DSP-Based PWM Carrier Transition Technique for Parallel Connected Two-level VSCs

  • Author / Creator
    Yapa, Dohitha
  • The developments in the field of electrical engineering over the years have expanded the types of electricity generation, distribution and utilization. With these developments, power conversion plays an important role. As the demand grows, higher power handling capacity is expected of the converters. Three-phase two level voltage source converters are connected in parallel to increase the current rating and thereby meet the increasing power handling requirement under restrained voltages. Interleaved switching of parallel converters improves the system performance and can be achieved using phase-shifted carrier-based PWM. The line-to-line voltage can be further improved by alternating between two sets of carriers, although it results in jumps in the circulating current and in the flux in the inductor cores between the parallel inverters.
    A transition technique to switch between carriers is presented, which eliminates the jumps in the circulating currents and the flux. The technique uses high frequency transitional carriers to switch from one set of carriers to the other. This technique ensures that the output voltage is unaffected and the output current waveforms are glitch-free during the transitions, which is an important feature over the techniques in already existing literature. The high frequency carrier transition technique is generalized for an arbitrary number of parallel converters and is tested in a coupled inductor inverter with 2 inverter legs per phase connected in parallel. It is implemented in a low-cost DSP environment. Sawtooth carriers are used to transition between carriers with different frequencies easily and reliably. But to maintain the quality of the output similar to that of the triangular carriers, the reference and the PWM switching logic is manipulated appropriately.

    The effectiveness of the developed PWM technique has been verified using simulations and experimental results obtained with a dc link voltage of 300 V. The performance of the technique is compared with regular phase-shifted PWM and enhanced phase-shifted PWM where carriers are changed instantaneously. The circulating currents, flux in the cores, line-to-line output voltages and load currents show significant improvement over the other techniques.

  • Subjects / Keywords
  • Graduation date
    Fall 2023
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.