Feedforward Control Strategy Research Articles

Development of a Controlled Continuous Low-Dose Feeding Process

This paper proposes a feed rate control strategy for a novel volumetric micro-feeder, which can accomplish low-dose feeding of pharmaceutical raw materials with significantly different powder properties. The developed feed-forward control strategy enables a constant feed rate with a minimum deviation from the set-point, even for materials that are typically difficult to accurately feed (e.g., due to high cohesion or low density) using conventional continuous feeders. Density variations observed during the feeding process were characterized via a displacement feed factor profile for each powder. The characterized effective displacement density profile was applied in the micro-feeder system to proactively control the feed rate by manipulating the powder displacement rate (i.e., computing the feed rate from the powder displacement rate). Based on the displacement feed factor profile, the feed rate can be predicted during the feeding process and at any feed rate set-point. Three pharmaceutically relevant materials were used for the micro-feeder evaluation: di-calcium phosphate (large-particle system, high density), croscarmellose sodium (small-particle system, medium density), and barium sulfate (very small-particle <10 μm, high density). A significant improvement in the feeding performance was achieved for all investigated materials. The feed rate deviation from the set-point and its relative standard deviation were minimal compared to operations without the control strategy.

Neural Decoding for Target Detection Using Multi-View Methods

Tendon–sheath mechanism (TSM) has inherent advantages in the development of flexible robotic systems because of its simplicity, safety, flexibility, and ease of transmission. However, the control of TSM is challenging due to the presence of nonlinearities, namely friction, backlash-like hysteresis and the time-varying configuration of the TSM during its operations. Existing studies of TSM found in the literature only address tendon transmission under the assumption of fixed configuration and a complex inverse model of backlash is required. In order to flexibly use the system in a wider range of applications, the aforementioned nonlinear effects have to be characterized for the purpose of compensation. In this paper, we endeavor to address these issues by presenting a series of controller strategies, namely a feedforward control scheme under the assumption of known backlash-like hysteresis profile, and an adaptive control scheme to characterize the nonlinearities with unknown backlash hysteresis and uncertainties. The proposed control schemes do not require information of the tendon–sheath configurations, which is challenging to obtain in practice, in the compensation structures. In the absence of output position feedback, a simple direct inverse model-based feedforward has been used that efficiently reduce the tracking errors. The feedforward compensation does not require any complex algorithm for the inverse model. In the presence of output position feedback, a nonlinear adaptive controller has been developed to enhance the tracking performances of the TSM regardless of the random change in the tendon–sheath configurations during compensation. In addition, exact values of the model parameters are not required. They are estimated online during the operations. A dedicated experimental setup is introduced to validate the proposed control approaches. The results show that the proposed control schemes significantly improve the tracking performances for the TSM in the presence of uncertainties and time-varying configurations during the operations. There is a significant decrease of 0.0158 rad2 (before compensation) to smaller value of 0.0012 rad2 (use feedforward control) and 8.2815 × 10−5 rad2 (use nonlinear controller) after compensation.

Small-signal model and control approach for a dual input boost converter with VMC

ABSTRACT The dual-input boost converter (DIBC) with voltage multiplier cell (VMC) and operating in continuous conduction mode (CCM) is feasible for applications with high voltage from low voltage renewable energy sources (RES). To achieve a high voltage gain, DIBC is operated with two VMC, and overlapping switch signals, i.e. at duty ratio higher than 0.5; these complicate the modelling and control design. The objective here is to achieve output voltage regulation under load and input voltage disturbances with the proposed feed-forward plus feedback (FFFB) control strategy for DIBC with two VMC. Nevanlinna–Pick interpolation method and MATLAB SISOtool are used to design the optimally stable feed-forward controller and feedback controller, respectively. The study of the non-minimum phase behaviour of the converter, followed by the control design, is done based on the derived averaged state-space small-signal transfer function models. The analytical model is validated using MATLAB and PSIM software and experimentally. A converter prototype of 250 W is built and experimentally tested; the control is realised using FPGA. The simulation and experimental results ensure that the converter with this proposed control design provides satisfactory voltage regulation.

