Tim A. Haskew

Modeling and Estimation for Electromechanical Thrust Vector Control of Rocket Engines

Increased use of electromechanical actuators (EMA) in high-power, x8f ight-critical applications where hydraulics have traditionally been employed has increased the need for accurate, measurable models of the EMA-load systems. Thrust vector control (TVC) of rocket engines is such an application. An intuitive, linearized model of a TVC –EMA system is presented along with practical and accurate methods of estimating the model parameters. The estimation techniques are a combination of calculations using engineering design data and of experiments based on x8e rst principles that are designed to isolate the effects of specix8e c parameters and/or combinations of parameters. The techniques use measurements that are commonly available in an EMA system and inputs that are easily generated with either a computer or signal generator. The validity of the model and the parameter estimation techniques are experimentally verix8e ed with a pendulum simulator of a rocket engine and an EMA designed for TVC. Nonlinearities are discussed and simulated, and resonance shifting caused by backlash is demonstrated with experimental data.

Impact of electric vehicles on electric power generation and global environmental change

Abstract The transportation industry is a major contributor to greenhouse gas and pollutant emissions. Of particular significance is the fleet of private vehicles powered by internal combustion engines utilizing petroleum-based fuels. The subject project was initiated to develop methodology to assess the impact of vehicle fleet electrification on electric power generation and global environmental change. While vehicle electrification will reduce vehicle emissions, the recharging energy will be generated at utility generation sites where emissions will increase. The project included a case study for Alabama. The vehicle emissions fleet model is based on the EPA software mobile 5a and employs Alabama Department of Transportation data as inputs to the case study. Electric vehicle penetration effects on vehicle emissions are computed by linear scaling of the base-case emissions. Power plant quarterly emission data from the EPA were employed in the case study for the State of Alabama. Values for feedstock and fuel emissions were taken from greet 1.5 to complete the fuel cycle calculations. In the 10% EV penetration Alabama case study, all light-duty vehicle emissions are reduced by 10%, and the total (light-duty vehicle and utility) emissions for the principle greenhouse gas CO2 were altered by −1.79%. Emissions for NOx and SO2 were altered by −4.37%, and +1.44%, respectively.

Characteristic study of vector-controlled direct driven permanent magnet synchronous generator in wind power generation

With the advance of power electronic technology, direct driven permanent magnet synchronous generators (PMSG) have drawn more and more interests to wind turbine manufactures due to the advantages in PMSG wind turbine integration with the electric grid. This paper focuses on the analysis of PMSG characteristics through computer simulation. Compared to other analytical approaches, the specific features of the paper are 1) a PMSG steady-state model in d-q reference frame, 2) simulation-based study that reflects general PMSG d-q control strategies, and 3) characteristic study in both fixed and variable speed point of view. Extensive simulation analysis is performed to inspect how PMSG characteristics are affected by different d-q control conditions, such as torque, and real and reactive-power versus speed characteristics.

Transient Force Reduction in Electromechanical Actuators for Thrust-Vector Control

There is a move within the aerospace community to use electromechanical actuators (EMA) in thrust-vector control (TVC) applications. However, shock-wave forces that occur during startup and shutdown of unthrottled TVC rocket engines excite resonance in the mechanical dynamics. This results in very large forces transmitted through the actuator. Additionally, with traditional compensation, the position control system must be designed with lowbandwidth because of the typically low resonant frequency. Dynamicforce feedback (DFF)compensation is proposed to reduce the effects of resonance. Utilizing a motor position sensor and a load cell in the actuator mount,aproportional-integral-derivative (PID)positioncontrolloopisclosedinparallelwithaforcecontrolloopto provideresonancereductionand transmitted forcereduction.Thisallowshigherpositioncontrolbandwidthswhile reducingthetransmittedforces.Thecontrollerdesignmethodologyusestwoindependentloop-shapingprocedures, which are separated by their effective frequency ranges. The techniques are validated with experimental data from an EMA-TVC simulator, showing improvements in both the position control and the transmitted forces. Additionally, the controller is shown to be robust with respect to variation in the resonance.

