Steady-state Output Research Articles

Data-driven model-free adaptive damping control with unknown control direction for wind farms

The wide-area damping control (WADC) designed by conventional model-based methods faces the challenge from the strong nonlinearity, time-varying structure, and disturbances from complex operating conditions of the interconnected multi-machine power systems. In this paper, as one of the data-driven methods, the model-free adaptive control (MFAC), which employs the pseudo-partial derivative (PPD) to linearize the nonlinear power system dynamically, is adopted to design WADC for its advantages of the low cost, simple structure & low calculation burden, and the analyzable stability. However, when applied to the WADC design, the prototype MFAC is infeasible due to the assumed known control direction, the non-zero steady-state controller output, and unconsidered disturbances. To solve these problems, a novel data-driven adaptive WADC, consisting of control direction correction, PPD updating, one-step-ahead weighted predictive control, is proposed, moreover, the stability of the closed-loop system considering disturbances is thoroughly analyzed. Finally, case studies with various disturbances are conducted to validate the proposed control strategy.

Observer-Based Incremental Predictive Control of Networked Multi-Agent Systems With Random Delays and Packet Dropouts

This brief addresses the cooperative output tracking control problem for a linear heterogeneous networked multi-agent system with random network-induced delays and packet dropouts in the feedback channel of each agent, which consists of one leader agent and multiple following agents. To compensate for adverse effects of those random communication constraints, an incremental networked predictive control scheme based on state observers is proposed. A necessary and sufficient condition is derived for the stability of the resulting closed-loop system, which is independent of random communication constraints. Experimental results on a networked multi-motor control test rig show the effectiveness and applicability of the proposed scheme, including a feature that zero steady-state output tracking errors can be achieved even for the case with plant-model mismatch.

High-quality Economic Growth under the Influence of Technological Innovation Preference in China: A Numerical Simulation from the Government Financial Perspective

China's economy has been transitioning from labor-driven and capital-driven at a stage of rapid growth to innovation-driven at a stage of high-quality development. In this paper, government's “technological innovation preference” (TIP) is introduced into the traditional neoclassical economic growth model which is Ramsey-Cass-Koopmans (RCK), as a factor affecting the utility of endogenous growth model with capital accumulation and technological innovation. Assumed that the government fiscal revenue is used for public and research spending, through which we can examine its impact on high-quality economic growth and transmission mechanism, as well as how TIP influences on the economy. Results indicate that the tax rates and the growth rates would be raised, while the proportion of public spending would fall if TIP enhanced by the government. Furthermore, though steady-state output level may be lower in short term, however, it may also achieve high-quality growth in long run.

Improved performance of perovskite solar cells using conjugated polymer-graphene oxide as the passivation material

