Abstract: In a magnetic bearing system, the longitudinal shaft position is shifted relative to the bearing position so that a force can be applied by the bearings away from a node at critical shaft speeds. In one embodiment, the shaft is shifted by end thrust bearings back and forth on an integral cycle basis. Alternatively, closely-spaced bearing pairs may be used and energized alternately on an integral cycle basis in order to shift back-and-forth the region at which the combined effective force of the bearing is applied.

Abstract: A pulse-width-modulated inverter in which equations relating switching angles, d.c. link distortion and a.c. inverter output distortion are determined empirically or by computer modeling. The amplitude of a d.c. link harmonic is the equation variable and stored constants particularize the equation for the phase of the harmonic and each switching angle which is to be controlled in response to d.c. distortion. As the d.c. link harmonics change, switching angle modifications are calculated using the stored constants.

Abstract: In a real time control of a pulse width modulated inverter, equations are developed relating switching angle, system parameter or parameters and output harmonics. Constants are stored which define a preferred angle for each switching event. Switching angles are calculated in real time by solving the equation in accordance with the value of the system parameter.

Abstract: A pulse-width-modulated inverter models the output response of the system for a given switching angle set under existent load and d.c. link conditions. Before implementation, a provisionally selected angle set is input to the model, which produces an output representative of system operation for the provisional selected set. The harmonics content of the model output is compared with criteria establishing maximally allowable amplitudes for the harmonics and the set is implemented only if the output meets the criteria.

Abstract: In a pulse width modulated inverter, the fit of a selected switching angle is monitored by counting zero crossings in a neighborhood of the function ##EQU1## for each harmonic of interest. If the fit is bad, a switching angle is moved to improve the fit.

Abstract: An inverter controller adjust a selected switching pattern to accommodate minor variations and loads in the neighborhood of that pattern. Pulse width modulated (PWM) patterns are determined for a range of loads and link ripple. For a pattern in use having A independent switching events, an A.times.B matrix is computed, where B is the number of controlled harmonics. The matrix elements represent sensitivity of controlled haromonics with respect to individual switching angles .theta..sub.i. The elements are ##EQU1## where n is the harmonic number of the controlled harmonic and .theta..sub.i is an independent switching angle. An unbalance vector comprised of the Fouier coefficient of the controlled harmonics in the inverter output is determined. This vector is a measure of the goodness of fit of a selected pattern for link ripple and load variation encountered with the selected pattern.

Abstract: An inverter controller adjusts a selected switching pattern to accommodate minor variations and loads in the neighborhood of that pattern. The controller realizes in real-time the equivalent of an iterative solution of predetermined patterns. A number of representative pulse width modulated (PWM) patterns are selected for a range of loads and link ripple. A portion of the fundamental output is inserted onto the d.c. link to control one or more higher harmonics.

Abstract: A PWM inverter takes into account the harmonic distortion produced by a d.c. link which is not constant. The controller determines switching angles in real time eliminating the need for storing PWM patterns in ROM. This is made possible by a "quick" Fourier transform which allows the determination of switching events in a PWM inverter in real time. The inverter controller develops pattern sets for rejecting selected harmonics and accounts for known fixed harmonic distortion on the d.c. link by determining the set of switching angles for each controlled selected harmonic.