IEEE Electrification - June 2021 - 17

Resonant
Switching Cell
L1
+
Vin
-
(a)
Cr
S1
Lr
R
Co
-
(b)
D1
Vin
+
S
Cr2
L1
Lr
D3
D2
Passive Snubber
D1
R
Co
-
(c)
Figure 12. Soft-switching dc-dc power converters with (a) a resonant switching cell, (b) a passive snubber, and (c) an active snubber.
computing systems for autonomous driving, increases the
load on the 12-V system. As a result, the average power has
significantly risen from the current 2~3.5 kW to 6 kW in
EVs. For example, replacing the hydraulic steering system
with a pure electric one can create a peak demand of 6 kW,
which is a considerable challenge for the 12-V system.
An example APM design was implemented using CoolMOS
and a phase-shift full-bridge converter, which can
yield >93% efficiency and has a power density of 1.5 kW/L
with a 2-kW peak output power. In addition, a current-fed
converter or DAB converter can be an excellent candidate
for this high step-down ratio conversion application. However,
large hard-switching currents at the low-voltage side
can cause serious problems, such as high switching losses
and EMI noises. Another approach employs an LLC resonant
converter. Typical one-stage designs, including the
LLC resonant converter and the previously discussed converters,
are simple and cost-effective. However, their output
power is limited, and it is hard for them to cover wide
input and output voltage ranges.
The limitation of single-stage design has led to the
consideration of two-stage designs, as shown in Figure 14.
The front end adopts an interleaved buck converter to
step down the high-voltage battery voltage to an intermediate
dc-bus voltage, which is then converted to the
low-voltage side through a resonance-based matrix
transformer, where the two transformer cells will take
half of the load. Overall, the front-end stage addresses
the wide voltage range requirement and relies on the
matrix transformer stage to avoid the high turn-off current,
thereby providing high efficiency. Another merit of
this design is its bidirectional feature, allowing symmetric
high voltage-to-low voltage (defined as the buck
mode) and low voltage-to-high voltage (defined as the
boost mode) power capabilities, which can provide emergency
power if the main high-voltage battery is bad or
Vin
+
L1
Cr
Sm
Cs
Sa
R
Lr
Co
Active Snubber
D1
VDS
VGS
Main Switch: ZVS
Figure 13. Measured soft-switching waveforms.
S1
VHV
+
-
S2
S4
S6
S8
S10
S13
1 : n
Lr3
S12
S15
C4
S14
Figure 14. A two-stage dc-dc converter with a high step-down ratio for the 12-V system.
IEEE Electrification Magazine / JUNE 2021
17
S16
+
-
VLV
C1
S3
L1
L2
S5
C2
S7
Cr
Lr1
1 : n
Lr2
S9
S11
C3

IEEE Electrification - June 2021

Table of Contents for the Digital Edition of IEEE Electrification - June 2021

Contents
IEEE Electrification - June 2021 - Cover1
IEEE Electrification - June 2021 - Cover2
IEEE Electrification - June 2021 - Contents
IEEE Electrification - June 2021 - 2
IEEE Electrification - June 2021 - 3
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IEEE Electrification - June 2021 - Cover3
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