Active Control Strategy Research Articles

Oscillatory valve effect on pressure drop oscillation in microchannel cooling system

Pressure drop oscillation (PDO) is one of the most common flow instabilities occurred in microchannel cooling systems, which could result in partial dry-out, heat transfer deterioration, and temperature fluctuation. In this study, the effects of three oscillatory electronic valve settings (square, sinusoidal, and sawtooth) on mass flow rate and PDO characteristics are examined numerically and experimentally. A one-dimensional lumped model is developed for the microchannel cooling system, which indicates that a specific range of valve oscillation amplitude and frequency can reduce PDO amplitude significantly. The PDO amplitude can be reduced by 85 % when the valve amplitude is 30 % and the frequency is 0.1 Hz. A smaller valve oscillation amplitude shows a weaker effect on the suppression of PDO. The square function has a better PDO suppression than the sinusoidal and sawtooth functions under the same pulsating valve amplitude and frequency. Experimental results demonstrate a similar effect of valve setting on PDO, for instance, a valve setting oscillates from 20 % to 80 % and a fixed frequency of 0.05 Hz can reduce pressured drop amplitude from 3 kPa to 0.5 kPa, and reduce the mass flow rate oscillation amplitude from 60 ml/min to 10 ml/min. The overly large oscillation amplitude of the valve setting could increase the oscillation amplitude of the mass flow rate and the overall pressure drop significantly. Thus, both the pressure drop through the microchannel evaporator and the valve should be considered in the selection of the oscillatory valve parameters. Based on the analysis of this study, an active control strategy could be developed to suppress flow oscillation and optimize the overall cooling performance using the oscillatory valve setting.

Adaptive feedback control of stability in an axial compressor with circumferential inlet distortion

The adaptive feedback control of stability with circumferential inlet distortion has been experimentally investigated in a low-speed, axial compressor. The flat-baffles with different span heights are used to simulate different distorted inflow cases. Compared with auto-correlation and root-mean-square analysis, cross-correlation analysis used to predict early stall warning does not depend on the distortion position. Hence, the cross-correlation coefficient was used to monitor the stable status of the compressor and provide the feedback signal in the active control strategy when suffering from different distortions. Based on the stall margin improvement of tip air injection obtained under different distorted inflow cases and the sensitivity analysis of cross-correlation coefficients to injected momentum ratios, tip air injection was adopted as the actuator for adaptive feedback control. The digital signal processing controller was designed and applied to achieve adaptive feedback control in distorted inflow conditions. The results show that the adaptive feedback control of air injection nearly achieves the same stall margin improvement as steady air injection under different distortion intensities with a reduced injection mass flow. Thus, the proposed adaptive feedback control method is ideal for the engine operation with circumferential distorted inflow, which frequently occurs in flight.

A dual-loop active vibration control technology with an RBF-RLS adaptive algorithm

Active control strategies have been widely used in micro-vibration isolation with higher performance requirements. Aiming at the problem of insufficient vibration isolation performance due to time delay in feedback control, the ground-based feedforward active control is introduced to compensate in advance for higher pursuit. However, the inaccuracy of the feedforward control reference model severely restricts the vibration isolation performance. With the assistance of RBF neural network algorithm for accurate real-time identification of online model, a feedforward-feedback dual-loop active hybrid control (DAHC) strategy based on the RBF-RLS adaptive algorithm is proposed in this paper. The adaptive feedforward control uses the RBF neural network algorithm to identify the accurate model of the system online, and input it to the transverse filter of the RLS adaptive control algorithm for recursive calculation, which can effectively reduce the system error caused by the inaccuracy of the model. The experimental results show that the accuracy of online model affects the amplitude attenuation performance by 57.1%. DAHC strategy can greatly reduce the resonance peak by 25.02 dB in micro-vibration. Real applicative experiment further proves the effectiveness of our proposed algorithm.

Novel Model-free Optimal Active Vibration Control Strategy Based on Deep Reinforcement Learning

Neural networks (NNs) can provide a simple solution to complex structural vibration control problems. However, most past NN-based control strategies cannot guarantee an optimal policy in structural vibration control. In this study, a novel active vibration control strategy based on deep reinforcement learning is proposed, which utilizes the learning ability of NN controllers and simultaneously provides control performance comparable to traditional model-based optimal controllers. The proposed learning algorithm can determine the control policy through interaction with the environment without knowing dynamic system models. This study shows that the proposed model-free strategy can provide optimal control performance to various systems and excitations. The proposed control strategy is first verified on a single-degree-of-freedom model and subsequently extended to a multi-degree-of-freedom shear-building model. Its control performance with full-state feedback is nearly the same as that of a classical linear quadratic regulator. Moreover, the learned policy can outperform a traditional output feedback controller in a partially observed system. The robustness of the proposed control strategy against measurement noise is also tested.

