20304726 Power Electronics Chapter 1

Overview to Power Power Electronics Electronics

Mohd Mo hd Sh Shaw awal al Bi Bin n Jad Jadin in Ext : 2321 A01-2074 [email protected]

Learning Outcom Outcomes es  At the end of the lecture, student should be able to:  ± Identify the function of electronics switches,, hence to select a proper switches swi wittch chin ing g for ce cert rtai ain n ap appl plic ica ati tion onss.  ± Outline the principles of energy recovery and also to calculate the power for nonsinus si nusoi oida dall per perio iodi dicc wave veffor orm m

Chapter 1    

Definition of Power Electronics Multidisciplinary Multidisciplinary Nature of  the Field Block Diagrams of Power Electronic Systems The Need for Power Electronics



Future Trends



Types of Power Conversion



Electronic Electronic Switch



Switch Selection



Energy Recovery

y1

x1 x2

Power Electronic "Power" Circuit

y2 yn

xm Electrical Inputs "Sources"

f 1

f 2

f k 

Feedback  "Control Circuit"

(input) Source Side

Load1 Load2

Loadn

Electrical or  Mechanical Output "Loads"

(output) Load Side

Power  Processing circuit (Ploss )

Load

What is Power Electronics? 

Generally:  ± Electronics: Solid State Electronics Devices and their Driving Circuits. Dynami c Requirements for for Generation,  ± Power: Static and Dynamic Conversion and Transmission of Power.

 ± Control: The Steady State and Dynamic Stability of the Closed Loop system.

 POWER ELECTRONICS may be defined as the application of Solid State Electronics for the Control and an d conversion of Power Power..

Definition of Power Electronics  DEFINITION: To convert, i.e to  process and control the flow of  electric power by supplying voltages and currents in a form that is optimally suited for user loads.

Power Electronics (PE) Systems  To convert electrical energy from one form to another, i.e. from t he source to load with:  highest efficiency,  highest availability  highest reliability  lowest cost,  smallest size  least weight

Detailed Block Diagram of Power

Electronics System o er proc. stage

re-stage Input

Filter 

Form o

& Recti y

ost stage

utput

Filter 

ircuit

electrical energy

ostly unregulate d dc voltage

& Recti y

mechan. energy lectrical echanical

oad

ould generate undesirable ave orms       h     s     c     e      t     v       i       i     r      D

ostly ac line voltage (single or three phase)

Form o elec. or 

ontrol ircuit

lectrical Variable Feedback  echanical Variable Feedback 

Inter ace bet een control and po er  circuits

rocess eedback  signals and decide on control

Applications  Static applications  ± involves non-rotating or moving mechanical components.  ± Examples:  DC Power supply  Un-interruptible power supply, Power generation and transmission  (HVDC), Electroplating, Welding, Heating,  Cooling, Electronic ballast

Applications  Drive applications  ± intimately contains moving or rotating components such as motors.  ± Examples:  Electric trains, Electric vehicles, Air-conditioning System, Pumps, Compressor,  Conveyer Belt (Factory automation).

Application examples  Static Application: DC Power Supply

Application examples  Drive Application: Air-Conditioning System

Other Applications

Electroplating, Welding

Photovoltaic Systems.

Heating, cooling, CFL

eV (fuel cell, Solar)

Wind--electric systems. Wind

Conversion concept: 

Supply from TNB: 50Hz, 240V RMS (340V peak). Customer need DC voltage for welding purpose, say.



TNB i iv z m



W

 El

-

v DC !

Av i

, MD Z i

ly

im l h lfifi . A fix DC i b i . im l E y m.

v v l Thi i

1

example 1

v l l

l m, UTM

Conversion



concept: example ( Cont)1

How about if customer wants variable DC voltage?

 ± More complex circuit using SCR is required.

Av



1

By f El

i

, MD Z i

lli v l

l m, UTM

h fi i i

l , , h b v i .

V l

DC v l

Advantages of  of Power Electronics 

High energy conversion efficiency  ± Instead of using 50/60Hz motor-generator



Higher Reliability and cost effective  ± Less maintenance, longer lifetime, light and small size, fast recovery time, unlimited range of conversion



Environmentally clean and safe  ± produce no hazardous waste products  ± Burning of fossil fuel emits gases such as C,0,, CO (oil burning), S02, NOx (coal burning) etc. Creates global warming (green house effect), acid raill and urban pollution h-oll)



Q uite operation

 ± has no moving parts, suitable for residential, hotels etc 

reduce dependence on fossil fuel (coal, natural gas, oil) and nuclear power resource (uranium).  ±



Effort to tap renewable energy resources such as solar, wind, fuel-cell etc. need to be increased.

Special effort is needed to reduce pollution in cities by enforcing t he use of electric vehicle.

PE growth  PE rapid growth due to:  ± Advances in power (semiconductor) switches 

  Advances in microelectronics (DSP, VLSI, microprocessor / microcontroller, ASIC)   New ideas in control algorithms   Demand for new applications

PE is an interdisciplinary field:  ±  Digital/analogue electronics  ±  Power and energy   ±  Microelectronics  ±  Control system  ±  Computer, simulation and software  ±   Solid Solid--state physics and devices  ±  Packaging  ±  Heat transfer

Power Electronics Converters AC

to DC: RECTIFIER

DC to DC: CHOPPER

DC to AC: INVERTER

AC

to AC: CYCLOCONVERTER

Power semiconductor devices (Power switches) C

b

i

i

h

 ± Uncontrolled: Diode  ± Semi-controlled: Thyristor (SCR)  ± Fully controlled: Power transistors e.g. BJT,MO FET, IGBT, GTO, IGCT

:

Photos of Power Switc hes (From Powerex Inc.)

