Virtual Output Research Articles

Periodic compensation of continuous‐time linear systems with norm‐bounded parametric uncertainties

AbstractThis article employs a recently proposed high frequency, continuous‐time periodic controller to compensate single‐input‐single‐output linear plants with norm‐bounded time‐varying uncertainties. To this end, the design of periodic controller is converted into designing a linear time‐invariant (LTI) controller for a single‐input‐two‐output equivalent uncertain system, following averaging technique. To represent this equivalent uncertain system into a standard form of linear uncertain systems, where uncertainties appear in system matrix A and input matrix B, the observer canonical form description of the original uncertain plant is exploited. Using the relationship between quadratic stability and ‐norm minimization result available in literature, it is proved that the presence of virtual output with the periodic feedback introduces a feedforward action on the disturbance input of the generalized plant, unlike an LTI one. By virtue of this, the proposed periodic controller can tolerate more uncertainty bound in the input matrix B than its LTI counterpart, while keeping the bound on system matrix A the same. Finally, a linear matrix inequality‐based method is used to design the periodic controller to achieve quadratic stability along with robust linear quadratic performance. Suitable examples are considered to show the superiority of the periodic control as compared to LTI ones.

Hybrid Electrothermal Simulations of GaN HEMT Devices Based on Self-Heating Free Virtual Electrical Characteristics

The electrothermal behavior of gallium nitride (GaN) HEMTs has been simulated by using a hybrid approach in which the problem is solved by coupling together an effective model (for the electrical part) and a 3-D finite element model (for the thermal part). The effective model relies on the estimation of the channel current at different temperatures in the absence of thermal gradients. This regime occurs in real devices only during the very initial stage of bias pulses, when self-heating effects are not yet developed, for time intervals shorter than 1 ns. Virtual output electrical characteristic, in which self-heating effects are negligible, have been derived from pulsed measurements of the electrical output characteristics and electrothermal transient simulations. The maximum temperature because of self-heating evaluated by using the virtual output characteristic are substantially higher than those obtained using the short time-pulsed measurements directly. The results have been validated by a comparison with temperature measurements obtained using Raman thermography. This approach has proven to be numerically very efficient and fast, allowing the analysis of realistic complex structures and circuits.

High throughput resource efficient reconfigurable interleaver for MIMO WLAN application.

Demand for high-speed wireless broadband internet service is ever increasing. Multiple-input-multiple-output (MIMO) Wireless LAN (WLAN) is becoming a promising solution for such high-speed internet service requirements. This paper proposes a novel algorithm to efficiently model the address generation circuitry of the MIMO WLAN interleaver. The interleaver used in the MIMO WLAN transceiver has three permutation steps involving floor function whose hardware implementation is the most challenging task due to the absence of corresponding digital hardware. In this work, we propose an algorithm with a mathematical background for the address generator, eliminating the need for floor function. The algorithm is converted into digital hardware for implementation on the reconfigurable FPGA platform. Hardware structure for the complete interleaver, including the read address generator and memory module, is designed and modeled in VHDL using Xilinx Integrated Software Environment (ISE) utilizing embedded memory and DSP blocks of Spartan 6 FPGA. The functionality of the proposed algorithm is verified through exhaustive software simulation using ModelSim software. Hardware testing is carried out on Zynq 7000 FPGA using Virtual Input Output (VIO) and Integrated Logic Analyzer (ILA) core. Comparisons with few recent similar works, including the conventional Look-Up Table (LUT) based technique, show the superiority of our proposed design in terms of maximum improvement in operating frequency by 196.83%, maximum reduction in power consumption by 74.27%, and reduction of memory occupancy by 88.9%. In the case of throughput, our design can deliver 8.35 times higher compared to IEEE 802.11n requirement.

Dual-Energy Computed Tomography Virtual Noncalcium Technique in Diagnosing Osteoporosis: Correlation With Quantitative Computed Tomography.