Amino Acid Variation at Hemagglutinin Position 193 Impacts the Properties of H9N2 Avian Influenza Virus.

Despite active control strategies, including the vaccination program in poultry, H9N2 avian influenza viruses possessing mutations in hemagglutinin (HA) were frequently isolated. In this study, we analyzed the substitutions at HA residue 193 (H3 numbering) of H9N2 and investigated the impact of these mutations on viral properties. Our study indicated that H9N2 circulating in the Chinese poultry have experienced frequent mutations at HA residue 193 since 2013, with viruses that carried asparagine (N) being replaced by those with alanine (A), aspartic acid (D), glutamic acid (E), glycine (G), and serine (S), etc. Our results showed the N193G mutation impeded the multiple cycles of growth of H9N2, and although most of the variant HAs retained the preference for human-like receptors as did the wild-type N193 HA, the N193E mutation altered the preference for both human and avian-like receptors. Furthermore, these mutations substantially altered the antigenicity of H9N2 as measured by both monoclonal antibodies and antisera. In vivo studies further demonstrated that these mutations showed profound impact on viral replication and transmission of H9N2 in chicken. Viruses with D, E, or S at residue 193 acquired the ability to replicate in lungs of the infected chickens, whereas virus with G193 reduced its transmissibility in infected chickens to those in direct contact. Our findings demonstrated that variations at HA residue 193 altered various properties of H9N2, highlighting the significance of the continued surveillance of HA for better understanding of the etiology and effective control of H9N2 in poultry. IMPORTANCE H9N2 are widespread and have sporadically caused clinical diseases in humans. Extensive vaccinations in poultry helped constrain H9N2; however, they might have facilitated the evolution of the virus. It is therefore of importance to monitor the variation of the circulating H9N2 and evaluate its risk to both veterinary and public health. Here, we found substitutions at position 193 of HA from H9N2 circulated since 2013 and assessed the impact of several mutations on viral properties. Our data showed these mutations resulted in substantial antigenic change. N193E altered the binding preference of HA for human-like to both avian and human-like receptors. More importantly, N193G impaired the growth of H9N2 and its transmission in chickens, whereas mutations from N to D, E, and S enhanced the viral replication in lungs of chickens. Our study enriched the knowledge about H9N2 and may help implement an effective control strategy for H9N2.

Optimal Control of a Single-Stage Modular PV-Grid-Driven System Using a Gradient Optimization Algorithm

There are many studies that focus on extracting harmonics from both DC and AC sides of grid-interfaced photovoltaic (PV) systems. Based on these studies, the paper introduces an efficient method depending on hybrid DC voltage, and an active and reactive power (DC-V PQ) control scheme in a single-stage three-phase grid-interfaced PV system. The proposed scheme is designed to regulate DC voltage to minimize power loss and energy share between the network reconfiguration and the utility grid. Moreover, the technique is more effective at dealing with uncertainty and has higher reliability under various operating scenarios. These operations are the insertion of linear load 1, nonlinear load, and linear load 2. Moreover, a novel objective function (OF) is developed to improve the dynamic response of the system. OF is coupled with a particle swarm optimization (PSO) algorithm and a gradient optimization (GBO) algorithm. The analysis and the comparative study prove the superiority of GBO with counterfeits algorithm.

Bayesian Optimization Based Adaptive Control of Thermoacoustic Instabilities

Thermoacoustics instability is one of the factors that limits the operational range of gas turbines. Both active and passive control strategies have been developed to suppress thermoacoustic instability. Active control strategies can adapt to the gas turbine's operational condition and hence provide a wider effectivity than the passive control strategies. However, it remains a challenge to best optimize the control parameters. This work proposes an adaptive control strategy by using Gaussian Process Regression with a modified Safe-Optimisation (SafeOpt) algorithm. The main benefit of the algorithm is it can safely explore the parameter space and minimize the cost function simultaneously. The performance of the algorithm in suppressing the thermoacoustic instability is experimentally demonstrated by stabilizing a turbulent combustor with loudspeakers actuation.

