Kai Zenger

Attenuation of Harmonic Rotor Vibration in a Cage Rotor Induction Machine by a Self-Bearing Force Actuator

In this paper, attenuation of flexural rotor vibration in electrical machines is considered. In order to generate force on the machine rotor, an electromagnetic actuator based on self-bearing machine working principle is examined. A control method for attenuating harmonic rotor vibration components is applied in a 30 kW two-pole cage induction machine. The machine is equipped with a four-pole supplementary winding for generation of lateral force on the rotor. Experimental results for the two-pole induction motor are presented. The main contribution of this paper is to apply a control method, specially designed for compensating harmonic excitations, by using a built-in electromagnetic actuator in an induction machine.

Dynamic Properties of Interconnected Power Systems - A System Theoretic Approach

Standard methods of system theory and control engineering are used to investigate the stability and performance of power units connected in series. The systems are first modelled in a normal multi-input multi-output form, and the dynamic properties are characterized in terms of poles and zeros. The series connection of such systems is shown to be of a similar normal form, and the internal and input-output stability can then be analyzed based on the general theory. The minor loop gain, which has long been used to study the stability of connected power systems, is shown to be a natural result of the system theoretic approach

Source-Reflected Load Interactions in a Regulated Converter

The use of distributed power supply (DPS) systems is continuously growing in powering different electronic systems and equipment. The systems compose of regulated switched-mode converters, which typically operate in a cascaded configuration constituting a dynamically demanding constellation prone to instability and performance degradation. It is well known that the origin of the interactions is the different impedances distributed within the system. The mechanism and characterizing parameters causing the source-reflected interactions is investigated in this paper both theoretically and experimentally using a buck converter under voltage-mode (VM), peak-current-mode (PCM) and input-voltage-feedforward (IVFF) control. The reflected interactions would be eliminated if the forward-voltage transfer function can be made zero but in practice such a condition cannot be fully achieved. The investigations show that the VM-controlled convert is very sensitive to the source-reflected interactions

QFT based robust controller design for a DC-DC switching power converter

In this paper, a quantitative feedback theory (QFT) was applied successfully to design a robust controller for a DC-DC buck converter operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The controller is designed to provide optimum attenuation of the load disturbances in spite of practical limitations on the achievable closed-loop performance and in the presence of other design constraints including closed-loop tracking and robust stability. The derived analytical results are verified by computer simulation of a voltage-mode (VM) controlled buck converter.

Simulation of variable delays in material transport models

The time for material to pass through a plug flow vessel is modelled by a delay function. If the flow rate is time-variable, the varying delay is difficult to calculate analytically even for general test functions of the flow rate. In this paper, the properties of delay functions are studied theoretically. Two different methods for the simulation of the delay are derived. Several examples are studied, in which known analytical solutions as well as simulations of delay functions are presented.

Input filter interactions in current-mode controlled converters-a unified analysis approach

A unified analysis approach in assessing the effect of an input filter on the performance of a current-mode controlled converter is presented. The analysis method is based on the use of two-port unterminated modeling technique. The describing formulas to assess the input-filter effect are presented based on the transfer functions of direct-duty-ratio control with modifications caused by the effect of inductor-current feedback in peak-current control. The analysis shows that the behavior of input impedance explains the phenomena noticed earlier.

Stability and Performance Analysis of Regulated Converter Systems

Systematic analysis of the stability of connected power devices is developed in the paper. A canonical model structure is used to represent linear small-signal models of all power units, and it is shown that this structure remains invariant in series and parallel connections of unit systems as well as in closed loop systems. Internal stability is shown to be the key issue to determine the stability of the whole complex system consisting of several subsystems. The minor loop gain is used instead of loop transfer function to study conditions for robust stability and robust performance

Analysis and Control of Time-Varying Flow Processes by using the State-Space Approach

Abstract A method for analysing time-varying flow processes is developed, and its properties are studied theoretically. The differential model of the system, which is described by a combination of ideally mixed vessels, plug flow vessels and bypass flows, can be transformed into a form with constant coefficients by replacing time with a new variable. Classical methods for analysis and control design are then applicable, and the results can be converted to time domain. The theory of the transformation in the case of differential systems is introduced in the paper

Pole Placement of Time-Varying State Space Representations

The pole sets of linear differential SISO systems are considered in the paper by using polynomial factorizations and state-space formalism. A state-feedback control algorithm is then constructed, which guarantees the stability of the closed-loop system. A similar methodology is used to form a stable time-varying observer to the system.

POLES AND ZEROS OF MULTIVARIABLE LINEAR TIME-VARYING SYSTEMS

Abstract In the paper it is shown that the pole set of a linear system can be calculated by suitable polynomial factorizations. The theoretical issues related to poles and zeros of time-varying systems are discussed. Further, it is shown how the poles and zeros can be defined starting from a state-space realization of the input-output system.