Prof. Dr. Joachim Holtz
Editor-in-Chief
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Prof. Dr. Joachim Holtz |
Power Electronics
- A Line-Frequency Commutated Rectifier complying with IEC 1000-3-2 Standards
by S. Buso, Giorgio Spiazzi
Abstract - Consumer and household appliances require low-cost ac/dc power supplies complying with EMC standards. The commonly employed passive solutions are bulky and do not provide output voltage stabilization. Active solutions, based on PFC's with high-frequency switching, provide compactness and regulation capability, but are generally expensive due to the need for fast-recovery diodes and complex EMI filters. This paper presents a high power factor rectifier, based on a modified conventional rectifier with passive L-C filter, which improves both the harmonic content of the input current and the power factor, by means of a low frequency commutated switch and a small line-frequency transformer, and allows to comply with IEC 1000-3-2 standard with reduced overall inductive components' volume.
- A Power Quality Prediction System
by Steven R. Shaw, Steven B. Leeb, Robert F. Lepard
Abstract - This paper describes two hardware prototypes and estimation schemes for determining the parameters of a simple, physically based, point-of-use electric utility model using transient measurements. Parameters of the utility model are estimated using data collected by the prototypes. Frequency dependent effects observed in previous work in this area are modeled. Performance of the techniques given is demonstrated by comparison of measured and predicted line voltage distortion during current transients created by several loads.
- Comparison between Current Driven Resonant Converters used for Single Stage Isolated Power Factor Correction
by H. Benqassmi, J.-Ch. Crebier, J.-P. Ferrieux
Abstract - The aim of this paper is to analyze the power factor correction capability of isolated current-source resonant converter topologies with two energy storage elements allowing to take advantage of the leakage inductance of HF transformer. These converter topologies are studied and modeled. Computer simulation results are also given. Thanks to its interesting characteristics, a converter topology is chosen and a converter prototype is built in order to validate theoretical study. Using this converter topology, a very good power factor is achieved.
- A Frequency Domain Analytical Model of an Uncontrolled Single-Phase Voltage Source Rectifier
by Hamish Laird, Simon Round, Richard Duke
Abstract - The harmonic currents generated by the single-phase rectifier are well known. As the levels of these currents become larger the use of power conditioners such as shunt active filters to lower the levels is becoming more attractive. In order to analyse the interaction between the condition, AC system and rectifier it is necessary to have an accurate model of the rectifier. This paper describes a frequency domain analytical model of the single-phase rectifier. The model includes the dominant frequency transfer mechanisms. These are the direct transfer and that due to the modulation of the switching instants. A small signal linearised analysis is presented and the behaviour predicted is confirmed by perturbation analysis using time domain simulation. Accurate results are obtained and the importance of including the switching instant modulation is shown.
- Modeling and Simulation of a Cycloconverter Drive System for Harmonic Studies
by Zhenyuan Wang, Yilu Liu
Abstract - This paper discusses the steady state harmonic modeling and simulation of a cycloconverter drive system (CDS). The operation and control of a cycloconverter drive and a synchronous motor load were modeled in time domain. Based on the duality principle of electric and magnetic circuits, four types of three-phase transformer models with detailed nonlinear magnetizing characteristics were implemented. The harmonic behaviors of the entire system were studied under several worst operation conditions. The goal of this study is to understand the harmonic problems associated with a CDS from an integrated system point of view, with special attention given to harmonic filtering and cancellation effect of converter coupling transformers.
- A Novel High Power Low Distortion Synchronous Link Converter based Load Compensator without the Requirement of Var Calculator
by Kishore Chatterjee, B. G. Fernandes, Gopal K. Dubey
Abstract - A high power low distortion static var compensator based on synchronous link converter is proposed in [1] and [2] where the harmonics are eliminated by incorporating a low power IGBT based controlled current auxiliary converter in conjunction with a high power GTO based converter. In this paper a new load compensator based on the topology of [1] and [2] is proposed which does not require the information of the volt-ampere required by the load. As the requirement of the reactive volt-ampere calculator is eliminated, the scheme becomes insensitive to system frequency variations, temperature and component ageing. The control scheme required for the compensator is developed. The operation of the scheme is validated through extensive simulation studies. Experimental results obtained from a laboratory prototype are provided to demonstrate the viability of the scheme.
- Modelling Adjustable Speed Drives with Long Feeders
by A. C. S. de Lima, H. Dommel, Richard M. Stephan
Abstract - This paper presents the modelling of different topologies of Electric Drive systems.The long motor leads, together with converter harmonics, decrease the performance of the motor. The harmonics produced by the inverter require a wide frequency model for the motor and for the cable models. The skin effect plays an important role in the cable, and the eddy current is very important to asses the motor behavior. Without the representation of these phenomena, the simulations would not represent the ringing effect at the motor terminals properly. A frequency dependent phase domain cable model was therefore used. This model is an extension of a frequency-dependent model developed for overhead transmission lines. The induction motor model takes the harmonic effect into account.
