POWER ELECTRONICS POWER ELECTRONICS INTRODUCTION TO. Dr. Adel Gastli. CONTENTS

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1 POWER ELECTRONICS INTRODUCTION TO POWER ELECTRONICS Dr. Adel Gastli CONTENTS 1. Definitions and History 2. Applications of Power Electronics 3. Power Semiconductor Devices 4. Control characteristics of power devices 5. Characteristics & specifications of switches 6. Design of power electronics equipment 7. Rms values of waveforms 8. Types of power electronic circuits 9. Peripheral effects 10. Power modules 11. Intelligent modules 12. Journals & References Dr. Adel Gastli Power Electronics: Introduction 2

2 DEFINITION & HISTORY Power electronics refers to control and conversion of electrical power by power semiconductor devices wherein these devices operate as switches. Advent of Silicon-Controlled Rectifiers, abbreviated as SCRs, led to the development of a new area of application called the Power Electronics. Dr. Adel Gastli Power Electronics: Introduction 3 Prior to the introduction of SCRs, mercuryarc rectifiers (1900) were used for controlling electrical power, but such rectifier circuits were part of industrial electronics and the scope for applications of mercury-arc rectifiers was limited. Once the SCRs were available (1957), the application area spread to many fields such as drives, power supplies, aviation electronics, high frequency inverters and power electronics originated. Dr. Adel Gastli Power Electronics: Introduction 4

3 APPLICATIONS OF POWER ELECTRONICS Power electronics has applications that span the whole field of electrical power systems, with the power range of these applications extending from a few VA/Watts to several MVA/MW. The main task of power electronics is to control and convert electrical power from one form to another form. Dr. Adel Gastli Power Electronics: Introduction 5 Power electronics is a subject of interdisciplinary nature. Power Control Analog Digital Electronics Devices Circuits Electronics Power Equipment Static Rotating Dr. Adel Gastli Power Electronics: Introduction 6

4 Some Applications of Power Electronics Adverting Air conditioning Aircraft power supplies Alarms Household Appliances Battery charger Chemical processing Computers Cranes, hoists, elevators Dimmers Displays Electric door openers Electric dryers, fans Electric vehicles & traction Electromagnets Gas turbine starting Generator exciters High voltage dc (HVDC) Motor drives Movie projector Oil well drilling Paper mills Photograph, photocopy machines TV, Radio, VCR Solar power supplies, etc Dr. Adel Gastli Power Electronics: Introduction 7 POWER SEMICONDUCTOR DEVICES Since the first thyristor (SCR) was developed in late 1957, there has been tremendous advances in the power semiconductor devices. Since 1970 various types of power semiconductor devices were developed and became commercially available. Dr. Adel Gastli Power Electronics: Introduction 8

5 Dr. Adel Gastli Power Electronics: Introduction 9 Power semiconductor devices are made of either silicon or silicon carbide. These devices can be divided broadly into three main types: Power diodes Thyristors Transistors Dr. Adel Gastli Power Electronics: Introduction 10

6 Classification of power semiconductors Dr. Adel Gastli Power Electronics: Introduction 11 Power Diodes General purpose Rating up to 6000V, 4500A High speed (or fast recovery) Rating up to 6000V, 1100A Reverse recovery time 0.1 to 5μs Essential for high-frequency switching Dr. Adel Gastli Power Electronics: Introduction 12

Power Diodes (cont.) Schottky Low on-state voltage Very small recover time (typically nanoseconds). Leakage current increases with voltage rating Rating limited to 100V, 300A Dr.

7 Power Diodes (cont.) Schottky Low on-state voltage Very small recover time (typically nanoseconds). Leakage current increases with voltage rating Rating limited to 100V, 300A Dr. Adel Gastli Power Electronics: Introduction 13 Power Diodes (cont.) Anode Cathode 2 terminals Conducts when its anode voltage is higher then that of the cathode (V A > V C ) Forward voltage drop (when on) is very low (typically 0.5 and 1.2V) If V C > V A the diode is said to be in blocking mode. Dr. Adel Gastli Power Electronics: Introduction 14

