International Research Journal of Applied and Basic Sciences
© 2013 Available online at www.irjabs.com
ISSN 2251-838X / Vol, 5 (10): 1329-1333
Science Explorer Publications
Investigation of PWM using Inductor-Switch for
each Leg of Inverter for Reduction of Total
Harmonic Distortion
Abdolreza Esmaeli1, Amir Moslemi Bidehendi2, Nabiollah Rezaei Charati2, Abdullah
Ahmadi3
1. Plasma Physics and Nuclear Fusion Research School, Nuclear Science and Technology Research
Institute,Tehran, Iran.
2. Faculty of Electrical Engineering, MaziarUniversity, Nour, Iran
3. Department of Electronic, Technical and Vocational College,. Mahmoud Abad, Technical and
Vocational University, Iran
*Corresponding Author email: aesmaeli@aeoi.org.ir
ABSTRACT: Many researchers have been done on PWM switching methods for finding better
schemes to supply the loads, which have lower harmonics in outputs. In SPWM, semiconductor
switches are directly connected to rectified voltage in output of rectifier. In this paper, the novel
technique of using Inductor-Switch for each Leg of Inverter has been presented. In this technique an
inductor is used between each semiconductor switch and rectified voltage of rectifier’s output. To
validate the proposed technique, simulation studies have been carried out with SABER software.
Results have been compared with conventional SPWM. The results confirm that this novel technique
causes lower total harmonic distortion and lower acoustic noise. Therefore, this new technique can
be used to decrease harmonics and total harmonic distortion in voltages and currents of output.
Keywords: Pulse Width Modulation, SPWM, Harmonics, SABER, Total Harmonic Distortion
INTRODUCTION
Increasing attention has been paid to multilevel dc/ac inverters in recent years (Bowes, 1975; Carrasco
et al., 2006). Various modulation methods have been developed for multilevel inverters. A very popular method
in industrial applications is the classic carrier-based sinusoidal pulse width modulation (SPWM) that uses the
phase shifting technique to reduce harmonics in the load voltage (Bowes,1975; Chiasson et al., 2004; Chiasson
et al., 2005). In SPWM, the states of power semiconductor switches are determined by the comparison
between reference signals and saw tooth signals. The determination of a switching instant can be easily carried
out in real-time by an analog circuit, a microprocessor or a digital signal processor (DSP). The space vector
PWM (Joachim, 1992; Lakshminarayanan et al., 2007) is also very popular in industries. The calculation to
determine switching instants for the space vector PWM is more complicated than that for the SPWM, but it can
still be handled by a microprocessor or a DSP.
Another important modulation method for multilevel inverters is the optimal PWM, which includes step
modulation (Liang and Nwankpa, 1999; Liu et al., 2005; Liu et al., 2006), multilevel selective harmonic
elimination (Ozpineci et al., 2005), and optimal combination modulation (Rech and Pinheiro, 2007).With the
same switching frequency, voltage quality generated by the optimal PWM is better than that by the popular
SPWM or the space vector PWM. The general procedure for implementing optimal PWM is as follows: based
on Fourier series analysis, equation sets whose variables are switching angles are built to meet a specific
optimization aim, for example the minimization of total harmonic distortion (THD) of the voltage or the
elimination of lower order harmonic components of the voltage. An equation set need to be solved with respect
to a certain amplitude value of the fundamental voltage component. Generally, the equation sets are nonlinear
and transcendental. Several methods, such as the Newton–Raphson iteration method with multiple variables
(Liu et al., 2005), methods based on the theory of symmetric polynomials and resultants (Rech and Pinheiro,
2007), and methods based on genetic algorithms (Rodriguez, 2002; Rodriguez et al., 2004), have been
proposed to solve nonlinear transcendental equation sets. Calculations based on all the methods above are
very time-consuming. Therefore, they cannot be done by a microprocessor or a DSP in real time. They can
only be done by a computer offline. Switching angles obtained offline have to be stored in a lookup table in a
Intl. Res. J. Appl. Basic. Sci. Vol., 5 (10), 1329-1333, 2013
microprocessor or a DSP. Therefore, one of the dominant drawbacks of the above methods is that they cannot
be implemented in real-time due to high overhead of the calculations. Another drawback is that data of
switching angles stored in the lookup table increase if the required resolution of the fundamental component of
the voltage increases.
