The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

The aim of this paper is to present the advantage of stator fault detection using an external stray flux sensor in a working induction machine. In the past 20 years, stray flux sensors have been used for diagnostic purposes but rarely in the presence of a complex power supply such as a voltage static inverter. In this paper, it is proved that a simple external stray flux sensor is more efficient than the classical stator current signature analysis to detect inter-turn short circuit in three-phase induction machines. The new result is that, even in the presence of power supply harmonics, it is possible to easily detect the stator winding faults in the low-frequency range of the flux spectrum with low-frequency resolution.

A frequency-domain detection of stator winding faults in induction machines using an external flux sensor

Control in Power Electronics : selected problems

Victims Of Groupthink A Psychological Study Of Foreign Policy Decisions And Fiascoes

The paper describes a method for the dynamic simulation of dynamic rotor eccentricity in squirrel cage rotor induction machines. The method is based on a winding function approach, which allows for all harmonics of magnetomotive force to be taken into account. It is demonstrated how this complex dynamic regime can be modeled using the mutual inductance curves of symmetrical machine using proper scaling techniques. Experimental results demonstrate the effectiveness of the proposed technique and validate the theoretical analysis.

Dynamic simulation of dynamic eccentricity in induction machines-winding function approach

Active suppression of nonlinear composite beam vibrations by selected control algorithms

This paper proposes a new 7-level inverter topology for induction motor drives. It is a hybrid topology formed by cascading a 5-level active neutral-point-clamped inverter with a 3-level T-type converter. It is obtained using low-voltage semiconductor devices with voltage blocking capability of Vdc/3 and Vdc/6. The topology uses three floating capacitors per phase, which are balanced within a pulsewidth modulation (PWM) switching duration using switching-state redundancies for each pole-voltage level. Topology forms two stacks at the front-end, which requires individual symmetrical dc source. The analysis of switching loss and conduction loss is performed and compared with some of the existing 7-level multi-level inverters reported in various literatures to show the advantages of the proposed topology. Furthermore, the single dc source operation with two stacked capacitors and closed-loop control of neutral-point voltage using symmetrical six-phase induction motor is proposed. The voltage-control algorithms for floating capacitors and dc-link stacked capacitors are proposed, which are independent of load power factor and modulation index. Open-loop V / f and closed-loop rotor field oriented control are performed, and various results at steady and transient states are presented to validate the aforementioned claims.

A Hybrid 7-Level Inverter Using Low-Voltage Devices and Operation With Single DC-Link

Purpose – In the dispersed generation system, power electronic converters allow for coupling between energy sources and the power grid. The requirements of Transmission System Operators are difficult to meet when the share of distributed energy sources of the total energy balance increases. These requirements allow to increase penetration of distributed generation sources without compromising power system stability and reliability. Therefore, in addition to control of active or reactive power, as well as voltage and frequency stabilization, the modern power electronic converters should support power grid in dynamic states or in the presence of nonlinear distortions. The paper aims to discuss these issues. Design/methodology/approach – The research methodology used in this paper is based on three steps: Mathematical modelling and simulation studies, Experiments on laboratory test stand, Analyzing obtained results, evaluating them and formulating the conclusions. Findings – The authors identified two algori...

Synchronization of voltage frequency converters with the grid in the presence of notching

Axial flux in an induction machine is formed as a result of asymmetry of electric and magnetic circuits In the paper particular attention is focused on determining an influence of nonsymmetrical air-gap on the flux spectrum An improved method of frequency analysis is discussed This method consists of taking into account only the most essential factors having an effect on the value and characteristics of axial flux In the presented description, only two the lowest harmonics of air-gap permeance are taken into account They create together with the fundamental harmonic of the field, supplementary electromagnetic couplings Knowledge of these couplings makes it possible to distinguish frequency lines that occur as a result of static rotor eccentricity Chosen test results are presented and certain problems concerning realisation of a diagnostic system are mentioned

Diagnostic characteristics of axial flux in an induction machine

This article proposes a fault-tolerant five-level inverter scheme for open-end induction motor (OEIM) drive application using a single dc link. The drive is fed with a primary inverter (a two-level inverter cascaded with a capacitor-fed H-bridge inverter) from one end and a secondary inverter (capacitor-fed two-level inverter) from the other end. The ratio of the dc-link voltage to the nominal capacitor voltage in the H-bridge and the secondary two-level inverter is maintained at 4:2:1. The capacitor balancing in the proposed scheme is achieved by space-vector (SV) redundancy. The proposed scheme gives five-level inverter operation with less number of components compared with other existing inverter topologies. Furthermore, the scheme provides fault-tolerant capability against a failure of the power switches in the H-bridges and the secondary two-level inverter. The experimental results in steady and transient states are presented. Also, the inverter operation during fault is provided to validate the effectiveness of the proposed scheme.

Wojciech Jarzyna

Papers

Active suppression of nonlinear composite beam vibrations by selected control algorithms

A Hybrid 7-Level Inverter Using Low-Voltage Devices and Operation With Single DC-Link

Synchronization of voltage frequency converters with the grid in the presence of notching

Diagnostic characteristics of axial flux in an induction machine

A Fault-Tolerant Five-Level Inverter Topology With Reduced Component Count for OEIM Drives