Neven Bulić

Performance evaluation of a bearingless flux-switching slice motor

The bearingless flux-switching slice motor represents a new motor design in the field of bearingless slice drives. This motor topology distinguishes itself from the state of the art bearingless slice motors by incorporating a magnet free rotor. The design offers an advantage in medical and industrial applications that require disposable rotors and high temperature working conditions. This work briefly describes the general working principle, drive setup, the implemented control theory and especially focuses on prototype measurements concerning force and torque generation, passive stabilization and drive efficiency.

Modeling and experimental verification of a flexible rotor/AMB system

Purpose – In this paper, the aim is to present a modeling strategy for a flexible rotor/active magnetic bearing (AMB) system with non‐collocation. Special attention is paid to the vibration reduction and the stable passage through the first critical speed.Design/methodology/approach – The finite element method based on Euller‐Bernoulli beam theory is applied in the formulation of the rotor model. Since rotor/AMB systems are complex mechatronic systems, reduced order approach is used in the control system design. This study applies the modal decomposition method and the modal truncation method, thus retaining the lower order bending modes. The obtained numerical results are compared with the measured open loop frequency responses and the existing differences are compensated in order to obtain accurate numerical model.Findings – Frequency response of the entire system model (flexible shaft, actuators, power amplifiers and sensors) with amplitudes expressed in rotor lateral displacements can be verified by t...

Simulation model of Neural Network based synchronous generator excitation control

Usage of neural network (NN) based excitation control on single machine infinite bus and its simulation studies are reported in this paper. The proposed feed forward neural network integrates a voltage regulator and a power system stabilizer. It is trained on-line from input and output signals of a synchronous generator. A modified error function used for training the neural network by the back propagation algorithm uses the reference and terminal voltage as controlling voltage and active power deviation to provide stabilization. The complete algorithm is simulated in Matlab Simulink. Synchronous generator (83 kVA, 50 Hz, 400V) is connected over transmission lines to AC power system. The proposed algorithm shows advantages of this method and satisfactory results.

Geometry optimization of a bearingless flux-switching slice motor

This paper presents a geometry optimization for a bearingless flux-switching slice drive. Bearingless slice drives consist of a magnetically suspended rotor disk and a stator with torque and force generation in one single unit. Active bearing forces are often generated in the same plane as the motor torque, while passive axial stabilization is achieved by reluctance forces due to the permanent magnetic bias flux in the air gap. For this operational principle, specific factors have to be taken into account while designing the drive. In addition to motor torque performance, these factors include passive axial force, tilting torque, active bearing force, saturation and liftoff capability. The first optimization cycle analyzes the influence of rotor diameter, motor height and air gap with the goal of maximizing the torque, while maintaining the bearingless operation capabilities. The second optimization cycle deals with the stator teeth geometry. Higher harmonics, saturation and overall performance are analyzed for different teeth width and PM width within the stator.

An FPGA implementation of the Goertzel algorithm in a Non-Destructive Eddy current Testing

The paper presents an implementation of the Goertzel algorithm in FPGA (Field Programmable Gate Array) logic as a proposed algorithm utilized in Eddy current NDT (Non-Destructive Testing) instrumentation equipment. The FPGA running a real-time Goertzel algorithm in Eddy current NDT application is a novel approach different from the usual methods; such are the quadrature demodulation and discrete FFT. The paper provides a brief overview of the Eddy current instrument hardware and gives a mathematical background on Eddy current signals. It also shows a real-time implementation of Goertzel algorithm in SoC (system-on-chip; FPGA/ARM based chip) and provides experimental results obtained by using common EC NDT probes. The results are compared to the results of several commercial Eddy current instruments.

