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MIT OpenCourseWarehttp://ocw.mit.edu
6.334 Power Electronicsprin! "##$
%or in&ormation a'out citin! these materials or our Terms
o& (se) *isit: http://ocw.mit.edu/terms .
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Chapter 1 Introduction and Analysis
Methods
1.1 Switching Power Electronics
Read Chapter 1 of Principles of Power Electronics !S"# $y %.
&. !assa'ian(M.
). Schlecht( and &. C. "erghese( Addison*+esley( 1,,1.
-inear Regulator
io
+ Vx
+ + Vin
Vo
)igure 1.1 -inear Regulator
Control /0 such that "o "o(RE) Si2ple( accurate( high*$andwidth(
$ut 13
C4AP5ER 1. I65R789C5I76 A68 A6A-:SIS
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Pdiss ;/0io Pin "oio
"inio "o
1.3#"in
? "in 1@/( "o@/> B 1.#
)or eDciency we will consider switching power con/erters
q(t) + VoVin 0 1 q(t) + DT T v(t) = dVin
)igure 1.3 Considering Switching Power Con/ertor
Add ltering
675E 7nly lossless ele2ents. -( C energy storage#.
9se se2iconductors as switches. Switches Floc' "( carry I( $ut
675 at the
sa2e ti2eG
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1.3. A6A-:SIS 5EC46IH9ES
+ + +
+Vin
Vo Vx
v(t)
Vx ~ dVin
+ + Vin
Vo
)igure 1. Add )iltering
1.3 Analysis 5echniues
1.3.1 Methods of Assu2ed States
Se2iconductor switches are typically not fully controlla$le.
-etJs consider how
to analyKe a switching circuit in ti2e do2ain
Si2ple Rectier
E0a2ple tri/ial $ut funda2ental#
Vd
+
id+
Vo
VsSin(t)
)igure 1.L Si2ple Rectier 8iodes 9ncontrolled
Cannot sustain positi/e /oltage will turn on#L C4AP5ER 1.
I65R789C5I76 A68 A6A-:SIS
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Cannot sustain negati/e Current will turn oN# id Vd
)igure 1.@ 8iode
5he 2ethod of assu2ed states allows us to gure out which
unOse2i*
controlled switches are on as a function of ti2e.
1. Assu2e a state onOoN# for all unOse2i*controlled
switches.
3. Calculate /oltages and currents in the syste2 linear circuit
theory#.
. See if any switch conditions are /iolated e.g.( on diode has
negati/ecurrent and oN diode has positi/e /oltage.#
L. If no /iolations( then done( else if /iolation assu2e a new
set of states go$ac' to step 1.
Vd
+
id+
Vo
VsSin(t)
)igure 1. Si2ple Rectier1.3. A6A-:SIS 5EC46IH9ES @ If "s
sinQt#< = and we assu2e diode oN
/d < =( since this is notpossi$le
diode 2ust $e on during this condition.
If "s sinQt# ; = and we assu2e diodeon
id ; =( since this is notpossi$le
diode 2ust $e oN during this condition.
"s sinQt# < = diode on
