Showing papers presented at "International Symposium on Industrial Electronics in 1998"

Multilevel converters for single-phase grid connected photovoltaic systems-an overview

Abstract: Multilevel voltage source inverters offer several advantages compared to their conventional counterparts. By synthesising the AC output terminal voltage from several levels of voltages, staircase waveforms can be produced, which approach the sinusoidal waveform with low harmonic distortion, thus reducing filter requirements. The need of several sources on the DC side of the converter makes multilevel technology attractive for photovoltaic applications. This paper provides an overview an different multilevel topologies and investigates their suitability for single-phase grid connected photovoltaic systems. Several transformerless photovoltaic systems incorporating multilevel converters are compared regarding issues such as component count and stress, system power rating and the influence of the photovoltaic array earth capacitance.

A fuzzy logic based photovoltaic peak power tracking control

Abstract: This paper describes the analysis, modeling and implementation of a fuzzy based photovoltaic peak power tracking system. The maximum power of a photovoltaic system changes with temperature, solar intensity and load. An analytical model is built for the solar cell on the basis of the manufacturer characteristics. The solar panel is integrated with the converter model and a fuzzy algorithm is developed so as to perform an on-line search procedure to track the maximum power continuously. The system is implemented by an inexpensive RISC microcontroller. Experimental results have shown excellent performance, robustness with parameter variation, modularity for parallel operation at higher power, and ready to retrofit existing installations.

A ZVS clamping mode-current-fed push-pull DC-DC converter

Abstract: This paper introduces a new technique to recover the energy trapped in the leakage inductor of the current-fed push-pull converter, by means of an active clamping mode circuit. Theoretical analysis and experimental results, taken from a 800 W/40 kHz are presented in the paper. The studied converter also features ZVS (zero voltage switching) in all switches, preserving all the main properties of the original circuit. As a result, the efficiency is improved and the electromagnetic disturbances are minimized.

An integrated maximum power point tracker for photovoltaic panels

Abstract: This paper proposes a maximum power point tracker (MPPT) for a photovoltaic panel, that is to be integrated with the panel during manufacturing. The MPPT is inexpensive, efficient and has few components that serve to increase the MPPT's mean time between failures (MTBF). The MPPT uses an inexpensive microcontroller to perform all of its functions. This includes maximum power point tracking, series battery voltage regulation, sensorless short circuit protection of the MPPT's converter and intelligent shutdown and wakeup at dusk and dawn. The MPPT can source 10 A to a 6-36 V lead-acid storage battery and can be connected in parallel or series with other MPPTs. The MPPT may be easily configured to perform output voltage regulation on passive and water pumping loads. It could also control the actuation of a diesel generator in a hybrid remote area power supply (RAPS). Energy transfer enhancements of up to 26%, compared to solar panels without MPPTs, have been measured, The complete component and materials cost of the MPPT is approximately 2.8% of the cost of photovoltaic panels with a peak power rating of 154 W. The integrated MPPT also consumes no stored energy at night.

Unified approach to power quality mitigation

Abstract: A unified approach to the compensation of multiple power quality phenomenon is described in this paper. It is shown that the converter-based power quality mitigation device is a viable solution to power quality problems on power networks since more than one power quality problem can be compensated by the same hardware. These devices should be capable of harmonic compensation or isolation, improving dynamic voltage regulation and flicker simultaneously, while capable of controlling power factor and power flow through the network. These functions can also be implemented independently. These power quality mitigating devices can be hybrid devices comprising passive components and converters. The drive is to minimize the converter power rating while maximizing the compensating performance. Several projects where this approach has been implemented are discussed in this paper.

A fuzzy adaptation technique for sliding mode controllers

Abstract: In this study a new fuzzy adaptation technique to be used in a sliding mode controller is developed for achieving robust tracking of nonlinear systems, Since conventional sliding mode control strategies suffer from high control gain and chattering problems a fuzzy adaptation for a sliding mode controller is proposed to overcome the problems. In the approach two fuzzy approximators are employed in such a way that the slope of the linear surface is updated by the first fuzzy approximator, to shape tracking error dynamics in the sliding regime, while a second fuzzy approximator regulates behaviour of the states in the reaching phase. Thus the fuzzy adapted sliding mode controller proposed in this study pushes the system states in the most appropriate way to achieve robust tracking. Examples demonstrate that results are highly satisfactory for both dynamics and steady-state responses, hence the method is confirmed through the simulations.

