High Rate Power Research Articles

Modified Droop Strategy for Wide Load Range Efficiency Improvement of Parallel Inverter Systems

Parallel inverters are used in many modern applications, and thus, improving the inverter system efficiency plays a key role in energy savings. The conventional droop strategy used for power sharing among inverters, however, leads to a low efficiency especially at light loads, as the low power demand is divided among inverters, forcing them to process a fraction of the low power at a low efficiency according to their efficiency curve. To avoid such operating conditions, a communicationless modified droop strategy is proposed in this article to select an optimal number of inverters to process fractions of the power demand that leads to a higher system efficiency considering the efficiency curve of the inverters. To achieve this objective at very light load situations, an online-inverter detection method is developed so that each inverter detects the online inverters and the unnecessary inverters turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> . The proposed method is employed in a system with three single-phase parallel inverters to evaluate the effectiveness of the method. It is observed that the proposed strategy can improve the system efficiency by up to 14% at light loads compared with the conventional droop. Additionally, the reliability of the system is enhanced by extending the lifetime of inverters with higher power ratings, which are considered as valuable assets of the system. Detailed derivations, simulations, and experimental results are presented to validate the proposed method.

High-sensitivity pattern discovery in large, paired multiomic datasets.

MotivationModern biological screens yield enormous numbers of measurements, and identifying and interpreting statistically significant associations among features are essential. In experiments featuring multiple high-dimensional datasets collected from the same set of samples, it is useful to identify groups of associated features between the datasets in a way that provides high statistical power and false discovery rate (FDR) control.ResultsHere, we present a novel hierarchical framework, HAllA (Hierarchical All-against-All association testing), for structured association discovery between paired high-dimensional datasets. HAllA efficiently integrates hierarchical hypothesis testing with FDR correction to reveal significant linear and non-linear block-wise relationships among continuous and/or categorical data. We optimized and evaluated HAllA using heterogeneous synthetic datasets of known association structure, where HAllA outperformed all-against-all and other block-testing approaches across a range of common similarity measures. We then applied HAllA to a series of real-world multiomics datasets, revealing new associations between gene expression and host immune activity, the microbiome and host transcriptome, metabolomic profiling and human health phenotypes.Availability and implementationAn open-source implementation of HAllA is freely available at http://huttenhower.sph.harvard.edu/halla along with documentation, demo datasets and a user group.Supplementary information Supplementary data are available at Bioinformatics online.

AC Losses in Form-Wound Coils of Surface Mounted Permanent Magnet Vernier Machines

Surface mounted permanent magnet Vernier (SPM-V) machines, because of their high torque density and multi-pole structure, are promising candidates for low-speed direct-drive applications. To achieve high torque density, the SPM-V machines are generally designed with high gear ratios. Therefore, their operating frequencies can be much higher than those of the conventional SPM machines. This potentially increases the alternating current (AC) winding losses, especially those with form-wound coils proposed for high-power applications. This article investigates the AC losses (including skin effect, proximity effect, rotor PM induced, and circulating current losses) in form-wound stator coils of a 3 MW direct-drive SPM-V machine with different slot/pole number combinations. The study reveals that the SPM-V machines have significantly higher AC winding losses than their conventional SPM counterparts for similar operating conditions. To reduce the AC winding losses in SPM-V machines, a novel flux shunt concept is proposed along with other conventional techniques such as increasing the number of turns/coil (with terminal voltage being kept constant) and parallel strands/turn, providing extra clearance at slot opening. With the loss reduction techniques implemented, the SPM-V machines can achieve comparable efficiency but much higher torque density than their conventional counterparts. Moreover, the proposed flux shunt was also found to be very effective in reducing the potential risk of permanent magnet (PM) irreversible demagnetization, a key issue for SPM-V machines at high power ratings.

