Two-stage Control Research Articles

Fringe-Projection-Based Normal Direction Measurement and Adjustment for Robotic Drilling

In a large-scale structure assembly, a highly accurate normal direction measurement for robotic drilling is required. However, the robustness and accuracy of the existing normal direction measurement method with a range sensor would dramatically decrease for a high-curvature surface, such as the surface edge, due to the low resolution of the range sensor. To this end, a high-resolution fringe projection sensor is proposed to improve the measurement robustness and accuracy. In this method, different from the control scheme design with a reconstructed three-dimensional point cloud in fringe projection profilometry, which involves a high computational complexity, a novel two-dimensional phase-map-based two-stage control scheme, including coarse and refined normal direction adjustments, is designed to improve the robustness and accuracy. The coarse normal direction adjustment uses a phase map to estimate the normal direction, which is used to synthesize a position-based control scheme, leading to high robustness; the refined normal direction adjustment uses a phase map to synthesize an image-based control scheme, resulting in high accuracy. The proposed method is validated by simulations and experiments, which indicate that the proposed method is effective.

Cost-Effectiveness Study of One-Stage Treatment of Chronic Osteomyelitis with Bioactive Glass S53P4.

This study was set up to evaluate the costs of a one-stage treatment of chronic osteomyelitis using bioactive glass S53P4 versus a two-stage treatment using gentamicin-loaded PMMA beads. Furthermore, a cost-effectiveness analysis was performed from a hospital’s perspective together with the evaluation of clinical outcome. A treatment group (n = 25) receiving one-stage surgery with bioactive glass was retrospectively compared with a two-stage control group (n = 25). An assessment was made of all costs included from first outpatient visit until one year after treatment. Bootstrap simulation and sensitivity analyses were performed. The primary endpoint was cost-effectiveness with clinical outcome as the secondary endpoint. The base case analyses shows dominance of the one-stage treatment with bioactive glass S53P4 due to lower costs and a better clinical outcome. Sensitivity analyses confirm these findings. This study is the first in its kind to show one-stage treatment of chronic osteomyelitis with bioactive glass S53P4 to be cost-effective.

Regularization methods for high-dimensional sparse control function models

Traditional penalty-based methods might not achieve variable selection consistency when endogeneity exists in high-dimensional data. In this article we construct a regularization framework based on the two-stage control function model, so called the regularized control function (RCF) method, to estimate important covariate effects, select key instruments, and replace the CF-based hypothesis test with variable selection to identify truly endogenous predictors. Under appropriate conditions, we establish theoretical properties of the RCF estimators, including the consistency of coefficient estimation and model selection. Simulation results confirm that the RCF method is effective and superior to its main competitor, the penalized least squares (PLS) method. The proposed method also provides insightful and interpretable results on a real data analysis.

Design optimization and two-stage control strategy on combined cooling, heating and power system

Combined cooling, heating and power (CCHP) is a promising energy supply technology to improve the overall energy utilization efficiency. It provides an opportunity to achieve low or zero carbon energy supply with tactful control strategies. In this study, the two-stage model predictive control (MPC) strategy with combined rolling optimization and real-time adjustment is demonstrated to be highly effective for CCHP system application. In most previous studies, the MPC strategy was performed under a given design configuration, which was not optimally constructed. In real practice, the system configuration, the installed equipment capacity, and the control strategy altogether affect the CCHP system performance. Both the system design optimization and the two-stage MPC strategy were conducted in our numerical analysis through a hypothetical case study. Our simulation results illustrated that the equipment selection affects the running cost of the CCHP system, and the desirable solution is well linked to the building load profile. The effect of forecasting error on the two-stage MPC was also investigated. The results showed that although the two-stage MPC strategy is able to give better performance than the traditional strategies in most cases, poor performance may still exist when the load forecasting error is more than 8.8%.

Seven-Level Active Power Filter Based on a Novel H-Bridge Power Topology Structure

This paper proposes a novel seven-level power topology, that increases the number of output levels by using fewer power switches and capacitors compared to the traditional seven-level topology. Moreover, the working mechanism of the proposed topology and its implementation method are given. Furthermore, a two-stage capacitor-voltage equalization control strategy with overall control and independent control is proposed. Finally, the proposed topology is applied to the active power filter system, and simulations and experimental research of two types of working conditions are performed. The results verify the effectiveness and feasibility of the new topology and control strategy.

