Study of the Switching Performance and EMI Signature ... - IEEE Xplore

Study of the Switching Performance and EMI Signature of SiC MOSFETs under the Influence of Parasitic Inductance in an Automotive DC-DC Converter Student Member, IEEE,

Di Han,

Bulent Sarlioglu,

Senior Member, IEEE

Wisconsin Electric Machines and Power Electronics Consortium (WEMPEC) University of Wisconsin-Madison Madison, WI 53706 USA sarlioglu@ wisc.edu

Abstract-With

low

loss,

fast

switching

speed,

and

.-----------,

hi gh

I I

temperature capabilities, silicon carbide (SiC) based devices are power converters in terms of efficiency increase and size reduction. Nevertheless, as a result of

Bidirectional

beneficial to the automotive

: L-":::=; :':::' -;":"'':':::'-l ':'

fast switching transitions and low on-state resistance of SiC devices, they are prone to overshoots and oscillations on switching waveforms, with the presence of parasitic inductances

I I I I I L __________ I

in the circuit. The overshoots and oscillations further contribute to increased EMI emissions. This paper aims at studying the influence of parasitic inductances on switching performance of SiC

MOSFETs

and

corresponding automotive DC-DC converters.

EMI

signatures

in

Engine

Transmission

Energy Management

Fig. I. Schematic of powertrain in HEV

Index terms-bidirectional DC-DC converter; EMI; hybrid! electric vehicle; parasitic inductance, silicon-carbide.

I.

DC-DC

I

As a result, the EMI emission of the converter also gets worsen [12]. Hence, the influence of parasitic inductances on SiC device performance is significant. In the literature, many

INTRODUCTION

efforts are spent on studying the parasitic influence on

It is widely acknowledged that silicon carbide (SiC) based devices outperform their silicon (Si) counterpart in terms of

conventional

Si

MOSFETs

[13-15].

However,

limited

number of papers can be found for the SiC devices in terms of

lower on-state resistance, faster switching speed, and lower

parasitic inductance influence [16]-[19]. In addition, most of

thermal conductance [1]. The fast switching capability of SiC

them mainly focus on the impact on converter loss. No one

devices

ever looks at the parasitic inductances from EMI emission

are

advantageous and

offers

since the

it

guarantees

freedom

to

the

low

switching

loss

increase

the

point of view. Hence, this paper aims to analyze the effect of

switching

frequency of power converters. However,

the

the parasitic inductance to the switching performance and

penalties that come with this high switching dv/dt and di/dt

EMI generation of SiC MOSFETs using an automotive DC­

are the induced overshoots and ringing on parasitic elements,

DC energy management converter as a study case.

as well as the resulted EMI emissions. Hence, this paper tries to analyze the switching performance of SiC MOSFETs and quantify the potential EMI emissions under the influence of parasitic inductances.

II.

SIC MOSFET AUTOMOTIVE DC-DC CONVERTER

The converter under study is the DC-DC converter that

Nowadays, the SiC technology has reached the level of

interfaces the battery at a lower voltage with the high voltage

maturity that a large number of SiC-based power switching

DC bus in a hybrid electric vehicle, as shown in the dashed

devices

are

commercially

available

from

various

red box in Fig. 1. This DC-DC converter is a high-power

manufactures. By replacing Si devices with comparable SiC

bidirectional converter and its typical topology is shown in

ones, dramatic improvements in the performance of power

Fig. 2. It is not mandatory to have a DC-DC converter in all

electronics system have been reported for a wide variety of

hybrid

applications [3]-[5]. When SiC devices are applied to power

converter

converters in hybrid/electric vehicles (HEV), the advantages

architecture of the power conversion and battery utilization.

are also obvious [6]-[8]. For example, in [6], it is predicted

Hence, some automotive manufacturers prefer having a DC­

that energy management DC-DC converter in HEVs can

DC converter in their power conversion architecture.

achieve 68% size and weight reduction or 1.2% higher efficiency when utilizing SiC devices. On the other hand, with the fast switching speed of SiC

vehicle can

applications, achieve

but

certain

utilizing

benefits

in

this the

DC-DC overall

The topology shown in Fig. 2 is a bi-directional half-bridge converter, which is investigated in this study. The converter can either work as a boost converter to supply power to the

devices, very large dv/dt and di/dt are observed during

inverter DC bus, or as a buck converter to charge the battery,

switching transitions, which will induce voltage spikes across

depending on the mode of operation of the HEV. The

parasitic inductances [9]. The energy stored in parasitic

specifications of the half-bridge converter that is simulated

inductances then tends to resonate with devices capacitances,

and analyzed are shown in Table I. These specifications are

leading to under-damped high frequency oscillation [10]-[11].

978-1-4673-6741-7/15/$31.00 ©2015 IEEE

1----i'\-I \:nA+-\\---+--.- +- . ..--.t-.--.--- .--190 � 400 �-·--·--·--·-·j -. -f·1-·�t.:::::1::::::t::::=160 Turn-on transient,Vds,ld,ideal case

----,-----,-----,------,---- -, 120 800 ,-

6 00

D2 L

Voul

c

Vballery

. .

.l!! g 200

.. .... ........ ..·..-..·..f

Fig. 2. Bi-directional DC-DC converter under study including the parasitic inductances.

I L J."", ... -i----i---j----10 Time(us)

-A - "" +' -'--'-"-'-" -+---'-'--"'+-'--'-'-'-'-l90 l l\4:.',,. ....II--... l =::t=== = =1 60

�

400f, - - ___ __

� � g 200

.

_-___ __._. ._._._. ._._

. _

Time(us)

'" 01

90

W

V \ \ /

400

.l!! g 200

The SiC MOSFETs (CMF20120D) and SiC Schottky

o

converter above. To match the power rating of the converter, As shown in Fig. 2, the model under study contains three one drain inductance

To study the different influence

L" Ld,

and

Lg,

respectively. The chosen inductance value of 35 nH is

6 00 1---h

� '" 01

I

--f-I

I

to

280

quantify the EMI behavior for each case, the high frequency compared.

The

EMI

signature was proposed to assess the EMI generation potential of a specific switching device, which is independent of the EMI coupling paths unique to each converter.

30 (,)

.l!! g 200 r--'-"-'-"-'-'+- I

consistent with the value usually encountered in a non­ waveforms are captured and compared. Furthermore,

�

---- ,---- .,---- -.---- � ---- -. 120 800 .-

of each type of inductance, circuit simulation is conducted in Table II. Case 1 represents the ideal case and serves as a

-60

Turn-on transient,vds,ld,Lg=35nH

Ld,

the simulation tool LTSpice for four test cases, as shown in

Time(�Ls)

\A�\

types of parasitic inductances for each active switch. They

280.2

280.1

280

three MOSFETs are paralleled to make one switch.

baseline. Cases 2-4 show the impact of

1 20

6 00

diodes (C4D20120D) from CREE are implemented in the

are

280.3

Turn-on transient,Vds,ld,Ls=35nH

800

vehicle.

which