Combined Control Method Research Articles

On the Effect of Combination of Statistical and Judgemental Stock Control Methods

Stock control is the most important aspect in an inventory system. It determines the safety stock in order to ensure that products are readily available when the customers require them. The decision makers in organizations tend to rely on software solution in obtaining stock control solutions since they have to manage a massive number of Stock Keeping Units (SKUs). However, managers intervene in the system and use their judgement to adjust or decide on various quantitative elements. This research discusses the effects of combination of stock control methods. An extended database of approximately 1,800 SKUs from an electronics company is analyzed. Then, a simulation experiment is performed in order to evaluate in a dynamic fashion what are the effects of applying combined stock control methods. The findings indicate that the combined method of stock control seems to improve the performance of the inventory system, especially in reducing inventory investment.

Spoilage by Alicyclobacillus Bacteria in Juice and Beverage Products: Chemical, Physical, and Combined Control Methods

AbstractAlicyclobacillus is a genus of spoilage bacteria causing contamination of juices and other beverage products that cannot easily be contaminated by other microbes because of their high acid contents. During the last 4 decades since the first species of Alicyclobacillus was isolated in 1967, Alicyclobacillus has become a major concern to the global juice and beverage industries, and many promising methods have been developed and applied to control them. After introducing the history and general characteristics of Alicyclobacillus, as well as their heat resistance and spoilage, this review focuses on the control methods against Alicyclobacillus, including chemical and physical methods and combined methods. All these control methods show inhibitory or killing effects against Alicyclobacillus to some extent and, moreover, some of them have been put to use in the juice and beverage industries for decades and shown to be quite effective, although further developments can be achieved and new methods are constantly being established and investigated. Although it is difficult to compare the effects with one another among these methods because of the different experimental conditions in different reports, some of them, such as the treatments of nisin and high hydrostatic pressure, are well studied and proved to have extensive application prospect. The inhibitory factors, test strains and media, and especially the detailed experimental conditions and main results of these control methods are summarized here. The limitations of some methods mainly relating to the changes of products’ sensory qualities are also presented.

Resonance Damping and Harmonic Suppression for Grid-Connected Current-Source Converter

Due to the inductor-capacitor (LC) filter, a pulsewidth-modulation (PWM) current-source converter may experience LC resonance. The resonance can be excited by system harmonics either from the PWM process or from the grid voltage distortions and hence results in the line current distorted. In this paper, feedback controls using different variables in the LC filter are first investigated and comprehensively analyzed. It is shown that the inductor-voltage feedback or the capacitor-voltage feedback can damp the current oscillations by increasing the damping ratio, while the inductor-current feedback or the capacitor-current feedback is able to suppress low-order harmonics by raising the resonance frequency. On this basis, a group of combined variable feedback control methods is presented by combining the feedbacks of the inductor/capacitor current and the inductor/capacitor voltage. Thus, not only the current oscillations can be damped, but also the low-order harmonics can be suppressed. Therefore, the line current waveform is improved, and the system performance can be flexibly optimized. A practical design method for feedback gains is also presented in this paper. Finally, the simulation and experimental results verify the feasibility and validity of the proposition.

2C31 BILATERAL TELEOPERATION CONTROL BASED ON SCATTERING AND VIRTUAL DAMPING(The 12th International Conference on Motion and Vibration Control)

This paper proposes a new bilateral control method of Single Master and Single Slave (SMSS) Tele-robot system. In this strategy, we propose a combination control method between PD and Scattering and Virtual Damping parameters to improve the tracking performance and transparency of Tele-robot, the reflecting force from slave side will be stable. Using Lyapunov technique, we can achieve the global stability of the control law. The achievement results of the proposed method are shown with the transparency improvement such as position and force between both sides of the Tele-robot system in two cases: the slave moves without any contact and the slave moves in contact with the environment. The simulation results showed the effectiveness of our proposed control method.

Control for Dc-Bus Voltage Using Grid Voltage Feed-Forward and Crowbar Circuit

The DC bus voltage is key variable for the operation of converter system in a wind power system. When grid voltage drops, a control of the DC bus voltage is needed to keep the smoothness of DC bus voltage for avoiding generator cutting off grid. A combined control method based on the grid voltage information feedforward with a crowbar circuit is proposed for a direct-drive wind power system in the paper. The unbalanced energy of the DC bus can be unleashed by the crowbar circuit during the dropping of grid voltage. At the same time, the output power of motor-side converter can be controlled to decrease according to the grid-side voltage information, and the mechanical speed of wind turbine and generator can be suppressed by the pitch angle regulation when the output power reduces. Thus, the DC-bus voltage can keep smooth. Results based on Matlab/Simulink simulation shows that this method not only improves dynamic response performance of DC bus voltages control, but also reduces the action time of crowbar circuit. It is benefit to the ability of the wind power system riding through the grid fault.