Adaptive Visual Regulation of Wheeled Mobile Robots: a Switching Approach

This paper deals with the visual regulation problem of wheeled mobile robots (WMRs) in the presence of uncalibrated camera-to-robot parameters and unknown image depth. A two-stage controller is designed by using a switching approach. Specifically, in the first stage, an invariant-manifold-based adaptive controller is presented to bring the lateral error and angular error within an arbitrarily small neighborhood of zero; in the second stage, the longitudinal error is regulated by employing a proportional controller. Utilizing the Lyapunov stability analysis, the exponentially bounded stability of the closed-loop system is proved. Both simulation and experimental results are presented to validate the effectiveness of the proposed approach.

Two-stage voltage control strategy for PV plants based on variable droop control

ABSTRACTVoltage violation is an important factor that restricts grid-connected photovoltaic system. The utilization of PV plant’s reactive power capability is an effective measure to mitigate voltage violation. This paper proposes two-stage voltage control strategy to enhance the voltage support capability of photovoltaic grid-connected system. In first stage, adaptive gains are set according to the maximum reactive capacity of each PV plant in order to distribute reactive power among PV plants more reasonably, avoiding certain PV plants operating in the limit state for a long time. In second stage, when the reactive power capacity is insufficient, the priority of active power curtailment for each PV plant is calculated in real time. Active power curtailment control will be performed in PV plants with high priority to released more reactive power capacity for voltage support. The simulation results carried out by PSCAD/EMTDC software demonstrated that this strategy can effectively solve the voltage violation problem. Meanwhile, the proposed strategy not only can exploit reactive capacity of each PV plant as much as possible to avoid certain PV plants operating in the limit state for a long time, but also can reduce the amount of active power curtailment when reactive power adequacy is insufficient.

Evaluating energy supply service reliability for commercial air conditioning loads from the distribution network aspect

The limited amount of dispatching flexibility has encouraged the development and implementation of demand response in the distribution system. Commercial air conditioning loads are promising demand response resources and tend to have greater potential for centralized regulation. From the perspective of distribution networks, evaluating the reliability of energy supply services for air conditioning loads should be of much concern because reliable services would directly affect the customers’ tendency to demand response. However, traditional load reliability evaluation does not fully explore the fact that the energy supply processes of air conditioning loads can be flexible. Modeling the energy demands as flexible loads, a reliability assessment algorithm for commercial air conditioning loads is proposed for distribution systems in this paper. The “loss of load” event is innovatively defined considering customer preferences. Novel systematic indices are established that are specialized for describing the reliability of energy supply services. Afterward, a two-stage control strategy is proposed considering the comfort requirements of customers, which would affect reliability performance. The first stage optimizes the operating state of the air conditioning system internal equipment collaboratively, while the second stage sacrifices some comfort for sufficient utilization of the thermal self-storage capacity and load rebound suppression. Finally, the proposed method is validated in a standard test system with voltage violation risks. The results demonstrate the impacts of different control strategies on the reliability performance of commercial air conditioning loads. Analysis drawn from the sensitivity of load reliability indices can assist distribution system operators in coordinating energy supply reliability and dispatching requirements.

Design and test of a new two-stage control scheme for SMES-battery hybrid energy storage systems for microgrid applications

This paper proposes a novel control scheme for a hybrid energy storage system (HESS) for microgrid applications. The proposed two-stage control method is used to control the HESS to stabilize a microgrid’s voltage level and extend battery service lifetime during the coupling/decoupling of a microgrid from the main power grid. The conventional HESS control method (the filtration method) is not suitable to compensate for a microgrid’s power demand when it is decoupled from the main grid. This research focuses on using a superconducting magnetic energy storage (SMES) and battery HESS to assist with the microgrid coupling/decoupling process. To compensate for the instantaneous high power demand during decoupling, the battery will need to rapidly discharge. Moreover, batteries have difficulty supporting high discharging rates, which results in ineffective compensation of the power demand. In this paper, the high power density of the SMES system combined with the high energy density of a battery shows good performance on stabilizing microgrid bus voltage during the decoupling process. A novel energy management method for the HESS is proposed to improve the battery performance when the microgird coupled/decoupled from main grid. The sizing design is simplified based on the control methodology. Moreover, a SMES and battery HESS experimental platform is built to validate the proposed control methodology and its reliability.

An Iterative Control Method for Voltage Source Converters to Eliminate Uncharacteristic Harmonics Under Unbalanced Grid Voltages for High-Power Applications

When voltage source converters (VSCs) are subjected to disturbances or faults, they may not be able to perform as per the desired control objective, which presents a significant challenge to system operations. One well-known situation is when the converter is subjected to an unbalanced ac voltage with a negative-sequence fundamental voltage injection. Under this condition, the VSC may generate undesired double-frequency ripples at the dc voltage and uncharacteristic harmonics at the ac current. This paper presents a new two-stage control method suitable for VSCs used in high-power applications. In the first stage, a simple proportional controller is used to suppress overshoots during the transients. Then, the iterative controller is activated to finely adjust the modulation indices and firing angles of the converter to compensate the uncharacteristic harmonics. To verify the performance of the proposed control method, the control algorithms are implemented in a 10 MVA VSC system and validated by means of PSCAD/EMTDC and hardware-in-the-loop simulations. The results show that the state variables converge within a few iterative steps, and the transient response is sufficiently fast. The proposed method is shown to perform better than conventional methods for attenuating and eliminating the uncharacteristic dc and ac harmonics caused by imbalances in the grid voltage.

