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Analysis and Design of New Three-Phase AC-DC Rectifier Systems with Higher Frequency Isolation
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The field of power electronics finds extensive application within the energy industry. In particular, three-phase AC-DC conversion is employed in many high power applications that require integration with the utility grid such as electric vehicle charging, adjustable speed drive systems, telecommunication power supplies, and renewable energy systems. The power electronics industry is constantly pushing the limits of three-phase AC-DC converters in terms of power density, efficiency, and input current quality. Thus, the driving force behind this research is to analyze and design new three-phase AC-DC rectifier systems which exhibit high power density and efficiency while complying with input current harmonic standards. Without losing generality, a particular application is suggested for each of the proposed three-phase AC-DC rectifier systems to demonstrate their value within the energy industry. In the first study, a push-pull based three-phase AC-DC rectifier with medium frequency galvanic isolation is proposed. The unique features of this topology include the simplicity of its modulation scheme, its minimized active switch count and its high power density. It is shown that operating at medium frequency of 600 Hz, the transformer size is 1/3 of the equivalent 60 Hz design. A 10 kW design example is shown to achieve 96.5% efficiency. In the second study, a full-bridge based three-phase AC-DC rectifier with high frequency galvanic isolation (20 kHz) is implemented to further improve power density and transformer utilization. Galvanic isolation is provided through a three-phase, five-limb ferrite core transformer. By operating at 20 kHz, the transformer size is reduced twenty-one times compared to the 60 Hz design. The output DC voltage is regulated with simple duty cycle control without affecting the low order harmonics in the input current making this topology suitable for electric vehicle charging applications. In the third study, a three-phase AC-DC PWM rectifier is proposed. The converter is modulated using programmed PWM switching functions. It is shown that selected harmonics are eliminated from the utility input current. The main advantages of this topology include the absence of electrolytic capacitors, good input current quality, and high power density. In the final study, a three-phase AC-DC rectifier with bidirectional power flow capability is proposed. The converter operates in soft switching conditions, improving the system’s efficiency. The utility input current exhibits unity power factor and low total harmonic distortion. High power density is achieved by employing high frequency isolation and by avoiding electrolytic capacitors in the front-end. The analysis and design principles of each topology are accompanied with mathematical modeling and detailed simulation results. Additionally, finite element analysis (FEA) software such as Ansys Maxwell is used to assess the performance of the medium and high frequency transformers. Furthermore, experimental results - on scaled down laboratory prototypes- are presented to validate the performance of the proposed systems. Overall, the results obtained indicate that the proposed topologies offer advantages in terms of power density, simplicity, and input current quality compared to conventional and state of the art three-phase AC-DC systems.
SubjectThree-phase AC-DC rectifier
high frequency isolation
medium frequency isolation
programmed PWM rectifier
Sandoval, Jose Juan (2017). Analysis and Design of New Three-Phase AC-DC Rectifier Systems with Higher Frequency Isolation. Doctoral dissertation, Texas A & M University. Available electronically from