A combined fault ride-through and power smoothing control method for full-converter wind turbines employing Supercapacitor Energy Storage System

As the wind power installations are increasing in number, Wind Turbine Generators (WTG) are required to have Fault Ride-Through (FRT) capabilities. Lately developed grid operating codes demand the WTGs to stay connected during fault conditions, supporting the grid to recover faster back to its normal state. However, forcing a WTG to remain connected during a grid fault has consequences on the conventional protection devices, as they might become blind to over-currents and short circuits. This paper proposes a new control algorithm combined with a power management method, which fulfills the demand to keep the WTG connected to the grid during a fault, but disconnects the WTG when the fault insists. The energy generated while riding through a grid fault, is stored in a Supercapacitor Energy Storage System (SCESS). Furthermore, the SCESS is exploited for smoothing medium frequency wind power fluctuations, providing a high quality power profile. The simulation results which are performed on a 2MW synchronous generator with external excitation, verify strongly the proposed power management method.

Adaptive walking control of quadruped robots based on central pattern generator (CPG) and reflex

This paper presents a central pattern generator (CPG) and vestibular reflex combined control strategy for a quadruped robot. An oscillator network and a knee-to-hip mapping function are presented to realize the rhythmic motion for the quadruped robot. A two-phase parameter tuning method is designed to adjust the parameters of oscillator network. First, based on the numerical simulation, the influences of the parameters on the output signals are analyzed, then the genetic algorithm (GA) is used to evolve the phase relationships of the oscillators to realize the basic animal-like walking pattern. Moreover, the animal’s vestibular reflex mechanism is mimicked to realize the adaptive walking of the quadruped robot on a slope terrain. Coupled with the sensory feedback information, the robot can walk up and down the slope smoothly. The presented bio-inspired control method is validated through simulations and experiments with AIBO. Under the control of the presented CPG and vestibular reflex combined control method, AIBO can cope with slipping, falling down and walk on a slope successfully, which demonstrates the effectiveness of the proposed walking control method.

Influence of Repetitive PI-P Control on Performance of Inverters Wireless Parallel System

For wireless parallel inverters system, there is a high requirement of control precision: otherwise current-sharing effect would be very poor. Based on this characteristic of wireless paralleling technology, this paper represents the combination control method of repetitive control with PI-P voltage and current double close loop control (abbreviation as PI control) in this system. This control method, which combines with PI control, has relatively faster dynamic response speed, improves not only the capacity with nonlinear load and parallel circulation characteristics by characteristics of repetitive control, but also the steady state control accuracy of the system, meanwhile reduces the harmonic content. Its an outstanding composite control method. This paper proves the feasibility and superiority of this method by MATLAB simulation.

A low density, high stiffness flat loudspeaker with combined feedback-feedforward response correction

This paper presents a novel perforated flat loudspeaker with improved sound frequency response by applying velocity feedback control. Flat loudspeakers provide advantages of compact dimensions and high durability. Known flat loudspeaker technology is based on high model density. However, the resonances in the panel are complex and difficult to control, which often leads to complicated computations and insufficient low frequency response. The flat loudspeaker in this paper comprises a novel panel structure, which offers low density, high stiffness, and efficient space utilization. Direct velocity feedback control provides a simple and stable control loop. We apply the multiple direct velocity feedback control method to obtain flat sound frequency response. Furthermore, a Linkwitz filter is applied to our system to increase response at very low frequencies. Experimental results show that a multiple combined feedback-feedforward control method effectively improves the performance of the flat loudspeaker with extended low-frequency response.

Methods to control low frequency pulsation in open-jet wind tunnel

Low frequency pulsation affects both aerodynamic and acoustic measurements in an open jet wind tunnel. Avoiding it and establishing a good experiment environment are primary concerns for the wind tunnels. The characteristics of the low frequency pulsation and a combination control method of changing angles of the collector flaps and opening a hole in the test section chamber above nozzle were researched in a 1:15 model wind tunnel. On the basis of the method, two new control methods that are based on a Helmholtz resonator and addition pipes connected with airline of wind tunnel were put forward and validation tests were done. The results show that although the method can reduce the magnitude of the pulsation, the control effect is not the acme of perfection. The new methods effectively reduce the pulsation in different wind speeds and frequency ranges, and they can make the pulsation to keep a stable level in whole wind speeds, which is beneficial to the application of a full scale wind tunnel.

