Showing papers presented at "International Symposium on Industrial Electronics in 2000"

A study of charging control of lead-acid battery for electric vehicles

Abstract: The object of this paper is to investigate the circuit topologies and control techniques for fast charging of battery for the electric vehicle (EV). Analysis and comparison of fast charging characteristics for different charging controls are presented. A charging and discharging monitoring system was implemented based on a DSP. To improve the utilization of EV, it is necessary to design a charger with the function of fast charging and the capability of charging control, thus to prolong the battery life. The charging characteristics (charging time, charging current, temperature, switching frequency, and pulse period) of different charging methods (two-step, pulse, and Reflex) are analyzed and presented. Experiments were carried out based on the battery set of four 26 Ah lead-acid batteries in series. A LabVIEW-based monitoring system was constructed to record the voltage, current and temperature for the batteries. The DSP-based charging control combined with the monitor system features fast charging, digital and adjustable control.

Short-current pulse based adaptive maximum-power-point tracking for photovoltaic power generation system

Abstract: This paper proposes a novel maximum-power-point tracking (MPPT) method with a simple algorithm for photovoltaic (PV) power generation systems The method is based on the use of a short-current pulse of the PV array to determine an optimum operating current for the maximum output power and completely differs from conventional hill-climbing based methods In the proposed system, the optimum operating current is instantaneously determined by taking a product of the short-current pulse amplitude and a parameter k because the optimum operating current is exactly proportional to the short current under various conditions of illuminance and temperature Also, the system offers an identification function of k by means of fast power-vs-current curve scanning, which makes the short-current pulse based MPPT adaptive to disturbances such as shades partially covering the PV panels The above adaptive MPPT algorithm has been adopted to a current-controlled boost chopper and a multiple power converter system composed by PV-chopper modules Various operating characteristics have been examined, and excellent MPPT performance has been confirmed through the experimental tests

Energy, environment, and advances in power electronics

Abstract: The technology of power electronics has gone through rapid technological advancement during the last four decades, and its applications are quickly expanding in industrial, commercial, residential, military and utility environments. In the global industrial automation, energy conservation and environmental pollution control trends of the 21st century, the widespread impact of power electronics is inevitable. The paper begins with a discussion on a global energy generation scenario and the corresponding environmental pollution problem. The mitigation of this problem is then discussed with particular emphasis on energy saving with the help of power electronics. A brief but comprehensive review of the advances of power electronics that includes power semiconductor devices, converter, machines, drives and control is incorporated in the paper. Finally, a prognosis for the 21st century has been outlined.

Active and hybrid filters for power conditioning

Abstract: This paper describes principles, system configurations, control strategies and implementations, and filtering characteristics of active and hybrid filters for power conditioning. Their practical applications are expanding not only into office-buildings, hospitals, water supply utilities and rolling stock but also into electric power utilities. For example, a hybrid filter consisting of a 5 MVA series active filter and a 25 MVA shunt passive filter has been installed at the Yamanashi test line for high-speed magnet-levitation trains. The series active filter makes a great contribution to damping of harmonic resonance between the supply inductor and the shunt passive filter.

Comparison of two current modulation strategies for matrix converters under unbalanced input voltage conditions

Abstract: In this paper, the input current performance of matrix converters is analyzed, especially with reference to the operating conditions determined by unbalanced supply voltages. The space vector modulation technique is utilized to calculate the duty-cycles of the active voltage vectors that must be applied, in each switching cycle period, in order to satisfy the input and output requirements. A detailed theoretical analysis of the input current harmonic content under unbalanced input voltage conditions is presented for two different current modulation strategies. On the basis of numerical simulations as well as measurements on a laboratory prototype set-up, the strategies are compared and the validity of the theoretical investigation confirmed.

Control strategies for PWM rectifier/inverter-fed induction motors

Abstract: The paper reviews the technology status and control strategies developed for PWM rectifier/inverter-fed induction motor drives with emphasis for its similarities. A review includes: new PWM techniques, field oriented and direct torque control of induction motor (FOC and DTC), voltage oriented and direct power control of a PWM rectifier (VOC and DPC), and novel virtual flux (VF) based sensorless control of a PWM rectifier. Also, neural network and fuzzy logic based intelligent controllers for motion control have been discussed. Selected oscillograms are shown in order to illustrate properties of the described control strategies.

