Standalone Research Articles

Standalone and Non-Standalone Beam Management for 3GPP NR at mmWaves

The next generation of cellular networks will exploit mmWave frequencies to dramatically increase the network capacity. The communication at such high frequencies, however, requires directionality to compensate the increase in propagation loss. Users and base stations need to align their beams during both initial access and data transmissions, to ensure the maximum gain is reached. The accuracy of the beam selection, and the delay in updating the beam pair or performing initial access, impact the end-to-end performance and the quality of service. In this paper we will present the beam management procedures that 3GPP has included in the NR specifications, focusing on the different operations that can be performed in Standalone (SA) and in Non-Standalone (NSA) deployments. We will also provide a performance comparison among different schemes, along with design insights on the most important parameters related to beam management frameworks.

Cage Subsidence and Fusion Rate in Extreme Lateral Interbody Fusion with and without Fixation

To examine the subsidence rate in patients undergoing extreme lateral interbody fusion (XLIF) using data from a 2-year retrospective study to assess the effect of supplemental fixation on the stand-alone procedure. Demographic and perioperative data for all patients who underwent XLIF for degenerative lumbar disorders between June 2012 and January 2016 were collected and divided into 4 groups: the stand-alone (SA), lateral fixation, unilateral pedicle screw, and bilateral pedicle screw (BPS) groups. The disk height (DH), lumbar lordotic (LL) angle, and segmental lordotic (SL) angle were measured preoperatively and 3 days, 3 months, 1 year, and 2 years postoperatively. Clinical outcomes were evaluated using Japanese Orthopaedic Association (JOA) and visual analog scale (VAS) scores. Fusion was defined according to computed tomography scan. There were 126 vertebrae in 107 patients treated. SL angle, LL angle, and DH significantly increased postoperatively in all groups. Although the preoperative and 2-year postoperative DHs in the SA group were similar, the other measures showed significant differences from baseline at each follow-up visit. No significant effects on SL angle or DH were found in any of the groups. Asignificant difference in the LL angle was found in the BPS group compared with the other groups. At the last follow-up, high-grade subsidence was found in 26.89% of all cases, the fusion rate was 85.71%, and the VAS and JOA scores were significantly improved in all groups. Supplemental fixation did not significantly influence cage subsidence or SL angle. Only BPS fixation significantly improved the LL angle. The 2-year fusion rate was satisfactory.

Implementation of a Smart Power Conditioning System for Energy Storage System with a Novel Seamless Transfer Strategy

Implementation of a smart power conditioning system with a novel seamless transfer method for an energy storage system (ESS) was proposed in this paper. The power conditioning system is to control the power quality or protect the grid system. Therefore, it requires various functions. One of the these functions, the uninterruptible power supply (UPS) function, was applied to proposed power conditioning system. In order for the grid-interactive power conditioning system to continuously supply power to the load, two operation modes are required depending on the grid state. One is the grid connected (GC) mode and the other is the stand-alone (SA) mode. Under normal grid condition, the power conditioning system is operated in GC mode and controls the current. On the other hand, under abnormal grid conditions such as grid outage, the power conditioning system operates in SA mode and supplies power to the load. Unintentional sudden changes in operating mode cause unwanted phenomena (e.g., voltage/current spike, inrush current) which can make system degradation or failure. To improve this situation, the seamless transfer function became necessary. In this paper, by adding seamless function to power conditioning system, it is possible to supply power to the load stably regardless of grid state. In addition, it is possible to prevent secondary accident and to operate stably even if non-detection zone condition occurs by using an active frequency method. The proposed control algorithm was verified through field experiments.