In PWM, various methods are used (Sirisukprasert et al., 2002) and SPWM is one of the popular
methods (Xu et al., 2004). In conventional SPWM the reference signal with nominal frequency is compared with
a triangular career signal with switching frequency and the output leads to the gate of switches such as IGBT's.
Therefore, the pulses are created in inverter’s output which supplies the load. In this paper, the new technique
of using Inductor-Switch for each Leg of Inverter has been represented. In this technique, an inductor is used
between each semiconductor switch and rectified voltage of rectifier’s output. The outputs of these novel
methods have been simulated and analysed using of SABER software, and the results have been compared
with conventional SPWM. For accurate comparison, all other conditions of two systems have set the same. The
frequency of reference signal is 50 Hz and the frequency of career signal is 10 kHz.
Conventional Spwm
In SPWM technique a triangular career signal and sinusoidal reference signal intersect each other. In
SPWM below equations are appeared. Reference signal equation:
y = * Sin ( 2 *
(1)
Where
is the amplitude of reference signal, and
is the frequency of the reference signal. career
signal equation:
(2)
y = Vtriangular
Below figure shows the circuit that has been used for triggering of inverter switches.
Figure 1. Trigger circuit of the inverter’s leg
d10
igbt _b3
igbt _b4
d8
d7
igbt _b2
200
v_dc
200
200
230
gnd
d9
d12
vcc
vgain
Volt age G ain
vcc
pp
sp
DC/ DC
k: 3
vt r i
n1: 1
lf 353_1
n2: 1
pm gnd
gndper iod: 0. 0001
igbt _b6
d11
igbt _b1
igbt _b5
sm
vee
v_sin
vee
vgain
gnd am plit ude: 0. 8
f r equency: 50
Volt age G ain
pp
DC/ DC
sp
k: 3
n1: 1
n2: 1
pm gnd
vcc
sm
vgain
Volt age G ain
vcc
pp
DC/ DC
sp
k: 3
n1: 1
lf 353_1
vt r i
n2: 1
pm gnd
sm
vee
gnd per iod: 0. 0001
vee
vcc
v_sin
vee
vgain
gnd
v_dc
v_dc
am plit ude: 0. 8
f r equency: 50
Volt age G ain
15
- 15
pp
DC/ DC
sp
k: 3
n1: 1
n2: 1
pm gnd
gnd
sm
gnd
vcc
vgain
Volt age G ain
vcc
pp
DC/ DC
sp
k: 3
lf 353_1
n1: 1
vt r i
n2: 1
pm gnd
sm
vee
gnd per iod: 0. 0001
v_sin
vee
vgain
gnd
am plit ude: 0. 8
Volt age G ain
pp
DC/ DC
sp
f r equency: 50
k: 3
n1: 1
pm gnd
n2: 1
sm
Figure 2. Three phases SPWM
DC supply of inverter has been considered as an ideal power supply. While in practice, a rectifier is
used to produce DC voltage, and rectifier’s output is not ideal and has problems such as voltage ripple. But this
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Intl. Res. J. Appl. Basic. Sci. Vol., 5 (10), 1329-1333, 2013
simplifying is useful to analyze the PWM techniques and its affect on harmonics. In above figure the frequency
of career signal is 10 KHz and the amplitude of career is 1 and the amplitude modulation ratio is 0.8.
Pwm Using Inductor-Switch For Each Leg Of Inverter
In novel technique an inductor is used between each semiconductor switch and DC voltage source.
Reference signal equation:
y = * Sin ( 2 *
(3)
Where
is the amplitude of reference signal, and is the frequency of the reference signal. Career
signal equation:
(4)
y = Vtriangular
Below figures shows the circuit of PWM using Inductor-Switch for each Leg of Inverter.
