Selective Noise Suppression in Random SVPWM to Shape the Voltage and Current Spectrum

The conventional space vector pulse width modulation (CSVPWM) is widely used in AC motor powered by two-level three-phase inverter, resulting in sideband noise near the switching frequency and its integer multiples in the motor. Random switching frequency space vector pulse width modulation (RF-SVPWM) and random pulse position space vector pulse width modulation (RP-SVPWM) can spread the voltage spectrum to eliminate sideband noise. However, the sideband electromagnetic force is broadband, and these methods increase the possibility that the motor will resonate at the modal frequency. In this paper, two novel selective noise suppression methods at specific frequency are proposed. The first method is to build the relationship between the pulse position and duty cycle. The simulation results show that a gap in Power Spectrum Density (PSD) at specific frequency can be achieved in the low modulation index. The second method combines RF-SVPWM and RP-SVPWM to build the relationship of the switching frequency, pulse position and duty cycle. And the simulation results show that selective noise suppression at specific frequency can be achieved with the advantage of wide modulation index range. The proposed methods provide a reference to eliminate the electromagnetic noise at the modal frequencies in motors.Comment: 8 pages, 10 figure

High Power Density, High Efficiency Single Phase Transformer-less Photovoltaic String Inverters

abstract: Two major challenges in the transformer-less, single-phase PV string inverters are common mode leakage currents and double-line-frequency power decoupling. In the proposed doubly-grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the common-mode ground-currents. The decoupling capacitance requirement is minimized by a dynamically-variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide-bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output has been developed using SiC MOSFETs with only 45 μF/1100 V dc-link capacitance. The proposed doubly-grounded topology is then extended for split-phase PV inverter application which results in significant reduction in both the peak and RMS values of the boost stage inductor current and allows for easy design of zero voltage transition. A topological enhancement involving T-type dc-ac stage is also developed which takes advantage of the three-level switching states with reduced voltage stress on the main switches, lower switching loss and almost halved inductor current ripple. In addition, this thesis also proposed two new schemes to improve the efficiency of conventional H-bridge inverter topology. The first scheme is to add an auxiliary zero-voltage-transition (ZVT) circuit to realize zero-voltage-switching (ZVS) for all the main switches and inherent zero-current-switching (ZCS) for the auxiliary switches. The advantages include the provision to implement zero state modulation schemes to decrease the inductor current THD, naturally adaptive auxiliary inductor current and elimination of need for large balancing capacitors. The second proposed scheme improves the system efficiency while still meeting a given THD requirement by implementing variable instantaneous switching frequency within a line frequency cycle. This scheme aims at minimizing the combined switching loss and inductor core loss by including different characteristics of the losses relative to the instantaneous switching frequency in the optimization process.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201