In this paper the stability problem of the three phase PWM converters with LCL filter without additional passive or active damping is analyzed. The system with the converter current feedback is considered where the stability problem is more acute. The analysis is performed using two theoretical methods, the discrete z-domain root locus technique and the nonlinear model simulation. The system with two different LCL filters is considered, one with the iron core inductors and the other with the air core inductors. In that way the influence of the iron losses on the system stability is investigated. It is shown that the stability margins obtained by means of the nonlinear model simulation are somewhat wider than the ones obtained by the root locus technique. The theoretical results are validated by the measurements performed on a 40 kW laboratory setup.Key words: PWM converter, LCL filter, Stability, Root locus, Nonlinear model, Iron losses Analiza stabilnosti trofaznog PWM energetskog pretvarača s LCL filtrom pomoću nelinearnog modela. U radu se analizira problem stabilnosti trofaznog PWM energetskog pretvarača s LCL filtrom bez dodatnog pasivnog ili aktivnog prigušenja. Razmatra se sustav s povratnom vezom po struji pretvarača gdje je problem stabilnosti izraženiji. Analiza je provedena koristeći dvije teorijske metode, geometrijsko mjesto korijena u diskretnom zpodručju i simulacija pomoću nelinearnog modela. Razmatran je sustav s dva različita LCL filtra, jedan koji koristi prigušnice sa željeznom jezgrom i drugi sa zračnim prigušnicama. Na taj je način istražen utjecaj gubitaka u željezu na stabilnost sustava. Pokazano je da su granice stabilnosti nešto šire kada se analizira stabilnost pomoću simulacijskog nelinearnog modela u odnosu na granice dobivene metodom geometrijskog mjesta korijena. Teorijski rezultati potvreni su mjerenjima koja su provedena na laboratorijskoj maketi nazivne snage 40 kW.Ključne riječi: pretvarač s pulsno-širinskom modulacijom, LCL filter, stabilnost, geometrijsko mjesto korijena, nelinearni model, gubici u željezu

Fast and accurate positioning and swing minimization of the containers and other loads in crane manipulation are demanding and in the same time conflicting tasks. For accurate positioning, the main problem is nonlinear friction compensation, especially in the low speed region. In this paper authors propose position controller realized as hybrid controller. It consists of the conventional linear state feedback controller with additional friction selflearning neural compensator in the feedforwad loop. Selflearning compensator is based on the B-spline artificial neural network which consists of the one hidden layer of the B-spline second order functions. The experimental results show that friction compensator is able to remove position error in steady state.

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Requirements of modern container terminals result in demand for sophisticated crane control and automation systems capable of handling loads fast and reliable connection to the particular information systems. This system continuously provide up-dated information about containers moves and crane status. The total function is built up of a number of distinct building blocks installed from the beginning or added on after. Many of the building blocks are tightly connected to each other to achieve the right functionality and performance. For steel mill cranes and another heavy duty material handling systems special attention is paid to the systems robustness, reliability and availability. Generally, the crane motion control system supports positioning, brake control, and another application function. In order to achieve a number of different possibilities to solve engineered problems, the mnltidrive concept is applied. Mentioned concept includes: powerful process controller with advanced multitasking, capable of handling several real time critical control loops simultaneously, high speed communication links between different clients, accurate measurement and fast transmission of drive positions and speeds and centralized interface for diagnostics of the complete system. This paper presents the important features of steel mill crane motion concept with Integrated Drive Controller (IDC) system. IDC system, based on operational flexibility through standardized hardware and software modules, offers a solution for many engineered erane application problems.