Organic-inorganic hybrid perovskite solar cells (PSCs) have achieved power conversion efficiency (PCE) from 3.8% to 25.2% in recent years. However, the charge transport ability of the transporting layers and the quality of crystalline films limit further development of PSCs. To fabricate highly efficient PSCs, effective charge transport to electrodes through transporting layers is a necessary requirement. Suitable interface engineering is very critical because it can not only benefit the charge extraction and transport, but also effectively passivate the traps on the surface and grain boundary of the perovskite. It has been shown that the passivation layer for the perovskite plays a vital role in the performance of PSCs. The close fit between the charge transport layer and the perovskite layer is required to reduce the interfacial recombination and accelerate the carrier extraction and collection. Besides, the appropriate passivation layer has a potential impact on the crystallization and the morphology of the perovskite film. To achieve high-performance devices, it is crucial to design an effective passivation layer with appropriate nanomaterials. In this work, we synthesized poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene] (MOPPV) on few-layer graphene oxide (GO) by in situ polymerization at room temperature. MOPPV-GO can fully combine the advantages of the two materials. The novel nanocomposite MOPPV-GO is used as the ultra-thin passivation layer of PSCs, of which the structure is ITO/TiO2/(FAPbI3) x (MAPbCl3)1– x /MOPPV-GO/spiro-OMeTAD/Ag. Since the surface morphology of the perovskite layer would affect the performance of devices significantly, the perovskite films with and without the passivation layer by atomic force microscopy is found that the MOPPV-GO can facilitate the growth of perovskite crystal with larger grains and enhance the quality of perovskite films. The root mean square roughness values of the perovskite films with and without MOPPV-GO were evaluated to be 19.87 and 25.85 nm, justifying the improvement of the surface flatness of the perovskite film with the decoration of MOPPV-GO, which would enhance the contact and carrier transport between the hole transport layer and the perovskite layer. As a result, the PSCs with MOPPV-GO exhibited considerably low hysteresis indices (0.02) and showed a short circuit current density of 23.54 mA cm–1, an open circuit voltage of 1.09 V, and a fill factor of 76.46%, corresponding to a high power conversion efficiency of 19.73%. By contrast, the control PSCs without MOPPV-GO showed a high hysteresis index of 0.18, with a poor power conversion efficiency of 16.42%. Meanwhile, it is shown that the EQE curve of MOPPV-GO modified PSC is higher than that of unmodified devices, which is consistent with the experimental results of J-V curve. The steady-state power output of various devices in ambient conditions under continuous AM 1.5G illumination was tested, which shows excellent stability of the PSC with MOPPV-GO during the period of 1000 s, indicating the positive contribution of MOPPV-GO interlayer to the stability. This work could provide a new idea for the synthesis and application of graphene-based materials in solar cells.

On the dynamics of two photons interacting with a two-qubit coherent feedback network

The purpose of this paper is to study the dynamics of a quantum coherent feedback network composed of two two-level systems (qubits) driven by two counter-propagating photons, one in each input channel. The coherent feedback network enhances the nonlinear photon–photon interaction inside the feedback loop. By means of quantum stochastic calculus and the input–output framework, the analytic form of the steady-state output two-photon state is derived. Based on the analytic form, the applications on the Hong–Ou–Mandel (HOM) interferometer and marginally stable single-photon devices using this coherent feedback structure have been demonstrated.

Fading Channel Signal-to-Noise Ratio Limitation for Closed-Loop Stabilizability

Explicit communication channels in the feedback loop introduce new key elements such as channel input power, channel variable gain, channel bandwidth, additive channel noise, transmission rate, quantization, packet losses, etc. In this article, we propose a stationary signal-to-noise ratio (SNR) analysis for the fading channel model. The channel SNR can be connected with most communication issues such as channel input power, additive channel noise, and quantization noise. Recently, a power analysis has also been used to characterize for every instant the effect of packet losses and channel fading. Here, we propose an equivalent average channel model that preserves the first and second moments of a fading channel output in steady state. The proposed equivalency is stated initially in an open loop, and then, with the assumption of a plant model with a relative degree greater or equal to one, extended to the closed-loop feedback allowing a stationary SNR analysis. As a result, we can compute the fading channel SNR for closed-loop stabilizability limitation, and then consider the presence of disturbance and setpoint signals.

Analysis of a three-phase to seven-phase transformer under unbalanced input

In the recent past, multiphase power generation, power transmission, and multiphase drive system are the main focus of research due to their several advantages over existing three phase system. Multiphase drives have better performance over three-phase drives. A multiphase transformer is required at the input of a fixed frequency multiphase drive, rectifier circuit for HVDC applications and multiphase generation and transmission systems. This paper investigates an static three-to seven-phase conversion technique and presents a design of transformer and control strategy to analyze the effect of unbalanced supply on a three-phase to seven-phase transformer. The transformer presented in this paper takes three phase input and a seven-phase output is obtained at the secondary terminals. The paper also discusses input–output unbalancing. A complete design, analysis and simulation of the proposed transformer is presented and experimental validation is also reported in this paper. Experimental and simulation results show that the presented transformer can produce a seven-phase power from three-phase ac power. Input unbalance is reflected at the output of the transformer but is less than the input unbalance. It is also shown that seven-phase output is not produced if one phase of input is open and the transformer has more than three limbs for flux to flow. But a balanced seven-phase output in steady state is produced even in one phase open condition for a three limb core type transformer. A new definition of sequence components of an unbalanced seven-phase system is required for unbalancing study so it is also defined in this paper.