Feedforward beta control in the KSTAR tokamak by deep reinforcement learning

In this work, we address a new feedforward control scheme for the normalized beta (β N) in tokamak plasmas, using the deep reinforcement learning (RL) technique. The deep RL algorithm optimizes an artificial decision-making agent that adjusts the discharge scenario to obtain a given target β N from the state–action–reward sets explored by its own trial and error in a virtual tokamak environment. The virtual environment for the RL training is constructed using a long short-term memory (LSTM) network that imitates the plasma responses to external actuator controls, which is trained using five years’ worth of KSTAR experimental data. The RL agent then experiences numerous discharges with different actuator controls in the LSTM simulator, and its internal parameters are optimized in the direction of maximizing the reward. We analyze a series of KSTAR experiments conducted with the RL-determined scenarios to validate the feasibility of the beta control scheme in a real device. We discuss the successes and limitations of feedforward beta control by RL, and suggest a future research path for this area of study.

An enhanced feedforward flux weakening control for high‐speed permanent magnet machine drive applications

Permanent magnet machines have been used in the high-speed drive applications due to their high-efficiency, high-power-density, and wide-speed range characteristics. However, control of such high-speed permanent magnet machines machine is always challenging and proper flux-weakening controller design is essential to achieve high performance of these machines. In this paper, an improved feedforward flux-weakening control scheme for interior permanent magnet synchronous machine (IPMSM) drives are proposed. The proposed method identifies optimal d-axis and q-axis currents under different operation regions using maximum-torque-per-ampere curve, voltage limit, and current limit curves with a fast Newton–Raphson algorithm. To ensure the optimal performance of the control mechanism, effects of inductance variations due to the magnetic saturation are considered and an innovative high-frequency staircase voltage injection method is used to identify the q-axis inductance. The experimental results show that compared with other existing flux-weakening methods, the proposed technique can improve the DC-link voltage utilisation without the need to tune any controller gains and can fully utilise maximum available torque with desirable transient performance.

Multilevel Energy Management of a DC Microgrid Based on Virtual-Battery Model Considering Voltage Regulation and Economic Optimization

This article presents a multilevel energy management framework for dc microgrids with multiple energy storage systems (ESSs) to ensure reliable power dispatch, stable voltage regulation, and daily economic operation. In the primary layer, an advanced virtual-battery drooped control is constructed for the ESSs, which can realize adaptive load sharing and state of charge (SOC) balancing. Decentralized bus-signaling control is proposed to prevent single point of failure, where the mode-switching voltages of the utility grid and photovoltaic system are adjustable based on the VirtualOCV curve of the virtual-battery model. A current feedforward control strategy is scheduled as the secondary control to reduce bus voltage deviation, which is verified through simulation. A small-signal model is developed to investigate the effects of the virtual-battery parameters, SOC value, and constant power load on system stability through root locus analysis. In the energy management level, an improved particle swarm optimization algorithm is applied to obtain the optimal setting of the virtual-battery model parameters for minimum daily operating costs. A discrete model is derived from calculating the capacity loss of the batteries. Finally, the proposed control hierarchy is verified in the MATLAB/Simulink environment and the simulation results prove the feasibility and priority of the proposed multilevel energy management.

A Feedforward Voltage Control Strategy for Reducing the Output Voltage Double-Line- Frequency Ripple in Single-Phase AC–DC Converters

This article proposes a feedforward voltage control strategy (FVCS), aimed to reduce the output voltage double-line-frequency ripple and the output capacitance of the single-phase ac–dc power factor correction (PFC) converters. It is known that a large capacitance is required to reduce the voltage ripple but it results in low power density. With the proposed FVCS achieving low output voltage ripple, the output capacitance can be reduced, so the size and cost of the converter can also be reduced. Moreover, the proposed FVCS only needs one voltage sensor which can get rid of the necessary current sensor in the conventional harmonic input current injection technique. In this article, the detailed mathematical analyses, harmonic current limitations, and key parameters, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </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">$N_{\Delta \text{ECo}}$ </tex-math></inline-formula> , of this proposed control strategy are derived. Also, the design procedures for a flyback converter are provided. Finally, computer simulations and experimental results of a 100-W prototype circuit are presented to verify the effectiveness and performance of the proposed FVCS.

Model Decoupled Synchronization Control Design with Fractional Order Filter for H-Type Air Floating Motion Platform.

H-type motion platform with linear motors is widely used in two-degrees-of-freedom motion systems, and one-direction dual motors need to be precisely controlled with strict synchronization for high precision performance. In this paper, a synchronous control method based on model decoupling is proposed. The dynamic model of an H-type air floating motion platform is established and one direction control using two motors with position dependency coupling is decoupled and converted into independent position and rotation controls, separately. For the low damping second-order oscillation system of the rotation control loop, a new fractional order biquad filtering method is proposed to generate an antiresonance peak to improve the phase and control gain of the open loop system, which can ensure system stability and quick attenuation for external disturbances. In the multiple-degree-of-freedom decoupled control loops, a systematic feedback controller design methodology is proposed to satisfy the given frequency domain design specifications; a feed-forward control strategy is also applied to compensate the disturbance torque caused by the platform motion. The simulation and experimental results demonstrate that the proposed synchronization control method is effective, and achieves better disturbance rejection performance than the existing optimal cancellation filtering method and biquad filtering method.