PV with multiple storage as function of geolocation

A real PV array combined with two storage solutions (B, battery, and H, hydrogen reservoir with electrolyzer-fuel cells) is modeled in two geolocations: Oxford, UK, and San Diego, California. All systems meet the same 1-year, real domestic demand. Systems are first configured as standalone (SA) and then as Grid-connected (GC), receiving 50% of the yearly-integrated demand. H and PV are dynamically sized as function of geolocation, battery size BM and H’s round-trip efficiency ηH.For a reference system with battery capacity BM=10 kW h and ηH=0.4, the required H capacity in the SA case is ∼1230 kW h in Oxford and ∼750 kW h in San Diego (respectively, ∼830 kW h and ∼600 kW h in the GC case). Related array sizes are 93% and 51% of the reference 8 kWp system (51% and 28% for GC systems). A trade-off between PV size and battery capacity exists: the former grows significantly as the latter shrinks below 10 kW h, while is insensitive for BM rising above it. Such a capacity achieves timescales’ separation: B, costly and efficient, is mainly used for frequent transactions (daily periodicity or less); cheap, inefficient H for seasonal storage instead.With current PV and B costs, the SA reference system in San Diego can stay within 2·104 $ CapEx if H’s cost does not exceed ∼7 $/kW h; this figure increases to 15 $/kWh with Grid constantly/randomly supplying a half of yearly energy (6.5 $/kWh in Oxford, where no SA system is found below 2·104 $ CapEx).Rescaling San Diego’s array (further from its optimal configuration than Oxford’s) to the ratio between local, global horizontal irradiance (GHI) and Oxford GHI, yields in all cases a 11% reduction of size and corresponding cost, with the other model outputs unaffected. The location dependent results vary to different extents when extending the modeled timeframe to 18 years. In any case, the variability stays within ±10% of the reference year.

A radiographic follow-up study of stand-alone-cage and graft-plate constructs for single-level anterior cervical discectomy and fusion.

Anterior cervical discectomy and fusion (ACDF) may be performed using an interbody cage or graft with an anterior plate or with a stand-alone (SA) interbody device without the anterior plate. The pros and cons of each vary. This study examined the radiographic outcome of the two techniques with a focus on implant subsidence. A retrospective review of cases of singe level ACDF by a single surgeon was undertaken. Medical and radiographic records were reviewed to determine subsidence, pre- and post-operative segmental and total lordosis in cohorts of both stand-alone and graft-and-plate constructs. The post-operative radiographs of 35 patients with a SA cage were compared with 41 patients with an allograft block and anterior plate (graft and plate; GP). There was no significant difference in overall subsidence between the two groups although there was a trend toward less clinically significant subsidence (2 mm) in the SA group. For single level ACDF, a SA device appears to be comparable in terms of undesired subsidence. Further studies with different implants and materials may offer further insight.

Comparison of Surgical Outcomes, Narcotics Utilization, and Costs After an Anterior Cervical Discectomy and Fusion

Study Design: Retrospective cohort analysis of a prospectively maintained registry. Objective: To compare the surgical outcomes, narcotic utilization, and costs between a stand-alone (SA) cage and anterior plating (AP) with an interbody device for 1-level anterior cervical discectomy and fusion (ACDF). Background Data: ACDF with a SA cage has gained popularity as a potential alternative to anterior cervical plating. Few studies have compared the surgical outcomes, narcotic utilization, and costs of ACDF utilizing a SA cage versus AP with an interbody device. Methods: Patients who underwent a primary 1-level ACDF for degenerative spinal pathology between 2010 and 2013 were analyzed. Patients were stratified on the basis of the type of implant system (SA cage vs. AP) and assessed with regard to demographics, comorbidities, smoking, visual analogue scale (VAS) scores (preoperative/postoperative), procedural time, estimated blood loss (EBL), length of hospitalization, complications, reoperations, narcotic consumption, and total costs. Statistical analysis was performed with independent sample T tests for continuous variables and χ2 analysis for categorical data. An α level of <0.05 denoted statistical significance. Results: Of the 93 patients included, 52 (55.9%) underwent an ACDF with a SA cage system. Patient demographics, comorbidity burden, body mass index, smoking status, and preoperative VAS score were similar between cohorts. The SA cohort incurred a significantly lower EBL (P<0.001) than the AP cohort. However, none required a transfusion and the procedural time, length of hospitalization, postoperative VAS score, complication rates, 1-year arthrodesis rate, and reoperation rates were similar between cohorts. Postoperative narcotics consumption and total costs were also similar between groups. Conclusions: Our findings suggest that the SA cage may be associated with a significantly lower EBL, which may not be clinically relevant. Perioperative outcomes, complications, reoperation rates, narcotics consumption in the immediate postoperative period, and total costs may be similar regardless of the instrumentation utilized in a 1-level ACDF.

Control Strategy Design of Grid-Connected and Stand-Alone Single-Phase Inverter for Distributed Generation

Dual-mode photovoltaic power system should be capable of operating in grid-connected (GC) and stand-alone (SA) modes for distributed generation. Under different working modes, the optimal parameters of inverter output filters vary. Inverters commonly operate in GC mode, and thus, a small capacitance is beneficial to the GC topology for achieving a reasonable compromise. A predictive current control scheme is proposed to control the grid current in GC mode and thereby obtain high-performance power. As filter are not optimal under SA mode, a compound control strategy consisting of predictive current control, instantaneous voltage control, and repetitive control is proposed to achieve low total harmonic distortion and improve the output voltage spectrum. The seamless transfer between GC mode and SA mode is illustrated in detail. Finally, the simulation and experimental results of a 4 ㎸A prototype demonstrate the effectiveness of the proposed control strategy.

