Simulation of Power Electronic Systems Using PSpice
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Simulation of Power ElectronicSystems Using PSpice
Presented by Nik Din Muhamad
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Presentation Outlines
Know background of SPICE Understand Power Electronics Circuits/Systems Know how to use VPULSE to generate useful
waveforms Know how to make simple models using ABM
In order to use Pspice for power electronic systems, we have to:
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Scope
PSpice System/Circuit Level Simulation Power Electronic Circuits/Systems Simulation
This presentation covers:
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SPICE/PSpice
SPICE turns 38 years old this year I Knew SPICE when she was 17 years old I love PSpice because she can do almost anything I need with FOC. I like to talk about her.
Did you know?
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Why simulation?
Saving of development time Saving of costs (‘burnt power circuits tend
to be expensive’) Better understanding of the function
Simulations are essential ingredients of the analysis and design process in power electronics:
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… continued
Testing and finding of critical states and regions of operation (Worst Case Analysis)
Stress test (Smoke Analysis) Optimization of system Testing new ideas
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Overview
Simulation of analog circuits normally uses three basic tools:
SPICE simulator, Mathematical analysis package, and Microsoft Excel.
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SPICE
Simulation Program for Integrated Circuit Emphasis
Intended for ICs, not for power electronics.
Uses iterative Newton-Raphson Algorithm to solve a set of nonlinear equations.
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SPICE LIMITATIONS
The Newton-Raphson algorithm is guaranteed to converge if the equations is continuous.
The transient analysis has the additional possibility of unable to converge because of the discontinuity in time.
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• Voltage and currents are limited to +/-1e10.• Derivatives in PSpice are limited to 1e14.• The arithmetic used in PSpice is double precision and has 15 digits of accuracy.
Computer Hardware Limitation:
SPICE LIMITATIONS
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Power Electronic Circuit
Power electronic circuits are characterized by switching on and off of power semiconductor switches; the generated waveform is passed through inductors and capacitors for filtering.
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Power Electronic Circuit
Due to switching action of the switch, discontinuity (in circuit variables and in time) can easily occur during simulation, which leads to convergence problem.
“Avoid discontinuity”
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Discontinuity Analogy: A Bump on the Road
“Whole car shakes when I hit a bump on the road”
PSpice doesn’t like discontinuity as we don’t like a bump on the road.
Unacceptable Bump
Acceptable Bump
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Avoid Discontinuity
G
S
VGS
t
VGS
t All signals must be made ‘less discontinuous’ All relationships must be continuous
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VPULSEWaveform generator
PULSE SAWTOOTH TRIANGULAR
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VPULSEWaveform generator
In order to use PSpice for power electronic circuits, the first thing you have to know is to program VPULSE to produce these waveforms:
PULSE Sawtooth Triangular
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VPULSEWaveform Generator Part
V1=V2=TD=TR=TF=PW=PER=
V1
V2
TDT
R
PWT
F
PER
has 7 parameters to set TD can be zero, others can not!
know what parameters to adjust and to fix.
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VPULSETo Generate Pulse Waveform
V1=0V2=12TD=0TR=10nTF=10nPW=10uPER=20u
Very small values for TR and TF Duty cycle = PW/PER
PW
TR ≈ 0 TF ≈ 0
PER
V1
V2
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A Typical applicationBuck Converter (Open Loop)
V2
20V
0
V+
MUR1520V3
TD = 0TF = 10nPW = 10uPER = 20uV1 = 0TR = 10nV2 = 12V
V-
10680uF
M2IRF150
100uH
A Pulse waveform is used to drive a MOSFET ON and OFF.
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Its Pulse (I)
V1=0V2=12TD=0TR=10nTF=10nPW=10uPER=20u
Duty Cycle, %5020
10
PER
PWD
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Its Pulse (II)
V1=0V2=12TD=0TR=10nTF=10nPW=5uPER=20u
Duty cycle of the waveform is adjusted by adjusting PW
%2520
5
PER
PWD
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V1=0V2=12TD=0TR={20u-20n}TF=10nPW=10nPER=20u
Very small values for TF and PW TR≈PER
TR
PW
TF
PER
VPULSETo Generate Sawtooth
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A Typical applicationBuck Converter (Closed Loop)
10
100uH
0
M2IRF150
V4
680uF
-++ -
E1
EGAIN = 4
0
MUR1520
V2
20V
Comparator
Sawtooth Gen.