Visual Experimental Study on Gradation Optimization of Two-Stage Gravel Packing Operation in Unconventional Reservoirs

During the development of unconventional reservoirs with high sand production rate and fine silt content such as heavy oil and hydrate reservoirs, silt sand blockage problem is a serious issue. A two-stage gravel-packing sand control technique is applied to solve the silt sand blockage now. However, traditional experiments on this technique could not obtain the dynamic distribution law of intrusive sand in the gravel pack. In this study, a new visualization experiment based on hydrodynamic similarity criterion for studying particle blockage in gravel packs was conducted. Real-time monitoring of sand particle migration in the gravel pack could be achieved. Also, the stable penetration depth and the distributing disciplinarian of invaded particles could be determined. The results show that when the gravel-to-sand median size ratio of gravel bed I is less than five, the sand bridge can be formed at the front end of the gravel pack. This could prevent sand from further intruding. As the grain size of gravel bed II is increased, the flow velocity is reduced. Thus, the sand invading into gravel bed II tends to settle at the interface. A large amount of sand intrusion can happen to gravel pack II when the pore filling front breaks through the gravel bed I.

Two-stage model free fuzzy adaptive controller for multiplicative disturbance rejection

Two-stage model free fuzzy adaptive controller for multiplicative disturbance rejection

Finite set model predictive control method for quasi‐Z source inverter‐permanent magnet synchronous motor drive system

In this study, a finite set model predictive control method is proposed for the quasi-Z source inverter-permanent magnet synchronous motor drive system. In the proposed method, the control variables of quasi-Z source network and motor are controlled uniformly, which can avoid the conflicts between the shoot-through duty cycle and the inverter modulation coefficient during the dynamic adjustment process in traditional two-stage control method. Due to the particularity of the motor connected to the quasi-Z source inverter, a power compensation control method is used to obtain the inductor current reference value. Whether the shoot-through vector is chosen as the optimal vector is determined by the inductor current, and the influence of undershoot phenomenon of capacitor voltage, which results from the non-minimum phase characteristics of quasi-Z source inverter, is avoided. Steady-state, dynamic, and input voltage dip experiments are performed on a quasi-Z source inverter-permanent magnet synchronous motor drive system. The experimental results verify the feasibility of the proposed predictive control method. Besides, compared with traditional two-stage control method, the proposed method has quicker response speed and stronger anti-disturbance ability.

A Two-Stage Control Strategy of Large-Scale Residential Air Conditionings Considering Comfort Sensitivity of Differentiated Population

Residential air conditionings (RACs) can be seen as one of the important flexible demand resources controlled to provide balance services for the power system due to their spatial thermal storage feature. However, such control on RACs will bring out the negative impact on the comfort level of residents inevitably, affecting their proactivity in demand response (DR). So, a novel two-stage control model of large-scale RACs is proposed to participate in DR considering different comfort sensitivity of various residents. The comfort sensitivity index is developed in terms of daily operation time and daily power consumption per area of RACs, classified by K-means clustering. Besides, the DR potential of RACs is established with the adjusted temperature setpoint, where the temperature setpoint is determined by the comfort sensitivity index. Moreover, a two-stage control model of large-scale RACs is proposed comprised of load response and recovery, where the corresponding control strategies at each stage are proposed. Simulations of the proposed method have been performed on residential 20,000 RACs to validate its effectiveness in Changzhou, China. The outcome reveals that the strategies could maximize the DR potential of RACs and ensure the stable recovery of RACs under the premise of meeting the comfort demand of differentiated population.

Attitude Tracking Control Reconfiguration for Space Launch Vehicle With Thrust Loss Fault

The thrust loss fault of the space launch vehicle is quite different from that of ordinary actuator efficiency loss. Focusing on the attitude tracking control problem of the launch vehicle with thrust loss fault, the special impacts of that fault on the control system are explored, and a two-stage control reconfiguration strategy based on the cascaded pseudo-inverse allocation method and the neuron adaptive gain scheduling method is proposed for faults with different severity. Meanwhile, a practical reconfigurability analysis for the faulty system based on the control state reachability is presented for some representative fault scenarios. Based on the nonlinear dynamical model of the faulty system, lots of numerical simulations under various fault scenarios are finally carried out. The results indicate that the designed control reconfiguration strategy not only can effectively deal with the thrust loss fault with high practicability but also is easy to implement.