Trabecular metal spacers as standalone or with pedicle screw augmentation, in posterior lumbar interbody fusion: a prospective, randomized controlled trial.

This prospective randomized comparative trial compared radiological and clinical outcome of Trabecular Metal™ (TM) spacers in PLIF, used as standalone (SA) devices, to TM spacers in PLIF with pedicle screw fixation (PF), in patients with single-level degenerative disc disease (DDD). Patients (n = 80) with chronic low back pain and single-level degenerative disc were randomly assigned to the SA PLIF (n = 40) or PLIF with PF (n = 40). The primary radiological outcome was the evaluation of a long-term (±6 years; range 6.0-7.7 years) stable construct measured by dynamic X-rays. CT scan does not allow judging the bony bridging between vertebrae, because of Tantalum artefacts. The clinical evaluation (6 weeks, 6, 12 and 24 months) consisted of the Oswestry Disability Index (ODI) score, intensity of low back pain (Visual Analogue Scale) and quality of life (Short Form-36). At 6-year follow-up, X-rays showed a stable construct in 94 % of patients treated by SA TM-500 spacers and in 97 % of those with additional PF. Neither subsidence nor migration was observed in either the SA or the PF group. The average improvement in ODI scores at 24-month clinical follow-up was 14.4 and 13.8 for the SA and PF group, respectively. The VAS score showed an average improvement of 6.4 (SA) and 6.7 (PF), 2 years after implantation. No significant difference between groups was observed at all the evaluation points. In this study, TM spacers were found to provide a solid construct at more than 6-year follow-up after PLIF for DDD both with and without additional pedicle fixation. The clinical, but also radiological results were not significantly different between both cohorts. Future studies focusing on the differences of SA and PF at L4/5 level should be powered to study differences in post-surgery stability at the long term.

An Effective Smooth Transition Control Strategy Using Droop-Based Synchronization for Parallel Inverters

This paper proposes a smooth transition control strategy for voltage-source inverters between stand-alone (SA) and grid-connected (GC) modes of operation. In both GC and SA modes of operation, the inverters use the droop control method to regulate the real power flow without the need of any external communication between them. One of the distributed energy sources working in the microgrid system is designated as a dispatch unit (DU) to facilitate interconnection with utility grid and achieve smooth transition between the modes of operations. During transition modes, this selected unit takes extra responsibility to ensure the continuous power delivery to the load. For smooth transition from GC to SA mode of operation, the DU compensates for the grid current immediately after the grid disconnection, and then, other units pick up this responsibility gradually through their individual droop controllers. The DU also adjusts its output power to synchronize the inverters with the grid during the transition from SA to GC mode. The simulation and experimental results, as well as the stability analysis, are provided to verify the effectiveness of the proposed control technique.

Universal Integrated Synchronization and Control for Single-Phase DC/AC Converters

The universal integrated synchronization and control (UISC) is proposed to operate a single-phase dc/ac converter in both grid-connected (GC) and stand-alone (SA) modes and offer seamless transition between these modes without any reconfiguration of control structure. As a matter of fact, the UISC does not need to use an islanding detection algorithm in the conventional sense. In GC mode, the UISC controls the real and reactive powers independently. In SA mode, it provides voltage and frequency support. The UISC is not based on direct current control or direct output voltage control. It adjusts the internal converter voltage through a nonlinear mechanism that amounts to the control of the current in GC mode and the voltage in SA mode. The UISC does not require a separate synchronization unit such as a phase-locked loop (PLL). In principle, the UISC is analogous to the combined governor and automatic voltage regulator controls in a synchronous machine (SM). In this sense, it may be considered among the converters that mimic the SMs such as the synchronverter. The proposed UISC is arguably the most unified method that can address different modes of operation of a converter within a microgrid environment without control switching actions. This paper presents the derivations, stability analysis, and numerical results to illustrate the performance of the proposed controller in a single phase situation. A mathematical analysis on the analogies and differences between the UISC and some similar methods is also presented.

