Feedforward Control Strategy Research Articles

Hardware-in-the-loop testing of current cycle feedback ILC for stabilisation and tracking control of under-actuated visual servo system

ABSTRACT This paper presents an iterative learning control (ILC) scheme augmented with the feedback control for solving the nonlinear stabilisation and tracking control problem of ball on plate system, which is a class of under-actuated visual servo system. To enhance the trajectory tracking performance and deal with the real-time challenges of ball on plate system including the nonlinearity, inter-axis coupling and uncertain dynamics, we present a feed-forward learning control scheme, which iteratively updates the control input from one trial to the next, integrated with the cascade control. The ILC update law is synthesised based on the current iteration tracking error (CITE), and the uniform convergence of the input control sequence is presented using the contraction mapping technique. From image processing standpoint, for detecting the foreground objects from a video stream, a background subtraction algorithm using frame difference technique is employed. The efficacy of the proposed scheme is tested on a laboratory scale ball on plate system using hardware-in-the-loop (HIL) testing. Experimental results substantiate that augmenting the learning control with the feedback control not only reduces the tracking error significantly but also enhances the robustness of the closed loop system against the poor lighting conditions.

Torque ripple compensation control for hybrid UGVs in mode transition based on current harmonic control of a PMSM

Load jumping and mode transitions both cause the unstable dynamic states for compound power-split hybrid Unmanned Ground Vehicles (UGVs), and these phenomena lead to vibrations of the transmission system and longitudinal buffeting of the vehicle. This study presents a feed-forward compensation control strategy for load jumping and mode transitions to reduce the corresponding torsional vibration in hybrid UGVs. The proposed method injects an appropriate harmonic current into a permanent magnet synchronous motor (PMSM) to generate a harmonic torque that is opposite to the load torque, which improves the dynamic response quality of the vehicle load. First, the multimode structure of a hybrid UGV and mode switching vibration and shock are investigated, as well as a feed-forward compensate control architecture is proposed. Second, two models are established the PMSM dynamic model based on the electromagnetic coupling principle and a 2-degree-of-freedom torsional vibration model of transmission system by simplifying the vehicle system. Third, the harmonic current injection method is proposed, and the harmonic current equation is derived. Based on the field-oriented control algorithm, a double closed-loop controller is designed for the torque and speed of the PMSM, and the internal model control method is applied to design the current controller. The simulation results show that the proposed strategy effectively suppresses jerk and that the harmonics current transfers the energy from the mechanical vibrations of the system into electric power fluctuations.

Research on a forecasted load-and time delay-based model predictive control (MPC) district energy system model

District energy system is an underground network used to cool and heat buildings efficiently, which has the characteristics of large scale, multiple equipment, large lag, nonlinear and time-varying dynamics. The traditional feedback control strategies not only cause mismatch and hysteresis of energy supply and load demand in time series but also lead to high energy consumption. Therefore, a forecasted load-and time delay-based model predictive control district energy system model is proposed in this paper. Taking a district energy system in Tianjin University as a test case, the superiority of the proposed control model is ascertained. A TRNSYS and MATLAB co-simulation platform is developed as the test platform. The results show that the proposed control model can not only improve matching the extent of energy supply and load demand in time series, but can also reduce the energy peak and total energy consumption of the district energy system. Specifically, energy consumption is reduced by 9.56% and 5.30% in summer and 7.75% and 2.61% in winter compared with the control models based on the traditional feedback control and load feedforward fuzzy control strategies, respectively.

Flatness Based Control of an Industrial Robot Joint Using Secondary Encoders

Due to their compliant structure, industrial robots without precision-enhancing measures are only to a limited extent suitable for machining applications. Apart from structural, thermal and bearing deformations, the main cause for compliant structure is backlash of transmission drives. This paper proposes a method to improve trajectory tracking accuracy by using secondary encoders and applying a feedback and a flatness based feed forward control strategy. For this purpose, a novel nonlinear, continuously differentiable dynamical model of a flexible robot joint is presented. The robot joint is modeled as a two-mass oscillator with pose-dependent inertia, nonlinear friction and nonlinear stiffness, including backlash. A flatness based feed forward control is designed to improve the guiding behaviour and a feedback controller, based on secondary encoders, is implemented for disturbance compensation. Using Automatic Differentiation, the nonlinear feed forward controller can be computed in a few microseconds online. Finally, the proposed algorithms are evaluated in simulations and experimentally on a real KUKA Quantec KR300 Ultra SE.

