Outer Control Research Articles

Validation of a closed-loop aim point management system at the Jülich solar tower

Due to modeling errors and disturbances caused by clouds, Solar Power Tower (SPT) plants consider high safety margins during operation leading to a significant loss of revenues. This conservatism contradicts the expansion of SPT plants despite their potential. In this work, an aim point management system is deployed at the open-volumetric receiver of the Jülich solar tower. It employs All Sky Imager (ASI)-based nowcasts as well as flux density and temperature measurements. While the temperature measurements provide feedback for an outer receiver control loop, the flux density measurements offer feedback for an inner heliostat field control loop of a cascade control. The receiver controller estimates flux density setpoints for the inner control loop. By comparing these flux density setpoints with measured flux densities, a static optimal control technique compensates for modeling errors and increases the intercept. This control requires a fast aim point optimization, the enhanced ant-colony optimization meta-heuristic. Furthermore, a feed forward controller compensates for disturbances due to clouds by scaling the heliostats’ reflected power used in the system model by DNI nowcasts. At the Jülich solar tower, the static optimal control compensates for changes in the allowable flux density in less than three control steps. The cascade control controls the subreceivers in a narrow temperature range of 15K, which has never been achieved before at this tower.

Real-Time Implementation and Control of Multi-Source Electric Vehicle Traction Motor under Various Drive Conditions

The hybridization of multiple energy sources is crucial for electric vehicles to deliver the same performance as modern fossil fuel-based automobiles. This paper presents a torque and speed control strategy for an electric vehicle DC traction motor by regulating the power flow from two energy sources, namely battery and supercapacitor systems, to resist unpredictable disturbances. A control system with three control loops is applied to regulate the speed of the traction motor. The outer speed control loop is a nonlinear state feedback controller with a disturbance observer, which is capable of handling non-linear systems with unpredictable disturbances. The inner voltage and current control loop are precisely tuned PI controllers. Using an adaptive energy management method that varies depending on the state of charge of the source, the total reference current needed to support the load demand is split between two sources. A laboratory prototype system model is generated, and the performance is analyzed under motoring and regenerative braking conditions. For monitoring and controlling the system, the dSPACE DS1202 real-time simulator is employed. The performance of the proposed control system is evaluated and it is found that the settling time to settle within a tolerance band of 1% is 0.75 s.

Leaching kinetics and permeability of polyethyleneimine added ammonium sulfate on weathered crust elution-deposited rare earth ores

At present, in-situ leaching of weathered crust elution-deposited rare earth ores (WCE-DREOs) encounter with problems such as long leaching cycles, slow infiltration rate and low product purity. In order to solve the above problems, the conventional leaching agent ammonium sulfate ((NH4)2SO4) was compounded with polymeric surfactant polyethyleneimine (PEI) to form a composite leaching agent. The effects of leaching temperature, PEI concentration, flow rate and pH on leaching kinetics and permeability of rare earths (RE) and aluminum (Al) in orebody were studied. It is found that with temperature increasing, the time required to reach leaching equilibrium for both RE and Al is shortened, the apparent activation energies of RE and Al are 14.79 and 13.45 kJ/mol, respectively, and the leaching processes are in accordance with the outer diffusion control. When the concentrations of (NH4)2SO4 and PEI in the composite leaching agent are 2.0 wt% and 0.4 wt%, the time required to reach leaching equilibrium for RE and Al is about 50% shorter than that using (NH4)2SO4 alone, and the leaching efficiencies of RE are slightly higher than that of Al. Properly increasing the temperature and flow rate of the composite leaching agent can improve the leaching efficiencies of RE and Al, but pH has neglected effects on the leaching efficiencies of RE. At PEI concentrations below 0.4 wt%, the addition of PEI promotes the leaching of RE and Al. In column leaching studies of the WCE-DREO, the addition of 0.4 wt% PEI to the traditional leaching agent (NH4)2SO4 has no impact on the leaching efficiencies of RE. However, it can significantly increase the infiltration rate of WCE-DREO, shortening the leaching time per 10 mL effluent from about 30 min for (NH4)2SO4 leaching system to 20 min for the composite leaching system. The leaching time is shortened by one-third, and the leaching cost is reduced, which can provide theoretical guidance for the development and commercial implementation of novel composite leaching agent for WCE-DREO.

