1-ph FULL BRIDGE INVERTER
-RajeshINVERTERS
1
ContentsIntroduction1-ph Half Bridge inverter1-ph Full Bridge
inverterHarmonic AnalysisBasic Series inverter1-ph Parallel
inverter
DC to AC power at desired output voltage and
frequency.Classification based on Nature of source: Voltage Fed
Inverter (VFI or VSI) and Current Fed Inverter (CFI or CSI).VSI -
negligibly small source impedance so terminal voltage remains
substantially constant for variations in load.Short circuit causes
current to rise instantaneously due to less time constant and
current should be interrupted by Fast Acting Fuses.CSI - supplies
with controlled current from a DC source with large
impedance.Typically a rectifier feeds the inverter with a regulated
current through large series inductor.Introduction
Classification based on wave shape of output: Square wave
inverterQuasi Square wave inverterPulse Width Modulated
inverterIntroduction
1-ph Half Bridge Inverter
LOAD
Vs/2Vs/2S1S2D2D1+-V0I0Is1Is2Schematic
LOAD
Vs/2Vs/2S1S2D2D1+-V0I0Is1
Mode1: S1-ON, V0 is +ve, Io is +ve, Is1 is +ve. Load takes power
from source; VT2=Vs , VD1=0V, VD2= -Vs.Mode 2: S1-OFF, D2 ON;V0 is
-ve, Io is +ve, Is2 is ve; Load delivers power to source,VT1=Vs,
VT2=0V, VD1=-Vs.Mode 3: S2-ON, V0 is -ve, Io is -ve, Is2 is +ve.
Load takes power from source; VT1=Vs, VD1= -Vs, VD2=0V.Mode 4:
S2-OFF, D1 ON;V0 is +ve, Io is -ve, Is1 is ve; Load delivers power
to source,VT1=0V, VT2=Vs, VD2=-Vs.Is2
LOAD
Vs/2Vs/2S1S2D2D1+-V0I0Is1Mode1: S1-ON, V0 is +ve, Io is +ve, Is1
is +ve. Load takes power from source; VT2=Vs , VD1=0V, VD2=
-Vs.Mode 2: S1-OFF, D2 ON;V0 is -ve, Io is +ve, Is2 is ve; Load
delivers power to source,VT1=Vs, VT2=0V, VD1=-Vs.Mode 3: S2-ON, V0
is -ve, Io is -ve, Is2 is +ve. Load takes power from source;
VT1=Vs, VD1= -Vs, VD2=0V.Mode 4: S2-OFF, D1 ON;V0 is +ve, Io is
-ve, Is1 is ve; Load delivers power to source,VT1=0V, VT2=Vs,
VD2=-Vs.Is2
t1t2t3t5t6t4Vo,i0iS1tiS2iD1iD2tttis+Vs/2T/2TWaveformsS1D2S2D1S1D2S2D1Is1Is2-Vs/2
1-ph Full Bridge Inverter
RL-LOAD
I0V0T1T3T2T4D1D3D2D4VsSchematic
4 Modes of operation:
Thyristors 1,2 in ON.Diodes 3,4 in conduction.Thyristors 3,4 in
ON.Diodes 1,2 in conduction.
RL-LOADT1T3T2T4D1D3D2D4Vs
MODE 1: T1, T2 ON, SOURCE DELIVERING POWER TO LOAD Vo +ve, Io
+ve. MODE 2: FREE WHEELING INTERVAL, LOAD DELIVERING POWER TO
SOURCE THROUGH D3, D4 Vo ve, Io +ve. MODE 3: T3, T4 ON, SOURCE
DELIVERING POWER TO LOAD, Vo ve, Io ve. MODE 4: FREE WHEELING
INTERVAL, LOAD DELIVERING POWER TO SOURCE THROUGH D1, D2 Vo +ve, Io
ve.
RL-LOAD
I0V0T1T3T2T4D1D3D2D4VsMODE 1: T1, T2 ON, SOURCE DELIVERING POWER
TO LOAD Vo +ve, Io +ve. MODE 2: FREE WHEELING INTERVAL, LOAD
DELIVERING POWER TO SOURCE THROUGH D3, D4 Vo ve, Io +ve. MODE 3:
T3, T4 ON, SOURCE DELIVERING POWER TO LOAD, Vo ve, Io ve. MODE 4:
FREE WHEELING INTERVAL, LOAD DELIVERING POWER TO SOURCE THROUGH D1,
D2 Vo +ve, Io ve.