Power Electronics Converters AC

to DC: RECTIFIER

DC to DC: CHOPPER

DC to AC: INVERTER

AC

to AC: CYCLOCONVERTER

The Need For Switching In Power Electronic Circuits 

The need to use semiconductor switching devices in power electronic circuits is based on their ability to control and manipulate very large amounts of power from the input to the output with relatively very low power dissipation in the switching device.

 Implication of low efficiency: 1. The cost of energy increases due to increased consumption. 2. Additional design complications might be imposed, especially regarding the design of device heat sinks

Example Investigate the efficiency of four different power electronic circuits whose function is to take power from a 24 V dc source and deliver a 12 V dc output to a 6; resistive load. load In other words, the task of these circuits is to serve as dc transformers with a ratio of 2 : 1. The four circuits are shown in Fig. 1 (a), (b), (c), and (d) representing a voltage divider circuit, zener regulator (assume IZ is 10% 10% of  of load current), transistor linear regulator, and switching circuit, respectively respectively. [Hint: For circuit (d), Vo=Vin*D]

Example (Cont)

(e) Zener diode i-v switc hing characteristics. (f) Switc hing waveforms for circuit

Example (Cont) Cicuit (a)



: Voltage Divider dc Regulator

 Since Vin=24V and RL=6; and desired Vo=12V. Hence, R = RL=6;.

L

!

 P  out 

Thus, !

%

 P  in  R  R

 L

 L



 P   L

!

%

 R

%

 P  in

6

!

6

6



%

50

!

%

 Cicuit (b) : Zener  Zener dc Regulator  

i = 12V. i A

V =12V, h

, R =6;. Th m

10% f l Th

i

I =2A.

h , IZ = 0.2A

h bl  I  T  ! ! ! ! in

,

out 

L

!

ki

v l

f

z

i

, VZ

  I   z

 I 



2

0 .2

2 . 2  A 2 .2

v 24

! 2 v 12 out  in

%

!

52

. 8 W 

! 24 W  !

24 52

%

.8

! 45 . 5

%

Example (Cont) 

Cicuit (c) : Transistor

dc Regulator

For Vo=12V, it is clear that V CE must be around 12V. Hence, the control circuit must provide base current, I B to put transistor in active mode with V CE=12V. For given Vo=12V and RL=6;, thus IL=2A. =2A Thus, IC = 2A since IB too small in such that to turn on transistor.  P  in  P  diss

@

L

V 

in

 I 

!

V 

CE 

}

V 

!

!

c

CE 

 P  out   P  in

2 ( 24

!

 I   I 

C  C 

%

 } !

V 

 BE 

12 24 48

)

!

 I 

48

W 

!

24

 B

2

v

%

!

50

W  %

Example (Cont)  Cicuit (d) : Switching dc Regulator  A m F m fi V 

 F

V

, v

h

=12V, h V 

 Due

to !

in

T 

L

, v

24 V  ,  P  in

!

V 

in

 P  in

lly

ff.

!

dt 

V 

in

 D

=24 x 0.5 =12V  I   L

!

( assume  P  out 

i

0

D=0.5 V !

i

 D

 s

´

 s

 switching   P  in ,

l by T 

1

!

o , ave

Since

 P  out 

i hi i f , V i iv

%

!

v

V 

!

in

ideal  48 48

%

!

2

v

24

), 100

%

!

48 W 

Ideal Switching Characteristics 1. No limit on the amount of current that the device can carry when in the conduction state (on-state) 2. No limit on the amount of device voltage (known as blocking voltage) when the device is in the nonconduction state (off-state) 3. Zero on-state voltage drop when in the conduction state 4. Zero leakage current when in the nonconduction state 5. No limit on the operating speed of the device when it changes state, i.e., zero rise and fall times

Ideal Switching Characteristics

Power loss

The Practical Switch 

The practical switch has the following switching and conduction characteristics: 1. Limited powerpower-handling capabilities 2. Limited switching speed 3. The existence of forward voltage drop in the on state, and reverse current flow (leakage) in the off state 4. Because of characteristics 2 and 3, the practical switch experiences power losses in the on and off states (known as conduction loss) and during switching transitions (known as switching loss)

Power Diodes

 When diode is forward biased, it conducts current with a small forward voltage (V  f ) across it (0.2-3V)  When reversed (or blocking state), a negligibly small leakage current (uA to mA) flows until the reverse breakdown occurs. Diode should not be operated at reverse voltage greater than V r . Thus, higher voltage blocking is needed.

Power Diode (Reverse Recovery)  When a diode is switched quickly from forward to reverse bias, it continues to conduct due to the mi nor i ty carri  ers which remains in the p-n  junction.  The minority carriers require finite time, i.e, t rr  (reverse recovery time) to recombine with opposite charge and neutralize.  Effects of reverse recovery are increase in switching losses, increase in voltage rating, overvoltage (spikes) in inductive loads

Power Diode (Reverse Recovery)

Types of Power Diodes 

Line frequency (general purpose) purpose) :

 on state voltage very low (below 1V)  large t rr (about 25us)  very high current (up to 5kA) and voltage (5kV) ratings  Used in line-frequency (50/60Hz)  applications such as rectifiers

 Fast recovery  ver y low trr (