Dead-time Effect Research Articles

A New Zero-Sequence Current Suppression Control Strategy for Five-Phase Open-Winding Fault-Tolerant Fractional-Slot Concentrated Winding IPM Motor Driving System

In this paper, a new zero-sequence current suppression control strategy for the five-phase open-winding fault-tolerant fractional-slot concentrated-winding interior-permanent-magnet (FTFSCW-IPM) motor drive system with a common dc bus is proposed. By unequal distribution of the zero voltage vector, the proposed method can well suppress the zero-sequence current caused by the dead-time effect that the conventional eliminating method cannot be achieved. First, the dead-time effect to the zero-sequence current is discussed. Then the zero-axis controller is designed to obtain the reference common-mode voltage. Last, according to the principle of the unequal zero voltage vector distribution, the switching sequence of the two inverters can be calculated, and the maximum modulation index is also first deduced in detail. The proposed method is proved by the simulation and experimental results.

Deadtime Elimination in a GaN-Based Grid-Connected Differential-Mode Ćuk Inverter

In this letter, the effect of deadtime in a gallium nitride (GaN) based grid-connected differential-mode Cuk converter with high-frequency (HF) transformer isolation is analyzed. It is shown that different levels of lower order harmonics appear in the grid current depending on the power factor of an operation. Utilizing the leakage inductance of the HF transformer, the deadtime is suitably eliminated to result in an improved grid-current total harmonic distortion (THD). Experimental results support the proposed solution.

Utilizing the Dead-Time Effect to Achieve Decentralized Reactive Power Sharing in Islanded AC Microgrids

In islanded ac microgrids, distributed energy storage systems (DESSs) are normally coupled to the grid through voltage source inverters (VSIs). To improve the operation efficiency and to avoid overloading, it is desirable that VSIs can share active and reactive powers in proportion to their respective power ratings. Although accurate active power sharing can be easily guaranteed by frequency droop control, it is difficult to achieve reactive power sharing as desired due to mismatched grid impedances and voltage sensor scaling errors. To overcome this challenge, a decentralized reactive power control scheme is proposed and used in conjunction with the conventional voltage droop control to enhance the reactive power sharing performance. Specifically, the proposed control scheme utilizes the dead-time effect to equalize the power factors of all VSIs. As a result, the reactive power sharing performance is improved in a fully decentralized manner. Finally, simulation and experimental results are provided to validate the effectiveness of the proposed control scheme.

Modeling and Optimization of Dual Active Bridge DC-DC Converter with Dead-Time Effect under Triple-Phase-Shift Control

Dead-time effect has become an apparent issue in high-switching-frequency high-power dual active bridge (DAB) DC-DC converter. This paper gives a detailed analysis of phase-shift errors effect caused by dead time, including output voltage offset, soft-switching failure, optimal scheme failure, etc. Phase-shift errors effect will invalidate traditional analyses of optimal control and mislead the design of DAB converter. To overcome these drawbacks, various operating modes and an accurate transmission power model incorporating dead time under triple-phase-shift (TPS) control are developed. On this basis, an optimal TPS incorporating dead time (TPSiDT) scheme is further proposed to minimize the current stress, while guaranteeing soft-switching operation by using Lagrange multiplier method (LMM) and Genetic Algorithm (GA). The novel transmission power model can provide accurate power flow computation to avoid phase-shift errors. Therefore, in practical applications, the minimum current stress and soft-switching operation can be guaranteed, and the efficiency of DAB converter can be improved. Finally, the experimental results verify the feasibility of the proposed TPSiDT scheme.

Integrated dead‐time compensation and elimination approach for model predictive power control with fixed switching frequency

To solve the problem of variable switching frequency in conventional model predictive power control (MPPC), many modified MPPCs with fixed switching frequency have been proposed. However, as the switching frequency increases, additional current harmonics caused by the dead-time are added into the grid current. In this study, an integrated approach with compensation process and elimination process is proposed to eliminate the adverse effect of dead-time. The elimination process with improving gate signals is applied when the phase current is large enough. In contrast, the compensation process is utilised when the phase current is relatively small and the elimination process is troubled by the misjudgement of the current polarity. The experimental results with different dead-time and active power reference are provided to demonstrate the validity of the integrated approach. The integrated approach can further reduces the total harmonic distortion compared to the pure dead-time compensation approach and almost removes the current harmonics caused by the dead-time. Besides, the static error of the power caused by dead-time is dramatically reduced by utilising the integrated approach.