A Study of Wind Power Inverter Operating in Grid-Connected and Stand-Alone Mode

Wind turbine system (WTS) is a representative distributed power generation (DG). Establishment of WTS model and control strategies is of important practical significance. One critical field is the research of inverter system. It should be operated in stand-alone (SA) or grid-connected (GC) mode. The purpose of this thesis is to establish simulation platform of WTS inverter control model in Matlab/Simulink environment, which includes two typical DG control strategies, PQ and V/f. The wind fluctuation makes inverter output power harder to follow wind turbine (WT) power. In GC mode, PQ strategy was adopted to balance inverter output power and WT generated power. In SA mode, V/f strategy was applied to keep emergency load voltage stable. The bidirectional smooth transitions between SA and GC mode were well accomplished. Simulation proves the model can survive grid failures or load shedding. The study can be used in research of DG operation control.

Transition Control Strategy Between Standalone and Grid-Connected Operations of Voltage-Source Inverters

This paper proposes a smooth transition control strategy for voltage-source inverters between standalone (SA) and grid-connected (GC) modes of operation. In the GC mode, the amount of power exchanged with the utility grid is controlled by regulating the phase currents. In the SA mode, the load voltage is regulated by the inverter with its phase dictated by the inverter control. The transition between SA and GC operations that will ensure continuous power delivery to the load requires continuation in the phase of the system voltage. The proportional-integral, trapezoidal, sinusoidal, and staircase frequency variation techniques have been analyzed to find the best approach for minimizing the total harmonic distortion (THD). A smooth frequency variation technique has been developed, which provides lower THD on the voltage waveforms compared with the other techniques. The new algorithm has been implemented on a 5-kW single-phase utility interactive inverter having the SA operation capability. The simulation and experimental results show that the proposed technique provides seamless transition between the inverter modes of operation with minimal distortion at the inverter output voltage.

Optimizing the Design and Deployment of Stationary Combined Heat and Power Fuel Cell Systems for Minimum Costs and Emissions—Part II: Model Results

The maximizing emission reductions and economic savings simulator (MERESS) is an optimization tool that evaluates novel strategies for installing and operating combined heat and power (CHP) fuel cell systems (FCSs) in buildings. This article discusses the deployment of MERESS to show illustrative results for a California campus town and, based on these results, makes recommendations for further installations of FCSs to reduce greenhouse gas (GHG) emissions. MERESS is used to evaluate one of the most challenging FCS types to use for GHG reductions, the phosphoric acid fuel cell (PAFC) system. These PAFC systems are tested against a base case of a CHP combined cycle gas turbine (CCGT). Model results show that three competing goals (GHG emission reductions, cost savings to building owners, and FCS manufacturer sales revenue) are best achieved with different strategies but that all three goals can be met reasonably with a single approach. According to MERESS, relative to a base case of only a CHP CCGT providing heat and electricity with no FCSs, the town achieves the highest (1) GHG emission reductions, (2) cost savings to building owners, and (3) FCS manufacturer sales revenue each with three different operating strategies, under a scenario of full incentives and a $100/tonne carbon dioxide (CO2) tax (scenario D). The town achieves its maximum CO2 emission reduction, 37% relative to the base case with operating strategy V: stand-alone (SA) operation, no load following (NLF), and a fixed heat-to-power ratio (FHP) (SA, NLF, and FHP; scenario E). The town’s building owners gain the highest cost savings, 25% with strategy I: electrically and thermally networked (NW), electricity power load following (ELF), and a variable heat-to-power ratio (VHP) (NW, ELF, and VHP; scenario D). FCS manufacturers generally have the highest sales revenue with strategy III: NW, NLF with a FHP (NW, NLF, and FHP; scenarios B, C, and D). Strategies III and V are partly consistent with the way that FCS manufacturers design their systems today, primarily as NLF with a FHP. By contrast, strategy I is novel for the fuel cell industry, in particular, in its use of a VHP and thermal networking. Model results further demonstrate that FCS installations can be economical for building owners without any carbon tax or government incentives. Without any carbon tax or state and federal incentives (scenario A), strategy I is marginally economical with 3% energy cost savings but with a 29% reduction in CO2 emissions. Strategy I is the most economical strategy for building owners in all scenarios (scenarios A–D) and, at the same time, reasonably achieves other goals of large GHG emission reductions and high FCS manufacturer sales revenue. Although no particular building type stands out as consistently achieving the highest emission reductions and cost savings (scenarios B-2 and E-2), certain building load curves are clear winners. For example, buildings with load curves similar to Stanford’s Mudd chemistry building (a wet laboratory) achieve maximal cost savings (1.5% with full federal and state incentives but no carbon tax) and maximal CO2 emission reductions (32%) (scenarios B-2 and E-2). Finally, based on these results, this work makes recommendations for reducing GHG further through FCS deployment. (Part I of II articles discusses the motivation and key assumptions behind the MERESS model development.)