Approximate Dynamic Programming Vector Controllers for Operation of IPM Motors in Linear and Overmodulation Regions

To improve the efficiency of a permanent magnet (PM) motor, it is usually required to extend the motor operation from linear to over or even six-step modulation regions based upon the space vector pulsewidth modulation technique. Traditionally, a PM motor is controlled by using the standard vector control technique. However, a recent study shows the decoupling inaccuracy of designing PM motor control using the conventional standard vector control approach. This issue has caused a challenge to control a PM motor, particularly when the motor operates from linear to overmodulation regions. In this article, a novel approximate dynamic programming (ADP) vector controller is developed to overcome the challenge. The ADP controller is developed using the full dynamic equation of a PM motor and implemented using an artificial neural network (ANN). A feedforward control strategy is integrated with the -based ADP controller to enhance the performance of the controller in both linear and overmodulation regions. The ANN-based ADP control is compared with the conventional standard vector control and a model predictive control. Simulation and hardware experiments demonstrate that the proposed controller can track reference changes better with high efficiency and reliability for PM motor operation in linear and overmodulation regions.

Dynamic Improvement with a Feedforward Control Strategy of Bidirectional DC-DC Converter for Battery Charging and Discharging

With the increasing importance of power accumulator batteries in electric vehicles, the accurate characteristics of power accumulator batteries have an important role. In order to evaluate the power accumulator battery, battery charging and discharging is indispensable. In this article, a H-bridge bidirectional DC-DC converter is presented which can charge and discharge the battery with different voltage levels and one of the merits of this topology is that a wide output voltage range can be easily achieved. In the control part, a proportional-integral (PI) control strategy is adopted to ensure a stable and reliable operation of the converter. Furthermore, compared with the PI control strategy, a duty ratio feedforward control is utilized to obtain the rapid current dynamic response. In this article, firstly, the system configuration for battery charging and discharging is introduced, then the operating principles and mathematical model of the DC-DC converter are analyzed and derived. Secondly, for bidirectional DC-DC converters, the PI control method and duty ratio feedforward control method are put forward and designed. Finally, the simulation model is established based on PSIM software and the experiment platform is also built in lab. The results of the simulation and experiment research show that the H-bridge bidirectional DC-DC converter can operate reliably and stably during the charging, discharging and power flow reverse modes. In addition, the dynamic response of the charging and discharging current can also be further improved by introducing the duty ratio feedforward control method.

Dual Rotating Microsphere Using Robotic Feedforward Compensation Control of Cooperative Flexible Micropipettes

High flexible and high precise manipulation is one of the most critical technique for complex microsystem’s measurement, manufacture, and assembly. Although recent advances in microrobotics have successfully realized the automatic manipulation and positioning of tiny objects, their flexible manipulation in 3-D free space remains a challenge, such as the wide-angle rotation manipulation of microsize sphere, due to the complicate surface forces. Herein, this article proposed a feedforward model and realized the precise rotation for microsized sphere by two cooperative flexible micropipettes. Firstly, a microrobotic manipulation system with six degrees-of-freedom (DOFs) was developed and integrated with the microscope. Then, a feedforward compensation control strategy involving dual rotation was proposed for the precise manipulation of microsized sphere ( ${\sim }90~\mu \text {m}$ ) based on the analysis of contact forces. As a result, the rotation of the microsized sphere in two different planes was realized and the microsized sphere release procedure was also accomplished after rotation. Compared with existing techniques only allowing limited amplitudes rotation, this article realizes wide-angle rotation manipulation of microsized sphere in 3-D free space. This research opens new prospects for the microsized object accurate manipulation, which is expected to give a long-term impact for complex microsystem’s manufacture and assembly. Note to Practitioners —This article is motivated by the problem of the flexible manipulation of tiny object in 3-D space. The proposed nanorobotic manipulation system, two micropipettes and feedforward compensation model control strategy could realize the precise translational and rotational manipulation of microbeads in 3-D space, which offers obvious advantages of existing techniques. The proposed system and method could be a general solution for precise and flexible micromanipulation. Thus, it could find wide applications ranging from fundamental research to industrial applications, such as biological cell positioning, characterization of a particular micro/nanoregion, microassembly, and manufacturing.

