Page 1
SINGLE PHASE PULSE WIDTH MODULATED INVERTERS
Introduction
The dc-ac converter, also known as the inverter, converts dc power to ac power
at desired output voltage and frequency. The dc power input to the inverter is
obtained from an existing power supply network or from a rotating alternator through
a rectifier or a battery, fuel cell, photovoltaic array or magneto hydrodynamic
generator. The filter capacitor across the input terminals of the inverter provides a
constant dc link voltage. The inverter therefore is an adjustable-frequency voltage
source. The configuration of ac to dc converter and dc to ac inverter is called a dc-
link converter.
Inverters can be broadly classified into two types, voltage source and current
source inverters. A voltage–fed inverter (VFI) or more generally a voltage–source
inverter (VSI) is one in which the dc source has small or negligible impedance. The
voltage at the input terminals is constant. A current–source inverter (CSI) is fed with
adjustable current from the dc source of high impedance that is from a constant dc
source.
A voltage source inverter employing thyristors as switches, some type of forced
commutation is required, while the VSIs made up of using GTOs, power transistors,
power MOSFETs or IGBTs, self commutation with base or gate drive signals for their
controlled turn-on and turn-off.
Page 2
SINGLE PHASE PULSE WIDTH MODULATED INVERTERS
Introduction
The dc-ac converter, also known as the inverter, converts dc power to ac power
at desired output voltage and frequency. The dc power input to the inverter is
obtained from an existing power supply network or from a rotating alternator through
a rectifier or a battery, fuel cell, photovoltaic array or magneto hydrodynamic
generator. The filter capacitor across the input terminals of the inverter provides a
constant dc link voltage. The inverter therefore is an adjustable-frequency voltage
source. The configuration of ac to dc converter and dc to ac inverter is called a dc-
link converter.
Inverters can be broadly classified into two types, voltage source and current
source inverters. A voltage–fed inverter (VFI) or more generally a voltage–source
inverter (VSI) is one in which the dc source has small or negligible impedance. The
voltage at the input terminals is constant. A current–source inverter (CSI) is fed with
adjustable current from the dc source of high impedance that is from a constant dc
source.
A voltage source inverter employing thyristors as switches, some type of forced
commutation is required, while the VSIs made up of using GTOs, power transistors,
power MOSFETs or IGBTs, self commutation with base or gate drive signals for their
controlled turn-on and turn-off.
A standard single-phase voltage or current source inverter can be in the half-
bridge or full-bridge configuration. The single-phase units can be joined to have
three-phase or multiphase topologies. Some industrial applications of inverters are for
adjustable-speed ac drives, induction heating, standby aircraft power supplies, UPS
(uninterruptible power supplies) for computers, HVDC transmission lines, etc.
In this chapter single-phase inverters and their operating principles are
analyzed in detail. The concept of Pulse Width Modulation (PWM) for inverters is
described with analyses extended to different kinds of PWM strategies. Finally the
simulation results for a single-phase inverter using the PWM strategies described are
presented.
Voltage Control in Single - Phase Inverters
The schematic of inverter system is as shown in Figure 2.1, in which the
battery or rectifier provides the dc supply to the inverter. The inverter is used to
control the fundamental voltage magnitude and the frequency of the ac output
voltage. AC loads may require constant or adjustable voltage at their input terminals,
when such loads are fed by inverters, it is essential that the output voltage of the
inverters is so controlled as to fulfill the requirement of the loads. For example if the
inverter supplies power to a magnetic circuit, such as a induction motor, the voltage
to frequency ratio at the inverter output terminals must be kept constant. This avoids
saturation in the magnetic circuit of the device fed by the inverter.
Page 3
SINGLE PHASE PULSE WIDTH MODULATED INVERTERS
Introduction
The dc-ac converter, also known as the inverter, converts dc power to ac power
at desired output voltage and frequency. The dc power input to the inverter is
obtained from an existing power supply network or from a rotating alternator through
a rectifier or a battery, fuel cell, photovoltaic array or magneto hydrodynamic
generator. The filter capacitor across the input terminals of the inverter provides a
constant dc link voltage. The inverter therefore is an adjustable-frequency voltage
source. The configuration of ac to dc converter and dc to ac inverter is called a dc-
link converter.