Fault tolerance of a quadrotor via feedback linearization approach

A control algorithm is proposed to efficiently control the state, position, and height of a nonlinear dynamic model of a quadcopter. Based on feedback linearization, a state space model is presented for the system with the controller with a two-loop control structure designed and implemented in it. The inner and faster controller is responsible for adjusting the quadcopter height and angles, and the outer and slower controller is responsible for changing the desired figures of roll and pitch angles to control the system position. Whenever a rotor of the quadcopter rotor fails, the status and position of the system are converged and the system is stabilized. Simulation results based on different scenarios indicate the proper performance of the control system whenever there are external disturbances. Note that the gyroscopic effects because of<em> </em>the propeller rotation were not considered.

Potential of Power Electronics to Improve the Power Quality of Network Grid

This study deals with voltage drop characterization of transmission systems by using power electronics circuits supplied from embedded generation. Many grid-connected power electronic systems, such as STATCOMS, UPFCs, and distributed generation system interfaces, use Voltage Source Inverters (VSI) connected to the supply network through a filter. This filter, typically a series inductance acts to reduce the switch harmonics entering the distribution network an alternative filter is an LCL network, which can achieve reduced levels of harmonic distortion at lower switching frequencies and with less inductance, and therefore has potential benefits for higher power application. However, systems incorporating LCL filters require more complex control strategies. This dissertation proposes a robust strategy for regulating the grid current connected via an LCL filter. The strategy integrates an outer loop grid current regulator with inner capacitor current regulation to stabilize the system. An asynchronous farm PI current regulation strategy is used for the outer grid current control loop. Linear analysis, simulation, and experimental results are used to verify the stability of the control algorithm across a range of operating conditions and finally, expressions for "harmonic impedance" of the system are derived to study the effects of supply voltage distortion on the harmonic performance of the system.

REALIZATION OF THE TECHNOLOGY OF DUAL USE OF OUTER SPACE CONTROL MEANS

Context. The radar means of outer space control are monofunctional systems, despite their potential multifunctionality. To ensure the effective implementation of target functions, only some of the total number of potential functions are used, other existing functions are not studied and as a result, don’t used. The target functions of most existing domestic and foreign radiolocation stations on space control RLS SC are practically reduced only to the control of space objects in different orbits. The obtained information is not fully used, so the new target doesn’t form. As the history of the development of defense complexes shows, in most industrialized countries there are examples of the use of military developments for civilian purposes (spin-off) and civilian developments for military purposes (spin-on). As a result of these synergy processes emphasis on the strategy of double technologies and double innovation increased. Objective. The aim of the work is to study the possibility of introducing an ionospheric channel into the domestic radar station 5N86 Dnipro (Hen House) and expanding its intended use by using most of its functional systems to implement the ionosphere control function. Method. The paper uses a comparative analysis of the main functional systems and technical characteristics of the 5N86 Dnipro radar and non-coherent scatter radars (PHR) of the global ionosphere control network. Results. The main characteristic features of the RLS 5N86 are analyzed and, taking into account the characteristics of the signals, the possibility of using the multifunctionality of the radar to form a new target function for monitoring outer space is substantiated. From an applied point of view, a number of specific scientific and practical solutions are given, aimed at the realization of dual-purpose technology in the implementation of the ionosphere control function by a radar station - both for solving the problems of increasing the own efficiency and for the interests of fundamental science. It is shown that the creation of new target RLS is based on both the use of already existing systems and the introduction of new ones. The importance of the scientific task on the implementation of the ionosphere control function and the possibility of integrating into the global ionosphere control network is substantiated. Conclusions. The presence of scientific and technical developments and the practical experience of the domestic RLS SC developer makes the new target function realization absolutely realistic. The implementation of the double-purpose technology will ensure an effective solution for both applied and fundamental scientific tasks.

