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Yan-Fei Liu

Dr. Yan-Fei Liu
Professor
Department of Electrical and Computer Engineering
410 Walter Light Hall
Queen’s University
Kingston, ON   K7L 3N6
Phone: (613) 533-6731
Fax: (613) 533-6615
yanfei.liu [at] queensu.ca

Yan-Fei Liu (Senior Member IEEE 1997) received his B.Sc and M.Sc degrees from the Department of Electrical Engineering, Zhejiang University, China, and his Ph.D degree from the Department of Electrical and Computer Engineering, Queen’s University, Canada, in 1994, all in Electrical Engineering.

Dr. Liu has been on the Faculty at Queen's University since 1999 and currently holds the position of Professor of the Department of Electrical and Computer Engineering. He is a past Coordinator of Graduate Studies in the department. From 1994 to 1999, he was a technical advisor with the Advanced Power System division of Astec (formerly Nortel Networks), where he was responsible for high quality design, new products and technology development. Dr. Liu and his research team have been conducting advanced research in the area of power electronics, including digital control technologies for DC-DC switching converters and AC-DC switching converters with power factor correction. Additional research has been conducted in EMI filter design methodologies for switching converters, technologies for high switching frequency low switching loss converters, and modeling and analysis of core loss and copper loss for high frequency planar magnetics. Dr. Liu and his team are also researching topologies and control for VRM (Voltage Regulator Modules) for CPU applications, and large signal modeling of switching converters.

He and his students have published over 90 papers in IEEE conferences and journals. Dr. Liu is also the inventor of 12 US patents and the inventor of three additional US patent applications.

Dr. Liu is the winner of the “Premier’s Research Excellent Award” (PREA) in 2001, and teaching award in 2000 and 2008, both at Queen’s University. At Nortel, he was awarded the “1997 Award in Excellence in Technology.” He is currently a member of the Professional Engineers of Ontario and an Associate Editor for IEEE Transactions on Power Electronics.

Dr. Liu is the principal contributor for two IEEE standards, IEEE Std 1515-2000, “IEEE Recommended Practice for Electronic Power Subsystems: Parameter Definitions, Test Conditions, and Test Methods”, and IEEE Std 1573-2003, “Recommended Practice for Electronic Power Subsystems: Parameters, Interfaces, Elements, and Performance.”

Research Area

1. Digital Control of Power Converters

With the rapid development of advanced high-speed digital circuits, digital control techniques will gradually replace analog controllers in high switching frequency converters. With this trend, intelligent power supplies are expected to play an important role in communication, automobile, computer and aerospace industries in the near future. Current research interests include the development of advanced digital control algorithms for high-performance, high frequency power converters. Current research interests include the development of advanced digital control algorithms for high-performance, high frequency power converters. Modern control theories, such as fuzzy logic control, neural network control, sliding mode control, adaptive control and nonlinear control have been developed to improve converter characteristics, such as large-signal dynamics and efficiency over wide range of loads. Low cost DSPs and FPGA based control systems have been developed to realize these novel techniques in both DC-DC and AC-DC applications.

2. High Efficiency Low Output Voltage Converters

With the continued demand to increase the power density, improve bandwidth, and reduce the size of power supplies, switching frequencies must be increased beyond the 1MHz level. In addition, the operating voltage has been reduced steadily. ICs operating at 3.3V are very common and new ICs operating as low as 0.5V are around the corner. These trends impose a big challenge to the power supply industry. The research in this area is focused on high frequency, high efficiency, low power DC-DC switching power supplies for telecommunication and computing applications. Work will take place for isolated and non-isolated applications. In addition, new packaging technologies will be investigated to help achieve switching frequencies beyond 1MHz.

3. PFC Technique Improvements

In order to improve power line quality, standards have been proposed to limit the harmonic content generated by AC-to-DC power supplies. Traditionally, a diode bridge and a bulk capacitor are used to achieve AC-to-DC conversion. Unfortunately, the power factor of these circuits are very low (around 70%). Various power factor correction circuits have been proposed to achieve a power factor greater than 99%, however further work needs to be done to improve the performance of these methods. The research is focused on finding new converter topologies to achieve high power factor, high efficiency, low EMI and eliminate the diode reverse recovery problem. In addition, research will be done on how to use DSP techniques for PFC control while achieving significant cost reduction and performance enhancement.

4. Modern Control Techniques in Electric Motor Drive Systems

Modern control theories, such as fuzzy logic control, neural network control, sliding mode control and adaptive control have been developed for electric motor drive systems. These techniques make the motor drive systems more robust against any possible disturbances so that the speed, or position of the motor accurately tracks the reference. The research in this area is focused on modern control theory applications and DSP based control systems design for induction motors, permanent magnet synchronous motors, brushless motors and switched reluctance motors.

5. EMI Filter Design

In communication systems, "off the shelf" power modules are used to convert the input voltage to a lower voltage to power digital and/or optical circuits. However, these power modules normally cannot meet the FCC, or CISPR EMI regulatory standards for conducted EMI. As a result, additional EMI filters, normally both common mode (CM) and differential mode (DM), are needed at the input of these power modules in order to filter out the switching noise and eliminate electromagnetic interference to other equipment. The research in this area is focused on new design methods for EMI filters for both DC-DC and AC-DC switching power supplies.

Publications
Communications Power Laboratory