ControlSignal
+-
Gate Driver
For Closed-loop, the control signal is compared with a sawtooth waveform to produce the pulse waveform.
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PSpice Implementation
Sawtooth VPULSEControl VDCVpulse
ComparatorControlSignal
Gate Driver
100uH
-++ -
E1
EGAIN = 1
0
10
0
M2IRF150
0
MUR1520
680uF
E2
V(%IN+, %IN-)
ETABLE
TABLE = (0,0 (200u,12)
OUT+OUT-
IN+IN-
V5
2.5Vdc
0
V2
20V
V3
TD = 0TF = 10nPW = 10nPER = 20uV1 = 1VTR = {20u-20n}V2 = 4V
Gate Driver EComparator ETABLE
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Its Waveform (I)
Sawtooth
Control
Pulse
D = 50 %
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Its Waveform (II)
Sawtooth
Control
Pulse
Duty Cycle of the Pulse is adjusted by adjusting Control Signal.
D = 33%
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V1= -1V2= +1TD=0TR= {10u-10n}TF= {10u-10n}
PW=20nPER=20u
Very small value for PW TR≈TF ≈ PER/2
TR
PW
TF
PER
VPULSETo Generate Triangular wave
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VPULSEIts Triangular Wave
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Triangular WaveTypical applications
VV1
TD = 0
TF = {(1/(FTRI*2)-10n)}PW = 20nPER = {1/FTRI}
V1 = -1
TR = {(1/(FTRI*2))-10n}
V2 = +1
SINE
0
V
V
0
TRI
PARAMETERS:Ma = 0.8Mf = 21FTRI = {FSINE*Mf}FSINE = 50VDC = 100
VDC*(V(SINE)-V(TRI))/ABS(V(SINE)-V(TRI))
SPWMV2
FREQ = {FSINE}VAMPL = {Ma}VOFF = 0
PHASE = {-90/Mf}
Bipolar SPWM
Comparator
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Triangular WaveTypical applications
Bipolar SPWM
Time [ms]
40ms 42ms 44ms 46ms 48ms 50ms 52ms 54ms 56ms 58ms 60msV(SPWM) 0
-100
0
100V(TRI) V(SINE) 0
-1.0V
0V
1.0V
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Triangular WaveTypical applications
Unipolar SPWM
BV2a
FREQ = {FSINE}VAMPL = {Ma}VOFF = 0
PHASE = {-90/Mf+180}
SINE1
V
V2
FREQ = {FSINE}VAMPL = {Ma}VOFF = 0
PHASE = {-90/Mf}
0
A
0
V
V
0
TRI
0.5*VDC*(V(SINE2)-V(TRI))/ABS(V(SINE2)-V(TRI))
SINE2
0.5*VDC*(V(SINE1)-V(TRI))/ABS(V(SINE1)-V(TRI))
VPARAMETERS:Ma = 0.8Mf = 21FTRI = {FSINE*Mf}FSINE = 50VDC = 100
VV1
TD = 0
TF = {(1/(FTRI*2)-10n)}PW = 20nPER = {1/FTRI}
V1 = -1
TR = {(1/(FTRI*2))-10n}
V2 = +1
Comparator 1
Comparator 2
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Triangular WaveTypical applications
Unipolar SPWM
Time [ms]
40ms 42ms 44ms 46ms 48ms 50ms 52ms 54ms 56ms 58ms 60msV(A)-V(B)
-100V
0V
100V
V(A)-V(B)
V(SINE1) V(SINE2) V(TRI)-1.0V
0V
1.0V
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Analog Behavior Model (ABM) Makes the Circuit Simpler
Use equations to model circuits Comparator Single Phase Rectifier Three Phase Rectifier Buck Converter in CCM Single Phase Inverter
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ABMBehavior Model of Comparator
IF the voltage at the terminal V(+) is greater than the voltage at terminal V(-) the output V(out) is HIgh, otherwise the output is LOw.