8 Stud-mounted type Disk, press pak, or hokey puck type Dr. Adel Gastli Power Electronics: Introduction 15 Thyristors Anode Gate Cathode 3 terminals When a small current is passed through the gate terminal to cathode, the thyristor conducts provided that the anode terminal is at higher potential than that of the cathode: i G >0 V A > V C Dr. Adel Gastli Power Electronics: Introduction 16

9 Thyristors (Cont.) Once a Thyristor is in a conduction mode, the gate circuit has no control and the thyristor continues to conduct. In conduction mode, forward voltage is very small (0.5 to 2 V). Thyristor can be turned off by making V AC 0V Line-commutated thyristors are turned off due to the sinusoidal nature of their input voltage Forced-commutated thyristors are turned off by an extra circuit called commutation circuitry. Dr. Adel Gastli Power Electronics: Introduction 17 Thyristors (Cont.) Natural or line-commutated thyristors are available with rating up to 6000 V, 4500A. Turn-off-time became very small (10 to 20 μs in 3000 V, 3600A). t i=0 Turn-off-time t VAC 0 Instant when the principle current has decreased to zero after external switching of the principle voltage circuit Instant when thyristor is capable of supporting a specified voltage without turning on. Dr. Adel Gastli Power Electronics: Introduction 18

10 Thyristors (Cont.) Can be subdivided into 11 types: 1. Forced-commutated 2. Line-commutated 3. Gate-Turn-Off (GTO) 4. Reverse Conducting Thyristor (RCT) 5. Static Induction Thyristor (SITH) 6. Gate-Assisted turn off Thyristor (GATT) 7. Light-activated Silicon-Controlled Rectifier (LASCR) 8. MOS Turn-Off (MTO) 9. Emitter Turn-Off (ETO) 10. Integrated Gate- Commutated Thyristor (IGCT) 11.MOS Controlled Thyristors (MCTs) Dr. Adel Gastli Power Electronics: Introduction 19 Self-Study Study (Outcome i: a recognition of the need for, and an ability to engage in life-long long learning) Page 8: main characteristics and applications of different types of thyristors. Dr. Adel Gastli Power Electronics: Introduction 20

11 Power Transistors There are 4 types: Bipolar Junction Transistors (BJTs) Power MOSFETS Insulated-Gate Bipolar Transistors (IGBTs) Static Induction Transistors (SITs) Dr. Adel Gastli Power Electronics: Introduction 21 Power Transistors (Cont.) Bipolar Junction Transistors (BJTs) NPN-BJT B I B C E I C I E I C 0 I B1 saturation I B2 I Bn I Bn > I B1 Used in power converters at frequency below 10 khz Power ratings up to 1200V, 400A. V BE > 0, I B >I TH conduction (on) mode V BE < 0, I B <I TH nonconduction (off) mode V CE Operates like a switch (on-off) Dr. Adel Gastli Power Electronics: Introduction 22

12 Power Transistors (Cont.) Power MOSFETs N-channel G D I D I D V GS1 > V GSn V GSn V GS0 S 0 Used in high-speed power converters at frequency range of several tens of khz. Power ratings up to 1000V, 100A (relatively low power ratings). V DS Dr. Adel Gastli Power Electronics: Introduction 23 Power Transistors (Cont.) IGBTs C I C I C G V GE1 V GEn V GEn > V GE1 V T E I E 0 Voltage controlled power transistors (better drive circuit) faster than BJTs but slower than MOSFETs. Used in power converters at frequency up to 20 khz Power ratings up to 1700V, 2400A (high voltage high current). V CE Dr. Adel Gastli Power Electronics: Introduction 24

13 Power Transistors (Cont.) SITs G D S I D I S I D 0 V GSn V GS1 =0V V GSn > V GS1 Used in high-power high frequency applications (audio, VHF/UHF, and microwave amplifiers) Power ratings up to 1200V, 300A. Has low-noise, low-distortion, high-audio-frequency power capability. Very short turn-on and turn-off times (typically 0.25μs) On-characteristic and high on-state drop limit its applications for general power conversions. V DS Dr. Adel Gastli Power Electronics: Introduction 25 Power ranges of commercially available power semiconductor devices V [V] SCR (Market) 6500V/600A (Eupec) 12000V/1500A (Mitsubishi) 7500V/1650A (Eupec) 6500V/2650A (ABB) 5500V/2300A (ABB) IGBT (Market) IGCT (Market) GTO (Market) 6000V/6000A GTO (Mitsubishi) 6000V/6000A IGCT (Mitsubishi announced) V/100A (SanRex) Power MOSFET (Market) 4800V/5000A (Westcode) 4500V/4000A (Mitsubishi) V/1000A (Semikron) I [A] Dr. Adel Gastli Power Electronics: Introduction 26

