电子技术基础课件第7章 软开关技术

D1D4
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(d ) fs < fo 处于容性工作状态
Inverter bridge variations
zFull bridge
S1
S2
S3
S4
io
R
zHalf bridge
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S1 and S2 gate signal are complement 50% Duty cycle Voltage on C1 and C2 are constant, =Vs/2
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on 电力电o子ff技术
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实际元件构成的Buck变换器(Practical Buck converter)
Ideal
Practice
Square Waveforms No Switching Loss
Parasitic Oscillations Switching Loss Snubber Loss
uDS
-
-
u gs
uDS , iDS
iD
Ii
I RM
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Ii Vd
t
Reverse recovery charge Qrr
vs.
dI F dt
Vo
¾ Turn-on loss in switch and boost diode
∫ Aturn _ on
=
QrrVo
+
trr
Ii uDSdt
0
简化:分析基波分量之间的关系，而忽略谐波分量的作用 Vi: square waveform Amplitude: ±Vdc freq: fs Amplitude of fundamental component
V1
=
4Vdc
π
+Vdc
-Vdc
In-out ratio:
Vo =
R
=
1
Vi
R2 + (ω L − 1 )2
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电力电子电路的高频化
可以减小滤波器、变压器的体积和重量，电力电子装置小型化、 轻量化。
开关损耗增加，电路效率严重下降，电磁干扰增大。
软开关技术
降低开关损耗和开关噪声。 使开关频率可以大幅度提高。
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软开关的分类（Types of soft switching）
Turn-off switching loss is reduced
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电力电子技术
Байду номын сангаас
21
串联谐振逆变器（Series resonant inverter）
S1
S2
S3
S4
io
R
S1,S4 S3,S2
Ts
Gate signal for S1 and S4 are the same Gate signal for S2 and S3 are the same Duty ratio of all the switches is 50%
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Gate-Drive Miller Effect
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Low Efficiency at HF
反激变换器（Flyback converter ）
without parasitic
with parasitic
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吸收电路
Primary switch RC snubber
Turn-off switching loss is 0
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零电压关断Zero voltage switch off(ZVS off)
Turn off with zero voltage
Overlap time still exist But integral of multiplication of uds and ids is reduced
(1) 理想开关（Ideal switch）
Static characteristics
ON state
R=0
Off state R=infinite
Dynamic characteristics
Turn on time=0 Turn off time=0
IAK
A
K
G
VAK
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1 ωs = fs ωo fo
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f*=fs/fo
Vo vs. f* curve w/ constant Q f*>1, decrement function f*<1, increment function Vo can be regulated by changing fs
Cut down turn-on loss:
ZCS on ZVS on
Cut down turn-off loss:
ZCS off ZVS off
ugs
uds
ids
ZCS on ugs
uds
ids
ZVS on
ugs ids
uds
ZCS off ugs
ids
uds
ZVS off
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零电流开通Zero current switch on(ZCS on)
Turn on with zero current
Overlap time still exist But integral of multiplication of uds and ids is reduced
Leakage inductance of the transformer
Stray inductance •Layout •Wire bonds in device packages •Leads of devices
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理想元件构成的Buck变换器（Ideal Buck converter）
Switch-on
@Vce=600V Ic=40A Rg=2.2Ω
Power meter
12
Ch1 I Ch1 V
Vdc
3 Lf
Ch3 V
Rload
Ch3 I
Cf
S1
S2
Ch2 V
Ch2 I
N
∑ Psw = f ⋅ ⎡⎣Eoff (io (n)) + Eon (io (n)) + Err (io (n))⎤⎦ n=1
+
1 2
CossVo2
trr
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寄生电容（Parasitic capacitance)
Power MOSFET Diode Layout stray capacitance Transformer winding capacitance
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寄生电感（Parasitic inductance)
io
D1D4
S1S 4
D2 D3
S2 S3
D1D4
S1 S 4
(c) fs > fo 处于感性工作状态 io
fs < fo
RLC load is capacitive Io is leading to Vi
ZCS switching off
S1S 4
D1D4
S 2 S3
D2 D3
S1S 4
-Vd
2018/9/3Switch-off
电力电子技术 Reverse recovery
5
二极管反向恢复过程（Diode reverse recovery）
IL
iDS
iD
IL
uD
Qrr
IRRM
High di/dt, EMI problem High loss on switch and diode
1+ (ω L − 1 )2
ωC
R ω RC
ω = 2π fs
fs: Switching frequency
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输入输出比（Input-output ratio）
Vo =
R
=
1
Vi
R2 + (ωL − 1 )2 ωC
1+
L R2C
(ω
L
C−
ω
1 L
)2 C
Quality factor
Turn-on switching loss is 0
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零电流关断Zero current switch off(ZCS off)
Turn off with zero current
Overlap time is zero integral of multiplication of uds and ids is 0
9 S1 and S3 operate complementally 9 S2 and S4 also operate complementally 9 Vi is square wave, freq: fs=1/Ts
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基波等效电路（Equivalent circuit ）
L
Q = ωoL = 1 = C R ωoRC R