Feedforward Compensation Research Articles

A novel proposal for harmonic compensation in the grid-connected photovoltaic system under electric anomalies

The accurate estimation and online calibration of the fundamental weight components (FWC) from harmonically contaminated load current is crucial to evaluate the performance of grid-integrated photovoltaic (PV) units especially when exposed to grid anomalies. Driven by this motivation, an adaptive regularized least logarithmic absolute difference (RLLAD) filter is proposed for FWC estimation during nonlinear loading. The proposed filter pertinently captures the FWC of the harmonically distorted load currents. The resulting FWC guarantees balanced and sinusoidal grid currents even under disturbances in the grid voltage and load current thereby achieving different power quality (PQ) improvement targets i.e., grid current balancing and harmonic suppression, active and reactive power management, neutral current compensation, and power factor correction. The proposed RLLAD filter ensures comparable convergence performance and minimum steady-state oscillations in the grid reference currents. Proceeding further, to counter the nonlinearity introduced by the PV array, a feed-forward compensator is judiciously equipped. From a practical standpoint, it ensures superior DC-link voltage stabilization especially under abrupt transition in solar insolation level. The performance of the RLLAD filter is comprehensively assessed through numerical simulations in MATLAB/Simulink software. Furthermore, the practical viability of devised RLLAD filter is confirmed under rigorous experimental scenarios through OPAL-RT control suite. The experimental results demonstrate practicability of the proposed adaptive RLLAD filter and thus, considered to be a promising solution as compared to existing benchmarks and state-of-the-art approaches for online FWC estimation and PQ improvement. Most importantly, in terms of nonlinear load tracking capability, the proposed RLLAD filter is shown to outperform the classical LLAD filter with a response speed of less than 400 μs.

High-Order Sliding-Mode Control Strategy for Improving Robustness of Three-Phase Interleaved Bidirectional Converter

In response to the era background of “comprehensive electrification” and “dual carbon plan” of electric vehicles, DC/DC converters have a good performance in terms of weight, volume, and efficiency and are widely used in fields such as solar power generation, UPS, communication, computers, and electric vehicles. At present, the DC bus voltage is an important indicator for measuring the safe and stable operation of high-voltage DC power systems in electric vehicles. Therefore, regulating the stability of bus voltage through converters has good economic benefits for the sustainable development of electric vehicles in terms of maintenance costs and effective energy management. In order to solve the problem of bus voltage resonance instability caused by negative impedance characteristics of constant power load in an electric vehicle DC power system, a sliding-mode control design strategy of three-phase interleaved bidirectional converter under constant power load was proposed. Firstly, a GPI observer was designed to estimate the state and concentrated disturbances of the system. Then, the estimated value was introduced into the controller for feedforward compensation, thereby achieving fast-tracking of the output voltage to the reference voltage. Finally, the simulation results show that the controller can effectively maintain the influence of disturbances and better improve tracking characteristics and robustness to disturbances and uncertainties.

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 a Fast Piezo-Driven Scanner in the UAV Image Stabilization System

The fast piezo-driven scanner (FPDS) compensates for vibrations in the unmanned aerial vehicle (UAV) image stabilization system. However, the hysteresis nonlinearity reduces the positioning accuracy of the FPDS. To address this challenge, this paper presents a novel weighted polynomial modified Bouc–Wen (WPMBW) model cascaded with a linear dynamic model to describe counterclockwise, asymmetric, and rate-dependent hysteresis loops of an FPDS. The proposed approach utilizes the weighted polynomial function to describe the asymmetric characteristic and the linear dynamic model to capture the rate-dependent behavior. By modifying the last two terms in the classical Bouc–Wen (CBW) model, the modified BW model directly characterizes the counterclockwise hysteresis loops with fewer parameters, circumventing the algebraic-loop problem that arises in the inverse CBW model. The pseudorandom binary sequence (PRBS) input is employed to decouple the linear dynamic model from the WPMBW model. The sinusoidal input is then applied to stimulate the hysteresis phenomenon, and the parameters of the WPMBW model are estimated by the particle swarm optimization (PSO) toolbox. Experimental results on a commercial FPDS show that the proposed model is superior to the CBW and traditional asymmetric BW models in modeling accuracy and feedforward hysteresis compensation.