t1t2t3t5t6t4Vo,i0iS1, iS2tiS3, iS4iD1, iD2iD3,
iD4tttis+VsT/2TWaveforms
T1, T2 are made ON at t=t1 sec (decided by the load angle :
tan-1(X/R) of the load.At t=t2, SCRs are force-commutated to OFF
which results in free-wheeling of current to source.T3, T4 are made
ON at t=t3 sec.At t=t4, SCRs are force-commutated to OFF resulting
in a free-wheeling action of current to source by the diodes.The
switching action here employed is Zero Current Switching (ZCS)
during turn-on.For a pure inductive load, T1, T2 are to be fired at
t=T/4 instant due to the nature of the inductor current lagging the
supply voltage by 900 ( half of an half cycle).
Harmonic Analysis
VoT/2Tt
Fundamental component of voltageFundamental component of
currentHarmonic Analysis with RL load(say):
Contd.,
Contd.,
Harmonics are unwanted components of frequency other than
fundamental frequency component.A square wave output voltage will
have odd numbered harmonics and the 3rd harmonic being dominant.To
eliminate harmonics, filters are designed and PWM schemes are
employed.As the filtering components size (size of L and C) mainly
depend upon frequency in a inverse proportional relation, designing
of filters are suitable for removing higher frequency components as
the size of the filter reduces with increasing frequency.The lower
order frequencies especially 3rd, 5th, 7th, 9th,etc could be
removed by employing pulse width modulation schemes such as single
pulse modulation, multiple pulse and sinusoidal pulse modulations
etc.
Basic Series Inverter
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Inverters in which commutating components are permanently
connected in series with the load are called Series Inverters.Also
called Load commutated inverters of self commutated inverters and
operate at 200Hz to 100kHz.
T1
T2LCRLOAD
IOVsSchematicThe circuit should be under-damped always.
T1
T2LCRLOADVs
Mode-1: T1 is made ON with T2 in OFF. Cap charges to Vs+Vco with
left plate +ve, current naturally comes to zero and T1 OFFs. Hence
load current is +ve.
Mode-3: T2 is made ON, cap discharges through T2, load, L. So
load current is ve.
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T1
T2LCRLOAD
Vs
IgIoVLVcIg1Ig2ttttt1t2t3t4t5t6T1 off T2 off
WaveformsT/2ToffVdc+Vc
Mode-I: During ON period of T1 with T2 in OFF, let the cap has
an initial voltage of Vco, then,
Mode-2: During this mode, both the SCRs are in OFF state, with
capacitor holding its voltage and inductor voltage is zero.Mode-3:
During this mode, T2 is made ON and cap discharges through L and R.
Nature of current is the same as that obtained in Mode-1.
Single phase Parallel Inverter
VdcIsisvc+-T1T2i0+-voN1N2+-v1iciT1iT2Schematic
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VdcIsVc=2Vs+-T1T2i0+-voiT1iT2MODE-1 Assumed that cap has initial
voltage of +2Vs with upper plate +ve. T1 is ON, load current is +ve
by dot convention. It can be seen that T2 is in forward blocking
state due to T1 (short circuited T1).
Cap will be charged to 2Vs because of the two halves of the
primary winding linking the same flux.
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VdcIs2Vs to 0 +-T1T2i0+-voiciT1iT2
MODE-2 T2 is turned ON due to which T1 is driven to OFF as it is
RB by cap voltage 2Vs. Cap now discharges to 0 upto which load
current is +ve assuming cap current > source current and by dot
convention.
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VdcIsVc=-2Vs T1T2i0+-voiT1iT2
+-MODE-3 Cap has been charged to -2Vs with lower plate +ve. T2
is in ON state and load current is ve by dot convention. It can be
seen that T1 is in forward blocking state due to T2 ( Short
circuited T2).
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VdcIs-2Vs to 0+-T1T2i0+-voiciT1iT2
MODE-4 T1 is turned ON due to which T2 is driven to OFF as it is
RB by cap voltage -2Vs. Cap now discharges to 0 upto which load
current is -ve assuming cap current > source current and by dot
convention.
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VdcIsVc=2Vs+-T1T2i0+-voiT1iT2
Cap has been charged to +2Vs with upper plate +ve. T1 is in ON
state, load current is +ve by dot convention. It can be seen that
T2 is in forward blocking state due to T1 (short circuited T1).
Again MODE-1 prevails.
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IgVcVT!VoIc,iT1Ig2Ig1Ig2ttttt-Vs-2VsVs2Vs2VsIoIIIIIIIVIWaveforms
