Pulse Width Modulation Inverter | Power Electronics - Electrical Engineering (EE) PDF Download

 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)