SOC Balancing Control Based on Predictive Power Model Amongst Supercapacitor Packs in MMC With Embedded Energy Storage System

Modular multilevel converter with supercapacitor (SC) packs-based energy storage system (MMC-SESS) can play a role in energy transition and renewable energy consumption. However, SESS's imbalance problem is caused by the inconsistency of its packs, which has a negative effect on the utilization of the MMC-SESS and has become a hot research topic. Confronting this problem, this paper proposes a state of charge (SOC) balancing control strategy amongst SC packs based on a discrete time-domain predictive power model in MMC-SESS based medium-voltage direct-current (MVDC). It is a double-loop control to accurately control the charging and discharging power. The outer power control establishes a discrete time-domain predictive power model for the SOC differences. The inner current loop designs a hybrid controller based on the continuous control set-model prediction control (CCS-MPC) and the feedback control strategy to accurately track the dynamic current reference. Simulations in PSCAD/EMTDC have shown that the proposed control can achieve SOC balancing amongst SC packs and improve the dynamic response as well as mitigate the SC pack current ripples.

A supervisory control scheme for uncertain constrained time-delay discrete-time linear systems

In this paper, a two-layer supervisory control scheme is proposed for discrete-time linear systems with state/input constraints, including multiple state time-delays, parametric uncertainties, and exogenous disturbance. The inner control layer is designed to achieve robust H∞ tracking performance considering the delays as extra states but neglecting the input/state constraints. On the other hand, in the outer control layer, a command governor (CG) is designed to robustly guarantee the satisfaction of state and input constraints by computing a minimal Robust Positively Invariant (mRPI). To this end, the CG manipulates reference inputs by generating the nearest admissible value to be applied to the closed-loop system in both transient and steady-state response through the computation of the Maximal Output Admissible Set (MOAS). Finally, the validity of the proposed scheme is assessed in simulation using a numerical example and a continuous stirred tank reactor (CSTR) system.

Effective phase utilization and efficiency improvement of high power interleaved DC–DC converter using modified rotating phase shedding control

The interleaved bidirectional DC–DC converters (IBC’s) have a poor efficiency profile at light load conditions because the switching and core losses are more dominant than conduction losses. A phase shedding control (PSC) approach is one of the methods for multi-phase IBC to maintain a good efficiency profile across all load circumstances. However, in a PSC of IBC, one phase remains active throughout the load change while the remaining phases only operate at the significant load change. This uneven utilization of phases causes the aging problem of over-exploited phase, which also may cause thermal instability and long-term reliability issues of the converter. This paper proposes an efficiency-based modified rotating phase-shedding control (MRPSC) algorithm for 3−ϕ IBC with an automatic phase selection to improve efficiency across all loading conditions and minimize the uneven aging effect in all phases by proper phase utilization. In addition, an auto-change inner loop-average current mode control (ACIL-ACMC) has been included in the proposed MRPSC algorithm to maintain equal current sharing and voltage regulations. The sampling and computational delay of ADC have also been considered for designing adequate inner and outer loop PI controllers of ACIL-ACMC. The proposed MRPSC algorithm has been implemented in the DSP (TMS320F28335) for 7.5kW IBC.

A novel Lyapunov-based robust controller design for LCL-type shunt active power filters using adaptive sliding-mode backstepping approach

