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A compact digitally controlled fuel cell/battery hybrid power source is presented in this paper. The hybrid power source composed of fuel cells and batteries provides a much higher peak power than each component alone while preserving high energy density, which is important and desirable for many modern electronic devices, through an appropriately controlled dc/dc power converter that handles the power flow shared by the fuel cell and the battery. Rather than being controlled to serve only as a voltage or current regulator, the power converter is regulated to balance the power flow to satisfy the load requirements while ensuring the various limitations of electrochemical components such as battery overcharge, fuel cell current limit (FCCL), etc. Digital technology is applied in the control of power electronics due to many advantages over analog technology such as programmability, less susceptibility to environmental variations, and low parts count. The user can set the FCCL, battery current limit, and battery voltage limit in the digital controller. A control algorithm that is suitable for regulating the multiple variables in the hybrid system is described by using a state-machine-based model; the issues about embedded control implementation are addressed; and the large-signal behavior of the hybrid system is analyzed on a voltage-current plane. The hybrid power source is then tested through simulation and validated on real hardware. This paper also discusses some important issues of the hybrid power source, such as operation under complex load profiles, power enhancement, and optimization of the hybrid system. The design presented here can not only be scaled to larger or smaller power capacities for a variety of applications but also be used for many other hybrid power sources. Index Terms--Battery, digital control, fuel cell, hybrid power source, microcontroller, power capacity.

An analog superconducting quantum interference device (SQUID) readout electronics for diverse applications is developed. These analog circuits are embedded into a digitally-controlled system including an in-system programmable microcontroller on the electronics board and a user interface which runs on a personal computer, to improve the their user-friendliness and flexibility.

In the conventional digitally controlled dc-dc converter with current-injected control, the overcurrent cannot be suppressed because of the intrinsic characteristics of the voltage-controlled oscillator (VCO) as an analog-to-digital signal converter. This paper presents a new digital current-injected control circuit to realize the overcurrent limiting characteristics and the design-oriented analysis of the overcurrent limiting characteristics of the proposed digitally controlled dc-dc converter. Index Terms - Current-injected control, dc-dc converter, digital control, overcurrent limited mode, overcurrent limiting characteristics, VCO.

It is well known that a stable discrete-time control system may become unstable when the digital controller is actually implemented with a digital control processor (DCP) due to the finite word length (FWL) effects and that the stability behavior of the system depends on the structure of the digital controller. Due to the difficulties in adopting the existing stability robustness measures, a new measure is derived, which is tractable and hence enables us to handle the digital controller structure problem easily. The optimal controller structure problem is formulated by maximizing this measure. An analytical solution is presented. An algorithm is developed for finding sparser structures. Index Terms - Optimal structure, pole sensitivity, stability.

A new distributed principle of bus protection is presented. The protection system description, its design features, hardware structure, data communication network construction and protection algorithms are discussed. Performance analysis and preliminary experiments show its distinguishing advantages over the traditional centralized principle. Keywords: Bus Protection, Data Communication, Digital Relaying

Digital control of a suspended 360 [[micro]meter] x 380 [[micro]meter] x 1.6 [[micro]meter]-thick surface-micromachined polysilicon plate is demonstrated in three degrees of freedom, with application to multimode accelerometers, vibratory rate gyroscopes, and actively positioned micromirrors. Plate displacement about the 2.2 [[micro]meter] nominal position above the substrate is measured with shielded capacitive sensors connected to CMOS buffer circuits fabricated adjacent to the microstructure. Four micromechanical sigma-delta loops are used to control eight electrostatic actuators that drive the plate vertically (z) and in out-of-plane rotation ([Theta] and [Phi]). Resonant frequencies are 2.7 kHz for the [Theta] rotational mode and 3.7 kHz for both z and [Phi] modes. The system is evaluated using a mixed mechanical/electromechanical/circuit simulation in SPICE. Closed-loop transient simulation of a 150-Hz square-wave position input signal is in good agreement with experimental results. Squeeze-film damping limits the plate slew rate to 0.83 mm/s in air. Position is controlled to within [+ or -] 25 nm, being limited by quantization noise at the 50 kHz sampling rate.

