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EPE 1991 - 31 - Session 3.9: DIGITAL CONTROL
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	A DIGITAL CURRENT TRANSDUCER   By C. P. Lewis; T. G. Hesketh	[View]   [Download]
Abstract: An electric current transducer is described which combines the properties of a closed-loop analog transducer with those of a sigma-delta modulator. The sampled-data, non-linear, system produces an output pulse stream suitable for data transmission. Typical measured characteristics and waveforms are used to describe the performance.
	DIGITAL TRACKING RESOLVER TO DIGITAL CONVERSION   By B. A. Murray; W. D. Li; M. F. McMullin	[View]   [Download]
Abstract: The brushless resolver and the resolver to digital converter are the ideal combination for motor commutation in AC servo drive systems. This transducer gives absolute position information and is well suited to the industrial environment. A hybrid tracking converter is normally used to process the resolver signals to give digital position and analog velocity signals. A digital implementation of the resolver to digital converter function eliminates the requirement for a hardware resolver converter in a digital servo drive. It also provides the velocity signal in the format required for a digital velocity loop. A number of possible systems are described including the use of look up tables and a software implementation of a tracking converter. The matching of the sample frequency and A / D converter to the ac servo requirements is discussed. A converter using the optimum combination of hardware and software elements to operate over a wide speed range is presented. A software tracking loop algorithm for this converter is developed. Simulation results for all the converter algorithms are presented.
	PERFORMANCE AND SENSITIVITY ANALYSIS OF AN OBSERVER-BASED MECHANICAL-SENSORLESS DATA-ACQUISITION SYSTEM   By Pradeep K. Nandam; Gerald F. Cummings; William G. Dunford	[View]   [Download]
Abstract: This paper analyses a mechanical-sensorless state-observer-based data-acquisition system for a dc drive. The speed signal of the drive Is obtained by state-estimation with an observer, and the position signal is computed from it. The effect of observer design on the sensitivity of the scheme to uncertainties or variations in the drive parameters is studied. Effects of Ioad torque and initial conditions are also studied. Both experimental and digital simulation results are presented to substantiate the theoretical analysis.
	STATE CONTROL OF AC-POSITION DRIVES   By R. K. Schönfeld; D. H. Dat; H. Lorenz; Ng. Ph. Quang	[View]   [Download]
Abstract: The cascade state control structure gives the possibility to combine the advantages of the classical cascade structure and the modern state control. The state control of the induction machines is combined with the state control of the mechanical system. Discrete state equations are used. They enable to set up and to adapt state observers very simply. A self-commissioning strategy is used to set in operation the drive and to optimise the state controller. Experimental results show the advantages of the state control. They are taken from a model-drive, equiped with a risc-processor TMS 320.20 as controller.
	A HIGH PERFORMANCE DSP BASED SYSTEM FOR ROBOTICS DRIVES   By T. Ghiara; M. Marchesoni; M. Mazzucchelli; G. Sciutto	[View]   [Download]
Abstract: Digital Signal Processors (DSPs) are particularly suitable tor the execution of control programs when a high computation speed is required. In particular we refer to the DSP32C AT&T processor which seems to be very suitable when both high accuracy (40 bit floating-point operatlons) and high speed (25 MFLOPS) are required. We have studied and developed an architecture to solve in an efficient way the interfacing problems arising from the use of the DSP32C processor. All specifications required by the use of the system in robotics actuators control applications have been met, fully exploiting the processor potentialities. The whole system has been built and tested in a Variable Structure controlled brushless AC synchronous motor drive.
	THE INTEGRATED INTELLIGENCE INCREASES THE PERFORMANCES OF STATIC APPARATUS   By G. Clerc; G. Rojat; Ph. Auriol	[View]   [Download]
Abstract: During the last couple of years, the introduction of power electronic semi-conductors into electrical apparatus has greatly improved its dynamic performances. This change, beyond a simple substitution, creates new functions. This paper presents the study of an "intelligent" contactor used with an induction motor. The switching module has a GTO-MOS cascade structure. It is controlled by an 8-bit microcontroller which integrates driving, protection and communication functions. The driving module analyses the electrical characteristics of the load before its connection to the power supply. Thus, it provides preventive protection for the motor and reduces the electrical and thermal stresses during starting. Short circuit protection is realized in a few hundreds of nanoseconds by the close drive of the contactor. The overload protection is based on a thermal image representation. The microcontroller calculates in real time the junction temperature of the static switches and the thermal state of the load. In order to provide a continuous protection during power failures, an autonomous numerical circuit registers the failure duration and initializes the microcontroller at the next power-on.