Two-Stage Control of Endpoint Temperature for Pebble Stove Combustion

Two-Stage Control of Endpoint Temperature for Pebble Stove Combustion

Labor migration and impact of remittances on poverty and income inequality: evidence from estate sector of Sri Lanka

There is a continuing debate over the impacts of migration on the developing nations despite the ever-increasing size of internal and international remittances. Moreover, a little attention has been paid to analyze the impact of these financial transfers on poverty and inequality of those countries. This study, using a nationally representative sample, assessed the impacts of migration and remittances on poverty and inequality of estate sector households of Sri Lanka. A multinomial logit-ordinary least squares two-stage selection control model and a simulation analysis were used to estimate the impact of migration and remittances on poverty and inequality. Results reveal that internal and international remittances reduce poverty incidence by 2.14% and 2.32%, depth of poverty by 1.33% and 0.98%, and severity of poverty by 0.63% and 0.48%, respectively. Results further suggest that income inequality slightly decreased due to internal and international remittances. Moreover, the findings support a growing view in the literature that migration is a livelihood strategy and it helps in alleviating poverty.

Efficient production of heat-stable antifungal factor through integrating statistical optimization with a two-stage temperature control strategy in Lysobacter enzymogenes OH11

BackgroundHeat-stable antifungal factor (HSAF) is a newly identified broad-spectrum antifungal antibiotic from the biocontrol agent Lysobacter enzymogenes and is regarded as a potential biological pesticide, due to its novel mode of action. However, the production level of HSAF is quite low, and little research has reported on the fermentation process involved, representing huge obstacles for large-scale industrial production.ResultsMedium capacity, culture temperature, and fermentation time were identified as the most significant factors affecting the production of HSAF and employed for further optimization through statistical methods. Based on the analysis of kinetic parameters at different temperatures, a novel two-stage temperature control strategy was developed to improve HSAF production, in which the temperature was increased to 32 °C during the first 12 h and then switched to 26 °C until the end of fermentation. Using this strategy, the maximum HSAF production reached 440.26 ± 16.14 mg L− 1, increased by 9.93% than that of the best results from single-temperature fermentation. Moreover, the fermentation time was shortened from 58 h to 54 h, resulting in the enhancement of HSAF productivity (17.95%) and yield (9.93%).ConclusionsThis study provides a simple and efficient method for producing HSAF that could be feasibly applied to the industrial-scale production of HSAF.

A Novel Two-Stage Photovoltaic Grid-Connected Inverter Voltage-Type Control Method with Failure Zone Characteristics

This paper investigates how to develop a two-stage voltage-type grid-connected control method for renewable energy inverters that can make them simulate the characteristics of a synchronous generator governor. Firstly, the causes and necessities of the failure zone are analyzed, and thus the traditional static frequency characteristics are corrected. Then, a novel inverter control scheme with the governor’s failure zone characteristics is proposed. An enabling link and a power loop are designed for the inverter to compensate fluctuations and regulate frequency automatically. Outside the failure zone, the inverter participates in the primary frequency regulation by disabling the power loop. In the failure zone, the droop curve is dynamically moved to track the corrected static frequency characteristic by enabling the power loop, resisting the fluctuation of grid frequency. The direct current (DC) bus voltage loop is introduced into the droop control to stabilize the DC bus voltage. Moreover, the designed dispatch instruction interface ensures the schedulability of the renewable energy inverter. Finally, the feasibility and effectiveness of the proposed control method are verified by simulation results from MATLAB (R2016a).

Space tether deployment with explicit maximum libration angle constraint and tension disturbance

This paper investigates the deployment control problem of tethered space systems subject to an explicit constraint of maximum libration angle and disturbance of tether tension. A two-stage control procedure is developed to design a simple and effective tension control law that is capable of limiting the magnitude of libration angle and suppressing the tension disturbance in the tether deployment process. First, the deployment reference trajectory is designed by a modified barrier Lyapunov function with an explicit constraint on the maximum libration angle. Then, a disturbance observer-based tension control law is developed to track the reference trajectory with the consideration of tension disturbance. Stability analysis of the controller shows that the estimate and tracking errors are bounded to desired ranges. Simulation results demonstrate the proposed simple tension control law is effective and robust in restricting the maximum amplitude of libration angle and suppressing tension disturbance, while guaranteeing a stable deployment without tether slack.