In this paper, a novel hybrid two-loop nonlinear controller is designed for stabilization and robust control of the LCL-type shunt active power filter (SAPF). To cope with the instability issue of the closed-loop system and the inherent resonance of the LCL coupling, backstepping, sliding mode and adaptive controllers are combined. DC link voltage of the grid-connected inverter is regulated in an outer control loop by determining a proper reference value for an inner loop. In addition to DC link voltage control, a major objective of the proposed closed-loop system is to make the grid current in phase with the grid voltage directly. Hence, active power filtering of the grid-connected inverter can be achieved without any current feedback from the local load. To stabilize the LCL-type SAPF in a wide range of changes, all uncertain parameters of the model including the DC link capacitor and equivalent impedances of the LCL coupling network are estimated by employing a proper Lyapunov function. For practical evaluation of the developed approach, the closed-loop system is implemented by using Texas Instruments’ digital signal processor (DSP-TMS28F335). Considering the application of an adaptive-robust nonlinear controller, it is proved that the system enjoys a stable and robust performance over the whole range of utilization, and it doesn't suffer from resonance issues of the LCL-type SAPFs. Moreover, considering the experimental results, it is observed that the steady-state error of the proposed nonlinear controller is zero in a wide range of operations.

Model reference adaptive controllers with improved performance for applications in LCL-filtered grid-connected converters

This work presents a control strategy combining a direct Model Reference Adaptive Control (MRAC) with a robust state feedback for current control of grid-connected converters with LCL filters operating under grid impedance variations. The MRAC is based on a gradient law, providing properly current reference tracking and voltage disturbance rejection. The inclusion of a state feedback inner loop provides robust active damping of the filter resonance for an entire range of grid impedances. A systematic control design procedure is proposed, and the combination of both control actions in a multi-loop approach does not add significant computational complexity. The proposal allows to increase the MRAC gains adaptation dynamics, providing suitable responses under grid current reference variations and under typical grid voltage disturbances, including grid faults. Performance indexes as the grid-currents total harmonic distortion and the mean squared error are also improved. In addition, robust stability analysis based on Lyapunov functions are carried out for the inner control loop and for the outer control loop, considering the grid impedance uncertain and with unmodeled dynamics. The strategy is implemented in a commercial digital signal processor, and the compliance of the grid currents with the IEEE 1547 Std. is verified with controller hardware-in-the-loop and experimental results in a 5.4 kW prototype.

The Friction of Radially Loaded Hybrid Spindle Bearings under High Speeds

Friction losses are an important parameter for evaluating the operational behaviour of high-speed rolling bearings. Specifically, in machine tool applications, the bearings are subjected to high radial loads and high speeds, which lead to increased forces in the rolling contact and, as a result, increased bearing friction. In this high-speed application, hybrid spindle bearings, typically made of ceramic balls and steel raceways, show better frictional behaviour compared to full steel-made bearings. Therefore, precise knowledge of the friction characteristics of high-speed hybrid bearings can improve friction models and generalise them to spindle bearings with different types, geometries, and operating conditions. In this article, a new straightforward and cost-efficient method for measuring the frictional torque in spindle bearings is presented. A rigidly arranged 7008 hybrid spindle bearing pair was tested up to rotational speeds of 24,000 rpm and high radial loads of 3 kN. The effects of oil–air and grease lubrication are discussed in characteristic diagrams of the tested bearings. Then, based on the test results, a friction calculation model is presented and validated for the outer race control and minimised power dissipation regarding the influence of radial forces.

Data-driven cascade control system: Response estimation and controller design

In this study, we propose a data-driven design method for a cascade control system with inner and outer control loops. First, the input–output response of a controlled plant, which varies with the controller parameters of a fixed-structure inner-outer control law, is estimated directly from open-loop input–output data. Next, based on the estimated response, the controller parameters are optimized to minimize the difference between a reference model with a controlled closed-loop system. In the proposed method, the response of a fictitious reference input, which varies with the controller parameters, is estimated, and then the closed-loop response is estimated. Therefore, a closed-loop input–output data is not required, and the controller parameters are determined directly from an open-loop input–output data. Furthermore, the time constant of a reference model is also optimized so as to reduce the control error. The proposed method is compared with both conventional single-loop and cascade data-driven methods by means of numerical examples.

