Showing papers presented at "International Symposium on Industrial Electronics in 1997"

A multilevel PWM inverter topology for photovoltaic applications

Abstract: A multilevel pulse-width modulated (PWM) single phase voltage-source inverter topology for photovoltaic applications is discussed in this paper. The use of the phase opposition (PO) carrier disposition multicarrier PWM switching technique for this topology is presented. Inverter switch control signals are derived. A 5-level and a 3-level PWM voltage waveform across the load is generated, for high and low modulation indexes respectively. Performance characteristics including total harmonic distortion for a range of operating conditions of the inverter are provided. Theoretical considerations discussed in this paper are supported with simulation and experimental results taken from a low power laboratory prototype.

Complete coverage path planning and guidance for cleaning robots

Abstract: This paper describes a complete coverage path planning and guidance methodology for a mobile robot, having the automatic floor cleaning of large industrial areas as a target application. The proposed algorithms rely on the a priori knowledge of a 2D map of the environment and cope with unexpected obstacles not represented on the map. A template based approach is used to control the path execution, thus incorporating, in a natural way, the kinematic and the geometric model of the mobile robot on the path planning procedure. The novelty of the proposed approach is the capability of the path planner to deal with a priori mapped or unexpected obstacles in the middle of the working space. If unmapped obstacles permanently block the planned trajectory, the path tracking control avoids these obstacles. The paper presents experimental results with a LABMATE mobile robot, confirming the feasibility of the total coverage path and the robustness of the path tracking behaviour based control.

Number plate reading using computer vision

Abstract: The main tasks of a number plate recognition system are the location of the number plate area in the image, the segmentation of the characters and their identification. These tasks are strongly inter-related, mainly because the way to check if the number plate has been correctly located is based on the result of the character identification process (it should correspond to a predefined syntax). Algorithmic improvements to previous versions of the system, based on the results of intensive testing, are described in this paper. For the location of the number plate area in the image, a new line-based method has been developed. The method, instead of looking for character like shapes in the image, takes advantage of the "signature" of the number plate area in a horizontal cross-section of the image. The method used for the segmentation of the characters is derived from a technique first proposed by Lu (1995). The identification of the characters uses the OCR engine developed by Barroso et al. (1995), based on the critical points method.

Direct torque control of induction motor drives

Abstract: Direct torque control (DTC) is an emerging technique for controlling PWM inverter-fed induction motor (IM) drives. It allows the precise and quick control of the IM flux and torque without calling for complex control algorithms. In principle, moreover, it requires only the knowledge of the stator resistance. The tutorial starts by reviewing the basic operation of an IM and of a PWM inverter using the space vector theory. The field-oriented (FO) control of an IM drive is also reviewed. Then the concept of DTC is illustrated and three DTC-based strategies [i.e. switching table (ST), direct self control (DCS), space vector modulation (SVIM)] are described. The ST strategy is dealt with in detail, discussing the results which can be obtained with different choices of the switching table. Problems associated with the selection of the amplitude of the hysteresis bands of the flux and torque controllers are illustrated by means of experimental data. Merits and limits of DTC are reported and a comparison with FO control is given.

A study on position control of piezoelectric actuators

Abstract: The hysteresis characteristic of piezoelectric actuators makes precise position control very difficult. In this study a tracking control method for a piezoelectric actuator based on PID controller augmented with a feedback linearization loop based on the Maxwell slip model is presented. Further, the controller design is extended to include a repetitive controller. Experiments were performed on a piezoelectric 2-axis linear positioner for tracking sinusoidal waveforms and circles. The experimental results show that the tracking control performance is noticeably improved by augmenting the PID controller with a feedback linearization loop and repetitive controller.

Sensorless speed control of a PM synchronous motor by sliding mode observer

Abstract: This paper presents a sensorless speed control of a permanent magnet synchronous motor using a sliding mode observer. A vector control strategy is considered, for a motor with sinusoidal flux distribution. The sliding mode observer detects the voltages induced by the magnet flux on the stator windings. These signals are used to calculate the rotor position and speed needed for vector control. Due to the sliding mode operation, filters are used to smooth the estimated variables. A speed-dependent compensation is also proposed, in order to achieve an accurate estimation of the rotor position. As the observed variables are not available below a limit frequency, an open loop starting procedure is implemented. The resulting observer has been fully analyzed by simulations, in order to test the performance both in steady-state and transient operations. Experimental results based on a DSP TMS320C50 controller are presented, showing the performance of the sensorless drive over a wide range of operating conditions.

