simulation of power electronic systems using pspice

1

Simulation of Power ElectronicSystems Using PSpice

Presented by Nik Din Muhamad

2

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:

3

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?

5

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:

6

… continued

Testing and finding of critical states and regions of operation (Worst Case Analysis)

Stress test (Smoke Analysis) Optimization of system Testing new ideas

7

Overview

Simulation of analog circuits normally uses three basic tools:

SPICE simulator, Mathematical analysis package, and Microsoft Excel.

8

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.

9

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

11

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.

12

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

14

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

16

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

17

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)


Duty Cycle, %5020

10

PER

PWD

21

Its Pulse (II)


Duty cycle of the waveform is adjusted by adjusting PW

%2520

5

PER

PWD

22

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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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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Unipolar SPWM

BV2a


PHASE = {-90/Mf+180}

SINE1

V

V2


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


V1 = -1

TR = {(1/(FTRI*2))-10n}

V2 = +1

Comparator 1

Comparator 2

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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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-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


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


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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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

46

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

51

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

52

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

53

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

54

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

55

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

56

Input DisturbanceHow to set an input disturbance ?Let the input disturbance is:

0 V

15 V

25 V

8 ms 8.5 ms

57

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)

58

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

59

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

60

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

61

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

62

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.

63

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.

64


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.


-

-AnalogSignals Digital

Signals

65

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

66


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

67

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

68


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

69

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

70

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)

71

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

72

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

73

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)

74


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.


-

-AnalogSignals Digital

Signals

75

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.

76

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.


77

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


We want to limit this current at 8A

Inductor Current

Output Voltage

78

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


What do we expect ?

Reset by EAO Reset by DutyMax

Reset by CurrentLimit

Reset by EAO

79

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


80

Knowing

“There is no substitute for knowing what we are doing”

81

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:

82

Q & A

simulation of power electronic systems using pspice

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