Martin Janda

Hologram synthesis for photorealistic reconstruction.

Computation of diffraction patterns, and thus holograms, of scenes with photorealistic properties is a highly complicated and demanding process. An algorithm, based primarily on computer graphics methods, for computing full-parallax diffraction patterns of complicated surfaces with realistic texture and reflectivity properties is proposed and tested. The algorithm is implemented on single-CPU, multiple-CPU and GPU platforms. An alternative algorithm, which implements reduced occlusion diffraction patterns for much faster but somewhat lower quality results, is also developed and tested. The algorithms allow GPU-aided calculations and easy parallelization. Both numerical and optical reconstructions are conducted. The results indicate that the presented algorithms compute diffraction patterns that provide successful photorealistic reconstructions; the computation times are acceptable especially on the GPU implementations.

Detail-driven digital hologram generation

Digital holography is a technology with a potential to provide realistic 3D images. However, generation of digital holograms is a computationally demanding task. Thus, the performance is a major concern. We propose a new method that reduces spatial resolution in order to accelerate hologram generation. It employs the propagation between parallel planes for efficient optical field values evaluation and a computer graphics approach for approximating visibility. Our results show that the proposed reduction has only a minimal impact on the visual quality, while the formal computational complexity confirms performance improvement.

Main problems and proposed solutions to induction machine drive control of multisystem locomotive

This project was motivated by demand of our industrial partners for proposal of prospective control of induction machine drive for new generation of multisystem locomotives. This paper presents proposed drive control including specifically optimized PWM algorithms. Designed control is based on rotor flux oriented vector control in Cartesian coordinates which is unusually operated due to employed synchronized PWM in whole speed range. Commutation angles for developed synchronous PWM have been found by multi-criteria optimization where the most important measure was reduction of danger frequency components of trolley-wire current which can harm function of railway safety systems. Proper function of proposed control is verified by tests on designed small-scale prototype of locomotive drive. Selected results of extensive experimental study into trolley-wire current spectrum and related drive interaction with railway safety systems, which is one of the most serious problems of modern locomotives and high-speed trains, are considerable part of this paper.

Full-Parallax Hologram Synthesis of Triangular Meshes using a Graphical Processing Unit

Application of the GPU to the computer generated holography is a topic of research for some time. While the majority of authors aim on performance, we aim on visual aspects. We present a new approach that is capable to synthesise a hologram of a scene described by triangles using the GPU and it is capable to respect a local intensity variation on a surface caused by textures and solve occlusion at the same time.

Frequency domain evaluation of a traction PMSM drive with direct torque control including field weakening area

This paper presents a method for frequency analysis of traction drives supplied from a dc trolley wire with an input LC filter. The proposed method is suitable for frequency analysis of the traction drive in whole speed range and enables to find resonant or other observed harmonics in the operating drive circuit which could cause dangerous oscillations particularly at resonant frequencies of the power circuit. The method is used for detailed frequency analysis of a direct torque controlled traction drive with a surface mounted permanent magnet synchronous motor. The analysis is performed in a wide speed range including field weakening area and the dangerous resonant frequency is found and the behaviour of the drive in dependence on the stator frequency is observed. A solution based on demanded machine torque correction is used for the drive stability enhancement. The behaviour of the drive with this improvement is evaluated with the proposed method as well. The proper function of the frequency analysis in the wide speed range for the non-stabilized and stabilized drive is verified by simulations as well as by experimental measurements on a down scaled traction drive with rated power of 10.7 kW.

Digital HPO Hologram Rendering Pipeline

This paper describes a rendering pipeline for digital hologram synthesis. The pipeline is capable of handling triangle meshes, directional light sources, texture coordinates and advanced illumination models. Due to the huge computational requirements of hologram synthesis only the HPO holograms are considered.

DTC controlled PMSM traction drive input LC filter stabilization using model predictive control

This paper describes a new method for active damping of an input LC filter in traction drives supplied from dc catenary. Specifically, there is described the configuration of a traction drive with a surface mounted permanent magnet synchronous motor controlled by a direct torque control algorithm which is supplied via trolley-wire LC filter from a dc catenary. Because input LC filters are naturally nearly undamped and dangerous voltage oscillation can appear in the circuit, a new method for dc-link voltage stabilization is proposed. This method uses model predictive control for correction of traction drive operating point (demanded motor torque) which leads to the capacitor voltage stabilization and hence, improvement of the drive stability. The proper function of the stabilization (damping) effect of the proposed method is evaluated by a special frequency characteristic measurement which we proposed particularly for traction drives connected to a dc catenary. This paper also offers a comparison of our approach with the most frequently used damping method in traction drives. The behaviour of the DTC controlled PMSM drive has been verified by experiments on a down-scale laboratory prototype of the traction drive with rated power of 10.7 kW as well as the frequency characteristics measurement of this drive has been performed and evaluated.

HPO Hologram Synthesis for Full-Parallax Reconstruction Setup

Digital hologram synthesis is a task that simulates a physical process. Currently, there is no working solution capable of handling continuous surfaces, solving visibility, and applying a local intensity variation efficiently. Due to the computational complexity an approximation is required. Our solution tries to address this issue by extending the most efficient HPO hologram synthesis in such way that the computed hologram does not require a special optical setup for reconstruction.

Frequency analysis and stability enhancement of DTC controlled PMSM drive with input LC filter

This paper presents a new method of frequency characteristic measurement for ac drives connected to a dc trolley-wire. The input part of a drive is composed of an input LC filter. The LC filter is a naturally almost undamped circuit and any change in the circuit (e.g. voltage drop or constant power taken from the circuit) causes dangerous capacitor voltage oscillations. This method helps to find dangerous resonant frequencies of the whole traction drive and it allows finding possible danger oscillations of the dc-link voltage appearing due the motor drive operation. Furthermore a method for dc-link capacitor voltage stabilization has been designed and employed in the permanent magnet synchronous motor drive. The stabilization effect of this method is verified in a using the direct torque control of the permanent magnet synchronous motor by simulations as well as by experimental evidence at a laboratory prototype of the traction drive with rated power 10 kW using the frequency characteristic measurement.

Scanline rendering of digital HPO holograms and hologram numerical reconstruction

This paper presents a fast and complete rendering method that can be used for creating digital horizontal parallax only (HPO) holograms of a scene consisting of triangle mesh objects. This method solves visibility and occlusion problems and is capable of working with triangles as the basic primitive instead of the usually used points. It is fast because it avoids the direct distance computation using the square root operation. Advanced numerical reconstruction techniques are used for presenting the results of the rendering method.