Solar Energy-Harvesting Buck–Boost Converter With Battery-Charging and Battery-Assisted Modes

In this article, a buck-boost converter is described which harvests energy from a solar cell and performs dc-dc conversion with only one inductor. If the harvested energy is larger than the system load, the buck-boost converter charges a battery with the residual energy, which is called the battery-charging mode. If system load is larger than the harvested energy, the load is supplied by both the harvested energy and the battery, which is called the battery-assisted mode. The optimum control scheme has been found to be the integral charging scheme for the maximized power efficiency (PE). The buck-boost converter implemented in a 180-nm complementary metal-oxide-semiconductor (CMOS) process operates at 97 kHz and shows the steady-state output ripple smaller than 25 mV with the maximum PE of 89.4% for 28-mW output power.

Stochastic resonance in a delay-controlled dissipative bistable potential for weak signal enhancement

This paper attempts to investigate the stochastic resonance (SR) phenomenon in a delay-controlled dissipative bistable potential with time-delayed feedback under the action of harmonic excitation and additive noise by using small delay approximation theory and signal-to-noise ratio (SNR) theory. The time delay and feedback strength are able to adjust the potential shapes precisely by fusing potential parameters. Moreover, the steady-state probability distribution (SPD) and output SNR are derived to demonstrate that time-delayed feedback is able to control and improve the SR for enhancing the useful signal embedded in a noisy signal, where moderate time delay and feedback strength can maximize the output SNR. Therefore, a controlled SR method via time-delayed feedback is proposed to enhance useful signals embedded in mechanical signals for mechanical fault diagnosis, where the widely used frequency-shifted and rescaling transform is used to preprocess large-parameter vibration signals of double row cylindrical bearings. The experimental results indicate that the controlled SR method via time-delayed feedback can enhance the useful signal embedded in the vibration signal from double row cylindrical bearings where its amplitude is amplified up to tenfold than that in the envelope spectrum of raw signal.

An Agile Supply Modulator With Improved Transient Performance for Power Efficient Linear Amplifier Employing Envelope Tracking Techniques

This article presents an agile supply modulator with optimal transient performance that includes improvement in rise time, overshoot and settling time for the envelope tracking supply in linear power amplifiers. For this purpose, we propose an on-demand current source module: the bang–bang transient performance enhancer (BBTPE). Its objective is to follow fast variations in input signals with reduced overshoot and settling time without deteriorating the steady-state performance of the buck regulator. The proposed approach enables fast system response through the BBTPE and an accurate steady-state output response through a low switching ripple and power efficient dynamic buck regulator. Fast output response with the help of the added module induces a slower rise of inductor current in the buck converter that further helps the proposed system to reduce both overshoot and settling time. This article also introduces an efficient selective tracking of envelope signal for linear PAs. To demonstrate the feasibility of the proposed solution, extensive simulations and experimental results from a discrete system are reported. The proposed supply modulator shows 80% improvement in rise time along with 60% reduction in both overshoot and settling time compared to the conventional dynamic buck regulator-based solution. Experimental results using the LTE 16-QAM 5 MHz standard shows improvement of 7.68 dB and 65.1% in adjacent channel power ratio (ACPR) and error vector magnitude (EVM), respectively.

Deletion of a conserved Gata2 enhancer impairs haemogenic endothelium programming and adult Zebrafish haematopoiesis

Gata2 is a key transcription factor required to generate Haematopoietic Stem and Progenitor Cells (HSPCs) from haemogenic endothelium (HE); misexpression of Gata2 leads to haematopoietic disorders. Here we deleted a conserved enhancer (i4 enhancer) driving pan-endothelial expression of the zebrafish gata2a and showed that Gata2a is required for HE programming by regulating expression of runx1 and of the second Gata2 orthologue, gata2b. By 5 days, homozygous gata2aΔi4/Δi4 larvae showed normal numbers of HSPCs, a recovery mediated by Notch signalling driving gata2b and runx1 expression in HE. However, gata2aΔi4/Δi4 adults showed oedema, susceptibility to infections and marrow hypo-cellularity, consistent with bone marrow failure found in GATA2 deficiency syndromes. Thus, gata2a expression driven by the i4 enhancer is required for correct HE programming in embryos and maintenance of steady-state haematopoietic stem cell output in the adult. These enhancer mutants will be useful in exploring further the pathophysiology of GATA2-related deficiencies in vivo.