IF(V(+)>V(-),HI, LO)
(1) Using IF-Then-Else function
(2) Using signum function
(V(+)-V(-))/ABS(V(+)-V(-))
-V(-)
V(out)
+V(+)
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ABMBehavior Model of Comparator
-V(-)
V(out)
+V(+)
(4) Using Op-amp alike
0
V(+)
V(-)
+- A*(V(+)-V(-))
V(out)
(3) Using I/O graph
0 V(+)-V(-)
V(out)
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ABMComparator in PSpice
TRI
V1
TD = 0
TF = {(1/(FTRI*2)-10n)}PW = 20nPER = {1/FTRI}
V1 = -1
TR = {(1/(FTRI*2))-10n}
V2 = +1
out3
V
LIMIT(10k*(V(SINE)-V(TRI)),10,-10)
0
IF(V(SINE)>V(TRI),10,-10)
V
out1
PARAMETERS:Ma = 0.8Mf = 21FTRI = {FSINE*Mf}FSINE = 50VDC = 10
0
out4
E1
V(%IN+, %IN-)ETABLE
TABLE = (-100u,-10) (100u,10)
OUT+OUT-
IN+IN-
TRI
V
V
V
V2
FREQ = {FSINE}VAMPL = {Ma}VOFF = 0
PHASE = {-90/Mf}
0
out2
V
SINE
SINE
VDC*(V(SINE)-V(TRI))/ABS(V(SINE)-V(TRI))
NO 2 is implemented using ETABLE Others are implemented using ABM part NO 2 & NO 4 are suitable for Op-amp (Error Amplifier)
1
2
3
4
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ABMBehavior Model of Comparator
Time [ms]
40ms 42ms 44ms 46ms 48ms 50ms 52ms 54ms 56ms 58ms 60msV(OUT3) V(OUT2) V(OUT1) V(OUT4)
-10V
0V
10VV(TRI) V(SINE)
-1.0V
0V
1.0V
These waveforms come from the outputs of four comparators
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ABMBehavior Model of Rectifier (I)
V1a
FREQ = 50VAMPL = 340
VOFF = 0R1a
1k
DbreakD6
0
DbreakD4
DbreakD5
DbreakD3
in
R1b
1k
E1
ABS(V(IN))EVALUE
OUT+OUT-
IN+IN-
V1
FREQ = 50VAMPL = 340
VOFF = 0
00
V(out)=ABS(V(IN))
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ABMBehavior Model of Rectifier (II)
Van
Vbn
Vcn
+
-
V(out) = 0.5*(ABS(V(an)-V(bn) +ABS(V(bn)-V(cn)) +ABS(V(cn)-V(an)))
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ABMBehavior Model of Buck in CCM
0
RLMUR1520
100uH
680uF
IRF540
V3
TD = 0TF = 10nPW = 10uPER = 20uV1 = 0TR = 10nV2 = 12V
V2
20 Vdc
+
-
Vd
Vd = d*Vin
100uH
d
0
680uF RL
Vin
E1
V(%IN+)*V( %IN-)EVALUE
OUT+OUT-
IN+IN-
+
-
Vd
d is a PWM signal with 1V amplitude.
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ABMBehavior Model of Inverter
a
b
+
-Vab
Bipolar SPWM
0
+
-
E1
VDC*(V(%IN+)-V( %IN-))/ABS(V(%IN+)-V( %IN-))
EVALUE
OUT+OUT-
IN+IN-
SINE
TRIVab
VDC
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#TIPS
There are many different ways to model the same thing. So, be creative! Use a simple model wherever possible to reduce modeling time and make simulation run faster and converge better!
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Quote about Model !
“Models are like shoes; there is no one-size- fits-all model.”
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Our Case Study A Buck Converter with VMC
A Simple PWM Controller IC Model A PWM IC Controller IC Model including Soft-start A PWM IC Controller IC Model Including Soft-start, Duty Cycle Max and Current Limiter
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Our Case Study A Buck Converter with VMC
SG3525PWM Controller IC
-++ -
0
0
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SG3525PWM Controller IC
Key Functions: Oscillator (Sawtooth Generator) PWM Comparatorand SR Flip-flop Error Amplifier 5.1 V Reference Pulse Steering Logic Shutdown and Soft-start Circuitry
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SG3525 We do not need to have SG3525 model in PSpice’s library to simulate buck converter with VMC.