	SLIDING MODE POSITION CONTROL OF INDUCTION MACHINE: A DISCRETE CASE   By G.A. Capolino; H. Henao	[View]   [Download]
Abstract: The technique of sliding mode control has been developed for the last twenty years and it begins to be more and more used in power electronics because of its non-linear character. For induction machine position control, the structure has been firstly proposed in 1985 on the based of continuous regulators. It can be easily shown that this control leads to very high frequency for the stator currents which is not compatible with both power converter technology and microcomputer control implementation. In this paper, a full discrete technique is proposed on the continuous scheme which has been modified with convenient sample-hold function. The complete scheme has been simulated in order to determine the parameters of the different regulators and to check their robustness.
	A COMPACT BIT-SERIAL ARRAY MACHINE FOR DSP   By V. Di Lecce; E. Di Sciascio	[View]   [Download]
Abstract: This paper presents the design and evaluation of an architecture based on a compact bit-serial, floating-point device for Fast Fourier Transform (FFT) computation in digital signal applications implementable on 32 bit ISA or EISA buses of 386/486 PCs. It is made of two ASIC chips, the array processor, made with 160 bit-serial processing elements (PEs) and able to compute up to 80 butterfly parallel computations that was originally developed as portion of a massively parallel processor for FFT, and the interface section for buffering and control, containing three corner turning dynamic register banks. An assembly program for the device management on the PC is proposed. Performance evaluations are presented, with comparisons made on commercially available devices.
	APPLICATION OF AN EXTENDED KALMAN FILTER TO THE ESTIMATION OF THE PARAMETERS OF A SOLID ROTOR ASYNCHRONOUS DRIVE WITH TWO DEGREES OF FREEDOM   By L. Loron; G. H. L. Peters	[View]   [Download]
Abstract: The theory of the Extended Kalman Filter for the combined state-parameter estimation has successfully been applied to a solid rotor asynchronous drive with two degrees of freedom (angular and linear motions). The Extended Kalman Filter has been found capable of correctly estimating the necessary parameter and states for the field-oriented control, such as the rotor time constant, and the stator and rotor flux of the solid rotor asynchronous drive. The rotor time constant estimated by the Extended Kalman Filter showed satisfactory agreement with the rotor time constant deduced from torque measurements.
	SPEED AND ROTOR RESISTANCE ESTIMATION IN OBSERVER SYSTEM OF INDUCTION MOTOR   By Z. Krzeminski	[View]   [Download]
Abstract: Recently developed control systems based on a multiscalar model of the induction motor requires measurement or estimation of a rotor flux vector. An observer system proposed in this purpose consists of observers of stator current vector components and a rotor flux model. Rotor flux vector components are interpreted as disturbances in the proposed observer system. Dependencies appearing in the multiscalar model of the induction motor are used to estimate the rotor speed and the rotor resistance. Simulations of the control system with the proposed observer are presented.
	INDUCTION MOTOR PARAMETER ESTIMATION VIA EKF   By A. Dell'Aquila; F. S. Lovecchio; L. Salvatore; S. Stasi	[View]   [Download]
Abstract: lt is known that the application of the field-oriented control strategy to induction motors needs the knowledge of the rotor flux components or the rotor resistance. The aim of this work is to show a method to estimate these quantities, based on the Kalman filter extended theory. The state equation of the Kalman filter results to be non-linear because the rotor resistance is considered as variable. The observation equation contains the rotor flux components, which are derived from the integration of voltage signals, and the stator current ones. Simulation results obtained from this method show its effectiveness.
	SLIDING MODE CONTROL OF THE COUPLED-INDUCTOR CUK CONVERTER   By Joan Majó; Luis Martinez; Alberto Poveda; Luis Garcia de Vicuna; Francisco Guinjoan; Antonio F. Sánchez; Jean Claude Marpinard; Max Valentin	[View]   [Download]
Abstract: In this paper the analysis and design of the sliding mode control of a coupled-inductor Cuk converter under conditions of order reduction are presented. Starting from the converter state equations in normalized form, the expression for the equivalent control is derived and the conditions established for sliding motions. Therefore, two sliding surfaces are analyzed. Namely, the surface representing the constant magnetizing current and the surface corresponding to the constant transference voltage. In both cases, conditions for stability of the equilibrium points are introduced. Subsequently, the sliding mode control circuit corresponding to the constant magnetizing current is implemented. Experimental results are in agreement with the theoretical predictions.
	A ROBUST POSITION CONTROLLER FOR A DC DRIVE USING SLIDING MODE: SOME IMPLEMENTATION REQUIREMENTS   By J. A. Dente; J. H. Maia	[View]   [Download]
Abstract: lt is presented a simple way for synthesizing a robust position controller for DC drives. The method uses the input-output linearization technic to achieve a more adequate representation for the system. The robustness is assured by the use of sliding mode operation. However, there are some implementation problems that constrains the system performance. Some of these problems are identified and guidelines for solution are indicated.