New open-winding configurations for high-power inverters

Abstract: New configurations of high-power inverters suitable for AC motor drives and static VAr controllers are presented. A usual method of supplying large AC drives rated at more than several thousands of kilowatts is to combine the outputs of two inverters using inter-phase reactors. However, such inter-phase reactors have several disadvantages such as losses and acoustic noise. To solve these problems, several new configurations which combine two different type of inverters or converters to both terminals of the open windings are presented.

Music on the Internet and the intellectual property protection problem

Abstract: Recent advances in audio compression technology coupled with trends toward higher network bandwidth, lower memory costs and lower storage costs indicate that the obstacles to music distribution on the Internet will soon be overcome. Because it provides benefits to consumers and to music content owners alike, networked music distribution may become one of the first compelling Internet consumer services. At the same time, these technological advances create opportunities for pirates. The authors believe that the music industry must prepare for network music distribution or face widespread theft of its music. In this paper, they first review the technological advances that are driving a change in the industry's business model. They then discuss the opportunities that these advances allow. Finally they focus on the dangers to content owners and discuss various ways to protect music content.

Equivalent circuit of mush wound AC windings for high frequency analysis

Abstract: The paper describes a lumped parameter equivalent circuit for the HF analysis of mush wound coils of AC windings. The equivalent circuit takes account of turn-to-turn and turn-to-iron stray capacitances. Dissipative phenomena due to eddy currents in the coil wires and the laminated iron core are also considered. The parameter identification is based on sinusoidal impedance measurements on a test coil. The model of a multi-coil AC stator winding can be easily derived from the proposed equivalent circuit. This model allows one to predict both common- and differential-mode conducted EMI in switching converters supplying AC motors. The simulation results obtained by PSpice are in good agreement with the experimental data.

Fuzzy logic control of a switched reluctance motor

Abstract: This paper presents the use of fuzzy logic control (FLC) for switched reluctance motor (SRM) speed. The PLC performs a PI-like control strategy, giving the current reference variation based on speed error and its change. The performance of the drive system was evaluated through digital simulations through the toolbox Simulink of the Matlab program.

The dynamic approach to autonomous robot navigation

Abstract: We present a dynamical systems approach to generate autonomous behavior. For the example of navigation and exploration of an autonomous agent, we develop a dynamical system, that produces classical control-type behaviors as well as complex behavioral sequences and discrete behavior selections. Examples for the control-type behaviors that are generated are obstacle avoidance, position estimation, recalibration and target acquisition. Examples for the complex behaviors are adaptive exploration, adaptive path planning, adaptive target selection and searching. The approach works with continuous differential equations throughout and combines the advantages of the formulation as a classical control problem and those of the formulation as an algorithmic problem.

Characteristics of three phase active power filter using extension pq theory

Abstract: In this paper, the authors propose a calculation method for the compensating current reference of an active power filter, where a nonlinear load exists in a three-phase three-wire unsymmetrical voltage system. This new method has been named the extension pq method. The authors have experimented with the extension pq method and the pq method, using the same current controlled IPM inverter for both methods. The results of the experiments proved that, in the unsymmetrical voltage system, the source current was distorted in case of the pq method, but undistorted in case of the extension pq method.

Docking of a mobile platform based on infrared sensors

Abstract: This paper presents a sensor based docking strategy for a nonholonomic mobile platform used to support material transportation operations in industrial like environments. A low cost infrared sensor system was designed and implemented, aiming at locating the mobile platform relative to the docking station where passive reflectors are installed. With this information, trajectories are generated and followed, docking the platform with a good accuracy (around /spl plusmn/0.5 cm in x and y, and /spl plusmn/1/spl deg/ in /spl theta/) considering that the system was designed based on low cost sensors. The paper presents relevant experimental results.