Polynomial interpolation for inversion-based control

To help to achieve high performances in the regulation of linear scalar (SISO) nonminimum-phase systems, an inversion-based (feedforward) control method is proposed. The aim is designing an inverse input to smoothly switch from a current, arbitrary, steady-state regime to a new, future, desired steady-state output. A new-found polynomial basis solves the related interpolation problem to join the current output to the future one while ensuring the necessary or desired smoothness. The (interpolation) transition time can be minimized in order to optimally reduce the delay with which the desired output occurs. By applying a behavioral stable inversion formula to the overall smoothed output, detailed expressions of the inverse input are finally derived. A simulation of a flexible arm rotating in the horizontal plane exemplifies the presented method.

Nonlinear analysis of axially loaded piezoelectric energy harvesters with flexoelectricity

In this work, nonlinear electromechanical models for energy harvesters based on axially preloaded piezoelectric beams incorporating flexoelectric effect are presented. Depending on the amplitude of the applied axial load, the proposed energy harvester could operate in either prebuckling or postbuckling configuration. According to the theory of flexoelectricity and the Hamilton's principle, the nonlinear electromechanical coupling equations of the proposed energy harvesters under base excitations are derived. For a simply-supported piezoelectric beam, the expression of the static buckling load is analytically determined. Then, for energy harvesters in the prebuckling and postbuckling configurations, we obtain the discrete nonlinear governing equations by employing the Galerkin's method. These coupling equations are solved numerically by the Runge–Kutta method. Case studies are provided to show the steady-state output voltage and power of the energy harvesters. Results indicate that the frequency response curves show a typical hardening nonlinear behavior in the prebuckling configuration and a softening nonlinear behavior in the postbuckling configuration. Such nonlinear behaviors of energy harvesters imply a wider frequency operation bandwidth of the proposed energy harvesters. We also find that the energy harvesters utilizing flexoelectricity have a better performance than those based on piezoelectricity in the prebuckling configuration. Moreover, we examine the influences of resistive load, mechanical damping coefficient and the amplitude of the base excitation on the performance of the energy harvesters as well as the size effect due to flexoelectricity. It is also interesting to observe that both intrawell and interwell oscillations of the energy harvesters could occur in the postbuckling configuration. This work provides an efficient route to design energy harvesting systems at micro- and nano-scales with enhanced performance.

Malaysia: 'Crouching Tiger, Hidden Dragon'

