All Classes Ppt

Digital Simulation of Power Electronic Systems 

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By the end of the course, you are some one who can confidently be a part of A research group, design & development group, prototype implementation/ testing group, Familiar with Modeling, implementing those models in Matlab/Simulink/Pspice.

Models:single phase/three phase controlled &uncontrolled rectifiers, choppers, inverters,filters,DC and AC motors, controllers and complete systems. Familiar with case studies of DSP based controllers of induction motors and switched reluctance motors

Power electronics system: Block Diagram

Key Features of Converter Circuits 

The circuit topology changes as the switches open and close as a function of time under the guidance of the controller

SPICE Simulation Program with integrated circuit emphasis

Transient analysis calculates all node voltages and branch currents over a time interval, and their instantaneous values are the outputs. Circuit behaviour in response to time varying sources(.TRAN) Dc and Fourier components of the transient analysis results (.FOUR)

ISPICE Interactive circuit simulation with graphic output. Types of Analysis : Dc Analysis .DC Dc sweep of an input voltage/current source,a model parameter,or temperature over a range of values(.DC) Determination of the linearized model parameters of non linear devices (.OP) Dc operating point to obtain all node voltages. (.OP) Small-signal transfer function with small-signal gain,input resistance,output resistance(.TF) Transient Analysis: Used for circuits with time-variant sources (ac sources and switched sources)

AC Analysis Used for small signal analysis of circuits with sources of variable frequencies. Calculates all node voltages and branch currents over a range of frequencies , and their magnitudes and phase angles are the outputs. Circuit response over a range of source frequencies (.AC) Noise generation at an output node for every frequency (.NOISE)

Use of computer Simulations Used as teaching aid to understand concepts.  In research to analyze the behaviour of new circuits  In industry to shorten the design process especially to study the influence of a parameter on the system behaviour through simulation than on a hardware bread board. 

Description and analysis of a circuit require the following specs: Element values Nodes Circuit elements Element models Sources Types of analysis Output variables PSPICE output commands Format of circuit files,Format of output files

Element Values :Scale suffixes and unit suffixes

F=1E-15 V=volt,A=amp,HZ P=1E-12 N=1E-9 U=1E-6 MIL=25.4E-6 M=1E-3 K=1E3 MEG=1E6 G=1E9 T=1E12

Outcomes of the Simulation  

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Calculate circuit waveforms Dynamic and steady state performances of systems. Voltage and current ratings of various components. Power loss calculations leading to optimum thermal design

Choices of Simulation Tools 

Circuit oriented simulators 

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User supplies the circuit topology and the component values. The simulator internally generates the circuit equations,which are transparent to the user. The user may have the flexibility of selecting the details of the component models depending on the simulator. Controllers may be specified by means of a transfer function or by models of components such as operational amplifiers and comparators etc.,

Simulation Tools 

Equation Solvers  Describing the circuit and the controllers by means of differential and algebraic equations.  The equations must be developed for all possible states in which the circuit may operate.  Describe the logic that determines the circuit state and the corresponding set of differential equationsbased on circuit conditions.  Solution of these algebraic/differential equations by means of software packages specifically designed for this purpose that provide a choice of integration routines,graphical output and so on.

Circuit –Oriented Simulators Sl.No

Key Features

Disadvantages

1.

Initial set up time is small

Little control over the simulation process

2.

Easy to make changes in circuit topology and control

Can lead to long simulation times.

3.

Focus is on the circuit rather than on the mathematics of the solution.

Can lead to oscillation problems

4

Built in models for the components and Steps to overcome these the controllers(analog and digital) are difficulties are not usually available. usually apparent and may require trial and error.

5.

Possible to segment the overall system into smaller modules/building blocks,that can be tested individually and then brought together.

Equation Solvers Sl.No

Key Features

Disadvantages

1.

Give total contrl over the simulation process, including the integration method to be used,time step of simulation,etc.,

Long time is required for the initial set up of developing all possible combinations of diffferential /algebraic equations.

2.

Smaller simulation time.

Even minor changes in the circuit topology and control may require just as much effort as the initial set up.

3.

