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.

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.

The NASA Glenn Research Center has been developing technology to enable the use of high speed flywheel energy storage units in future spacecraft for the last several years. An integral part of the flywheel unit is the three phase motor/generator that is used to accelerate and decelerate the flywheel. The motor/generator voltage is supplied from a pulse width modulated (PWM) inverter operating from a fixed DC voltage supply. The motor current is regulated through a closed loop current control that commands the necessary voltage from the inverter to achieve the desired current. The current regulation loop is the innermost control loop of the overall flywheel system and, as a result, must be fast and accurate over the entire operating speed range (20,000 to 60,000 rpm) of the flywheel. The voltage applied to the motor is a high frequency PWM version of the DC bus voltage that results in the commanded fundamental value plus higher order harmonics. Most of the harmonic content is at the switching frequency and above. The higher order harmonics cause a rapid change in voltage to be applied to the motor that can result in large voltage stresses across the motor windings. In addition, the high frequency content in the motor causes sensor noise in the magnetic bearings that leads to disturbances for the bearing control. To alleviate these problems, a filter is used to present a more sinusoidal voltage to the motor/generator. However, the filter adds additional dynamics and phase lag to the motor system that can interfere with the performance of the current regulator. This paper will discuss the tuning methodology and results for the motor/generator current regulator and the impact of the filter on the control. Results at speeds up to 50,000 rpm are presented.

The numerical simulation of catalytic reactor with periodic flow reversal generally requires a great deal of computing time, since its dynamic behavior is characterized by steep local gradients moving along the coordinate axis and cyclic transients. This paper discusses the use of adaptive grid methods and demonstrates that the moving spline collocation method presents better characteristics for efficient adaptation of the mesh-point grid to the travelling reaction front than other adaptive grid methods and that a periodic integration method can speed up the dynamic simulation of the cyclic transient process significantly.

The purpose is to show that an orthogonal collocation method using a moving spline point technique combined with a modified version of Petzold's integration method may provide an efficient dynamic simulation of a cycled distributed parameter system. The dynamic simulation method is illustrated with a fixed bed reactor in periodic cycled operation. The method is potentially very time saving since it uses lower number of grid points than those used with the modified Cranck-Nicholson technique with non-equidistant space steps. Besides, only a few cycles need to be evaluated in detail before prediction several cycles ahead becomes sufficiently accurate.