Figure 3. Phase voltage waveform in SPWM
The amount of total harmonic distortion in output’s currents has been measured, which has been
indicated in table 1. These harmonics are result of pulse width modulation, and high frequency effects of circuit
such as parasitic elements of circuit are not considered.
Figure 4. PWM using Inductor-Switch
1m
1m
1m
d10
igbt _b3
igbt _b4
d8
d7
igbt _b2
200
v_dc
200
200
230
gnd
d9
d12
igbt _b6
d11
igbt _b1
igbt _b5
1m
1m
vcc
vgain
Volt age G ain
vcc
pp
sp
DC/ DC
k: 3
vt r i
n1: 1
lf 353_1
n2: 1
pm gnd
gndper iod: 0. 0001
1m
sm
vee
v_sin
vee
vgain
gnd am plit ude: 0. 8
f r equency: 50
Volt age G ain
pp
DC/ DC
sp
k: 3
n1: 1
n2: 1
pm gnd
vcc
vcc
pp
vcc
DC/ DC
sp
k: 3
n1: 1
lf 353_1
vee
sm
vgain
Volt age G ain
vt r i
n2: 1
pmgnd
sm
vee
gnd per iod: 0. 0001
v_dc
v_dc
v_sin
vee
15
- 15
vgain
gnd
gnd
am plit ude: 0. 8
f r equency: 50
Volt age G ain
pp
DC/ DC
sp
k: 3
gnd
n1: 1
n2: 1
pmgnd
vcc
sm
vgain
Volt age G ain
vcc
pp
DC/ DC
sp
k: 3
lf 353_1
n1: 1
vt r i
n2: 1
pmgnd
sm
vee
gnd per iod: 0. 0001
v_sin
vee
vgain
am plit ude: 0. 8
gnd
f r equency: 50
Volt age G ain
pp
DC/ DC
sp
k: 3
n1: 1
pmgnd
n2: 1
sm
Figure 5.Three phases PWM using Inductor-Switch for each Leg of Inverter
Other setting of the circuit doesn't change. The frequency of career signal is 10 KHz and the amplitude
of career is 1 and the amplitude modulation ratio is 0.8.
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Intl. Res. J. Appl. Basic. Sci. Vol., 5 (10), 1329-1333, 2013
SIMULATION RESULTS
To verify the proposed novel technique, simulation studies have been carried out and the results have
been compared with conventional SPWM. By employing Fourier transform for output waveform of currents, the
magnitude of frequency components are obtained. The amount of total harmonic distortion for frequency
components up to 20 KHz is calculated in output currents. The results of conventional SPWM and PWM using
Inductor-Switch for each Leg of Inverter have been shown in below table.
Figure 6. Phase voltage waveform in PWM using Inductor-Switch for each Leg of Inverter
The amount of total harmonic distortion in output’s currents has been measured, which has been
indicated in table 1.
Table 1. Comparison of the PWM using Inductor-Switch for each Leg of Inverter and conventional SPWM
Phase currents
Ia
Ib
Ic
Total Harmonic
Distortion in PWM
using InductorSwitch for each Leg
of Inverter
0.8394
0.8381
0.8405
Total Harmonic
Distortion in SPWM
Variation
in percent
0.912
0.9094
0.9119
8.6490%
8.5073%
8.4949%
The above table displays that SPWM has significant higher THD in all phases. The average of
difference in THD is 8.5504 %.
CONCLUSION
In this paper the novel technique, PWM using Inductor-Switch for each Leg of Inverter has been
represented. From the simulation results, it is observed that conventional SPWM has considerably higher total
harmonic distortion in output’s currents. It should be noted that amount of applied inductance should be enough
small compared with impedance of load or motor, Because although bigger impedance of applied inductance
causes better results, but voltage drop across inductance will cause decreasing the efficiency of inverter. All in
all, this new technique has beneficial effects on declining harmonics and total harmonic distortion in voltages
and currents of output.
REFERENCES
Bowes SR. 1975. New sinusoidal pulse width-modulated inverter. Proc. IEE. 122(11): 1279 -- 1285.