This paper metaphorically suggests that Malaysia could have been the 5th Asian Tiger if it were able to discover its special hidden talents as the idiom from the Chinese mythology “Crouching Tiger, Hidden Dragon” infers. Malaysia’s astounding economic track record (1985-96) underpinned by tamed inflation and high future prospects fell short of expectations in the late 1990s. Malaysia’s autocratic leaders and their instability-inflicting policies augmented uncertainty and undermined any potential recovery efforts in the aftermath of the homegrown Asian crisis of 1997-98. As a result, Malaysia’s promising outlook had abruptly shifted from being a model for the future to Asian myth. Malaysia’s GDP contracted mindboggling -7.4% in 1998 after averaging 9.2% in the period of 1992-96. The unthinkable shrinkage in the steady state output amounted to a loss of about $30 billion, the country’s GDP declined from $101 billion in 1996 to $72.2 billion in 1998. Malaysian people become a lot poorer after the crisis; the per capita income was $4,797 in 1996 as opposed to $3,264 in 1998, a decline of $1,533 in per capita income. Malaysia managed to escape the severe impacts of the near global financial meltdown with a minor dent; unlike the contraction observed in 1998 (-7.4%), Malaysia’s GDP dropped from 6.3% to 4.83% (2007-08) before contracting -1.51% in 2009. Despite the transparent and open economy (ranked 16th place in 2008 GCI) plus fast rise in the Human Development Index ranking (61st out of 190 countries in 2018), Malaysia’s heavy reliance on exports and its elongated addiction to the U.S. dollar made it become more prone to financial, currency, trade, and economic crises. The propagation of contemporaneous crises since the late 1990s have distinctly proved that Malaysia is hardly immune to shocks resulting from the slower economic growth in China and monetary normalizations in Europe and the U.S. which are causing interest rates to rise and exchange rate pressures to increase. Although the remarkable transition of Malaysia into a middle-income country was rather easy fostered by unusually favorable macroeconomic environment, but it seems to have been stuck in the middle-income trap and the next major economic leap to achieve a high-income status will require so much more than cheap labor and “mobilization of resources” based on “perspiration rather than inspiration”. Malaysia is struggling to figure out how to develop comprehensive skills which are essential to support future economic growth. Another problem is that educational institutions in Malaysia are not well aligned with industries to meet their demands; furthermore, a seamless coordination as well as collaboration between them is missing. Accordingly, a decade after the 2008 global financial crisis, Malaysia ranks 44th in pillar 4 (Health and Primary Education) and 41st in pillar 5 (Higher Education and Training). Malaysia also ranks 43rd in pillar 9 (Technological Readiness) due to a lack of lifelong learning programs, weakness in Technical and Vocational Education and Training (TVET), and unready for disruptive technologies. Without significant improvements in these, Malaysia will remain in the middle-income trap.

Time-Domain Modeling and Analysis of Switched-Capacitor Converters

This article proposes time-domain modeling and analysis of switched-capacitor converters (SCCs) by homogenizing the state-space model, resulting in a closed-form expression of the output voltage as a function of time without requiring discretization and subsequent numerical solution. The proposed technique facilitates obtaining the steady-state output voltage at any arbitrary time within a period, rather than at one discrete time at the beginning or end of the clock period. Circuit-level simulations for various SCC topologies, viz. , series–parallel (SP), ladder (LD), Fibonacci (FB), and Dickson (DK), show excellent agreement of the time-domain behavior as well as the equivalent resistance of the converter with the proposed technique. The proposed technique gives more than an order-of-magnitude improvement in simulation time. Experimental data for SP and LD topologies have been used to validate the accuracy of the proposed technique.

Monetary Policy When Preferences Are Quasi-Hyperbolic

We study discretionary monetary policy in an economy where economic agents have quasi-hyperbolic discounting. We demonstrate that a benevolent central bank is able to keep inflation under control for a wide range of discount factors. If the central bank, however, does not adopt the household’s time preferences and tries to discourage early consumption and delayed-saving, then a marginal increase in steady state output is achieved at the cost of a much higher average inflation rate. Indeed, we show that it is desirable from a welfare perspective for the central bank to quasi-hyperbolically discount by more than households do. Welfare is improved because this discount structure emphasizes the current-period cost of price changes and leads to lower average inflation. We contrast our results with those obtained when policy is conducted according to a Taylor-type rule.

Coordinated Optimal Control of Multiple Reactive Power Devices at Different Voltage Levels in UHVDC Near Zone

Affected by different steady-state reactive power output ratios among generators, capacitors and other reactive devices in the end-to-end power grid, voltage collapse may occur due to the failure of the receiving-end AC system, and the problem of voltage stabilization in multi-DC feed systems is particularly common. For suppressing voltage collapse, sufficient dynamic reactive power support is an effective measure, and there are some differences in the dynamic support effect of different reactive power sources. The dynamic reactive power response of the generator and its reactive power margin are two important factors affecting the coordination and optimization of the reactive power of the generator. The comprehensive evaluation index is adopted to optimize the sequencing of the reactive power output of the generator near the DC drop point. A coordinated control method of dynamic and static reactive power for DC near-point systems at different voltage levels is proposed. By controlling the steady-state reactive power output ratio between multiple reactive devices, the node voltage is maintained near the target value, and reactive power control schemes at different voltage levels can be given to meet load changes. Finally, taking the actual situation of Central China Power Grid as an example, the results of different reactive voltage control strategies are compared and analyzed, which proves that the coordinated control strategy of multiple reactive power devices can significantly improve the stability of the receiving grid voltage.