	CLOSED LOOP OBSERVERS FOR INDUCTION MOTORS   By F. Alonge; T. Raimondi	[View]   [Download]
Abstract: An approach for designing robust sliding estimators of rotor flux of induction motors is given. The requirements considered are the convergence rate of the rotor flux estimation error and the robustness against rotor and stator resistances and supply voltage variations, which are modelled as disturbances. These requirements are satisfied by assigning the poles of the system during the sliding motion in such a way as to minimize the effects of the above disturbances on the rotor flux estimation error, in presence of an inequality constraint on the real part of the poles themselves. The observer is tested by digital simulation experiments.
	CONTROL CIRCUIT WITH FOUR COMPARATORS FOR FOUR-QUADRANT CHOPPER DRIVING   By Hisaichi Irie; Hideyuki Okui; Katsunori Taniguchi	[View]   [Download]
Abstract: This paper describes a circuit, operations and characteristics of an integrated voltage control circuit with four hysteresis comparators for bridged four-quadrant chopper driving. In the circuit, the output of the error voltage integrator is fed to four comparators in parallel. Each comparator drives a switching device of the bridge circuit in charge of each quadrant. This control method determines on/off of the four switching devices for four-quadrant operation automatically without current detection. It has no offset voltage and little transient distortion for transferring across quadrant operations. It also has the same advantages as the basic integrated voltage control: the control circuit is highly stable; the output voltage regulation is zero; the response time is within one cycle of the switching period; and it is easy to combine with current limiters of instantaneous current control circuits.
	PARAMETER AND STATE ESTIMATION OF AN INVERTER FED INDUCTION MOTOR BY EXTENDED KALMAN FILTER   By Teruo Kataoka; Tetsuya Iwasaki	[View]   [Download]
Abstract: Estimation of the parameters and the state of an induction motor is very important from the viewpoint of control applications. In this paper an extended Kalman filter is employed to estimate the parameters and the state of an inverter fed induction motor. The rotor resistance, magnetizing inductance, rotor flux linkages, and stator currents are estimated. The detailed Kalman filter algorithm and the induction motor model suitable for the Kalman filter are shown including the initial setting of the state and parameter vectors as well as the covariance matrix of the estimation error and the setting of the covariance matrices of the noises. The estimated results for an experimental motor are included to show the usefulness of the Kalman filter.
	ULTRA-WIDE SPEED CONTROL WITH A QUICK TORQUE RESPONSE AC SERVO BY A DSP   By I. Takahashi; T. Kanmachi	[View]   [Download]
Abstract: The field oriented control of an induction motor has been widely used in high performance servo systems. As well known, it has two major problems; the system is complex and strongly sensitive to the motor parameters. The authors proposed the direct torque control and ultra-wide speed control of an induction motor. The direct torque control realized the torque response as high as 2(kHz) without a position sensor, and the ultra-wide speed control enable the motor to operate at l(rpd) by introducing the impulsive torque drive and using high loop gain which decreasing the lag time of the control circuit. In this paper, a combined approach of the two methods is presented. It makes possible both ultra-low speed control under l(rph) and high torque response corresponding to field oriented control. By adjusting the PI gain, the speed control range is obtained over 1:200000. Implementing with a digital signal processor (DSP 320C25), the control system is made very simple and free from adjustment of the circuit parameters.
	IMPROVED SLIDING-MODE CONTROLLER FOR UPS SYSTEMS   By D. Zadravec; K. Jezernik	[View]   [Download]
Abstract: A design of a control algorithm suitable for UPS systems, called the sliding mode control, is proposed in this paper. The variable structure plant with external disturbances is used to realize a controller in the sliding regime. Invariance of the controlled system in sliding mode for external disturbances will be examined. For the description of the system dynamics under the sliding mode a formal approach called the equivalent control is used. A combined control law is used to assure minimal ripples of the inductor current preserving fast dynamic response of the entire system. A mathematical description, simulations and an experimental result for a single-phase inverter are presented. With new switching devices a very fast response for nonlinear loads, like the computer power supplies, is achieved even for medium power systems.
	SIMULATING OBSERVER OF PHASE IN ASYNCHRONOUS THYRISTOR GROUP DRIVE   By K. Jagiela; M. Sorkowski	[View]   [Download]
Abstract: Algorithen of computer calculations for current phase observer of the asynchronous group of motors will be presented in this paper. Calculations procedure encloses a pack of information concerning first harmonic phase of current derived by motors in transient and steady state for given loading sequence. Loading character encloses cases of synchronous and asynchronous table rollers work. As the result of realized numerical calculations, some interesting characteristics of current phase reverses in steady and transient state are being receired.
