Showing papers presented at "International Symposium on Industrial Electronics in 1996"

A new panel-integratable inverter concept for grid-connected photovoltaic systems

Abstract: This paper describes the problems of conventional inverter concepts for photovoltaic power systems and presents a new, panel-integratable inverter concept as a solution. This concept is advantageous regarding safety (no DC-lines), flexibility (modular concept), converted energy per year (no mismatch losses due to individual MPP tracking of each panel) and costs (no reinforced isolation due to AC distribution). Furthermore a 250 W DC to AC inverter is developed, which consists of a series resonant DC-DC power converter and a line inverter. The inverter has a high efficiency and consumes little power itself. Meeting international standards, sinusoidal line current with low distortion is achieved. The inverter has a built-in controller to operate the panel in the maximum power point. Above this, the concept allows the flexible use with many different combinations of solar panels. To realize an inexpensive system, the controller is built up using standard low-cost components.

An overview of modern PWM techniques for three-phase, voltage-controlled, voltage-source inverters

Abstract: An overview of modern PWM techniques for three-phase, voltage-controlled, voltage-source inverters is presented. Five classes are distinguished: (1) modulating-function techniques, (2) voltage space-vector techniques, (3) programmed and quasi-programmed techniques, (4) feedback and quasi-feedback techniques, and (5) random techniques. Underlying principles and general characteristics of each class are briefly described. It is stressed that a practical high-performance PWM technique must offer a sensible tradeoff between the often conflicting technical requirements.

A dynamometer performing dynamical emulation of loads with nonlinear friction

Abstract: A dynamometer capable of emulating linear, nonlinear and discontinuous loads for rotating systems is described. The controllable load is produced by a servo drive system. Applications for the dynamometer are steady state load tests and dynamical load tests with linear, nonlinear or discontinuous loads for testing of electrical machines in variable speed drive systems. The configuration of the dynamometer is presented, together with simulation models and simulation results. The simulated torque and speed time responses show that the dynamometer tracks the required torque with a high degree of accuracy, for both linear, nonlinear and discontinuous loads.

A DSP and FPGA based integrated controller development solutions for high performance electric drives

Abstract: Modern drive control algorithms require advanced hardware and software platforms suitable for fast, efficient and reliable implementations. The development process includes in most cases the following engineering steps: off-line software simulations, hardware design and software implementation in a target system. This paper presents the general requirements connected with microprocessor-based digital control systems for drive control applications. An integrated and flexible hardware and software environment for electric drives control is described. The hardware part of the system includes flexible stand-alone boards and PC-cards set based on the digital signal processors (DSP) family and advanced field programmable gate arrays (FPGA). The flexibility of FPGAs provides multiprocessor and open architecture interface. The PC-based simulation environment offers hardware-in-the-loop options and extended data acquisition functions. After simulation and evaluation procedures the software structure of the controllers can be transfered into the stand-alone DSP board ready for commercial application. The proposed integrated system is very useful in the high-performance AC drives and double-fed machine controller designs. Currently, the project of the DSP controller for the voltage source inverter with the power range above 100 kW is under way in the Gdansk Branch of the Electrotechnical Institute. Several simulation and experimental results are presented and summarised.

Parameter estimation of inverter and motor model at standstill using measured currents only

Abstract: Methods for the estimation of the parameters in the electrical equivalent diagram for an induction motor, based on especially designed experiments, are given. In all experiments, two of the three phases are given the same potential, i.e., no net torque is generated and the motor is at standstill. Input to the system is the reference values for the stator voltages given as duty cycles for the PWM power device. The system output is the measured stator currents. Three experiments are described giving respectively: (1) the stator resistance and inverter parameters; (2) the stator transient inductance; and (3) the referred rotor resistance and magnetizing inductance. The method developed in the two last experiments is independent of the inverter nonlinearity. New methods for system identification concerning saturation of the magnetic flux are given and a reference value for the flux level is derived. Experimental results are compared to factory measured values, and the difference may be explained by temperature variations and saturation effects.