A Novel Model Predictive Control Strategy to Eliminate Zero-Sequence Circulating Current in Paralleled Three-Level Inverters

The main contribution of this paper is the proposal of a novel finite control set model predictive control (MPC)-based zero-sequence circulating current (ZSCC) elimination strategy for parallel operating three-level inverters without any modification or extra hardware on the three-level inverters. An equivalent model of the ZSCC is first developed, and the voltage differences of common-mode voltages (CMVs) among paralleled inverters as well as those of the neutral point potentials (NPPs) are proved to be the exciting sources of the ZSCC. With the analysis, an MPC-based zero CMV method (ZCMV-MPC) is presented to reduce the difference of CMVs among the paralleled inverters, meanwhile, an active NPP perturbation-based ZSCC feedback control method is proposed to further eliminate the ZSCC, that may be caused by dead-time effects and the asymmetries of both hardware and control parameters. With the proposed method, the ZSCC between paralleled inverters can be eliminated effectively, and both grid current tracking and NPP balance control can also achieve satisfactory performances. Simulation and experimental results supported the theoretical study and verified the effectiveness of the proposed scheme.

Characterization on Practical Photon Counting Receiver in Optical Scattering Communication

We characterize the practical photon-counting receiver in optical scattering communication with a finite-sampling rate and electrical noise. Finite-small pulse width incurs dead time effect that may lead to sub-Poisson distribution on the recorded pulses. We analyze the first-order and second-order moments on the number of recorded pulses with a finite-sampling rate at the receiver side under two cases, where the sampling period is shorter than or equal to the pulse width as well as longer than the pulse width. Moreover, we adopt the maximum likelihood (ML) detection. In order to simplify the analysis, we adopt binomial distribution approximation on the number of recorded pulses in each slot. A tractable holding time and decision threshold selection rule is provided to maximize the minimal Kullback-Leibler (KL) distance between the two distributions. The performances of proposed sub-Poisson distribution and the binomial approximation are verified by the experimental results. The equivalent photon arrival rate and pulse holding time predicted by the sub-Poisson model and the associated proposed binomial distribution are well validated by the simulation results, where the finite-sampling rate and electrical noise are considered. The proposed holding time and decision threshold selection rule performs close to the optimal ML receiver.

Using a switchable detector array to reduce the effect of single-photon detectors deadtime in a multibit/photon quantum link

Using a switchable detector array to reduce the effect of single-photon detectors deadtime in a multibit/photon quantum link

Control Strategies of Mitigating Dead-time Effect on Power Converters: An Overview

To prevent short-circuits between the upper and lower switches of power converters from over-current protection, the dead time is mandatory in the switching gating signal for voltage source converters. However, this results in many negative effects on system operations, such as output voltage and current distortions (e.g., increased level of fifth and seventh harmonics), zero-current-clamping phenomenon, and output fundamental-frequency voltage reduction. Many solutions have been presented to cope with this problem. First, the dead-time effect is analyzed by taking into account factors such as the zero-clamping phenomenon, voltage drops on diodes and transistors, and the parameters of inverter loads, as well as the parasitic nature of semiconductor switches. Second, the state-of-the-art dead-time compensation algorithms are presented in this paper. Third, the advantages and disadvantages of existing algorithms are discussed, together with the future trends of dead-time compensation algorithms. This article provides a complete scenario of dead-time compensation with control strategies for voltage source converters for researchers to identify suitable solutions based on demand and application.

Analyzing Boron in 9-12% Chromium Steels Using Atom Probe Tomography.

Small additions of boron can remarkably improve the long-term creep resistance of 9-12% Cr steels. The improvement has been attributed to boron segregation to grain boundaries during quenching, and subsequent boron incorporation into certain families of precipitates during tempering. However, the detailed mechanisms are not yet fully understood. Atom probe tomography (APT) is an excellent technique for gaining insights into boron distribution, however, in order to acquire accurate analysis of boron in 9-12% Cr steels using APT, there are several key challenges. In order to better understand and address these challenges, we developed a novel method for site-specific APT specimen preparation, which enables convenient preparation of specimens containing specifically selected grain boundaries positioned approximately perpendicular to the axis of the APT tip. Additionally, when analyzing boron at boundaries and in carbides (as diluted solute) and borides, a widening of the profile of boron distribution compared to other elements was repeatedly observed. This phenomenon is particularly analyzed and discussed in light of the evaporation field of different elements. Finally, the possible effects of detector dead-time on quantitative analysis of boron in metal borides are discussed. A simple method using 10B correction was used to obtain good quantification.