The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bears

Designing a population monitoring program for Asian bears presents challenges associated with their low densities and detectability, generally large home ranges, and logistical or resource constraints. The use of an occupancy-based method to monitor bear populations can be appropriate under certain conditions given the mechanistic relationship between occupancy and abundance. The form of the occupancy–abundance relationship is dependent on species-specific characteristics such as home range size and population density, as well as study area size. To assess the statistical power of tests to detect population change of Asian bears, we conducted a study using a range of scenarios by simulating spatially explicit individual-based capture-recapture data from a demographically open model. Simulations assessed the power to detect changes in population density via changes in site-level occupancy or abundance through time, estimated using a standard occupancy model or a Royle-Nichols model, both with point detectors (representing camera traps). We used IUCN Red List criteria as a guide in selection of two population decline scenarios (20% and 50%), but we chose a shorter time horizon (10 years = 1 bear generation), meaning that declines were steeper than used for IUCN criteria (3 generations). Our simulations detected population declines of 50% with high power (>0.80) and low false positive rates (FPR: incorrectly detecting a decline) (<0.10) when detectors were spaced at > 0.67 times the home range diameter (home-range spacing ratio: HRSR, a measure of spatial correlation), such that bears would tend to overlap no more than two detectors. There was high (0.85) correlation between realized occupancy and N in these scenarios. The FPR increased as the HRSR decreased because of spatial correlation in the occupancy process induced when individual home ranges overlap multiple detectors. The mean statistical power to detect more gradual population declines (20% in 10 years) with HRSR > 0.67 was low for occupancy models 0.22 (maximum power 0.67) and Royle-Nichols models (0.24; maximum power 0.67), suggesting that declines of this magnitude may not be described reliably with 10 years of monitoring. Our results demonstrated that under many realistic scenarios that we explored, false positive rates were unacceptably high. We highlight that when designing occupancy studies, the spacing between point detectors be at least 0.67 times the diameter of the home range size of the larger sex (e.g., males) when the assumptions of the spatial capture-recapture model used for simulation are met.

Investigation on the radial distribution of electron density in a miniaturized ECR ion thruster of wide-range operations

A miniaturized thruster with a wide tuning range of thrust plays an important role for the drag-free control in the task of space-borne gravitational wave detection. For the design of a high-precision miniaturized thruster, it is necessary to study the spatial distribution of the electron density in its discharge chamber. This work investigates the electron density distribution in an ECR ion thruster of 2-cm diameter, with the input microwave power and mass flow rate tuned in a wide range. At relatively low power and flow rate, there is a peak of electron density at the radial position r = 4 mm, which is around the region of resonant power absorption. However, the density distribution in the center region becomes flat with the increase of power and flow rate; at high power and flow rate, it tends to be a Bessel function with a peak in the center (r = 0 mm). In the view of tuning of thrust, it is found that the above variation of electron density distribution can be as important as (or even more important than) the variation of peak value of electron density. A further discussion on the influence of the evolution of electron density distribution is given by considering the thruster design, operation, and control for the task of space-borne gravitational wave detection.

Potential of damage accumulation during segmented rotor blade fatigue tests

Modern wind turbines have higher rated power and improved capacity factors. This results in very long and slender blades which are also designed closer to the material limits. As a consequence, blade test facilities need to be upgraded for static and fatigue full-scale blade testing to carry larger loads and deal with larger tip deflections. Another aspect is the adaption of the test methods to avoid high overloads, which can cause premature damage and require time-consuming repairs. One drawback of traditional full-scale tests with a full-length rotor blade is the long time needed for certification as the blades have low eigenfrequencies and hence high fatigue test durations. This work presents an alternative fatigue testing approach for rotor blades which combines full-length and segmented fatigue tests, each contributing to the accumulated fatigue damage. The proposed approach is benchmarked with the traditional approach by means of a numerical optimization study. applying this approach to a current offshore rotor blade design illustrates the potential for reducing the fatigue test duration by 66% and the local fatigue damage overload to a mere fraction.