Error Amplifier Comparator Sawtooth generator
To verify the controller design, all we need are functional models of these:
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SG3525A Simple Model
To MOSFETDriver
-
++
-
Sawtooth
Error Amp.Comparator
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A Buck Converter with VMC
-++ -
-
0
-
VPULSE
0
Vref
+
0
0
+
Comparator Error Amp.
Sawtooth
Buck Converter
Consider we know all circuit parameters.
Our interest is to simulate the system.
The controller is used to regulate the output voltage at 5 V.
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The controller is a linear controller and the design is based on a small-signal model.
So, the controller can not cope with large signal scenario such as start-up.
Initial values, which are equal to their steady state values, for the inductor current and the capacitor voltage must be set.
A Buck Converter with VMC
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Load DisturbanceHow to set a load disturbance ?Let the load disturbance is:
0 A
1 A
8 ms 8.5 ms
3A
R = 5 R = 1.666
R = 5
R is changed from 5 to 1.666
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Our Case StudyHow to set load disturbance ?
Using IPULSE
I1
TD = 8m
TF = 0.1u
PW = 0.5m
PER = 1m
I1 = 1
I2 = 3
TR = 0.1u
ILOAD
Allocate enough times for TR and TF
1
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Load DisturbanceHow to set load disturbance ?
5
TOPEN = 8.5m
1 2
TCLOSE = 8m
2.5
Using SW_tclose and SW_topen
5//2.5 =1.666
2
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Load Disturbance: PSpice
0
R4av
{R3}
R7av
{R1}
R2av
{Resr}
ILOAD0VdcI
0
0
I1
TD = 8m
TF = 0.1uPW = 0.5mPER = 1m
I1 = 1I2 = 3
TR = 0.1u
-++ -
E1
EGAIN = 3
0
DbreakD5
L1
{L}
IC = 1A
E1av
-V(%IN+, %IN-)ETABLE
(0,0) (250u,6)
OUT+OUT-
IN+IN-
0
IV
E2av
V(%IN+, %IN-)ETABLE
(0,0) (250u,5)
OUT+OUT-
IN+IN-
C4av
{C1}
input
V2av
{Vref}
C2av
{C2}
M1IRF150
R2
{Rbias}
R1av
50m
V1
TD = 0
TF = 10nPW = 10nPER = 10u
V1 = 0
TR = {10u-20n}
V2 = 3
V215Vdc
C1av
{C}IC = 5V
C3av
{C3}
out
R6av
{R2}
0
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Load Disturbance: Results
Time [ms]
7.8ms 7.9ms 8.0ms 8.1ms 8.2ms 8.3ms 8.4ms 8.5ms 8.6ms 8.7ms 8.8msI(L1) I(ILOAD)
0A
2.0A
4.0AV(OUT)
4.8V
5.0V
5.2V
Inductor Current
Output Voltage
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Input DisturbanceHow to set an input disturbance ?Let the input disturbance is:
0 V
15 V
25 V
8 ms 8.5 ms
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Input DisturbanceHow to set an input disturbance ?
Use VPWL (Piece-Wise Linear Voltage Source)
0 V
15 V
8 ms 9 ms
25 V
PWL(T1,V1)(T2,V2)(T3,V3)(T4,V4)(T5,V5)
PWL (0,15) (8m,15) (8.0001m,25) (9m,25) (9.0001m,15)
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Input DisturbanceResponses
Time [ms]
7.8ms 8.0ms 8.2ms 8.4ms 8.6ms 8.8ms 9.0ms 9.2ms 9.4ms 9.6ms 9.8ms 10.0msI(L1)
0A
1.0A
2.0AV(OUT)
4.8V
4.9V
5.0V
5.1V
V(INPUT)10V
20V
25V
30V
Input Voltage
Inductor Current
Output Voltage
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Start-up Scenario Previous simulation skips start-up scenario. To know how the controller handles start-up, set the initial values for iL and vc to zero.
Time [s]
0s 100us 200us 300us 400us 500us 600us 700us 800usI(L1) V(OUT)
0
5
10
15
20
Output Voltage
Inductor Current
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Start-up Scenario A very large overshoot and undershoot occur in inductor current. The duty cycle is at first at 1 for a long time and later at 0 for a long time too, then after that it gradually increases.
Convergence problem can easily occurs at this extreme condition.
