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This paper will present a dead-time elimination scheme for a pulsewidth-modulation (PWM)-controlled inverter/ converter. The presented dead-time elimination scheme does not require separated power supplies for freewheeling-current detection of high- and low-side power devices. The presented scheme includes the freewheeling-current polarity detection circuit and the PWM control generator without dead time. It will be shown that the presented scheme eliminates the dead time of PWM control for inverter/converter and therefore dramatically improves output voltage loss and current distortion. Experimental results derived from a field-programmable-gate-array-based PWM-controlled inverter are shown to demonstrate the effectiveness. Index Terms--Dead-time elimination, pulsewidth modulation (PWM).

This note proposes a unified 2 degrees of freedom (2DOF) robust dead-time compensator (DTC), for both stable and integrative plants. Using the performance and robustness as closed loop specifications simple and effective tuning rules are derived for the proposed controller. A comparative analysis with some structures of dead-time compensators that have been recently proposed in literature is presented. The analysis is made using the two most typical models of processes with delay that are found in the process industry. The comparative analysis shows that for the cases studied the proposed controller gives better or at least the same performance as the others. It is also shown that the tuning of this structure is simple because the tuning parameters have the usual physical meaning. Some simulation and experimental results illustrate the good performance of the controller. Index Terms--Dead-time compensators (DTCs), robustness, stable and integrated processes.

We have developed and validated a realistic simulation of random coincidences, pixelated block detectors, light sharing among crystal elements and dead-time in 2D and 3D positron emission tomography (PET) imaging based on the SimSET Monte Carlo simulation software. Our simulation was validated by comparison to a Monte Carlo transport code widely used for PET modeling, GATE, and to measurements made on a PET scanner. Methods: We have modified the SimSET software to allow independent tracking of single photons in the object and sepia while taking advantage of existing voxel based attenuation and activity distributions and validated importance sampling techniques implemented in SimSET. For each single photon interacting in the detector, the energy-weighted average of interaction points was computed, a blurring model applied to account for light sharing and the associated crystal identified. Detector dead-time was modeled in every block as a function of the local single rate using a variance reduction technique. Electronic dead-time was modeled for the whole scanner as a function of the prompt coincidences rate. Energy spectra predicted by our simulation were compared to GATE. NEMA NU-2 2001 performance tests were simulated with the new simulation as well as with SimSET and compared to measurements made on a Discovery ST (DST) camera. Results: Errors in simulated spatial resolution (full width at half maximum, FWHM) were 5.5% (6.1%) in 2D (31)) with the new simulation, compared with 42.5% (38.2%) with SimSET. Simulated (measured) scatter fractions were 17.8% (21.3%) in 2D and 45.8% (45.2%) in 3D. Simulated and measured sensitivities agreed within 2.3% in 2D and 3D for all planes and simulated and acquired count rate curves (including NEC) were within 12.7% in 2D in the [0:80 kBq/cc] range and in 3D in the [0:35 kBq/cc] range. The new simulation yielded significantly more realistic singles' and coincidences' spectra, spatial resolution, global sensitivity and lesion contrasts than the SimSET software. Index Terms--Block detectors, dead-time, light sharing, Monte Carlo simulation, positron emission tomography, random coincidences.

A novel dead-time elimination method is presented in this paper for voltage source inverters. This method is based on decomposing of a generic phase-leg into two basic switching cells, which are configured with a controllable switch in series with an uncontrollable diode. Therefore, dead-time is not needed. In comparison to using expensive current sensors, this method precisely determines the load current direction by detecting which anti-parallel diode conducts in a phase-leg. A low-cost diode-conduction detector is developed to measure the operating state of the anti-parallel diode. In comparison with complicated compensators, this method features simple logic and flexible implementation. This method significantly reduces the output distortion and regains the output RMS value. The principle of the proposed deadtime elimination method is described in detail. Simulation and experimental results are given to demonstrate the validity and features of this new method. Index Terms--Dead-time, gate drive, harmonic, phase-leg, pulsewidth modulation (PWM) control.