Sound Radiation from a Plate with Embedded Active Acoustic Black Holes

Acoustic Black Holes (ABHs) can be realised as tapered structural features that focus and absorb vibrational energy. In a plate, the damping effect of ABHs can be used to reduce the radiation efficiency, particularly above the critical frequency of the plate. However, at lower frequencies, there is still significant radiation due to the low order modes of the plate. It has previously been shown that the combination of active control and ABHs can result in an effective broadband control solution with lower computational and power requirements compared to a standalone active configuration. This paper presents an investigation into how two different active control strategies affect structural response and radiated sound power of a plate with active ABHs (AABHs). It is shown, through an active vibration control strategy and an active noise control strategy, that the AABHs can be used to successfully control either the global structural response of the plate or the radiated sound power. However, it is also shown that controlling either response can lead to an enhancement in the other.

Active Power Control Integrated With Reactive Power Compensation of Battery Energy Stored Quasi-Z Source Inverter PV Power System Operating in VSG Mode

The battery energy stored quasi-Z source inverter (BES-qZSI)-based photovoltaic (PV) power system combines the advantages of the qZSI and energy storage system. However, as the BES-qZSI is a fast-response power converter without any inertia, when applied as a grid-connected system, it leads to decreased power system inertia. The low inertia problem will degrade the system’s performance and affect the system’s stability. Moreover, the BES-qZSI PV power system usually employs a phase-locked loop and PR regulator to control the grid current to track the desired reference in phase with the grid voltage. These do not reflect the characteristics of frequency modulation and voltage regulation. To enhance the system’s frequency and voltage self-adjustment ability, a control strategy based on the virtual synchronous generator (VSG) technique for the BES-qZSI PV power system is proposed in this article. By introducing the concept of synchronous generator, the BES-qZSI PV power system has the characteristics of the heavy moment of inertia, droop frequency active, droop characteristic of voltage–reactive power, and so on. Then, an active power control strategy integrated with reactive power compensation is proposed to implement PV generation and reactive power compensation at the same time. The simulation and experimental results verify the proposed control strategy.

Limitations of FxLMS in Feedforward Active Vibration Control of a Nonlinear Two-Degree-of-Freedom System

Active control systems are often used to surmount the challenges associated with passive noise and vibration control measures to control low frequency disturbances, since they achieve control without the application of large or heavy control treatments. Historically, linear active control strategies have been used in feedforward control systems to drive the control source to minimise the signal measured at the error sensor. Amongst the various control algorithms available, the Filtered-reference Least Mean Squares (FxLMS) algorithm has become extremely popular in the last few decades due to its relatively good performance and high level of robustness, as well as simplicity in both design and application. However, when the system under control contains nonlinearities, either in the primary or secondary paths, the performance of the FxLMS algorithm can degrade dramatically. This paper explores the performance limitations of the FxLMS algorithm when applied to the control of a two degree of freedom mass-spring-damper system with linear and cubic nonlinear stiffness terms. The aim of this study is to improve understanding of and inspire better design of nonlinear control systems. The statistical uncertainty present in the linear plant model and control filter is discussed, as well as the effect of this on control performance and control effort. The effect of nonlinearity on the maximum convergence parameter of the algorithm is also discussed.

Steps towards Decarbonization of an Offshore Microgrid: Including Renewable, Enhancing Storage and Eliminating Need of Dump Load

A novel control strategy to manage the integration of a wind turbine (WT) and an energy storage unit to an existing stand-alone microgrid servicing an oil and gas (O&G) rig is the topic of this paper. The control strategy includes a primary and a secondary controller that, using the battery in tandem with the WT, does not require any dump load (A). The secondary controller includes an energy management system (EMS) which uses the estimated wind production and other specific local information to size the battery to avoid the curtailment of the WT (B) and simultaneously provide the framework for the economic analysis (C). Points A, B and C are the main novelties introduced with this work. Additionally, a primary controller operates the original microgrid source, a gas turbine (GT), at its maximum efficiency through an active power control strategy to lower fuel consumption, by prioritizing the exploitation of the renewable energy source through the combination EMS and battery sizing. The microgrid is simulated and the combined controller of the battery and GT bench-tested.

