Closed-loop Operation Research Articles

A full-bridge flux pump using two switches: numerical model and experimental prototype

Abstract High-temperature superconducting (HTS) magnets are promising in high field applications. However, due to inevitable joint resistance and flux creep, HTS magnets still face challenges in maintaining field stability in their closed-loop operation. HTS flux pumps can charge closed HTS magnets wirelessly, thus allowing lower cryogenic loading and more flexible arrangements in HTS magnet systems. In this work, a full-bridge flux pump using two AC field-controlled switches is proposed, which can charge HTS magnets during whole cycles. Therefore, the charging speed of the proposed full-bridge flux pump is at least one time larger than half-bridge flux pumps. A numerical model and an experimental prototype are developed to verify the working principle of the proposed full-bridge flux pump. Simulation and experimental tests are carried out to investigate the working characteristics of the proposed flux pump. The proposed flux pump has huge potential in the application scenarios where high charging speed is required.

Chaotic attractor reconstruction using small reservoirs—the influence of topology

Abstract Forecasting timeseries based upon measured data is needed in a wide range of applications and has been the subject of extensive research. A particularly challenging task is the forecasting of timeseries generated by chaotic dynamics. In recent years reservoir computing has been shown to be an effective method of forecasting chaotic dynamics and reconstructing chaotic attractors from data. In this work strides are made toward smaller and lower complexity reservoirs with the goal of improved hardware implementability and more reliable production of adequate surrogate models. We show that a reservoir of uncoupled nodes more reliably produces long term timeseries predictions than more complex reservoir topologies. We then link the improved attractor reconstruction of the uncoupled reservoir with smaller spectral radii of the resulting surrogate systems. These results indicate that, the node degree plays an important role in determining whether the desired dynamics will be stable in the autonomous surrogate system which is attained via closed-loop operation of the trained reservoir. In terms of hardware implementability, uncoupled nodes would allow for greater freedom in the hardware architecture because no complex coupling setups are needed and because, for uncoupled nodes, the system response is equivalent for space and time multiplexing.

Stress Fields Distribution and Simulation in 3C-SiC Resonators

In this paper the stress field distribution in 3C-SiC (111) resonators has been studied by micro-Raman measurements and COMSOL simulations. The measurements show that the asymmetry of the anchor points configuration produce an asymmetry in the stress filed distribution. This behavior has been confirmed also by the simulations. Furthermore, from the simulations the importance of the reduction of the under etching of the anchor points of the resonators has also been observed. In fact the reduction of this under etch produces a decrease of the stress in the double clamped beams, a small reduction of the resonance frequency, and a large reduction of the Q-factor and then of the oscillation frequency stability of the resonators in closed-loop operation.

A novel low-resistance solder-free copper bonding joint using a warm pressure welding method for REBCO coated conductors

Abstract Constrained by the fabrication of second-generation high-temperature superconducting (2G HTS) tapes, connecting multiple pieces of tapes through joints is often necessary in large-scale applications. In the application of HTS magnets, joint technology is key for achieving closed-loop operation and reducing thermal loads. However, most soldered joints still cannot achieve the expected results. Thus, there is an urgent need to find a method for easily fabricating low-resistance joints. In this study, a low-resistance solder-free copper bonding joint for 2G HTS copper-plated tapes is proposed. The formation mechanism of the joint is presented, and the effects of the bonding temperature and pressure on the electrical and mechanical properties of the copper bonding joint are investigated. The results show that the copper bonding joint can be manufactured by pretreating the tape for 5 minutes and bonding it in the air for 3 minutes at 333 MPa at temperatures higher than (or equal to) 150 °C or at pressures greater than (or equal to) 250 MPa and 180 °C. The characteristic resistance of this joint is approximately 16.8 nΩ·cm2, which is approximately one-third lower than that of soldered joints, and it has mechanical properties similar to those of soldered joints under axial tension. We believe that the application of this type of copper bonding joint can significantly aid in the design and manufacturing of large HTS magnets.

