Design and application of electromechanical actuators for deep space missions

During the period 8/16/92 through 2/15/93, work has been focused on three major topics: (1) screw modeling and testing; (2) motor selection; and (3) health monitoring and fault diagnosis. Detailed theoretical analysis has been performed to specify a full dynamic model for the roller screw. A test stand has been designed for model parameter estimation and screw testing. In addition, the test stand is expected to be used to perform a study on transverse screw loading

Design and application of electromechanical actuators for deep space missions

This progress report documents research and development efforts performed from August 16, 1993 through February 15, 1994 on NASA Grant NAG8-240, 'Design and Application of Electromechanical Actuators for Deep Space Missions.' Following the executive summary are four report sections: Motor Selection, Tests Stand Development, Health Monitoring and Fault Management, and Experiment Planning. Three specific motor types have been considered as prime movers for TVC EMA applications: the brushless dc motor, the permanent magnet synchronous motor, and the induction motor. The fundamental finding was that, in general, the primary performance issues were energy efficiency and thermal dissipation (rotor heating). In terms of all other issues, the three motor types were found to compare quite equally. Among the design changes made to the test stand since the last progress report is the addition of more mounting holes in the side beams. These additional holes allow the movable end beam to be attached in a greater number of positions than previously. With this change the movable end beam can move from full forward to full back in three inch increments. Specific mathematical details on the approach that have been employed for health monitoring and fault management (HMFM) have been reported previously. This approach is based on and adaptive Kalman filter strategy. In general, a bank of filters can be implemented for each primary fault type. Presently under consideration for the brushless dc machine are the following faults: armature winding open-circuits, armature winding short-circuits (phase-to-phase and phase-to-ground), bearing degradation, and rotor flux weakening. The mechanically oriented experiments include transient loading experiments, transverse loading experiment, friction experiment, motor performance experiment, and HMFM experiment

Design and application of electromechanical actuators for deep space missions

This third semi-annual progress report covers the reporting period from August 16, 1994 through February 15, 1995 on NASA Grant NAG8-240, 'Design and Application of Electromechanical Actuators for Deep Space Missions'. There are two major report sections: Motor Control Status/Electrical Experiment Planning and Experiment Planning and Initial Results. The primary emphasis of our efforts during the reporting period has been final construction and testing of the laboratory facilities. As a result, this report is dedicated to that topic

Design and application of electromechanical actuators for deep space missions

The annual report Design and Application of Electromechanical Actuators for Deep Space Missions is presented. The reporting period is 16 Aug. 1992 to 15 Aug. 1993. However, the primary focus will be work performed since submission of our semi-annual progress report in Feb. 1993. Substantial progress was made. We currently feel confident in providing guidelines for motor and control strategy selection in electromechanical actuators to be used in thrust vector control (TVC) applications. A small portion was presented in the semi-annual report. At this point, we have implemented highly detailed simulations of various motor/drive systems. The primary motor candidates were the brushless dc machine, permanent magnet synchronous machine, and the induction machine. The primary control implementations were pulse width modulation and hysteresis current control. Each of the two control strategies were applied to each of the three motor choices. With either pulse width modulation or hysteresis current control, the induction machine was always vector controlled. A standard test position command sequence for system performance evaluation is defined. Currently, we are gathering all of the necessary data for formal presentation of the results. Briefly stated for TVC application, we feel that the brushless dc machine operating under PWM current control is the best option. Substantial details on the topic, with supporting simulation results, will be provided later, in the form of a technical paper prepared for submission and also in the next progress report with more detail than allowed for paper publication

Design and application of electromechanical actuators for deep space missions

This progress report documents research and development efforts performed from August 16, 1993 through August 15, 1994 on NASA Grant NAG8-240, 'Design and Application of Electromechanical Actuators for Deep Space Missions.' Since the submission of our last progress report in February 1994, our efforts have been almost entirely focused on final construction of the test stand and experiment design. Hence, this report is dedicated solely to these topics. However, updates on our research personnel and our health monitoring and fault management efforts are provided in this summary. Following this executive summary are two report sections. The first is devoted to the motor drive being constructed for the test stand. The thrust of the next section is the mechanical and hydraulic design and construction based on the planned experimental requirements. Following both major sections are three appendices

