1
Advanced Industrial Electronics
Resonant Power Converters
References[1] Kazimierczuk M., Czarkowski D., Resonant power converters, John Wiley and Sons, Inc. 1995
[2] Kazimierczuk M., Czarkowski D., Solutions manual for - Resonant power converters, John Wiley and Sons, Inc. 1995
[3] Brown M., Power supply cookbook, Newnes, 2001
[4] Luo F. L., Ye H. Synchronous and resonant DC/DC conversion technology, energy factor, and mathematical modeling, Taylor and Francis Group, 2006
[5] Hagerman J., Calculating optimum snubbers, Hagerman Technology, 1995
[6] International Rectifier, AN-978 HV floating MOS-Gate driver ICs, International Rectifier Application Note, (www.irf.com)
[7] Hang-Seok Choi, AN-4151 Half bridge LLC resonant converter design using FSFR-series Fairchild Power Switch, Fairchild Semiconductor Corporation Application Note, 2007
[8] STMicroelectronics, AN2450 LLC resonant halfbridge converter design guidline,STMicroelectronics Application Note, 2007, (www.st.com)
References[9] Bosso C., AND8311/D Understanding the LLC structure in resonant applications, ON Semiconductor, 2008, (www.onsemi.com)
[10] Cree Inc., C2D05120-Silicon Carbide Schottky Diode, Cree Data Sheet, 2006, (www.cree.com)
[11] IXYS Corporation, IXDN430 30 amp low-side ultrafast MOSFET/IGBT driver, IXYS Corporation Data Sheet, 2004, (www.ixys.com)
[12] IXYS Corporation, EVDD 430S/ EVDD 430CY 30A Ultra Fast MOSFET/IGBT driver evaluation board, IXYS Corporation, 2003, (www.ixys.com)
[13] IXYS Corporation, IXFL32N120P Polar Power MOSFET HiperFET, IXYS Corporation Data Sheet, 2008, (www.ixys.com)
[14] IXYS Corporation, IXFN60N80P PolarHV Power HiperFET MOSFET, IXYS Corporation Data Sheet, 2006, (www.ixyys.com)
[15] STMicroelectronics, L6599 High-Voltage resonant controller,STMicroelectronics Data Sheet, 2006, (www.st.com)
[16] Infineon Technologies AG, SKW25N120 fast IGBT in NPT technology, Infineon Data Sheet, 2006
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Introduction
PWM and resonant power converting ideas
Introduction
Block diagram of a typical PWM/resonant switching power supply
Low frequencyrectifier, filter
with PFCcorrection
MAINS AC230V/400V
50 Hz PWM/Resonantinverter
DC320V/560V
Vin High frequencyrectifierand filter
ACLoad
DCVout
ConverterController
PFCController
DC-DC converter
Introduction
The function of DC-DC converter are as follows:
- to convert a DC input voltage (Vin) into a DC output voltage (Vout)
- to control the DC output voltage (Vout) against load and mains variations
- to reduce the AC ripple on the DC output voltage (Vout) below the required level
- to provide isolation between the input source and the load
- to protect the supplied system from electromagnetic interference (EMI)
- to satisfy various international and national safety standards
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Introduction
Voltage-switching half-bridge inverters with various resonant circuits
Introduction
Main features of the resonant circuits:
- circuits a), f) and g) supply a sinusoidal output current and are compatible with current-driven high frequency rectifiers
- inverters (b)-(e) produce a sinusoidal output voltage and are compatible with voltage-driven rectifier
- for the circuits (b)-(g) resonant frequency depends on the load
LLC inverter basics
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LLC inverter basics
- the ratio of the inductance:2
1
L
LA =
- the equivalent inductance: ( )
+=+=+=A
LALLLL1
11 2221
- the undamped natural frequency: ( )CLLLC 21
0
11
+==ω
- the characteristic impedance:C
L
CLZ ===
000
1
ωω
LLC inverter basics
- the loaded quality factor at f0:00
0 Z
R
L
RCRQ LL
LL ===ω
ω
- the equivalent inductance of the damped circuits:
seq LLL += 1
2
22
22
1L
s
R
L
LL
ω+=where
- the resonant frequency: ( )CLLCL seq
r +==
1
11ω
( )s
sr
srr R
LL
CRQ
+== 11 ωω
- the quality factor at the resonant frequency:
where ( )22
22 /1 LR
RR
rL
Ls ω+
=
LLC inverter basics
f0
Gain
f
Mmax
capacitive regionZCS
inductive regionZVS
peak gain
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LLC inverter basics
Capacitive region – current leads the voltage, bridge MOSFETs operate in zero current switching (ZCS). It means that power MOSFETs are turned-off (Vds decreases from Vin to 0) at zero current. Switching-off losses can be neglected.
Inductive region – current lags the voltage. Power switches are turned-on (Is is increasing from 0 to Ismax) at zero volts (ZVS). Switching-on losses can be neglected.
For frequency fsw = f0 the MOSFETs turn on and turn off at zero currents, resulting in zero switching losses and high efficiency.