Analysis and Mitigation of Subsynchronous Resonance in Series-Compensated Grid-Connected System Controlled by a Virtual Synchronous Generator

Analogizing the subsynchronous resonance (SSR) phenomenon of the series-compensated grid-connected system based on synchronous generator, the virtual synchronous generator (VSG) also has the low-frequency oscillation problem owing to the impedance interaction between VSG and series-compensated network. Stability of the series-compensated grid-connected system controlled by VSG is analyzed by the impedance-based Nyquist stability criterion. Due to the inductive impedance of VSG, VSG is easy to couple with the series-compensated network in the low-frequency areas, which can lead to the SSR. With the increase of the series compensation level, the stability of VSG becomes worse and the induced oscillation frequency becomes higher. Therefore, a modulation signal feedforward active-damping control strategy with time-delay compensation is proposed to suppress this SSR, which directly feeds the active-damping control signal to the pulsewidth modulation modulator for reshaping the output impedance of VSG from the inductance to the resistance–inductance. Moreover, a value range of virtual resistance is given with considering the influence on the regular operation of VSG. Finally, the simulation and experimental results verify the correctness of the SSR analysis and the feasibility of the proposed active-damping control strategy.

Wideband Harmonic Voltage Feedforward Control Strategy of STATCOM for Mitigating Subsynchronous Resonance in Wind Farm Connected to Weak Grid and LCC HVDC

For the wind farm connected to line-commutated converter-based high-voltage direct-current (LCC HVDC) and weak grid at sending end, subsynchronous resonance (SSR) is prone to occur due to the impedance interactions among wind farm, weak grid, and LCC HVDC. First, the mechanism and characteristics of this SSR are analyzed based on the impedance method. With the increase of the output power for wind farm or the decrease of the transmission power for LCC HVDC, the wind farm tends to cause SSR. Moreover, with the decline of the grid stiffness at sending end, the studied system easily causes SSR. Then, a wideband harmonic voltage feedforward control strategy of static synchronous compensator (STATCOM) is proposed to suppress this SSR. For the proposed damping controller of SSR, a constant voltage amplitude-based harmonic extraction method is designed without using filter. The harmonic extraction error of the proposed strategy is a constant |V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> |, which is induced by the difference between the constant voltage amplitude V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> and actual voltage amplitude V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> . By the theoretical analysis and simulation, this constant error |V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> | can be automatically counteracted by the PI controller of STATCOM. Finally, experimental results verify the validity of the proposed strategy.

Constrained real-time control of hydromechanical powertrains – methodology and practical application

Axial piston motors and pumps are core components in many hydromechanical systems as for instance the powertrain of wheel loader vehicles. The optimal performance of the individual components as well as the entire powertrain requires a fast and exact control of both the motor’s swivel angle as well as the pressure difference over the pump by means of the currently available information and despite their respective a-priori unknown reference signal generated by the driver with a joystick or gas pedal operation. Therefore, it is essential that the swivel angle and pressure controllers fully exploit the possible dynamics and the constrained resources of the nonlinear swivel angle displacement and the pressure adjustment system, respectively. In this work, a flatness-based feedforward control strategy for the motor’s swivel angle as well as a flatness-based tracking two-degree-of-freedom controller for the pump pressure are proposed. For the realization of the flat feedforward and the tracking controller, a constrained online trajectory generation by means of a nonlinear (switched) state variable filter is designed for each. Therefore, both controllers are capable of considering the relevant state and input constraints in real-time and without relying on an online optimization. The proposed control algorithms are both discussed and their performance is illustrated with measurement data from a wheel loader vehicle.

Real-Time Hybrid Testing of Strut-Braced Wing Under Aerodynamic Loading Using an Electrodynamic Actuator

Real-Time Hybrid Simulation (RTHS) is an experimental framework that allows the testing of components or substructures under realistic, dynamic boundary conditions, by imposing the reactions calculated from a model of the rest of the assembly through one or more actuators. In the context of rapid prototyping of mechanical components, RTHS could be used to explore the design space of a device while at the same time physically validating its interaction with other components of the final assembly from the early stages of the design-to-production cycle. In this work, RTHS was applied for the first time to the investigation of aerodynamic gust loading alleviation devices in a highly flexible strut-braced wing. The model wing was taken as the physical substructure and tested in a low-speed wind tunnel equipped with gust generators. The load alleviation device was simulated through a real-time feedforward-feedback controller, and its response imposed via an electro-mechanical linear actuator, in contrast with the hydraulic actuators more commonly used in standard RTHS. The controller-actuator subsystem was studied in detail to assess and minimise errors at the physical interface with the wing. The behaviour of the electromechanical subsystem showed a strong dependence on the characteristics of the numerical substructure and the frequency of excitation, and resulted in a significant discrepancy between the simulated and real displacements at the interface between the actuator and the wing. A narrow-band feedforward displacement control scheme based on a model of this subsystem alone was therefore developed and shown to significantly reduce synchronisation errors at the interface.