Direct torque control of induction motors: stability analysis and performance improvement

Abstract: Practitioners in the electric drives community have introduced a novel torque control strategy for high power induction motor applications called direct torque control (DTC), which has three distinctive features: it focuses on stator (instead of rotor) flux regulation, it does not aim at an asymptotic system inversion (hence it does not require additional current loops), and it explicitly takes into account the discrete nature of the control actions, which are simply points of a finite set obtained from a switching logic. Besides its simplicity, it is claimed that the achieved performance is (in some instances) superior to classical field oriented strategies because of the digital form of the control structure and the reduced dependence on parameter variations of the stator flux calculations. Our objective in this paper is twofold, first to carry out a mathematical analysis of the stabilization mechanism of DTC, which helps us assess the achievable performance of the current scheme and provide guidelines for its tuning. Second, to propose a modified DTC to improve its dynamical behavior. Experimental results are presented to illustrate the main points of our paper.

Fuzzy logic direct torque control

Abstract: A brief review of the different induction motor drives is done and its reason of being such a high matter of interest is summarised. Next, the direct torque control (DTC) in induction motors with its fundamental principles and schemes is described. Once the DTC is described, its main drawbacks are introduced. One of the goals of the paper is to overcome one of the worst disadvantages of the DTC, which is the existence of a considerable ripple in its torque response. The previously explained DTC limitations involve plenty of nonlinear functions. Therefore, artificial intelligence is suggested to overcome the DTC limitations. Hence, a fuzzy logic DTC controller, which is based on the classical DTC but includes a fuzzy logic controller, is described. Finally an optimised method of calculating the stator reference flux value is presented, which can be applied in any kind of induction motor drive. This optimised stator flux reference value not only improves the torque ripple, but also reduces the power consumption from the mains. Simulated results are shown to corroborate all the presented work and the updated workbench where all the experimentation is realised is also described.

Automatic identification and damping of torsional vibrations in high-dynamic-drives

Abstract: The paper deals with the identification and damping of torsional oscillations in high dynamic industrial drives. Based on a model with two concentrated masses with an elastic coupling and driven by a field-orientated induction machine, methods for the identification and damping of torsional oscillations were developed. On a downscaled laboratory setup, well-known and newly developed procedures for the identification of the resonance frequencies were compared regarding their effectiveness and effort of implementation and under consideration of an automatic identification. Besides, experimental results of several methods for the active damping of the torsional oscillations are presented. They were completed by measurements carried out on a high dynamic industrial drive for a cross cutter for paper (sheeter).

Stability issues in three-phase PWM current/voltage source rectifiers in the regeneration mode

Abstract: Pulse-width modulated current-source and voltage-source rectifiers are becoming an interesting alternative as a source of variable DC power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including reactive power compensation. Consequently, literature has recently reported different control strategies, where the active power flows from the AC mains into the load. Unfortunately, when active power flows from the load into the converter, it is usually dissipated in the DC link by means of switched resistors. Such approach reduces the overall efficiency; specially, when regeneration is the normal operating mode as in down-hill belt conveyors and electrical shovels in mining applications. In these cases, the regenerative operating mode should be permanently sustained. This work reviews several important issues concerning such an operating mode; specifically, the stability of the converter-load system, and stability analysis of closed loop operation. The paper shows that PWM rectifiers controlled by a regular linear controller (such as PIs) may become unstable under the regenerative operating mode and analyses a control strategy to overcome such difficulties. Simulated results confirm the validity of theoretical considerations.

Intelligent autonomous mobile robot control through the Internet

Abstract: With rapid growth of computer technology, Internet-based teleoperation of robotic systems has created new opportunities in resources sharing, long-distance learning, and remote experimentation. This paper presents a basic architecture and its functional components for remote control of robotic systems. A variety of control modes for existing robotic systems were surveyed and the Internet transmission latency was discussed. An illustrative application was used to demonstrate the effectiveness of the proposed architecture and the control scheme. Experimental results clearly indicate that the proposed behavior control mode is superior to direct control mode in terms of efficiency, operating environment, complex task handling, and control capability.

Sensorless control of induction motors-performance and limitations

Abstract: Controlled induction motor drives without mechanical sensors for speed or motor shaft position have the attraction of low cost and high reliability. The identification of rotor speed is generally based on measured terminal voltages and currents. Dynamic models are used to estimate the magnitude and spatial orientation of the fundamental magnetic flux waves in the stator or in the rotor. Open loop estimators and closed loop observers differ with respect to accuracy, robustness, and sensitivity against model parameter variations. Dynamic performance and steady-state speed accuracy in the low speed range is achieved by exploiting parasitic effects of the machine. The overview in this paper uses signal flow graphs of complex space vector quantities to provide an insightful description of the systems used in sensorless control of induction motors.