PWM voltage and current control of four-leg VSI

Abstract: In the paper, two control methods of a four-leg three-phase invertor for UPS and active filter applications are discussed. The inverter output voltage is represented as a three-dimensional space vector. Two PWM schemes are investigated: open loop sinusoidal PWM; and feedback multilevel hysteresis PWM current control. Some simulated figures and experimental oscillograms illustrating the properties of the both presented PWM methods are given.

PC based number plate recognition system

Abstract: A PC based number plate recognition system is presented Digital gray-level images of cars are thresholded using the Niblack algorithm, which was found to outperform all binarization techniques previously used in similar systems A simple yet highly effective rule-based algorithm detects the position and size of number plates Characters are segmented from the thresholded plate using blob-colouring, and passed as 15/spl times/15 pixel bitmaps to a neural network based optical character recognition (OCR) system A novel dimension reduction technique reduces the neural network inputs from 225 to 50 features Six small networks in parallel are used, each recognising six characters The system can recognize single and double line plates under varying lighting conditions and slight rotation Successful recognition of complete registration plates is about 861%

Solid state class DE RF power source

Abstract: Class DE represents a new family of inverters, based on a Class D LCR series resonant inverter. Class DE differs in that the method of operation utilises the devices output capacitance to obtain zero voltage, zero current switching transitions. Hence switching losses (and switching EMI) can be very low, permitting operation to a high frequency. This paper presents the problems, solutions, results and feasibility of a Class DE inverter as an RF power source for frequencies up to 5 MHz and a power of 1 kW. At this frequency, the theoretical design requirements put some tight restrictions on dead time, phase and output capacitance. This presents some formidable problems in practically implementing the inverter. The most significant problems are: the gate drive circuitry including layout, isolation of the high side gate drive, nanosecond control of dead time, synchronization of high and low side gate drive pulses, phase control of the driving voltage and general layout of the power devices. Some novel solutions to the above problems are described. The simulation and experimental results are presented and the practical power and frequency limits of a Class DE inverter are discussed. The information presented should be useful in applications such as MHz DC-DC power converters, RF power sources for industrial heating and AM transmitters.

Novel hybrid load-adaptive variable-speed generating system

Abstract: Light loading of generator sets has long been the cause of accelerated aging and premature engine failure This problem is exacerbated by impact and nonlinear loads because generator sets are oversized to cope with this condition whilst maintaining the voltage within the specified limits A new hybrid engine-friendly load-adaptive variable speed generating system has been developed which decouples the engine from the load by means of a decoupling converter The engine load torque can be precisely controlled independently of the load so that optimal engine operation is achieved for a wide range of load power demands Test results show outstanding performance under the worst load conditions, superior to that of comparable systems

Power converter analysis and design using Matlab: a transfer function approach

Abstract: The design and steady-state analysis of static power converters has usually been realized in the time domain. This approach however is subject to numerical convergence problems and long simulation times, which worsen as the converter's switching frequency increases. This paper proposes a novel design and steady-state analysis method to overcome these problems using Matlab. The method is based on the Fourier transform (FT) and a generalized converter transfer function. Thus obtains steady-state results without requiring the transient power-up, neither the circuit components' initial conditions. The FT and converter transfer function are used to model and solve the converter in the frequency domain. Desired variables are then obtained in the time domain using the inverse FT. The method eliminates numerical problems and reduces simulation times significantly. For example, the simulation of a PWM voltage source inverter operating at 5 kHz takes 320 times longer in PSpice than in the proposed method. It also presents a minor processing time dependency from the converter's switching frequency. The paper includes a detailed presentation of the proposed method, a complete analysis example using Matlab 4.02, together with an evaluation comparing it to conventional simulating techniques. Finally, experimental results with a 10 kVA AC motor drive are presented to validate the proposed analysis and design method.

An integrated network for agricultural management applications

Abstract: Modern concepts on methods and techniques for the management and control of agricultural systems-such as greenhouse and animal live stocks-claim for the use of computer systems. Tasks like climate, irrigation and nutrient supply must be controlled, in an economically way, to produce the best crop/living conditions. To comply with these objectives, it is necessary to apply adequate control actions as the result of an integrated system that co-ordinates each action according with specific combination of different sensor inputs. Moreover, this control must be often performed from a remote site. This paper describes the design and implementation of an integrated network that links several communications platforms, as different as controller area network (CAN), wireless technology and Transfer Control Protocol-Internet Protocol (TCP-IP). The main goal is to develop a system that guarantees a low-cost, high performance and flexible distributed control system with an increased functionality. The user interacts with this distributed control system using a transparent and intuitive graphical user interface, (GUI) accessible from remote places.

