A Non-segmented PSpice Model of SiC MOSFETs Hong Li, Xingran Zhao, Ruixiang Hao
Kai Sun Department of Electrical Engineering Tsinghua University Beijing, China
[email protected]
School of Electrical Engineering Beijing Jiaotong University Beijing, China
[email protected] Abstract—To solve the simulation convergence problem of Silicon Carbide metal-oxide semiconductor field effect transistor (SiC MOSFET) models, this paper proposes a non-segmented model for SiC MOSFETs, which uses non-segmented, smooth continuous equations to describe the static and dynamic characteristics of SiC MOSFET. Further, the static characteristic of SiC MOSFET obtained by the non-segmented model is verified by comparing the simulation curves with the static curves provided in datasheet, and the dynamic characteristic is verified by comparing the simulation rise time and fall time of voltage with the datasheet based on the double pulse simulation circuit. The accuracy and good convergence of non-segmented model provide a good way to research the power converters with SiC MOSFETs by simulation way. Keywords—non-segmented model; SiC MOSFET; PSpice model; simulation convergence
I. INTRODUCTION At present, power semiconductor devices are mostly based on the mature Si technology, but Si exhibits some important limitations in blocking voltage capability, operation temperature, and switching frequency. These irreversible physical limits greatly reduce the efficiency of power converters and require complex and expensive cooling systems and expensive passive components [1]. Consequently, a new generation of power devices based on wide band-gap (WBG) semiconductor materials is expected for power converters. Compared to the silicon transistors, WBG field-effect transistors are characterized by low conduction losses, low switching losses, high blocking voltage, high switching frequency, and high junction temperature tolerance [2], [3]. For power electronics circuit designers, SiC devices are more attractive than GaN due to the mature manufacturing process and related technology. Currently, there are many commercial SiC devices, including SiC MOSFET, SiC JFET, SiC diode, SiC IGBT, etc. [4]. With the marketization of 1700V voltage rating, SiC MOSFET has been more and more favored by power electronics industry and researchers [5]. In order to better exert the performance advantage of SiC MOSFET and optimize the design process of power electronics converters, it is necessary to establish an accurate simulation model of SiC MOSFET [6]. Up to now, the study of SiC MOSFET simulation model is becoming more and more concerned, among them the models based on PSpice are mostly divided into three categories:
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physics-based model, semi-physics model and behavioral model [7]. The physics-based model is based on the semiconductor physics, which is very accurate, but it is not suitable for power electronics circuit simulation due to the complexity and long simulation time [8], [9]. The semi-physics model is partly based on semiconductor physics, and some equations and sub-circuits are included in the model. The semiphysics models established in [10] and [11] are based on the traditional Si MOSFET structure, combined with peripheral sub-circuits, which is simpler than physics-based model. However, the traditional Si MOSFET model in PSpice has many parameters, and these parameters are coupled with each other, so it is difficult to get accurate parameters to fit the characteristic curves of SiC MOSFET. Behavioral model is based on behavioral equations of SiC MOSFET, and the information about the internal structure and physical parameters of SiC MOSFET is not necessary, so it’s very suitable for power electronics circuit simulation. The universal method is using segmented equations to describe the static characteristics of SiC MOSFET, and the behavioral model established in [12] just uses three equations, which represents the cutoff region, linear region and saturation region, respectively. But, the segmented equations are not continuously differentiable, which will make the behavioral model suffers from the simulation convergence problem [13]. In order to improve the simulation convergence, this paper proposes a new behavioral model with non-segmented, smooth continuous equations [14]. This paper chooses C2M0045170D (1700V/72A) from Cree as modeling object [15]. The modeling and parameter extraction process of the proposed non-segmented SiC MOSFET model are introduced in detail, furthermore, the accuracy of the proposed non-segmented model is verified by PSpice simulation. II. THE ESTABLISHMENT OF NON-SEGMENTED SIC MOSFET MODEL The non-segmented model of SiC MOSFET is shown in Fig. 1. This model includes voltage-dependent current source Ids, gate-drain voltage-dependent capacitance Cgd, gate-source constant capacitance Cgs, internal gate resistance Rg and body diode Db.
where p(Vgs) and q(Vgs) are equations with gate-source voltage Vgs as the variable. The specific equations are different on different types of SiC MOSFET.
drain Id Cgd
gate
Rg
Ids Cgs
+ Vds
-
Then the equation of voltage-dependent current source Ids can be obtained as follows: Db
I ds = I ds1 ⋅ I ds 2 = k ⋅ {1 + tanh[a ⋅ (Vgs + m) + b ⋅ (Vgs + n) 2 ]} . ⋅
source
A. Voltage-dependent Current Source Ids The voltage-dependent current source Ids describes the static I-V characteristic of SiC MOSFET, which includes the transfer characteristic equation and output characteristic equation. The transfer characteristic equation takes the gatesource voltage Vgs as the variable, and the output characteristic equation takes the drain-source voltage Vds as the variable. The equation of the transfer characteristic is based on the Angelov model, which uses the hyperbolic tangent function so that the first derivative of the gate-source voltage Vgs has a similar shape to the transconductance curve, and the hyperbolic tangent function is high order continuous differentiable, which is helpful to simulation convergence [16], [17]. The specific equation is shown in (1), (1)
where k1, a, b, m and n are related parameters of the transfer characteristic. The output characteristic equation is shown in (2),
I ds 2 = p ⋅
Vds , 1 + q ⋅ Vds
(2)
where p and q are related parameters of the output characteristic. According to the output characteristic curves provided in the datasheet, it can be found that the output characteristic curves are different under different gate-source voltage Vgs, so the gate-source voltage should also be taken into account in the output characteristic equation, then the output characteristic equation can be expressed in (3),
I ds 2 = p(Vgs ) ⋅
Vds , 1 + q (Vgs ) ⋅ Vds
p(Vgs ) ⋅ Vds 1 + q(Vgs ) ⋅ Vds
The related parameters can be obtained by using (4) to fit the transfer characteristic and output characteristic simultaneously and the detailed fitting process will be described in section III.
Fig. 1. The non-segmented model of SiC MOSFET.
I ds1 = k ⋅ {1 + tanh[a ⋅ (Vgs + m) + b ⋅ (Vgs + n) 2 ]} ,
(4)
(3)
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B. Gate-drain Voltage-dependent Capacitance Cgd According to the capacitance-voltage (C-V) characteristic curves provided in the datasheet, gate-drain capacitance Cgd has strong non-linearity, so constant linear capacitance can’t accurately reflect the dynamic characteristic of SiC MOSFET. At present, the more commonly used model for Cgd is based on the Siemens improved “switching model”, as shown in Fig. 2 [11]. When gate-drain voltage Vgd>0, the value of Cgd remain constant; when Vgd