ObjectiveThe aim of this study was to evaluate dual-energy computed tomography (CT) virtual noncalcium (VNCa) technique as a means of quantifying osteoporosis.MethodsDual-energy CT scans were obtained prospectively, targeting lumbar regions of 55 patients with chronic low back pain. A standard quantitative CT (QCT) phantom was positioned at the waist during each procedure, using proprietary software (QCT Pro; Mindways, Tex) to measure bone mineral density (BMD) in each vertebral body. Vendor dual-energy analytic software was altered with a specially modified configuration file to produce a “Virtual Non Calcium” or “VNCa” output, as such output variables were remapped to produce the following calcium values rather than iodine, yielding the following QCT parameters: CT value of calcium (originally “contrast media” [CM]), CT value of mixed energy imaging (regular CT value [rCT]), calcium density (originally “contrast agent density” [CaD]), and fat fraction (FF). Pearson test served to assess correlations between BMD and these parameters. Multiple linear regression analysis was applied to construct an equation for generating regressive BMD (rBMD) values. In gauging diagnostic accuracies, the criterion-standard BMD cutoff point (<80 mg/cm3) was adopted for QCT, whereas the rBMD threshold was defined by receiver operating characteristic curve.ResultsContrast media, rCT, CaD, and FF values (reflecting CT value of calcium, regular CT value, calcium density, and fat fraction, respectively) significantly correlated with BMD (r values: 0.885, 0.947, 0.877, and 0.492, respectively; all P < 0.01). Contrast media, CaD, and FF showed independent associations with BMD; the regressive equation was formulated as follows: rBMD = 54.82 − 0.19 × CM + 20.03 × CaD − 1.24 × FF. The area under the curve of rBMD in diagnosing osteoporosis was 0.966 ± 0.009 (P < 0.01). At an rBMD threshold of less than 81.94 mg/cm3, sensitivity and specificity were 90.0% and 92.0%, respectively.ConclusionsDual-energy CT VNCa technique may constitute a valid alternative method for quantifying the mineral content and marrow fat composition of bone in diagnostic assessments of osteoporosis.

Speculative Packet Dispatch for Virtual Output Queuing Architecture Using LSTM Recurrent Neural Network

Virtual Output Queuing (VOQ) is an architecture widely employed in modern networking products. Traffic from every ingress port is stored in a set of queues mirroring the structure of the egress ports. This architecture allows congestion on one egress port to be isolated from the other ports. A request-grant protocol is used to route packets from ingress to egress. When a packet is received, a request signal is issued. After the request reaches the egress side, a grant signal is generated based on some fixed threshold indicating there is space in the egress buffer to absorb the largest packet size dispatched from ingress. The buffer must be sized deep enough to accommodate in-flight traffic associated with a scenario where heavy congestion is found after the grant is issued. Awaiting a grant signal to arrive before dispatching packets incurs significant end-to-end latency. To alleviate this problem, a speculative packet dispatch approach (SPD) is proposed in which the request grant protocol is completely eliminated. Packets are dispatched speculatively from ingress to egress based on predictions that there is enough space in the egress buffer. This is achieved by incorporating an LSTM recurrent neural network as part of the VOQ controller. The LSTM is trained by time-series data sets generated from past observations on the queue occupancy. The experimental results show that SPD delivers excellent improvement on the system performance, reduces buffering requirements and preserves the property of VOQ.

Research on &amp;quot;Hot Zone&amp;quot; in Coal Mine Based on Multihop Uneven Clustering Algorithm for Vitual MIMO

In view of the special geographical environment of mine tunnel, this paper analyzes why improved Low Energy Adaptive Clustering Hierarchy (LEACH) protocols and virtual Multiple Input Multiple Output (MIMO) algorithms cause "hot zone" which shortens the life of Wireless Sensor Network (WSN) and forms the “blind area”. Based on this problem, this paper proposes a multihop non-uniform clustering algorithm named Virtual Multiple Input Multiple Output-Improved (VMIMO-I). The advantages of this algorithm are: (1) the competition radius of the cluster closer to the Sink node should be smaller, in order to the cluster head has enough energy to forward the information of other clusters. (2) There are several cooperative nodes in each cluster for multihop data transmission between clusters to save energy consumption of cluster heads; (3) There should be several clusters near the Sink node can directly transmit data to the Sink node, instead of sending all the data to the cluster head nearest to the Sink node. Then, this paper introduces the transmission process model based on this algorithm and analysis the energy consumption within and between clusters. With the simulation result on Matlab based on Minimum energy formula of VMIMO-I algorithm model, VMIMO-I algorithm is more applicable to be used in mine tunnel with lower energy consumption and more network lifetime than LEACH protocol.

