research

Center for Advanced Electric Machinery (CAEM)

First Row: Profs. Yuanli Bai, Thomas Wu and Louis Chow.

We focus on the research of advanced electric machineries. Our major interests can be summarized as follows:

A. High Speed Electric Machines

(1) Design, Modeling and Optimization of High Speed Aircraft Generator

We work on the design, modeling and optimization of aircraft synchronous generator with high power-density at kW and MW level. We proposed a method to more accurately model the air-gap of a salient pole rotor through expanding the inverse of an effective air-gap function. The corresponding magnetic fields from the rotor and stator windings, as well as the expressions of back EMF, are derived using the air-gap model. The stator inner diameter and length are designed by considering a proper cooling scheme and maximum peripheral-speed of the rotor. This allows for design of the stator winding and slot geometry, including the derivation of a formula for the stator core thickness. The air-gap and salient pole shoe face can be designed using the desired specifications for power factor and torque angle. The rotor windings and geometry are subsequently designed.

main machine exciter

Publications related to this topic:

· T. Wu, T. Camarano, J. Zumberge, M. Wolff, El Lin, H. Huang and X. Jia, “Electromagnetic Design of Aircraft Synchronous Generator with High Power Density,” to appear at the 50^th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Nashville, Tennessee, Jan. 9-12, 2012.

We proposed an innovative nonlinear simulation approach for the modeling of kW and MW aircraft synchronous generator systems. Due to high power density, the generator operates in nonlinear region of the magnetic materials. Magnetic Finite Element Analysis (FEA) makes nonlinear simulation possible. Neural network technique provides nonlinear functions for system level simulation. Dynamic voltage equation provides excellent mathematical model for system level simulations. Voltage, current, and flux linkage quantities are applied in Direct-Quadrature (DQ) rotating frame. The simulated system includes main machine, exciter, rectifier bridge, bang-bang control, and PI control circuitry, forming a closed loop system. Each part is modeled and then integrated into the system model. We have successfully built a nonlinear model for 2.5 MW, 15krpm aircraft synchronous generator for Electrodynamics Inc. in Air Force SBIR program.

Publications related to this topic:

· T. Camarano, T. Wu, J. Zumberge, and M. Wolff, “Nonlinear Neural Network Modeling of Aircraft Synchronous Generator with High Power Density,” SAE 2012 Power Systems Conference, Phoenix, AZ, 2012.

· J. Chen, T. Wu, J. Vaidya, and J. Tschantz, “Nonlinear Electrical Simulation of High-Power Synchronous Generator System,” 2006 SAE International Power Systems Conference, New Orleans, LA, Nov. 6-9, 2006.

We have also worked on 200kW, 62 krpm high speed induction generator. Simulation model based on FEA analysis and adaptive control schemes were investigated for Electrodynamics Inc. in Air Force SBIR program.

MS thesis related to this topic:

· Othman Elkhomri, “DSP Implementation of DC Voltage Regulation Using Adaptive Control for 200 kW 62000 rpm Induction Generator,” Spring 2006.

(2) Highly Efficient, Super High Speed, and Highly Compact Permanent Magnet Synchronous Motor

The work was concerned with the design of permanent magnet synchronous motors (PMSM) to operate at super-high speed with high efficiency. The designed and fabricated 2kW PMSM was successfully tested to run up to 210,000 rpm. The test results showed the motor to have an efficiency reaching above 92%. This achieved efficiency indicated a significant improvement compared to commercial motors with similar ratings. Particular design strategies were adopted for super-high speed applications since motor losses assume a key role in the motor drive performance limit. Mechanical issues such as thermal analysis, bearing pre-load, rotor stress analysis, and rotor dynamics analysis are also discussed. Suitable control schemes for super high- speed PMSM were considered.

Shaft

Stator

In the last four decades, we have witnessed tremendous developments in the field of cryogenics, which led to numerous newer applications for cryocoolers. Spaceport operations of the near future are one of the prominent applications for usage of large quantities of cryogenic propellants. Efficient storage and transfer of these fluids is necessary for reducing the launch costs. In addition, for future manned and unmanned deep space missions and other missions to Mars, NASA is planning for extended cryogenic propellant storage durations of the order of several months as opposed to a few days or weeks. There would be boil-off of propellant in the transfer lines and in the propellant storage tanks in space due to heat leak. The key objective of this project is to design a reliable, compact, lightweight, affordable and highly efficient in their class cryocooler for distributed cooling of liquid hydrogen systems for spaceport applications and to develop an appropriate integrated compressor/motor system for the said cryocooler. The 2kW, 200krpm super high speed motor was applied to drive the cryocooler. The overall cryocooler system is as follows:

Publications related to this topic:

· D. Acharya, L. Zhou, L. Zheng, T. Wu, J. Kapat, L. Chow and N. Arakere, “Systems Design, Fabrication and Testing of a High-Speed Miniature Motor for Cryogenic Cooler,” International Journal of Rotating Machinery, vol. 2009, Article ID 936251, 9 pages, 2009.