Its circuit parameters are capable of representing the current density variation, and consequently the impedance variation along the bar. The models were validated through experimental results carried out on an actual oil platform and from a prototype system. The latter system was used to test the system performance when very long motor leads (longer than 5 km) are involved. The application of the modelling techniques is discussed.- A Two Degrees of Freedom Current Control Scheme for Dead-Time Compensation
by Namho Hur, Kwanghee Nam, Sang-Chul Won
Abstract - A current controller having an inverse dynamic model and a PI controller has been proposed with the aim of compensating the effects of dead time. The proposed control scheme, having two degrees of freedom (DOF), can be used for compensating the effects of disturbance without degrading tracking performance. To be specific, the disturbance rejection property is enhanced by increasing the gains of the PI controller, but the PI gain does not affect the transfer function between the current command and its output. By nature, it is robust to the parameter mismatch error between the model and the plant, since the mismatch error can be counted as another disturbance. With the experimental results, we have shown the superiority of the proposed method in suppressing the current distortion caused by dead time.
- VRLA Battery State of Charge Estimation in Telecommunication Power Systems
by Adnan H. Anbuky, Phillip E. Pascoe
Abstract - This paper presents the logical analysis of VRLA battery discharge behaviour and suggests a model for obtaining estimates of the state of charge (SOC) and reserve time throughout discharge. The basis of the model is the relationship between the discharge voltage and SOC. This relationship is valid for a wide range of discharge rates and ambient temperatures as related to the telecommunications backup power supply application. Due to the robust nature of this relationship only a single discharge characteristic under nominal operating conditions is required by the model. Case studies reveal that the model enables accuracy in estimation of SOC of better than 10% of actual SOC after discharging 10% of the rated capacity. As the discharge proceeds the error reduces substantially. A feature of the model is that it is easily adaptable to changes in battery characteristics which occur as a result of extreme stress.
Drive Control
- An Adaptive Sliding Mode Controller for Nonlinear Systems
by David Munoz Q., Daniel Sbarbaro H.
Abstract - This paper presents a sliding mode controller for a class of non-linear discrete time systems. The proposed controller uses a modified switching function that produces a low chattering control signal. In order to improve the controller performance, an adaptive term is added to the original sliding mode algorithm. This new feature uses an artificial neural network for on-line identification of the modelling error. Simulations and experimental results illustrate the main characteristics and performance of this approach.
- New Adaptive Sliding Observers for Position and Velocity Sensorless Controls of Brushless DC Motors
by Zhiqian Chen, Mutuwo Tomita, Shinji Doki, Shigeru Okuma
Abstract - A new adaptive sliding observer is proposed for a position and velocity sensorless control of a cylindrical brushless dc motor. Stability of the proposed observer is guaranteed easily, because it is based on a linear model of the motor. Sliding mode is applied for the current estimation. Under the sliding mode, the order of the observer's error equation is reduced. This makes the stability analysis easier so that robust position and velocity estimations might be achieved by the pole assignment. Experimental results show that the proposed method is very effective.
- Tuning Rules for the PI Gains of Field-Oriented Controllers of Induction Motors
by Gi-Won Chang, Romeo Ortega, Gerardo Espinoza-Perez, Eduardo Mendes
Abstract - In a recent contribution we have shown that field-oriented controllers for induction motors preserve stability under a wide range of variations of the motor and controller parameters. However, as is well known, the transient performance critically depends on the tuning of the gains of the PI velocity loop, a task which is rendered difficult because of the high uncertainty on the rotor resistance. The problem we address in this paper is how to develop an off-line procedure to choose these gains. The main contribution of our work is a very simple frequency domain test that, for each setting of the PI gains, evaluates the maximum range of the relative rotor resistance estimate for which global stability is guaranteed. In this way we provide a quantitative estimate of the performance of the PI controller. The stability result may also be used in a dual manner, fixing now the range of the rotor resistance, and estimating an admissible interval for the PI gains that preserves global stability. Instrumental for our study is the exploitation of an energy dissipation (strict passivity) property of the system.
- Speed Control of Two-Inertia System by PI/PID Control
by Guoguang Zhang, Junji Furusho
Abstract - Our purpose is to develop systematic analysis and design methods for two-inertia system. A conventional PI speed control system with a torsional load is redesigned, and the damping characteristic of the system is derived and analyzed. It is shown that the dynamic characteristic of the system strongly depends on the inertia ratio of load to motor. Three kinds of typical pole assignments with identical radius/damping coefficient/real-part are applied and compared, and the merits of each pole assignment designs are concluded. Furthermore for small inertia ratio, we present how to improve the damping of the system by a derivative feedback of motor speed.