Robust Observer-Based Visual Servo Control for Quadrotors Tracking Unknown Moving Targets

This article addresses the image-based control problem of a quadrotor for tracking an unknown moving target under external disturbances. Based on the continuous observer design, a constructive image-based visual servoing (IBVS) geometric tracking control strategy is proposed and utilized. First, a higher order sliding mode observer is designed based on image dynamics for continuous estimation of unmeasurable linear velocities and time-varying disturbances. Furthermore, exploiting the linear quadratic regulator optimal design method, an outer loop IBVS controller is proposed such that the position of the quadrotor converges to the desired tracking pattern. Next, an inner loop geometric controller is designed using Lie algebra functions to regulate the attitudes. Based on the Lyapunov stability theory, it is rigorously proven that the proposed IBVS geometric controller achieves asymptotic stability. Finally, the effectiveness and robustness of the proposed approach against uncertain targets, time-varying disturbances, and large initial inclination angles are demonstrated through numerical simulations and experiments.

Load frequency regulation of multi-area power systems with communication delay via cascaded improved ADRC

Load frequency regulation (LFR) is regarded as a significant method for the stable operation of modern power grids. However, the LFR is facing many challenges such as communication delays in the area control error, and external disturbances caused by renewable energy integrating into power grids. This paper presents a cascaded improved active disturbance rejection control (ADRC) to handle these control challenges, where the inner and outer controllers are the improved ADRC and regular ADRC, respectively. The advantages of the improved ADRC to reject external disturbances and system uncurtains are discussed by simulations. Then a practical parameter tuning method is provided to guide the selection of controller parameters. Finally, comparative simulations are implemented to illustrate the abilities of the proposed control scheme in different cases. The proposed control structure can handle the communication delay well and have a strong ability to reject the disturbances of uncertain consumed power and wind power. The simulation results imply that the cascaded improved ADRC may have broad application prospects for the LFR.

A Non-Integer High-Order Sliding Mode Control of Induction Motor with Machine Learning-Based Speed Observer

The induction motor (IM) drives are prone to various uncertainties, disturbances, and non-linear dynamics. A high-performance control system is essential in the outer loop to guarantee the accurate convergence of speed and torque to the required value. Super-twisting sliding mode control (ST-SMC) and fractional-order calculus have been widely used to enhance the sliding mode control (SMC) performance for IM drives. This paper combines the ST-SMC and fractional-order calculus attributes to propose a novel super-twisting fractional-order sliding mode control (ST-FOSMC) for the outer loop speed control of the model predictive torque control (MPTC)-based IM drive system. The MPTC of the IM drive requires some additional sensors for speed control. This paper also presents a novel machine learning-based Gaussian Process Regression (GPR) framework to estimate the speed of IM. The GPR model is trained using the voltage and current dataset obtained from the simulation of a three-phase MPTC based IM drive system. The performance of the GPR-based ST-FOSMC MPTC drive system is evaluated using various test cases, namely (a) electric fault incorporation, (b) parameter perturbation, and (c) load torque variations in Matlab/Simulink environment. The stability of ST-FOSMC is validated using a fractional-order Lyapunov function. The proposed control and estimation strategy provides effective and improved performance with minimal error compared to the conventional proportional integral (PI) and SMC strategies.

Experimentally investigating the influence of changing payload stiffness on outer loop iterative learning control strategies with shaking table tests

Shaking tables are widely used across numerous engineering research and industrial sectors, including mechanical (e.g. automotive and aerospace testing), electrical (e.g. instrumentation testing) and civil (e.g. structural and geotechnical testing) engineering. It is commonly required to replicate the shake table motions accurately and precisely. Iterative learning control algorithms can be used to complement traditional proportional–integral–differential feedback control algorithms to optimize drive signals using a test payload prior to the real experiment. Historically, the design of these test payloads has focused on matching the mass of the actual payload and neglected its dynamic response. In this study, experimental results from shake table tests using multiple geotechnical containers with dry and saturated beds that exhibit a range of stiffnesses and material damping when shaken are presented. Errors between the demanded and achieved motions are explored and compared to the changing secant stiffness abstracted from the dynamic shear stress–strain loops of the payload. A clear trend emerges that demonstrates increased errors as the payload stiffness deviates from the constant stiffness test payload originally used with the open loop iterative learning control, and further the errors are not necessarily bounded by test payloads significantly softer or stiffer than the actual specimen. The findings support that in cases where repeatable, accurate and precise shake table motions are required for payloads that exhibit a complex material response that is not readily modelled mathematically, it may be necessary to reproduce the specimen’s overall dynamic response during the iterative learning control process.