Chaos-based spread spectrum communication systems

Abstract: A new scheme is proposed for spread spectrum communication which modulates directly both analog data and binary data sequences via chaotic carriers. The proposed systems have some standard properties of spread spectrum communication. Computer simulations and performance analysis are given to examine the validity of this scheme.

Review on diamond based piezoresistive sensors

Abstract: Nearterm industrial applications require pressure sensors and acceleration sensors which are able to operate at elevated temperatures and in harsh environments where conventional silicon devices do not work. Many properties of diamond (e.g. its physical hardness, high Young's modulus, high tensile yield strength, chemical inertness, low coefficient of friction and high thermal conductivity) make diamond an excellent material for micromechanical device applications which include piezoresistive (e.g. pressure and acceleration) sensors. The measurement of the gauge factor of B-doped, polycrystalline CVD diamond thin films leads to the result that the longitudinal piezoresistive effect is larger than the transverse piezoresistive effect for all B-doping concentrations. Furthermore, the transverse piezoresistive effect shows a pronounced nonlinearity. Therefore, a "longitudinal" pressure sensor lay out should be preferred. In general, the longitudinal gauge factor increases with decreasing doping concentration and can be larger than 100, which is comparable to single-crystalline silicon, and larger than the reported gauge factors of SiC. First prototype pressure sensors with B-doped polycrystalline diamond piezoresistors connected to form a Wheatstone bridge on top of a silicon square membrane (1300 /spl mu/m/spl times/1300 /spl mu/m/spl times/30 /spl mu/m) show an excellent linearity. The sensitivity of 1.64/spl times/10/sup -5/ mV/(V Pa)/sup -1/ can be improved using a lower doping concentration of the piezoresistors.

VLSI analog multiplier/divider circuit

Abstract: Intelligent systems require signal processing which can be done quickly and accurately. The commonly used digital approach has many advantages, but some disadvantages as well. Analog signal processing is in many cases much simpler, faster, and easier for performing parallel processing. In this paper a new accurate CMOS multiplier/divider circuit is presented. Contrary to previous solutions, which use the square law formula for MOS transistors operation, in the strong inversion mode, the multiplier/divider circuits employ MOS transistor characteristics in the subthreshold conduction mode. It is shown that the circuit generates very accurate results. With some modification, the basic circuit can also be used as a four-quadrant multiplier, which may operate for both positive and negative input signals. The circuit itself may have many applications such as multiplier, divider, signal squaring, square root calculations, frequency modulation, frequency doubling, etc. Most importantly it can be used for analog signal processing in many intelligent systems of industrial electronics.

Grid connected/solar water pump for rural areas

Abstract: A novel water pumping system is proposed with a view to implementation in either a mini-grid or a single-wire-earth-return (SWER) scenario. The system utilises a three-phase inverter which can draw power either from a solar energy input or from a single phase AC supply to drive a three-phase induction motor. On the AC side, one phase of the inverter is connected to the supply through an inductor. By changing the phase relationship between the two waveforms, bi-directional power flow results. This front-end rectifier enables the inverter to draw sinusoidal input current at unity power factor while also reducing the switch count. On the DC side, the output power of the solar array is monitored and the system allows the bus voltage to fluctuate within bounds in order to track the optimum power point. Voltage regulation of the output is then achieved through adjusting the modulation index of the PWM control signals. This paper presents initial results from a small-scale test system and discusses the merits of the proposed scheme.

On non uniform sampling of signals

Abstract: In a variety of applications, it is desirable to represent a signal by a set of nonuniformly distributed samples. In particular, this is of interest in the case of nonbandlimited signals where an alternative method to uniform sampling is required. In this work, a new approach to nonuniform sampling is introduced and discussed. The proposed method is based on estimation of a time distortion transformation, under which the original signal becomes practically bandlimited and can thus be reconstructed. The time distortion transformation is estimated using an iterative algorithm. According to this approach, the distortion function is accumulated where each iteration is aimed at compensating for differences in the instantaneous bandwidth after the previous iteration. This process converges and reaches a stage where the signal has practically a constant instantaneous bandwidth over the distorted time axis. Due to the iterative nature of the estimation process, most available techniques of localized bandwidth approximation may be used. The resultant mapping can be considered also as a new means for the definition of local bandwidth.

Maximum power point tracking-implementation strategies [for PV power systems]

Abstract: The cost of PV modules dictate that maximum use be made of the available power that can be produced. To achieve this goal, it is necessary to match the PV module characteristics with that of the load. Although this fact is not new, many charge regulation products and water pumping systems still operate on less than optimum principles. Especially, small systems (50-80 W) make use of direct coupling to the PV module or rely on fixed voltage operation. The purpose of this work is to investigate the reasons for the status quo and to seek acceptable solutions, both technically and economically. The need for extracting maximum power from a PV module is obvious. A cost-effective method, which is reliable, will make optimum power point tracking feasible, even for low power applications.

