PhD defence by Yanfeng Shen on Reliability Oriented Design and Optimization of PV Microinverters
26.10.2018 kl. 13.00 - 16.00
Yanfeng Shen, Department of Energy Technology, will defend the thesis "Reliability Oriented Design and Optimization of PV Microinverters".
Reliability Oriented Design and Optimization of PV Microinverters
Professor Frede Blaabjerg
Associate Professor Yongheng Yang
Professor Stig Munk-Nielsen, Dept. of Energy Technology, Aalborg University (Chairman)
Johan Driesen, Dept. of Elektrotechniek/ELECTA, K.U. Belgium
Robert S. Balog, Texas A&M University at Qatar
The market share of microinverters in residential PV systems has been increasing due to their abilities to achieve the module-level maximum power point tracking (MPPT), and module-level monitoring and troubleshooting. Nevertheless, there are still challenges with PV microinverter systems, e.g., relatively low power conversion efficiency, higher price per unit of electricity, trend of integration of PV microinverter and module, and low reliability under harsh environment. The main focus of this PhD project is on the reliability-oriented design and optimization of PV microinverters.
In order to maintain high efficiencies over a wide PV voltage range, a new series resonant converter (SRC) is proposed for two-stage PV microinverters. The operation principle and key characteristics of the proposed converter are analyzed, and a 1-MHz 250-W PV microinverter prototype has been built and tested for verifications. The electro-thermal modeling is crucial to the junction/hotspot temperature prediction and reliability evaluation of devices and PV mciroinverter systems. In this regard, critical parameters and power loss characteristics are modeled for a series of 650-V GaN enhancement-mode high-electron-mobility transistors (eHEMTs). As another important part in high-power-density power electronic converters, printed circuit board (PCB) vias and pads are also analytically modeled concerning their thermal resistance. An optimal design trajectory and an algorithm are proposed for PCB vias and pads, respectively. Finite element method (FEM) simulations and experimental tests are further conducted to verify the built thermal models.
A cost-volume-reliability Pareto optimization method is proposed for a PV microinverter. The modeling process of power loss, thermal impedance, lifetime, cost, and volume of components are conducted. Then the cost-volume-reliability Pareto optimization method is executed, yielding a Pareto front which enables a design trade-off among the three performance metrics. Furthermore, this PhD thesis exemplifies the procedure and function of a reliability-oriented design method. As a case study, the electro-thermal and lifetime modeling of components is carried out for an impedance-source PV microinverter product. Then, the wear-out performance of the PV microinverter product is analyzed to identify the weakest link which is the DC-link capacitor. Accordingly, the previous DC-link capacitor is replaced with a better one, and a variable DC-link voltage control is introduced to the PV microinverter. It turns out that the adopted measures can significantly improve the system reliability.
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ALL ARE WELCOME. THE DEFENCE WILL BE IN ENGLISH.
AFTER THE DEFENCE THERE WILL BE AN INFORMAL RECEPTION AT PONTOPPIDANSTRAEDE 111 IN ThE COFFEE ROOM.
Department of Energy Technology
Pontoppidanstræde 105, room 4.127