Feedforward Control Strategy Research Articles

Synchronous disturbance suppression of active magnetic bearing rotor systems using variable period adaptive control algorithm

This paper aims to investigate the issue of suppressing synchronous vibration in active magnetic bearing (AMB) systems. The rotor mass imbalance is a challenging problem for the AMB system, which will cause synchronous vibration and severely affect the system stability and safety. However, existing algorithms based on the iterative feed-forward control strategy find it difficult to simultaneously ensure system’s stability and competent convergence performance. They struggle to maintain tolerable robustness within the system operating bandwidth. This paper proposes a variable period adaptive control algorithm to address these challenges. The overall control scheme can achieve current and displacement elimination separately by switching control structures and is applicable to variable speed conditions. This algorithm can adaptively adjust the iteration period based on rotational speed to ensure both splendid convergence performance and system dynamic performance. Furthermore, this work employs the Lyapunov method to analyze the algorithm’s asymptotic stability and provides a lookup table for algorithm parameters. This could significantly enhance the robustness and stability of the algorithm within the system operating bandwidth. Finally, this methodology has proven to be effective and superior in simulations and experiments.

Primary frequency regulation for multi‐infeed HVDC system using model predictive control and local estimation

AbstractThis paper proposes a novel primary frequency regulation (PFR) scheme for multi‐infeed high voltage direct current (HVDC) (MIDC) system. First, a dynamic model for frequency response in the MIDC system is carried out to involve line‐commutated‐coveter (LCC)‐HVDCs in frequency regulation. Then, a disturbance observer (DO) is proposed to estimate both the power imbalance and the full order states of the system. By combining a Kalman filter, this DO gets an accurate estimation quickly with local frequency measurement. On the basis of the estimated disturbance and state variables, feedforward control schemes can be concluded to fully utilize the fast adjustability of LCC‐HVDCs. In this paper, a model predictive control based scheme is designed to coordinate LCC‐HVDCs under constraints of HVDC capacity and frequency boundaries. As a result, the optimal power‐sharing property of LCC‐HVDCs is achieved to enhance the PFR dynamic performance of the AC main system. Further, the stability of the proposed method is analysed using the Lyapunov method. Finally, numerical simulations are concluded to verify the effectiveness and the merits of the proposed method, by comparing it to typical droop controls.

Application of Feedforward Cascade Compound Control Based on Improved Predictive Functional Control in Heat Exchanger Outlet Temperature System

Aiming at the problems of large delay and poor anti-disturbance ability in the outlet temperature control system of the heat exchanger to optimize the control accuracy of the system and improve the control performance, this paper proposes a control scheme combining predictive functional control with proportional-integral-derivative control. Using the incremental proportional-integral-derivative control algorithm to improve the optimization objective function of the predictive functional control algorithm, a predictive functional control optimization model with a proportional-integral-derivative structure is established. The feedforward compensation control is adopted to eliminate the influence of external disturbances on the heat exchanger temperature control system. Through simulation, the proposed control scheme is compared with the feedforward cascade compound control scheme based on a proportional-integral-derivative main controller. The results show that the scheme has a small over harmonic and strong anti-interference ability. The adaptability and stability of the system are significantly improved, and the exit temperature of the heat exchanger can be effectively controlled.

Hysteresis Modeling and Compensation for Tendon-Sheath Mechanisms in Robot-Assisted Endoscopic Surgery Based on the Modified Bouc-Wen Model With Decoupled Model Parameters

The tendon-sheath mechanism (TSM) has been widely applied in flexible endoscopy (FE) and natural orifice transluminal endoscopic surgery (NOTES) owing to its advantages of remote force and displacement transmission, size reduction, compactness, and convenient implementation. However, the positioning accuracy of TSMs is highly restrained by the motion hysteresis due to the complex friction condition between the tendon and sheath. The hysteresis phenomenon has posed significant challenges for modeling and controlling TSMs. This paper proposes a modified Bouc-Wen-based mathematical model to characterize the asymmetric hysteresis loop with distinct inflection points. The model parameters are decoupled, facilitating identification and reducing computational costs. Moreover, the model has retained the Bouc-Wen model structure, allowing for efficient derivation of the feedforward compensator based on the inverse multiplicative structure. The compensator was derived and cascaded with the TSM system to suppress the hysteresis phenomenon. Totally 120 trials of experiments were conducted to validate the proposed model and the feedforward control scheme on the two TSMs with different accumulated curvatures of 180∘ and 360∘. The results indicated that the proposed method achieved a 25.5% and 43.9% lower estimation and compensation error than the classical Bouc-Wen model. Further, it is worth noting that the model parameter identification time consumption has been significantly reduced to 5.8ms. The proposed model and the feedforward compensator can effectively linearize the TSM system and further facilitate delicate operations in robot-assisted surgical procedures.

