eletronica de potencia ii - pwm
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Pulse-Width-Modulated Inverters
Pulse-Width-Modulation or PWM
Chan in the out ut volta e usin hi h switchin fre uenc
Pulse-Width-Modulated Inverters
V1
t
S1, S2 S3, S4
Several pulses per half cycle.
Switches operate at high frequency.
Voltage harmonics pushed towards higher frequencies
,with two switches.
Higher switching losses
Average value of a pulsed waveform
vVs
0(t)
S
ii
+tTt on t off
0
RVs V0
-Vs0
V0
ss1s1
t
00 kVfVtVT
tdtv
T
1V
1
==== Vsv0(t)
tTt on t off
tk on= tTt on t off
V0
v (t)
s0 VV01k0
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Pulse-Width-Modulated Inverters
- AB sFor k=0.8 VAB=0.6VsFor k=0.2 V =-0.6VS 3
D3S1 D1
A B
is
High frequency operation, small passivecomponents.
D4S2 D2
L Rs
For k=0.5 VAB =0 this means the positivepulses will be equal to the negative ones.
=
S 4
sAB
Pulse-Width-Modulated Inverters
Consider k varying periodicallyz e ween comp emen ary
values of k (0.2 and 0.8).
= =-. , s
If k=0.8 VAB=0,6Vs
lower then the switching frequency(carrying wave), the output voltage will
- , sand 0,6Vs.
Filtering the output voltage, it willresult in a rectangular and periodicwave with the frequency of k.
Pulse-Width-Modulated Inverters
Frequency and magnitude of the output voltage can be controlled. The magnitude is modified through changes in the value of k, according to the relation
(k+ + k-=1). k must change in each half period of the frequency from k+ to k-.
The output voltage with low presence of harmonics, as consequence the filteringrequirement is less.
Pulse-Width-Modulated Inverters
A tenso de sada, que aplicada carga, formadapor uma sucesso de ondas retangulares de amplitude
igual tenso de alimentao CC e durao varivel.
A relao entre a onda moduladora Vm e ondaportadora Vp, definida como ndice de Modulao, permite
inversor.
Na prtica o nmero de pulsos limitado pela mximafreqncia de comutao das chaves.
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Pulse-Width-Modulated Inverters
Impulsiona os harmnicos da tenso de sada para altasreq nc as, conseq en emen e o ro as an e s mp es.
Possibilita controlar a freqncia e o mdulo da tenso
de sada.
Generation of a Sine Wave
+= ABV
10,5k
s
360sin(V += tVD3S1 D1
is
AB
V
V3
L R
A B
s
= s n
V,
sS 4
D42 D2
)1k2(VV sAB =ts nm, ++=
. f = System frequency (50Hz / 60Hz) Carrier frequency 10 x output frequency
[ ])ft360sin(*m10,5k ++=S
is
m chamada de amplitude deVS 3
31
L R
A B
s
.
S 4
D4S2 D2
)1k2(VV sAB =
x .
S1 e S4 operam simultaneamente
S2
e S3
operam simultaneamente
Generation of a Sine Wave - Example
VABmax = 100Vis Output voltage frequency = 83.33Hz Carrier frequency = 1000Hz V = 200VV
S 3
D3S1 D1
A B
s
S1 e S4 operate simultaneously Number of carrier per cycle:
S
D4S2 D2
, = 12 carriers per cycle
AB
V
= s nV
,s
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Generation of a Sine Wave - Example
k0 VAB0=100sin0=0
5,0200
0
10,5k =
+=
k30VAB30=100sin30=50
625,0200
5010,5k =
+=
k60 VAB60=100sin60=86,6
716,0200
86,610,5k =
+=
Generation of a Sine Wave - Example
Generation of a Sine Wave - Example
Knowin k for each interval thetime, that S1 and S4 are on, isdetermined that S1 and S4 are on.
> S3 e S3 VAB
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Triangular carrier wave
Modulao PWM Senoidal a Dois Nveis
Caractersticas
A Tenso instantnea de sada pode atingir dois nveis, +E ou E.
Pode ser a licada tanto nas estruturas em Ponte Com leta como nasestruturas em Meia Ponte.
- , ,apenas um nico pulso de comando para cada par de chaves.
Exemplo de Aplicao - Inversor MonofsicoMeia Ponte
Se Vm > Vp, tem-se Vo = + E < - = --
S1 D1E/2
,
Vm Vp
- +Vo
Io
+E / 2
0V
- E / 2
Vo
Modulao PWM senoidal a trs nveis
arac er s cas
A tenso de sada pode assumir trs nveis, +E, 0 e -E.
Na tenso de sada aparece o dobro de pulsos se comparado ao dedois nveis, mantendo-se a mesma freqncia de comutao das
.
Apresenta menor contedo harmnico que a modulao a dois nveis.
vezes superior em relao modulao a dois nveis.
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Generation of a three-phase Sine Wave