Application of a DSP-based control system in a course in synchronous machines and excitation systems

The paper presents educational tools for students of an undergraduate course in synchronous generators and excitation systems. Laboratory exercises are based on the work with a laboratory model which consists of a digital control system and a synchronous generator connected to the power network. The code development is supported by two software tools where the code can be developed in the C or C++ programming language or in a graphical environment. In the Electrical Machines Laboratory, the presented laboratory model allows students to develop the code for excitation control, to learn how a conventional excitation control structure and various types of power system stabilisers function, to carry out experiments with a step change in the active power reference or voltage reference, and to record generator responses. The proposed approach offers students the opportunity to apply the knowledge they have acquired in lectures through practical work in the laboratory.

Magnetic Bearing Control System based on PI and PID Controllers

This paper describes the implementation of magnetic bearings and their active control system. The working principle of the special combined axial and radial magnetic bearings and their implementation is explained. The overall laboratory system consists of two magnetic bearings with their housings, the suspended shaft and control system with sensors and power electronics. Sensor electronics are used to measure the position of the shaft within a bearing and to determine the appropriate bearing current with outer position control loops and nested current control loops. The motor control board featuring the TMS320F28335 DSP and LDC1000 proximity sensors is used for control and power electronics. In order to implement the control system the X2C tool is used. This is an open source model based development and code generation tool embedded in the Scilab/Xcos environment. The sensor data acquisition time is optimized to increase the speed of the control system.

Eddy current sensor simulation

Purpose This paper aims to present a simulation concept and an experimental verification of a novel sensor design for the shaft position measurement based on the eddy current principle and the phase-shift measurement. The simulation method for the sensor characteristic determination is presented. Possible application of a new sensor type is theoretically presented, verified in simulation and compared with experimental results. Design/methodology/approach Sensor is based on the injection-locking phenomenon between coupled oscillators. Only one sensor per axis is used for position measurement. A pair of the sensing and reference oscillators in the sensor is electrically coupled via the coupling resistor. A change in the inductance for the eddy current sensor is simulated in the finite element method (FEM) software Flux and behavior of the sensor circuit is simulated in the SPICE simulator software LTSpice program. Finally, the simulation results are compared with the measurements conducted on the laboratory test rig. Findings A novelty in this approach is the usage of only one sensor per axis compared to the well-known differential measurement of the position that uses the opposite pair of the sensing oscillators in the same axis. A methodology for the sensor characteristic determination is presented and experimentally verified. Originality/value A new variation of a coupled-oscillator eddy current sensor design is introduced. A simulation approach for the characteristic determination of the sensors based on the weakly coupled oscillators and the injection-locking mechanism is presented.

Control design of a bearingless flux-switching slice drive

The bearingless flux switching slice drive is a recently introduced motor topology in the field of bearingless drives. It combines the magnetic rotor suspension of bearingless slice drives with the torque generation of flux-switching motors. Due to lack of magnets embedded in the rotor, the topology offers advantages in applications with high temperature working conditions. This paper describes the general working principle and control of both bearing force and motor torque. A prototype was built and the control was implemented on a TI DSP. The control was built using the X2C toolbox. This toolbox enables developers to generate the DSP code from a Simulink® or Xcos-Scilab control model.

Synchronous Generator Advanced Control Strategies Simulation

Three different structures for the excitation control of a synchronous generator were simulated in Matlab Simulink: the first structure is a conventional control structure which includes a PI voltage controller, while the second structure includes a fuzzy logic controller, and the third structure includes a neural network- based voltage controller. Performances of the proposed algorithms were tested for step changes in voltage reference in the excitation system of a synchronous generator, which was connected to an AC network through a transformer and a transmission line. For the performance analysis of the proposed control structures two numerical criteria were used: the integral of absolute error and the integral of absolute error derivative. In the comparison with the PI voltage controller neural network-based controller and the fuzzy logic controller show a significant damping of oscillations. It is important to emphasize that the stabilizer was not used in the conventional control structure, which would definitely reduce the difference between the conventional and the proposed control structures. The simulation results show justification for the use of the advanced control structure based on neural networks and fuzzy logic in the excitation control system of a synchronous generator. Also, using the software package Matlab Simulink allows users to easily test the proposed algorithms.