Self-Sustained Turn-Off Oscillation of SiC MOSFETs: Origin, Instability Analysis, and Prevention

Abstract

This paper presents a comprehensive investigation on the self-sustained oscillation of silicon carbide (SiC) MOSFETs. At first, based on the double pulse switching test, it is identified that the self-sustained oscillation of SiC MOSFETs can be triggered by two distinct test conditions. To investigate the oscillatory criteria of the two types of self-sustained oscillation, a small-signal ac model is introduced to obtain the transfer function of the oscillatory system. The instability of the oscillation is thereby determined by the two conjugate pole pairs of the transfer function. By analyzing the damping ratios of the two pole pairs, the parametric sensitivity of various circuit and device’s parameters on the two types of self-sustained oscillation are obtained. The analyses reveal the oscillatory criteria of the self-sustained oscillation for SiC MOSFETs. Based on the oscillatory criteria, necessary methods are proposed to prevent the oscillation. The proposed oscillation suppression methods are validated by the experiment at the end of the paper.

Self-Sustained Turn-OFF Oscillation of Cascode GaN HEMTs: Occurrence Mechanism, Instability Analysis, and Oscillation Suppression

“…This phenomenon contradicts the conventional knowledge presented in [14]- [17], [23]. In the previous studies, the gate resistance is widely acknowledged to have a very strong damping effect on the self-sustained switching oscillation of GaN EHEMTs [17], SiC MOSFET [14], [15], [23] and SiC JFET [16]. The self-sustained oscillation can be suppressed when few ohms of gate resistance is utilized [15], [17].…”

“…In the previous studies, the gate resistance is widely acknowledged to have a very strong damping effect on the self-sustained switching oscillation of GaN EHEMTs [17], SiC MOSFET [14], [15], [23] and SiC JFET [16]. The self-sustained oscillation can be suppressed when few ohms of gate resistance is utilized [15], [17]. In this case, since the self-sustained switching oscillation of cascode GaN HEMTs becomes more unstable with the increase of R GE , the oscillation can not be suppressed by increasing the gate resistance.…”

“…Since the freewheeling diode D 2 forward conducts during the turn-off transient, its junction capacitance C D2 is linearized at 0V. Following the approach presented in [14], [15], the G m1 and G m2 are linearized at the threshold voltages of DHEMT and LV MOSFET, respectively. At the dc operating point, the device parameters are extracted base on the data provided by the device manufacturer.…”

“…Recently, many studies [14]- [18] show that the selfsustained switching oscillation of the wide bandgap power devices is determined by the instability of resonant circuit. When the circuit is unstable, self-sustained oscillation can be excited in the SiC MOSFETs [14], [15], SiC JFETs [16] and GaN EHEMTs [17], [18] based half-bridge circuits during the switching transient. With an underdamped LC tank in the gate loop of the GaN DHEMT, the GaN cascode HEMTs based half-bridge circuit can also be unstable and excite the selfsustained oscillation [19].…”

Characterization Circuit, Gate Driver and Fixture for Wide-Bandgap Power Semiconductor Device Testing

“…SiC MOSFETs offer the ability to work at higher voltage levels and frequency, but this can introduce unwanted side effects, such as the self-sustained oscillations, which might unintentionally turn on the gate driver. The authors in [14] experimentally investigate this phenomenon using a DPT-based test bed. This paper experimentally validates the importance of minimizing the gate and power loop parasitic inductance, to suppress the oscillations, but without hardware description or design.…”