LLC inverter basics
*Taken from „Resonant power converters”,
KazimierczukM.,Czarkowski D.[1]
LLC inverter basics
Operating below resonant frequency (ZCS):
a) conductive sequence is Q1, D1, Q2, D2
b) there are a few detrimental effects of switching-on MOSFET:
- reverse recovery of the antiparallel diode of the opposite switch
- second breakdown of the MOSFET parasitic bipolar transistor
- discharging of transistor output capacitance (additional losses)
- Miller’s effect
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LLC inverter basicsOperating below resonant frequency:
d) IGBT transistors or thyristors with antiparallel diode should be used instead of MOSFETs
*Taken from „ SKW25N120 fast IGBT in NPT technology, Infineon Data Sheet, 2006 [16]
LLC inverter basics
Operating at frequency fsw=f0:
- transistors turn on and turn off at zero currents
- efficiency is high because of lack the conducting losses
- antiparallel diodes never conduct
- output power or output voltage of the converters can not be controlled
LLC inverter basics
Operating at frequency fsw > f0:
- the conduction sequence of the semiconductor devices is D1-Q1-D2-Q2
- MOSFETs
operates at ZVS
t
Vgs1
Vgs2Td
Vin
Vds2
ZVS
i
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LLC inverter basics
The LLC resonant converter with a transformer center-tapped rectifier
LLC inverter basics
S2 in ON, D4 is conducting
LLC inverter basics
S2 is ON, D1 – D4 are blocked
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LLC inverter basics
S1, S2 are OFF, Coss1 id discharging, Coss2 is charging
LLC inverter basics
VCoss2=Vin+Vf, D1 conducts; S1, S2 are OFF; D3, D4 are blocked
LLC inverter basics
S1 is ON, D3 is conducting
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LLC inverter basics
S1 is ON; D3, D4 are blocked
LLC inverter basics
S1, S2 are OFF, Coss1 is charging, Coss2 id discharging
LLC inverter basics
S1, S2 are OFF, VCoss2 = -Uf, D2 is conducting
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LLC inverter basics
*Taken from „AND8311/D Understanding the LLC structure in resonant applications”, Bosso C.ON Semiconductor, 2008 [9]
LLC full-bridge converter
High frequency rectifiers
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High frequency rectifiers
The features of current driven diode rectifiers:
- have to be driven by current source
- the DC output current is directly proportional to the amplitude of the input current
- the diode threshold voltage Uf, the diode forward resistance Rf and filter capacitor ESR reduce efficiency of the rectifiers
- the center-tapped rectifier has the highest efficiency, while the half-wave has the lowest
High frequency rectifiersThe features of current driven diode rectifiers:
- half-wave and bridge rectifier are suitable high voltage applications because the diode peak reverse voltage is Vdm
= -V0
- for the half-wave rectifier both the source and the load can be connected to the same ground
- the RMS current of capacitor is very high and therefore the capacitor must be rated accordingly
- the ESL of the filter capacitor may destroy the filtering effect at very high frequency
High frequency rectifiersFeatures of the rectifier:
- it has the highest efficiency
- its efficiency is low at light loads
- its not suitable for high frequency because of increasing the gate-driver power
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High frequency rectifiers
High frequency rectifiers
The features of voltage driven diode rectifiers:
- have to be driven by voltage source
- have a second-order LC output filter
- the DC output voltage is directly proportional to the amplitude of the input voltage
- the peak-to-peak and RMS through the filter capacitor is relatively low
- the conduction loss in the ESR of the filter capacitor is low
High frequency integrated
transformer
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High frequency integrated
transformer
The transformer turn ratio:2
1
N
Nnt =
The real transformer turn ratio:ondary
primary
L
Lkn
sec
=
‘k’ is the transformer coupling ratio.
21
2
t
LL
n
LL = λ+=+= 1n
L
LLnn
m
rmt
Equivalent load resistance
2
2
==
s
pLLac N
NRnRR
Transformation the load resistance to the primary side of transformer
Equivalent load resistance
The half-wave rectifier:
2
22
πL
ac
RnR =
The center-tapped transformer and the bridge rectifier:
2
28
πL
ac
RnR =
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LLC design procedureThe design procedure of LLC converter was taken from STMicroelectronics, „AN2450 - LLC resonant half-bridge converter design guideline”,STMicroelectronics Application Note, 2007 [8].
Design specification:
– Input voltage range: Vdc.min - Vdc.max
– Nominal input voltage: Vdc.nom
– Regulated output voltage: Vout
– Maximum output power: Pout
– Resonant frequency: fr
– Maximum operating frequency: fmax
LLC design procedure
Additional info:
– Parasitic capacitance of the MOSFETs half-bridge: Czvs
– Dead time of driving circuit: TD
General criteria for the design:
– The converter will be designed to work at resonance at nominal input voltage.
– The converter must be able to regulate down to zero load at maximum input
voltage.
– The converter will always work in ZVS in the whole operating range.