Cooperation in human-robot-teams

Abstract: The concept of a human-robot-team is presented. Because of its high flexibility and adaptability, the human-robot cooperation is expected to have a wide range of applications in uncertain environments not only in future construction and manufacturing industries but also for services. A Multi-agent control architecture gives an appropriate frame for the flexibility of the human-robot-team. Robots are considered as intelligent autonomous assistants of humans, which can mutually interact on a symbolic level and a physical level. This interaction is achieved with the communication between human and robots, the interpretation of the transmitted information, the coordination of the activities and the cooperation between independent agents. Equipped with some sensing modalities for the perception of the environment, the two-arm Karlsruhe Autonomous Mobile Robot (KAMRO) is introduced to demonstrate the principles of the cooperation among human and robot agents. Finally, guidelines are given for future studies on human-robot-cooperation.

Autonomous wheelchair for disabled people

Abstract: This paper describes the RobChair assistive navigation system The RobChair project was conceived with the aim to assist disabled people in the difficult task of manoeuvring a powered wheelchair This paper describes the overall hardware and software architecture including the communication system, a friendly graphical user interface which also works as a simulator and introduces a natural human-machine interface The system's architecture follows a behaviour-based control architecture

Communication system for industrial automation

Abstract: The authors main concern is to efficiently integrate video and audio devices alongside robots, programmable logic controllers (PLCs), numerical control (NC), manufacturing computers and process control systems. They present an experimental platform that implements their manufacturing communication system. This platform has been developed in the laboratory for the support of high bandwidth and real-time distributed applications. In this paper, they have chosen two challenging communication protocols to define their communication system. These protocols are the asynchronous transfer mode (ATM) and the manufacturing message specification (MMS) application layer protocols. They give the specification of an MMS-ATM communication system that guarantees high quality of services for real-time multimedia applications. This guarantees results from an ATM intelligent communication board and a reduced OSI stack.

On-line parameter commissioning in sensorless PMSM drives

Abstract: Sensorless drives based on extended Kalman filter (EKF) techniques are deeply studied and developed. It is acknowledged that one major weak point is their parameter sensitivity. This paper investigates the application of a recursive parameter identification (RPI) method to the online estimate of the electrical parameters of permanent magnet synchronous motors (PMSM). The availability of well-approximated values increases the robustness of the EKF, and leads thus to superior performances of the drive.

Biometry: the characterisation of chestnut-tree leaves using computer vision

Abstract: The Department of Biology of the University of Tras-os-Montes e Alto Douro analyses every year a large number of chestnut-tree leaves, in order to measure their biometric characteristics, namely the leaf area, dimensions of the enclosing rectangle, number of teeth and secondary veins. Because for a human operator this is a time consuming and error prone task, a computer vision system has been set up to improve the process. The task of measuring the leaf presents no major problems, while counting the number of teeth and secondary veins has proved to be complex at the resolutions used. This paper describes the state of the project, going into some detail on the algorithms. A complete system has been assembled, based on a PC connected to an imaging system. A windows-based application has been developed, which integrates the control of the operations to grab, store and analyse images of different varieties of chestnut-tree leaves in an organised way. Because the accuracy of the computer vision algorithms used is not sufficient for the system to be completely autonomous, a semi-automatic solution has been adopted. The operator validates or corrects the results of the automatic analysis. This solution leads to a significant improvement in the performance of the human operator, both in terms of speed and quality of the results.

An experimental assessment of AC contactor behavior during voltage sags

Abstract: This paper presents experimental results that demonstrate the impact of voltage sags on AC contactors. Duration and amplitude are the parameters that have been normally used to classify voltage sags. This paper proves the necessity to include the point-in-wave of voltage sag initiation to explain the impact of sags on the behavior of AC contactors. The experimental setup used to obtain the results is described in detail. Several experiments are presented that describe the effects of point-in-wave on the performance of AC contactors. The outcome of the experiments show that the magnitude and duration alone do not adequately explain the behavior of AC contactors during voltage sags.

