Novel evaluation method of internal temperature in IGBT using gate voltage pattern diagnosis

Abstract

It is preferred to measure the power loss for estimating the internal temperature of IGBT in case of the fast high current switching with conducting current, leakage current, on-state voltage drop, and off-state voltage detection circuit[l][2]. The existing method to estimate the internal temperature of IGBT requires complex additional auxiliary circuit components. Furthermore, it has a limitation to protect IGBT when the thermal breakdown is occurred by hot spot phenomena at relatively low temperature around 50°C [3]. It proposes newly developed the estimation method to evaluate the internal temperature of IGBT through the diagnosis of the applied gate voltage pattern with the reference gate voltage waveform. The proposed method uses dominating switching parameters of IGBT that indicate g, gain value of P type BJT at PNP junction effect of IGBT, and Cgc, gate-collector junction capacitance of MOSFET and BJT structure at IGBT[3]. Based on the reference gate voltage waveform by initial operation, the value of g and Cgc is calculated at certain types of IGBT and the thermal variation of the dominating switching parameters are estimated with the thermal model of IGBT. Because the estimated thermal variation of the switching parameters can directly relate to the gate switching waveform of IGBT at the specific temperature, it is able to monitor the internal temperature of IGBT more simple and effective than the existing method. It is designed to generate pulsed current using flyback type of power modulator that IGBT supplies high de voltage at the secondary and makes series connected SI-thyristor which is fast turn-on switch in the secondary to be forced turn-off very fast in this paper. Thus, it demands high stability of IGBT switching with fast switching frequency. Apart from simple and effective estimation of the internal temperature, the proposed method is determined to protect the power supply from the switching fault with simple gate driver. Therefore, the proposed method would be applied to zero current switching and the other types of power modulator effectively.