieving high switching speed.Fast feedback circuits based on voltage controlled current source sample and process the di/dt and dv/dt signals,and then regulate the gate drive current during IGBT switching transients.Thus,the switching speed and switching stresses are controlled.The ACSD just controls the di/d/at the collector current rising and falling stages and the dv/d/at the collector voltage rising stage.The switching time,therefore,is little affected and the switching losses are significantly reduced compared to the CGD.The double pulse method is used to test the performance of the ACSD and CGD.The experimental results verify that the ACSD can effectively control the switching stresses with short switching time and low switching losses.Moreover,the ACSD can limit the switching stresses under various collector currents and achieves soft turn-off.A high speed short-circuit protection method is achieved by combining the ACSD feedback circuits with a fast short-circuit detection circuit based on the integration of the di/dt feedback signal.This method achieves fast and accurate short-circuit detection and can shut down the IGBT quickly.The protection time and peak short-circuit current are limited.The voltage stress is controlled due to soft turn-off.The IGBT collector current/voltage rising or falling time is short,typically between tens of nanoseconds and hundreds of nanoseconds,leading to high control bandwidth and stability requirements for the ACSD.The stability is influenced by the circuit parasitic inductances,IGBT module parasitic parameters and feedback parameters.And this dissertation presents accurate small signal models for the IGBT and ACSD to analyze the stability issues.The key parameter influences on the stability are studied and discussed to optimize the parameter design and improve the stability of the ACSD.There are extra crosstalk issues caused by the closed-loop active gate drives in the phase-leg configuration.The ACSD is taken as an example to establish a theoretical model for the crosstalk signal generation.The crosstalk issues are analyzed and a crosstalk suppression circuit for the ACSD is proposed to solve the reliability problem of closed-loop active gate drives in the phase-leg configuration.The switching stresses are also related to the load current and bus voltage.When the load current or bus voltage is low,the switching stresses are low too,and the IGBT switching speed can be properly increased to reduce the switching losses.To achieve switching loss optimization,this dissertation presents an adaptive ACSD whose feedback resistors can be intelligently adjusted when the load current or bus voltage changes.A 5kW Buck converter prototype is built to evaluate the performance of the adaptive ACSD.The experimental results verify that the adaptive ACSD can optimize the switching losses under different load conditions.The efficiency of the Buck converter with the adaptive ACSD is increased by about 0.6%over different output power ranges compared to that with CGD.The adaptive ACSD is suitable for converters with frequent load changing and inverters with periodically changing load current.