Inverters can be broadly classified into two types, voltage source and current
source inverters. A voltage–fed inverter (VFI) or more generally a voltage–source
inverter (VSI) is one in which the dc source has small or negligible impedance. The
voltage at the input terminals is constant. A current–source inverter (CSI) is fed with
adjustable current from the dc source of high impedance that is from a constant dc
source.
A voltage source inverter employing thyristors as switches, some type of forced
commutation is required, while the VSIs made up of using GTOs, power transistors,
power MOSFETs or IGBTs, self commutation with base or gate drive signals for their
controlled turn-on and turn-off.
A standard single-phase voltage or current source inverter can be in the half-
bridge or full-bridge configuration. The single-phase units can be joined to have
three-phase or multiphase topologies. Some industrial applications of inverters are for
adjustable-speed ac drives, induction heating, standby aircraft power supplies, UPS
(uninterruptible power supplies) for computers, HVDC transmission lines, etc.
In this chapter single-phase inverters and their operating principles are
analyzed in detail. The concept of Pulse Width Modulation (PWM) for inverters is
described with analyses extended to different kinds of PWM strategies. Finally the
simulation results for a single-phase inverter using the PWM strategies described are
presented.
Voltage Control in Single - Phase Inverters
The schematic of inverter system is as shown in Figure 2.1, in which the
battery or rectifier provides the dc supply to the inverter. The inverter is used to
control the fundamental voltage magnitude and the frequency of the ac output
voltage. AC loads may require constant or adjustable voltage at their input terminals,
when such loads are fed by inverters, it is essential that the output voltage of the
inverters is so controlled as to fulfill the requirement of the loads. For example if the
inverter supplies power to a magnetic circuit, such as a induction motor, the voltage
to frequency ratio at the inverter output terminals must be kept constant. This avoids
saturation in the magnetic circuit of the device fed by the inverter.
Battery
or
Rectifier
Inverter
d
V
d
C
AC
Voltage
Figure 2.1: Schematic for Inverter System
The various methods for the control of output voltage of inverters can be classified as:
(a) External control of ac output voltage
(b) External control of dc input voltage
(c ) Internal control of the inverter.
The first two methods require the use of peripheral components whereas the third
method requires no external components. Mostly the internal control of the inverters
is dealt, and so the third method of control is discussed in great detail in the following
section.
Pulse Width Modulation Control
The fundamental magnitude of the output voltage from an inverter can be
controlled to be constant by exercising control within the inverter itself that is no
external control circuitry is required. The most efficient method of doing this is by
Pulse Width Modulation (PWM) control used within the inverter. In this scheme the
inverter is fed by a fixed input voltage and a controlled ac voltage is obtained by
Page 4
SINGLE PHASE PULSE WIDTH MODULATED INVERTERS
Introduction
The dc-ac converter, also known as the inverter, converts dc power to ac power
at desired output voltage and frequency. The dc power input to the inverter is
obtained from an existing power supply network or from a rotating alternator through
a rectifier or a battery, fuel cell, photovoltaic array or magneto hydrodynamic
generator. The filter capacitor across the input terminals of the inverter provides a
constant dc link voltage. The inverter therefore is an adjustable-frequency voltage
source. The configuration of ac to dc converter and dc to ac inverter is called a dc-
link converter.
Inverters can be broadly classified into two types, voltage source and current
source inverters. A voltage–fed inverter (VFI) or more generally a voltage–source
inverter (VSI) is one in which the dc source has small or negligible impedance. The
voltage at the input terminals is constant. A current–source inverter (CSI) is fed with
adjustable current from the dc source of high impedance that is from a constant dc
source.
A voltage source inverter employing thyristors as switches, some type of forced
commutation is required, while the VSIs made up of using GTOs, power transistors,
power MOSFETs or IGBTs, self commutation with base or gate drive signals for their
controlled turn-on and turn-off.
A standard single-phase voltage or current source inverter can be in the half-
bridge or full-bridge configuration. The single-phase units can be joined to have
three-phase or multiphase topologies. Some industrial applications of inverters are for
adjustable-speed ac drives, induction heating, standby aircraft power supplies, UPS
(uninterruptible power supplies) for computers, HVDC transmission lines, etc.