Generation of High Peak Power Pulses With Controllable Repetition Rate in Doubly Q-Switched Laser With AOM/SnSe2

By simultaneously employing self-made SnSe2 saturable absorber (SA) and an acous-to-optic modulator (AOM), a dual-loss-modulated Q-switched Nd:YVO4 laser with short pulse width, high peak power and adjustable pulse repetition rate is presented. The maximum pulse peak power of 37.57 KW with the minimum pulse duration of 5.52 ns were obtained under the pump power of 8 W and the pulse repetition rate of 5 kHz. The experimental results demonstrate that the dual-loss modulation technology with AOM and SnSe2 SA is a simple and efficient method to generate short pulses with high peak power and adjustable low repetition rates.

Detecting Measurement Noninvariance with Continuous Indicators Using Three Different Statistical Methods under the Framework of Latent Variable Modeling

Under the framework of Latent Variable Modelling, three statistical methods, namely, the free baseline method (FR), the Benjamini-Hochberg method (B–H), and the alignment method (AM), were applied to identify the noninvariant measurement parameters at the indicator level through a simulation study. Model noninvariance was manipulated through varying the locations, degrees and magnitudes of noninvariant parameters with different sample sizes. As a result, the B-H method was discovered to possess a higher power rate in detecting noninvariant parameters than the other two methods, and the AM method performed the best in controlling the type I error rates in the process of parameter estimation. Comparatively speaking, the FR method performed the worst in almost all situations due to the choice of a fixed noninvariant reference indicator. The suggestions on which method is better used for model noninvariance detection was discussed and elaborated.

Identifying Key Aspects of Thermal Runaway Modelling for Lithium-ion Battery Cells

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Electrification and hybridization of powerplants in the transportation sector is one of the most important changes in the last few decades. Lithium-ion batteries are the main energy storage systems, but despite the maturity of this technology, it has certain constrains compared to traditional internal combustion engines in the day-to-day usage. As the operating conditions of the batteries are pushed to the limits to overcome certain disadvantages relative to other conventional systems like charge and discharge times or vehicle driving range, new concerns and safety limitations must be considered. High power rates and cooling deficiencies can produce excessive operating temperatures within the cells, leading to problems with degradation or even unchain chemical reactions that can end in thermal runaway, one of the most worrying failure modes attaining electric platforms nowadays. One of the main challenges in the ordeal of designing the system considering these effects is the crossed interaction between the different thermochemical and electrochemical phenomena present during the usage of the battery cell. The objective of the present work is to study the effect of different factors and their interdependence by means of a virtual environment developed using GT-Power that is experimentally validated to include electrochemical phenomena with the package GT-AutoLion. This package allows for the consideration of internal heat generation and aging of the battery cell together with thermal runaway mechanisms to include the possibility of failure modes under extreme operating conditions. With this tool, different parameters like the cell state of charge, heat transfer or grade of aging are considered to study the interdependence of these factors and how they can affect the cell performance. The results show that while temperature dependencies are well captured by the independent models, secondary effects such as state of charge and battery aging are not well captured by the formulation of current state-of-the-art thermal runaway mechanisms.&lt;/div&gt;&lt;/div&gt;

Position control of a DC servo motor using various controllers: A comparative study

In contrast to Direct Current (DC) motors, the angular position of a DC servo motor (DSM) can be regulated at a specific angle using a control signal. Due to its high power rating and speed, DSM is frequently preferred. The aim of the study is to compare the time domain characteristics of system response using proportional (P), proportional-integral (PI), proportional-integral-derivative (PID) controller, state-feedback controller (SFC), and SFC with Integral Action (SFCIA). The DSM is a 3rd order system, and the study differentiates different types of controllers for position control of the DSM in MATLAB. The P, PI, and PID controllers are designed by the Ziegler and Nichols (ZN) method. The SFC is designed by determining the state feedback gain matrix using Ackermann’s formula. However, the SFCIA is designed by placing the poles and adding an integrator to the DSM. According to the simulation results, SFCIA has the best performance in terms of peak overshoot (Mp) and settling time (ts) as compared to other controllers (P, PI, PID, and SFC). The proposed method could be applied to the higher-order systems also.