14 Dr. Adel Gastli Power Electronics: Introduction 27 CONTROL CHARACTERISTICS OF POWER DEVICES Thyristor switch 1 v G Gate signal v G 0 Input voltage V s _ Thyristor R Output voltage v 0 _ -1 V s v 0 First pulse turns it on and stays always on Dr. Adel Gastli Power Electronics: Introduction 28

15 GTO/MTO/ETO/IGCT/MCT/SITH switch SITH Input voltage V s _ A A A _ v G K K GTO R K G MCT Polarity of v G is reversed for MCT Output voltage v 0 _ v G v 0 V s t 1 T t Positive pulse turns them on and negative pulse turns them off Dr. Adel Gastli Power Electronics: Introduction 29 BJT/MOSFET/IGBT switch Input voltage V s _ v B R Output voltage v 0 _ 1 v B /v GS C E 0 t 1 T t G D Input voltage V s _ v GS S R Output voltage v 0 _ V s v 0 t 1 T t Positive voltage turns them on and zero voltage turns them off Dr. Adel Gastli Power Electronics: Introduction 30

16 Classification 1. Uncontrolled turn on and turn off (e.g. diode) 2. Controlled turn on and uncontrolled turn off (e.g. SCR) 3. Controlled turn on and off (e.g. BJT, MOSFET, IGBT, GTO, SITH, SIT, MCT) 4. Continuous gate signal requirement (e.g. BJT, MOSFET, IGBT, SIT) 5. Pulse gate requirement (e.g. SCR, GTO,MCT) 6. Bipolar voltage-withstanding capability (e.g. SCR, GTO) 7. Unipolar voltage-withstanding capability (e.g. BJT, MOSFET,GTO, IGBT, MCT) 8. Bidirectional current capability (e.g. TRIAC, RCT) 9. Unidirectional current capability (e.g. SCR, GTO, BJT, MOSFET, MCT,IGBT, SITH, SIT, Diode) (See Table 1.4 page 15 of the textbook) Dr. Adel Gastli Power Electronics: Introduction 31 CHARACTERISTICS & SPECIFICATIONS OF SWITCHES Ideal Switch On state: carry high forward current, I F = Low forward voltage drop, V ON =0 low on-state resistance, R ON =0 Off state: High forward or reverse voltage, V BR = Low off-state leak current, I OFF =0 High off-state resistance, R OFF = (low off-state power losses) Requires very low thermal impedance from internal junction to ambient, R JA =0, so that it transmits heat easily to the ambient Must have high i 2 t, to sustain any fault current for a long time. Turn-on & turn-off processes: Controllable Must turn on with gate signal (e.g. positive) Must turn off with another gate signal (e.g. zero or negative) Instantaneous (high frequency) Low delay time, t d =0 Low rise time, t r =0 Low storage time, t s =0 Low fall time, t f =0 Low gate-drive power, P G =0 Low gate-drive voltage, V G =0 Low gate-drive current, I G =0 Device must be capable of handling rapid voltage changes across it, dv/dt= Device must be capable of handling rapid current changes across it, di/dt= Dr. Adel Gastli Power Electronics: Introduction 32

17 Practical Devices v SW V CC R L V CC V SW(sat) I SWs i SW t on t off t I G _ VG i SW V SW _ Controlled switch I SW0 i G I G(sat) v G t d t r t n t s t f t 0 T s =1/f s t t P P P ON SW D 1 = T s tr ts s pdt pdt 0 0 = f = P P ON t 0 ON pdt SW P G t 0 f V G(sat) pdt P SW Switching power losses t t Conduction Switching Gate-driver power losses power losses power Dr. Adel Gastli Power Electronics: Introduction 33 Switch Specifications Voltage ratings Forward & reverse repetitive peak voltages On-state forward drop-voltage drop Current ratings Average, rms, repetitive peak, nonrepetitive peak, off-state leakage Switching speed or frequency di/dt dv/dt Switching losses Gate drive requirements Safe operating area (SOA): limits on the allowable steady-state operating points in the v-i coordinates I 2 t for fusing Temperatures Thermal resistance Dr. Adel Gastli Power Electronics: Introduction 34

