B. Grzesik

Capacitance and inductance selection of the modular multilevel converter

The paper presents a proposal for capacitance and inductance selection procedure of the modular multilevel converter. Two analysis criteria are taken into consideration, the circulating current and voltage ripple across submodule capacitors. Results are obtained numerically by using the converter averaged model based on state equations. In the modular multilevel converter operating under a direct modulation method, based on sinusoidal modulating signals, circulating currents flows through the converter arms. These currents are strongly dependant on the component parameters of the converter, such as: submodule DC-link capacitor capacitance and arm inductor inductance. Both components form a series resonance circuit in each converter arm. Resonance that occurs in the converter arm has to be avoided and therefore it is important to properly select component parameters while taking into account all possible resonances. Such components selection should be carried out at an early stage of the converter design.

Self-Capacitance of Coupled Toroidal Inductors for EMI Filters

This paper presents a derivation of an expression for the self-capacitance of single-layer coupled toroidal inductors, which are commonly used in EMI filters and other applications. A physics-based geometrical method is used in the derivation. This method requires information about the inductor geometry and material properties, such as dimensions of core, technique of winding, as well as diameter, thickness, and permittivity of winding wire isolation. The geometrical method is very useful because it saves time and does not require an impedance analyzer. However, all information about material properties has to be known. The theoretical results are validated by experimental results. The agreement between the calculated and measured results was very good.

Analytical and numerical power loss analysis in Modular Multilevel Converter

This paper presents two approaches to semiconductor power loss analysis in Modular Multilevel Converters (MMC) controlled without feedback of the switching cell capacitor voltage. The first one is a novel analytical approach - basing on an averaged model of the MMC. The second one is basing on detailed model in Matlab-Simulink - used as a reference for the analytical one. Analyses are performed for five MMC switching cells scenario. The analytical method has been proven as sufficient and fast solution for the MMC power losses estimation.

Design and implementation of 6-DOF parallel manipulator driven by permanent magnet brushless DC motors

This paper presents selected issues connected with the design and implementation of the 6-DOF parallel manipulator driven by permanent magnet brushless DC motors. The consideration of platform kinematics structure, computer design and simulation of mechanical framework as well as building and utilization of the reduced-scale physical are presented. The development, implementation and testing of the described model allowed to identify some important implementation issues related to the control of a parallel manipulator. The achieved results has made possible to modify the objectives of design and implementation for the designed target Stewart platform based on PM brushless BLDC motors.

The piecewise‐affine model of buck converter suitable for practical stability analysis

A generalized geometrical piecewise-affine continuous-time model (GMD) of buck converter under pulse-width modulated (PWM) voltage-mode control is presented in this paper. In general, such a model can be applied to any DC-DC power electronic converter (PEC) in which the valves are modelled as ideal switches. The GMD is suitable and convenient to analyse PEC practical stability which is a completely different concept in relation to the notion of its stability in the classical Lyapunov sense. The PEC GMD is based on its commutation structure which is a general geometrical model of its commutation. The general idea of this model consists in determining the local dynamic behaviour of PEC trajectories on the faces of its commutation structure and/or their sections. These faces and sections are treated as geometrical objects with generalized local dynamics. The analysis of buck converter practical stability is carried out using a new method based directly on the definition of this term but not Lyapunov-like functions as in the direct method. It has been shown that PEC Lyapunov stability does not imply its practical stability. These two concepts are complementary to each other. Copyright

DC-link voltage balancing method for a hybrid asymmetric multilevel converter

The paper presents the dc-link voltage balancing method for a five-level hybrid asymmetric multilevel converter based on a neutral point clamped (NPC) converter with H-bridge (HB) converters. The considered converter, which is referred to as NPC-HB, is treated in this paper as a modification of the classic three-level NPC converter. It improves the harmonic performance of output voltage compared to the NPC converter. This improvement is made by increasing the number of levels in the converter output voltage. Nevertheless, due to the use of floating H-bridge converters inside the NPC-HB topology, the dc voltage balancing method is implemented. Basing on the converter ac side current and HB converter dc link voltage, the proposed method modifies the PWM modulation scheme in both NPC and HB converters. This modification is applied to each switching period while the converter output voltage reference is kept unchanged. Such modulation scheme is characterized as robust and guaranteeing the low harmonic content in the output voltage. Other dc voltage balancing methods of the hybrid NPC-HB converter are compared in this paper. The proposed method is experimentally verified.

A brief review of models of DC–DC power electronic converters for analysis of their stability

A brief review of models of DC–DC power electronic converters (PECs) is presented in this paper. It contains the most popular, continuous-time and discrete-time models used for PEC simulation, design, stability analysis and other applications. Both large-signal and small-signal models are considered. Special attention is paid to models that are used in practice for the analysis of the global and local stability of PECs.

Tests of a vacuum gauge for an HTS hydrogenerator

The paper describes the methodology, test rig and results of vacuum gauge tests under rotational conditions. The gauge is dedicated to measurements of vacuum in the rotor of an HTS power generator. The tests were performed using a dedicated test rig where the data of the measurements were transmitted using a Bluetooth device.

HTS toroidal helical transformer

The paper describes novel HTS toroidal transformer with helical windings, operating at 50 Hz. The turns of outer winding are parallel to turns of inner one. This arrangement of windings results in the same length and shape of each turn. The latter ensures homogeneous distribution of flux density. The magnetic core, in turn, improves coupling between windings, giving at the same time homogeneous magnetic flux distribution in windings. Proposed shape of windings reduces perpendicular component of flux density in HTS wires. It allows for the best possible utilisation of the HTS wire. The transformer has the magnetic core cooled with LN2. The transformer has turn-to-turn ratio 1:1 as it is designed for modular system. Its windings are made of Bi2Sr2Co2Cu3Ox wire. Material of magnetic core has accepted power losses in LN2. The magnetic core is also kept in ambient temperature. Thorough analysis of proposed HTS transformer will be carried out using Finite Element Method (FEM) and measurements resulting in critical current, rated power density and rated efficiency. The circuit model of the transformer is also given.

Design considerations for high frequency buck converter

The paper reports on design, simulation and development of a test bed prototype for microfabricated, chip-integrated inductor developed by Tyndall National Institute, Cork, Ireland. A test circuit is developed for a buck DC/DC converter topology. The device is powered from Li-Ion battery or with use of a similar source (approximately 3.6 V) and should be able to deliver approximate 0.5 W with output voltage of 1.0-1.2 V. The main issue is to achieve high switching frequency-between 5 MHz and 15 MHz.