This paper proposes a technique to compensate the effects of dead time in sinusoidal pulsewidth-modulated voltage-source inverters. The compensation is implemented by adjusting the switching frequency to avoid unfeasible pulsewidths of the gating signals, as well as to minimize the total harmonic distortion of the inverter output voltage. The technique can be used at any switching frequency, but the best results are obtained in the high-frequency range. The experimental results of the proposed technique that is applied in a three-phase induction motor drive system are presented. Index Terms--Dead time, harmonic distortion, sinusoidal pulsewidth modulation (PWM), voltage-source converter.

A new dead-time compensation method for vector-controlled ac motor drives is proposed. The method only compensates the fundamental and sixth harmonic component of the inverter-output distortions in synchronous reference frame. The fundamental component is compensated by feedforwardly adding a predetermined compensation signal to the voltage reference of ac motor drive. To compensate the harmonic distortions, the harmonic compensator with all-pass-based adaptive bandpass filter is proposed and builds up the feedback loop with current controllers in order to minimize the distortions due to dead-time effects. The method is software intensive and independent of the polarity of the phase currents and nonlinear-switching characteristics varied with operating conditions of the inverter. It is simulated and implemented on a 750-W laboratory ac motor drive, where its effectiveness is verified. Index Terms--AC drives, dead-time compensation, induction motor.

This paper presents an adaptive dead-time compensation strategy to obtain fundamental phase voltage for inverter-fed vector-controlled permanent magnet synchronous motor drives. A phase dead-time compensation voltage (DTCV) to compensate the disturbance voltage due to undesirable characteristics of inverter, such as dead time, turn on/off time of switching devices, and on-voltages of switching devices and diode, is transformed into q-axis DTCV in the rotor reference frame. The relationship between q-axis DTCV and a dead-time compensation time (DTCT) is investigated. DTCT is identified online by using q-axis disturbance voltage, which is estimated by a disturbance observer. The amplitude of phase DTCV is adaptively determined according to the identified DTCT. The accuracy of identified DTCT is experimentally confirmed by calculating the mean absolute percentage error (MAPE) between calculated active power and measured one. MAPE for adaptive DTCT is within 5% at any operating point and is less than that for the fixed DTCT. Index Terms--Dead-rune compensation time (DTCT), dead time compensation voltage (DTCV), disturbance voltage, permanent magnet synchronous motor (PMSM), voltage source inverter.

In this paper, an adaptive self-tuning speed control for a permanent-magnet synchronous motor (PMSM) drive with dead time is proposed. Firstly, to equivalently place the dead time element outside the closed-loop speed control, a dead time compensator (DTC), based on the Smith predictor and a self-tuning proportional-integral model-following controller (ST-PI-MFC) is proposed. The model-following error is used to adaptively update the gains of the ST-PI-MFC via the affine projection algorithm (APA). Secondly, a disturbance observer, based on the time delay control (TDC) approach is used for torque feed forward control. The system's model is greatly simplified when the disturbance observer is combined with the motor. Relying on the simplified model, a natural adaptive observer is used to estimate the motor speed. Unknown motor parameters are estimated by minimizing the state estimation error using an iterative gradient algorithm offered by the affine projection. The estimated parameters are used to update the gains of the integral-proportional (IP) servo loop controller, the disturbance observer and the Smith model. The validity and usefulness of the proposed control scheme are verified through simulation and experimental results. Index Terms--Adaptive control, dead time, permanent-magnet synchronous motor.

An adaptive control method, to be called maximum efficiency point tracking (MEPT), is presented in this paper. This method tracks system efficiency, which is dc-dc converter efficiency in this paper, and adaptively optimizes system parameters to maximize efficiency. The MEPT method is used in this paper to optimize the primary-to-secondary switches' dead-time parameter in an isolated topology to reduce the switches' body diodes conduction during commutation periods and to reduce body diodes conduction and reverse-recovery related losses in order to improve efficiency. MEPT tracks converter efficiency while changing the dead-time and detects the optimized dead-time value at the maximum efficiency point at different load and line conditions. In this paper, the MEPT method is discussed and analyzed, and its digital control algorithm and experimental implementation are presented. Index Terms--Adaptive, converter, dead time, digital control, efficiency, isolated, maximum efficiency point tracking (MEPT) method, non-isolated, tracking.