Ribosome Flow Model with Different Site Sizes

We introduce and analyze two general dynamical models for unidirectional movement of particles along a circular chain and an open chain of sites. The models include a soft version of the simple exclusion principle, that is, as the density in a site increases the effective entry rate into this site decreases. This allows one to model and study the evolution of “traffic jams" of particles along the chain. A unique feature of these two new models is that each site along the chain can have a different size. Although the models are nonlinear, they are amenable to rigorous asymptotic analysis. In particular, we show that the dynamics always converges to a steady state, and that the steady-state densities along the chain and the steady-state output flow rate from the chain can be derived from the spectral properties of a suitable matrix, thus eliminating the need to numerically simulate the dynamics until convergence. This spectral representation also allows for powerful sensitivity analysis, i.e., understanding how a change in one of the parameters in the models affects the steady state. We show that the site sizes and the transition rates from site to site play different roles in the dynamics, and that for the purpose of maximizing the steady-state output (or production) rate the site sizes are more important than the transition rates. We also show that the problem of finding parameter values that maximize the production rate is tractable. We believe that the models introduced here can be applied to study various natural and artificial processes including ribosome flow during mRNA translation, the movement of molecular motors along filaments of the cytoskeleton, pedestrian and vehicular traffic, evacuation dynamics, and more.

Enhancement of Power Quality in Domestic Loads Using Harmonic Filters

This study deals with the mitigation of current harmonics, which is primarily important to alleviate power quality problems in modern times. Current harmonics produced by different widely used loads have been evaluated and related parameters have been tabled. Using the data obtained, a non-linear load was modelled to serve as the test load. Different mitigation solutions and techniques were studied to select an appropriate filter design for domestic single-phase application. The Active Power Filter (APF)'s steady-state and dynamic output was evaluated with reference current extraction techniques like PQ and SRF theories in Simulink. For a fair comparison, various parameters related to the filter design were kept identical between the tests conducted; and to test the dynamic performance, a highly inductive load was connected halfway through simulation. The reactive power compensation offered by the filter was studied by using various waveforms and parameters are investigated and tabulated. The study was carried out to identify a reference current extraction technique that yields the best performance and understand the implementation of the same to identify inherent issues that can sometimes be overlooked because of their simplicity and ease of implementation. The performance of two commonly used reference current extraction techniques were analyzed by subjecting it to highly non-linear and highly inductive loads that were modelled based on various loads that were analyzed.

Anti-windup Disturbance Rejection Control Design for Sampled Systems with Output Delay and Asymmetric Actuator Saturation Constraint

A novel anti-windup disturbance rejection control design is proposed for industrial sampled systems with output delay and asymmetric actuator saturation constraint. To deal with the asymmetric actuator saturation constraint as often encountered in engineering practice, the input constraint is equivalently transformed into a symmetric actuator saturation constraint for the convenience of control design. Based on the equivalent system description, a model-based extended state observer (MESO) is designed to simultaneously estimate the system state and disturbance, which becomes an anti-windup compensator when the actuator saturation occurs. In order to compensate for the delay mismatch in MESO, a generalized predictor is utilized to estimate the undelayed system output. Accordingly, a pole placement approach is given to design the feedback controller. A set-point pre-filter is designed to ensure no steady-state output tracking error, in terms of a desired transfer function for the set-point tracking. Based on the delay-dependent sector condition and generalized free-weighting-matrix (GFWM), a sufficient condition guaranteeing the stability of the closed-loop system is established in terms of linear matrix inequalities (LMIs). An illustrative example from the literature is used to demonstrate the effectiveness and advantage of the proposed control method.