Electro-thermal simulation of current sharing in silicon and silicon carbide power modules under short circuit condition of types I and II

Highlights

• Current sharing

• Electro-thermal compact modelling

• Silicon and Silicon

• Carbide IGBT and MOSFET modules

• Short circuit of types I and II

Abstract

Current sharing during short circuit events of types I and II has been investigated by electro-thermal compact simulation of semiconductor devices paralleled in a 650 V power module. The response of silicon IGBTs has been compared to that of silicon carbide MOSFETs. The study of current unbalance due to symmetrical and asymmetrical interconnect topologies has been followed by isothermal and full electro-thermal simulation of the power modules. It has been shown that replacing in the simulation the active devices within the module by resistors leads to misleading results, because the current unbalance under short circuit conditions is mainly due to the difference in the gate-source/gate-emitter voltage among the individual paralleled devices. Finally, it has been demonstrated that in the investigated power modules, self-heating contributes to the mitigation of current unbalance.

Introduction

IGBT power modules have been developed to face the increasing demand for high-power conversion. Multiple IGBT devices are mounted within a module in parallel both to achieve higher current densities and to reduce losses. As switching speed and current densities get higher than those encountered in today's devices, proper current balancing among paralleled chips within a power module becomes a critical issue. Therefore, current balancing is an unavoidable challenge to be tackled to increase current density and for safe power switching in silicon and wide band gap devices. When it comes to the investigation of current balancing under large current switching, electro-thermal simulation is mandatory, since current sharing within the devices in a module is strongly affected by the local temperature and this dependency becomes even stronger at high current density levels.

Several investigations [1], [2], [3], [4] have been published in the past dealing with various switching conditions. Present paper focuses on the electro-thermal simulation of current sharing among paralleled chips for harsh switching modes, in particular under the short-circuit conditions of types I and II (SC I, SC II). All simulations have been carried by assuming five paralleled devices assembled in a representative power module. The components that have been considered in this investigation are a 650 V–300 A silicon IGBT power module [5] and a power module consisting of five paralleled 650 V–30 A silicon carbide MOSFETs [6]. Simulation tools and procedures are defined in Section 2. In Section 3, the effect of the module terminals and of the related parasitic inductances on current sharing is investigated by isothermal simulation of a symmetrical and of an asymmetrical topology, where the active devices have been replaced in the compact model by equivalent resistors. In Section 4, the parasitic inductances of the asymmetric module are extracted by electromagnetic simulation and the current sharing among the active devices is calculated by full electro-thermal circuit simulation.