The static var generator（SVG）consisted by IGBT has such advantages as high switching frequency and flexible controletc. However

the transient characteristic of IGBT is easily affected by its transient characteristic during operation of IGBT and the output voltage distortion is caused. In view of above problem

an electric-thermal coupled model about IGBT junction temperature and the mathematical relationship between switching delay time and junction temperature is established and the influence of switching delay time on the output voltage harmonics of SVG is analyzed. The rule of junction temperature variation of SVG in the voltage sag of grid is studied by the time domain simulation method and the influence of above situation on the output voltage harmonic of SVG is analyzed further. It is shown by the simulation result that with the rise of the junction temperature of IGBT

its opening and closing delay time will also be increased. In case of high IGBT temperature

the variation of its transient switching characteristic will lead to distortion of voltage waveform and

at this time

the transient switching characteristic cannot be neglected.In case of considering the transient characteristic of IGBT

the output voltage of SVG will contain DC component

the total harmonic distortion rate and high order harmonic contents will increase.