It is known that both [H.sup.2] and [H.sup.[infinity]] optimization problems for dead-time systems are solved by controllers having the so-called modified Smith predictor (dead-time compensator) structure. This note shows that this is also true for the [L.sup.1] control problem. More precisely, it is demonstrated that the use of the modified Smith predictor enables one to reduce the standard [L.sup.1] problem for systems with a single loop delay to an equivalent delay-free problem. The (sub)optimal solution therefore always contains the modified Smith predictor. Index Terms--Dead-time compensation, [L.sup.1] control, time-delay systems.

This paper describes the implementation of a four-pole neutral-point-clamped (NPC) three-phase inverter that produces virtually no common-mode voltage. The low common-mode voltage output is achieved by constraining the switch states of the NPC inverter to only those states that produce zero common-mode voltage in dead-time compensation, which enhances the capability of the circuit to produce low common-mode voltage by compensating common-mode voltages produced by reverse diode commutations. The low common-mode voltage performance is achieved at the expense of reduced voltage utilization and loss of dc-link voltage balance control. In order to overcome this limitation, a fourth pole and associated control are added to balance the upper and lower dc-link voltages. This paper describes the control implementations and simulation results compared to measured results used in tuning and commissioning of the system. A 450-V 78-kW system is implemented in hardware, and experimental results are provided, showing its differential mode transient and steady-state harmonic performance as well as its common-mode output voltage. Index Terms--Electromagnetic compatibility, grounding, power systems, pulse width modulated inverters.

This work presents a simple criterion for tuning a deadtime compensator for plants with an integrator and long dead time. The criterion is based on the definition of a closed-loop performance and considers that the model of the process is not precisely known. Using an estimation of the dead time and velocity gain of the plant, the proposed control law has only one tuning parameter that determines the closed-loop performance and robustness. By tuning this parameter it is possible to attain some robust performance specifications. In order to compare the proposed criterion with previous algorithms proposed in the literature, a comparative analysis of robustness is presented. Some simulation examples demonstrate the good properties of the proposed compensator. Index Terms - Dead-time compensators, integrated processes, robustness.

A novel high-efficiency space vector modulation (SVM) strategy is proposed ill this paper. It is based on the simultaneous and combined use of two strategies. The former consists of commutating only one switch of each inverter leg within each modulation period. In this way, there is no need to impose the dead time. The latter performs a step-by-step change of the modulation frequency in order to reduce the distortion of the inverter output voltage. The proposed system has been implemented and carried out on a programmable logic device (PLDI digital hoard. For validation, an experiment has been set up and several tests have been performed. The results have been compared with the ones achieved by means of the traditional SVM technique. Index Terms--Dead time, frequency modulation, space-vector modulation, voltage-source inverter.

This paper presents an adaptive dead-time compensation strategy to obtain fundamental phase voltage for inverter fed vector controlled permanent magnet synchronous motor drives. The amplitude of phase dead-time compensation voltage (DTCV) to compensate disturbance voltage due to undesirable characteristics of inverter, such as dead-time, turn-on/off time of switching devices, and on-voltages of switching devices and diodes is adaptively determined according to a dead-time compensation time (DTCT). DTCT is identified on-line with using a [delta]-axis disturbance voltage in the current reference frame that is synchronized with current vector. The [delta]-axis disturbance voltage is estimated by a disturbance observer. The accuracy of identified DTCT is experimentally confirmed by calculating the mean absolute percentage error (MAPE) between a calculated active power and a measured one. MAPE for adaptive DTCT is almost within 5% at any operating point. Index Terms--Current vector, dead-time, disturbance observer, permanent magnet synchronous motor (PMSM), voltage source inverter (VSI).

The selective harmonic control (SHC) method of pulsewidth modulation is meant to place switching edges to eliminate or set precisely given harmonics. This manuscript discusses the practical impact of edge placement sensitivity due to dead time that occurs in generalized SHC. It further provides experimental validation to theoretical work presented in a previous publication. Index Terms--Digital signal processors (DSPs), pulsewidth modulation (PWM), selective harmonic elimination (SHE).