Robust fixed-order [formula omitted] controller synthesis for multi-phase converters with input voltage feed-forward

Generated DC voltages of batteries, fuel cells, or supercapacitors as power sources connected in series with DC-DC converters change according to operating conditions. In such cases, the output voltage stability of the multi-phase DC-DC converters is an issue, particularly being subject to noises in the input voltage and load current disturbances. Input voltage feed-forward (IVFF) compensation approaches can improve the output voltage stability of the DC-DC converters in such scenarios. This paper proposes a robust fixed-order H∞ based IVFF control framework by considering sensor noise, input voltage, and load current disturbances to improve output voltage stability and reference tracking performance. The mismatched disturbance transfer functions depending on parasitic resistances are derived to include in the controller synthesis process. An iterative convex-concave optimization-based robust fixed-order controller design algorithm is proposed to optimize the feedback and feed-forward controllers under the stability and performance constraints. This algorithm allows the designing of the controllers simultaneously. The feed-forward controller, whose structure is independent of the system transfer functions, is optimized without any model inversion or extra design steps. The performance of the proposed controller is compared with an integral linear quadratic regulator controller, a sliding mode PID controller augmented with a nonlinear disturbance observer, and a fixed-order robust controller designed with non-smooth techniques. Real-time implementation of the fixed-order control systems is performed on a 2-leg 200 W interleaved boost converter. The performances are discussed under external disturbance effects to show the validity of the proposed control approach.

A novel whale optimization smith predictor based on feedforward compensation for controlling wave rotor refrigeration process

AbstractAiming at the difficulty of temperature control and disturbance rejection control in wave rotor refrigeration process (WRRP), a novel whale optimization two‐degree‐of‐freedom (2DOF) Smith predictor based on feedforward compensation method (WO‐2DOFSP‐FC) is proposed. Firstly, the obtained test data of the WRRP are used for system identification and the approximate second‐order model with time‐delay is obtained by using the suboptimal reduction algorithm. This procedure also yields a first‐order model of the disturbance. Then, the whale optimization 2DOF Smith predictor based on feedforward compensation (2DOFSP‐FC) method is proposed. This proposed method improves the 2DOFSP and introduces feedforward compensation control to reduce the influence of the measurable disturbance on the temperature control system. In addition, the Whale Optimization Algorithm (WOA) is proposed to optimally tune the 2DOFSP‐FC controller parameters. Finally, the simulation results show that the proposed WO‐2DOFSP‐FC method can make the controlled system have good characteristics of both set value tracking and disturbance rejection.

Research on Cogging Force Suppression for Toroidal PMLSM Based on Disturbance Observer

For a new type of toroidal permanent magnet linear motor(TPMLSM), this paper analyzes the thrust fluctuation in the constant acceleration operation of the motor from the Angle of the cogging force of the linear motor. For the motor whose structure has been determined and processed, the structural parameters of the motor cannot be changed, and its performance cannot be improved from the perspective of the motor body. Therefore, this paper tries to consider the influence of the cogging force on the normal operation of the motor from the perspective of control. In this paper, starting from the body structure of motor, first on the annular linear motor of the cogging force characteristics were extracted, and its expression is obtained by Fourier decomposition, then investigated considering the cogging force and does not consider the cogging force control of motor model, it can be seen that the control performance deteriorates significantly after considering cogging force of the motor, and the acceleration fluctuation increases significantly during the operation of the motor. On this basis, disturbance observation algorithm is introduced, and feedforward compensation is carried out by extracting the characteristic values of the disturbance model. The results show that the disturbance observer can suppress the thrust fluctuation caused by the motor cogging force to a large extent, and it can reduce the peak-to-peak value of the thrust fluctuation by more than 85% during the motor acceleration operation.