- Fuzzy Logic applied to Robust Speed Control of a Stepping Motor Drive
by Franck Betin, Daniel Pinchon, Gérard-André Capolino
Abstract - Nowadays, thanks to the development of microprocessors, stepping motors are widely used in robotics and in the numerical control of machine tools where they have to perform high-precision positioning operations. Nevertheless, the variations of the mechanical configuration of the drive, which are common to these two applications, can lead to a loss of synchronism for high stepping rates. Moreover, the classical open-loop speed control is weak and a closed-loop control becomes necessary. In this paper, the fuzzy logic principle is applied to control the speed of a stepping motor drive with feedback. An advanced test bed is used in order to evaluate the tracking properties and the robustness capacities of the fuzzy logic controller when variations of the mechanical configuration occur. The experiment has been performed using a low-cost 16-bit microcontroller in order to verify the design performances.
- Amplitude and Frequency Control of a Vibratory Pile-Driver
by C. M. Bingham, D. A. Stone, N. Schofield, D. Howe, D. Peel
Abstract - The paper describes the digital control of a vibratory pile-driver in which the vibration is generated via two tandem pairs of electrically driven, geared, contra-rotating eccentrics. Experimental results are included to show the controller induced system dynamics for a variety of load conditions, and to highlight the fact that, if the relative phase of the eccentric pairs is not controlled, the natural tendency at high excitation frequency is for the pile-driver to operate with a low vibration amplitude. An analytical technique for identifying the system parameters is presented, and analytical performance predictions are compared with experimental results. Analysis of the power flow in the system shows that, although significant power transfer occurs between the two electrical drives, the net power dissipation during pile-driving is relatively low.
- The Operation of an Inverter-Assisted Single Phase Induction Generator,
by Olorunfemi Ojo, Obasolhan Omuzusi, Adisa A. Jimoh
Abstract - The enhancement of the operability range of a stand-alone, single-phase induction generator scheme with an inverter-battery system connected to the auxiliary winding is the theme of this paper. The reactive power requirement of the load connected to the main winding is met by the inverter system operating with either of two proposed pulse-width modulation techniques, in the process of which the load voltage and frequency are regulated. The proposed schemes have potential application as power sources for autonomous systems and for utility interface to single-phase power system grids. Simulation and calculation results of the generator system connected to an impedance and motor loads, confirmed with some experimental results, are also set forth to validate some of the conclusions of the paper.
Robotics and Vision
- Position/Force Control of Robot Manipulators for Geometrically Unknown Objects using Fuzzy Neural Networks
by Kazuo Kiguchi, Toshio Fukuda
Abstract - Performing sophisticated tasks with an object is an important issue in the use of robot manipulators. In order to carry out the tasks of grinding, deburring, polishing, or wiping, the end-effector of the robot manipulator has to follow the contour of an object as it applies force perpendicularly to the objects surface. If the shape of an object is unknown, it is difficult to perform such tasks since it requires information about force control direction and position control direction. In this paper, we propose a fuzzy vector method to search the direction of the constraint surface of an unknown object in order to adjust force control direction. The intelligent controller is realized using fuzzy vector method and fuzzy neural controllers for the robot manipulator dealing with an object whose shape and property are unknown. The controller searches force control direction using fuzzy vectors as it applies force to the unknown object and controls the position of the end-effector using fuzzy neural networks. The controller is able to deal with force sensor signals which include noise and/or unknown vibrations caused by the working tool efficiently using the fuzzy vector method. The effectiveness of the proposed method is evaluated by experiment using a 2DOF planar robot manipulator.
Signal Processing
- Wavelet Packet Feature Extraction for Vibration Monitoring
by Gary G. Yen, Kuo-Chung Lin
Abstract - Condition monitoring of dynamic systems based on vibration signatures has generally relied upon Fourier based analysis as a means of translating vibration signals in the time domain into the frequency domain. However, Fourier analysis provided a poor representation of signals well localized in time. In this case, it is difficult to detect and identify the signal pattern from the expansion coefficients because the information is diluted across the whole basis. The Wavelet Packet Transform (WPT) is introduced as an alternative means of extracting time-frequency information from vibration signature. The resulting wavelet packet transform coefficients provide one with arbitrary time-frequency resolution of a signal. With the aid of statistical based feature selection criteria, many of the feature components containing little discriminant information could be discarded resulting in a feature subset having a reduced number of parameters without compromising the classification performance. The extracted reduced dimensional feature vector is then used as input to a neural network classifier. This significantly reduces the long training time that is often associated with the neural network classifier and improves its generalization capability.