In this chapter single-phase inverters and their operating principles are
analyzed in detail. The concept of Pulse Width Modulation (PWM) for inverters is
described with analyses extended to different kinds of PWM strategies. Finally the
simulation results for a single-phase inverter using the PWM strategies described are
presented.
Voltage Control in Single - Phase Inverters
The schematic of inverter system is as shown in Figure 2.1, in which the
battery or rectifier provides the dc supply to the inverter. The inverter is used to
control the fundamental voltage magnitude and the frequency of the ac output
voltage. AC loads may require constant or adjustable voltage at their input terminals,
when such loads are fed by inverters, it is essential that the output voltage of the
inverters is so controlled as to fulfill the requirement of the loads. For example if the
inverter supplies power to a magnetic circuit, such as a induction motor, the voltage
to frequency ratio at the inverter output terminals must be kept constant. This avoids
saturation in the magnetic circuit of the device fed by the inverter.
Battery
or
Rectifier
Inverter
d
V
d
C
AC
Voltage
Figure 2.1: Schematic for Inverter System
The various methods for the control of output voltage of inverters can be classified as:
(a) External control of ac output voltage
(b) External control of dc input voltage
(c ) Internal control of the inverter.
The first two methods require the use of peripheral components whereas the third
method requires no external components. Mostly the internal control of the inverters
is dealt, and so the third method of control is discussed in great detail in the following
section.
Pulse Width Modulation Control
The fundamental magnitude of the output voltage from an inverter can be
controlled to be constant by exercising control within the inverter itself that is no
external control circuitry is required. The most efficient method of doing this is by
Pulse Width Modulation (PWM) control used within the inverter. In this scheme the
inverter is fed by a fixed input voltage and a controlled ac voltage is obtained by
adjusting the on and the off periods of the inverter components. The advantages of the
PWM control scheme are [10]:
a) The output voltage control can be obtained without addition of any external
components.
b) PWM minimizes the lower order harmonics, while the higher order
harmonics can be eliminated using a filter.
The disadvantage possessed by this scheme is that the switching devices used in the
inverter are expensive as they must possess low turn on and turn off times,
nevertheless PWM operated are very popular in all industrial equipments. PWM
techniques are characterized by constant amplitude pulses with different duty cycles
for each period. The width of these pulses are modulated to obtain inverter output
voltage control and to reduce its harmonic content. There are different PWM
techniques which essentially differ in the harmonic content of their respective output
voltages, thus the choice of a particular PWM technique depends on the permissible
harmonic content in the inverter output voltage.
Sinusoidal-Pulse Width Modulation (SPWM)
The sinusoidal PWM (SPWM) method also known as the triangulation, sub
harmonic, or suboscillation method, is very popular in industrial applications and is
extensively reviewed in the literature [1-2]. The SPWM is explained with reference to
Figure 2.2, which is the half-bridge circuit topology for a single-phase inverter.
Page 5
SINGLE PHASE PULSE WIDTH MODULATED INVERTERS
Introduction
The dc-ac converter, also known as the inverter, converts dc power to ac power
at desired output voltage and frequency. The dc power input to the inverter is
obtained from an existing power supply network or from a rotating alternator through
a rectifier or a battery, fuel cell, photovoltaic array or magneto hydrodynamic
generator. The filter capacitor across the input terminals of the inverter provides a
constant dc link voltage. The inverter therefore is an adjustable-frequency voltage
source. The configuration of ac to dc converter and dc to ac inverter is called a dc-
link converter.
Inverters can be broadly classified into two types, voltage source and current
source inverters. A voltage–fed inverter (VFI) or more generally a voltage–source
inverter (VSI) is one in which the dc source has small or negligible impedance. The
voltage at the input terminals is constant. A current–source inverter (CSI) is fed with
adjustable current from the dc source of high impedance that is from a constant dc
source.
A voltage source inverter employing thyristors as switches, some type of forced
commutation is required, while the VSIs made up of using GTOs, power transistors,
power MOSFETs or IGBTs, self commutation with base or gate drive signals for their
controlled turn-on and turn-off.