The objective of this paper is to investigate the optimal common-mode voltage reduction pulsewidth modulation (PWM) technique when dead-time effect is taken into account. The effect of dead time on common-mode voltage for inverter control and the associated solution are discussed. Based upon these results, an optimal common-mode voltage reduction PWM technique, which requires no extra voltage/current sensors and compensation mechanism while not being affected by the dead time, is recommended. The common-mode voltage can be reduced to one-third for the inverter with diode front end, which is widely used in industry. Intensive measured results are presented to fully support the claims. Index Terms--Common-mode voltage, pulsewidth modulation (PWM), space-vector modulation.

Conventional dead-time compensation methods, for pulsewidth-modulated (PWM) inverters, improve the current output waveforms; however, the zero-current crossing effect is still apparent. This letter proposes a new method, based on angle domain repetitive control, to reduce the distortions in the PWM inverters output waveforms caused by the dead time and the zero-crossing problem. Index Terms--AC servo drive, angle domain, dead-time compensation, pulsewidth-modulated (PWM) inverter, repetitive control, zero-current crossing.

Orbiting rod source coincidence acquisitions may exhibit a significant amount of dead-time, depending on the system geometry and the rod source activity. This dead-time is a function of the relative location between the rod source and the crystals in the block detector and, therefore, varies across the sinogram row. Methods: Normalization scans were acquired on a GE Discovery ST positron emission tomography (PET)-CT system using three different rod activities and of duration such that the total acquired counts (T + S + R) were held constant. To develop a model of the dead-time, acquisitions at six static source locations, centered over each crystal in a single block detector, were acquired for each of the rod activity levels. The resultant block busy data were analyzed such that the profile of block busy as the rod traversed all lines-of-response (with respect to the said block) was found. The profile was fit with a Gaussian function and parameterized by full-width at half-maximum and amplitude. For image analysis, a 20 cm uniform cylinder and a whole-body patient scan were analyzed in reconstructed image space. The datasets were reconstructed with each uncorrected normalization, then with the normalization corrected for dead-time. Results: A model has been determined allowing application of dead-time correction to an orbiting rod normalization scan based on measured block-busy in the normalization raw data. Bias and variance effects were removed from reconstructed images. Conclusion: The model corrects for dead-time effects in the normalization. Analysis of image quality impact shows that bias and variance effects can be reduced to insignificant levels. Index Terms--Calibration, nuclear imaging, positron emission tomography (PET).

Current control in inverter-driven machine systems is the inner most component of the hierarchy of control loops. If the control of current in the machine is not fast and accurate then it is difficult, if not impossible, to build a high-performance drive system. Unfortunately, the implementation of current control in power electronic systems is not ideal. Practical effects can have a significant influence on its performance. This paper examines one of these effects, dead time, and considers the influence it has on the performance of predictive current controllers (PCCs). The paper presents analysis that shows that a PCC implicitly compensates for voltage loss due to dead time. Also, a modified PCC is introduced that reduces the zero-current-clamp problem caused by dead time. Simulation and experimental results are presented to verify the analysis and confirm the performance of the new algorithm. Index Terms--Current clamp, inverter dead time, predictive current controller (PCC), pulsewidth modulation (PWM).

A new on-line dead-time compensation method for a permanent magnet (PM) synchronous motor drive is proposed. Using a simple disturbance observer without any additional circuit and off-line experimental measurement, disturbance voltages in the rotor reference dq frame caused by the dead time and non-ideal switching characteristics of power devices are estimated in an on-line manner and fed to voltage references in order to compensate the dead-time effects. The proposed method is applied to a PM synchronous motor drive system and implemented by using software of a digital signal processor (DSP) TMS320C31. Simulations and experiments are carried out for this system and the results well demonstrate the effectiveness of the proposed method. Index Terms--Dead-time, DSP, on-line compensation, PM synchronous motor.