A General Double-Input Synchronous Signal Processor for Imbalanced Vibration Mitigation in AMB-Rotor Systems

Imbalanced vibration is an urgent yet challenging problem in active magnetic bearings (AMBs) rotor manufacturing due to the rotor mass imbalance effect. The virtue of active control in AMB systems lies in enabling substantial online mitigation of imbalanced vibrations. However, in practice, due to the lack of speed sensors in most of the existing AMB-rotor systems, efficient rotational speed feedback is still on the way. As a remedy, this article proposes a rotational speed sensor-free synchronous signal processor (SSP) with the double inputs: <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$</tex-math> </inline-formula> -and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$y$</tex-math> </inline-formula> -axes direction displacement measurements of radial AMBs. The proposed SSP is capable of estimating the rotational speed and accordingly generating synchronous signals of the imbalanced vibrations by filtering noise in both directions. Such signals are afterward implemented as a feedforward compensator for eliminating the periodical imbalance effects. With the assistance of the Lyapunov theory, the conditions of the proposed SSP method together with the feedforward imbalance compensator are derived to guarantee the stability of the closed-loop AMB-rotor system. Extensive experimental results substantiate the effectiveness and superiority of the proposed SSP method in terms of imbalanced vibration suppression.

A precision-drive hysteresis model with an equal-density weight function for GMA feedforward compensation

Giant magnetostrictive actuators (GMAs) are a widely used type of micro-nano actuator, and they are greatly significant in the field of precision engineering. The accuracy of a GMA often depends on its hysteresis model. However, existing models have some limitations, including the difficulty of identifying their parameters and the tradeoff between the quantity of modeling data required and the level of precision achieved. To solve these problems, in this paper, we propose a Preisach inverse model based on equal-density segmentation of the weight function (E-Preisach). The weight function used to calculate the displacement is first discretized. Then, to obtain a finer weight distribution, the discretized geometric units are uniformly divided by area. This can further minimize the output displacement span, and it produces a higher-precision hysteresis model. The process of parameter identification is made easier by this approach, which also resolves the difficulty of obtaining high precision using a small amount of modeling data. The Preisach and the E-Preisach inverse models were investigated and compared using experiments. At frequencies of 1 and 5 Hz, it was found that the E-Preisach inverse model decreases the maximum error of the feedforward compensation open-loop control to within 1 µm and decreases the root-mean-square error in displacement to within 0.5 µm without the need to increase the number of measured hysteresis loops. As a result, the E-Preisach inverse model streamlines the structure of the model and requires fewer parameters for modeling. This provides a high-precision modeling method using a small amount of modeling data; it will have applications in precision engineering fields such as active vibration damping and ultra-precision machining.

Application research of gun servo system based on Stribeck friction model

The gun servo system has strong friction resistance moment. The traditional solution is to reduce the influence of friction disturbance on system control through speed closed-loop. The disadvantage of this method is that the control accuracy of the system is not high due to the lag effect of feedback. To solve this problem, based on the analysis of the composition and working principle of the gun servo system, the friction data of the servo system is obtained through the test, the Stribeck friction model of the system is identified by the method of curve fitting, and the disturbance of the friction torque is compensated and controlled by the control method of feedforward compensation based on disturbance. The simulation results show that this method has good compensation and control ability for the disturbance of friction resistance moment. After using this method, the dynamic tracking accuracy and control performance of the system are greatly improved.

Voltage Control Strategy for Improving Disturbance Rejection Performance in Stationary Reference Frame During Parallel Operation of Multimodular UPS

This paper proposes a voltage control strategy to improve the disturbance rejection performance during the parallel operation of multi-modular uninterruptible power supply (UPS). In the standalone operation of UPS, feed-forward control can improve the dynamic performance of output voltage regulation. However, a circulating current can occur when feedforward control is applied in the parallel operation of UPS modules, causing uneven load sharing among the modules. In this study, the reason for the occurrence of the circulating current was analyzed using a circulating current impedance model. A partial feedforward control technique was proposed, which compensates for a portion of the load current by considering the circulating current impedance in the parallel operation of the UPS. However, this reduced the disturbance rejection performance compared with the standalone operation of the UPS, which uses full feedforward compensation gain. Therefore, an additional feedforward control technique was proposed to enhance the disturbance rejection performance. The effectiveness of the proposed control strategy was verified through the experimental result of the parallel operation of 500 W modular double-conversion UPSs.