Position control of ultrasonic motors using neural network

Abstract: The ultrasonic motor is a newly developed motor and it has excellent performance and many useful features, therefore, the ultrasonic motor is expected for many practical applications. However, the drive principle of the ultrasonic motor is different from that of other electromagnetic type motors, and the mathematical model of the motor has not been developed yet. Furthermore, the speed characteristics of the motor hold heavy nonlinearity and they vary with drive conditions. Therefore, the precise position control of an ultrasonic motor is generally difficult. In this paper, we propose a new position control scheme for an ultrasonic motor using a neural network. The proposed controller can approximate the nonlinear input-output mappings of the motor using the neural network, and can compensate the characteristic variations by online learning based on the general backpropagation algorithm. The trained network finally makes an inverse model of the plant. The usefulness and validity of the proposed control scheme is examined in experiments.

An on-line identification method for both stator and rotor resistances of induction motors without rotational transducers

Abstract: In this paper, the authors propose an effective method of identifying, online, both stator and rotor resistances, which are useful in the speed control of induction motors without rotational transducers, a scheme which is robust with respect to variations in motor parameters. Their identification method for both stator and rotor resistances uses only information of stator currents and voltages. It can provide fairly good identification accuracy regardless of load conditions. Some experimental results are presented to demonstrate the practical use of this identification method.

Discrimination of material property by pressure-conductive rubber sheet sensor with multi-sensing function

Abstract: A new technique for discrimination of material property by a pressure-conductive rubber sheet sensor with multi-sensing function is proposed. Firstly, we found the thermal conductivity and hardness of four typical materials when the rubber sheet, of which the resistance is influenced by not only pressure but also temperature, is put on the flat surface of the material. Furthermore, we proposed a tactile sensor with eight latticed small patch rubber elements and three kinds of surface models for discriminating the difference of the surface situation of materials, and obtained a good result to recognize the thermal property and the hardness property of material and also the surface situation of the model surface of the material.

DC/DC-converters in parallel operation with digital load distribution control

Abstract: The parallel operation of power supply circuits, especially in applications with higher power demand, has several advantages. One of the most important aspects is to improve the power system reliability and the operational redundancy by it. There is also a trend in producing standard power converter modules which can be connected in parallel to cover a wide power range. This significantly reduces the costs of development and existing systems can be extended easily. A main problem of the parallel operating power converters is to attain an accurate equalization of the modules' output currents. There are different solutions of this problem arising in literature. All these approaches try to reach this goal with a minimum of technical complexity in order to keep costs at a low level. In recent years the implementation of digital control concepts in switching power supply systems seems to be of growing interest. Digital control offers several possibilities: functions of communication can be embedded quite easily; control structures and parameters can be changed by modifying only the software; adaptive control systems are realizable; and complex control strategies become possible. In this paper, parallel operating DC/DC power converters are combined with a digital control unit, thus allowing a complex control strategy called load distribution control (LDC) possible. This new method of LDC is described in detail in the paper. Simulation results are presented as well as experimental verifications.

Evaluation of converter topologies for improved power quality in DC traction substations

Abstract: A high power converter is developed for improved power quality in DC traction substation applications. The proposed converter can be used as both an inverter and an active power filter (APF). As an inverter, it can recycle regenerative energy caused by decelerating trains and as an APF, it can compensate for harmonic distortion produced by the rectifier substations. This paper evaluates the different topologies which can be used to implement this converter. A multilevel topology for the converter is considered because of the high power and high dynamic bandwidth requirements. A comparison is made between using a multilevel inverter and using a combination of a multilevel chopper and a lower voltage inverter.

Power transformers life expectancy under distorting power electronic loads

Abstract: The proliferation of nonlinear loads causes harmonic voltage distortion on public and industrial networks. The transformer's thermal loss of life, estimated for sinusoidal loads, can be slightly reduced if we consider the harmonic currents. In this paper we study a distribution transformer (630 kVA) loss of life, driving a load cycle including a sinusoidal load and a weighted distorting one. The transformer thermal and electrical models are presented and the simulation results are analyzed. We propose a general expression to characterize loss of life derating; this expression includes only the current total harmonic distortion and two transformer specific parameters.

Fixed-frequency sliding mode control of a single-phase voltage source inverter with input filter

Abstract: This paper describes a sliding mode controller for a single-phase voltage source inverter. The work is motivated by power converter systems including two input filters with well separated corner frequencies. Since the inverter input current contains a low frequency component at twice the output voltage frequency, the high frequency input filter is designed to have low damping (no supplementary ohmic resistance). The stability of the closed-loop system is ensured by the control scheme resulting in stable large-signal behaviour while maintaining fast dynamic response to external disturbances. The analytical study provides general tools to design variable and fixed-frequency control implementations. It is shown that for the voltage source inverter, the simplest way to realise the proposed variable structure control law consists of adding a three level disturbance signal to the switching function. As a result, the power converter operates at constant switching frequency in the steady-state. The steady-state error is determined and a method is proposed to reduce the resulting harmonic distortion of the output voltage. The static and dynamic performances of the sliding mode controller are verified by an experimental 5 kVA inverter.

