ABSTRACT:
Use
of conventional two-level pulse width modulation (PWM) inverters provide less
distorted current and voltage but at the cost of higher switching losses due to
high switching frequencies. Multilevel inverters are emerging as a viable alternative
for high power, medium voltage applications. This paper compares total harmonic
distortion and switching losses in conventional two-level inverters with
multilevel inverters (three-level and five-level) at different switching frequencies.
An optimized switching frequency has been obtained for a lower level of total
harmonic distortion and switching losses. Diode-clamped, three-phase topology
is considered for study. A sinusoidal PWM technique is used to control the
switches of the inverter. Simulation study confirms the reduction in harmonic
distortion and switching losses as the number of the levels increases.
KEYWORDS:
1.
Harmonics
2.
Multilevel
inverters
3.
Pulse width
modulation
4.
Switching
losses
5.
Total
harmonic distortion.
SOFTWARE: MATLAB/SIMULINK
CIRCUIT DIAGRAM:
CONCLUSION:
A
comparative study of THD of the output voltage waveform and switching losses of
two-level, three-level and five-level three-phase diode clamped inverters has been
presented in this paper using the SPWM technique. It has been observed that
both THD and switching losses decrease with the increase in the number of
levels in the output voltage. However, with the decrease in carrier frequency,
the THD level increases and switching losses reduce proportionately. Figures
10, 12 and 14 can be referred to optimize the switching losses and harmonic contents
for operation of an inverter at an optimized switching frequency. The above
investigation is made without an output filter. By using suitable filters, the harmonic
content can be further reduced.
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1.
F. Z. Peng & J. S. Lai, ‘Multilevel Converters - A new breed of power converters’,
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2.
Jose Rodriguez, J. S. Lai & F. Z. Peng, ‘Multilevel Inverters: A Survey of Topologies,
Controls, and Applications’, IEEE Transaction on Industrial Electronics,
Vol. 49, No. 4, Aug 2002, pp. 724-738.
3.
Mohan Ned, Undeland T.M. & Robbins W.P., ‘Power Electronics: Converters,
Applications and Design’, John Wiley and Sons, Second Edition, 2001.
4.
G. Bhuvaneswari & Nagaraju, ‘Multilevel Inverters - A Comparative Study’, IETE
Journal of Research, Vol. 51, No.2, Mar-Apr 2005, pp. 141-153.
5.
B. Kaku, I. Miyashita & S. Sone, ‘Switching Loss Minimized Space Vector PWM
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