A simultaneous energy self-sufficient desalination and energy output process based on a novel membrane stack design

Electrodialysis (ED) uses electric energy to conduct the desalination, while bipolar membrane reverse electrodialysis (BMRED) converts the chemical energy containing in acids and alkalis into electric energy. Here, a novel membrane stack (BMRED-ED) based on BMRED and ED was designed to realize the simultaneous energy self-sufficient desalination and energy output process. The stack was studied in two different operation modes systematically. Results of the open-loop operation mode demonstrate that the maximum power density (Pd,max) can obtain a highest value of 4.53 W·m−2, and the maximal average apparent permeability (α) between the open circuit voltage (OCV) and theoretical electromotive force (EMF) is 92.23 %. Results of the closed-loop operation mode indicate that the final desalination ratio (ξdel) can attain as high as 89.57 %, and the corresponding energy utilization ratios of the desalination (ηdes) and the energy output (ηout) are 0.90 % and 14.00 %, respectively. Moreover, the effect of desalinated salt solution concentrations and discharging current densities on the closed-loop operation performance are much more remarkable than that of cation species in the alkali and salt solutions. This work provides a feasible and competitive strategy for simultaneous energy self-sufficient desalination and energy output.

Model predictive control of switched nonlinear systems using online machine learning

This work introduces an online learning-based model predictive control (MPC) approach for the modeling and control of switched nonlinear systems with scheduled mode transitions. Initially, recurrent neural network (RNN) models are constructed offline, utilizing sufficient historical operational data to capture the nominal system dynamics for each mode. Subsequently, we employ real-time process data to develop online learning RNN models, aiming to approximate the dynamics of switched nonlinear systems in the presence of of bounded disturbances. In cases where the initial RNN model is unavailable for a specific switching mode due to very limited historical data, we use real-time data from closed-loop operations under a proportional–integral (PI) controller to build online learning RNN models. To evaluate the predictive performance of online learning RNNs, a theoretical analysis on their generalization error bound is developed using statistical machine learning theory. Additionally, considering the presence or absence of initial RNN models, two MPC schemes are developed. These schemes employ RNNs as prediction models to stabilize switched nonlinear systems, ensuring closed-loop stability by accounting for the generalization error bound derived for online learning RNNs. Finally, the effectiveness of the proposed MPC schemes is demonstrated through a nonlinear process example with two switching modes.

Machine learning & conventional approaches to process control & optimization: Industrial applications & perspectives

Technologies based on Artificial Intelligence (AI) and Machine Learning (ML) concepts are advancing at a rapid pace. The new paradigms are challenging the status-quo of mature automation and control technologies in industry. Autonomous operation is a frequently stated goal of AI evangelists and technology providers. This white paper gives an overview of the current state of art of advanced process control and optimization technologies. It also provides a brief summary of the AI and ML-based approaches that address the closed-loop control and optimization space. Some results from industrial implementations are shared for both conventional and AI/ML-based approaches. Experience from four industrial applications is shared, covering rigorous model-based, machine learning and hybrid approaches to real-time optimization and control problems. The applications range from unit-based control & optimization to refinery & network wide optimization. A set of high-level requirements that need to be satisfied regardless of the underlying technology for closed-loop autonomous operations is reviewed. The article concludes with some future directions and perspectives highlighting areas where the emerging technologies may have significant impact in industry.

Design and analysis of soft-switching isolated step-up/down DC–DC converter for fuel cell vehicles and EV battery charging applications

ABSTRACT With the increasing adoption of non-conventional energy sources, there is a significant demand for DC energy conversion systems as they play a crucial role in integrating power sources and loads that operate at different voltage levels. In this paper, a novel DC–DC converter topology is presented, which can efficiently perform Buck-boost operation with minimal duty cycle operation, making it an attractive option for DC energy conversion applications. Furthermore, its switching voltage stress is less than the voltage present at the output, allowing the use of low power rated devices. Additionally, the topology contains isolation between the load and source, which prevents circulating currents and protects the source from load harmonics. The proposed converter has the ability to achieve soft switching without using any extra circuitry. Moreover, the presented converter is evaluated against recently developed topologies in terms of active/passive components, gain, efficiency, and switching stress. Closed-loop analysis is done for the proposed converter using small-signal modeling. The converter is tested by subjecting it to a sudden step change at the input voltage from 20 V to 40 V in boost condition while maintaining a constant output voltage of 240 V. Additionally, load disturbances are introduced to assess the system’s robustness in closed-loop operation. In the laboratory, A 100-W prototype of the presented converter is built, which gives an efficiency of 95% at the rated load condition.