Optimal sliding mode design for motion control

Abstract: Motion control has been a fruitful ground for applying variable structure systems (VSS) theory. This paper provides an assessment of the state of the art of the relevant theoretical results for motion control, and through a number of control design problems (namely classical, discrete-time, observer based discrete-time and frequency shaped discrete-time sliding mode control) demonstrates the practical use of sliding mode in solving a number of critical design problems which are universal to both motion control and robotic manipulator control. Experimental results of a transputer-controlled single-degree-of-freedom motion-control system are presented.

New configuration of high-power inverter drives

Abstract: New configurations for high-power and high performance drives suitable for steel rolling mill drives are presented. Three-level inverters using 6 inch, 6 kV, 6 kA GTOs, can deliver 10000 kVA output. But in case of drives rated more than several thousands of kW, this capacity is still insufficient. Usually, two three-level inverters are then combined using bulky, expensive inter-phase reactors. To meet these problems, a new configuration using the wound rotor induction motor and two inverters is proposed. In this configuration, the outputs of the two inverters are combined electromechanically in the machine; then novel features suitable for high-power drives can be obtained.

Internal model control using neural networks

Abstract: We propose a design procedure of neural internal model control systems for processes with delay. We assume that a stable discrete-time neural model of the process is available. We show that the design of a model reference controller for internal model control necessitates only the training of the inverse of the model deprived from its delay, provided this inverse exists and is stable. As the robustness properties intrinsic to internal model control systems are only obtained if the inverse model is exact, it is also shown how to limit the effects of a possible inaccuracy of the inverse model due to its training. Computer simulations illustrate the proposed design procedure.

Fault diagnosis of voltage-fed inverter for induction motor drive

Abstract: A research on fault diagnosis in a voltage-fed inverter for induction motor drives has been conducted with the aid of the TCAD circuit simulator and the experimental laboratory unit. Classification and a base knowledge of failures has been derived from the frequency conversion chain of the decomposed power system. Sensor available variables are considered as stator currents and voltage across the filter capacitor. A method of fault diagnosis has been proposed based on current space vector trace inspection combined with the Fourier series processing. Simulation and experimental results on fault diagnosis during operation of 2.2 kW induction motor drive are given.

Dual DSP based fully digital control of an AC induction motor

Abstract: This paper proposes a fully digital control scheme for high-performance induction servo drives. A software current vector control in synchronous rotating reference frame with feedforward back EMF compensation has been developed for the current-regulated PWM inverters. A dual-DSP based digital controller using the TMS 320C14 and TMS 320C50 from Texas Instruments has been employed to realize the proposed software servo control scheme. Experimental results show the proposed control scheme can achieve robust servo requirements and at the same time maintain a fast current response with small current ripples.

Further development of direct self control for application in electric traction

Abstract: Direct self control was primarily developed for optimal steady-state and dynamic torque quality at the low switching frequencies of high power traction inverters. Though DC line harmonics and peak inverter current can be compared with those of PWM drives with same switching frequency there are now new possibilities by new digital signal processors to improve that too. The 6-pulse DC link reaction of the inverter is cancelled by introducing an eighteen-corner track curve. The same track curve can be employed advantageously with blocked pulsing as synchronous switching mode to avoid subharmonic torques in the high speed area. A current limitation detaching the torque two-level control increases the average torque up to 24% with same peak current, but with increased torque pulsation. The excellent dynamic properties of all DSC modes show how DSC is suited optimally for electric traction.

Review of flux-weakening in high performance vector controlled induction motor drives

Abstract: This paper is a tutorial review of flux-weakening operation in high performance vector controlled induction motor drives (VCIM). Flux-weakening has become very important due to the enhanced benefits of high speed operation of many processes and due to the impending introduction of electrical vehicles with propulsion drives having a range of operational speed up to 14,000 r/min. All of these applications demand precision dynamic torque and speed control over the entire speed range. Flux-weakening control, though familiar in the pretext of low performance V/Hz type controllers, takes on complex proportions in the context of high performance vector controlled induction motor drives. Stator flux control emerges as the obvious candidate for high speed operation but is unsuitable or incompatible with indirect vector controllers. A hybrid combination of rotor flux linkages reference with the imposed voltage limit due to the limited DC link voltage is a very attractive alternative at this juncture for indirect VCIMs. This paper presents the fundamentals of flux weakening operation, presents the hybrid algorithm, critically reviews control algorithms for high performance flux-weakening and summarizes solution methodologies available for constant power operation over a wide speed range. In the process, an important solution for this problem in the form of coordinating the design of inverter-fed induction machines and control variables emerges in this paper.

