Multi-Level Converters using 2-Level Converters

• Author / Creator

  Singh, Sukhjit

• Multi-level converters have been accepted as promising candidates to replace the conventional converter systems in applications like electric vehicles, flywheels, and aerospace systems due to the benefits like low device voltage stress, low current THD, and compactness. However, multi-level converters and their pwm schemes when used as the motor drive system, produce low-quality pwm output voltages and generate high-frequency losses in motors and inductor filters. The magnetic materials used in inductors for filtering purposes can be bulky and increase the size and cost of machine drives. Therefore, a new multi-level converter system using the coupled inductor inverters has been developed along with two new pwm schemes to produce high-quality pwm output voltages: dual inverter drive using a floating capacitor inverter and multi-level coupled inductor inverter system.
  A dual inverter drive (DID) with an open winding machine can be used to decrease the high-frequency pwm losses in motor drives while lowering the dc supply requirement. Two carrier-based pwm schemes are presented for this drive when using an induction machine: single reference dual carrier (1R2C) and dual reference dual carrier (2R2C) to produce high-quality machine voltages, that lower the motor copper and iron losses. These schemes are examined for a DID that uses the main inverter powered from a dc power source with a second inverter supplied from a floating capacitor inverter. With the proposed pwm scheme, DID can produce high-quality pwm output while experiencing a variable phase shift between the output voltages of the two inverters. Experimental comparison and verification of the two pwm schemes are presented.
  Coupled Inductors can be used to reduce the size and weight of the magnetics by canceling the fundamental flux inside the magnetic cores. Negligible fundamental voltage drop can be seen as a result and multi-level pwm output voltages can be produced at high fundamental frequencies with a very low output series impedance. Carrier and Reference signal manipulation pwm techniques have described that result in high-quality multi-level output voltages with a pwm frequency much higher than the inverter switching frequency. Coupled inductor topologies are described that allow for modular design and has been built using standard 2-level inverters and off-the-shelf magnetics. Hence, reducing the size and cost of the developed system.

• Subjects / Keywords

  • Power Electronics

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-cx1s-0v33

• License

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