To perform Monte-Carlo simulations of PET tomographs, we used SimSET (a simulation system for emission tomography). Since we need to estimate performance characteristics of different tomographs, this widely used simulation package had limited properties for our use. We integrated a module to generate random events from a singles simulation and we modeled dead time losses. The count rate model we used is based on the method developed by Moisan et al. for the Siemens HR+ scanner. We needed a reliable simulation tool, which could provide data such as scatter fraction, sensitivity, count rates or noise equivalent count rate (NEC). So, we carried out a two-steps validation of SimSET in 3-D alone and with additional features. First, we compared results obtained with SimSET and with two other simulators (GePEToS, a PET simulator using Geant4 and a simulator developed by Adam et al.). We estimated energy spectrum and sensitivity to scattered events. Second, we compared our simulated data with experimental data obtained on two Siemens tomographs: the ECAT HR+ and the ECAT ACCEL. We determined spatial resolution, scatter fraction, sensitivity (global and for each plane) and all the different count rates (true, scattered, and random). We found that SimSET can be used to simulate the physical response of different tomographs with a medium accuracy. This lost of accuracy is mainly due to a too simple modeling of the detector (no block detectors). Further validation is planned concerning 2-D mode. Index Terms--Dead time, Monte Carlo, positron emission tomography (PET), random events, simulation, validation.

A high-resolution oncologic transformable positron emission tomography (HOTPET) is currently under development. The detector ring of the camera consists of 12 detector modules. Because the high-yield-pile-up-event-recovery (HYPER) front-end electronics are applied in this new-generation PET camera, a low-dead-time coincidence circuitry is needed to take advantage of the improved efficiency from this technology. The coincidence matching of events coming from different detector modules is performed by an AND-logic on the arriving edges of the module output timing pulses. A flexible modular architecture has been adopted to facilitate the use of the coincidence circuitry for different detector module configurations in addition to different electronic and mechanical implementations. The application of backplane/plug-in architecture and programmable devices (EPLD/FPGA) along with a digital signal processor (DSP) provide reprogrammable flexibility and expandability, allowing scans ranging from animal and breast PET to whole-body PET. There are 42 possible combinations of module pairs derived from the maximum 12 detector modules in coincidence with seven opposite modules. Both the accidental and total (true + accidental) coincidences are simultaneously collected in real time; the accidental timing shift is [greater than or equal to] 200 ns relative to true events. The timing-gate window for the coincidence AND-logic can be dynamically, digitally adjusted during data acquisition between 6.5 and 16 ns to optimize the signal-to-noise ratio in the data. The prototype circuit showed that the timing accuracy is far better than 0.5 ns and the coincidence dead-time is less than 21 ns. Index Terms--Coincidence circuits, digital signal processor, positron emission tomography (PET), programmable logic array.

A novel approach to control design for dead-time (DT) systems is proposed. The underlying idea is to treat the DT element not as a part of the generalized plant, but rather as a (causality) constraint imposed upon the controller (estimator). This enables one to use well-understood parametrizations of all delay-free controllers in the DT design. In particular, DT controllers can be extracted from such delay-free parametrizations. In this paper, the extraction procedures are developed in both [H.sup.2] and [H.sup.[infinity]] settings. It is shown that the proposed approach yields simple solution procedures and new transparent and intuitively appealing structures for the resulting controllers and estimators. Index Terms--Dead-time (DT) compensation, DT systems, delay systems, [H.sup.2] optimization, [H.sup.[infinity]] optimization.

A deadbeat disturbance response of integral processes with dead-time is obtained by intentionally using two adjustable delay elements in the controller. These delays are tuning parameters of the controller. The shorter delay is optimally determined to minimize the robustness indicator (equivalently, to maximize the allowable uncertainty bound) while the longer delay (i.e., the deadbeat time itself) is determined with compromise of robustness. An example with comparison to conventional control schemes has been given to show the effectiveness of the proposed controller. Some interesting topics, such as input shaping techniques and dual-locus diagrams, are involved in this note. Index Terms--Dead-time compensator, deadbeat, disturbance observer, input shaping, integral process, robustness.

It is essential to insert a switching delay time in sinusoidal pulsewidth modulation (PWM) voltage-fed inverters to prevent a short circuit in the dc link. This causes well known dead-time effect which is detrimental to the performance of the output voltages. Many compensation schemes were proposed to overcome the drawbacks. In this paper, based on a systematic approach, a new approach to accurately compensate the dead-time effect is presented. The system analysis and compensation synthesis are straightforward without averaging the output voltage deviation. The model of the PWM voltage inverter with time delay circuit leads us to a systematic approach of compensation. The simulation responses and experimental results show the validity of the analysis and verify the effectiveness of the proposed compensation method. Index Terms--Dead-time compensation, PWM voltage inverters, systematic approach.

