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This paper presents dynamic modeling of rotor bearing systems with rigid disks, distributed parameter finite rotor elements and flexible, discrete multibearings. The previous works have included the effects of rotary inertia, gyroscopic moment, axial load, internal viscous and hysteretic damping and transverse shear deformations, but have not considered them all in the same model. A computer program is developed in this work to calculate the forward and backward whirl speeds, the corresponding mode shapes, the dynamic unbalance response of multibearing rotor systems and to evaluate rotor stability. It utilizes the banded property of the system matrices to reduce the computational effort for the complex eigensolution. A combined bisection and inverse iteration technique is used for the complex eigenvalue problem. The combined effect of shear deformations and internal damping on the stability, forward and backward whirl speeds, as well as on the response to unbalance excitation, are investigated with the numerical examples given. This study confirms that any inherent material damping in the shaft itself does not affect the unbalance response if the bearings are isotropic, which is, however, not the case when the bearings are orthotropic causing elliptical synchronous whirl orbits. Modeling and Governing Equations Coordinates and Shape Functions. A typical flexible 72

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In three-phase three-wire (3P3W) voltage-source converter (VSC) systems, utilization of filter inductors with deep saturation characteristics is often advantageous due to the improved size, cost, and efficiency. However, with the use of conventional synchronous frame current control (CSCC) methods, the inductor saturation results in significant dynamic performance loss and poor steady-state current waveform quality. This paper proposes an inverse dynamic model based compensation (IDMBC) method to overcome these performance issues. Accordingly, a review of inductor saturation and core materials is performed, and the motivation on the use of saturable inductors is clarified. Then, two-phase exact modelling of the 3P3W VSC control system is obtained and the drawbacks of CSCC have been demonstrated analytically. Based on the exact modelling, the inverse system dynamic model of the nonlinear system is obtained and employed such that the nonlinear plant is converted to a fictitious linear inductor system for linear current regulators to perform satisfactorily.

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