Accelerometer-Assisted Disturbance Feedforward Control of an Inertially Stabilized Platform

Inertially stabilized platforms (ISPs) are extensively utilized to stabilize the line of sight (LOS) and achieve precise tracking regardless of various disturbances, whereas their disturbance suppression ability (DSA) is always limited by the system bandwidth. Therefore a disturbance feedforward method based on accelerometer measuring is proposed in this article, which breaks the feedback loop bandwidth limitation and thus improves the closed-loop performance of an ISP. To avoid signal coupling effects between traditional inertial loops, the feedback loop is designed which encompasses the inner loop based on a high-bandwidth encoder as a non-inertial loop and the gyro-based outer loop as an inertial loop. The conventional model-based inverse control reduces the control bandwidth and high-frequency DSA due to the unrealizable differentiation in the system. Hence, the novel accelerometer-based feedforward controller is developed. We adopt the accelerometer integral to obtain high-bandwidth and high-precision disturbance signals and construct the low-pass filter instead of the conventional integrator. Finally, an accelerometer feedforward control scheme that combines acceleration integration with acceleration is conducted to further enhance the system DSA. Simulations and experiments demonstrate the validity of the presented approach.

Control of new energy‐intensified triple column extractive distillation using feed split technique

AbstractBACKGROUNDHere, we investigated the control performance of extractive distillation intensified with ‘feed split’ (FS) technique – a process intensification technique that has not been widely applied to extractive distillation. Today, only a handful of studies have been reported on this topic, with only one focusing on the control performance and reporting the significant trade‐off between the steady‐state and dynamic performances. Nonetheless, the previous control study was based on the complex double column FS configuration. Recently, a new triple column FS configuration was reported (Sep. Purif. Technol. 2022 (297) 121467), but its control performance was not investigated. Hypothetically, the triple column FS configuration is less complex and does not involve any column integration and thus, may demonstrate a better dynamic performance. This study analyzed the control performances of the triple column FS configuration and the conventional configuration for the binary azeotropic separation of tetrahydrofuran and ethanol.RESULTSTwo types of control structures were examined for both configurations, i.e., the basic temperature control structure and the different feed forward temperature control schemes. The best control structure from each configuration is compared and findings showed that the conventional configuration provides better controllability performance.CONCLUSIONOur results suggested that the conventional configuration can bring the product qualities closer to their setpoint, while providing a lower transient deviation. © 2023 Society of Chemical Industry (SCI).

Controller Design and Stability Analysis of an MSR Plant Based on a Nonlinear Distributed-Parameter Model

A molten-salt reactor (MSR), in which the nuclear waste can be separated and taken away from the liquid fuel through online chemical treatment, has remarkable advantages in safety and economics. To ensure the safe operation of an MSR plant, it is necessary to carry out a controller design and stability analysis of the whole system. In this work, a nonlinear distributed-parameter model of an MSR plant with a graphite-moderated liquid core was established and verified by the reference model. By applying a joint feedforward and feedback control strategy, the power controller and steam temperature controller were designed to adjust the plant load. The Nyquist criterion was used to assess the stability of the control system. The system responses to four different perturbations at the nominal power level were simulated, and the results show that the designed controllers have good reliability. In addition, the control performance was tested in two load change cases: a step load reduction and a linear load change. The dynamic response characteristics of the system parameters show that the developed control system based on the nonlinear distributed-parameter model is capable of fast and accurate regulation.