Vibration absorber implementation for space launch vehicle vibration reduction

Vibration is a major problem in space launch vehicles during burning sequences. These vehicles are vulnerable to impulsive and pulsed vibrations like those produced by rocket engines. The Ares I launch vehicle is anticipated to produce vibration in the organ pipe mode. The problems may be particularly severe if the pulses occur at the natural frequencies of the vehicle structure. In the case of the Ares, as the rocket burns, the excitation frequency drifts through the frequency corresponding to a longitudinal mode of the vehicle. Although it is not certain, there is concern that the corresponding vibrations are potentially severe enough as to be lethal to crew members and thus some consideration of vibration mitigation is warranted. Common approaches to dealing with vibration problems - structural redesign, addition of mass or damping materials - are not thought to be viable solutions; structural redesign through addition of mass and/or damping would result in excessive weights with corresponding performance limitations in terms of payload. The alternative approach is to retrofit the aft skirt with one or more tuned vibration absorbers (TVA). Application of an undamped TVA to a primary system introduces a zero in the frequency response of the primary system that is located at the TVA natural frequency. In the case of the Ares, however, the excitation frequency, while easily measured, is not fixed, but varies as the rocket burns. The effect of a TVA on the vibration of a primary system experiencing such an excitation is not known. The main objective of this research was to predict and simulate the behavior of a two degree of freedom (two-mass) system experiencing sinusoidal excitation with a linearly-varying frequency. In doing so, a framework for analyzing a primary system with a TVA implemented was realized. The resulting software was then used to model implementation of a specific TVA solution. Through analytical and simulated solutions, it was confirmed that a specific TVA could be used to effectively absorb the response at target frequencies when acted upon by a linearly changing oscillatory input. (Published By University of Alabama Libraries

Voltage and power control of inverter-interfaced distributed generation systems using combined direct current vector control and droop control method

In recent years, distributed generation (DG) systems have become a signicant power source for remote areas and local loads. Almost all of the DG sources are inverter-interfaced to deliver the power to the loads in the desired form, which is ac. On the other side, most of the loads are very sensitive not only to changes in voltage levels and frequency of the power supply system, but also to harmonic distortion. Therefore, the use of diesel driven synchronous generators and similar power sources will be limited for many applications in the near future because of the high harmonic content of the output voltage when a non-linear load is applied. A solution to these limitations is to use an inverter to generate high quality sinusoidal voltages within a system which controls the instantaneous voltage. Proliferation of distributed resource (DR) units in the form of distributed generation (DG) and distributed storage (DS) has brought about the concept of the microgrid. A microgrid is dened as a cluster of DR units and loads that can operate in a) the gridconnected mode, and b) the islanded mode. Proper operation of the microgrid in both the grid-connected and islanding modes requires the implementation of high-performance power ow control and voltage regulation algorithms. Grid-connected operation consists of delivering power to the local loads and to the utility grid. In the absence of the grid, the inverters are normally operated in the island mode, in which inverters are responsible for establishing the ac bus voltage and supplying a high-quality power to the loads. This research presents a novel control strategy for parallel operation of inverters within the distributed ac power supply systems. The proposed control technique, based on the droop control method, uses only locally measurable feedback signals. This method is usually applied to achieve good active and reactive power sharing when communication between ii the inverters is dicult due to physical separation. To improve the voltage regulation and reactive power sharing, integrating the direct-current vector control (DCVC) with droop method is proposed in this thesis. (Published By University of Alabama Libraries

Magnetic resonance coupled wireless power transfer systems

Wireless power transfer (WPT) technology has many potential applications such as consumer electronics and electric vehicles (EV). High transmission efficiency with long transmission distance and with large lateral misalignment is desired in WPT systems. Magnetic resonance coupled (MRC) WPT systems are suitable for midrange high efficiency wireless power transfer (WPT). In chapter 2, commonly used four-loop and two-loop MRC-WPT system configurations are analyzed and compared in terms of transmission efficiency and transmission distance first based on the simplified circuit model. An example symmetrical system simulation shows that with the same Tx, Rx, source and load, the four-loop system has longer transmission distance but with relatively lower transmission efficiency compare to the two-loop system. Then, A 3-D physical model of 5-turn, 400mm outer diameter spiral shape four-loop WPT system is developed and simulated by using ANSYS® HFSS® software package. Operation distance of 550mm with nearly constant maximum transmission efficiency of 92.3% is achieved. Laterally misaligned MRC-WPT system is investigated in chapter 3. The TEVD, a region on the transmission efficiency versus Rx lateral misalignment amount curve where the transmission efficiency first sharply drops from high efficiency down to zero and then recovers to a low efficiency value, is identified in this work. The identification of TEVD is verified by simulation results obtained from a developed ANSYS® HFSS® 3-D physical model. Simulation results of the ANSYS® HFSS® 3-D physical model with 5-turn, 60cm outer diameter spiral shape MRC-WPT system show that when the Rx is 30cm vertically away from the Tx, TEVD exists when the lateral misalignment value ranges from 50cm to 70cm. An elimination method for TEVD is proposed in chapter 4. The proposed method utilizes angular rotation of the Rx (or Tx) to eliminate the zero-coupling point which causes the TEVD and boosts the coupling coefficient such that the TEVD is eliminated and the high efficiency region is extended. ANSYS® HFSS® 3-D physical model simulation results show that the proposed method eliminates the TEVD and extends the high efficiency region from 50cm lateral misalignment (83.3% of the Rx diameter) to 70cm lateral misalignment (117% of the Rx diameter). Chapter 5 summarizes the thesis conclusions and sheds the light on future work. (Published By University of Alabama Libraries