Projective synchronization for a new class of chaotic/hyperchaotic systems with and without parametric uncertainty

The term “chaotic system” refers to a kind of dynamical system that is characterized by its extreme sensitivity to its initial conditions. The ability of such dynamical systems to maintain synchronization is one of the extremely crucial features of these systems. There is an increasing fascination in chaotic systems with real-state variables, and they are being discovered as well as explored in greater depth in a variety of areas of nonlinear science. In this manuscript, a mixture of active nonlinear control scheme as well as adaptive control scheme has been recommended to investigate the full-order and reduced-order projective synchronization for a unique class of chaotic and hyperchaotic systems with as well as without uncertain parameters. Active nonlinear control technique is an effective method, which has been extensively used to synchronize two chaotic systems in master–slave configuration when parameters of the systems under consideration are fully known in advance. However, in practical scenarios, system parameters are not exactly known in advance. This often occurs due to the factors such as limitations associated with the experimental conditions, mutual interference among system components or due to the influence of external environmental factors. Therefore, in such cases, the designer has to go for the adaptive control technique to develop the adaptation control laws for unknown system parameters. Adaptive active nonlinear controller and parameter adaptation laws have been introduced here using Lyapunov stability criteria to confirm that the error dynamics of the synchronizing chaotic systems become asymptotic stable. Furthermore, numerical simulations on Lorenz hyperchaotic fourth-order system and Pehlivan chaotic third-order system are shown to demonstrate that the proposed synchronization scheme is working effectively.

Linear Active Disturbance Rejection Control for a Laser Powder Bed Fusion Additive Manufacturing Process

Functional metal parts with complicated geometry and internal features for the aerospace and automotive industries can be created using the laser powder bed fusion additive manufacturing (AM) technique. However, the lack of uniform quality of the produced parts in terms of strength limits its enormous potential for general adoption in industries. Most of the defects in selective laser melting (SLM) parts are associated with a nonuniform melt pool size. The melt pool area may fluctuate in spite of constant SLM processing parameters, like laser power, laser speed, hatching distance, and layer thickness. This is due to heat accumulation in the current track from previously scanned tracks in the current layer. The feedback control strategy is a promising tool for maintaining the melt pool dimensions. In this study, a dynamic model of the melt pool cross-sectional area is considered. The model is based on the energy balance of lumped melt pool parameters. Energy coming from previously scanned tracks is considered a source of disturbance for the current melt pool cross-section area in the control algorithm. To track the reference melt pool area and manage the disturbances and uncertainties, a linear active disturbance rejection control (LADRC) strategy is considered. The LADRC control technique is more successful in terms of rapid reference tracking and disturbance rejection when compared to the conventional PID controller. The simulation study shows that an LADRC control strategy presents a 65% faster time response than the PID, a 97% reduction in the steady state error, and a 98% reduction in overshoot. The integral time absolute error (ITAE) performance index shows 95% improvement for reference tracking of the melt pool area in SLM. In terms of reference tracking and robustness, LADRC outperforms the PID controller and ensures that the melt pool size remains constant.

Design and Implementation of Permanent and Electromagnet Composite Vibration Isolation System Based on Negative Stiffness Theory

In order to decrease the transmission of vibration and achieve the attenuation of the vibration magnitude of an isolated object, a new type of permanent and electromagnet composite vibration isolation system is designed based on negative stiffness theory. Firstly, according to the characteristic analysis, the design of a permanent and electromagnet hybrid actuator is accomplished; secondly, the vibration isolation system model is established, and the active control strategy based on the fuzzy PID algorithm is designed. Finally, a test platform is built to verify the vibration isolation effect. The results indicate that the developed permanent and electromagnet composite vibration isolation system renders the sharp attenuation of external vibration in multiple frequency bands. When the external vibration frequency is within the frequency range of 20 Hz to 100 Hz, the vibration attenuation is greater than 80%; when the external vibration frequency is within the frequency range of 100 Hz to 500 Hz, the vibration attenuation rate is greater than 90%.

An active oscillation reduction method for off-highway front loaders

Cabin vibration in construction machines is a known issue affecting both comfort and safety of the operators, and it also induces losses in machine productivity. The solution offered in commercial machines, known as the passive ride control, has the drawbacks of limited performance on a wide range of operating conditions and component costs, which has motivated research toward “active” alternatives that utilize electro-hydraulic systems without additional components. Nonetheless, the nonlinearities and the dynamic response of these systems constraint the performance of such alternatives, when compared to the commercial solution and therefore, their diffusion on the market. To address the challenges mentioned above, this article proposes an alternative hydraulic system layout to perform the ride control function based on connecting the boom lift actuators of the front-end loader in differential mode. This article describes the development of two active control strategies for this new ride control system that utilizes pressure and acceleration information to suppress cabin oscillations and presents the experimental tests on a full-size wheel loader. The results show a similar capability for reducing the oscillations achieved by the commercial solution and the one proposed in this research. In certain scenarios, the proposed formulation offers up to 10% of further improvement in terms of cabin oscillation reduction.