Investigation of Distribution Transformers Vibrations in Terms of Core and Winding Condition Assessment

This work refers to the criterion values used to assess the state of the active part of the transformer based on the analysis of the effective value of the total vibration acceleration and the frequency spectrum. It was proved in the work that the criteria values should be differentiated for transformers of different rated power. Transformers with lower rated power are characterized by lower RMS values of vibration acceleration than units with higher rated power, which cannot remain without impact on the criteria values. Trend analysis of the total aRMS values may reveal increasing defects before the currently applicable criteria values are exceeded. In addition, the influence of the position of the sensor on the frequency spectrum of the obtained signals was analyzed. It was proved that the sensors should be mounted in the middle of the transformer tank, between its lower part and the cover. The dependence of RMS value of vibration acceleration on no-load losses was also determined for transformers of different types but the same rated power. This relationship will not have a large share in the total vibrations of the transformer, due to slight changes in the value of aRMS occurring for all analyzed units.

Lightweight Low‐Noise Linear Isolator Integrating Phase‐ and Amplitude‐Engineered Temporal Loops

AbstractThe quest for efficient and versatile microwave and optical isolators has recently led to spawn space–time‐modulated isolator structures. However, such space‐time isolators suffer from a large profile and complex architecture that is required for a progressive nonreciprocal space–time coupling. To overcome these limitations, here a nonmagnetic phase‐engineered temporal loop‐based isolator featuring large isolation levels, suppressed undesired time harmonics while exhibiting a low profile is proposed. The proposed isolator is composed of two temporal loops that provide desired constructive and destructive interferences of different time harmonics. Furthermore, these two loops are designed in a way to assure that the circulation and reflection of different time harmonics strengthen a unidirectional signal transmission with low insertion loss. An experimental demonstration of the proposed time‐modulated isolator is provided at microwave frequencies, featuring strong unidirectional wave transmission through the isolator with more than 27 dB contrast between the forward and backward waves, across a fractional bandwidth of 14.3%. The proposed technique outperforms alternative approaches, that is, space–time modulation, ferrite magnets, nonlinearity, and HBT/CMOS transistors. It features a highly linear response with OP1dB of higher than 31 dBm, high power rating of more than 47 dBm, and a low noise figure of 3.4 dB.

Parameter Matching Method of a Battery-Supercapacitor Hybrid Energy Storage System for Electric Vehicles

To satisfy the high-rate power demand fluctuations in the complicated driving cycle, electric vehicle (EV) energy storage systems should have both high power density and high energy density. In order to obtain better energy and power performances, a combination of battery and supercapacitor are utilized in this work to form a semi-active hybrid energy storage system (HESS). A parameter matching method of battery-supercapacitor HESS for electric vehicles (EVs) is proposed. This method can meet the performance indicators of EVs in terms of power and energy for parameter matching. The result shows that optimized parameter matching is obtained by reducing the weight and cost.

A Novel Fuzzy PI Control Method for Variable Frequency Brushless Synchronous Generators

With the application of more electric aircraft (MEA) technology, variable frequencies and high power ratings become import features of aero-generators. The brushless synchronous generator, which has a three-stage structure, is the most commonly used type of aero-generator. Due to the variation of operating conditions, the implementation of generator controllers becomes more and more difficult. In this paper, a state space model of a generator is derived and the influence of different operating conditions on the frequency response characteristics of the generator is revealed. Based on a fuzzy PI controller, an additional fuzzy logic controller is applied to modify the PI parameters of the voltage loop by introducing the generator speed to cope with the speed variation. Finally, the results of the simulations and experiments demonstrate that the dual fuzzy PI controller can improve both the steady-state and dynamic performance of the brushless synchronous generator, verifying the previous theoretical study.