High performance DSP/FPGA controller for implementation of computationally intensive algorithms

Abstract: Increasingly complex power electronic control algorithms are continually being developed and refined. Most of these algorithms are only proven through simulation, because of the lack of easy-to-use high performance controllers. The design of such a controller involves specialised knowledge of high-speed digital engineering, to which a lot of power electronic engineers do not have access. This leads to the current situation where these algorithms are not as widely used, as their performance would suggest. This paper discusses the evaluation of digital controllers and presents a high performance, easy-to-use DSP/FPGA controller. The controller's performance is illustrated by the implementation of a real time, predictive, inner loop current controller, for a single-phase full-bridge IGBT converter.

Analysis of a power conditioning system for superconducting magnetic energy storage (SMES)

Abstract: A power conditioning system (PCS) which can be utilized for the compensation of nonlinear and pulsating loads is analyzed in this paper. The PCS consists of a voltage source inverter and a DC current chopper, and uses a SMES as its energy storage device. The whole system is controlled by three regulators acting on the superconducting coil stored energy, the DC-link voltage, and the inverter AC currents. Numerical simulations have been carried out by PSpice to verify the performance of the PCS in different operating conditions.

Reluctance synchronous machine drive for hybrid electric vehicle

Abstract: The reluctance synchronous machine drive is amazingly not mentioned in literature as a possible alternative drive for electric vehicle propulsion. The paper describes the use of a small, compact reluctance synchronous machine drive for a series hybrid electric vehicle. The advantages and disadvantages of this drive compared to other drives are highlighted. It is shown that a finite element optimum designed flux barrier rotor reluctance synchronous machine has good torque density and efficiency. The machine is current angle-controlled for maximum torque per ampere or minimum kVA. This ensures that the machine is operated reasonably close to optimal efficiency for all loads. The simple drive controller together with an optimum layout three-phase IGBT inverter forms a compact power controller for the vehicle. The calculated and measured results of the reluctance synchronous machine drive system for the electric vehicle are given. The 28 kW peak reluctance synchronous machine is used to drive the front wheels of a sedan, series hybrid electric vehicle through a differential with a gear ratio of 4.5:1. Simulation results show, amongst others, that with the single RSM drive generating a peak torque of 120 Nm, the 1445 kg vehicle accelerates from 0-80 km/h in 25.5 seconds. The maximum speed is 120 km/h.

The sensor-control Jacobian as a basis for controlling calibration-free robots

Abstract: A method for controlling the motions of robots is presented. It is based on the newly introduced sensor-control Jacobian matrix and avoids all quantitative modeling of the robot and the sensor system. The sensor-control Jacobian contains the coefficients that relate those changes in sensor data which are caused by a motion of the robot to the robot control words that caused the robot to move and, thus, the sensor data to change. A wide variety of tasks of robots can be reduced to minimizing the differences between actual sensor data and a set of hypothetical sensor data corresponding to some desired state. All these tasks can be solved by this method. The method is especially useful for calibration-free robots, since neither quantitative models of the mechanical, kinematic and control characteristics of the robot, nor knowledge of the sensor characteristics are required. The sensor-control Jacobian may be determined automatically in real time while the robot is operating. This yields a high degree of adaptability and flexibility against unforeseen changes in the robot's parameters. Because the concept has an open structure it allows further extensions and improvements, e.g., in terms of the utilization of sensor data redundancy and machine learning. For the purpose of evaluation, the concept has been implemented on a calibration-free camera-manipulator system. Real-world grasping experiments have demonstrated the effectiveness of the method.

Hierarchical genetic fuzzy controller for a solar power plant

Abstract: To regulate the significant variations of the dynamic characteristics of the distributed collector field in a solar power plant, in this paper, a unique hierarchical genetic algorithm (HGA) has been employed for the design and optimization of the fuzzy logic controller for this purpose. This method not only fulfils the required performance, but also minimises the number of fuzzy membership functions and rules applied. This can be a valued asset for the design of a simple hardware implementable fuzzy controller.