A new dead-time compensator for controlling higher-order processes with integral action and long dead-time is proposed. Tuning formulas are derived. If the velocity gain and the dead-time are estimated experimentally, only one parameter, the time constant defining the speed of the closed-loop setpoint response, has to be tuned manually. The same setpoint response is obtained as in the modified Smith predictor, while the load disturbance rejection is considerably faster. Index Terms - Dead time compensator, process control, Smith predictor, tuning formulas.

A new on-line dead-time compensation technique for low-cost open-loop pulsewidth modulation voltage-source inverter (PWM-VSI) drives is presented. Because of the growing numbers of open-loop drives operating in the low-speed region, the synthesis of accurate output voltages has become an important issue where low-cost implementation plays an important role. The so-called average dead-time compensation techniques rely on two basic parameters to compensate for this effect: the magnitude of the volt seconds lost during each PWM cycle and the direction of the current. In a low-cost implementation, it is impractical to attempt an on-line measurement of the volt-seconds error introduced in each cycle - instead an off-line measurement is favored. On the other hand, the detection of the current direction must be done on line. This becomes increasingly difficult at lower frequencies and around the zero crossings, leading to erroneous compensation and voltage distortion. This paper presents a simple and cost-effective solution to this problem by using an instantaneous back calculation of the phase angle of the current. Given the closed-loop characteristic of the back calculation, the zero crossing of the current is accurately obtained, thus allowing for a better dead-time compensation. Experimental results validating the proposed method are presented. Index Terms: AC drives, blanking time, current measurement, induction motors, volt-second compensation, volts per hertz.

Due to the use of high-power devices and slow-switching frequency in a three-level neutral point clamp inverter, the dead-time effect may not be compensated sufficiently fast by using methods developed for the two-level inverter. In this paper, the dead time effect in a three-level inverter with snubber circuits is analyzed to reveal that it does not only depend on load current direction, but also on magnitude. The snubber network also plays an important role in determining the output phase voltage during the dead-time period. Software techniques are proposed to compensate the dead-time effect as soon as it occurs as demanded by the slow-switching frequency. Experimental results show their effectiveness. Index Terms: Dead time, PWM, three-level topology.

The main theme of this paper is to demonstrate the applications of the newly developed common-mode voltage reduction pulsewidth-modulation (PWM) technique, which restricts the common-mode voltage to one-third of DC-link voltage, to vector-controlled induction motor drives. As compared to previous common-mode voltage reduction techniques, the presented technique can be applied to the inverter with diode front end and has no adverse effect on the linear modulation range. Therefore, vector-controlled drives using the developed technique for inverter control have a wide speed range. Moreover, the effects of the common-mode voltage reduction PWM technique on speed response for vector-controlled induction motor drives will be fully investigated in this paper. It will be demonstrated by intensive experimental results that speed performance does not deteriorate significantly within the rated speed range. Index Terms--Common-mode voltage, induction motor drives, pulsewidth modulation (PWM), space-vector modulation, vector control.

A novel method for measuring dead time in nuclear pulse processing circuitry has been developed using the autocorrelation measurement capability of the Nuclear Weapons Inspection System (NWIS). Initially developed for active neutron interrogation of nuclear weapons and other fissile assemblies, NWIS employs a custom gallium arsenide application specific integrated circuit and a new signature analysis software package to simultaneously acquire and display the autocorrelation and cross-correlation spectra of up to five detector/electronics systems. The system operates at clock frequencies up to 1 GHz, permitting the collection of timing pulses in bins as narrow as 1 ns. In normal operation NWIS uses well characterized detectors and constant fraction discriminators, but it may also be configured to accept pulses from any circuit and to use the autocorrelation spectrum to accurately determine dead-time. Unlike traditional dead-time assessment techniques that typically require multiple sources and an assumed dead-time model, NWIS provides single-measurement assessment of circuit dead time and does not require an assumed dead-time model or a calibrated high count-rate source.