The Sensitivity of Grid-Connected Synchronverters With Respect to Measurement Errors

The synchronverter algorithm is a way to control a switched mode power converter that connects a DC energy source to the AC power grid. The main features of this algorithm are frequency and voltage droops as well as synthetic inertia, so that the inverter resembles a synchronous generator (SG). Many versions of this algorithm have been proposed and tested, but all share the same “basic control algorithm”, which is based on the equations of a SG. We analyze the sensitivity of the output currents of a synchronverter, with respect to the measurement errors. We show that some of the sensitivity functions exhibit high gains at the relevant frequencies, leading to distorted grid currents, which makes the use of this inverter control algorithm problematic. We then do a similar analysis assuming that we have controlled current sources available at the grid output of the converter, that we control using virtual currents generated in the algorithm. The virtual currents are flowing through virtual output inductors, that we can choose to be significantly larger than the actual output inductors. We show that using the current sources reduces the sensitivity considerably, thus indicating a better approach to synchronverter design.

Simulation and comparative analysis of single-phase H bridge micro inverters with conventional PI control and virtual output impedance control: a case study

In this paper, it has been proposed that microgrids can form economically and technically viable option for the rural electrification. It has been observed that inverters form the basic building bl...

Simulation and comparative analysis of single-phase H bridge micro inverters with conventional PI control and virtual output impedance control: a case study

Simulation and comparative analysis of single-phase H bridge micro inverters with conventional PI control and virtual output impedance control: a case study

Virtual water output intensifies the water scarcity in Northwest China: Current situation, problem analysis and countermeasures

With 80% water resources in the south and 65% arable land in the north, China is facing a rigorous challenge due to the spatial mismatch between water distribution and food & energy production to make a balanced development of economy and ecosystem. In the past decades, the northwest has played a prominent role in maintaining national food and energy security. However, the lack of water resources in this region poses a great threat to sustainable development. Based on this, this study quantitatively analyzed the evolution trend of water footprint (WF) of major crops and energy products in Northwest China from 2000 to 2015 and revealed the virtual water (VW) transfer pattern with commodity trade and its water resource stress caused by the virtual water output. The results show that, although the improvement of technology has greatly reduced the WF per unit production, the northwest region is still a net VW output area, whose net VW output associated with food and energy trade is increasing sharply from 287.2 × 108 m3 (2000) to 328.5 × 108 m3 (2015) with a growth rate of 14.4%, seriously aggravating the local water resource pressure. To ensure the water, food and energy safety of the northwest, we proposed countermeasures and suggestions on technological development and strategic planning, including water-saving technology promotion, industrial and agricultural structure optimization, and the coordinated management of physical and virtual water. The above findings provide a scientific reference to ensure the sustainable development of Northwest China.

Passivity-Based Decentralized Control for Discrete-Time Large-Scale Systems

Passivity theory has recently contributed to developing decentralized control schemes for large-scale systems. Many decentralized passivity-based control schemes are designed in continuous-time. It is well-known, however, that the passivity properties of continuous-time systems may be lost under discretization. In this letter, we present a novel stabilizing decentralized control scheme by ensuring passivity for discrete-time systems directly and thus avoiding the issue of passivity preservation. The controller is synthesized by locally solving a semidefinite program offline for each subsystem in a decentralized fashion. This program comprises local conditions ensuring that the corresponding subsystem is locally passive. Passivity is ensured with respect to a local virtual output which is different from the local actual output. The program also comprises local conditions ensuring that the local passivity of all subsystems implies the asymptotic stability of the whole system. The performance of the proposed controller is evaluated on a case study in DC microgrids.

A novel method for computing single output for DEA with application in hospital efficiency

There are two main methods for measuring the efficiency of decision-making units (DMUs): data envelopment analysis (DEA) and stochastic frontier analysis (SFA). Each of these methods has advantages and disadvantages. DEA is more popular in the literature due to its simplicity, as it does not require any pre-assumption and can be used for measuring the efficiency of DMUs with multiple inputs and multiple outputs, whereas SFA is a parametric approach that is applicable to multiple inputs and a single output. Since many applied studies feature multiple output variables, SFA cannot be used in such cases. In this research, a unique method to transform multiple outputs to a virtual single output is proposed. We are thus able to obtain efficiency scores from calculated virtual single output by the proposed method that are close (or even the same depending on targeted parameters at the expense of computation time and resources) to the efficiency scores obtained from multiple outputs of DEA. This will enable us to use SFA with a virtual single output. The proposed method is validated using a simulation study, and its usefulness is demonstrated with real application by using a hospital dataset from Turkey.