The discontinuous perturbation analysis (DPA) method is presented to deal with discontinuous sample performance functions. This method is applicable to derivative estimation with respect to most threshold-type problems in discrete-event dynamic systems (DEDS). Through modeling of discontinuities by step function, we are able to provide a unified framework for constructing the derivative estimation of a DEDS. As a result, we offer an alternate approach to derive derivative estimation in DEDS's. Finally, some relationships with other PA techniques are discussed, and a numerical example is presented.

In this paper we study sufficient observation and work spaces for supervisors of a class of discrete-event dynamical systems (DEDS). We use finite state automata to model a DEDS. The finite automata generates a formal language defined over the set of events in the DEDS. A supervisor is a feedback system that observes a generated trace of events and dynamically disables (or enables) a subset of controllable events such that the closed-loop system behaves as desired. We model the desired behavior of the DEDS by a sublanguage defined over the set of events. A sufficient observation space is a collection of events whose observation by a supervisor is enough to realize a given desired behavior. A sufficient work space is a sufficient observation space such that the control action of the supervisor is limited to only the controllable elements of the work space. In many cases, there exists a sufficient work (or observation) space that is smaller than the set of all events. In this work, we construct algorithms to evaluate a sufficient work (or observation) space. The reduction of work (or observation) spaces results in reducing the number of event detectors, communication, and command channels between the supervisor and the plant.

This paper addresses two issues: 1) converting a continuous-time uncertain system to an equivalent discrete-time interval model; and 2) constructing a robust digital control law from a robust analogue control law for hybrid control of sampled-data uncertain systems. The system matrices characterizing the state-space representation of the original continuous-time uncertain systems are assumed to be interval matrices. The Pade approximation method together with a geometric-series approximation method is employed to obtain the generalized enclosing discrete-time interval models. The generalized enclosing interval models are able to tightly enclose the exact discrete-time uncertain model, and can be utilized for digital simulation and digital design of continuous-time uncertain systems. A new family of digitally redesigned interval controllers is constructed from a continuous-time robust controller for robust digital control of continuous-time uncertain systems. Using the newly digitally redesigned interval controllers, the dynamic states of the digitally controlled sampled-data uncertain systems are able to closely match those of the original analogously controlled continuous-time uncertain systems for a relatively longer sampling period.

Many facilities, such as patient health care centers, data processing systems, and critical telecommunication links, rely on uninterruptible power supplies (UPS) to maintain a continuous supply of power in case of a line outage. In addition to requiring continuous power, many critical nonlinear loads are sensitive to incoming line transients and input harmonic voltage distortion. Conventional UPS systems operate to protect against such disturbances using complex filtering schemes, often employing large passive components. This paper presents the advantages of using real time digital signal processing (DSP) control of UPS systems. A DSP controlled UPS inverter and harmonic conditioning system is described and the performance is verified on a 150 kVA system.

Within this brief paper, a stable indirect adaptive controller is presented for a class of interconnected nonlinear systems. The feedback and adaptation mechanisms for each subsystem depend only upon local measurements to provide asymptotic tracking of a reference trajectory. In addition, each subsystem is able to adaptively compensate for disturbances and interconnections with unknown bounds. The adaptive scheme is illustrated through the longitudinal control of a string of vehicles within an automated highway system (AHS).

This paper shows a new digital frequency control system for a microwave spectrometer to investigate ferromagnetic resonance spectra at 11.5 GHz. In order to fulfill the measurement conditions, the measuring frequency and resonance frequency of the cavity must be equal. However, the determination of the cavity's resonance frequency containing a ferromagnetic sample with field variant characteristics is not possible directly within acceptable measuring times. For the digital control system the model of the cavity is a static and nonlinear channel with unknown and timevariant transmission characteristics. A narrow frequency modulation ([Delta]f < 50 kHz) causes an output sequence used for an adaptive recursive algorithm. The resonance frequency of the cavity is regulated by a parameter estimator which uses a least-squares fit performed on a digital signal processor. The transient behavior and the characteristics of the digital control system are excellent. Approximately, the deviation from resonance is less than 2 kHz. As an example, the real part of the susceptibility of a small, diluted, and single-domain hexaferrite sample could be detected for the first time with signal amplitude equal to 220 kHz peak to peak.