LLC design procedure
The converter circuit
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LLC design procedure
Step 1 - to fulfil the first criterion, impose that the required gain at nominal inputvoltage equals unity and calculate the transformer turn ratio:
out
nomDC
nomDC
outnom V
Vn
V
VnM ,
, 2
112 =⇒==
Step 2 - calculate the max. and min. required gain at the extreme values of the input voltage range:
min,max 2
DC
out
V
VnM =
max,min 2
DC
out
V
VnM =
LLC design procedure
*Taken from „AN2450 - LLC resonant halfbridge converter design guidline”,STMicroelectronics Application Note, 2007 [8].
LLC design procedureStep 3 - calculate the maximum normalized operating frequency (according to the definition):
rn f
ff max
max, =
Step 4 - calculate the effective load resistance reflected at transformer primaryside:
out
outLac P
VnRnR
22
22
2
88
ππ==
Step 5 - impose that the converter operates at maximum frequency at zero load and maximum input voltage, calculating the inductance ratio
1
12
max,
2max,
min
min
−−=
n
n
f
f
M
Mλ
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LLC design procedureStep 6 - calculate the max Q value to work in the ZVS operating region atminimum input voltage and full load condition
1
195.0%95
2max
2max
maxmax1 −
+=⋅=M
M
MQQZVS λ
λ
Step 7 - calculate the max Q value to work in the ZVS operating region at no-load condition and maximum input voltage
( ) ZVSac
D
n
nZVS CR
T
f
fQ
λλλ
π −+= 2
max,
max,2
1
2
Step 8 - choose the max quality factor for ZVS in the whole operating range, such that:
{ }21,min ZVSZVSZVS QQQ ≤
strayOSSZVS CCC += 2
LLC design procedureStep 9 - calculate the minimum operating frequency at full load and minimum input voltage, according to the following approximate formula:
−+
=
+
4
max
1max
min
11
11
1
Q
Q
r
ZVS
M
ff
λ
Step 10 - calculate the characteristic impedance of the resonant tank and allcomponent values
acZVS RQZ =0
02
1
ZfC
rr π
=r
r f
ZL
π20=
λr
m
LL =
LLC design procedure
Step 11 - calculate the transformer parameters
( ) mrSOp LLL +=
( ) rSSp LL =
λ+= 1nnt
primary inductance (with secondary windings open)
primary inductance (with secondary windings shorted)
transformer turn ratio
Next, choose a core with an appropriate AL value.( )
AL
LN SOp
p =t
ps n
NN =
Find experimentally the core gap (with secondary winding shorted) to satisfy appropriate Lr value.
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MOSFETs protection
RC Snubbers
MOSFETs protection
MOSFETs protectionRC snubber designing
Step 1 – you have to know parasitic L or parasitic C of the MOSFET half bridge. Calculate characteristic impedance of resonant circuits:
If we know L
If we know C
fLZ π2=
fCZ
π2
1=f is the ringing frequency
We assume that the initial value of the snubber resistor R = Z.
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MOSFETs protection
Then we can calculate value of the snubber capacitor C:
fRC
π1=
Power dissipation of the resistor is given by expression:
swfCVP 2=
Where V is the voltage across MOSFET when it is OFF, fsw
is the converter switching frequency.
MOSFET driversThe MOSFET drivers have following features:
- driving high capacitive load
- supply MOSFET gate with high current
- low propagation delay
- low rise and fall times
- low output impedance
MOSFET drivers
*Taken from „AN-978 HV floating MOS-Gate driver Ics”, International Rectifier Application Note, [6].
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MOSFET driversSupplying the high-side driver by bootstrap capacitor.
Resonant converters controllersThe resonant converter controllers features:
- variable frequency control of resonant half or full-bridge
- high accuracy oscillator
- converter protection functions: frequency shift and latched shutdown
- Interface with PFC controller
- Latched disable input
- Burst-mode operation at light load
- Non-linear soft-start for monotonic output voltage rise
Resonant converters controllers
*Taken from „L6599 High-Voltage resonant controller,STMicroelectronics Data Sheet, 2006, [15].
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Resonant converters controllers
*Taken from „L6599 High-Voltage resonant controller,STMicroelectronics Data Sheet, 2006, [15].
Resonant converters controllers
*Taken from „L6599 High-Voltage resonant controller,STMicroelectronics Data Sheet, 2006, [15].
Resonant converters controllers
*Taken from „L6599 High-Voltage resonant controller,STMicroelectronics Data Sheet, 2006, [15].
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Resonant converters controllers
Burst mode
*Taken from „L6599 High-Voltage resonant controller,STMicroelectronics Data Sheet, 2006, [15].
Resonant converters controllers
*Taken from „L6599 High-Voltage resonant controller,STMicroelectronics Data Sheet, 2006, [15].
Soft start
High Power MOSFETs
*Taken from „ IXFN60N80P PolarHV Power HiperFET MOSFET, IXYS Corporation Data Sheet, 2006, [14].
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High Power, Fast Switching
Schottky Diodes
*Taken from „C2D05120-Silicon Carbide Schottky Diode, Cree Data Sheet, 2006, [10].
Summary