Insights into the effect of operating parameters and hydrodynamics on hydrolysis reaction in Copper–Chlorine thermochemical water splitting cycle for hydrogen production: Modelling and experimental validation

Copper–Chlorine (Cu–Cl) thermochemical cycle is being explored as one of the promising technologies for large scale production of clean hydrogen from water using nuclear or renewable energy. In this method, water splitting is achieved through a series of reactions in a loop producing only hydrogen and oxygen with complete recycle of all the intermediate copper and chlorine compounds. The first step of the cycle is the hydrolysis reaction wherein steam reacts with solid CuCl2 to form solid Cu2OCl2 (copper oxychloride) and HCl gas. The products enter the subsequent steps of the cycle and are recycled back to complete the loop. Multiple side reactions in the hydrolysis step result in reduced yield and loss of chemicals from the cycle. Efficient reactor design and optimal operating conditions of hydrolysis reactor is imperative towards achieving sustained closed loop operation and reducing the energy demand of Cu–Cl cycle. This paper presents a mathematical model for the simulation of hydrolysis reaction in a bubbling fluidized bed reactor. The one-dimensional model is developed based on modified two-phase theory of fluidization and is coupled with kinetics of multiple side reactions to investigate the effect of operating parameters and hydrodynamics on the conversion and yield of Cu2OCl2. The model results are validated with experimental data in 50 mm and 100 mm semi-batch fluidized bed reactors. The developed model clearly brings out the effect of different process parameters for process optimization and scale-up of the hydrolysis reactor for efficient integration in the cycle.

A closed-loop smart dressing based on microneedle and electrochemical micropump for early diagnosis and in-time therapy of chronic wound

Early diagnosis combined with in-time treatment is a promising strategy for chronic wound care, preventing wound deterioration and promoting healing. Different smart dressings have recently emerged to enable real-time wound status monitoring and offer active intervention. However, the drawbacks of existing smart dressings, including limited drug loading capacity and poor drug penetration into the deeper wound dermal and subcutaneous tissues, are yet to be addressed, resulting in unsatisfactory therapeutic effectiveness. In this study, a Microneedle-embedded closed-loop smart Dressing (MelD) is developed to simultaneously achieve chronic wound early diagnosis and in-time therapy. The simple impedance sensing electrodes are utilized to monitor wound impedance for chronic wound early diagnosis. Based on the sensing data, the drug delivery micropump in MelD is automatically activated for in-time therapy. By integrating micropump electrodes with a drug reservoir coupled-microneedle array, a practice solution for delivering enough drug fluid into deeper wound dermal/ subcutaneous tissues is developed. Compared to untreated diabetic mice, MelD, delivering sufficient growth factor to the wound and promoting drug entry into deep tissue layers, induces faster wound healing in treated mice. Meanwhile, MelD facilitates tissue formation and nascent collagen deposition. The enhanced drug storage dosage, improved drug penetration and closed-loop operation of Meld enable the first successful attempt of ensuring sufficient and efficient drug delivery by miniaturized all-in-one smart dressing, expanding the usage of closed-loop chronic wound care from laboratorial demonstration on limited kinds of superficial wounds to a wider range of wound types.

Closed-loop Koopman operator approximation

This paper proposes a method to identify a Koopman model of a feedback-controlled system given a known controller. The Koopman operator allows a nonlinear system to be rewritten as an infinite-dimensional linear system by viewing it in terms of an infinite set of lifting functions. A finite-dimensional approximation of the Koopman operator can be identified from data by choosing a finite subset of lifting functions and solving a regression problem in the lifted space. Existing methods are designed to identify open-loop systems. However, it is impractical or impossible to run experiments on some systems, such as unstable systems, in an open-loop fashion. The proposed method leverages the linearity of the Koopman operator, along with knowledge of the controller and the structure of the closed-loop (CL) system, to simultaneously identify the CL and plant systems. The advantages of the proposed CL Koopman operator approximation method are demonstrated in simulation using a Duffing oscillator and experimentally using a rotary inverted pendulum system. An open-source software implementation of the proposed method is publicly available, along with the experimental dataset generated for this paper.

Multifunctional nanorobot system in precise evaluation and manipulation of virus capsid