Stoichiometry-driven heuristic feedforward control for oxygen supply in a biological gas desulfurization process

In this work, a stoichiometry-driven heuristic feedforward control strategy is proposed for controlling the oxygen supply to a biological gas desulfurization process that treats biogas, landfill, and high-pressure natural gas containing H2S and volatile organic sulfur compounds (VOSC). Traditionally, PI or PID feedback control is used when the feed gas contains H2S only. Because the oxidation–reduction potential (ORP) is mostly dominated by the dissolved sulfide concentration, the feedback controller maintains a constant sulfide concentration in the bioreactor by maintaining an ORP setpoint value through controlling the oxygen supply. However, when the feed gas also contains VOSCs, e.g., thiols, it appears from our research that controlling ORP at a fixed value does not lead to stable process performance. Hence, an alternative control strategy is proposed, which controls the O2/H2S supply ratio based on the stoichiometry of the dominant chemical reaction and experimental experience. The heuristic feedforward control strategy was validated by a fluctuating supply of H2S (26.5 to 126.5 mM S day−1) in the absence and presence of ethanethiol (0.8 to 1.16 mM S day−1). A sulfur selectivity above 95 mol%, and complete removal of H2S, was achieved at an O2/H2S supply ratio of about 0.63 mol mol−1 compared to 56 mol% when a PI/PID controller was used at a randomly varying, stepwise H2S dosing rate This work shows that fluctuations in the H2S loading rate and presence of ethanethiol in the feed gas of full-scale systems can be controlled by applying the heuristic feedforward control strategy. However, online measurements of the H2S concentration in the feed gas are required to implement the proposed strategy in full-scale installations successfully.

Autonomous drone race: A computationally efficient vision-based navigation and control strategy

Drone racing is becoming a popular sport where human pilots have to control their drones to fly at high speed through complex environments and pass a number of gates in a pre-defined sequence. In this paper, we develop an autonomous system for drones to race fully autonomously using only onboard resources. Instead of commonly used visual navigation methods, such as simultaneous localization and mapping and visual inertial odometry, which are computationally expensive for micro aerial vehicles (MAVs), we developed the highly efficient snake gate detection algorithm for visual navigation, which can detect the gate at 20 HZ on a Parrot Bebop drone. Then, with the gate detection result, we developed a robust pose estimation algorithm which has better tolerance to detection noise than a state-of-the-art perspective-n-point method. During the race, sometimes the gates are not in the drone’s field of view. For this case, a state prediction-based feed-forward control strategy is developed to steer the drone to fly to the next gate. Experiments show that the drone can fly a half-circle with 1.5 m radius within 2 s with only 30cm error at the end of the circle without any position feedback. Finally, the whole system is tested in a complex environment (a showroom in the faculty of Aerospace Engineering, TU Delft). The result shows that the drone can complete the track of 15 gates with a speed of 1.5m∕s which is faster than the speeds exhibited at the 2016 and 2017 IROS autonomous drone races.

Application Research on Quality Stability Control of a Spray Drying Tower for Naphthalene Superplasticizer based on Siemens PLC

This article introduced a control scheme based on Siemens PLC to handle the quality stability issue in operation of the spray drying tower for Naphthalene Superplasticizer. A series feed-forward control scheme is proposed to solve the problems of water content fluctuation of naphthalene series water reducer slurry and solid content fluctuation caused by frequent and wide range fluctuation of gas pressure as fuel. The practical application shows that the control scheme can handle the fluctuation of water content well.

