High-Performance Single-Phase Line-Interfaced Power Converters

Danish Shahzad
2021
The use of single-phase line-interfaced power converters in electrical power systems is rapidly growing due to the changing nature and power quality requirements of electrical loads. Most applications require these single-phase line-interfaced power converters to be compact and efficient, and depending on application meet additional performance, cost, and reliability targets. This thesis presents innovative system architectures, circuit topologies, design methodologies, and control strategies
more » ... r highly compact and efficient single-phase acdc and ac-ac line-interfaced power converters. First, a comprehensive design methodology for step-down isolated two-stage ac-dc converters is presented which compares various designs and operating modes and selects the optimal design based on overall volume and efficiency. Additionally, a new control strategy is presented for a compact front-end soft-switched powerfactor correction (PFC) stage to ensure compliance with strict electromagnetic interference (EMI) regulations. A 1-kW universal-input to 28V-output isolated ac-dc prototype converter is built to showcase performance benefits of proposed design and control strategies. This prototype achieves a high-power-density of 84W/in 3 and maintains greater than 93% efficiency across a wide output power range. Next, the functionality of the proposed ac-dc converter is further enhanced by incorporating a new droop control strategy for parallel operation of multiple similar ac-dc converter modules. The proposed control strategy uses the input current of the secondary dc-dc stage of two-stage ac-dc converters in conjunction with variable droop iv resistance to achieve near-perfect parallel operation. A multi-module ac-dc conversion system is built to validate the proposed droop control strategy. The parallel modules achieve a current distribution error of less than 2% near their maximum output power. Multiple ac-ac conversion applications are also addressed in this thesis. For highly cost-sensitive applications, two compact and efficient single-stage ac-ac converters are presented which utilize a comprehensive design methodology centered around minimizing the total cost of components. Moreover, innovative control strategies are presented for both ac-ac converters to enable output voltage regulation under input voltage and output load fluctuations. Both single-stage ac-ac prototype converters, utilizing the proposed design and control strategies, are built and tested. The 600-W 480Vrms-to-264Vrms prototypes achieve power densities exceeding 40W/in 3 while maintaining conversion efficiencies of greater than 96% across majority of the output load. Finally, a much more feature-rich ac-dc-ac converter is also proposed for advanced ac-ac conversion applications, such as data center online uninterruptible power supplies (UPS). The proposed transformer-less two-stage ac-ac converter is based on a new circuit topology which can operate at high switching frequencies (up to several MHz) and utilize 50% lower dc-bus capacitance than conventional split-dc-bus topologies. A 1-kVA 120Vrms prototype ac-dc-ac converter is built and extensively tested to showcase performance improvements. This prototype achieves high peak conversion efficiency of greater than 95% and high power density of 26.4W/in 3 while utilizing long-life but relatively bulky film dc-bus capacitors. v
doi:10.7298/4n4v-w755 fatcat:ca3jlo5gijgrnjzqhxkiwvzr5i