An inherently fault tolerant control of sodium cooled fast reactors and its stability analysis using particle swarm optimization

In this study we propose a simple, yet inherently fault-tolerant and robust controller utilizing a combination of both feedforward and feedback control schemes. Feedback controllers are known to be robust, but feedforward controllers can be reliable in the context of safety as they can be less dependent on measurements. Though, many combined feedforward and feedback controllers have been proposed in the literature, to the best of our knowledge a controller tolerant to the failure of power feedback signal is nowhere demonstrated. In this scheme, major corrections are effected by a model predictive forward control unit, while bounded uncertain part is corrected by a feedback control unit. The feedforward control is implemented using the inverse equations of the nuclear reactor point kinetics model. The bounded error control is effected by a simpler limited Proportional–Integral–Derivative (PID) feedback controller. Stability analysis of the controller is carried out numerically by Lyapunov’s direct method with the help of Particle Swarm Optimization (PSO) technique. The proposed controller (referred to as Inverse Dynamics Corrected Control (IDCC)), is studied for reactor power control with model error plus uncertainty and a principal feedback signal failure case ( i.e. power sensor failure). It is shown that the IDCC has excellent load tracking performance for a challenging demand profile with model error, in comparison to Sliding Mode Controller (SMC) and a manually tuned PID controller. For the loss of principal feedback signal case, there is a trade off between the tracking performance of IDCC and safety aspects. While both PID and SMC drive the reactor power to unsafe levels, IDCC maintains the reactor power within a safer bound.

Control Study for Compensating Rotor Vibration of Four-DOF Six-Pole Hybrid Magnetic Bearings Based on Variable Step Size LMS Algorithm

In order to solve the problem that the unbalance vibration caused by rotor mass eccentricity of the four-degree-of-freedom (four-DOF) six-pole hybrid magnetic bearings (HMBs), a feed-forward compensation control strategy based on variable step size least-mean-square (LMS) adaptive filter is proposed. First, the structure, operation principle and mathematical model of the four-DOF six-pole HMBs are introduced, the motion law of rotor vibration is analyzed, and the dynamic equation is derived. Second, the variable step size LMS adaptive filter is improved by using the Versoria function. The step size of LMS algorithm is adjusted adaptively by using Versoria function model and Takagi–Sugeno (TS) fuzzy inference machine. The LMS adaptive filter can generate a signal with the same frequency, amplitude, and phase as the rotating speed to offset the vibration signal, so as to realize the vibration compensation control of the four-DOF six-pole HMB rotor. Finally, the simulations and experiments not only prove the effectiveness of this method but also show that the method has good compensation accuracy. The result shows that the Versoria function used in variable step size LMS adaptive filter for vibration compensation is better than the traditional variable step size filtering algorithm based on Sigmoid function.

A Novel Feedforward Model of Piezoelectric Actuator for Precision Rapid Cutting.

The piezoelectric actuator has been widely used in modern precision cutting technology due to its fast response speed and high positioning accuracy. In recent years, with the development of precision technology, modern cutting requires higher and higher cutting accuracy and efficiency. Therefore, this paper proposes a feedforward control method based on the modified Bouc-Wen (MBW) model. Firstly, a novel asymmetrical modified Bouc-Wen model with an innovative form of shape control function is developed to model the hysteresis nonlinearity property of piezoelectric actuators. Then, a self-adaptive cooperative particle swarm optimization (PSO) algorithm is developed to identify the parameters of MBW model. The comparative evaluation reveals that the MBW model outperforms the classical Bouc-Wen (CBW) model by 66.4% in modeling accuracy. Compared with traditional PSO algorithm, the self-adaptive cooperative PSO algorithm can obtain minimum fitness in parameter identification. Furthermore, the feedforward control strategy is realized to improve the position tracking accuracy. A position tracking experiment verifies that the feedforward control strategy improves the tracking accuracy of piezoelectric actuators significantly compared with the open-loop control strategy.

Time-varying modeling and intelligent compensation control of singletendon-sheath structure of surgical robot

The inaccurate force and position control of tendon sheath system (TSS) due to nonlinear friction during surgery seriously hinders its development in the field of precision surgical robots. To this end, this paper proposes a time-varying bending angle estimation method under the state of sensorless offline identification combined with robot kinematics by analyzing the friction of the TSS and the deformation of the robot during the movement, and establishes a force and position transfer model with time-varying path trajectory (SJM model). The model uses B-spline curve to fit tendon-sheath trajectory. In order to further improve the control accuracy of force and position, a new intelligent feedforward control strategy that integrates the SJM model and a neural network algorithm is proposed. In order to gain an in-depth understanding of the transmission process of force and position and to demonstrate the validity of the SJM model, an experimental platform for the TSS was built. A feedforward control system under the MATLAB environment was built with the aim of verifying the accuracy of the intelligent feedforward control strategy. The system innovatively combines the SJM model with BP and RBF neural networks, respectively. The experimental results showed that the correlation coefficients (R2) of force and position transfer are above 99.10% and 99.48%, respectively. Ultimately, we compared the intelligent feedforward and intelligent control strategy under a single neural network, and observed that the intelligent feedforward control strategy has a better effect.