Time0s 100us 200us 300us 400us 500us 600us 700us 800us
I(L1) V(OUT)
0
5
10
15
20V(E1:1)
0V
2.5V
5.0V
Gate Signal
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Start-up In practical circuit, another auxiliary controller is required to handle start-up. This circuit is known as soft-start.
Soft-start circuit works by gradually increasing the duty cycle. So do the inductor current and capacitor voltage.
Time [s]0s 100us 200us 300us 400us 500us 600us 700us 800us
I(L1) V(OUT)
0
5
10
15
20V(E1:1)
0V
2.5V
5.0V
Gate Signal
Soft startController
VMCController
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Soft-startTo add Soft-start
The previous PWM IC model is very useful and it is simple to set-up in PSpice.
It is enough to verify the design of controller based on small signal model.
However, to add soft-start controller and other protection circuits, we need a more flexible PWM IC model.
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A Modified PWM IC Model
RS
Oscillator
-
++
- Q
Sawtooth
Clock
Error Amp.
Comparator SR Flip-flop
The output of SR flip-flop is set by the Clock. The output of SR flip-flop is reset by Comparator.
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A Modified PWM IC Model
Analog signals can be added at minus terminals of the comparator. Digital signals can be added at the input Resets of FF.
RS
RR
Oscillator
-
++
-Q
Sawtooth
Clock
Error Amp.
Comparator SR Flip-flop
-
-AnalogSignals Digital
Signals
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Soft-startTo add Soft-start Signal
Sawtooth is still compared with the control signal.
But, Control Signal can be either Error Amp. output (EAO) or Soft-start signal (SS), whichever is lower.
-
+
-
Sawtooth
Error Amp.Output
Soft-start
To R of SR Flip-FlopControl
Signal
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Soft-startTo add Soft-start Signal
The soft-start voltage is the capacitor voltage. The capacitor C is charged by a constant current source of 50 A. The result is a ramp voltage. C determines the duration of soft-start.
-
+
-
Sawtooth
Error Amp.Output (EAO)
Soft-start (SS) To R of SR Flip-Flop
C
50 A
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Soft-startHow Soft-start works?
10 ms
Soft-start Voltage
t
Use PWL to emulate soft-start voltage For the graph, PWL(0,0)(10ms,4V)
t
VCI
4 V
Slope =C
50
C = 125 nF
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Soft-startTo add Soft-start Signal
We need a selector to select either SS or EAO, whichever is lower, to be Control Signal. We can use IF-Then-Else function IF(SS < EAO, SS, EAO)
+
-
Sawtooth
EAO
SS To R of SR Flip-Flop
C
50 A
ControlSignal
Selector
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Soft-startIn PSpice
IF( V(%IN2)<V(%IN1),V(%IN2),V(%IN1) )
13
2
0
R4av
{R3}
C2av
{C2}
0
C4av
{C1}
0
R6av
{R2}
0
err_outcontrol
V3
TRAN = PWL(0,0)(10m,4)
E2av
-V(%IN+, %IN-)
ETABLE
(0,0) (250u,5)
OUT+OUT-
IN+IN-
E1av
-V(%IN+, %IN-)ETABLE
(0,0) (500u,5)
OUT+OUT-
IN+IN-
0
R7av
{R1}
R
0
V2av
{Vref}
R2
{Rbias}
C3av
{C3}
SoftSV1
TD = 0
TF = 10nPW = 10nPER = 10u
V1 = 0
TR = {10u-20n}
V2 = 3
Sawtooth
Vout
SawtoothGenerator
IF-Then-ElseSELECTOR
Error Amplifier
Comparator
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Soft-startStart-up Signals
Time [ms]
Control Signal
0s 1.0ms 2.0ms 3.0ms 4.0ms 5.0ms 6.0ms0V
1.0V
2.0V
0V
2.5V
5.0V
0V
2.5V
5.0V
Soft-Start Signal
Error Amplifier Output
Control = IF(SS < EAO, SS, EAO)
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Soft-startC = 125 nF (Too Small!)