It is imperative to have high adaptive techniques for sensing and manipulating biological targets at the nanoscale. This necessity becomes particularly crucial when dealing with fragile living bio-organisms like viruses, where the expression of capsids is closely linked to viral functions and genome constitution. Therefore, the development of a comprehensive system for dissecting and measuring viruses holds significant implications for the pharmaceutical industry and drug manufacturing. Leveraging the sub-nanometer spatial resolution and controllable tip-cantilever architecture of atomic force microscopy (AFM), a probe-laser system has been integrated as a self-sensing robotic end effector. To address intrinsic challenges in AFM-based robotic systems such as the lack of real-time monitoring, low scanning rates, and nonlinear motion caused by piezoelectric actuators, an augmented reality robotic system has been implemented. This system incorporates stereoscopic vision, a haptic feedback controller, a position recovery scheme, and a real-time force control algorithm. The integration of these components enhances the system’s capability to accurately dissect virus capsids. Operators can now perform highly efficient nanoscale tasks with multidimensional perception, utilizing the combination of stereoscopic vision and haptic force control. The position correction during manipulation can achieve a frame rate of over 30 frames per second, imperceptible to the operator, enabling closed-loop operation control. By adopting the proposed nanorobotic system in virology studies, it becomes possible to achieve accurate manipulation and dissection of SARS-CoV-2 pseudovirus capsids, and derive multi-parametric properties such as structural integrity, protein fragment thickness, and adhesive forces. The established nanobot system and experimental results serve as a guiding platform for high-accuracy evaluation in drug manufacturing development.

A Common Grounded Voltage Quadrupler ASL/PSC Hybrid Converter With Reduced Voltage Stress

Active switched inductor (ASL) dc-dc converters have very high step-up voltage gain but practically they suffer from high voltage stress across switches because of the resonance caused by the mismatch among the inductor values and switch parameters. This paper presents a new hybrid dc-dc converter topology derived from ASL and passive switched capacitors (PSC). The proposed topology has high step up voltage gain over wide range of duty cycle. The resonance due to mismatch of parameters is eliminated. The proposed converter has low voltage stress, low current stress on circuit elements and common ground between input and output ports. The circuit configuration, operating principle and steady state analysis of the proposed converter are presented. The key performance parameters are compared with that of other high-gain dc-dc converters. A 300W laboratory prototype is developed and experimental verification is carried out for the voltage step-up from 30V to 400V. The closed-loop operation is also verified experimentally and results are presented.

Digitally Controlled Hybrid Switching Step-Up Converter

This paper focuses on the digital closed-loop design for a step-up converter with hybrid switching. For this purpose, for the first time, the control-to-output small-signal transfer function of a hybrid switching converter is determined in the rational form. Based on it, a type 3 analog controller is designed, and then, its digitized counterpart is found, and the digital controller is designed using a digital signal processor. The closed-loop operation is then validated both through simulation and practical implementation.

Adaptive control of A class of nonlinear systems with guaranteed parameter estimation: A concurrent learning based approach

AbstractRecent advances in concurrent learning based adaptive controllers have relaxed the persistency of excitation condition required to achieve exponential tracking and parameter estimation error convergence. This was made possible via the use of additional concurrent learning stacks in the parameter estimation algorithm. However, the proposed concurrent learning components, that is, the history stacks, needed to be filled with “selected” values dependent on the actual system states. Therefore, the previously proposed concurrent learning adaptive controllers required the system to be stable initially for a finite time so that the corresponding history stacks can be filled (finite excitation condition). In this work, motivated to remove the finite excitation condition, a novel desired system state based concurrent learning adaptive controller is proposed. In order to remove the system state dependencies in the controller and estimation algorithms, a filtered version of the dynamics and a novel prediction error formulation have been designed. The overall exponential stability, parameter error convergence and boundedness of the system states during closed loop operations are ensured via Lyapunov based arguments. The main advantages of the proposed method are its dependence on the desired system states and the overall stability results that paved the way in removing the need for finite excitation condition. Numerical studies performed on a two link robotic device are also presented to illustrate the feasibility of the proposed method.

AC Networks With Microgrids: Passivity-Based Controllers in Single Phase Electric Network

—This paper is an investigation of the possible integration of distributed energy resources (DERs) in single-phase alternating current networks, using voltage-controlled converters, based on passivity-based control theory. In closed-loop operation, Hamiltonian representations facilitate the development of passive controllers that guarantee stability. The trajectory tracking problem can be solved as a regulation problem by transforming the non-autonomous dynamical model into an incremental model. In this work, the primary contribution is the ability to control active and reactive power flows between DERs and the grid according to the availability of primary energy resources and converter capacity. Simulated results indicate that all passive controllers achieve the control objective, maintaining asymptotic stability and achieving the same dynamic performance as integral proportional controllers. SimPowerSystems library is used to develop all simulations under the MATLAB/Simulink environment. The paper presents a novel approach to integrating distributed energy resources into single-phase alternating current networks, utilizing voltage-controlled converters and leveraging passivity-based control theory.