Linear uncertain modelling of LIDAR systems for robust wind turbine control design

Light detection and ranging (LIDAR) sensors measure the free wind ahead of the rotor, enabling the use of new feedforward control strategies. However, there exist some sources of error inherent to the measuring process that should be considered during the design of LIDAR-based controllers. Typically, the coherence function is used for that purpose, but it is not compatible with some robust design methodologies. This paper presents an analytic relation between the coherence function and a non-parametric uncertainty model of LIDAR sensors, suitable for the design of controllers via μ-synthesis or Quantitative Feedback Theory. Such a relation is applied to a realistic LIDAR simulator. First, the linear non-parametric uncertainty model is identified using simulation data obtained from the well-known NREL 5 MW wind turbine. Then, it is validated against the coherence model by comparing linear predictions of the simulation outputs.

Feedforward Control Strategies for Rapid Phase Adjustment of Superconducting Cavities

Rapidly adjusting (or scanning) the phase of a superconducting radio-frequency (SRF) cavity (on a millisecond or sub-millisecond time-scale) under closed-loop control is crucial in various applications of many SRF facilities. However, the transient dynamic response of the feedback (FB) control loop is usually unsatisfactory (e.g., the cavity field amplitude is seriously disturbed) during the phase adjustment process because of the restricted closed-loop bandwidth and limited power budgets. Herein, we proposed a feedforward (FF) control strategy derived from a cavity differential equation to accelerate the control loop’s regulation process, thereby improving the system’s dynamic behavior. We demonstrated the validity of the FF-based strategy in the Chinese ADS Front-end (CAFe) proton facility demo SRF linac. The preliminary results showed that the combined FF+FB control strategy significantly improved the dynamic performance compared to the FB individual control. This study provides the basis for the FF scheme validation and may serve as a reference for applications requiring rapid SRF cavity phase change.

Passivity-based analysis and design for selective harmonic resonant control

This paper analyses the impedance passivity of selective harmonic resonant control for voltage-source converter. It is found that the phase-lead compensation of harmonic resonant controller may fail to eliminate the negative damping above certain harmonic frequency, depending on the size of time delay. Further, a trade-off between the internal stability margin of harmonic control and the impedance-passivity shaping is identified. To overcome these drawbacks, a feedforward control scheme is proposed in this work, which guarantees both impedance passivity and sufficient internal stability margin for the selective harmonic resonant control. Electromagnetic transient simulations verify the theoretical analyses and the effectiveness of the control method.

Selecting control schemes and tuning rules in feedforward control*

This paper treats the problem of feedforward control from measurable load disturbances. Most of the tuning rules based on IAE or ISE optimization for feedforward compensators that have been presented in recent years are compared with each other as well as with optimal compensators. There are two different feedforward control schemes that may be used, and these schemes are also compared and analyzed. The paper gives recommendations for selection of both control schemes and tuning rules.

Run-to-Run Adaptive Nonlinear Feedforward Control of Electromechanical Switching Devices

Feedforward control can greatly improve the response time and control accuracy of any mechatronic system. However, in order to compensate for the effects of modeling errors or disturbances, it is imperative that this type of control works in conjunction with some form of feedback. In this paper, we present a new adaptive feedforward control scheme for electromechanical systems in which real-time measurements or estimates of the position and its derivatives are not technically or economically feasible. This is the case, for example, of commercial electromechanical switching devices such as solenoid actuators. Our proposal consists of two blocks: on the one hand, a feedforward controller based on differential flatness theory; on the other, an iterative adaptation law that exploits the repetitive operation of these devices to modify the controller parameters cycle by cycle. As shown, this law can be fed with any available measurement of the system, with the only requirement that it can be processed and converted into an indicator of the performance of any given operation. Simulated and experimental results show that our proposal is effective in dealing with a long-standing control problem in electromechanics: the soft-landing control of electromechanical switching devices.

