Design and Realization of a Novel Buck-Boost Phase-Modular Three-Phase AC/DC Converter System with Low Component Number

TL;DR

This work introduces a novel three-phase inverting buck-boost converter constructed by paralleling three inverting buck-boost DC-DC stages, yielding a single-stage bidirectional buck-boost AC-DC interface with phase-modularity and a CM voltage degree of freedom. It evaluates three modulation schemes (PWM, DPWM, BCM) and identifies DPWM as the most suitable for both rectifier and inverter contexts, supported by a detailed control architecture and simulation results. The study applies the topology to two applications: a rectifier for a More Electric Aircraft and an FCV-based high-speed motor drive, showing high efficiency and compact power density (approximately 3.8 kW/L at 1 kW nominal) with a DPWM-based control strategy, CM-smoothing techniques, and an accompanying calorimetric measurement setup for GaN devices. The work advances the state of modular power electronics by reducing active components, enabling high-density, bidirectional AC-DC interfaces with robust control, and guiding future hardware realization and optimization for aerospace and automotive electrification.

Abstract

Scalability and modularity are key features for future power converters, such that these systems can be easily employed in many applications with different electrical specifications. In this thesis, the potential of a new bidirectional phase-modular three-phase AC/DC converter with buck-boost capability is evaluated by means of studying two potential application cases and developing a hardware prototype for one of them. The DC-DC inverting buck-boost converter is a well-known and established topology. By connecting three such systems in parallel, a phase-modular bidirectional buck-boost DC-AC converter employing a minimum number of active components results, where for given AC voltage amplitudes, an arbitrary DC voltage can be generated and vice versa. Such a three-phase converter was not yet described in literature and this project aims at investigating the fundamental topology properties, as well as its performance limits. A hardware demonstrator is designed for one potential application in order to verify the basic operation and the expected high performance in terms of efficiency and power density.

Figures (41)

• Figure 1: Inverting Buck-Boost Converter Topology
• Figure 2: Inverting buck-boost converter justification. Conventional solution: DC-DC boost + VSI (a); Replacing DC-DC buck stages with DC-DC buck-boost stages (b); and three-phase inverting buck-boost converter topology (c)
• Figure 3: DC-DC inverting buck-boost stage. Topology (a); Steady state current waveforms in DC-DC operation $i_L(L_1)$ and $i_L(L_2)$ (b)
• Figure 4: Theoretical inverting buck-boost stage DC-AC waveforms. Duty cycle over fundamental period (a); Inductor current over one switching period (b); Converter voltages over fundamental period (note $V_{an} \leq 0$)(c); Inductor current over fundamental period (d)
• Figure 5: A three-phase inverting buck-boost converter realized as a paralleling of three DC-DC inverting buck-boost stages. Topology (a); Steady state voltage waveforms (b)