Carrasco JM, Franquelo LG, Bialasiewicz JT, Galvan E, PortilloGuisado RC, Prats MAM, Leon JI, Moreno-Alfonso N. 2006. “Powerelectronic systems for the grid integration of renewable energy sources: A survey,” IEEE Trans. Ind. Electron., vol. 53, no. 4, pp.
1002– 1016, Jun.
Chiasson JN, Tolbert LM, McKenzie KJ, Du Z. 2004. “A unified approach to solving the harmonic elimination equations in multilevel
converters,” IEEE Trans. Power Electron., vol. 19, no. 2, pp. 478–490, Mar.
Chiasson JN, Tolbert LM, McKenzie KJ, Du Z. 2005. “Elimination of harmonics in a multilevel converter using the theory of symmetric
polynomials and resultants,” IEEE Trans. Control Syst. Technol., vol. 13, no. 2, pp. 216–223, Mar.
Joachim H. 1992. “Pulse width modulation – A survey” IEEE Trans. Ind. Electron.., vol. 39, no. 5, Dec pp. 410-420.
1332
Intl. Res. J. Appl. Basic. Sci. Vol., 5 (10), 1329-1333, 2013
Lakshminarayanan S, Mondal G, Tekwani PN, Mohapatra KK, Gopakumar K. 2007. “Twelve-sided polygonal voltage space vector based
multilevel inverter for an induction motor drive with common-mode voltage elimination,” IEEE Trans. Ind. Electron., vol. 54, no. 5,
pp. 2761– 2768, Oct.
Li L, Czarkowski D, Yaguang L, Pillay P.2000. “Multilevel selective harmonic elimination PWMtechnique in series-connected voltage
inverters,” IEEE Trans. Ind. Appl., vol. 36, no. 1, pp. 160–170, Jan./Feb.
Liang Y, Nwankpa CO. 1999. “A new type of STATCOM based on cascading voltage-source inverters with phase-shifted unipolar SPWM,”
IEEE Trans. Ind. Appl., vol. 35, no. 5, pp. 1118–1123, Sep./Oct.
Liu Y, Du Z, Huang AQ, Bhattacharya S. 2006. “An optimal combination modulation strategy for a seven-level cascade multilevel converter
based STATCOM,” in Conf. Rec. IEEE IAS Annu. Meeting, Oct. pp. 1732–1737.
Liu Y, Luo F. 2005. “Trinary hybrid multilevel inverter used in STATCOM with unbalanced voltages,” Proc. Inst. Electr. Eng.— Elect. Power
Appl., vol. 152, no. 5, pp. 1203–1222, Sep.
Ozpineci B, Tolbert LM, Chiasson JN. 2005. “Harmonic optimization of multilevel converters using genetic algorithms,” IEEE Power
Electron. Lett., vol. 3, no. 3, pp. 92–95, Sep.
Rech C, Pinheiro JR. 2007. “Hybrid multilevel converters: Unified analysis and design considerations,” IEEE Trans. Ind. Electron., vol. 54,
no. 2, pp. 1092–1104, Apr.
Rodriguez J, Lai JS, Peng FZ.2002. “Multilevel inverters: A survey of topologies, controls, and applications,” IEEE Trans. Ind. Electron., vol.
49, no. 4, pp. 724–738, Aug.
Rodriguez J, Pontt J, Correa P, Cortes P, Silva C. 2004. “A new modulation method to reduce common-mode voltages in multilevel
inverters,” IEEE Trans. Ind. Electron., vol. 51, no. 4, pp. 834–839, Aug.
Sirisukprasert S, Lai JS, Liu TH. 2002. “Optimum harmonic reduction with a wide range of modulation indexes for multilevel converters,”
IEEE Trans. Ind. Electron., vol. 49, no. 4, pp. 875–881, Aug.
Tolbert LM, Peng FZ, Habetler TG. 1999. “Multilevel converters for large electric drives,” IEEE Trans. Ind. Appl., vol. 35, no. 1, pp. 36–44,
Jan./Feb.
Xu X, Zou Y, Ding K, Liu F. 2004 “Cascade multilevel inverter with phase-shift SPWM and its application in STATCOM,” in Proc. IEEE
IECON, vol. 2, pp. 1139–1143.
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