THE ANALYSIS OF REDUCTION IN SWITCHING LOSS WITH FEEDFORWARD CONTROL IN GRID-TIED MICRO GRID SYSTEM

This paper proposes the simplified pulse widthmodulation (PWM ) strategy in the bidirectionalac/dc single-phase converter with the feed-forwardcontrol scheme. In this, the number of switching ofthe proposed simplified PWM strategy is reduced toone-fourth to that of the unipolar & bipolar PWM.The feed-forward control scheme is used to achievebetter performance of the ac/dc converter in both therectifier & inverter mode as compared with theconventional dual-loop control scheme. Thesimplified PWM strategy with feed-forward controlscheme has higher efficiency than that of the unipolarPWM & bipolar PWM strategies. Also, the totalharmonic distortion is less in this PWM strategy. Thesimulation & experiments are carried out to verify thevalidity of the proposed PWM strategy & controlscheme. The proposed simplified PWM strategy withthe proposed feedforward control scheme has lowertotal harmonic distortion than the bipolar PWM andhigher efficiency than both unipolar and bipolarPWMs. Furthermore, the proposed simplified PWMoperated in the inverter mode also has largeravailable fundamental output voltage VAB than boththe unipolar and bipolar PWMs. A prototype systemis constructed and the control scheme is implementedusing FPGA Spartan-3E XC3S250E. Both simulationand experimental results verify.

A Feasibility Study of the Use of PZT Actuators for Active Control to Enrich Engine Sound

This study examines the feasibility of a novel active sound enrichment (ASE) system using piezoelectric actuators as sound generators and an inverse control filter to supplement poor engine sound at the driver’s ear location in a passenger car instead of using an interior audio system. The proposed ASE algorithm is developed as a purely feedforward control strategy to track the pre-defined target engine sound (three engine orders). Theoretical and experimental analyses are investigated in-depth on the vibro-acoustic characteristics of a PZT (lead zirconate titanate) actuator bonded on a steel plate and a dedicated control filter to supplement sound using an inverse method to compensate for the secondary path. The location of the PZT-plate actuator was carefully chosen to satisfy the causality condition and robustly stable control of the ASE algorithm. The experimental ASE system was set up in a test car, and the ASE algorithm was implemented in a real-time controller. The real-time ASE experiment results showed that the measured sound of the three orders was well supplemented as the tracking of the target sound was achieved robustly with small errors without any divergent instability. Thus, this study suggests that the proposed ASE system using the PZT-plate actuator and the dedicated control filter is a feasible method for enriching sound in cars, and this approach can be considered as a masking tool against some exotic noise frequently observed in various vehicles including electric vehicles.

Characteristic Prediction and Temperature-Control Strategy under Constant Power Conditions for Lithium-Ion Batteries

Accurate characteristic prediction under constant power conditions can accurately evaluate the capacity of lithium-ion battery output. It can also ensure safe use for new-energy vehicles and electrochemical energy storage. As the battery voltage continues to drop under constant power conditions, the battery current output will accordingly increase, which brings a risk of thermal runaway in instances of weak heat dissipation. Therefore, knowing how to control the battery temperature is very critical for safe use. At present, the model-based method for characteristic prediction and temperature control has been used by most scholars, and that is also the key to this method. This work firstly extends a cell model to a pack-based electrochemical two-dimensional thermal coupling model, considering the heterogeneity of different cells inside the pack, and obtains the model parameters for a prismatic lithium-ion battery with a rated capacity of 42 Ah. Characteristic prediction under constant power conditions is then conducted based on an iterative solution method. Validations of characteristic prediction indicate the convenience of the developed models, with average absolute errors of voltage and temperature less than 36 mV and 0.4 K, respectively, and power error less than 0.005%. Finally, two model-based temperature feed-forward control strategies with lower cooling costs and shorter prediction times were developed based on the battery characteristic predictions, which leaves room for further controller development.

Generalized Stabilizer-Oriented Design for GFVSG Integrated Into Weak-Stiffness Power Networks

This letter proposes a generalized stabilizer-oriented design method for grid-forming virtual synchronous generator (GFVSG) attached to weak-stiffness power networks, where a rate of change of frequency feedforward control strategy (RoCoF-FCS) is put forward to improve frequency stability, enhance damping performance, and avoid aperiodic loss of synchronization (ALoS). In addition, the feedback analytical framework, which connects RoCoF and rate of change of voltage (RoCoV), is proposed to identify both wideband oscillation and ALoS. Finally, the proposed method is validated by time-domain simulations.