Design of fuzzy power system stabilizer using adaptive evolutionary algorithm

Abstract: This paper presents a design methodology of fuzzy system stabilizer (FPSS) using an adaptive evolution algorithm (AEA). The AEA consists of a genetic algorithm for a global search and evolution strategy for a local search in an adaptive manner when the present generation evolves into the next generation. The AEA is used to optimize the membership functions and scaling factors of FPSS. A single machine infinite system is applied to evaluate the usefulness of the FPSS. The results show that the proposed FPSS has a better control performance than the conventional power system stabilizer (CPSS) in the case of a three-phase fault under heavy load. To show the robustness of FPSS, it is applied to the system with disturbances such as change of mechanical torque and three-phase fault under the normal and light load. The results of the FPSS show a better robustness than that of the CPSS.

From interpreted Petri net specification to reprogrammable logic controller design

Abstract: The goal of this paper is to present the design methodology for the modelling and synthesis of discrete event controllers for compact, fast and reliable embedded systems, using related Petri net theory, rule-based system theory (conditional mathematical logic), and hardware description languages (VHDL, Verilog). The well structured specification, which is represented in the human readable logic language, has a direct impact on the validation, formal verification and implementation of application specific logic controllers (ASLC) mapped into reconfigurable logic devices (FPGA). Reprogrammable logic controllers (RLC) may replace traditional PLCs in many industrial applications.

Dynamic ZVS direct on-line start up of current fed resonant converter using initially forced DC current

Abstract: ZVS (zero voltage switching) is critical for the reliable operation of normal current fed DC-AC resonant converters. In the steady state, ZVS can be achieved by many available techniques such as PLL, VCO and other integral controllers. However, during the transient process like start up, to achieve ZVS is not an easy task for these controllers and consequently switch failure may occur. Based on numerical and analytical analyses, this paper proposes a novel method using an initially forced DC current to achieve ZVS during start up. Start up conditions are discussed and complete dynamic ZVS is achieved. Considering the ramp up delay of the DC power supply, the start up can be controlled completely overshoot free at no extra cost. The validity of this method has been proven with PSpice simulations and experimental results.

On-line estimation of instantaneous torque in switched reluctance machine control

Abstract: An inextensive and simple method to estimate the instantaneous torque of a switched reluctance machine online is developed and discussed in this paper. The presented technique is characterized by its simplicity and robustness in two ways. Only phase current and voltage are required as input variables. Therefore, shaft position-sensors can be avoided. Furthermore, the estimation algorithm can be realized in hardware, i.e. no processor is needed, the digital unit consists only of a simple memory device such as an EPROM. The estimation technique requires the machine characteristics. The method presented in this paper estimates torque as a function of flux linkage and phase current. With this real-time estimation and feedback of the instantaneous torque it is possible to control the torque with a hysteresis controller to obtain high performance drives. Furthermore, it is shown that the performance of the drive regarding torque-ripple can be significantly enhanced. The system is developed for the control of high performance drives as they are used in traction application. Experimental and simulation results are presented in this paper.

Direct power control with virtual flux estimation for three-phase PWM rectifiers

Abstract: A new method of virtual flux (VF) based instantaneous power estimation without line voltage sensors is proposed. The new solution is employed in the direct power control (DPC) of three-phase PWM rectifiers. Theoretical principles, steady-state operation and dynamic performance of the DPC with VF-based power estimation are presented and compared with the conventional voltage-based estimation. Both power estimators are investigated under purely sinusoidal as well as unbalanced and distorted line voltages. Computer simulations and laboratory experiments have shown that the new method offers significant advantages. In particular, it results in a sinusoidal current even when the supply voltage is far from ideal.

Topologies and control of active filters for flicker compensation

Abstract: The paper deals with the analysis of topologies and control strategies of active filters (AF) for voltage flicker compensation. The strategies based on parallel and series active filters, both working with the reactive power compensation (without an energy storage device) have been analyzed and compared. The basic operational characteristics for the parameters of a real distribution power system with an arc furnace and a static VAr compensator have been calculated to promote the installation of an active filter for the mitigation of the voltage fluctuation. The control strategies of the active filters have been analyzed in the frequency domain as well. Neither the parallel AF nor the series AF, both working with the reactive power compensation and without the static VAr compensator (SVC), do not represent an appropriate solution in the case of the study: the parallel AF would need a high power rating, while the series AF has a too narrow working area. The combined application of the current SVC and the AF is a beneficial solution, the series AF being preferred to the parallel one for a substantial reduction of the AF power rating.

