This paper describes techniques to be used to model megawatt Electrified Aircraft Propulsion (MW EAP) components, specifically motor/generators and inverters, DC-DC converters, and long power leads; resulting in impedance-based models which require no information from the component manufacturers. A custom curve fitting method is described, and an example power supply model is fit using measured impedance data. A method called subscale measurement, employing measurement equipment which has much lower power capability than the MW EAP system under test, is described, simulated, and used to generate an impedance transfer function model of a load. Finally, stability analysis using a Nyquist based approach is performed on the combined supply and load system, using the generated models.

Partially superconducting machines with cryocooler-cooled rotors are a potential near-term technology that can achieve the motor performance needed by future fixed wing electric aircraft. For this type of machine, minimizing cryogenic heat load is one of the keys for enabling high machine performance. Rotor eddy current loss is often the most difficult cryogenic heat load to mitigate due to current ripple from the motor drive. This paper presents the concept design for a 20 kW/kg, 99.5% efficient motor drive that has sufficiently low current ripple to enable high performance partially superconducting machines by minimizing eddy current loss in the rotor. The motor drive concept design uses a resonant, interleaved, and multilevel topology to achieve these high-performance metrics with little current ripple. Rotor magnetic loss analysis using NASA’s 1.4 MW High Efficiency Megawatt Motor (HEMM) is used in the design process to down select the motor drive topology and show that the final design generates less than 5 W of magnetic loss in the rotor.

In standard motor applications, traditional mechanical bearings represent the most economical approach to rotor suspension. However, in certain high performance applications, rotor suspension without bearing contact is either required or highly beneficial. Such applications include very high speed, extreme environment, or limited maintenance access applications. This paper extends upon a novel bearingless motor concept, in which full five-axis levitation and rotation of the rotor is achieved using two motors with opposing conical air-gaps. By leaving the motors' pole-pairs unconnected, different d-axis flux in each pole-pair is created, generating a flux imbalance which creates lateral force. Note this is approach is different than that used in previous bearingless motors, which use separate windings for levitation and rotation. This paper will examine the use of feedforward control to counteract synchronous whirl caused by rotor imbalance. Experimental results will be presented showing the performance of a prototype bearingless system, which was sized for a high speed flywheel energy storage application, with and without feedforward control.

In standard motor applications, traditional mechanical bearings represent the most economical approach to rotor suspension. However, in certain high performance applications, rotor suspension without bearing contact is either required or highly beneficial. Such applications include very high speed, extreme environment, or limited maintenance access applications. This paper presents a novel bearingless motor concept, in which full five-axis levitation and rotation of the rotor is achieved using two motors with opposing conical air-gaps. By leaving the motors' pole-pairs unconnected, different d-axis flux in each pole-pair is created, generating a flux imbalance which creates lateral force. Note this is approach is different than that used in previous bearingless motors, which use separate windings for levitation and rotation. This paper will examine the predicted and achieved motor performance of a prototype bearingless system, which was sized for a high speed flywheel energy storage application.

A novel control algorithm for the charge and discharge modes of operation of a flywheel energy storage system for space applications is presented. The motor control portion of the algorithm uses sensorless field oriented control with position and speed estimates determined from a signal injection technique at low speeds and a back electromotive force technique at higher speeds. The charge and discharge portion of the algorithm use command feedforward and disturbance decoupling, respectively, to achieve fast response with low gains. Simulation and experimental results are presented demonstrating the successful operation of the flywheel control up to the rated speed of 60000 r/min.

Energy storage and attitude control are two distinct subsystems of the typical satellite. Energy storage is provided using batteries and active attitude control is accomplished with control moment gyroscopes or reaction wheels. A system mass savings can be achieved if these two subsystems are combined using multiple flywheels for simultaneous kinetic energy storage and momentum transfer. This paper develops, simulates, and experimentally demonstrates the control algorithms to accomplish integrated power and single-axis attitude control using two flywheels.

A flywheel energy storage device stores energy in a rotating mass. These devices can be used to perform the same function as traditional chemical batteries. In terms of the energy storage function, a flywheel system has significant advantages over chemical batteries: length of life, energy density, power density, and the capability of deep depth of discharge. Also, flywheels can be used to control the attitude of the spacecraft. This paper describes an experiment using two flywheels to simultaneously regulate a DC bus and provide single axis angle regulation on an air table. Models of the mechanical and electrical systems are developed, and simulations are run, then compared to experimental results. The correspondence of the simulations and experiments shows the sufficiency of the modeling of subsystems.

A computer simulation of a flywheel energy storage single axis attitude control system is described. The simulation models hardware which will be experimentally tested in the future. This hardware consists of two counter rotating flywheels mounted to an airtable. The airtable allows one axis of rotational motion. An inertia DC bus coordinator is set forth that allows the two control problems, bus regulation and attitude control, to be separated. Simulation results are presented with a previously derived flywheel bus regulator (Kascak, 2001) and a simple PID attitude controller.