Being general purpose tools, can be useful in applications other than power electronics simulation

Method of solving in Circuit solving programs SPICE?EMTP

Linear differential equations: Trapezoidal method of integration used in SPICE and EMTP.  Non Linear differential equations : Newton Raphson iterative procedure. 

Principles of Steady –State (DC steady state)converter analysis

Current waveforms of a switch mode converter 

D=ton/Ts ;where Ts=1/fs;where fs=switching freq

Representing the functions of a switching converter by an equivalent circuit The dc transformer model: Correctly represents the relationships between the dc voltages and currents. The model can be refined by including losses,such as semiconductor forward voltage drops and on – resistances, inductor core and copper losses. The resulting model can be directly solved ,to find v, i, losses and η in the actual non ideal converter. 

Equations     

V=M(D)*Vg M(D)=equilibrium conversion ratio; M(D)=D ….. for buck converter M(D)=1-D …..for boost converter Ig=M(D)* I

The DC transformer Model

There are three ports: A power input A power output A control port These functions are ideally performed with 100%η and hence, Pin=Pout Vg*Ig =V*I 

Circuit Model of a buck converter

Ideal Dc Transformer Model  

V=M(D) Vg ; Ig=M(D) I.

a)Use of DC transformer model of switching converter(power source modeled by thevenin equivalent) b)Simplification by referring all elements to secondary side

Output voltage=M(D)V1 R/ (R+M2DR1)

Modeling of Inductor copper loss via series resistor RL

RL

L

Extension of dc transformer model to model other properties of the converter. Non idealities such as power loss,/converter dynamics can be modeled by adding inductors and capacitors to the equivalent circuit.

'

0  Vg  I R L  D V

RL

'

0  Vg  I R L  D V

I + _

Vg

+ -

D’V

V '  V  i C (t )  D  R   D  I  R  V ' 0  DI  R

'

V/R

D’I

0  DI 

R

V R

Circuit Model I

RL +

Vg + _

D’V

+ -

V D’I -

R

'

0  Vg  I R L  D V '

0  D I V / R I

V RD

'





 

V 1  '  Vg D

1 



  1   

R D' R L



2

         

This is the desired solution for the converter output voltage V.





 

V 1  '  Vg D

1 



  1   

R ' D R L

2



         

1 ' D

The first term

is the ideal conversion ratio, with R 

The second term 

1  





  1  

L

D R

<

However as

2

R

R D' R L

2





R

         

Describes the effect of the inductor winding resistance

the conversion ratio is equal to the ideal value

is increased, in relation to D ' R 2

L

V Vg

in value, and Decreasing the . R

L

0





'

L

The second term is reduced

is reduced as well. At D=1, the converter η =0 increases

V Vg

1 ' D

but results in large inductance

Construction of equivalent circuit model

Obtained by refining the dc transformer model, to account for converter losses. This allows us to determine the converter voltages, currents,and η using techniques of circuit analysis.

Inclusion of Semiconductor conduction lossess in the converter model

v

L

(t )  Vg  i R L  i R on  Vg  I R L  I R on

i

C

(t )  

i v

L

C

v V  R R

(t )  i 

v V I R R

(t )  Vg  i R L V D  i R D  v  Vg  I R L 

Inductor voltage and capacitor current waveforms for the converter

v

L

(t )

Vg  I R L  I R on

Vg  I R L  I R D V D

I

i

C

t

V R

(t )

t 

V R

The dc component of the inductor voltage is given by D  Vg  I R L  I R on   D '  Vg  I R L  I R D V D   0

By collecting terms and noting that D+D’=1, we obtain Vg  I R L  ID R on  D 'V D  I D ' R D  D 'V  0

This equation describes the dc components of the voltages around a loop containing the inductor , with loop current equal to the dc inductor current I. IR ID R ID'R I D 'V L

on

D

D

+ Vg

-

I

-

+

-

+

-

+

+

-

D 'V

The dc component of the capacitor current is i

C

V  V  (t )  D    D '  I    0 R  R 

Upon collecting terms,one obtains, D'I 

V 0 R

R ++ D’I

V _

V/R

I D ' RD

D 'V D

+ -

I

-

+

-

+

-

+

+

-

++ D 'V

V _