Chapter 4: Switch realization

Transcription

1 Chapter 4. Swtch Realzat 4.. Swtch applcats Sngle-, two-, and four-quadrant swtches. Synchrous rectfers 4.2. A bref surey of power semcductor deces Power dodes, MOSFETs, BJTs, IGBTs, and thyrstors 4.3. Swtchng loss Transstor swtchng wth clamped nducte load. Dode recoered charge. Stray capactances and nductances, and rngng. Effcency s. swtchng frequency Summary of key pts

2 SPST (sngle-pole sngle-throw) swtches SPST swtch, wth oltage and current polartes defned V g wth SPDT swtch: 2 Buck certer L L (t) C R V All power semcductor deces funct as SPST swtches. wth two SPST swtches: A A A V B g B B L L (t) C R V 2

3 Realzat of SPDT swtch usng two SPST swtches A ntral step: two SPST swtches are not exactly equalent to e SPDT swtch It s possble for both SPST swtches to be smultaneously ON or OFF Behaor of certer s then sgnfcantly modfed dsctnuous cduct modes (ch. 5) Cductng state of SPST swtch may depend appled oltage or current for example: dode 3

4 Quadrants of SPST swtch operat swtch -state current A sngle-quadrant swtch example: ON-state: > OFF-state: > swtch -state oltage 4

5 Some basc swtch applcats Snglequadrant swtch swtch -state current swtch -state oltage Currentbdrectal two-quadrant swtch swtch -state current swtch -state oltage swtch -state current swtch -state current Voltagebdrectal two-quadrant swtch swtch -state oltage Fourquadrant swtch swtch -state oltage 5

6 4... Sngle-quadrant swtches Acte swtch: Swtch state s ctrolled exclusely by a thrd termnal (ctrol termnal). Passe swtch: Swtch state s ctrolled by the appled current and/or oltage at termnals and 2. SCR: A specal case turn- transt s acte, whle turn- transt s passe. Sngle-quadrant swtch: -state (t) and -state (t) are unpolar. 6

7 The dode Symbol nstantaneous - characterstc A passe swtch Sngle-quadrant swtch: can cduct poste state current can block negate state oltage proded that the ntended -state and -state operatng pts le the dode - characterstc, then swtch can be realzed usng a dode 7

8 The Bpolar Junct Transstor (BJT) and the Insulated Gate Bpolar Transstor (IGBT) BJT C IGBT C nstantaneous - characterstc An acte swtch, ctrolled by termnal C Sngle-quadrant swtch: can cduct poste state current can block poste -state oltage proded that the ntended -state and -state operatng pts le the transstor - characterstc, then swtch can be realzed usng a BJT or IGBT 8

9 The Metal-Oxde Semcductor Feld Effect Transstor (MOSFET) C Symbol 9 (reerse cduct) nstantaneous - characterstc An acte swtch, ctrolled by termnal C Normally operated as snglequadrant swtch: can cduct poste -state current (can also cduct negate current n some crcumstances) can block poste -state oltage proded that the ntended state and -state operatng pts le the MOSFET - characterstc, then swtch can be realzed usng a MOSFET

10 Realzat of swtch usng transstors and dodes Buck certer example V g A A A B B B L L (t) C R V Swtch A: transstor Swtch B: dode SPST swtch operatng pts A swtch A L swtch A swtch B B swtch B L V g A V g B Swtch A Swtch B

11 Realzat of buck certer usng sngle-quadrant swtches V g A A B L L (t) L (t) B A B swtch A L swtch B L swtch A swtch B V g A V g B

12 4..2. Current-bdrectal two-quadrant swtches C BJT / ant-parallel dode realzat (transstor cducts) (dode cducts) nstantaneous - characterstc Usually an acte swtch, ctrolled by termnal C Normally operated as twoquadrant swtch: can cduct poste or negate -state current can block poste -state oltage proded that the ntended state and -state operatng pts le the composte - characterstc, then swtch can be realzed as shown 2

13 Two quadrant swtches (transstor cducts) (dode cducts) swtch -state current swtch -state oltage 3

14 MOSFET body dode (transstor cducts) C (dode cducts) Power MOSFET characterstcs Power MOSFET, and ts ntegral body dode 4 Use of external dodes to preent cduct of body dode

15 A smple nerter A Q V g D A (t) = (2D ) V g L L V g D 2 C R Q 2 B B 5

16 Inerter: snusodal modulat of D (t) = (2D ) V g Snusodal modulat to produce ac output: V g D(t) =.5 D m sn (ωt).5 D The resultng nductor current arat s also snusodal: V g L (t) = (t) R = (2D ) V g R 6 Hence, current-bdrectal two-quadrant swtches are requred.

17 The dc-3øac oltage source nerter (VSI) a V g b c Swtches must block dc nput oltage, and cduct ac load current. 7

18 Bdrectal battery charger/dscharger D L bus Q spacecraft man power bus Q 2 D 2 batt bus > batt A dc-dc certer wth bdrectal power flow. 8

19 4..3. Voltage-bdrectal two-quadrant swtches C BJT / seres dode realzat (dode blocks oltage) (transstor blocks oltage) nstantaneous - characterstc 9 Usually an acte swtch, ctrolled by termnal C Normally operated as twoquadrant swtch: can cduct poste -state current can block poste or negate -state oltage proded that the ntended state and -state operatng pts le the composte - characterstc, then swtch can be realzed as shown The SCR s such a dece, wthout ctrolled turn-

20 Two-quadrant swtches swtch -state current (dode blocks oltage) (transstor blocks oltage) swtch -state oltage C 2

21 A dc-3øac buck-boost nerter V g L ab (t) bc (t) φ a φ b φ c Requres oltage-bdrectal two-quadrant swtches. Another example: boost-type nerter, or current-source nerter (CSI). 2

22 4..4. Four-quadrant swtches swtch -state current swtch -state oltage Usually an acte swtch, ctrolled by termnal C can cduct poste or negate -state current can block poste or negate -state oltage 22

23 Three ways to realze a four-quadrant swtch 23

24 A 3øac-3øac matrx certer 3øac nput 3øac output a an (t) bn (t) b cn (t) c All oltages and currents are ac; hence, four-quadrant swtches are requred. Requres nne four-quadrant swtches 24

25 4..5. Synchrous rectfers Replacement of dode wth a backwards-cnected MOSFET, to obtan reduced cduct loss C (reerse cduct) deal swtch cental dode rectfer MOSFET as synchrous rectfer nstantaneous - characterstc 25

26 Buck certer wth synchrous rectfer V g A Q A C C Q 2 B B L L (t) MOSFET Q 2 s ctrolled to turn when dode would normally cduct Semcductor cduct loss can be made arbtrarly small, by reduct of MOSFET resstances Useful n lowoltage hgh-current applcats 26