Research on Flocculation and Sedimentation Characteristics of Extremely Fine Coal Slime Based on Computer PID Algorithm

Coal slime water treatment is a very important process in coal preparation plant, its treatment effect directly affects the reuse of washing water and closed-circuit circulation index, and on the other links of coal preparation plant such as separation efficiency, the number of product quality index has a great impact, and even restricts the economic and social benefits of an important system. Based on improved grey prediction fuzzy control principle, an improved slurry flocculating settling process of feed forward and feedback control strategy, the improvement is: using fuzzy algorithm to replace the current use of conventional fuzzy control algorithm, namely according to the online setting parameters of fuzzy rules, both to overcome the difficult to eliminate the steady-state error and fuzzy control to realize accurate control weaknesses, and overcome the difficulty of parameter setting, make them form a complementary advantages. Therefore, it is of great significance to study advanced control method and improve control effect in coal preparation plant.

Grid-connected Inverter Control Strategy Based On Capacitor Reference Voltage Feedforward

In view of the disadvantage that grid-connected power is not high and the phase margin of the grid-connected current is greatly reduced with the increase of impedance of many grid voltage feedforward control strategies. A grid-connected inverter control strategy based on capacitor reference voltage feedforward is proposed. In this control, the error between the filter capacitor voltage and its reference voltage is combined with the proportional controller as the inner loop control, the error between the inverter side current and its reference current is combined with the current controller as the outer loop control to improve the robustness of the system. The phase difference between grid-connected current and grid voltage is reduced by using capacitor reference voltage feedforward. In addition, by using the grid voltage resonance feedforward, the system can not only retains the ability to suppress harmonics, but also prevents the system’s phase margin from decreasing greatly under weak power grid. The proposed strategy has good dynamic performance, it can obtain good grid-connected current quality and high grid-connected power, and it has strong robustness to the change of LCL parameters and the fluctuation of grid voltag. At the same time, it has better adaptability to weak power grid.

직동외란의 효율적 억제기능을 갖는 서보계 설계법에 관한 연구

This paper presents an interference disturbance compensation method for the connected system. The disturbance is generated from the system motion such that it directly affects the relative motion. For example, in the robot system, the arm motions influence each other because the arms are connected in series. If we design a servosystem for controlling the robot motions including arm angle, the interference disturbance should be carefully considered. The reason for this is that it influences and works as the disturbance which degrades the tracking performance. Therefore, the authors developed a novel interference disturbance rejecting method by simple feedforward control strategy based on the framework of robust servosystem design. By applying the proposed method to a 2DOF robot system, its effectiveness was evaluated.

Adaptive feedforward vibration compensation control strategy of bearingless induction motor

In order to solve the unbalanced vibration problem of bearingless induction motor caused by the rotor mass eccentricity, an adaptive feedforward vibration compensation control strategy is researched. Firstly, the inverse dynamic decoupling control me

Feedforward control for underactuated bipedal walking on compliant continuous steps with varying height

This study develops a feedforward control strategy based on the motion state of center-of-mass (CoM) of a robot for underactuated biped robot stable walking on compliant continuous steps with a known varying height. First, considering ground deformation, a compliant contact model is employed to characterize foot-ground interaction, and a robot–step coupling dynamic model of sagittal and lateral planes are established through decoupling modelling. Second, based on the gait characteristics of human variable-step walking, a feedforward control strategy based on the motion state of CoM is proposed. Varying height step is equivalent to varying slope, an equivalent slope angle and a desired step length can be calculated for each step according to their height. Underactuated bipedal walking control is decoupled into sagittal and lateral master-slave control. The velocity of robot CoM is considered as a system output. It is controlled through the displacement of CoM in a single walking cycle, and thus walking is stabilized. By the proposed method, the walking system is modelled as a polynomial with definite number of degrees and the controlled input is derived through a simple inverse operation on it. Its effectiveness is validated through simulations in an environment with a step varying height of less than 0.032 m. Simulation results show that the proposed method can improve the tracking performance of robot CoM velocity on varying height steps, as compared to a hybrid zero dynamic (HZD)-based controller.

Design and control of the accelerator grid power supply-conversion system applied to CFETR N-NBI prototype

The acceleration grid power supply (AGPS) rated 200 kV/25 A is a key component devoted to supply the acceleration grids of the China fusion engineering test reactor negative-ion-based neutral beam injector (N-NBI) prototype system. This paper focused on the design and control of the AGPS conversion system (AGPS-CS), with emphasis on the requirement of the wide range output voltage and rise time. A voltage regulation switch at the front of step-down transformer is applied to optimize the grid current and DC-link voltage. Moreover, a new feedforward control strategy with piecewise PI compensator is proposed to improve the characteristics of AGPS. The simulation results of the proposed AGPS-CS are presented, proving the performance of the power supply to achieve the desired requirements.