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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2021)

Ac-dc (and dc-ac) power converters are the interfaces between the electrical grid and thesystems for emerging applications such as electric vehicle (EV) charging, renewable energy source integration, data center power delivery, consumer electronics and numerous other applications. In this dissertation, new circuit topologies and control techniques to improve the performance for both single-phase and three-phase grid-tied converters are explored for three major conversion scenarios: high power bidirectional single-phase ac-dc converters for EV charging and data center applications, low power single-phase ac-dc converters for consumer electronics, and high power three-phase ac-dc converters. For single-phase conversion, the challenge of twice-line frequency energy buering is addressed with active buering techniques that can signicantly reduce the required capacitor size compared to conventional solutions. Through the development of active buers with systematic multi-objective optimization methods and associated advanced digital control, the energy utilization ratios of the passive components are much improved, and the system losses are optimized. For threephase conversion, control and modulation techniques to reduce computational complexity and inductor current ripple are proposed and validated. The proposed circuit topologies and control techniques for both single-phase and three-phase are all validated with high performance hardware demonstrations. Some of the highlighted ones in this dissertation are: a 6 kW, 400 Vdc single-phase liquid-cooled EV charger with optimized series-stacked buer, achieving record power density; a 6 kW 400 Vdc three-phase multilevel rectier with advanced digital control techniques; an active single-phase buer with the smallest reported capacitor size for 2 kW, 400 Vdc inverters; a compact active buer for 65 W USB-C charger.

    Cover page: Circuits and Control for High-Performance Grid-tied Ac-Dc Conversion Systems
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2021)
    Next generation hybrid electric aircrafts rely on improvements in electric drivetrains. This work explores the advantages of incorporating high-density, high-efficiency dc-dc converters to enable flexible battery configurations, as well as increased dc bus voltages for reduced cable weight. A dc-dc frontend stage with wide operating range also enables a constant (and optimum) inverter input voltage, irrespective of battery state-of-charge, enabling increased inverter efficiency. Practical challenges such as gate drive power delivery, level shifting, commutation loop and converter start-up are addressed in this work to increase overall performance and reduce weight. Finally, this work demonstrates a high-voltage hardware prototype capable of achieving 99.3% peak efficiency and 28.2 kW/kg specific power density.
      Cover page: A Lightweight Multilevel Power Converter for Electric Aircraft DrivetrainCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2022)
      Single-phase rectifier and inverter applications require an additional reactive circuit branch tied to the dc-link in order to remove the twice line frequency power pulsation that couples to the dc bus. The series-stacked buffer (SSB) has been identified as an active buffer topology that buffers this reactive power with a high energy utilization factor. However, the SSB requires an additional loss compensation control that injects real power into the SSB branch. Consequently, residual ac current and voltage ripple remain coupled to the dc-link. This paper proposes a novel loss compensation method featuring augmented hardware and control that introduces charge injection which eliminates this twice line frequency ripple from the dc-link. A 1.5 kW hardware prototype was built and tested to verify the effectiveness of the newly proposed charge injection method.
        Cover page: A Charge Injection Loss Compensation Method for a Series-Stacked Buffer to Reduce Current and Voltage Ripple in Single-Phase Systems
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2020)
        On-board electric vehicle (EV) chargers convert grid ac voltage to dc voltage to charge a high-voltage battery pack. High efficiency and high power density single-phase ac-dc converters are desirable in such applications to reduce the heat loss, volume and weight of these chargers. Moreover, the capability of bidirectional conversion is preferred for potential vehicle-to-grid applications. This paper presents the system ar-chitecture and embedded digital control implementation of a 7 kW, universal ac (120-240 VAC) to 400 VDC single-phase ac-dc bidirectional converter. The converter features an interleaved 6-level flying capacitor multilevel (FCML) ac-dc stage and a series-stacked buffer for buffering twice-line frequency pulsating power to achieve high efficiency and power density. Test results that demonstrate both ac-dc power factor correction (PFC) and inverter operation at kilowatt levels are provided.
          Cover page: Architecture and Control of An Interleaved 6-Level Bidirectional Converter With an Active Energy Buffer for Level-II Electric Vehicle Charging
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2021)
          On-board electric vehicle (EV) chargers provide ac to dc conversion capability to charge a high-voltage battery pack. As they are carried within a vehicle at all times, high efficiency and high power density are desirable traits for such a converter, in order to reduce the size, weight, and power loss of the system. Bidirectional capability is also desirable for an on-board charger to support vehicle-to-grid ancillary applications. This paper presents the implementation of a bidirectional single-phase ac-dc converter, converting between universal ac (120-240 VAC) and 400 VDC. Discussions of system architecture, control, mechanical design and assembly, and thermal management of an interleaved 6-level flying capacitor multilevel (FCML) power factor correction (PFC) stage with a twice-line-frequency series-stacked buffer (SSB) stage are included. Experimental results demonstrating dc-ac inverter operations at the kilowatt scale are provided. A peak efficiency exceeding 99% is observed, and a maximum power of 6.1 kW is tested.
            Cover page: An Interleaved 6-Level GaN Bidirectional Converter with an Active Energy Buffer for Level II Electric Vehicle Charging
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2022)
              Cover page: A Bidirectional Liquid-Cooled GaN-based AC/DC Flying Capacitor Multi-Level Converter with Integrated Startup and Additively Manufactured Cold-Plate for Electric Vehicle Charging
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