	NEW INCREMENTAL METHOD OF Q-PULSE CONVERTER CONTROL   By S. Kapka; K. Tymburski	[View]   [Download]
Abstract: The paper presents a new digital method of controlling a q-pulse converter. Among others two major questions are considered. The first one-generation of phase control angle delta-alpha of the values: zero, plus, minus. The following factors have been taken into account: possibility of introducing absolute values of alpha-angle from microprocessor system, possibility of the cooperation with a PID controller of analog or digital structure, with single reference voltage of the shape of saw or cosine curve, of output function generated in analog or digital way, of alpha-max settings control, of limiting plus/minus delta-alpha-max increments. The time of controller reaction to input function is externally comparable with the one of a classical analog controller. The second one-generation of optimum shape of the thyristor gate current. The digital controller constructed according to the proposed method has the following qualities: alpha-angle increment dynamics of the range 90°/network period, alpha-angle resolutlon below 0 05°, simple interface controller-microprocessor system.
	COMPARISON OF z-TRANSFORMATION AND PULSE TRANSFER FUNCTION METHODS FOR THE STABILITY ANALYSIS OF SAMPLED DATA SYSTEMS   By H. A. Kojori; F. P. Dawson	[View]   [Download]
Abstract: Stability analysis and closed loop design of power converter systems by direct computation of their open-loop pulse transfer function is presented. This technique is compared with the z-transformation method and its advantages are discussed. As an illustrative example. the pulsed stability analysis of a current controlled AC-DC thyristor converter with a PI controller which is a typical sampled data system is considered. lt will be shown that the prediction of the region of absolute stability by the z-transformation method is quite tedious and does not provide any information about the relative stability of the system. In contrast, the pulse transfer function method is based on a direct computation in the s-domain and is therefore much simpler. Furthermore, the concept of absolute stability may be extended to predict relative stability of the system. The predicted region of stability and the dynamic performance of the illustrating example are verified with the Electro-Magneric Transients Program (EMTP).
	AC MOTOR DYNAMIC STUDY WITH THE INSENSIBLE TO "TR" CHANGES STATE OBSERVER   By S. Lorenzo; J. I. Lobo; L. A. López; J. Amigo	[View]   [Download]
Abstract: In this Paper we present in first place a new study method for AC Motor Dynamic Performances. This method is based on the Field Orientation Theory (Ref.1), applicated to the vectorial composition of induction motors magnitudes. Motor vectorial magnitudes are represented in field coordinates, flux-axis referred. Then we study the dynamic evolution of defined motor variables in rotatory vectorial diagrams. We include a new Induction motor state observer insensible to TR changes, that give us a satisfactory response to the accurate test for the real simulation of the AC motor functioning. The main state observers characteristic in any system to control and aplication is to reflect accurately their functioning either in steady state or transient state. To do this the state observers must know the internal changes that are going to happen in every system along its work. Finally, we present several simulations on AC motors, both regulated and non-regulated in order to show clearly the proposed study method. Simulations verify the accurate with real induction motor.
	APPLICABILITY OF TRANSPUTERS FOR DISTRIBUTED MULTIPLE AC DRIVE CONTROL SYSTEMS   By D. C. Levy; R. G. Harley; M. R. Webster; A. M. Gillespie	[View]   [Download]
Abstract: This paper addresses key issues in the design of a high performance controller for distributed multi-motor servo systems, specifically using transputers and the Helios Operating System . The following aspects are considered: synchronisation, redundancy, communication protocols and real-time constraints. Central to this research is the design of a high performance communications network suitable for coordinating both local and geographically distributed multimotor control systems. Helios is chosen as it is a distributed operating system which facilitates high-level development, testing and control of user tasks.
	REAL-TIME ISSUES OF HIGH PERFORMANCE MOTION CONTROL SYSTEMS USING TRANSPUTERS   By A. W. M. Hemme; R. G. Harley; D. C. Levy, M. R. Webster	[View]   [Download]
Abstract: Transputers have emerged as an attractive technology with which to implement high performance AC drive systems. lf transputers are used in such applications, there are several real-time issues which have to be addressed including event response-times, scheduling strategies, I/O and real-time kernel performance. This paper describes the implementation of part of a multiple event handler and efficient scheduler for the transputer to improve the real-time performance. The real-time kernel implements, in addition to supporting high performance controller tasks, features such as parameter sampling and user interaction. The kernel is intended to form a platform to support a highly programmable and configurable controller suitable for a wide range of motion control applications. The performance of the kernel will be measured and test results are presented.