Power electronics reliability impact on service dependability for railway systems: a real case study

Abstract: Service dependability has been recognized in the transportation literature as an effective measure of transit systems quality. Dependability models link this measure of service quality with reliability, availability and maintainability characteristics of the subsystems operating in the transport system. The purpose of this paper is to present a dependability model for the analysis of the impact of power electronics reliability on the service dependability in the case of a vehicle for high speed railway applications.

Experimental analysis of the EMI reduction in PWM inverters using random space vector modulation

Abstract: Two random space vector modulation (SVM) techniques are analysed. They combine the inherent advantages of the straightforward digital implementation of the SVM an a low-cost microcontroller, with improvements in the EMI characteristics of the inverter, due to the random switching technique.

Loss minimisation control of induction motor drive for electrical vehicle

Abstract: In this paper, a simple mathematical model of induction motors in the field-oriented frame, including power losses, is presented. The parameter identification and influence of supply and load conditions on the induction motor parameters are discussed. Changes of motor parameters are expressed as polynomial functions of stator angular frequency, slip angular frequency and temperature of motor windings. Sensitivity of control systems with regard to the changes of motor parameters was decreased by applying open-loop adaptive control. Based on this model, a loss minimisation control algorithm is proposed. Experimental investigations were carried out on a laboratory model of an inverter-fed induction motor drive.

A neural network approach to identification of structural systems

Abstract: Artificial neural networks are widely used for identification of nonlinear control systems Two common approaches are multichannel neural networks and recurrent networks The nonlinear autoregressive moving averages with exogenous input (NARMAX) model is usually used as a general input-output representation Using the NARMAX model it is not necessary to make any assumptions regarding the structure of identified system except for the maximal values of delays Another problem considered here is identification of a structural system, ie, a system consisting of a few interconnected subsystems First, we assume the internal structure of the identified system to be known and containing interconnected nonlinear static and linear or nonlinear dynamical subsystems Identification of the system can then be performed using a neural network of a mixed linear-nonlinear perceptron architecture Next, it is shown that recurrent models should be used to obtain uncorrelated residuals in the case of additive output noise Finally, we also show how the backpropagation learning algorithm can be specialized to adjust weights of both the linear and nonlinear parts of the network Some simulation examples show the high effectiveness of the structural approach (in comparison with the technique of NARX modeling)

Automatic IM parameter measurement under sensorless field-oriented control

Abstract: A novel approach of automatic induction motor (IM) parameter measurement under sensorless field-oriented control (FOC) is presented. No additional hardware is required in this approach. Before start-up, the inverter drive automatically performs the DC test, the no-load test and the locked-rotor test for the driven IM. Only input current signals are measured and sent to the field-oriented controller. The concepts of no-load test and DC test can be modified under the FOC structure. The conventional locked-rotor test requires that the rotor shaft has to be locked mechanically. This prohibits automatic measurement by the FOC inverter drive. A pseudo locked-rotor test for FOC structure is presented in this paper to facilitate automatic IM measurement. The test data are then computed to get the IM parameters and the exciting current command for FOC. The presented method has been tested on a 3-HP inverter-driven motor system. Its effectiveness is illustrated by experimental recordings.

Discrete-time simplified adaptive control algorithm and its application to a motor control

Abstract: Simplified adaptive control (SAC) is originally proposed for the class of plant which satisfies an almost strictly positive real (ASPR) condition. There have been two main methods to circumvent this condition. One is to add parallel feedforward compensation to an original plant resulting in a new augmented plant which satisfies the ASPR condition. The other is to contrive the signal in parameter adjustment law which is a linear combination of output error and control law. One of the authors has proposed a discrete-time algorithm which belongs to the former. In this paper, a new discrete-time algorithm is proposed which belongs to the latter. This algorithm can reduce the output error between plant and model to be bounded and moreover to zero if the steady state gain of the plant is kept constant under parameter variation. The stability of the algorithm is proved by using a Lyapunov function. This algorithm is applied to the position control of a DC servomotor. Experimental results illustrate satisfactory performance even if its load is largely changed.