Clubroot management of highly infested soils

Clubroot (Plasmodiophora brassicae) is a disease that causes severe damage to cruciferous crops in Brazil. This study aimed to evaluate the chemical control of clubroot disease using flusulfamide at different concentrations compared with quintozene, chlorothalonil and pH reduction using lime. The efficiency of the chemical control and pH reduction combined with solarization was also tested in a commercial field. Three experiments were conducted using cauliflower cabbage and Chinese cabbage in fields located in Quatro Barras County (Paraná State, Brazil) to determine the efficacies of flusulfamide, quintozene, chlorothalonil and lime. A fourth experiment was performed using broccoli with various combined control methods (pH reduction with lime, chemical control using flusulfamide and physical control with soil solarization in a factorial design). The fresh weight (g), commercial units and gall severity in the roots were evaluated. The quintozene, chlorothalonil and lime treatments, when applied alone, were not effective in controlling clubroot. The best treatment was flusulfamide at a rate of 20 L ha−1 for the three studied species. The combination of lime to reduce pH with solarization and flusulfamide was effective to control clubroot and can be recommended to treat soils highly infested with P. brassicae.

Design and Analysis of Comprehensive Control System for Hydroturbines

The control system and the characteristics of the turbine governor are reviewed and the analysis is provided, based on which the combined control method is proposed. The simulation results show that this method enables the turbine to maintain stable work in a smooth state, so as to solve the severe turbine vibrations caused by turbine speed instability. These vibrations are apt to cause damage to the equipment and the recovery system does not work properly and so on. Thus the integrated control mode would keep safe and stable operation of the hydraulic turbine, and then energy recovery systems could run efficiently.

Sliding Mode Control of Magnetic Levitation Systems Using Hybrid Extended Kalman Filter

This paper presents an approach to control a magnetic levitation system with uncertainty in the dynamics and the measurements. First, Sliding Mode Controller (SMC) is applied to the magnetic levitation system. Then, Hybrid Extended Kalman Filter (HEKF) is used to increase the robustness of the magnetic levitation system to uncertainties. The efficiency of such combined control method is verified by simulation results and performance parameters. Key words : Magnetic levitation system; Sliding mode control; Hybrid extended kalman filter

A Research on Design Method and Theoretical Analysis of Electromagnetic Suspension System Considering Magnetic Interface Between Coils

This paper deals with the design and operating characteristics analysis of electromagnetic suspension (EMS) system. The EMS system consists of a rail, a U-shaped iron core, a high temperature superconductor (HTS) coil, a couple of DC control coils. The HTS coil generates a high magnetic field in the U-shaped iron coil and the rail. As wall as, the U-shaped iron core can be attracted by the coupled high magnetic field. We calculated turns and operating current conditions of HTS coil considering the decay of critical current when perpendicular magnetic fields are applied to the HTS coil. In addition to the design of the HTS coil, a Linear Quadratic (LQ) control method used to design the DC control coils that control the gap distance between the rail and U-shaped iron core. That is, if the gap distance is varied due to the several external disturbances, the DC control coils generated a magnetic field and then keep the constant interval. Thus, the operation of DC control coils would affect the magnetic flux density at the air gap. In this study, we verified the effect of distributions of magnetic flux density using finite element method (FEM) and MATLAB Simulink simulations. Furthermore, we numerically calculated the appropriate control current of DC control coils and the perpendicular magnetic field density on the HTS coil under the external disturbance. Based on these results, the appropriately combined current conditions and control method of EMS system to realize the stable levitation force were achieved.

Design optimisation of the LCsCp resonant inverter to drive 1 kW high-pressure sodium lamps

A novel design optimisation for the half-bridge series–parallel (LCsCp) resonant inverter used for high-power high-pressure sodium (HPS) lamp electronic ballasts is presented. A series of analyses and calculations are presented to obtain the ideal values of input DC voltage and resonant components meeting the requirement of approximate zero current switching (ZCS) behaviour over the lamp lifetime, ensuring the optimal design with minimised switching and conduction losses at steady-state operation. A new combined power control method is fulfilled to maintain the desired maximum lamp power under the optimal input voltage. Corresponding illustrations are provided to confirm the analysis result. The developed design optimisation method has been implemented into a 1 kW LCsCp resonant inverter prototype. The measured efficiency is about 98.1% for a new lamp and 99% for an ageing lamp.

A New Approach of Combined Shape and Gauge Control

Due to the coupled function of shape and gauge control in rolling process, mutual effects must be considered when shape control or gauge control is carried out. Traditional shape and gauge control theories are of independent and the control systems are also separated, so it is difficult to ensure the quality of shape and gauge simultaneously. Based on the updated shape theory and a single parameter model of load distribution method, a combined shape and gauge control method was developed, which can adjust rolling regulations on-line according to the deviation of strip crown measured at the exit of the rolling mill. The method can ensure gauge precision while strip crown is adjusted and the purpose of combined shape and gauge control is reached.