Advances in Dual-Three-Phase Permanent Magnet Synchronous Machines and Control Techniques

Multiphase electrical machines are advantageous for many industrial applications that require a high power rating, smooth torque, power/torque sharing capability, and fault-tolerant capability, compared with conventional single three-phase electrical machines. Consequently, a significant number of studies of multiphase machines has been published in recent years. This paper presents an overview of the recent advances in multiphase permanent magnet synchronous machines (PMSMs) and drive control techniques, with a focus on dual-three-phase PMSMs. It includes an extensive overview of the machine topologies, as well as their modelling methods, pulse-width-modulation techniques, field-oriented control, direct torque control, model predictive control, sensorless control, and fault-tolerant control, together with the newest control strategies for suppressing current harmonics and torque ripples, as well as carrier phase shift techniques, all with worked examples.

Compressed Air Energy Storage and Future Development

Power generation around the world is changing dramatically as a consequence of the demand to lower greenhouse gas releases and present a mix of power supplies. Energy storage technology is considered to be the fundamental technology to address these challenges and has great potential. This paper presents the current development and feasibilities of compressed air energy storage (CAES) and provides implications for upcoming technology advancement. The paper introduces various primary categories of CAES (Advanced Adiabatic-CAES, Liquid Air Energy Storage and Supercritical CAES). Compared with other energy storage technologies, CAES is considered a fresh and green energy storage with the distinctive superiorities of high capacity, high power rating, and long-term storage, and shortcomings of low power density, high transportation losses, and geological restriction. CAES is regarded as a promising technology that is able to be applied in renewable energy production, cogeneration, and distributed energy and microgrid systems. It’s also considered to be integrated with other technologies, such as renewable energy, gas turbine, solid oxide fuel cells, and other systems in the future.

Two-color, intracavity pump-probe, cavity ringdown spectroscopy.

We report a proof-of-principle demonstration of intracavity pump-probe, cavity ringdown (CRD) detection in a three-mirror, traveling-wave cavity. With cavity-enhanced pump power and probe absorption path length, the technique is a generally applicable, high-sensitivity, high-selectivity detection method. In our experiments, the pump radiation is switched off during every other probe ringdown, which allows uncorrelated measurements of analyte and background cavity decay rates. The net, two-color signal from the difference between the pump-on and pump-off decay rates is immune to empty-CRD drifts and spectral overlaps from non-target molecular transitions. The immunity to the ringdown drifts allows longer signal-averaging and, thus, higher detection sensitivity. The ability to compensate for the background absorption enhances the detection selectivity in spectrally congested regions. Our technique is well-suited for trace-detection in the mid-IR region, where pump-probe schemes based on strong rovibrational transitions can be applied. In this work, two-color CRD detection is implemented on a ladder-type, three-level system based on the N2O, ν3 = 1 ← 0, P(19) (pump) and ν3 = 2 ← 1, R(18) (probe), rovibrational transitions. By frequency-locking two-quantum cascade lasers to the p-polarization (pump, Finesse = 5280) and s-polarization (probe, Finesse = 67700) cavity modes, we achieve high intracavity pump power (36W) and high probe ringdown rates (>2 kHz). The observed two-color spectra are simulated by a density-matrix, three-level system model that is solved under the constraints of the cavity resonance conditions. In addition to its background compensation capability, experimental flexibility in the selection of pump-probe schemes and signal insensitivity to intracavity laser power are further features that enhance the utility of our technique for mid-IR trace-detection.