In the case of voltage-source gate-turn-off thyristor (GTO) inverters, the conventional dead-time compensation methods do not work well, since the terminal voltage of an inverter leg is not constant during the dead-time period, due to the presence of the snubber circuit. We propose a closed-loop dead-time compensation method that regulates the voltage error by a proportional-integral (PI)-type compensator. We show its superior performance by the reduction in current ripple and in the sixth harmonic component of the motor current in the synchronous frame. Index Terms - Dead-time compensation, gate-turn-off thyristor inverters, proportinal-integral-type compensator, snubber circuits.

A low-power, sparse-scan, readout architecture has been developed for the ATLAS pixel front-end electronics. The architecture supports a dual discriminator and extracts the time over threshold (TOT) information along with a 2-D spatial address of the hits and associates them with a unique 7-bit beam crossing number. The IC implements level-1 trigger filtering along with event building (grouping together all hits in a beam crossing) in the end of column (EOC) buffer. The events are transmitted over a 40 MHz serial data link with the protocol supporting buffer overflow handling by appending error flags to events. This mixed-mode full custom IC is implemented in 0.8 [Mu] HP process to meet the requirements for the pixel readout in the ATLAS inner detector. The circuits have been tested and the IC has been found to provide dead-time-less ambiguity-free readout at 40MHz data rate.

3D PET has higher sensitivity than 2D PET. Sensitivity is dependant on detector properties such as density, stopping power, photofraction, etc, but for a given detcetor material the sensitivity of a tomograph is primarily determined by two components: the geometric solid angle for detection, and the fractional dead time, i.e., the time for which the detector is unavailable for accepting events. The loss in overall sensitivity as a function of radioactivity concentration due to these factors for 3D PET has been characterised by a parameter, the effective sensitivity, which combines absolute sensitivity and noise equivalent count rates. This parameter includes scatter, system sensitivity, dead time, and random coincidence rates, and permits comparisons between different tomographs as well as the same tomograph under different conditions. Effective sensitivity decreases most rapidly for larger, open 3D tomographs. The loss in effective sensitivity with increasing count rate suggests that new faster scintillation detectors will be needed to realize the sensitivity gain of 3D PET over a wide dynamic range of radioactivity concentrations.

The dead time necessary to prevent the short circuit of the power supply in pulsewidth-modulated (PWM) voltage inverters results in output voltage errors. Although individually small, when accumulated over an operating cycle, the voltage errors are sufficient to distort the applied PWM signal. This paper presents a method to correct for the dead-time errors. The pulse-based dead-time compensator (PBDTC) is less hardware- and software-intensive than other dead-time compensation methods providing a low-cost solution. The pulse-based technique is developed by analyzing the effects of dead time on a pulse-by-pulse basis and correcting each pulse accordingly. The technique is evaluated through simulation and experimental results. Other compensation methods are evaluated, and the results compared with the pulse-based technique. This comparison indicates previous methods can produce magnitude and phase errors in the applied terminal voltage, whereas the proposed method compensates for the dead time without significant magnitude and phase errors in the terminal voltage of PWM voltage source inverters. Index Terms - Dead time (DT), instabilities, power semiconductor devices, pulse-based dead-time compensator (PBDTC), turn-on delay (TD), unsymmetrical pulses.

A modification of the Smith predictor for controlling higher-order processes with integral action and long dead-time is proposed. The controller has a quite simple structure which is obtained based on the model consisting of an ideal integrator and dead-time and which includes only three tuning parameters: the dead-time, velocity gain of the model, and the desired time constant of the first-order closed-loop setpoint response. By adjusting these three parameters, high performance can be obtained both for the setpoint response and for the load disturbance rejection.

In this paper, a speed controller considering the effects of system dead time and parameter variations for indirect field-oriented induction motor drives is presented. First, an indirect field-oriented induction motor drive is implemented, and its dynamic model is found based on the stochastic approach. Second, a two-degree-of-freedom speed controller is designed to match the prescribed speed command tracking and load regulating specifications. Since the performances of the closed-loop controlled plant are much influenced by the presence of the inherent system dead-time and parameter variations during wide-range operations, a dead-time compensator and a model following controller are proposed to enhance the robustness of the two-degree-of-freedom speed controller. The simulated and experimental results show that good control performances both in speed command tracking and load regulating characteristics are achieved.