· L. Zhao, C. Ham, L. Zheng, T. Wu, K. Sundaram, J. Kapat, and L. Chow, “A Highly Efficient 200,000 rpm Permanent Magnetic Motor System,” IEEE Trans. on Magnetics, vol. 43, No. 6., pp. 2528-2530, June 2007.

· L. Zheng, T. Wu, D. Achaya, K. B. Sundaram, J. Vaidya, L. Zhao, C. H. Ham, N. Arakere, J. Kapat, and L. Chow, “Design of Super-High Speed Cryogenic PMSM,” IEEE Trans. on Magnetics, pp. 3823-3825, Oct., 2005.

· L. Zhao, C. Ham, L. Zheng, T. Wu, K. Sundaram, J. Kapat, and L. Chow, “New Design of Optimal Digital Controller for a Stable Super-High Speed Permanent magnet Synchronous Motor,” IEE Proceedings - Electric Power Applications, vol. 153, No. 2, pp. 213-218, March 2006.

· L. Zheng, T. Wu, J. Vaidya, M.G. Sarwar, K.B. Sundaram, C.H. Ham, H. Seigneur, L. Zhao, N. Vanasse, A. Canale, J. Kapat, and L. Chow, “Design of a Super-High Speed Axial Flux Permanent Magnet Synchronous Motor,” Electromotion, pp. 9-17, Jan. – Mar. 2005.

PhD dissertations related to this topic:

· Liping Zheng, “Super High-Speed Miniaturized Permanent Magnet Synchronous Motor,” Fall 2005.

· Limei Zhao, “New Optimal High Efficiency DSP-Based Digital Controller Design for Super High Speed Permanent Magnet Synchronous Motor,” Fall 2005.

B. Modeling of Dynamic Heat Generation and Transfer for Electro-Mechanical Actuator (EMA)

Accurately modeling heat generation, including transients, is important in developing good thermal management of the EMA system. Transient heat generation simulation of an EMA system involves comprehensive multi-physics, multi-scale, and multi-domain simulation efforts. The procedure can be divided into two steps: (1) First, we perform comprehensive electrical simulations including non-linear magnetic fields, rotor dynamics, and power electronic circuits to get the transient heat generated from the motor windings, the core, and the power electronics board with its power devices, copper traces, and magnetic components. In the system simulation, the motor will be integrated in a complete system that consists of an input voltage source, various load conditions, a feedback control scheme, etc. Rotor dynamics can also be included in the system dynamical equations. For the transient simulation of the power electronics unit, the electromagnetic (EM) environment requires that simulation be comprehensive including the power semiconductor devices, passive components, circuit board layout, and packaging. Research will be mainly done in the time domain using the finite element method (FEM). (2) Second, we perform transient heat transfer simulation. Since the heat transfer process is a much slower process compared to electric power transmission, if we assume the acceleration and deceleration process takes about 50 ms, heat transfer simulation can be run once every twenty time iterations of electrical simulation. Our modeling work is also useful for building real-time prognostic and health management system (PHMS) for EMAs.

· D. Woodburn, T. Wu, L. Chow, Q. Leland, J. Bindl, Y. Hu, L. Zhou, Y. Lin, N. Rolinski, W. Brokaw, B. Tran, B. Jordan, E. Gregory, S. Lin and S. Iden, “Integrated Nonlinear Dynamic Modeling and Field Oriented Control of Permanent Magnet (PM) Motor for High Performance EMA,” SAE Paper No. 2010-01-1742, SAE Power Systems Conference, Ft. Worth,, TX, Nov. 2-4, 2010.

· L. Zhou, Q. Leland, E. Gregory, W. Brokaw, L. Chow, Y. Lin, J. Bindl, Y. Hu, T. Wu, B. Tran, D. Woodburn, B. Jordan, and N. Rolinski, “Lumped Node Thermal Modeling of EMA with FEAValidation,” SAE Paper No. 2010-01-1749, SAE Power Systems Conference, Ft. Worth,, TX, Nov. 2-4, 2010.

· N. E. Rolinski, Q. Leland, E. Gregory, B. Jordan, D. Woodburn and T. Wu, “Dynamic Testing of Electromechanical Actuators Using Time-history Data,” SAE Paper No. 2010-01-1748, SAE Power Systems Conference, Ft. Worth,, TX, Nov. 2-4, 2010.

· D. Woodburn, T. X. Wu, L. Chow, Q. Leland, W. Brokaw, J. Bindle, N. Rolinski, Y. Lin, L. Zhou, and B. Jordan, “Dynamic Heat Generation Modeling of High Performance Electromechanical Actuator,” 48^th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Paper AIAA-2010-0290, Orlando, Jan. 4-7, 2010.