A stochastic differential equation for neutron count with detector dead time and applications to the Feynman-α formula

Detector dead time, caused by both physical components in the detection system and the electronic data acquisition, may have a dramatic effect on the regulation system and in-pile experiments. For example, when conducting the Feynman-α experiments in a marginally sub-critical configuration, the dead time effect is known to bias the variance to mean ratio. Analytic computations of the influence of the dead time on the detection count distribution are hard. Therefore, conducting Feynman-α experiments, or other noise experiments, in the presence of a noticeable dead time effect, is challenging. In the present study, we develop the stochastic differential equations approach to stochastic transport, by providing a model for the detection count in a sub-critical configuration under a non-paralyzing detector dead time.The analysis is based on tools from renewal processes and on a nonlinear filter for detection losses. After constructing the full model, a second order approximation is provided and solved, suggesting a novel first order correction to the Feynman-Y function. The proposed correction is compared with experimental results and past known results, showing improvement and high accuracy.

An applicable count rate saturation correction approach on gamma camera for I-131 labeled radiopharmaceuticals

Abstract Background Gamma camera count rate saturation and high-rate dead time are the most important problems of quantitative measurement in dosimetric studies. In this study, we aimed to assess an algorithm for correction of the measured counting rates in the entire energy spectrum (327–400 keV) for camera dead-time effects. Methods In our study, whole body (WB) scan was performed by using a tissue-equivalent phantom, and that the radioactive Iodine (I-131) source with activities of 0.3, 0.6, 1.2, 1.5, 2.07, 2.7, 3.7, and 5.55 GBq was applied. WB scans of the 20% width energy windows were acquired for 420 s. Results Camera dead-time parameters were obtained from different activities of I-131 in a tissue-equivalent thyroid Phantom, then the saturation curve and coefficients α and β were obtained by using those parameters. Conclusions We concluded that in high-administered activity, it is possible to determine actual count rate of the system in saturation areas. Operation and accuracy of our gamma camera were determined for high activities of iodine-131, which can contribute to various applications of dosimetry in different fields.

Switching State Sequences-Based Modulation Scheme for T-Type 5L-ANPC Converter

A switching state sequences (SSSs)-based modulation scheme along with a dead-time effect compensation method is proposed in this paper. In the proposed modulation scheme, the converter’s switching states changing sequence in one carrier period, i.e., the SSS, is treated as the basic unit to control the T-type 5L-ANPC converter. Because there are only two possible voltage levels in each SSS, the converter can be controlled as a traditional two-level converter within each SSS. Thus, a switching pulse modification-based method is proposed to compensate the dead-time effect within each SSS. Moreover, an SSS transition rule and the transition diagram are furtherly presented to avoid the dead-time effect between different SSSs. Consequently, both the output voltage delay and the unwanted voltage glitches that caused by the dead-time effect are avoided in the whole modulation range. Besides, a balancing strategy is proposed to balance the flying capacitor voltage based on the charging abilities of SSSs. The performance and effectiveness of the proposed modulation scheme are validated by both simulation and experimental results.

A Stability Analysis of Output Voltage Control for DAB DC-DC Converter with Discrete Time Model

This paper presents a stability analysis of a closed loop controlled dual active bridge (DAB) dc-dc converter. At first, a discrete time model of a DAB dc-dc converter considering dead time effects is developed. Then, the stability of the output voltage control for DAB dc-dc converter is analyzed. Finally, the theoretical results are verified with a circuit simulator.

Harmonic Quantitative Analysis for Dead-Time Effects in SPWM Inverters

Dead-time is commonly designed to avoid shoot-through phenomenon within each arm in voltage source converter. The presence of dead-time tends to cause a power quality issue. Quantitative analysis for dead-time effects is important to mitigate power quality issue. This paper presents two harmonic quantitative analysis methods for dead-time effects in SPWM inverters. First, the harmonic analysis method based on double Fourier series is modified to adapt any initial phase angle and calculate additional harmonics from dead-time effects. Then, a calculation method for switching angles in sinusoidal pulse width modulation (SPWM) is presented. Based on the obtained switching angles and single Fourier series, a more concise calculation method is proposed to perform quantitative analysis for the impact of dead-time on harmonics. The harmonic model is able to reveal the mechanism of harmonics generation from dead-time. Finally, the inner relationship and essential difference between double- and single-Fourier series are summarized. The simulation and experimental results show that both of the proposed quantitative analysis methods can accurately evaluate the effect of dead-time on harmonics.

