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Power converter for ion thrustors using electronic gate controlled switches in two phase-shifted parallel inverters
Brushless DC motors are frequently used in electric aircraft and other direct drive applications. As these motors are notactually direct current machines but synchronous alternating current machines; they are electronically commutated by a power inverter. The power inverter for brushless DC motors typically used in small scale UAVs is a semiconductor base delectronic commutator that is external to the motor and is referred to as an electronic speed control (ESC). This paper examines the performance changes of a UAV electric propulsion system resulting from ESC degradation. ESC performance is evaluated in simulation and on a new developed test bed featuring propulsion components from a reference UAV. An increase in the rise fall times of the switched voltages is expected to cause timing issues at high motor speeds. This study paves the way for further development of diagnostic and prognostic methods for inverter circuits which are part of the overall electric UAV system.
The paper discusses the direct relationship between the auroral kilometric radiation (AKR) power flux observed by the eccentric orbiting Hawkeye spacecraft and energetic electron precipitation in the nighttime auroral zone measured by the low-altitude polar orbiting AE-D spacecraft. The results of this study show that AKR is more closely associated with inverted V electron precipitation than with plasma sheet precipitation. It is found that as the observed AKR power flux increases, so does the simultaneously observed peak energy in inverted V electron precipitation increase. There is an evidence that suggests that the efficiency of generating AKR from inverted V particle participation ranges from 1/100,000% to a maximum efficiency of about 1%.
Power electronic converter will be a key enabler for future electrified aircraft propulsion system. In aircraft applications, superconducting technologies such as superconducting motors and generators along with supporting power systems will grow in importance. Utilizing cryogenic cooling for power converter potentially can significantly improve the inverter system efficiency and specific power. This paper presents the cooling, hardware,and testing of a cryogenically-cooled MW inverter developed for electrified aircraft propulsion system. The 1 MVA full load testing with cryogenic cooling is demonstrated. The developed inverter system achieves 18 kVA/kg specific power and 99% efficiency, which provides a promising solution to achieve high power density and efficiency for future electrified aircraft propulsion system.
Advanced static inverter utilizing digital techniques and harmonic cancellation
This report summarizes the work performed on the 40 BP electro-mechanical actuator (EMA) system developed on NASA contract NAS3-25799 for the NASA National Launch System and Electrical Actuation (ELA) Technology Bridging Programs. The system was designed to demonstrate the capability of large, high power linear ELA's for applications such as Thrust Vector Control (TVC) on rocket engines. It consists of a motor controller, high frequency power source, drive electronics and a linear actuator. The power source is a 25kVA 20 kHz Mapham inverter. The drive electronics are based on the pulse population modulation concept and operate at a nominal frequency of 40 kHz. The induction motor is a specially designed high speed, low inertia motor capable of a 68 peak HP. The actuator was originally designed by MOOG Aerospace under an internal R & D program to meet Space Shuttle Main Engine (SSME) TVC requirements. The design was modified to meet this programs linear rate specification of 7.4 inches/second. The motor and driver were tested on a dynamometer at the Martin Marietta Space Systems facility. System frequency response and step response tests were conducted at the Marshall Space Flight Center facility. A complete description of the system and all test results can be found in the body of the report.
Results are presented from a statistical study of the spectral characteristics of the (power-law-portion) secondary electrons associated with inverted-V electron precipitation events (IVEs). A total of 106 IVEs observed at low altitudes (below 1000 km) by the DE 2 spacecraft are included in data base. Spectral parameters for the electrons between 20 eV and 100 eV are plotted against the different parameters pertaining to the locations of the IVEs and the primary beams to determine their empirical dependences. It is found that the differential spectrum of the secondary electrons can be modeled by a power law, J proportional to E exp -gamma, with an averaged gamma of 1.85. This spectral parameter is relatively insensitive to the variation of locations of the IVEs, but it depends on the primary beam parameters. These results are compared with predictions, and theories on the generation of the low-energy auroral power-law secondary electrons are assessed. The analysis shows that collisional processses are the dominant source of the secondary electrons.
A control system for achieving high-speed torque for a joint of a robot includes a printed circuit board assembly (PCBA) having a collocated joint processor and high-speed communication bus. The PCBA may also include a power inverter module (PIM) and local sensor conditioning electronics (SCE) for processing sensor data from one or more motor position sensors. Torque control of a motor of the joint is provided via the PCBA as a high-speed torque loop. Each joint processor may be embedded within or collocated with the robotic joint being controlled. Collocation of the joint processor, PIM, and high-speed bus may increase noise immunity of the control system, and the localized processing of sensor data from the joint motor at the joint level may minimize bus cabling to and from each control node. The joint processor may include a field programmable gate array (FPGA).
An inverter is connected between a source of DC power and a three-phase AC induction motor, and a microprocessor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .theta., where .theta. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands for electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.
An inverter is connected between a source of DC power and a three-phase AC induction motor, and a micro-processor-based circuit controls the inverter using pulse width modulation techniques. In the disclosed method of pulse width modulation, both edges of each pulse of a carrier pulse train are equally modulated by a time proportional to sin .THETA., where .THETA. is the angular displacement of the pulse center at the motor stator frequency from a fixed reference point on the carrier waveform. The carrier waveform frequency is a multiple of the motor stator frequency. The modulated pulse train is then applied to each of the motor phase inputs with respective phase shifts of 120.degree. at the stator frequency. Switching control commands of electronic switches in the inverter are stored in a random access memory (RAM) and the locations of the RAM are successively read out in a cyclic manner, each bit of a given RAM location controlling a respective phase input of the motor. The DC power source preferably comprises rechargeable batteries and all but one of the electronic switches in the inverter can be disabled, the remaining electronic switch being part of a flyback DC-DC converter circuit for recharging the battery.