Time [ms]
I(L1)
V(OUT)
0s 1.0ms 2.0ms 3.0ms 4.0ms 5.0ms 6.0ms0A
2.0A
4.0A
0V
2.5V
5.0V
7.5V
Soft-start signal ramps up too fast
tstart-up = 1ms
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Soft-startStart-up Current and Voltage
Time [ms]
0s 1.0ms 2.0ms 3.0ms 4.0ms 5.0ms 6.0ms
I(L1)
0A
1.0A
2.0A
V(OUT)
0V
2.5V
5.0V
7.5V
Still has a small overshoot and undershoot in inductor current has a room for improvement by increasing C.
tstart-up = 3.2 ms
C = 25 nF
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Soft-startStart-up Current and Voltage
C = 125 nF ; Start-up time is 30 ms. Time
0s 5ms 10ms 15ms 20ms 25ms 30ms 35msI(L1)
0A
1.0A
2.0A
SEL>>
V(OUT)0V
2.0V
4.0V
6.0V
I(L1)
V(OUT)
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A Modified PWM IC Model
To add digital signals for protection. For examples, Maximum Duty Cycle and Current Limiter Flip-flop can be reset either by PWM comparator, or Maximum duty cycle, or Current Limiter.
RS
RR
Oscillator
-
++
-Q
Sawtooth
Clock
Error Amp.
Comparator SR Flip-flop
-
-AnalogSignals Digital
Signals
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To Add Digital SignalsDutyMax and CurrentLimit
Maximum duty cycle limiter is in digital form. It can be applied directly to the Reset of FF.The switch current (or inductor current) must be compared with its limit value to produce a digital signal.
0U12A7432
1
23
U16A7432
1
23
8A
U11A7402
2
31 R
I(L1)
0
U10A7402
2
31
VClock
TD = 0
TF = 1nPW = 0.1uPER = 10u
V1 = 0
TR = 1n
V2 = 5V
Vdutymax
TD = {10u*0.85}
TF = 10nPW = {(10u-10u*0.85)-20n}PER = 10u
V1 = 0
TR = 10n
V2 = 5V
0
S
QEcurr_limit
+V(%IN+, %IN-)ETABLE
(0,0) (250u,5)
OUT+OUT-
IN+IN-
Dutymax
RESET 1 (EAO)
RESET 2 (CL)
RESET 3 (DMax)
SET
Set only by one i. e. the clock Reset can be done by three, whichever
comes first.
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Time
0s 20us 40us 60us 80us 100us 120us 140us 160us 180us 200usV(SAWTOOTH)
0V
2.0V
4.0VV(DUTYMAX)
0V
2.5V
5.0V
V(DUTYMAX)
V(S)0V
2.5V
5.0V
DUTYMAX
CLOCK
SAWTOOTH
DUTYMAX signal will only reset FF if the duty cycle is more than 0.85 This DUTYMAX is to make sure that the MOSFET always turns-off for each cycle CurrentLimit signal will only appear and reset FF if the peak switch is greater than pre-specified value.
To Add Digital SignalsDutyMax and CurrentLimit
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Time
5.6ms 5.7ms 5.8ms 5.9ms 6.0ms 6.1ms 6.2ms 6.3ms 6.4ms 6.5ms 6.6msV(OUT) I(L1)
0
5
10
To Add Digital SignalsDutyMax and CurrentLimit
We want to limit this current at 8A
Inductor Current
Output Voltage
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Time
5.6ms 5.7ms 5.8ms 5.9ms 6.0ms 6.1ms 6.2ms 6.3ms 6.4ms 6.5ms 6.6msV(OUT) I(L1)
0
5
10
Output Voltage
Inductor Current
8A Limiter
To Add Digital SignalsDutyMax and CurrentLimit
What do we expect ?
Reset by EAO Reset by DutyMax
Reset by CurrentLimit
Reset by EAO
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A Load disturbanceat 6.0 ms
Time [ms]5.90ms 5.95ms 6.00ms 6.05ms 6.10ms 6.15ms 6.20ms
V(DUTYMAX) V(Q)
0V
2.5V
5.0VV(CURRENTLIM) V(Q)
0V
2.5V
5.0VV(PWMCOMP) V(Q)
0V
2.5V
5.0VV(CLOCK)
0V
2.5V
5.0V
To Add Digital SignalsDutyMax and CurrentLimit
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Knowing
“There is no substitute for knowing what we are doing”
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CONCLUSION
Know how to program VPULSE for Pulse, Sawtooth, and Triangular waveforms. Avoid discontinuity at any cost Use the simplest model possible Use a simple model first, and add complexity in stages. No replacement for good understanding
In order to simulate power electronic circuit:
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Q & A