Potential threat of malaria epidemics in a low transmission area, as exemplified by São Tomé and Príncipe

BackgroundPlasmodium falciparum is the major cause of malaria infection in the island of São Tomé, in the Republic of São Tomé and Príncipe (STP), with an incidence of 40 - 50% before 2004. Since 2004, through the coordination of the Ministry of Health of STP and their Centro Nacional de Endemias (CNE), an integrated malaria control programme has been intensively deployed on the island of São Tomé. Malaria morbidity and mortality decreased by 95% after three years of effective intervention. In the low transmission settings, however, malaria seasonal fluctuation can be a potential problem directly related to epidemics if ongoing control measures are interrupted. Studies on a number of associated factors with malaria epidemics and the measures taken to respond to outbreaks are presented.MethodsThe integrated malaria control programme included indoor residual spraying (IRS), long-lasting insecticidal nets (LLINs), intermittent preventive therapy for pregnant women, as well as early diagnosis and prompt treatment with artemisinin-based combination therapy (ACT). Regular implementation of an island-wide IRS programme was carried out yearly in 2004-2007, and enhanced throughout the island in 2009. Malaria incidence and prevalence were estimated based on passive case detection and mass screening, respectively. Slide positivity rates were used for monitoring the beginning of a malaria epidemic or a seasonal peak.ResultsA steep decline of ca. 95% of malaria morbidity and mortality was observed between 2004 and 2008 with use of the combined control methods. Malaria incidence was 2.0%, 1.5%, and 3.0% for 2007, 2008, and 2009, respectively. In April 2008, a cross-sectional country-wide surveillance showed malaria prevalence of 3.5%, of which 95% cases were asymptomatic carriers. Only 50% of asymptomatic carriers were cured with ACT treatment, while 90% of the symptomatic patients were cured by ACT treatment as confirmed with a follow up study. Malaria morbidity increased by three-fold during the first half of 2009 as compared to the same period in 2008. Over this period of six months, severe malaria was also noted in all age groups and malaria mortality increased by two-fold in children less than five years old. After an emergency IRS was deployed, with increased use of LLINs, and an active search of asymptomatic carriers was followed and given complete ACT treatment, malaria incidence decreased to less than 1% in the second half of 2009.ConclusionAt the initial stage of the integrated malaria control programme, IRS contributed to the visible effect on the rapid reduction of malaria morbidity and mortality, while this programme highlights an urgent demand for the improvement of other measures, particularly promotion of LLINs usage, with close monitoring of asymptomatic carriers and with ACT treatment in malaria transmission hotspots. In addition, both daily reports and a regular active surveillance to prevent malaria outbreaks should be established permanently, so that a fast response to epidemics can be effectively made when necessary.

The influence of higher-order effects on the transmission performances of the ultra-short soliton pulses and its suppression method

Under the condition of the higher order effects, a propagation equation is established to investigate the way to suppress the soliton self frequency shift and timing jitter in the picosecond and femtosecond soliton communication system using a combined control method of time domain and frequency domain. By the use of the variational approach, the evolution of the chirping Gaussian quasi-soliton pulse is analyzed in the presence of the effects including third order dispersion, intrapulse Raman scattering (IRS), and self steepening. Considering the soliton evolution properties and the mechanism of the timing jitter under the higher-order effects, the combined control method is adopted to eliminate the influence from Raman scattering and self-steepening. The soliton central frequency is stabilized and the timing jitter is suppressed effectively. A 160 Gb/s long-haul soliton transmission system is designed and its performance is numerically simulated. The simulation results are in good agreement with our theoretical analysis.

THE SMOOTH SLIDING MODE CONTROLLER AND FILTER

This paper proposes a combined state feedback and control method based on the concept of variable structure systems (VSS). This method is defined as the smooth sliding mode controller and filter (SSMCF) and can be applied to a class of nonlinear systems. This paper provides a derivation of the SSMCF and defines the conditions for its stability. The experimental application of the SSMCF to a nonlinear hydraulic system is illustrated. The results indicate that the SSMCF maintains the advantages of VSS, such as fast response and robustness.

Comments on “On-line optimal tracking control of continuous-time systems”

In this note, we discuss a previously published paper by Chou et al. [Chou JH, Hsieh CH, Sun JH. On-line optimal tracking control of continuous-time systems. Mechatronics 2004;14:587–97]. The method proposed by authors is based on a sequential on-line identification and optimal control idea. We show that the identification part is not correct in the suggested form and we modify the identification part by suggesting a version of recursive least-squares algorithm. In addition, the identifiability of an arbitrary system is questioned and a counter-example is given. Next, we show that the application of optimal control to the identified linear moving model is not based on any theoretical basis and we present reasons why the method will not work for general systems. In summary, it is shown that the combined on-line identification and control method will not work in general as claimed. Finally, we propose an alternative control method to be applied for dimensionally restricted systems.