Reverse Conducting IGBT Desaturation Control Applied To Four-quadrant Converter

With the rapid development of rail transit,four-quadrant converters,which are an important part of traction drive systems,place higher demands on the power density and reliability of switching devices.The silicon-based IGBT has been developed as a mainstream device in a four-quadrant converter for more than three decades,and its performance has approached the theoretical limit.At present,there are two main methods for improving the performance of IGBT:one is to use a wide band gap new material such as gallium nitride or silicon nitride.The second is to improve and integrate the traditional silicon-based IGBT in structure and process to produce functional integrated IGBT.Although the former performs well in device performance,there are still many problems in materials and processes,and the cost is higher than that of silicon devices.Currently,it is only partially used in small and medium power applications.IGBT reverse conducting by modifying the configuration of IGBT chip on the chip functionality IGBT additional freewheeling diode.Increased overall power density of the IGBT module,reduced device cost and increased stability.The paper studies the reverse-conducting IGBT desaturation control method applied to four-quadrant converters,and proposes an improved current threshold desaturation control scheme based on transient current control.This scheme improves the continuity of the overall control system and solves the problem.In the current threshold de-saturation control method,the forced-segment of the pulse causes a problem that the upper and lower arms are straight-through in practical applications.Secondly,considering the factors affecting the value of the current threshold,it is proposed to determine the optimal current threshold by combining the actual measurement with the calculation method.It avoids the problem that the current threshold is too small,causing the system to issue an erroneous desaturation pulse,or the current threshold is too large,so that the advantage of the reverse conduction IGBT type under the desaturation control cannot be fully utilized.Then the simulation model is built in MATLAB/Simulink software to verify the feasibility of the improved current threshold desaturation control scheme based on transient current control.Through the simulation waveform and device manual,combined with the current threshold loss calculation method proposed in the paper,the loss calculation and comparative analysis of the four-quadrant converter using reverse-conductivity IGBT and the four-quadrant converter using ordinary IGBT are carried out.The conventional PWM control procedure is then improved and a DSP program adapted to the transient current control of the desaturation control is programmed.At the same time,the improved pulse delay timing control logic is proposed to solve the problem that the delay logic is widened when the delay time is longer than the pulse width,and the CPLD program of desaturation control is written in Verilog HDL language.Finally,a small power platform was built,and the correctness and feasibility of the proposed scheme were proved by experiments.