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In last month's 'LC Troubleshooting' (1) we looked at problems two readers had with ghost peaks in gradient runs. This month, we'll continue looking at submitted questions and examine one [...]

Stanford, CA: Stanford UP, 2001. Pp. 222, ISBN 0-8047-4072-0 / 4071-2. Choosing Les Fleurs du Mal and Madame Bovary as exemplary monuments of 'contemporary modernity,' Marder approaches them through Walter [...]

Often considered a necessary evil, the first peak in a chromatogram can be a useful diagnostic tool for troubleshooting liquid chromatographic (LC) separations. Most people I encounter refer to this [...]

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).

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2008.11.005 Byline: Manuel Galvez-Carrillo (a), Robin De Keyser (b), Clara Ionescu (b) Keywords: Nonlinear model predictive control; Dead-time compensator; Solar power plant Abstract: This paper presents the application of a Nonlinear Model Predictive Controller (NMPC) extended with a dead-time compensator (DTC) to the control of a distributed solar collector field. This nonlinear controller uses the Nonlinear Extended Prediction Self-Adaptive Controller (NEPSAC) algorithm. A nonlinear grey-box model of the plant, based on first principles and tuned according to real measurements, is used in the simulation tests. The resulting controller is compared to other architectures based on DTC, showing very good performance for reference tracking and for disturbance rejection. Author Affiliation: (a) Department of Control Engineering and System Analysis, Universite Libre de Bruxelles, Av. F.D. Roosevelt 50-CP 165/55, B1050 Brussels, Belgium (b) Department of Electrical Energy, Systems and Automation, Ghent University, Technologiepark 913, B9052 Ghent, Belgium Article History: Received 18 June 2008; Revised 10 November 2008; Accepted 11 November 2008 Article Note: (footnote) [star] Statement of first printing: Material in this manuscript has neither been published in or submitted to a journal previously, nor will it be submitted to another journal during the SEJ review process . The author(s) have read these instructions and adhered to them.

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 dead time of the detector significantly distorts the fluorescence correlation function of fluorescent particles in solution. This distortion of the correlation function is similar to the saturation effect of the correlation function in a high-power excitation region. The correlation amplitude is significantly reduced by the dead time. The deviations in the number of molecules and the diffusion time are empirically given by the deviation of the fluorescence intensity linearity. The empirical curves of the deviations can be applied to the systematic error estimation of the parameters. The proportionality of the number of' molecules to the concentration of fluorophores is no longer maintained with a large dead time, although almost all of the proportionality of the diffusion time to the inverse diffusion constant remains. This fact makes the dead-time effect different from the saturation effect, which is due to photokinetics. In practice, these distortions can be reduced by use of a smaller excitation power in which the proportionality of the fluorescence intensity is maintained. OCIS codes: 030.5290, 170.3890, 180.1790, 300.2530.

Phase Doppler interferometry (PDI) is a nonintrusive technique frequently used to obtain information about spray characteristics. Understanding spray characteristics is of critical importance in many areas of science, including liquid fuel spray combustion, spray coatings, fire suppression, and pesticides. PDI measures the size and velocity of individual droplets in a spray. Due to the design of the instrument, recordings of the PDI contain gaps, called dead times. The presence of recurring dead times greatly complicates estimation of the diffusion rate of the droplets. Modeling the spray process as a homogeneous Poisson process, we construct consistent and asymptotic normal estimators of the diffusion rate (Poisson intensity) under various conditions. Simulation produced a good agreement between our estimators (in the presence of dead time) and the maximum likelihood estimates obtained without dead time. We use experimental data to illustrate the estimation method. KEY WORDS: Estimation; Incomplete data; Interarrival time; Phase Doppler interferometry; Poisson process; Residual lifetime; Spray.

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).