Power Electronics Introduction

Transcription

1 Power Elecronics nroducion Y. Baghzouz EE

2 Power Elecronics: an Overview Power elecronics is an inerdisciplinary subjec wihin elecrical engineering. 1-2

3 Power Elecronic Sysem A power elecronic sysem consiss of power elecronic swiching devices, linear circui elemens, digial circuis, microprocessors, elecromagneic devices, DSPs, filers, conrollers, sensors, ec. deal swich: conrols energy flow wih no loss. a) when on, i has zero volage drop and will carry any curren, b) wen off, i blocks he flow of curren regardless of he volage. Desired Feaures: a) 100% efficiency b) 100% reliabiliy 1-3

4 Power Converer Converer is a general erm - an AC/DC converer is shown above. Recifier Mode of operaion when power from AC o DC nverer Mode of operaion when power from DC o AC Power converers can also conver DC-o-DC AC-o-AC Pracical swiching devices are seleced based on heir power handling raing he produc of heir volage and curren raings raher han heir power dissipaion raings. 1-4

5 Types of Semiconducor Swiches 1-5

6 Power Elecronic Applicaions 1-6

7 Example: Fluorescen Lighing The line-frequency AC is convered o DC, hen o high-frequency AC. 1-7

8 Example: Swich-Mode Power Supply Transisor is operaed in swich mode (eiher fully ON or fully OFF) a high swiching frequency. Elecrical isolaion achieved by high-frequency ransformer (smaller, ligher and more efficien) Resul: compac and efficien power supply 1-8

9 Example: Adjusable Speed Drives Convenional drive wases energy across he hroling valve o adjus flow rae. Using power elecronics, moor-pump speed is adjused efficienly o deliver he required flow rae. 1-9

10 AC Moor Drive Converer 1 recifies line-frequency AC ino DC Capacior acs as a filer; sores energy and decouples he wo converers. Converer 2 invers dc o variable frequency AC as needed by he moor. 1-10

11 Pure Elecric and Plug-n Hybrid Vehicles Elecric Drive Sysem: DC-AC Converer Baery Charger: AC-DC converer 1-11

12 Example: Renewable Power Generaion (PV) PV nverer: DC-AC Converer 1-12

13 Example: Renewable Power Generaion (Wind) The recifier-inverer convers variable-frequency AC o fixed line-frequency AC. 1-13

14 Example: HVDC Transmission Because of he large fixed cos necessary o conver ac o dc and hen back o ac, dc ransmission is only pracical in specialized applicaions long disance overhead power ransfer (> 400 miles) long underwaer cable power ransfer (> 25 miles) providing an asynchronous means of joining differen power sysems. 1-14

15 Power elecronic circuis are non-linear. Periodic waveforms bu ofen no sinusoidal analyical expressions in erms of Fourier componens 1-15

16 Fourier Analysis 1-16

17 Example of simple non-sinusoidal periodic signals 1-17

18 1-18 Curren Decomposiion Curren decomposiion of ino fundamenal (i s1 ) and disorion curren (i dis ): ) / arcan(, 2, ) cos( 2 ) sin( ) cos( ) ( ) ( ) ( ) ( ) ( ) ( h h h h h sh h sh h h sh dis s h sh s s a b b a Herein h h b h a i where i i i i i

19 RMS Value and Toal Harmonic Disorion The rms value of a disored waveform is equal o he square-roo of he sum of he square of he rms value of each harmonic componen (including he fundamenal). s s1 sh s1 dis h1 Toal Harmonic Disorion THD(%) 100 dis s s s1 2 s1 1-19

20 Power and Power Facor Average (real) power: P V h h0,1,... sh cos( ) h Apparen Power: S V s s Power facor: PF P S Case of sinusoidal volage and non-sinusoidal curren: P V s s cos( 1 ) 1 1 PF V s1 s 1 cos( 1) V s1 s s1 s cos( ) 1 s1 s DPF 1 1 ( THD) 2 DPF Displacemen Power Facor: DPF cos( 1 ) 1-20

21 Curren-volage in an inducor and capacior n an inducor, he volage is proporional o he rae of change of curren. An inducor canno susain a consan volage for a long ime. n a capacior, he curren is proporional o he rae of change of volage. A capacior canno susain a consan curren for a long ime. 1 L d i v L i v( ) d i( 0 ) d 0 i C d d v v 1 C 0 i d v( 0 ) 1-21

22 nducor response in seady-sae o T 0 v d

23 Capacior response in seady-sae o T 0 i d

24 Swiching Funcion (swich conrol) Swich ON Swich OFF T: period o : ime delay (used in recifiers) f = 1/T : swiching frequency D: duy raio - fracion of ime during which he swich is ON 1-24

25 Example 1: Simple Power Converer Assume he diode is ideal, and le Vac = 170 sin (377), and R = 120 Ω 1. Average value of oupu volage Vou = V 2. Average (DC) curren o = 0.45 A 3. Average (acive) power supplied by source P = 60 W 4. RMS value of curren = A 5. RMS value of fundamenal curren = 0.5 A 6. Phase angle of fundamenal curren = 0 deg 7. RMS Value of disorion curren = 0.5 A 8. Apparen power S = VA 9. Non-acive power = 60 (?) 1-25

26 Assignmen 1: Diode wi RL Load Repea he previous example afer placing and inducor L = 200 mh (use any manual our compuer ool). Verify he values below: 1. Average value of oupu volage Vou = 50 V 2. Average (DC) curren o = A 3. Average (acive) power supplied by source P = W 4. RMS value of curren = A 5. RMS value of fundamenal curren = A 6. Phase angle of fundamenal curren = deg 7. RMS Value of disorion curren = A 8. Apparen power S = VA 9. Non-acive power = (?) 1-26

27 Assignmen 2: Diode wih RC Load Repea he previous example afer placing and capacior C = 150 uf in parallel wih he 120 Ohm resisive load (use any manual our compuer ool). 1. Average value of oupu volage Vou =. V 2. Peak value of capacior curren =.. A 3. Average (acive) power supplied by source P =..W 4. RMS value of source curren =.A 5. RMS value of fundamenal curren (source) =. A 6. Phase angle of fundamenal curren (source) =.. deg 7. RMS Value of disorion curren (source) =..A 8. Apparen power S =..VA 9. Non-acive power = (?) 1-27

28 Obey KCL and KVL closed KVL and KCL place necessary consrains on he operaion of swiches. n he case of volage sources, swiches mus no ac o creae shor-circui pahs among unlike sources. n he case of KCL, swiches mus no aemp o inerconnec unequal curren sources. 1-28

29 High-frequency vs. Low-frequency Transformers Nickel-seel is used (insead of silicon-iron) o reduce core losses a high frequency. Fewer copper winding urns are needed o produce he same flux densiy. An increase in frequency permis a large increase in power capaciy. For he same power capaciy, a high frequency ransformer is much smaller, cheaper, more efficien and ligher han a 60 Hz ransformer. Example: 60 Hz, 120/24 V, 36 VA, B = 1.5 T, core loss = 1 W, N1/N2 = 600/120, weigh = 500 g. 6 khz, 120/24, 480 VA, B = 0.2 T, core loss = 1 W, N1/N2 = 45/9, weigh = 100 g. 1-29