PS-PWMPhase-Shifted Pulse Width Modulation
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As mentioned before, PS-PWM method leads to an even power distribution between the inverter cells, which in turn results in harmonic cancelations of the input current at grid side [15].
The output voltage waveforms of both PS-PWM and H2-PWM methods have quarter waveform symmetry for both even and odd [m.sub.f] values (i.e.
For PS-PWM and H1-PWM methods, the harmonic cancellation up to 4[f.sub.c] and its sidebands in the voltage waveform is achieved, whereas H2-PWM method results in the harmonic cancellation up to 2[f.sub.c] and its sidebands in the inverter voltage output.
Furthermore, for the odd [m.sub.f] value, the minimum WTHD indices of CHB voltages are related to the PS-PWM and H2-PWM switching patterns.
In case of the even [m.sub.f] value ([m.sub.f]=40), the lowest THD and WTHD values belong to PS-PWM method, which are due to the lower harmonic amplitudes and higher harmonic frequencies, respectively.
The PS-PWM, H1-PWM, and H2-PWM in comparison with LS-PWM methods result in higher carrier frequencies ([f.sub.c]).
R-PD, R-POD, and R-APOD), PS-PWM, and H2-PWM switching techniques, the 5th and 7th harmonic orders will not appear in the frequency spectrum of input current and therefore, the harmonic distortion will be reduced in comparison with other modulation schemes.
R-PD, R-POD, and R-APOD), PS-PWM, and H2-PWM techniques reduce the harmonic contents of the input current.
In other words, the R-LS-PWM methods join the privileges of both PS-PWM and the traditional LS-PWM modulations.
The CHB output voltage with PS-PWM for a) even [m.sub.f] ([m.sub.f] =4), b) odd [m.sub.f] ([m.sub.f] =3)
The dark blue signal represents voltage on ac converter terminals [u.sub.v_a] seven voltage levels for this case (it is due the correct functions of PS-PWM for three H-bridge cells).