Current mode controlled LCC resonant converter for electrical discharge machining applications

Abstract: In this paper, a contribution to the electrical discharge machining (EDM) technology is presented. The final aim of this research is to develop small size EDM systems and determine the influence of the voltage and current of the output electrical arc on the quality and efficiency of the workpiece machining. The proposed system is a DC to DC LCC resonant converter intended to generate current controlled arc pulses at a constant frequency that erode the workpiece. The benefits of this proposal are: (1) the system has inherent protection under short circuit; (2) a simple linear controller results in a highly robust feedback control under load changes; and (3) the transistors turn-on at zero voltage is guaranteed at any load value. The output voltage is intended to be adjusted by an external system that controls the arc distance.

Operating region in active-front-end voltage/current source rectifiers

Abstract: Commercial active-front-rectifiers based upon three-phase voltage source topologies are capable of both supplying or absorbing reactive power from the electrical distribution system while serving as high DC power supplies. This is an important feature in industrial facilities where high power factor operation is of concern. This paper shows that the available range of reactive power in such topologies depends upon the actual active power being supplied by the topology to the load. Moreover, both the voltage and current source based topologies have limited and variable maximum reactive power compensation capabilities. In fact, both topologies are capable of providing maximum reactive power compensation when supplying 0.707 pu active power when operating passive loads in the rectifier mode. Extended analysis shows that during regeneration both topologies are also capable of supplying or absorbing limited amounts of reactive power from the electrical distribution system. Simulated and experimental results confirm the theoretical considerations.

Petri net-based specification, analysis and synthesis of logic controllers

Abstract: The logic control program is usually specified by drawing the Petri net in terms of interface with the electro-mechanical devices and the environment of the system. In such case it is not immediately evident that the control system behaves in a satisfactory way. Industrial engineers prefer frequently a form of specification, like interpreted Petri Net, sequential function chart (SFC), Grafcet or Grafchart. On the other hand, some popular techniques are informal and do not provide means to validate the design. In the paper, modelling, analysis and synthesis of logic controller described by Petri nets is presented. Additional, the use of design/CPN system for modelling, testing and analysis of logic controllers described by means of coloured, interpreted Petri nets is shown. The proposed methods are especially useful in designing of industrial application specific logic controller (ASLC) with FPGA.

Performances analysis of Ethernet networks in the process control

Abstract: The main obstacle to using Ethernet in real-time communications is the fact that these systems require network behaviour to be as deterministic as possible, while Ethernet, cannot provide connected stations with deterministic channel access times and therefore guarantee that data delivery deadlines will be met. Traffic smoothing can be a good solution to this problem. In this paper we introduce dynamic traffic smoothing, which consists of dynamically assigning each station a portion of bandwidth according to the current workload on the network. Whereas in static smoothing the available bandwidth is shared equally between the various stations, in dynamic smoothing it is entirely available only for stations that are actually transmitting, thus optimising its use. In the paper, the results of a series of simulations made to compare the performance obtained without smoothing, with static smoothing, and with dynamic smoothing respectively are presented and discussed.

Induction motor space vector control using adaptive reference model direct and indirect methods

Abstract: In this paper, we present the simulation results of vector speed control of an induction motor. In this case, both the direct and indirect methods were simulated using MATLAB (SIMULINK). In the indirect method, an estimate of the rotor time constant was obtained using a model reference adaptive system (MRAS) in a fuzzy control scheme. The estimation of the rotor flux in the direct method was achieved using the fixed reference model considered in the MRAS. A squirrel cage induction motor model was used, taking the reference coordinates as the rotor magnetic field.

Image-based visual servoing control of a SCARA type dual-arm robot

Abstract: Visual servoing is the fusion of results from many elemental areas including high-speed image processing, kinematics, dynamics, control theory, and real-time computing. It has much in common with research into active vision and structure from motion, but is quite different from the often described use of vision in hierarchical task-level robot control systems. We present a new approach to visual feedback control using image-based visual servoing with the stereo vision in this paper. In order to control the position and orientation of a robot with respect to an object, a new technique is proposed using a binocular stereo vision. The stereo vision enables us to calculate an exact image Jacobian not only at around a desired location but also at the other locations. The suggested technique can guide a robot manipulator to the desired location without giving such priori knowledge as the relative distance to the desired location or the model of an object even if the initial positioning error is large. This paper describes a model of stereo vision and how to generate feedback commands. The performance of the proposed visual servoing system is illustrated by the simulation and experimental results and compared with the case of a conventional method for dual-arm robot made by Samsung Electronics Co. Ltd.

