10-06-2017, 06:46 AM
Efficient Hybrid Carrier Based Space Vector Modulation for a Cascaded Multilevel Inverter
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INTRODUCTION
Multilevel inverters have become a popular choice in recent
years, because improving the output waveform of an inverter
reduces its respective harmonic content and, hence, the size
of the filter used and the level of electromagnetic interference
(EMI) generated by the switching operations [1]. Various
multilevel converters structures are reported in the literature,
and the cascaded multilevel inverter appears to be superior
to other multilevel structures in applications at high power
ratings due to its modulation, control and protection of each
full bridge inverter [2]. The power circuit for a five level
cascaded inverter topology, shown in Fig. 1, is used to examine
the proposed PWM technique.
HYBRID CARRIER BASED SPACE VECTOR MODULATION DEVELOPMENT
The principle behind this hybrid modulation is to mix
fundamental frequency PWM and carrier based space vector
modulation for each inverter module of a cascaded multilevel
inverter. Therefore, the output contains the features of fundamental
frequency PWM and CBSVM. In this modulation
technique, the four switches of each inverter module are
operated at two different frequencies, two being commutated
at the fundamental frequency, while the other two switches
PERFORMANCE ANALYSIS
A. Spectral Analysis of the output voltage and current waveform
The performance index namely the current total harmonic
distortion (THDi) and the weighted total harmonic distortion
(WTHD) are chosen for the quantification of the proposed
hybrid CBSVM. The weighted total harmonic distortion
(WTHD) is superior to the THD as a figure of merit for a nonsinusoidal
inverter waveform in which the lower portion of the
frequency spectrum is weighted heavily,
are pulse width modulated at CBSVM.