Selection of carrier waveforms for PWM inverter

Abstract

In this paper the influence of different carrier waveforms upon the output characteristics of PWM inverter is described in detail. When a triangular carrier waveform is used in hard-switching PWM inverters, harmonics exist in the neighborhood of the output frequency of the inverter output voltage and current due to the dead time. The triangular carrier waveform used in soft-switching PWM inverter will cause difficulties in controlling resonance-trigger time, higher loss in the resonant circuit, and less utilization of the DC bus voltage. If a sawtooth carrier is used in hard-switching PWM inverter, there will be severe distortion in the current waveform. When sawtooth carriers with alternate positive and negative slopes are used in soft-switching PWM inverters, the resonancetrigger time is easy to control, and distortion in the output voltage and current caused by the dead time will not appear.

Hydrogen production by aqueous-phase reforming of ethylene glycol over a Ni/Zn/Al derived hydrotalcite catalyst

“…But a certain amount of H 2 is still generated by reusing catalysts for two times. The SEM pattern of Ni 2 Zn 2 Al derived hydrotalcite aer reduction is exhibited in 34,35 As suggested in Fig. 5, the Ni-rich regions still remained aer exposure to aqueous-phase reforming reaction conditions, which displays in Fig.…”

“…Fig. 34,35 As suggested in Fig. The composition of catalyst contains mainly Ni, ZnO, H 2 O and AlNi alloy with different ratios.…”

“…Fig.5(C). The structure is composed of three phase: porous Nirich compact regions occupied much of the pattern, nanorod of ZnO regions around the Ni-rich regions and crystalline regions sticking to the Ni-rich regions containing AlNi alloy with different ratios 34,35. As suggested in Fig.5, the Ni-rich regions still remained aer exposure to aqueous-phase reforming reaction conditions, which displays in Fig.5(D).…”

A zero-voltage transition for three-phase double-PWM voltage-fed converter

“…Both parts share a set of commutation circuit that includes L R ∼ L T , L U ∼ L W , VD 1 ∼ VD 12 , and V T , and all auxiliary resonant links share one auxiliary device V T . Because the left rectifier and the right inverter are symmetry in structure, Fig.3 Fig.3 Main circuit diagram of a double-PWM converter 4 Control strategy Fig.4 shows the PWM method of the double-PWM converter, which adopts an optimum sine modulation wave-saddle wave [11] and can enhance 15.47% of output voltage. From Fig.3, as every power device in 12-bridge has one paralleled snubber that prevents immediate voltage change, the power devices always turn off in a ZVS state.…”

“…Therefore, in order to realize soft-switching for all power device actions, only turning-on of power devices in a ZVS state is necessary. To achieve softswitching conveniently, a saw-tooth carrier with alternative positive and negative slopes is used in modulation instead of the conventional triangular carrier [11] . It is defined here that when it flows to power device, phase current is positive and the saw-tooth carrier has a positive slope; or when flows from power device, phase current is negative and the saw-tooth carrier has a negative slope, see Fig.4.…”