The Design and Processor-In-The-Loop Implementation of a Super-Twisting Control Algorithm Based on a Luenberger Observer for a Seamless Transition between Grid-Connected and Stand-Alone Modes in Microgrids

The abrupt transfer from grid-connected (GC) to stand-alone (SA) operation modes is one of the major issues that may threaten the stability of a distributed generation (DG) system. Furthermore, if the islanding mode happens, it is vital to take into consideration the load voltages or load current waveforms as soon as feasible. This paper develops an advanced control technique based on a super-twisting sliding mode controller (ST-SMC) for a three-phase inverter operating in both the GC and SA modes. This control scheme is proposed to ensure a smooth transition from the GC to SA mode and enhance the load voltage waveforms under the islanding mode. In addition, to minimize the operational costs of the system and the complexity of the studied model, a digital Luenberger observer (DLO) with a proper design is adopted for estimating the inverter-side current. The control scheme of the whole system switches between a current control mode during the GC mode and a voltage control mode during the SA mode. The super-twisting control algorithm is applied to the outer voltage control loop involved in the cascaded voltage/current control scheme in the SA mode. Simulation tests of a three-phase inverter are performed for the purpose of assessing the suggested control performance by using the PowerSim (PSIM) software and comparing it with a classical PI controller. Furthermore, a processor-in-the-loop (PIL) implementation in a DSP board TMS32F28335 while debugging is conducted using code composer studio 6.2.0. The obtained results show efficient control properties, such as a smooth transition among the microgrid (MG) operating modes, as well as effectiveness and robustness during both the GC and SA operation modes.

Performance Investigation of Dual Trench Split-Control-Gate MOSFET as Hydrogen Gas Sensor: A Catalytic Metal Gate Approach

In this article, Dual Trench Split-Control-Gate MOSFET (DT-SCG-MOSFET) based hydrogen gas sensor considering catalytic palladium metal gate approach is simulated using SILVACO ATLAS TCAD. The inner gate architecture in addition to the outer control gates provides enhanced carrier control. Shift in surface potential, subthreshold current, linear current and threshold voltage are used to investigate the performance of the proposed gas sensor. The contribution of analog metrices like the transconductance and parasitic capacitances are explored thoroughly. Sensitivity as a function of subthreshold current as well as change in threshold voltage for the presence and absence of hydrogen gas molecules have been discussed. Results exhibit the superiority of the proposed gas sensor compared with the reported models in terms of sensitivity and Ion/Ioff ratio and suitable for hydrogen gas detection.

Robust adaptive composite control of DC–DC boost converter with constant power load in DC microgrid

Power electronic loads are penetrating in DC microgrid. These loads are usually regarded as constant power loads (CPLs) with negative impedance characteristics, which seriously affect the dynamic performance of DC bus voltage and may result in instability of the DC microgrid system. To improve the performance and stability of a boost converter with CPL, proposed herein is a robust adaptive composite control strategy, which mainly includes two control loops. An affine nonlinear mathematical model is established. Based on the differential geometry theory, the minimum phase problem is analyzed under different output functions. In the inner control loop, the inductor current is linearized by using exact feedback linearization theory to a linear system. Meanwhile, sliding mode control method is studied to control the linear system, and an adaptive law is designed to update the sliding mode switching gain. In the outer control loop, the output voltage is regulated by proportional–integral control technology to achieve no steady-state error for the DC bus voltage. Furthermore, the robustness of the closed-loop system is verified, and the global asymptotic stability of the control system is proved. Compared with the existing method, both simulation results and experimental results verify the validity and superiority of the presented control strategy.