Adaptive output feedback control of uncertain nonlinear systems with input saturation

AbstractThis article concerns with the tracking control problem for a class of control‐affine nonlinear systems subject to input saturation, parametric uncertainties and unmodeled uncertainties. The proposed scheme consists of a nested‐saturation‐function‐based controller integrated with feedforward model compensation. A saturated linear extended state observer (SLESO) and parameter adaptation law are constructed to compensate for the unmodeled uncertainties and parametric uncertainties, respectively. By using these mechanisms, the steady‐state tracking performance can be guaranteed through uncertainty compensation. Additionally, the issue of conservativeness in the input saturation problem is effectively addressed through online‐updating the available unsaturated region, which improves transient performance. The proposed scheme results in asymptotic stability when unmodeled uncertainties are constants and ultimate boundedness when unmodeled uncertainties are time‐varying. Finally, simulation studies are presented to demonstrate the effectiveness of the proposed approach.

Real-Time Hybrid Test Control Research Based on Improved Electro-Hydraulic Servo Displacement Algorithm

Real-time hybrid testing (RTH) is a test method for dynamic loading performance evaluation of structures, which is divided into digital simulation and physical testing, but the integration of the two may lead to problems such as time lag, large errors, and slow response time. The electro-hydraulic servo displacement system, as the transmission system of the physical test structure, directly affects the operational performance of RTH. Improving the performance of the electro-hydraulic servo displacement control system has become the key to solving the problem of RTH. In this paper, the FF-PSO-PID algorithm is proposed to control the electro-hydraulic servo system in real-time hybrid testing (RTH), which uses the PSO algorithm to operate the optimized PID parameters and the feed-forward compensation algorithm to compensate the displacement. First, the mathematical model of the electro-hydraulic displacement servo system in RTH is presented and the actual parameters are determined. Then, the objective evaluation function of the PSO algorithm is proposed to optimize the PID parameters in the context of RTH operation, and a displacement feed-forward compensation algorithm is added for theoretical study. To verify the effectiveness of the method, joint simulations were performed in Matlab/Simulink to compare and test FF-PSO-PID, PSO-PID, and conventional PID (PID) under different input signals. The results show that the proposed FF-PSO-PID algorithm effectively improves the accuracy and response speed of the electro-hydraulic servo displacement system and solves the problems of RTH time lag, large error, and slow response.

Design and Test of Sowing Depth Measurement and Control System for No-Till Corn Seeder Based on Integrated Electro-Hydraulic Drive

An electro-hydraulic profiling mechanism has been gradually applied to provide suitable downforce for a no-till row unit and to ensure the consistency of the seed sowing depth. In order to improve the control effect of the sowing depth system and solve the problems of a complex structure, scattered valve sets and equipment suitability of an existing electro-hydraulic row unit, this paper takes the 2BJ-470B no-till row unit as the carrier and innovatively designs an integrated pressure-reducing cylinder (IPRC) based on electro-hydraulic technology by analyzing the sowing depth control process of an electro-hydraulic seeder. In addition, we develop the integrated electro-hydraulic-driven sowing depth measurement and control system. Combined with the feedforward compensation PID control algorithm, the dynamic regulation of the downforce is realized with the IPRC. The field test shows that under the setting of a sowing depth of 50 mm and a vehicle speed of 9~10 km·h−1, the qualified rate of the sowing depth under the three adjustment methods of self-weight adjustment, spring adjustment and electro-hydraulic adjustment is 89.2%, 96.7% and 98.6%, respectively, and the corresponding maximum coefficient of variation of the sowing depth is 16.7%, 12.9% and 6.4%, respectively. The seed groove environmental qualification rate (SFEQ) is further analyzed in combination with the soil compaction, and the mean values of the qualification rates of the three control methods at different vehicle speeds are 88.3%, 91.6% and 98.6%, respectively. The integrated electro-hydraulic-driven row unit has significant advantages over mechanical and self-weight regulation, and its whole machine integration degree and high adaptability realize the comprehensive control of the sowing depth and soil compaction strength.