A standard single-phase voltage or current source inverter can be in the half-
bridge or full-bridge configuration. The single-phase units can be joined to have
three-phase or multiphase topologies. Some industrial applications of inverters are for
adjustable-speed ac drives, induction heating, standby aircraft power supplies, UPS
(uninterruptible power supplies) for computers, HVDC transmission lines, etc.
In this chapter single-phase inverters and their operating principles are
analyzed in detail. The concept of Pulse Width Modulation (PWM) for inverters is
described with analyses extended to different kinds of PWM strategies. Finally the
simulation results for a single-phase inverter using the PWM strategies described are
presented.
Voltage Control in Single - Phase Inverters
The schematic of inverter system is as shown in Figure 2.1, in which the
battery or rectifier provides the dc supply to the inverter. The inverter is used to
control the fundamental voltage magnitude and the frequency of the ac output
voltage. AC loads may require constant or adjustable voltage at their input terminals,
when such loads are fed by inverters, it is essential that the output voltage of the
inverters is so controlled as to fulfill the requirement of the loads. For example if the
inverter supplies power to a magnetic circuit, such as a induction motor, the voltage
to frequency ratio at the inverter output terminals must be kept constant. This avoids
saturation in the magnetic circuit of the device fed by the inverter.
Battery
or
Rectifier
Inverter
d
V
d
C
AC
Voltage
Figure 2.1: Schematic for Inverter System
The various methods for the control of output voltage of inverters can be classified as:
(a) External control of ac output voltage
(b) External control of dc input voltage
(c ) Internal control of the inverter.
The first two methods require the use of peripheral components whereas the third
method requires no external components. Mostly the internal control of the inverters
is dealt, and so the third method of control is discussed in great detail in the following
section.
Pulse Width Modulation Control
The fundamental magnitude of the output voltage from an inverter can be
controlled to be constant by exercising control within the inverter itself that is no
external control circuitry is required. The most efficient method of doing this is by
Pulse Width Modulation (PWM) control used within the inverter. In this scheme the
inverter is fed by a fixed input voltage and a controlled ac voltage is obtained by
adjusting the on and the off periods of the inverter components. The advantages of the
PWM control scheme are [10]:
a) The output voltage control can be obtained without addition of any external
components.
b) PWM minimizes the lower order harmonics, while the higher order
harmonics can be eliminated using a filter.
The disadvantage possessed by this scheme is that the switching devices used in the
inverter are expensive as they must possess low turn on and turn off times,
nevertheless PWM operated are very popular in all industrial equipments. PWM
techniques are characterized by constant amplitude pulses with different duty cycles
for each period. The width of these pulses are modulated to obtain inverter output
voltage control and to reduce its harmonic content. There are different PWM
techniques which essentially differ in the harmonic content of their respective output
voltages, thus the choice of a particular PWM technique depends on the permissible
harmonic content in the inverter output voltage.
Sinusoidal-Pulse Width Modulation (SPWM)
The sinusoidal PWM (SPWM) method also known as the triangulation, sub
harmonic, or suboscillation method, is very popular in industrial applications and is
extensively reviewed in the literature [1-2]. The SPWM is explained with reference to
Figure 2.2, which is the half-bridge circuit topology for a single-phase inverter.
S
11
S
12
d
V
2
d
V
2
d
V
+
+
C
C
o
V
Figure 2.2: Schematic diagram for Half-Bridge PWM inverter.
For realizing SPWM, a high-frequency triangular carrier wave is
compared with a sinusoidal reference of the desired frequency. The intersection of
and waves determines the switching instants and commutation of the modulated
pulse. The PWM scheme is illustrated in Figure 2.3 a, in which v is the peak value of
triangular carrier wave and v that of the reference, or modulating signal. The figure
shows the triangle and modulation signal with some arbitrary frequency and
magnitude. In the inverter of Figure 2.2 the switches and are controlled based
on the comparison of control signal and the triangular wave which are mixed in a
comparator. When sinusoidal wave has magnitude higher than the triangular wave the
comparator output is high, otherwise it is low.
c
v
r
v
c
v
r
v
c
12
r
11
S S
v > is on ,
r c
v
11
S
2
d
out
V
= V (2.1)
and
< is on ,
r
v
c
v
12
S
2
d
out
V
- = V (2.2)
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