Sliding mode control of voltage sourced boost-type reversible rectifiers

Abstract: A robust sliding mode controller, suitable for the output voltage PWM control of voltage sourced, reversible boost-type rectifiers, presenting no steady-state errors, is described. This "just in time" switching controller samples the output voltage and two line input currents, to provide bidirectional power flow, near unity power factor operation, input currents with low harmonic content and fast dynamic response of the output voltage. Simulation results are presented and the performances compared with the behaviour of the conventional proportional integral (PI) output voltage control, aided by inner loops for the PWM current mode modulators. Comparison with other sliding mode alternatives, suggested elsewhere for these PWM rectifiers, shows that this proposal has faster dynamics and does not present steady state errors. The results confirm that the performance of the controller is independent of system parameters and load and far exceeds the performance of existing hysteretic current mode control systems.

Specification of industrial digital controllers with object-oriented Petri nets

Abstract: The main purpose of this paper is to present an object-oriented PN model (shobi-PN) to specify industrial digital controllers. The shobi-PN model (synchronous, hierarchical, object-oriented and interpreted Petri net), was developed to support the use of hierarchy to model both the control unit and the plant of the systems. A CAD environment, SOFHIA, was developed to model digital controllers, to validate their properties and to simulate their behaviour. SOFHIA has an open architecture, which eases the integration of multiple code generator blocks to allow the implementation of the system in a wide range of technologies (hardwired, microprogrammed, programmed). Modelling of an industrial reactor control system is considered as a case study to illustrate the model's applicability and capabilities.

Fuzzy logic techniques applied to the control of a three-phase induction motor

Abstract: Until not long ago, most fuzzy logic based control applications were limited to the management of user interfaces, sensors and actuators, corresponding to slow software operation. These techniques are specially appropriated whenever the system model is nonlinear and/or difficult to obtain. Is it viable to use fuzzy logic in faster "real time" applications? Is it interesting to use these techniques even when the system model is known (including linear cases)? The authors are trying to answer some of these questions by applying fuzzy logic to control electrical machines. In this paper, they use a slip control scheme for a three-phase induction motor fed by a voltage-source PWM inverter as an example. The evaluation of the fuzzy logic controller behaviour is made through the comparison with a traditional technique (PI controller with antiwindup mechanism), using computer simulation (performed with Matlab/Simulink) and experimental results. Implementation was made using the fuzzyTECH software tool to design the fuzzy logic controller and to produce C-code for an Intel 80C196KC microcontroller. An 1 kW three-phase induction motor fed by a voltage source IGBT power module was used in the experiments.

Remote supervisory control of an autonomous mobile robot via World Wide Web

Abstract: A remote supervisory control architecture which combines a computer network and an autonomous mobile robot is constructed. The main feature of this architecture is that users just need a general purpose computer and a World Wide Web browser; they can command the mobile robot in a remote location through the Internet and home page. Hardware configuration of this architecture includes a mobile robot, as server workstation, and other computers, each of them is able to communicate with others via computer network. Software design includes assignment of the server, communication between the server and robot, and the user interface. The architecture has extensive capabilities for teleoperation, telerobotics operations, and other multimedia services. Based on this architecture we have implemented multilevel operations for the user on various remote applications. At present, the system allows users to directly control our mobile robot via the Internet and a user friendly interface (via our home page), and they can receive live images captured by a CCD camera which is mounted on the robot and other data from sensor measurement.

A noninvasive telemetric heart rate monitoring system based on phonocardiography

Abstract: A reliable, noninvasive, biotelemetric heart rate monitoring system, causing minimal constraints to patients, for studies of heart rate variability, is described. Heart sounds arise from the activity of muscles, valves or blood flux in the heart. Piezoelectric transducers allow the detection on the human chest surface of the acoustic vibration produced by the mechanical action of the heart. As such, it is feasible to develop a small-size intelligent probe, with sensor, signal processing and telemetric capabilities, which is glued to the chest surface for heart rate monitoring. The concept of telemetric phonocardiography has some advantages over electrocardiography in heart rate monitoring, since it only requires a single probe, there are no wire connections and the patient does not need to carry an Holter. This new heart rate monitoring system relies on the identification of heart sound S1, the most prominent natural sound signal occurring during each cardiac cycle. The S1 detection is complicated by two factors: (i) wide variation in heart sounds' morphologies and rhythms, and (ii) noise from various sources may corrupt the phonocardiogram recording. These conditions imply the use of a heart sound probe self-adjustable to sound signal levels and selecting only heart sounds.