A power processor unit for powering and controlling the 30 cm Mercury Electron-Bombardment Ion Thruster was designed, fabricated, and tested. The unit uses a unique and highly efficient transistor bridge inverter power stage in its implementation. The system operated from a 200 to 400 V dc input power bus, provides 12 independently controllable and closely regulated dc power outputs, and has an overall power conditioning capacity of 3.5 kW. Protective circuitry was incorporated as an integral part of the design to assure failure-free operation during transient and steady-state load faults. The implemented unit demonstrated an electrical efficiency between 91.5 and 91.9 at its nominal rated load over the 200 to 400 V dc input bus range.
The paper describes the principal features and special testing of a high-frequency high-power low-specific-weight (0.57 kg/kW) 2.3-kW electronic power transformer developed for space applications. The transformer is operated in a series resonant inverter supplying beam power to a 30-cm mercury ion thruster. High efficiency (above 98.5%) is obtained through careful detailed design. A number of unique heat removal techniques are discussed which control the winding temperature using only the available conductive cooling.
Rotating solar photovoltaic cells or batteries connected to suitable mechanical and/or electronic commutators produce nearly sinusoidal alternating current. Eliminates need for inverter circuitry and its attendant power-consumption and heat-dissipation problems, but imposes need for low-power-consumption rotary mechanism. Intended for use aboard spacecraft, also useful in special terrestrial situations where solar electric power must be transmitted over powerlines from one remote location to another.
This report presents an evaluation of advanced motor drive systems as a replacement for the hydrazine fueled APU units. The replacement technology must meet several requirements which are particular to the space applications and the Orbiter in general. Some of these requirements are high efficiency, small size, high power density. In the first part of the study several motors are compared, based on their characteristics and in light of the Orbiter requirements. The best candidate, the brushless DC is chosen because of its particularly good performance with regards to efficiency. Several power electronics drive technologies including the conventional three-phase hard switched and several soft-switched inverters are then presented. In the last part of the study, a soft-switched inverter is analyzed and compared to its conventional hard-switched counterpart. Optimal efficiency is a basic requirement for space applications and the soft-switched technology represents an unavoidable trend for the future.
The increasing use of power electronics, such as high-current semiconductor devices and modules, within space vehicles is driving the need to develop specialty thermal management materials in both the packaging of these discrete devices and the packaging of modules consisting of these device arrays. Developed by Applied Nanotech, Inc. (ANI), CarbAl heat transfer material is uniquely characterized by its low density, high thermal diffusivity, and high thermal conductivity. Its coefficient of thermal expansion (CTE) is similar to most power electronic materials, making it an effective base plate substrate for state-of-the-art silicon carbide (SiC) super junction transistors. The material currently is being used to optimize hybrid vehicle inverter packaging. Adapting CarbAl-based substrates to space applications was a major focus of the SBIR project work. In Phase I, ANI completed modeling and experimentation to validate its deployment in a space environment. Key parameters related to cryogenic temperature scaling of CTE, thermal conductivity, and mechanical strength. In Phase II, the company concentrated on improving heat sinks and thermally conductive circuit boards for power electronic applications.
The goal of this work is to develop robust, lightweight, and low-power control units that can be used to suppress structural vibration in flexible aerospace structures. In particular, this paper focuses on active damping, which is implemented using compact decentralized control units distributed over the structure. Each control unit consists of a diamond-shaped piezoelectric patch actuator, three miniature accelerometers, and analog electronics. The responses from the accelerometers are added together and then integrated to give a signal proportional to velocity. The signal is then inverted, amplified, and applied to the actuator, which generates a control force that is out of phase with the measured velocity. This paper describes the development of the control system, including a detailed description of the control and power electronics. The paper also presents experimental results acquired on a Plexiglas window blank. Five identical control units installed around the perimeter of the window achieved 10 dB peak reductions and a 2.4 dB integrated reduction of the spatially averaged velocity of the window between 500 and 3000 Hz.
The Component Development Division of the Propulsion Laboratory at Marshall Space Flight Center (MSFC) is currently investigating the use of electromechanical actuators for use in space transportation applications such as Thrust Vector Control (TVC). These high power servomechanisms will require rugged, reliable, and compact power electronic modules capable of modulating several hundred amperes of current at up to 270 Vdc. This paper will discuss the design and implementation of a zero-voltage-switched PWM (Pulse Width Modulation) inverter which operates from a 270 Vdc source at currents up to 100 A.
The potential of achieving up to 30 per cent more spacecraft payload or 50 per cent more useful operating life by the use of electric propulsion in place of conventional cold gas or hydrazine systems in science, communications, and earth applications spacecraft is a compelling reason to consider the inclusion of electric thruster systems in new spacecraft design. The propulsion requirements of such spacecraft dictate a wide range of thruster power levels and operational lifetimes, which must be matched by lightweight, efficient, and reliable thruster power processing systems. This paper will present electron bombardment ion thruster requirements; review the performance characteristics of present power processing systems; discuss design philosophies and alternatives in areas such as inverter type, arc protection, and control methods; and project future performance potentials for meeting goals in the areas of power processor weight (10 kg/kW), efficiency (approaching 92 per cent), reliability (0.96 for 15,000 hr), and thermal control capability (0.3 to 5 AU).