The energy storage and attitude control subsystems of the typical satellite are presently distinct and separate. Energy storage is conventionally provided by batteries, either NiCd or NiH, and active attitude control is accomplished with control moment gyros (CMGs) or reaction wheels. An overall system mass savings can be realized if these two subsystems are combined using multiple flywheels for simultaneous kinetic energy storage and momentum transfer. Several authors have studied the control of the flywheels to accomplish this and have published simulation results showing the feasibility and performance. This paper presents the first experimental results showing combined energy storage and momentum control about a single axis using two flywheels.

A magnetic bearing control system for a high-speed flywheel system is described. The flywheel utilizes a five axis active magnetic bearing system, using eddy current sensors for position feedback to the bearing controller. Magnetic bearing controller features designed to improve flywheel operation and testing are described. Operational improvements include feed forward control to compensate for rotor imbalance, moving notch filtering to compensate for synchronous and harmonic rotational noise, and fixed notching to prevent rotor bending mode excitation. Testing improvements include adding safe gain, bearing current hold, bearing current zero, and excitation input features. Performance and testing improvements provided by these features are measured and discussed.

This paper describes the position sensorless algorithms presently used in the motor control for the NASA in-house development work of the flywheel energy storage system. At zero and low speeds a signal injection technique, the self-sensing method, is used to determine rotor position. At higher speeds, an open loop estimate of the back EMF of the machine is made to determine the rotor position. At start up, the rotor is set to a known position by commanding dc into one of the phase windings. Experimental results up to 52,000 rpm are presented.

This paper describes the DC bus regulation control algorithm for the NASA flywheel energy storage system during charge, charge reduction and discharge modes of operation. The algorithm was experimentally verified with results given in a previous paper. This paper presents the necessary models for simulation with detailed block diagrams of the controller algorithm. It is shown that the flywheel system and the controller can be modeled in three levels of detail depending on the type of analysis required. The three models are explained and then compared using simulation results.

An experimental flywheel energy storage system is described. This system is being used to develop a flywheel based replacement for the batteries on the International Space Station (ISS). Motor control algorithms which allow the flywheel to interface with a simplified model of the ISS power bus, and function similarly to the existing ISS battery system, are described. Results of controller experimental verification on a 300 W-hr flywheel are presented.

ABSTRACTThis paper describes the flywheel test facility developed atthe NASA Glenn Research Center with particular emphasis onthe motor drive components and control. A 4-pole permanentmagnet synchronous machine, suspended on magneticbeatings, is controlled with a field orientation algorithm• Adiscussion of the estimation of the rotor position and speedfrom a "once around signal" is given. The elimination of smalldc currents by using a concurrent stationary frame currentregulator is discussed and demonstrated. Initial experimentalresults are presented showing the successful operation andcontrol of the unit at speeds up to 20,000 rpm.INTRODUCTIONOne of the key components of the flywheel energy storagesystem is the electric motor and its control. Energy storage andrecovery are achieved by using the motor to increase ordecrease the flywheel rotor speed as necessary. Good control ofthe motor is thus very important for the proper operation of theflywheel system. As part of the flywheel technologydevelopment effort, NASA Glenn Research Center has built atest facility with the capability to rapidly test and evaluateadvanced motor control algorithms. It is the purpose of thispaper to describe the test facility (with particular emphasis onthe motor control portion), the basic motor control algorithmsdeveloped and to present initial experimental results.NOMENCLATURELq is the q-axis machine inductance, henries.Ld is the d-axis machine inductance, henries.ffq q-axis voltage or current in the rotor reference frame.f_ d-axis voltage or current in the rotor reference frame.f_ q-axis voltage or current in the stator reference frame._d d-axis voltage or current in the stator reference frame.p is the derivative operator, d/dt.Or is the angle between the stator q-axis and the rotor q-axis, radians._af is the flux linkage due to the rotor magnets, volt-see.o_ is the electrical rotor speed, radianslsecond.FLYWHEEL TEST FACILITYThe flywheel system test facility consists of a test cell anda control room. The test cell is physically separated from thecontrol room for safety purposes. The present flywheel systemunder test consists of a 4 pole permanent magnet synchronousmachine, a high strength composite rotor, magnetic bearingsand a housing structure which is sealed and pumped to a lowvacuum with water cooling capability• The flywheel systemitself is housed in a containment structure that is closed duringoperation. Power for the motor is derived from a standard sixswitch three phase inverter with a dc power supply source. Theinverter is a commercial off the shelf intelligent power module(gate drive circuitry included in the unit) rated at 600 volts, 200amps and uses IGBTs for the power switches.