150 W inverter-an optimal design for use in solar home systems

Abstract: Single-frequency photovoltaic inverters have been on the market since a need arose to produce AC power from a DC source, probably long before the beginning of PV power systems. With the growth in the PV industry, the need for better, more cost-effective inverters is ever present. Producing an inverter of high quality at a low cost is a challenge. A high quality inverter at high cost cannot compete in the low quality inverter market. Solar home systems are often offered inverters that do not look after the assets of the client, i.e. the lifetime of lights and various loads used on inverters. A investigation was done, looking at various 150 W inverters (law as well as high cost), comparing and evaluating the results. A low cost inverter was then developed that caters for most loads at an affordable price.

Nano tele-manipulation using virtual reality interface

Abstract: A telemanipulation system from macroscale world to nanoscale world with a user-friendly virtual reality-based human-machine interface has been proposed in this paper. This paper focuses on the direct telemanipulation of nano objects with sizes 1 nm-1 /spl mu/m. A home-made AFM device has been utilized as the nano vision and force sensor as well as the nano manipulator. As the teleoperation interface, a force-feedback device and 3-D virtual reality graphics visualization environment have been constructed. Preliminary simulation and experimental results are presented.

Refrigerator temperature control using fuzzy logic and neural network

Abstract: This paper describes the quick and precise control method for domestic refrigerators. The proposed controller is based on the fuzzy logic and neural network designed maintaining the constant inner temperature of the refrigerator and improving the refrigerator efficiency. The fuzzy logic controller is used to maintain the inner temperature in spite of the environmental variations such as the outer temperature change or the volume change of the stored foods of the refrigerator. A neural network is used and trained to recognize the user-pattern such as the number of door openings of the refrigerator. The 1st order approximated model of the refrigerator is used for the simulation. Through the simulation in the case of the outer temperature change like summer or winter, the proposed fuzzy logic controller with a neural network is shown to be more efficient than the conventional on-off controller.

An alternative Chua's circuit implementation

Abstract: This paper proposes a novel nonlinear smooth function to implement the Chua's circuit. This new function provides a similar smoothness as to the cubic polynomial function, but a faster response and a simpler circuitry can be obtained. Some bifurcation phenomena and the chaotic attractors are observed experimentally from a practical circuit point of view.

Inspection- and repair robots for waste water pipes a challenge to sensorics and locomotion

Abstract: Sewerage is a very large and important infrastructure in the water industry. Because around 20% of the municipal pipe network is estimated to be significantly damaged, it is of high priority to inspect, maintain and repair public sewers. During recent years mobile robots have been developed to inspect but also to repair the pipes. To navigate through the hostile environment, they are generally only equipped with video cameras and connected to the outside world via an umbilical cord which transmits the image information. The tethered robots are tele-operated from a remote service station placed at the end of a maintenance shaft. These pipe robots are commonly wheeled systems especially adapted to withstand the adverse conditions of the waste pipe environment. In this paper the actual state of the art in the field of mobile robots for repair and inspection of sewerage is given and the possible improvements of the next generation of robots caused by developments of the sensors, the material, the tele-operation techniques and the locomotion principles are reported. This will allow the robots to increase their capabilities and to enlarge the application areas to pipes with smaller diameters and pipes in industrial plants.

Advances in power electronics-its impact on the environment

Abstract: Power electronics is one of the fastest changing and evolutionary technologies in electrical engineering in the recent years. This last decade of the 20th Century can be truly defined as the era of power electronics-or more truly, power electronics and information era. The solid-state power electronics revolution (often called the second electronics revolution) started by the invention of the thyristor in the late 1950s, and then continued ceaselessly by invention of many power devices, such as GTOs, triacs, BJTs, power MOSFETs, IGBTs, SITs and MCTs. The advent of new devices and the dramatic improvement of their ratings and characteristics gave a solid foundation for power electronics which resulted in the development of many power converter topologies, analytical and simulation techniques, variable frequency drives, and their control and estimation methods. As a result, the cost of power electronics apparatus fell significantly and their performance improved considerably, which correspondingly, spurred the dramatic surge of power electronics applications everywhere. This contributed to the present era of global industrial automation. Besides the improvement of industrial productivity and product quality, recently another dimension of the importance of power electronics-energy conservation and the corresponding control of environmental pollution-has been realized.

A practical PWM inverter control circuitry for induction heating and studying of the performances under load variations

Abstract: In induction heating applications, the heating coils may have different types for different loads. A suitable control method is often needed to let the power electronic circuit working in most fit condition to supply power to the load. In this paper, a simplified control strategy following the features of induction heating is described. The most outstanding advantage of this method is to allow a design of a simple PWM gate signal and zero-voltage-switching (ZVS) operation. Another advantage of this technique is variable-frequency (VF) control. So that, switching loss is reduced under varying loads.