Energy capture, conversion, and control study of DFIG wind turbine under weibull wind distribution

A doubly-fed induction generator (DFIG) is a ‘special’ variable speed induction machine widely used in modern large wind turbines. Unlike a fixed-speed wind turbine, a DFIG wind turbine depends strongly on the controls of the system under variable wind conditions. This paper investigates statistical properties of energy capture, conversion, and control of a DFIG wind turbine under Weibull wind distribution. Power extracted from the wind and variable speed operation of the induction generator are studied by considering DFIG control properties and statistical characteristics of the wind. DFIG speed control characteristics are investigated under random wind conditions by considering the effects of gear ratio, generator pole number, and grid frequency. An evaluation study is performed to investigate how different generator speed probability distribution affects DFIG power characteristics. Extensive simulation results are given to illustrate DFIG operating properties under random wind and different dq control conditions.

Marginal cost-based pricing of wheeling transactions and independent power producers considering security constraints

Various proposed pricing policies for wheeling transactions and independent power producers under open transmission access do not compensate, in a direct manner, parties who participate in maintaining network security and provide the system reactive power requirements. Within this paper, a pricing structure that provides such compensation, based on physically meaningful price components, is developed. Prices determined by the proposed method reflect the cost of incurred losses and those of satisfying network security constraints. The effects of security constraint specifications on price calculations is investigated. Results are presented for the IEEE 6- and 30-bus test systems.

Simulation of the brushless DC machine

Research efforts on the brushless DC machine (BDCM) have produced a computer simulation model of the machine applicable for analysis of the machine during fault conditions. Several failure modes have been studied using this simulation technique. Modeling the motor during flux weakening, bearing failure, armature winding open circuiting, and armature winding short circuiting along with the operation of the machine under normal conditions is presented. This simulation model will facilitate further study of the BDCM and its utilization in the electromechanical actuation and control application.<<ETX>>

Two-phase on drive operation in a permanent magnet synchronous machine electromechanical actuator

Brushless machine technology provides a new and feasible option for high-power actuation applications historically serviced by hydraulic devices. Two types of brushless permanent magnet machines exist: the brushless DC machine and the permanent magnet synchronous machine. While the brushless DC machine is ideally suited for operation with a two-phase on drive, the permanent magnet synchronous machine is ideally suited for operation with a three-phase on drive. Within this paper, the impact of the torque ripple induced by using a two-phase on drive with the permanent magnet synchronous machine is examined for viability, though not compared with the three-phase on drive. The focus application is thrust vector control of the Space Shuttle Main Engines, and test results indicate that such operation is acceptable.

Dynamic load testing of roller screw EMAs

In the electromechanical actuators (EMA) laboratory at The University of Alabama, USA, a dynamic load test stand has been designed and built. This test stand uses large load, high bandwidth and hydraulic actuation to generate load profiles under force control. The test stand can accommodate EMAs up to six feet in length. It can generate dynamic loads of up to 100,000 lb at fundamental frequencies of up to 12 Hz against a stiff environment. This test stand has been used to generate severe loading conditions on a large roller screw in an attempt to qualify the effects of large, high frequency loads on roller screw. During the tests performed in the EMA laboratory the screw was fixed at one end and axial loads were applied to the roller nut at the other. Since the end opposite the nut was fixed, only a small amount of relative rotation between the nut and screw was achieved. This rotation was the result of elastic deformation (wind up) of the screw along the length between the fixed end and the nut. This simulates a severe, but likely, application of the roller screw. The results of the tests performed demonstrate that roller screws may be damaged by dynamic loading with load magnitudes that are well within the static load rating of the screw. While the damage that was observed is not catastrophic, it would be expected to substantially decrease the life of the screw.

Power generation characteristic study of integrated DFIG and its frequency converter

The doubly-fed induction generator (DFIG) is a special variable speed induction machine widely used in modern large wind turbines. It is a standard, wound rotor induction machine with its stator windings directly connected to the grid and its rotor windings connected to the grid through a back-to- back PWM converter. The DFIG power generation consists of power delivered from two paths, one from the stator to the grid and the other from the rotor, through its frequency converter, to the grid. The DFIG power production characteristics, therefore, depend not only on the induction machine but also on the two back-to-back AC/DC converters as well as how they are controlled. This paper studies power generation characteristics of a DFIG system through computer simulation. Steady-state models in dq reference frame are developed for both the DFIG and its frequency converter. A simulation system is built by integrating the models of the two parts together with effective consideration of d-q control strategies applied to both rotor- and grid-side converters. An extensive analysis is conducted to examine power generation characteristics of the integrated DFIG and its frequency converter under different d-q control conditions.