Firmware development for the fibre-optic seismometer based on FOG

The main goal of the article is to present the concept of using a simulation environment when designing an advanced fibre-optic seismometer (FOS) using a field-programmable gate array (FPGA) computing system. The first part of the article presents the advanced requirements regarding the FOS principle of operation, as well as the measurement method using a closed-loop operation. The closed-loop control algorithm is developed using the high-level language C++ and then it is synthesised into an FPGA. The following part of the article describes the simulation environment developed to test the operation of the control algorithm. The environment includes a model of components of the measurement system, delays, and distortions in the signal processing path, and some of the measurement system surroundings. The article ends with a comparison of simulation data with measurements. The obtained results are consistent and prove correctness of the methodology adopted by the authors.

Performance Comparison of a DC–DC Boost Converter With Conventional and Non-linear SMC Controller in Dual Loop Structure

Generally, the control system confronts various control techniques in the dual-loop control concept. Most of the studies deal with two different controllers in their loops, which increases the problem of designing two distinct procedures with lengthened calculations. In this article, different control techniques like conventional proportional integral (PI), proportional integral derivative (PID), and nonlinear sliding mode control (SMC) have been discussed, and the implementation of SMC in the Dual loop control of a DC–DC Boost converter is presented. The converter’s dynamic behavior is observed by driving their analytical equations. The effective controller for the proposed converter is ascertained by their comparative analysis. The proposed concept is validated with MATLAB/Simulink and a hardware prototype. The controller’s response is compared for various disturbances. Here, dual-loop SMC is put forward in both loops and its competence is confirmed with a minimal settling period of 0.005 sec and a percentage overshoot of 0.2% during the startup conditions, whereas during the line disturbances a minimum peak time of 0.0001 sec is achieved with a settling time of 0.025 sec. Additionally, a nil percentage overshoot and a settling time of 0.02 sec with a 0.001 sec peak time are attained during the load variations. Furthermore, a settling time of 0.01 sec and a percentage overshoot of 0.8% is reached during the reference voltage variations. From the numerical analysis, it is contemplated that an appropriate selection of SMC controllers in both the outer and inner loop results in optimal performance of the converter during the closed loop operation. Finally, the SMC + SMC controller exhibits superior controlling action compared to PI + PI and PID + PID controllers.

Operation of a Ramsey-CPT microcell atomic clock with driving current-based power modulation of a VCSEL

We report on the operation of a coherent population trapping (CPT) microcell atomic clock using a pulsed Ramsey-like interrogation. The Ramsey-CPT sequence, defined by two-step optical pulses separated by a free-evolution dark time, is produced by switching on and off the output power of a low-power vertical-cavity surface-emitting laser, through direct modulation of its driving current. High-contrast and narrow Ramsey-CPT fringes are detected without the use of any external optical modulator stage. We demonstrate closed-loop operation of the clock based on high-speed digital signal processing implemented in a field programmable gate array board. The clock's short-term fractional frequency stability is 1.3 × 10−10τ−1/2 until 2000 s. A power light-shift coefficient of 8 × 10−11/μW, in relative value, is obtained for a dark time of 150 μs. This value is about ten times lower than in the continuous regime. These results show the feasibility of fully integrated atomic clocks based on Ramsey spectroscopy, which could provide enhanced long-term stability.

Membrane processes used to treat scrubber gas desulfuration washwater.

Since 2020, hybrid exhaust gas cleaning systems have been installed on container ships to be in line with the International Maritime Organisation regulations. This technology allows the removal of gaseous sulphur oxide compound before atmospheric rejection of exhaust gas with a concentration lower than 0.1% sulphur equivalent. To be also compliant with water discharge criteria, membrane processes used as a water treatment system have been complementary installed onboard maritime vessels. Objectives of our research are to demonstrate the membrane efficiency and performances for this field of application and their reliability for reaching future regulations. Half industrial scale experiments are first carried out in controlled areas. Results allow optimum parameter definition for a sustainable long-term operation as a permeate flux of 60 L h-1 m-2 and a backwash frequency of 40 min. Experiments are scaled up to onboarded units, and previous settings have been validated. The fleet autonomy for a longer period of closed-loop operation is highlighted. Consequently, the fleet is well prepared and able to overcome new regulation for the future sulphur emission area defined for the Mediterranean Sea in 2025. In addition, the usage of membrane processes allows the reduction of pollutants as suspended solid and heavy metal rejection inside the natural environment with a respective retention higher than 100 and 95%.