Remote fieldbus system management with Java and XML

Abstract: This paper introduces CANINSIGHT which was developed to create a device and platform independent fieldbus management system for highly distributed enterprises. System data are represented as XML documents which are instances of the CANopen Markup Language (CoML). CoML is an XML application for Controller Area Network (CAN) device profiles, setup information, and process data. The system uses a CoML-based Java client/server architecture to access arbitrary CANopen fieldbus devices via the Internet. The CANINSIGHT client, realized as a Java applet, provides convenient, interactive access to CANopen automation systems at remote locations. The CoML documents which are used for the client/server communication can also be exported to remote database systems and form a central process information repository for an entire manufacturing enterprise. It is possible to use standard database clients to request specific CoML information which can be processed either by dedicated CoML tools or a wide variety of general purpose XML tools.

Stroke-length control of a MEMS device

Abstract: Microelectromechanical systems (MEMS) have a variety of potential civil and military applications. As MEMS become widely implemented, the application of closed-loop control methods to MEMS will lead to higher degrees of certainty and reliability of microelectromechanical operation in physically demanding environments. This paper presents an overview of research and development progress in the area of MEMS control at West Virginia University. The implementation and simulation of a closed-loop stroke-length control of a lateral comb actuator is presented. The closed-loop scheme implemented is based on a common proportional, integral, derivative (PID) linear feedback control. The position signal of the lateral comb actuator device was obtained using a through-wafer free-space optical probe. The paper also includes further progress in both linear and nonlinear feedback position control schemes.

Modeling conducted EMI noise generation and propagation in boost converters

Abstract: Models to predict generation and propagation mechanisms of conducted EMI noise in switch mode converters comprising of a diode-bridge rectifier input stage, and a 250 kHz boost converter stage are presented. It is demonstrated that a converter employing ZVT PWM generates lower levels of both conducted and radiated EMI emissions compared with hard-switched PWM operation. It is also shown that the effect of active input current wave shaping is to slightly reduce common-mode conducted emissions but increase differential-mode conducted emissions. Additionally, it is shown that the presence of the boost inductor leads to quasi common-mode conduction and that the parasitic capacitance between main switching device's heat sink and ground plane primarily determines common-mode conducted emissions. Mathematical equations to predict both differential- and common-mode conducted emissions are derived. Experimental results and important operational waveforms obtained using a 750 W unit are presented and compared with analytical and simulated results.

Image comparison method for visual quality control based on matrix decomposition

Abstract: The image processing applied on the original tile image and the replica images in serial production is used for visual quality control. The image of a tile that contains no visual quality error represents the original image. The images of the tiles from the production line that could contain some of the visual quality errors represent the replicas. The image processing is based on the image matrix decomposition method. The matrix form of the original image is transformed to a vector. The images made by the variations of a good original image are transformed to the matrix made by such vectors. Using the SVD of the matrix of variations of the original image makes the image comparison duration shorter. The number of computer operations decreases by using SVD approximation by a lower rank matrix. The SVD calculation of the matrix is done just once so that the image processing time is shorter. Too low a rank of the matrix could yield bad comparison results. The development and testing of this method are used for an early design of the computer aided visual control.

A PIC controller for grid connected PV system using a FPGA based inverter

Abstract: The propose of this work is to describe the implementation of a controller for tracking the point of maximum power transfer based on neural networks, using a microcontroller of the PIC family, on energy systems that use photovoltaic panels. A neural network is used to determine, at each instant, the output voltage in a DC-DC boost converter connected to the solar panels, in way to obtain the maximum power transfer of these panels. This implementation releases the use of a great performance computer, once the neural network was already trained and this way, it can be implemented in a dedicated system. The maximum power transfer of the system is obtained adjusting the duty cycle of the DC-DC boost converter. One three-phase inverter was implemented with a new control circuit to generate the PWM signal.

Frequency control of a current-fed inverter for induction heating

Abstract: A miniature high frequency induction furnace has been developed for the melting and alloying of small quantities (50g) of metal for laboratory and jewellery applications. The induction heating load forms part of a resonant circuit whose frequency is determined by the electrical characteristics of the work-piece placed inside the heating coil. The dynamic nature of the induction-heating load is such that it causes a shift in the natural resonant frequency of the load circuit. Automatic frequency control of the power source enables continuous operation at the resonant frequency of the tank circuit, resulting in a high conversion efficiency due to zero-voltage switching (ZVS) and maximum power transfer to the load at all times. This paper describes a PLL frequency control system for the prototype miniature induction furnace. Some basic design criteria as well as the actual implementation of the system are presented. Experimental results are presented to illustrate the effectiveness of the automatic frequency control system.