Rudder/fin joint anti-rolling control system based on interference model predictive control and sliding mode observer

To overcome the difficulties of time-varying disturbance, model mismatch, and frequent operation in the rudder/fin joint control system, an interference model predictive control (I-MPC) rudder/fin joint control system with sliding mode observer is proposed. Considering that the model mismatch problem occurs when the ship is sailing, the model mismatch and external disturbance are regarded as the total disturbance. A discrete 3-degree-of-freedom ship disturbance mathematical model is established. The rudder angle and fin angle are selected as the system inputs, then a sliding mode observer is designed to observe the time-varying disturbance and system output in real time. Different from traditional MPC and feedforward compensation, I-MPC will predict the output based on the disturbance observation value, and the control law is solved under rudder/fin angle and angular velocity constraints. Simulation results show that the proposed method improves the tracking performance and anti-disturbance performance of the rudder/fin system. The observer has high observation accuracy for constant, sinusoidal, and time-varying disturbances. Mechanism wear and energy loss caused by frequent operation are avoided.

Intelligent Tracking Error Prediction and Feedforward Compensation for Nanopositioning Stages With High-Bandwidth Control

In this paper, an intelligent feedforward prediction and compensation scheme to combine with a dual-loop high-bandwidth controller is proposed for high-speed and high-precision tracking control of a nanopositioning stage. Firstly, the dual-loop controller (DLC) consisting of an inner-loop damping and an outer-loop tracking controller is developed with all the parameters optimized simultaneously, which could provide a control bandwidth over the first resonant frequency of the stage. Next, the Gaussian process (GP) machine learning model is employed to capture the dynamic characteristics of the tracking error of the dual-loop controlled plant. Then, a feedforward compensator is constructed to add a compensation term to the initial reference trajectory. Experimental investigations on a self-made piezoelectric-actuated stage validate the effectiveness of the intelligent tracking error prediction method and the excellent performance of the control strategy for high-precision tracking of high-frequency reference trajectories.

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.

Tracking control of a piezo-actuated compliant mechanism based on an improved Bouc–Wen hysteresis model with variable parameters

To deal with the challenges that the classical Bouc–Wen model fails to precisely characterize amplitude-dependent hysteresis and asymmetric hysteresis, an improved Bouc–Wen model with variable parameters is presented. The proposed model introduces asymmetric terms and parameter functions related to sinusoidal excitation amplitudes into the classical Bouc–Wen model. It has a relatively simple mathematic form and can be easily identified and applied for inverse feedforward compensation in real-time applications. By comparison with the classical Bouc–Wen model and other existing hysteresis models, the superiority of the proposed model has been verified. Furthermore, inverse hysteresis control and hybrid control combining the developed inverse control and proportional-integral feedback control are proposed. Several comparative experiments are conducted on a piezo-actuated micro-scanner. Results demonstrate that inverse control and hybrid control using the improved Bouc–Wen model with variable parameters can achieve better tracking performance and are meaningful in actual trajectory-tracking applications.

A Fast Kernel-Based Optimal Control Framework for Autonomous Driving

A novel, promising strategy to improve path-tracking performance for autonomous driving is to combine a nominal model with an additive residual model. The residual part is identified by a kernel method Gaussian process (GP) regression from continuous data streaming. However, the high computational complexity of simultaneously using both numerical optimization and supervised learning is a critical challenge for applications with fast dynamics. This also limits the generalization capability in untrained circumstance. To address these issues, we design a feedforward compensator to handle the stochastic GP model. This allows an analytical solution to optimize the formulation, and therefore greatly lowers the computational burden. Our experimental results show that the computational time was reduced by 40 ms in comparison to the classical general-source solver. Consequently, the learning part can now track 19% more data points in one control step, saving more computation power to be allocated to prediction. In addition, we optimize the prediction dimension and apply the local technology to cluster intractable dictionary. Together, these improvements allow our fast kernel-based optimal control (FKB-OPT) framework to exhibit superior performance under inexperienced trajectories in the road tests.

단상 멀티 레벨 인버터의 출력 전력 전향 보상

This study proposes a feedforward compensation method based on output power estimation for 2-stage single-phase multilevel inverter-based solid-state transformer. The proposed method consists of the output power estimation by phase reference of DAB (Dual Active Bridge) converter and feedforward the d-axis current reference of AFE (Active Front-End) converter. Feedback controller for AFE and DAB converters is designed based on small signal model of each converter for verifying the proposed method. Simulations and experimental results are provided to confirm the effectiveness of the proposed method.