Robust control of active suspensions for high performance vehicles

Abstract: This paper aims to outline the main steps of the design of a slow-active suspension controller able to deal with parametric uncertainties of the plant. The most relevant noise inputs to a suspension system are caused by road surface roughness (fast varying inputs) and by cornering and fore and aft acceleration (slow varying inputs). A previous paper was devoted to the design of a semiactive suspension which consisted of a backup passive system managing fast-varying inputs and of an active one managing slow-varying inputs. The suspension design was developed assuming a relatively simple model-the two-degree-of-freedom quarter-car model-and replacing the conventional components, spring and damper, with a simple hydraulic device. A proper control law, designed by means of the linear quadratic frequency-shaped (LQ) methodology, achieved the result of minimizing the sprung mass movements caused by a slow varying downforce acting on it. In practice, however, all suspension states are not directly measurable, thus a Kalman filter has to be introduced for state estimation: it yields a linear quadratic Gaussian (LQG) controller. Both the fact that the suspension dynamics depends on the static load and the fact that some parameters may vary while the suspension works, have suggested comparison of the LQ and the LQG active suspension from the point of view of stability robustness. This paper demonstrates that the robustness properties of the LQG active suspension are not necessarily bad and depend strongly on the design of the backup passive suspension.

Electric vehicles

Abstract: The basic advantages of electric vehicles (EVs) are: (a) no emissions at the point of their operation, (b) very low emissions, if the energy is produced in normal power stations, (c) lower energy consumption compared to conventional cars, and (d) very low noise during operation. Their main disadvantage is the limited driving range due to the limited capacity of the battery which cannot be usually recharged quickly. Since most of the cars in cities don't drive more than 50 km during a day and since this is easily possible for electric vehicles they are the best vehicles which help to improve the environmental conditions in cities and their suburbs. This paper describes the components of electric vehicles, the demonstration projects with electric vehicles in Europe and the necessary infrastructure for introducing electric vehicles on a large scale.

Simulation in power electronics

Abstract: The use of simulation has always been a powerful tool for technology in all its various fields of application. Especially from an economical point of view, it appears to be profitable. Basic mistakes in a system design can be recognized fast and by this fail investments are avoided. The euphory which accompanies such a description must be handled with care. A broad range of simulation program packages is offered to the engineer. Behind each of these programs hide different simulation techniques and topologies. The aim of this paper is to show in which field of application, which kind or simulation methods can be used and how it can be used for simulating power electronic circuits. The following programs were tested on a PC-based network: PSpice 6.2, ICAP/4, KREAN 4.1, CASPOC, SIMPLORER 3.2, SIMSEN, Micro-Cap/V, ELECTRONIC WORKBENCH, and MATLAB-SIMULINK.

Two degree of freedom internal model control for single tubular heat exchanger system

Abstract: A two degree freedom internal model control (IMC) is implemented for the temperature control of a single tubular heat exchanger system. The experimental heat exchanger system is a very simple structure, however, the characteristics are regarded as a distributed parameter system and time delay made by software; the plant is regarded as complex system. With the aim of applying IMC structure, we approximate the heat exchanger system to a time delay model from a frequency response examination. In the laboratory experiment, it is clear that: (1) the two degree of freedom IMC is effective for the time delay system; (2) the two degree of freedom performance of IMC was superior to one degree freedom IMC; the disturbance was reduced compared to a PI controller or one degree of freedom IMC design; (3) since the controller had two degrees of freedom, the one tuning filtering parameter of the IMC controller effected the tracking of the reference and the other tuning parameters of IMC reduce disturbance; (4) the design method was as simple as an ordinary one degree of freedom IMC design; and (5) since the IMC controller was constructed from the system model, there were some problems to set up the modeling and identification.

Electric railway traction in Europe. A survey of the state-of-the-art

Abstract: The paper describes the state of the art and the main evolutionary trends In the field of electric railway traction technology in Europe emphasizing inverter-fed three-phase drives. The important low-loss snubber circuits for GTO converters are discussed as well as the special circuits in use for multi-system locomotives and the appropriate cooling systems. The survey is completed by an overview of the field-oriented control strategies employed for traction machines.