A novel control strategy for parallel operation of multi-inverters in low-voltage microgrids

Droop control is an effective method for the parallel operation of voltage sources without any communication among modules. However, in low-voltage microgrids (MGs) the line impedance is predominantly resistive that causes the control of active and reactive power can be no longer decoupling, and then finally influences the power sharing accuracy among inverters. It has been demonstrated that adding a virtual output impedance (VOI) in control loops can regulate the Total Equivalent Impedance (TEI) between module and common bus to be predominantly inductive, thus improves the power sharing accuracy. However, this method causes another problem that the common bus voltage will fall because of the voltage loss on the VOI. In this paper, the theories of power sharing and traditional droop control are studied in-depth. VOI is applied to make the TEI predominantly inductive, and a novel strategy aiming at regulating the bus voltage into reasonable range is proposed, which is based on the Real-time Estimation of Load Power (RELP). The proposed method is verified through a MG experimental platform composed of two 100 kVA inverters.

Invariance Principles and Observability in Switched Systems With an Application in Consensus

Using any nonnegative function with a nonpositive derivative along trajectories to define a virtual output, the classic LaSalle invariance principle can be extended to switched nonlinear time-varying (NLTV) systems, by considering the weak observability associated with this output. The concept of weak observability reflects the information of the limiting behavior of state trajectories hidden in the zero locus of the output. In the context of switched NLTV systems, weak observability can be explored using the recently established framework of limiting zeroing-output solutions. Adding to this, a new approach to show uniform global attractivity of a closed set (without assuming uniform Lyapunov stability or dwell-time conditions) is proposed. A further extension of the generalized LaSalle invariance principle allows the consideration of cascaded switched NLTV systems, which is used to characterize how consensus in a leaderless swarm of nonholonomic robots allowing for switching communication topologies may be established.

Analysis of the Relationship between Vegetable Virtual Water Trade and Saltwater Intrusion in Shouguang City, China

Shouguang City is located in north-central of Shandong, distributing the piedmont plain and coastal plain from the south to north. This area, as a vegetable base in northern China, not only meets local needs but also has a large number of vegetables exported to domestic and foreign countries in the form of virtual water. The vegetable production in this area mainly depends on groundwater exploitation, which causes saltwater intrusion problems. This study establishes the linear model of virtual water and vegetable production, irrigation water consumption, total population, per capita vegetable sales volume, and the purchase amount of vegetable trade. The output of vegetable virtual water from 1980 to 2012 is calculated. 3.79 billion kg of vegetables were exported in the form of virtual water with a volume of 145 million m3 in 2012, accounted for 78% of the average annual groundwater resources in the region. The vegetable trade development in Shouguang City from 1980 to 2002 can be divided into two stages: bare land vegetable cultivation in 1980–1990 and greenhouse vegetable cultivation in 1991–2002. The correlations among the annual virtual water output volume of vegetable trade, annual groundwater cumulative storage, groundwater depth at the center of depression area, and saltwater intrusion area are established and analyzed. In the first stage, for every 10 million m3 of vegetable virtual water was transferred, the salt water intrusion area in this area increased by 13.8 km2; in the second stage, the saltwater intrusion area increased correspondingly by 5 km2. The influence of saltwater intrusion on adjusting crop-planting structure is also analyzed to achieve the purpose of effectively alleviating the ecological and environmental problems in the area.

A Consensus-Based Adaptive Virtual Output Impedance Control Scheme for Reactive Power Sharing in Radial Microgrids

This article presents a distributed secondary control scheme for accurate reactive power sharing in an islanded multibus radial microgrid. The scheme employs consensus control to adaptively tune the virtual output impedance (VOI) into achieving reactive power correction. The adaptive VOI-based control structure is essentially nonlinear. However, this work shows that the approximate range of stable coupling gain can be established by linearizing the problem about every probable operating point of the distributed energy resources (DERs). On the basis of islanding mode, it is also shown that only the dynamic VOI component is needed while the static component, which has been used extensively to date, can be nullified. It will also be shown that under the established gain tuning guideline, the virtual reactance typically results in quicker correction dynamics as compared to the virtual resistance. The proposed control scheme can realize an accurate power sharing among the DERs regardless of the microgrid topology, load condition, and communication delay (within the allowable limits defined by the consensus theorem). This study is carried out in conjunction with an islanded microgrid model modified from the IEEE 34 Node Test Feeder.