The extended pole placement (EPP) method extends the well-known pole placement method to digital servo-control with known control inputs. A servo-control system designed using the EPP method achieves an accurate command response through the use of a noncausal reference model and an accurate approximation of nonminimum-phase zeros. The phase error of the command response between the desired output and the actual output may be made arbitrarily small, while its gain extends uniformly to a selectable bandwidth. A selectable feedforward bandwidth is important in controlling flexible structures where unmodeled resonances might be excited by rough feedforward inputs. Experimental results on a machine tool slide show that a controller designed by the EPP method yields better servo performance for cornering and contour tracking tasks than an E-filter-enhanced zero phase error tracking controller.

We derive the optimal LQR controller for asynchronous multirate digital control. Independent processors operating without synchronization update different components of the control vector at Poisson arrival times. An iterative algorithm to compute the steady-state control law and optimal cost is described and its convergence is demonstrated.

Mechanical descriptor systems, i.e., constrained mechanical systems, have many applications in practice. This paper studies the control of mechanical descriptor systems. First, a class of the state feedback controllers assigning the finite poles of mechanical descriptor systems at any desired locations is presented. Second, based on the degrees of freedom of pole-assignment controller, an optimization method for designing the controller that assigns the finite poles of closed-loop mechanical descriptor system and simultaneously minimizes a quadratic performance index is proposed. The necessary condition for the pole-assignment controller to be optimal is derived and the corresponding algorithms are discussed. An example is given to illustrate the validity of method in this paper.

The frequency domain design methodology developed in Jayasuriya and Franchek (1988) for the synthesis of controllers that maximize the allowable size of an unknown-but-bounded disturbance in the presence of several time domain constraints is revisited. It is shown that (i) the basic ingredients of the methodology stays essentially the same for systems with nonminimum phase zeros and/or unstable poles, and (ii) two modifications can facilitate the loop shaping step. In particular, a nonminimum phase problem may be converted to one of frequency shaping a minimum phase loop; and a prestabilization scheme may be used for unstable systems. Two examples illustrate the proposed modifications with one compared to results obtained by the so called Set-Theoretic (ST) approach.

This paper presents an approach for optimal digital feed-forward tracking controller design. The tracking problem is formulated as a model matching problem, in which the distance between a specified tracking reference model and the achievable tracking performance by feedforward compensation is minimized. Desired input/output characteristics, finite length preview action, tracking of specific classes of constrained signals, time domain reference signal velocity or acceleration bound, and frequency domain weighting are conveniently incorporated in the proposed controller design and their roles in tracking performance are discussed. The tracking error bound is also explicitly expressed in terms of the controller design parameters. An [l.sub.1] norm optimal tracking controller is proposed as a solution to the mechanical tolerance control problem. A motion control example illustrates the design approach and several aspects of the resulting optimal feedforward controller, including the optimality of the zero phase error tracking controller.

A new approach for digital feedback control of PWM inverter is proposed, in which an output DB (dead beat) control is achieved combined with a disturbance observer. In the proposed scheme, the pole placements of the state observer and the disturbance observer are chosen separately. When the two observers employed the same pole placements, the experimental setup had tendency to become unstable due to the detection error. By selection of the different pole placements, the disturbance observer quickly estimates the disturbance and feedforward disturbance cancellation is achieved. Then the state observer estimates the state variables at the next sampling instant, and the deadbeat controller is applied to the nominal system. This scheme has advantages in robustness in the practical application. From the view point of UPS applications, the advantages and disadvantages are discussed through simulations and experiments. And compared with other digital control laws, the superiority of the proposed control law is verified.

This paper investigates the robustness of fuzzy logic stabilizers using the information of speed and acceleration states of a study unit. The input signals are the real power output and/or the speed of the study unit. Non-linear simulations show the robustness of the fuzzy logic power system stabilizers. Experiments are also performed by using a micro-machine system. The results show the feasibility of proposed fuzzy logic stabilizer. Keywords - Fuzzy logic control scheme, ondine computer control, digital control, power system stabilizer

This paper describes the laboratory environment for experiments in digital control of a coupled tank system. The control process consists of upper and lower containers with draining orifices. As the cross section of the lower container varies with the level, the dynamic of the process changes extensively with the selected steady-state operating level. Measurements of the tank levels are available, while the flow rate into the upper tank is forced by a pump driven by an electric motor. A nonlinear model is employed to study various features of the process. The control strategy is to stabilize the level in the lower tank by adjustment of the flow rate into the upper tank. An IBM AT, equipped with an universal analog input/output board is used to control the process. The interactive real-time software frame, available under MS-DOS, uses selectable operating modes to analyze the performance of different control algorithms. Digital state-feedback algorithm is presented as an illustration.

