Event
Ph.D. Research Proposal Exam: Ayooluwa Adeolu Ajiboye
Monday, May 5, 2025
1:00 p.m.-3:00 p.m.
AVW1146
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: Ph.D. Research Proposal Exam
Name: Ayooluwa Adeolu Ajiboye
Committee:
Professor Alireza Khaligh(Chair)
Professor Sahil Shah
Professor Xin Zan
Date/time: Monday, May 5th, 2025 at 1:00pm to 3:00pm
Location: AVW1146
Title: Advanced Decoupling Strategies for SiC-based Power Conversion Systems in Renewable Energy Applications
Abstract:
Renewable energy integration in power distribution systems form the major component in the pivot to sustainable energy infrastructure as a response to the global climate change and in meeting the growing global energy demand. Some major applications of renewable systems are highlighted in photovoltaic (PV) residential \& industrial power systems as well as transportation electrification. Renewable power distribution systems can be developed as a stand-alone islanded microgrid network for applications such as rural electrification. However, to increase renewable energy penetration, achieve higher power levels, improve overall system reliability, provide better energy regulation, and to overcome the intermittent nature of renewable energy sources, these microgrid systems can be interconnected with the utility power grid and/or with other microgrid networks. Power conversion systems (PCS) which facilitate the transformation of electrical power between various forms are an important requirement for the interconnection of various energy sources and loads. Traditionally, in power management systems, distributed individual power conversion units are typically used to meet the electrical requirements of the various energy sources and load. However, to improve efficiency due to reduced number of conversion stages, and to foster a higher level of system integration, a centralized power conversion framework can be alternatively utilized. This high-level of inter-connectivity and integration of multiple energy sources and loads in a unified power conversion infrastructure creates additional challenges in the form of inter-dependencies and cross-coupling between the interconnected energy sources and loads.
One of the challenges resulting from the interconnection of multiple sources and loads sharing a common DC-link source is the coupling of switching noise oscillations between the various nodes on the network. Power electronic converters are characterized by their incorporated switching network for the electrical power conversion process. In older power electronic systems, silicon-based switching devices (e.g. MOSFETS, IGBTS, thyristors etc.) were utilized for power conversion. However, in recent years, wide-bandgap devices such as silicon carbide (SiC), and Gallium Nitride (GaN) devies have been adopted to form the switching network within power converters due to their numerous benefits. Such benefits include higher electron mobility resulting in lower conduction losses, wider band-gap resulting in higher breakdown voltage, increased operating temperature, and lower on-state drain-source resistances. Additionally, wide band-gap devices have higher commutation speeds or higher slew rates which enable lower switching losses during power conversion. However, a drawback for the increased commutation speeds is the exacerbation of undesired voltage overshoots and oscillations across the drain-source port of the devices during the switching transition. In this dissertation, a Thevenin-based frequency domain approach for modelling the switch voltage overshoot and oscillations with respect to the commutation power loop is proposed. The switching transition and its associated slew rate is modelled using a clamped-ramp function. The two figures of merit used to quantify the effect of the circuit elements in the commutation power loop with respect to the resonant oscillations are the voltage overshoot and time to steady state. Using the clamped-ramp function and the two figures of merit, the effect of the parasitic inductance and the decoupling capacitor on the power loop is analyzed. The trends observed from the analyses are used to obtain recommendations regarding the sizing and placement of the decoupling capacitor in the power loop. The proposed Thevenin-based frequency domain model is experimentally validated by comparing the analytical results with both LTspice simulations and the experimental waveforms for a SiC-based 400V, 20A double pulse test.
Moreover, an additional challenge resulting from the integration of single-phase DC-AC inversion systems is the injection of a double-line frequency (DLF) circulating power component. In PV systems, the propagation of the double-line frequency power component to the PV panels could cause the damage of the PV modules. Traditionally, bulky electrolytic capacitors are placed in parallel with the PV modules to absorb this circulating power component. However, the rapid degradation and limited lifetime of the electrolytic capacitors gave rise to the adoption of active power decoupling (APD) techniques using power converters as an alternative to decouple the DLF power from the PV modules. Furthermore, in a unified multi-port power conversion system, the inherent cross-coupling of active power between the different ports serves as a major bottleneck which prevents the independent dynamic operation and power flow between the interconnected ports. This can be attributed to the use of a mutual multi-winding magnetic structure integrating the different energy sources and loads at its ports. The effect of the cross-coupling within a multi-port system can be observed when fluctuations in voltage/current at a port impacts the power flow to or from other ports thereby injecting unwanted voltage/current fluctuations at the other ports.
To address these challenges, an n-port multi-active bridge (MAB) converter with integrated active power decoupling is proposed in this dissertation. Multi-active bridge (MAB) converters have gained a wide level of adoption in several multi-port applications due to its inherent high-level of integration, multidirectional power flow, soft-switching capability, scalability, and galvanic isolation. The star (Y) or delta (Δ) equivalent models are traditional methods to represent the high-frequency n-port magnetic link of the MAB converter. However, these models become reduced-order for higher order n-port MAB structures and do not fully capture the dynamics of the converter. A systematic approach to experimentally derive the full-order n x n impedance matrix used to characterize the terminal relationships of the n-port high-frequency magnetic link is proposed. A generalized harmonic analysis (GHA) and a zero-voltage switching (ZVS) modeling framework which can be scaled to any number of ports is established. Furthermore, this work presents a detailed analytical study on the inherent cross-coupled active power flows in the MAB converter. A control strategy based on feedforward compensation of a power decoupling matrix is used for facilitating the decoupling of the active power flow between the ports. The transient and steady-state performance of the decoupler feedforward compensator is experimentally validated on a SiC-based 3kW experimental MAB prototype with its ports rated at 400V, 440V, 300V, and 240V.