18 Device Choices Non of the existing switching devices is ideal. For high power applications from the ac 50-60Hz main supply, phase control and bidirectional thyristors are the most economical choices. COOLMOS and IGBTs are potential replacements for MOSFETS and BJTs, respectively, in low and medium power applications. Dr. Adel Gastli Power Electronics: Introduction 35 Device Choices (cont.) GTOs and IGCTs are most suited for high-power applications requiring forced commutation. With the increased advances in technology, IGBTs are increasingly employed in high-power applications and MCTs may find potential applications that require bidirectional blocking voltages. Dr. Adel Gastli Power Electronics: Introduction 36

19 DESIGN OF POWER ELECTRONICS EQUIPMENT 1. Design of power circuits 2. Protection of power devices 3. Determination of control strategy 4. Design of logic and gating circuits Dr. Adel Gastli Power Electronics: Introduction 37 In this course, power devices are assumed ideal switches unless stated otherwise. Effect of stray inductance, circuit resistances, and source inductance are usually neglected. Before prototype is built, the designer should investigate the effects of the circuit parameters and device imperfections. The design should be modified if necessary. Only after the prototype is built and tested, the designer can be confident about the validity of the design proposed and can estimate more accurately some circuit parameters (e.g. stray inductance). Dr. Adel Gastli Power Electronics: Introduction 38

20 RMS VALUES OF WAVEFORMS rms values of current waveforms must be known: To accurately determine losses in a device To accurately determine current ratings of the device and components Current waveforms are rarely sinusoids or rectangles Dr. Adel Gastli Power Electronics: Introduction 39 I rms = 1 T T 0 i 2 dt See page 25 (Fig. 1.17) for some rms values of commonly encountered waveforms Time period If a waveform can be broken into harmonics whose rms values can be calculated individually, the rms value of the actual waveform can be approximated satisfactory as: I = I I I L rms 2 dc 2 rms(1) 2 rms(2) I 2 rms( n) dc component Harmonics rms values Dr. Adel Gastli Power Electronics: Introduction 40

21 Problems Solving: Find the average and rms values of the following waveforms. 100V v o 100V v o 8ms 20ms t 0 π 2π ωt 100V v o 100V v o 0 π 2π ωt 0 π/2 π 2π ωt Dr. Adel Gastli Power Electronics: Introduction 41 TYPES OF POWER ELECTRONIC CIRCUITS Diode rectifiers Ac-dc converters (controlled rectifiers) Ac-ac converters (ac voltage controllers) Dc-dc converters (dc choppers) Dc-ac converters (inverters) Static switches (ac or dc) Dr. Adel Gastli Power Electronics: Introduction 42

22 v i ac supply Diode rectifiers Converts ac into a fixed dc voltage. Input could be either single phase or three phase Diode D 1 vs = Vm sinωt _ Load resistance R v o v _ s Diode D 2 V m v s sinωt Dr. Adel Gastli Power Electronics: Introduction 43 v s = V 0 π 2π v o V m 0 π 2π Find the expressions of average and rms values. m ωt ωt v i ac supply Ac-dc converters Converts ac into a variable dc voltage. Input could be either single phase or three phase Thyristor T 1 vs = Vm sinωt _ Load resistance R v o v _ s Thyristor T 2 V m v s Dr. Adel Gastli Power Electronics: Introduction 44 v o v s = V m sinωt 0 π 2π α -V m V m 0 α π 2π Find the expressions of average and rms values as a function of α. ωt ωt