Lyapunov-Induced Model Predictive Power Control for Grid-Tie Three-Level Neutral-Point-Clamped Inverter With Dead-Time Compensation

In this paper, a new power control strategy based on a model predictive power control for the grid-tie three-level neutral point clamped inverter is presented. A dynamical model based on the orientation of grid voltage is used to predict the performance of control variables required for the system. A cost function that includes the tracking power ability, the neutral-point voltage balancing and switching frequency reduction is used to achieve the optimal switching state. A proposed selection scheme of control input is introduced to comprehend the stability of the closed-loop system and reduce the computational cost. At each sampling time, only candidate switching state inputs that guarantee the stability condition through a control Lyapunov function is evaluated in the cost function of the MPC algorithm. Thus, the execution time is remarkably decreased by 26% in comparison with traditional model predictive control. Moreover, the dead-time effect is compensated by incorporating its influence in the proposed prediction model. Simulation and experimental results compared with the traditional model predictive control are used to confirm the effectiveness of the proposed scheme.

Steady-State Performance Improvement for LQR-Based PMSM Drives

Considering the periodic disturbances caused by nonideal factors like dead time effect, permanent magnet flux harmonics, and current sampling errors in the permanent magnet synchronous motor (PMSM) drives, this paper establishes an augmented state space model (SSM), which contains information of periodic disturbances, and then more accurate description for the PMSM system is achieved. Meanwhile, since the three augmented state variables related to periodic disturbances in the augmented SSM cannot be measured directly, a novel periodic disturbance observer (PDO) depending on the Kalman filter is designed to estimate these state variables. On the basis of the augmented SSM and PDO, a linear-quadratic-regulator (LQR)-based state feedback controller is established, which can achieve a successful suppression of periodic disturbances and at the same time ensure a more smooth speed output. Finally, the proposed PDO-LQR is tested in a 6 kW PMSM, and the experimental results show that the proposed controller can efficiently improve the steady-state performance of the PMSM system without sacrificing dynamic-state performance.

New Dead-Time Compensation Method of Power Inverter using Carrier Based Sinusoidal Pulse-Width Modulation

<p>A new dead-time compensation method of power inverter circuits is suggested and presented in this paper. The proposed method utilizes carrier based sinusoidal pulse width modulation technique to produce driving signals of the inverter power switches with dead-time correction capability. The proposed method able to eliminate dead-time effects such as reducing the waveform distortion of the inverter output current, and increasing the fundamental component amplitude of output current. An analysis of the proposed method is presented. Some computer simulations were carried out to investigate the principle operation, and to test performance of the new method. The developed method was validated through experimental test of H-bridge voltage source inverter circuits. The data obtained from the computer simulation and prototype experiments have confirmed that that the proposed method worked well compensating the dead-time in the voltage source power inverter circuits.</p>

Impact of Undercompensation and Overcompensation of Dead-Time Effect on Small-Signal Stability of Induction Motor Drive

Inverter dead-time is known to make open-loop induction motor drives oscillatory, while operating at light-loads in particular. While dead-time compensation schemes exist, precise compensation of the same is often challenging as it involves factors such as device and driver delays and switching transition times, which are difficult to be quantified accurately. Hence, the effect of dead-time could be under or overcompensated. This paper presents a comprehensive analysis of the impact of such undercompensation and overcompensation on the stability of a 100-kW induction motor drive, along with experimental investigations of the same. The effects of undercompensation and overcompensation on the inverter output voltage are analyzed on a switching-cycle average basis. Further, small-signal models are proposed for an open-loop drive, when it is undercompensated and overcompensated. Stability analysis of the above motor drive is reported, which predicts oscillatory behavior with both under and overcompensation, over certain fundamental frequency ranges, respectively. Further, two different types of oscillatory behavior, characterized by different oscillating frequencies, are observed for the cases of under and overcompensation. The analyses are supported by simulations. Experimental investigations carried out also support the analyses and simulation results.

Dead Time Compensation for High-Flux Ranging

Dead time effects have been considered a major limitation for fast data acquisition in various time-correlated single photon counting applications, since a commonly adopted approach for dead time mitigation is to operate in the low-flux regime where dead time effects can be ignored. Through the application of lidar ranging, this work explores the empirical distribution of detection times in the presence of dead time and demonstrates that an accurate statistical model can result in reduced ranging error with shorter data acquisition time when operating in the high-flux regime. Specifically, we show that the empirical distribution of detection times converges to the stationary distribution of a Markov chain. Depth estimation can then be performed by passing the empirical distribution through a filter matched to the stationary distribution. Moreover, based on the Markov chain model, we formulate the recovery of arrival distribution from detection distribution as a nonlinear inverse problem and solve it via provably convergent mathematical optimization. By comparing per-detection Fisher information for depth estimation from high- and low-flux detection time distributions, we provide an analytical basis for possible improvement of ranging performance resulting from the presence of dead time. Finally, we demonstrate the effectiveness of our formulation and algorithm via simulations of lidar ranging.