A comparison of tri-level and bi-level current controlled grid-connected single-phase full-bridge inverters

Abstract: The performance of current-controlled single-phase full-bridge tri-level and bi-level grid-connected inverters is discussed in this paper. A comparative evaluation is made against identical inverters to demonstrate the advantages of tri-level inverter systems. Several parameters have been selected for comparison, such as instantaneous inductor current and its associated error, the instantaneous switching frequency, the inductor input voltage and the magnitude spectrum of the inductor current. It is revealed through extensive simulations that the tri-level approach is far superior than the bi-level counterpart.

Neural network application for flux and speed estimation in the sensorless induction motor drive

Abstract: Sensorless field-oriented control (SFOC) of induction motor drives requires the knowledge of instantaneous magnitude and position of the rotor flux as well as the rotor speed. This paper deals with the application of artificial neural networks (ANN) for estimation of the rotor flux vector and motor speed on the basis of phase current measurement only. Various structures of the neural estimators were simulated and their performances were compared. The influence of changing rotor parameters during the drive were tested. The neural network is able to estimate accurately the rotor flux and speed during line-start operation and load torque changes of the motor. The results of simulation experiments indicate that the neural network estimator may be a feasible alternative to other flux and speed estimation methods.

Audio streaming on the Internet. Experiences with real-time streaming of audio streams

Abstract: An increasing number of applications include real-time audio streaming over a communication network. Well-known examples are teleconferencing, tele-presentation, Internet Radio live streams and on-demand services. In cooperation with various broadcasters, GMD provides live and on-demand audio services over the Internet. Applications are based on commercial products as well as on own software developments. This paper describes some approaches to provide a real-time audio service over the Internet, discusses problems and experiences and presents an outlook for a streaming service in the future.

An error feedback model based adaptive controller for nonlinear systems

Abstract: In this paper, a method of designing an adaptive controller is proposed to solve some problems in model reference adaptive control (MRAC) for nonlinear plants. The MRAC was originally designed for the unknown plant which should be linear and completely disturbance free. Practically, since real plants have nonlinearities, such as disturbances and unmodelled dynamics, the performance of the controller is worsened. This paper describes an error feedback model which is a reference model with the output error feedback, for improving robustness and stability to nonlinear characteristics. The proposed model can be used for MRAC using the measurable output of the plant and the states of the proposed model. Experiments on an SR (switched reluctance) motor have been done in order to illustrate the validity of the proposed controller.

Digital audio broadcasting in the FM band

Abstract: It is envisioned that all broadcasting will be digital in the future. There are standards work and system development going on in various parts of the world to make this vision reality. In Europe, the emphasis has been on broadband systems (EUREKA) with multiple program channels in a new frequency band. In the United States, the broadcasting industry is favoring a solution where broadcasting is compatible with the existing analog FM and AM systems. A number of new digital audio radio systems have been proposed and evaluated. In this paper we present a conceptual overview of some of the properties of these systems. We also present the transmission channel properties of the FM systems. The most challenging part of the transmission is broadcasting to vehicles. We discuss details of key subsystems such as audio coding, channel coding, and digital modulation in the proposed in-band on channel (IBOC) and in-band adjacent channel (IBAC) as well as in-band reserved channel (IBRC) systems for the FM band.

Optimal filtering schemes for linear discrete-time systems-an LMI approach

Abstract: This paper deals with the optimal filtering problem constrained to input noise signal corrupting the measurement output for linear discrete-time systems. The transfer matrix /spl Hscr//sub 2/ and/or /spl Hscr//sub /spl infin// norms are used as criteria in an estimation error sense. First, the optimal /spl Hscr//sub 2/ filtering gain is obtained from the /spl Hscr//sub 2/ norm state-space definition. Then the attenuation of arbitrary input signals is considered in an /spl Hscr//sub /spl infin// setting. Using the discrete-time version of the Bounded Real Lemma on the estimation error dynamics, a linear stable filter guaranteeing the optimal /spl Hscr//sub /spl infin// attenuation level is achieved. Finally, the central /spl Hscr//sub /spl infin// filter problem is solved, yielding a compromise between the preceding filter designs. All these filter design problems are formulated in a new convex optimization framework using LMIs. A numerical example is presented.