The control of plants with unknown dead time and parameters is considered. The goal of control is to stabilize plant output at a given level. The performance of the optimal, nonadaptive algorithm in the case of uncertain knowledge of parameters is evaluated and compared with that of the adaptive algorithm proposed in the article. The effective regions for both algorithms are evaluated. Simulation results confirming the efficiency of the adaptive algorithm and the performance estimates are presented.

The design and construction of the first of two Ba[F.sub.2]-TMAE large area detectors to be incorporated in a unique double headed whole body PET system (PETRRA) has been completed. Preliminary experimental work carried out with the first large area detector shows an absolute detection efficiency of 20.5% and a time resolution of 3.5ns (FWHM) and 8.0ns (FWTM), using 8mm thick scintillation crystals. An analytical model of the electronic read-out system has been developed to investigate the rate capability of the new scanner. This model predicts that under typical imaging conditions, with 40MBq of activity in the field of view, the proposed scanner will acquire coincidence data at 20-25kcps.

A simple and iterative algorithm is devised in this letter with the help of the small-gain theorem to determine the current polarities of pulsewidth-modulation voltage-source-inverter drives. Experimental results are also presented to show the effectiveness of the method when used in the dead-time compensation. Index Terms--Dead-time compensation, small-gain theorem.

We discuss a new approach to the design of single channel analyzers (SCAs) for high rate Nuclear Spectroscopy with an emphasis on accelerator-based X-ray Absorption Fine Structure (XAFS) applications. A brief overview of the entire spectroscopy system and a detailed description of the SCA circuit design are given together with some insight into the application and the reasons that led us to design a new concept in order to build our single channel analyzer. The advantages of this instrument are then highlighted and the experimental results are presented.

A new Smith predictor for control of a process with an integrator and long dead-time is proposed in this note. The controller decouples the setpoint response from the load response. This simplifies both design and tuning. Simulation results obtained by controlling a typical process show that the new controller has superior performance compared to previous algorithms.

A predictive algorithm is presented in this paper, which allows the compensation of the dead-time effects in a voltage-source inverter feeding an induction motor, with space-vector pulsewidth modulation. It is based on the modification of the reference space vector of the feeding voltage according to a step-by-step analytical prediction of the stator phase currents. In this way, the effects of the dead time can be taken into account and compensated. The validity and feasibility of the proposed algorithm are confirmed by simulation and proved by experimental implementation. Index Terms--AC motor drives, digital signal processor applications, modulation.

A mixed sensitivity H[infinity] problem is solved for dead-time systems. It is shown that for a given bound on the H[infinity]-norm causal stabilizing controllers exist that achieve this bound if and only if a related finite-dimensional Riccati equation has a solution with a certain nonsingularity property. In the case of zero time delay, the Riccati equation is a standard Riccati equation and the nonsingularity condition is that the solution be nonnegative definite. For nonzero time delay, the nonsingularity condition is more involved but still allows us to obtain controllers. All suboptimal controllers are parameterized, and the central controller is shown to be a feedback interconnection of a finite-dimensional system and a finite memory system, both of which can be implemented. Some H[infinity] problems are rewritten as pure rational H[infinity] problems using a Smith predictor parameterization of the controller. Index Terms--Dead-time systems, delay systems, H[infinity] control, infinite-dimensional systems, Riccati equations, Smith predictors, spectral factorization.

This paper presents a single-phase auto-reclosing study of a 500 kV Vietnamese transmission line. The success of the single-phase auto-reclosing depends on the extinction of the secondary arc. Therefore, the influences of several factors such as shunt and neutral reactors, faulted phase and location, capacitive and inductive coupling and series capacitor discharge on the extinction of secondary arc are investigated. This paper presents the influence of single-phase auto-reclosing on the transient stability of the Vietnam system. A new method in order to reduce the dead time for single-phase auto-reclosing is proposed. Index Terms--Recovery voltage, secondary arc current, single-phase auto-reclosing, stability.