Power quality investigation of CHB nine‐level converter based large‐scale solar PV system with different modulation schemes

Multilevel converters (MLCs) are extensively used in solar photovoltaic (SPV) applications owing to their advantages such as low total harmonic distortion (THD) in the converter voltage, reduction in device stress, and switching losses. A suitable modulation technique is important for the efficient closed-loop control of megawatt (MW)-scale solar photovoltaic plants. This work utilises different modulation techniques, such as phase-shifted (PS) multicarrier pulse width modulation (PWM), selected harmonic elimination (SHE), and nearest level modulation (NLM), for switching of cascaded H-bridge (CHB) converter-based large-scale SPV systems. The investigation on improving power quality is presented with a suitable fast Fourier transform (FFT) analysis and comparative graphs. The presented control and modulation enhance the power quality of the output current being fed to the grid in the dynamic solar profile. Moreover, the low switching frequency employed in this photovoltaic converter at a high power rating increases the system efficiency. Graphical illustrations of losses with fundamental and PWM switching were analysed for the MW-rated system. The obtained results show that SHE-PWM provides the best performance for large-scale solar power plants. Furthermore, the IEEE-519 standard was met for both grid voltages and currents. The system was modelled and simulated in MATLAB/Simulink and validated in a real-time environment.

Efficient milling and cutting of borosilicate glasses through a thin flowing water film with a picosecond laser

Direct laser ablation allows high-quality processing, precision, and cutting of complex shapes. Unfortunately, this technology is usually not considered as the primary candidate for cutting and milling of glasses due to low processing speeds. Thus, laser-based rear side drilling and crack generation techniques are chosen instead. However, we report on the milling and cutting of borosilicate glass plates with high average power and high pulse repetition rate picosecond laser. We optimised laser processing parameters for the efficient direct material ablation and employed water-assisted ablation to improve the ablation efficiency and the cutting speed of borosilicate glasses. The laser process was realised through a thin flowing water film, which was formed by spraying water mist on the surface of the workpiece. Firstly, we characterised thin water film parameters, such as film thickness, flow velocity, and defined a working area with constant processing conditions. Next, we optimised laser processing parameters for both processing environments: ablation through the thin water film and in air. Under optimal parameters, ablation through the thin water film was much more effective, increasing the cutting speed of 420 μm thick glass plates nearly ten times – from 0.52 to 5 mm/s. Furthermore, the morphology of the cuts was improved as well: cut wall roughness and edge chipping were reduced, spatter deposition was avoided in the vicinity of the cut. We investigated the milling of 130 to 1700 μm wide and 50 to 500 μm deep grooves with a maximum depth-to-width ratio of 3.8. Findings revealed that the ablation efficiency increase provided by the water layer did not depend on the depth or the width of the groove and remained constant. Therefore, it became possible to predict the ablation efficiency through the thin water film by knowing the ablation efficiency in air and an absolute ablation efficiency difference between two processing environments. • Efficient borosilicate glass milling and cutting in the air and through the water film was conducted with a picosecond laser. • Optimal laser fluence for efficient glass ablation was 40% higher than in air. • An absolute change in ablation efficiency between two environments did not depend on the transverse dimensions of the groove. • Water film improved ablation efficiency significantly, resulting in nearly 10 times higher cutting speed than in air.

A New Press Pack IGBT for High Reliable Applications With Short Circuit Failure Mode

The modular multilevel converter (MMC or M2C) technology becomes the mainstream solution in today's voltage source converter-high voltage direct current (VSC-HVDC) transmission lines because of its unique performance. Recently press pack IGBT (PPI) has come into focus as a preferred realization for high power rating VSC-HVDC stations, it could offer the highest current rating IGBTs and advanced features in reliability. A new PPI is introduced in this paper, which is designed for several innovative improvements based on the application demands from VSC-HVDC systems. The chip is optimized for low on-state voltage with advanced trench technology, and well protected in a chip-stack by double side sinter process. The disc package is designed with hermetic sealed ceramic housing to avoid environmental erosion and could provide a robust feature of short circuit failure mode (SCFM), which is fully qualified under the worst-case scenario. In addition to the PPI device, system solutions had also been developed and investigated to support field developments, including electrical and mechanical design. An example of a power stack is analyzed in commutation loop, pressure distribution, and power losses.