Research

     The charging convenience of electric vehicles determines the user experience and is one of the most important indicators affecting the popularization of electric vehicles. The onboard charger (OBC) is the interface that links the AC grid to the onboard battery pack. Its conversion efficiency directly affects the electrical mileage of electric vehicles, and its performance impacts the life cycle of battery packs. In the next generation of grid-connected electric vehicles, the onboard battery packs will play the role of a distributed energy storage system. Therefore, it requires the OBC to have the function of feeding power back to the grid, namely V2G. The DCX is the core element of the OBC adapted to V2G. For DCX, how to adapt to the ultra-wide voltage range of the battery terminal, squeeze the frequency modulation range, and improve the conversion efficiency over the wide voltage range are key research topics.

     With the evolvement of energy storage technology, rechargeable battery has become the most common portable power supply. In energy storage systems, individual cells have mismatch in capacity, voltage rate, and temperature characteristics due to the manufacturing process. Mismatched battery cells are expected to be equalized via properly designed management and equalization strategies to maintain safety and reliability. However, due to battery electrochemistry characteristics, there exists voltage recovery after equalization, causing the final equalization result inaccurate. Therefore, the behavior of batteries is worth further study, and more accurate and intelligent control strategies are needed.

     With the deep penetration of emerging technologies including big data and cloud computing, there is a growing demand for low voltage, ultra-high current power management systems, such as data center voltage regulator modules and point-of-load converters. The power supply requirements of these applications pose significant challenges to power electronics. Multi-phase interleave technology is a feasible solution to resolve this technical challenge. However, for multi-phase systems, the temperature mismatch between modules will seriously deteriorate the system lifespan. Therefore, the thermal equalization control strategy is needed to improve the operation of a multi-phase interleaved parallel system, prolong the system life, and improve the system reliability.

     The modern data center has consumed nearly 3% of the world’s power production, and it is becoming the critical infrastructure with the rapid development of emerging information technologies such as 5G communications, big data, cloud computing, and artificial intelligence. The rising energy consumption motivates the relative research on cost-effective, reliable, and greener electricity. In data centers, terminal loads such as memory and computing units operate at a very low logic voltage (sub 1V) and high current, which makes it challenging to optimize the design of the point-of-load (PoL) converters. For PoL converters, high conversion efficiency, high power density, and low cost are the major desired features.

     Renewable energy such as photovoltaics (PV) generation is gaining popularity due to the inexhaustibility and zero carbon emission in the context of a global energy shortage. It is expected that PV power will count 76% global electricity generation within 30 years. However, significant power mismatch exists between the PV source and load side due to the intermittent nature of PV sources. Energy storage systems (ESS) is introduced to serves as the energy buffer to compensate the mismatched power. Therefore, an integrated multi-port energy router is required to process the power flow among PV source, dc microgrid, and ESS. High efficiency, high power density, and multiple function are the main targets of the designed converter.

     Solid-state transformers (SSTs) with modular series-parallel structures have customized architectures and designs that make them suitable for various industrial applications. The main objective of series-parallel systems is to ensure the balanced sharing of input/output voltages/currents. The power imbalance among the modules lead to many problems, for instance, the degradation of input current, overheating, and damage. Potentially, in the worst case, it may cause the failure of the entire system. Hence, an power balance scheme with easy implementation and good tracking balance performance is required.

     A number of producers and their component suppliers are now gearing up to introduce 800V drive systems. Higher voltages supply the same amount of power with less current, which means higher charging speed, lower self-weight, and longer electric range. The power density and efficiency are very important indicators of the onboard power management system. Gallium Nitride (GaN) devices can boost the switching frequency of the converter to increase the power density. My research is mainly to explore solutions for GaN-based high-efficiency and ultra-compact onboard power management systems for next-generation 800V EV architecture.

     Inductive power transfer (IPT) systems have been widely applied in medical implants, portable devices, and electric vehicles due to the advantages of flexibility, convenience, and safety. First Harmonic Approximation (FHA) is the basic solution for modeling the resonant converters’ circuits. However, FHA has relatively low accuracy especially under high distortion operation, which usually occurs under light load conditions. Time-domain analysis has previously been proposed to improve the accuracy of circuit modeling of IPT systems. However, those time-domain modeling methods are complicated. My research focuses on investigating the simplified time-domain modeling method for IPT systems, which is universally suitable for different topologies, modulation schemes, and compensation networks.

     Nowadays, high-voltage pulse generators have been applied in various fields such as controllable nuclear fusion, precision semiconductor lithography, and X-rays. Traditional high-voltage pulse generators use magnetic compression switches or spark gap switches, which have great limitations in terms of size and weight, and the repetition rate is difficult to control. Therefore, using semiconductor devices to replace traditional mechanical switches can greatly limit the volume of the device while achieving high-precision, high-repetition frequency output. My research interest is an ultra-high-speed high-voltage pulse generator based on solid-state switches, in order to provide high-precision and reliable pulse signals for the PJMIF drive system and help realize the ultimate energy system.