23 Ac-ac converters Converts fixed ac into a variable ac voltage. Input could be either single phase or three phase Triac vs = Vm sinωt ac supply v o Load resistance R V m v s v s = V m sinωt 0 π 2π -V m Vm v o α 0 α π 2π ωt ωt Find the expressions of average and rms values as a function of α. Dr. Adel Gastli Power Electronics: Introduction 45 Dc-dc converters (Choppers) Converts fixed dc into a variable dc voltage. v s _ V GE dc supply δ = t 1 T Transistor Q 1 v o Duty cycle Load v s 1 0 t 1 Τ v V o s ωt V 0 =δv s ωt Dr. Adel Gastli Power Electronics: Introduction 46

24 Dc-ac converters (Inverters) Converts fixed dc into a variable ac voltage. Output can be single phase or three phase 1 v g1, v g2 v s dc supply M 1 M 3 G v g1 _ Load _ v o v g3 M 4 M 2 G _ G G 0 v T/2 T g3, v g4 v o v s ωt ωt -v s ωt Dr. Adel Gastli Power Electronics: Introduction 47 Static switches Power electronic devices can operate as static switches or contactors to transmit either ac or dc power to loads. Example: Uninterruptible Power Supply (UPS) Mains 1 ac supply Load Mains 2 Rectifier/charger Inverter Isolation transformer Static bypass switch Battery Dr. Adel Gastli Power Electronics: Introduction 48

25 PERIPHERIAL EFFECTS (Effects of Power Converters) Problems: Introduce current and voltage harmonics into the supply system and on converters output. Distortion of the output voltage. Harmonic generation into supply system Interference with communication and signaling circuits Dr. Adel Gastli Power Electronics: Introduction 49 Solutions: It is normally necessary to introduce filters in the input and output of a converter system to reduce the harmonic level to an acceptable magnitude. Power Source Input filter Power converter Output filter Output Switching control signal generator Dr. Adel Gastli Power Electronics: Introduction 50

26 Power quality issues Application of power electronics poses a challenge on the power quality issues and raises problems and concerns to be resolved by researchers. Important factors that measure the quality of a waveform are: Total harmonic distortion (THD) Displacement Factor (DF) Input power factor (IPF) Harmonic content of the waveforms is required to find these factors. Dr. Adel Gastli Power Electronics: Introduction 51 To evaluate the performance of a converter, the input and output voltages and currents of a converter are expressed in a Fourier series. The control strategy of a power converter play an important part on the harmonic generation and output waveform distortion, and can be aimed to minimize or reduce these problems. Electromagnetic radiation and interference can be avoided by grounded shielding. Dr. Adel Gastli Power Electronics: Introduction 52

POWER MODULES Power devices are available as a single unit or a module. A power converter often requires two, four, or six devices, depending on its topology.

27 POWER MODULES Power devices are available as a single unit or a module. A power converter often requires two, four, or six devices, depending on its topology. Power modules with dual (in half-bridge configuration), or quad (in full bridge) or six (in three phase) are available for almost all types of power devices. Dr. Adel Gastli Power Electronics: Introduction 53 Modules offer the advantages of lower on-state losses, high voltage and current switching characteristics, high speed (switching frequency) Some modules include transient protection and gate drive circuitry. Gate drive circuits are commercially available to drive individual devices or modules. Dr. Adel Gastli Power Electronics: Introduction 54

28 INTELLIGENT MODULES Intelligent modules, which are the state of the art of power electronics, integrate the power module and the peripheral circuit. Peripheral circuits consists of: Input or output isolation from, and interface with, the signal and high-voltage system, A drive circuit Protection and diagnostic circuit Microcomputer control Control power supply Dr. Adel Gastli Power Electronics: Introduction 55 Users need only to connect external (floating) power supplies. An intelligent module is also known as smart power. Smart power technology can be viewed as a box that interfaces power source to any load. These modules are used increasingly in power electronics. Page 28: list of websites of some manufacturers of these modules Dr. Adel Gastli Power Electronics: Introduction 56

29 JOURNAL & REFERENCES See section 1.11 in your textbook at page 28. Search the internet for more recent sites (keywords: power electronics, tutorials, circuits, devices, ) Dr. Adel Gastli Power Electronics: Introduction 57

ELG4139: Power Electronics Systems Objective To Realize and Design Various Power Supplies and Motor Drives!

ELG4139: Power Electronics Systems Objective To Realize and Design Various Power Supplies and Motor Drives! Power electronics refers to control and conversion of electrical power by power semiconductor