The problem of microcomputer-based digital control of naturally commutated cycloconverters operating with frequency-wild input voltage waveform is discussed. The hardware modification, using frequency multiplier, based on cosine wave crossing pulse timing control, is proposed. A computer simulation was made for preliminary testing of the proposed method.

This paper addresses the analysis and design of digital motion control system with machine vision as a feedback measurement in the servo loop. The camera vision is modeled as a discrete time-delayed sensor. A multirate formulation is proposed based on the fact that vision update rate is slower than the digital servo-control update rate and is analyzed through the lifting technique which converts the periodic time varying multirate system to a time invariant one. Some interesting properties of this specific multirate system are found and are utilized in control system design. An l-1 norm optimal control problem is formulated to minimize the maximum time domain error, which has direct connection to camera field of view and mechanical tolerance. A numerical example is given to demonstrate the presented methods.

This paper presents the development of robust digital tracking control algorithms and their real-time implementation on an electrohydraulic servo-actuator for tool positioning in noncircular machining. Robust adaptive feedforward controller for tracking arbitrary signals and robust repetitive controller for tracking periodic signals against disturbances and unmodeled dynamics have been developed. Experimental results are presented to illustrate the control system synthesis procedures and tracking performance.

This paper synthesizes and develops a universal field oriented (UFO) controller for induction machines. The UFO controller decouples flux and torque in an arbitrary flux reference frame. Due to its high degree of generality the UFO controller lends itself to be fully compatible with all existing field oriented controllers, indirect as well as direct field orientation. As a consequence, the digital implementation of the UFO scheme is identical for all induction motor drives enabling the usage of identical hardware and software. Examples of UFO control block diagrams for different field oriented controllers are presented. The execution time of the UFO algorithm is compared with the classical rotor flux field orientation method when using a high speed digital signal processor. Further, this paper indicates that the flexibility of changing the flux reference frame can extend the stability region of the drive especially at high speed during flux weakening. Detuning problems in field orientation are handled in an optimal manner for each field oriented controller by proper selection of the model of the induction machine and its reference frame.

The fine positioning problem of the gripper of flexible robotic manipulators is addressed in this study. A two-axis cartesian micro-manipulator is implemented to reduce the sensitivity of the gripper to the structural deformations of a single flexible link. A laser head with a dual axis photodetector are used to provide direct measurements of the transverse deflections at the free-end of the beam and to detect mechanical inaccuracies caused by manufacturing imperfections and assembly misalignment. The advantages of the integrated system of the micro-manipulator with a single compliant beam are demonstrated and compared to the one without the micro-manipulator for two different control schemes, 'rigid body controller (RBC)' and 'rigid and flexible motion controller (RFMC).' Both theoretical and experimental results have proven the capability of the micro-manipulator in significantly improving the gripper positional accuracy. Furthermore, it was demonstrated that the micro-manipulator tends to complement rather than overlap the efforts exerted by the host beam controller.

New digital control algorithms have been developed to achieve the desired transmissibility function for a microgravity isolation system. Two approaches have been presented for the controller design in the context of a single degree of freedom system for which an attractive electromagnet is used as the actuator. The relative displacement and the absolute acceleration of the mass have been used as feedback signals. The results from numerical studies are presented. It has been found that the resulting transmissibility is quite close to the desired function. Also, the maximum coil currents required by new algorithms are smaller than the maximum current demanded by the previously proposed lead/lag method.

The real-time digital control of induction motors and ac servo drives often involves estimation, identification, and adaptive control algorithms. An efficient and numerically stable discrete model of induction motor is required to implement these algorithms in real time. This paper deals with the development of a predictor-corrector discrete model of induction motors for real-time control applications. The numerical stability of the model is analyzed by a discrete root locus technique. The digital simulation of the model is presented and compared with a rigorous solution, and satisfactory results are obtained.