- Regulations of GMA Welding Thermal Characteristics via a Hierachical Predictive Control Scheme Assuring Stability
by Spyros G. Tzafestas, E. J. Kyriannakis
Abstract -
- Look-Up Table Modeling for Control of a Hot Coil Strip Process using On-Line Re-Trainable RBF Network
by Minho Lee, So-Young Jeong, Soo-Young Lee, Jin-Man Cho, Cheol Hoon Park
Abstract - This paper presents an on-line re-trainable Radial Basis Function (RBF) network to control the coiling temperature for a hot coil strip at the Pohang Iron & Steel Company in Korea. The proposed RBF network is designed to replace the conventional rule-based look-up table, the output of which is a heat transmission coefficient in the temperature control system. In order to make the controller more adaptable to the changing environments in the steelmaking process, specific interconnection weights were additionally devised for the hidden-to-output weights of a conventional RBF network. These weights were locally adjustable to reduce the immediate temperature error of a coil strip, while the global information of the RBF network trained with off-line past data was largely unaltered. As a result, the proposed RBF network substantially alleviated the effect of catastrophic interference - completely forgetting old information in the presence of new inputs. Moreover, a rejection network was incorporated within the proposed control scheme to ensure reliable operations in the actual process. Results applied to real steelmaking process indicated an improvement of 2.2% in control performance compared to conventional methods.
- Blind Identification of Quadratic Nonlinear Models using Neural Networks with Higher-Order Cumulants
by Hong-Zhou Tan, Tommy W. S. Chow
Abstract - A novel approach to blindly estimate kernels of any discrete and finite extent quadratic models in higher-order cumulants domain based on artificial neural networks is proposed in this paper. The input signal is assumed an unobservable i.i.d. random sequence which is viable for engineering practice. Because of the properties of the third-order cumulant functions, identifiability of the nonlinear model holds even when the model output measurement is corrupted by a Gaussian random disturbance. The proposed approach enables a nonlinear relationship between model kernels and model output cumulants be established by means of neural networks. The approximation ability of the neural network with the Weights Decoupled Extended Kalman Filter (WDEKF) training algorithm is then used to estimate the model parameters. Theoretical statements and simulation examples together with practical application to the train vibration signals modeling corroborate that the developed methodology is capable of providing a very promising way to identify truncated Volterra models blindly.
Emerging Technologies
- Current Sensor-Based Feed Cutting Force Intelligent Estimation and Tool Wear Condition Monitoring
by Xiaoli LI, Alexandar Djordjevich, Patri K. Venuvinod
Abstract - Tool wear condition monitoring has the potential to play a critical role in ensuring the dimensional accuracy of the workpiece and prevention of damage to cutting equipment. It could also help in automating cutting processes. In this paper, the feed cutting force estimated with the aid of an inexpensive current sensor installed on the AC servomotor of a CNC turning center is used to monitor tool wear condition. To achieve this, the feed drive system is modeled, using neuro-fuzzy techniques, to provide the framework for estimating the feed cutting force based on the feed motor current measured. Functional dependence of the feed cutting force on tool wear and cutting parameters are then expressed in the form of a difference equation relating variation in the feed cutting force to tool wear rate. The computerized system automatically compares successive feed cutting force estimates and determines the onset of accelerated tool wear in order to issue a request for tool replacement. Experimental results show that the tool wear condition monitoring is effective and industrially applicable.
- An Implementation of Fuzzy Logic Controller on the Reconfigurable FPGA System
by Daijin Kim
Abstract - This paper concerns an implementation of a fuzzy logic controller (FLC) on a reconfigurable FPGA system. In the proposed implementation method, the FLC is partitioned into many temporally-independent functional modules and each module is implemented individually on the FADIS (FLC Automatic Design and Implementation System), which is an integrated development environment for performing many subtasks such as automatic VHDL description, FPGA synthesis, optimization, placement and routing, and downloading. Each implemented module forms a downloadable hardware object that is ready to configure the FPGA chip. Then, the FPGA chip is consequently reconfigured with one module at a time by using the run-time reconfiguration method. This implementation method is effective when a single FPGA chip can not fit the FLC due to the limited size of its constituent cells. We test the proposed implementation method by building the FLC for the truck backer-upper control on the VCC's EVC-1 reconfigurable FPGA board directly.
Letters to the Editor
- A Single Stage Electronic Balast with High Power Factor
by Jang-Hyoun Youm, Bong-Hwan Kwon
Abstract -A single stage electronic ballast with high power factor is proposed in this letter. The proposed topology using the single-phase boost-type rectifier provides simultaneously high power factor to the utility line and high frequency voltage to the fluorescent lamp. A saturable transformer constituting the self-oscillating drive limits the lamp current and dominates the switching frequency of the ballast. The proposed ballast has high energy efficiency, low cost, and high reliability compared to the conventional high-power-factor (HPF) electronic ballasts. Experimental results obtained on a 40 W fluorescent lamp are discussed.