Erratum to “Consensus Virtual Output Impedance Control Based on the Novel Droop Equivalent Impedance Concept for a Multi-Bus Radial Microgrid” [Jun 20 1078-1987

Erratum to “Consensus Virtual Output Impedance Control Based on the Novel Droop Equivalent Impedance Concept for a Multi-Bus Radial Microgrid” [Jun 20 1078-1987

Development and research of a virtual test bench for electric impedance tomography channel main components simulation

When developing and determining the principles of construction and algorithms for the operation of electrical impedance tomography devices, it is necessary to verify the adequacy of the adopted circuitry solutions, their technical level and the possibility of practical implementation. To assess the technical capabilities and operating parameters of the device and its components, it is advisable to develop specialized tools for research and adjustment. Considering that the devices for electrical impedance tomography being developed are hardware and software solutions, and their components are complete electronic units that interact with each other, it seems possible to develop an experimental bench. The development of a virtual automated experimental bench for preliminary tests of the main components of the electrical impedance tomography channel is proposed. On the basis of the operating principles of the hardware bench, the principles of building a virtual bench are formulated. The correspondence of the main elements of hardware and virtual benches in terms of their functional purpose is shown. For each of the software components of the virtual bench, input actions and output parameters are determined. A schematic diagram of the analog part of the electrical impedance tomography channel has been developed to test the performance of the virtual bench. Studies have shown that the developed virtual bench is suitable for preliminary testing of all analog components of the channel. The use of the developed virtual bench will allow optimizing the time and material costs for conducting experimental research in the process of developing hardware for technical means of electrical impedance tomography

Algorithmic Enhancement of Automotive MEMS Gyroscopes With Consumer-Type Redundancy

In this paper a novel fusion algorithm for a setup of redundant MEMS gyroscopes is proposed. Six cost-efficient, tri-axial, consumer-type sensors are combined with three single-axis vibration-robust automotive-type devices. The proposed algorithm provides a virtual sensor output that has both low noise due to redundancy averaging, as well as good mitigation of external, high-frequency vibration disturbances. Thereby the advantages of both sensor types, consumer and automotive, are combined. If one sensor is compromised by vibration influences, the conflicting sensor signals are challenging to conventional fusion methods. To overcome this, a two-stage fusion algorithm, called topological conflict measure (TCM), is proposed. It is based on weighted sums, where the weights for each sensor diminish as the signal reliability decreases. The method can be utilized to (1) assess a measure of multi-sensor conflict, (2) to improve fusion of redundant devices by lessening weighting for sensors with high conflict, and (3) to combine the fused signals calculated from sensors with inherently different characteristics, like vibration robustness in this case. Furthermore, a selection of other possible methods is implemented and compared to TCM: simple Bayesian averaging (BA), Dempster-Shafer Evidence Theory (DSET), Kalman filtering (KF) and fuzzy inference system (FIS). All methods offer similar, improved noise levels while the TCM, KF and FIS methods achieve the best vibration rejection. Among those, TCM has the best computational efficiency and adaptability to other types of redundant sensor setups.

Coordinated Control Strategy of PMSG and Cascaded H-Bridge STATCOM in Dispersed Wind Farm for Suppressing Unbalanced Grid Voltage

This article proposes an unbalanced voltage compensation method for a dispersed wind farm (DWF) by cooperating permanent magnetic synchronous generators (PMSGs) with a star-connected cascaded H-bridges (CHB) static synchronous compensator (STATCOM). The topology of a typical DWF is given and the mathematical models of CHB-STATCOM and PMSG inverter are established to show that the unbalanced grid voltage can be suppressed by controlling their virtual negative-sequence output admittance (NSOA). The relationship between maximum phase voltage and dc voltage corresponding to zero-sequence voltage injection is obtained to quantitatively analyze the negative-sequence current injection ability of the CHB-STATCOM. Moreover, the phase current limit is introduced to address the over-current problem, and a virtual NSOA method for sharing unbalanced voltage is proposed. An allocation coefficient calculation method is also proposed in consideration of both remaining capacity and voltage unbalanced factor (VUF) for different PMSGs. Furthermore, a coordinated control strategy of PMSGs and CHB-STATCOM for unbalanced voltage suppression is proposed. The effectiveness of the proposed coordinated control strategy is verified by simulation on a 50 MW DWF with a ±5 MVar star-connected CHB-STATCOM.