Position control of electro-hydraulic servo system using active disturbance rejection control for upper-limb exoskeleton

This paper presents a two-degree-of-freedom(2-DOF) upper-limb exoskeleton actuated by electro-hydraulic servo system (EHSS), and position control based on active disturbance rejection control (ADRC) strategy. Proportional integral derivative (PID) controller is widely used in EHSS system because it is model free, and its parameters can be adjusted easily. However, the nonlinear dynamics of EHSS is subject to parameter variations and friction effects during operation. The trajectory tracking performance of this method is limited due to the uncertain model parameter and external disturbance of EHSS in exoskeleton. To actively compensate the total disturbance including the system uncertainty and external disturbance, and ensure the finite time convergence of disturbances, the ADRC controller is developed. The disturbances can be estimated by the extended state observer (ESO) and compensated during each sampling period in the ADRC method. The proposed control strategy not only satisfies the steady-state accuracy demands, but also effectively resists to the system uncertainties and the disturbance. To validate the feasibility of the proposed control strategy, the simulations were carried out. The numerical simulation results clearly indicate the superior performance of proposed ADRC method over the regular PID control approach.

AC-DC Fuzzy Linear Active Disturbance Rejection Control Strategy of Front Stage of Bidirectional Converter Based on V2G

Aiming at the problems of output voltage fluctuation and current total harmonic distortion (THD) in the front stage totem-pole bridgeless PFC of two-stage V2G (Vehicle to Grid) vehicle-mounted bi-directional converter, a fuzzy linear active disturbance rejection control strategy for V2G front-stage AC-DC power conversion system is proposed. Firstly, the topological working mode of the totem-pole bridgeless PFC is analyzed, and the mathematical model is established. Combined with the system model and the linear active disturbance rejection theory, a double closed-loop controller is designed with the second-order linear active disturbance rejection control as the voltage outer loop and PI control as the current inner loop. The controller can realize self-adaptive tuning of the proportional gain coefficient of the active disturbance rejection controller through fuzzy reasoning and realize self-adaptive control. Simulation and experimental results show that this method can better solve the problems of slow system response and high total harmonic distortion rate of input current and effectively improve the system’s robustness.

Stability analysis of chaotic generalized Lotka-Volterra system via active compound difference anti-synchronization method.

This work deals with a systematic approach for the investigation of compound difference anti-synchronization (CDAS) scheme among chaotic generalized Lotka-Volterra biological systems (GLVBSs). First, an active control strategy (ACS) of nonlinear type is described which is specifically based on Lyapunov's stability analysis (LSA) and master-slave framework. In addition, the biological control law having nonlinear expression is constructed for attaining asymptotic stability pattern for the error dynamics of the discussed GLVBSs. Also, simulation results through MATLAB environment are executed for illustrating the efficacy and correctness of considered CDAS approach. Remarkably, our attained analytical outcomes have been in outstanding conformity with the numerical outcomes. The investigated CDAS strategy has numerous significant applications to the fields of encryption and secure communication.

Mitigating borehole drill string torsional vibration and shock

This paper provides an analysis of one of the dysfunctions in borehole drill strings, which is torsional vibration. Additionally, an analysis of mitigation through systematic adjustment of the key parameters of Weight on the Bit (WOB) and Rotations per Minute (RPM) is conducted. One of the key forms of dysfunction is undesired vibration and shocks on the drill strings. The vibration and shock experienced by drill strings have a detrimental impact on equipment life, resulting from damage to the drill bit and the drill string components. This paper studies a generalized lumped-parameter model of the drill-string system to provide a fundamental understanding of the torsional stick-slip vibrations during drilling operations. The impact of various parameters such as the weight on the bit, rotational speed, and damping on the severity of vibration, in particular, stick-lip vibration, is analyzed. Various passive, active, and semi-active control strategies to mitigate the torsional vibrations have been studied and implemented with varying degrees of success, subject to continual development. From the simulation, the WOB, the drive torque, and rotational velocity determine the stick-slip onset and severity. This paper focuses on active control of the rotational speed and the weight on the bit by systematic adjustment to eliminate stick-slip while avoiding other undesirable effects and thus achieving optimum performance. Further study will be on multi-stability analysis to define the optimum operation zones and the design of vibration reduction tools and control strategies.

SiC JFETs Modular Cascaded Method with Active Clamp Control Strategy for DC Solid-State Circuit Breaker

SiC JFETs Modular Cascaded Method with Active Clamp Control Strategy for DC Solid-State Circuit Breaker