태양광 및 풍력 하이브리드 발전 시스템에 관한 연구

In this paper, a solar-wind hybrid system is decsribed for Stand-Alone(SA) power generation system. Mostly SA power generation system for ocean facilities composes a solar system. Normally, the output power of solar system is decreased with weather condition as cloudy and rainy. Solar-wind hybrid system can be operated as complement system each other. In this paper, the characteristic simulation of solar and wind is performed by LabVIEW. The hybrid power generation system is designed according to simulation results, and is tested for checking the complement characteristic.

Quantitative Coronary Angiographic Analysis of Spasm and Elastic Recoil After High Speed Rotational Atherectomy

This study evaluates the short‐term changes in coronary artery segments treated with high speed rotational atherectomy (HSRA). Quantitative coronary angiographic (QCA) analysis indices, such as degree of expected ablation, elastic recoil, and segmental spasm, were examined in 133 patients and restudied 24 hours after HSRA. The study was also designed to compare the early results of three different HSRA strategies: stand‐alone (SA) HSRA; HSRA with adjunctive high (≥ 4 atm) pressure (HP BA) and low (≥ 2 atm) pressure balloon angioplasty (LP BA). Previous studies have suggested negligible elastic recoil after HSRA as well as demonstrated the possibility of further continuous improvement in vessel patency up to 24 hours postprocedure. From a total of 656 patients treated with HSRA, a cohort of 133 patients with successful HSRA of 167 lesions were restudied angiographically at 24 hours. Serial QCA evaluation of the treatment site was performed. Analysis of the relative gain in minimal luminal diameter (MLD) assessed at 24 hours postprocedure showed that the highest gain group (> 40%) had narrower initial lesions compared to moderate gain (1%–40%), or MLD loss groups (MLD 0.5 ± 0.4 mm vs 1.0 ± 0.3 and 1.5 ± 0.4, respectively, P < 0.01). The initial percent diameter stenosis was also higher in the high gain group (77.1 ± 16.0 vs 61.9 ± 11.8 and 53.0 ± 11.9, P < 0.01). Immediately postprocedure there was a significant increase in MLD and a decrease in percent diameter stenosis. There was no difference in residual lesion characteristics postprocedure. While progressive MLD decrease was observed in the loss group (MLD postprocedure 1.6 ± 0.5 and 1.2 ± 0.6 at 24 hours, P < 0.01), a continuous increase in MLD was noted in the high gain group (MLD postprocedure 1.7 ± 0.5 mm vs at 24 hours 2.0 ± 0.5 mm, P < 0.01). The high gain group was characterized by the most lesion debulking, the most pronounced segmental spasm, and the least elastic recoil. Adjunctive HP BA was associated with the largest size vessels (D ref. in SA HSRA group was 2.6 ± 0.8 mm vs 2.9 ± 0.6 mm in LP BA and 3.0 ± 0.7 mm in HP BA groups, P < 0.01), the lowest elastic recoil (SA HSRA 23.8%± 20.9% vs LP BA 15%± 16.8% and HP BA 5.7%± 14.4%, P < 0.05), and the highest incidence of vessel dissection (SA HSRA 8.1% vs LP BA 14.7% and HP BA 34.0%, P < 0.05). However, these larger vessels underwent the least amount of lesion debulking (SA HSRA 46.4%± 27.2% vs LP BA 38.6%± 24.0% and HP BA 30.5%± 19.5%, P SA HSRA vs. HP BA < 0.001). There are measurable degrees of elastic recoil and local spasm observed after HSRA. HSRA of the most severe lesions yields the highest procedural gain, the lowest elastic recoil and the highest index of lesion ablation. In addition, some late increase in the MLD due to the resolution of spasm is observed at 24 hours postprocedure. SA HSRA is associated with higher degrees of expected lesion ablation. This is comparable to the degree of improvement in MLD, where adjunctive percutaneous transluminal coronary angioplasty is utilized as assessed at 24 hours postprocedure. HSRA with adjunctive HP BA yields immediate results showing the least elastic recoil and spasm at the expense of the highest incidence of dissection and side branch loss.