Multidimensional harmonic current feedforward compensation control of single‐phase alternating current–direct current power factor correction converter

AbstractGenerally, low‐bandwidth condition of control voltage loop is used for single‐phase alternating current–direct current (AC–DC) power factor correction (PFC) converter, which eliminates the influence of the second harmonic component in the output voltage on control loop but degrades the load dynamic performance. However, the high‐bandwidth condition of voltage loop would cause multiharmonic distortions both in the input current and output voltage. Regarding this issue, this paper proposes a multidimensional harmonic current feedforward compensation control (MHCFC) scheme, to eliminate multiharmonic distortion of the PFC system using a high‐bandwidth condition of voltage loop and improve the dynamic performance as well. In the proposed scheme, the odd harmonics of the input current are extracted through multidimensional band‐pass filters and further converted into even harmonic compensation signals via the coordinate transformation, so as to offset the negative effects of the even harmonics of the output voltage. Taking boost PFC circuit as an example, a digital controlled experimental prototype is built to verify the feasibility of the proposed control scheme. The experimental results show that, compared with the traditional low‐pass filter (LPF) scheme, the proposed scheme guarantees a high‐quality input current while its load dynamic response is improved by about 70%.

Enhancement of DC‐bus voltage regulation in cascaded converter system by a new sensorless load current feedforward control scheme

Enhancement of DC‐bus voltage regulation in cascaded converter system by a new sensorless load current feedforward control scheme

A feed-forward control strategy of virtual synchronous generator under non-ideal grid

Virtual synchronous generator technology (VSG), which simulates the electro-mechanical transient characteristics of synchronous generators, enables the power supply or load that adopt a converter with a number of its external characteristics, including inertia, damping, frequency and voltage regulation. However, when the grid voltage is not ideal, the traditional VSG control will lead to unbalanced three-phase grid-connected current, so a control method of specific sub-voltage component feed-forward is proposed. First of all, the problems of VSG in non-ideal grid voltage are analysed. Based on this, the harmonic components are extracted by sinusoidal amplitude integral method, and the control strategy of specific voltage component feed-forward is proposed, which can suppress the grid voltage’s negative sequence components and harmonic components. Simulation and experimental results show that the proposed control strategy is correct and effective.

Circulating Current Mitigation and Harmonic Current Compensation for Multifunction Parallel Three-Level Four-Leg Converters

The multifunction parallel three-level four-leg converters are proposed for high-power applications, which combine grid-connected renewable generation and active power filter (APF). However, the challenge of zero-sequence circulating current (ZSCC) is inevitable which degrades the output currents’ quality and reduces the stability of the system. To overcome this limitation, a proportional integral (PI) + feedforward control strategy and space vector modulation based on the nonaxial redundant vectors (NARVs) are proposed in this article. First, the model of ZSCC is established and analyzed in detail. The analysis reveals that ZSCC is determined by zero-sequence duty-cycle difference and zero-sequence benchmark function. Then, by analyzing the space vector of the three-level four-leg converter, it is concluded that ZSCC is affected by different NARVs. Consequently, a PI + feedforward control strategy is proposed to mitigate ZSCC by adjusting the duty cycle of NARVs in each pulse width modulation (PWM) sampling period. The simulation and experimental results verify the effectiveness of the proposed control strategy.

New feed-forward control strategy of single-phase grid-connected inverter

Traditional proportional feed-forward strategy can well restrain harmonic disturbance from grid background, but in the weak grid, positive feedback channel and grid-connected current inner-loop are coupling with each other by grid impedance, and robustness is substantially decreased. According to the above situation, a kind of new feed-forward control strategy is proposed, and adding more resonant link on positive feedback channel of point of common coupling voltage to change full pass characteristics of positive feedback channel which only make positive feedback channel have feedback effect on the frequency of main grid background harmonics. Inverter can both have great robustness and harmonic suppression ability in weak grid. In the end, the effectiveness and correctness of proposed control strategy is verified by the simulation model of single-phase grid-connected inverter.

Enhanced Model Reference Adaptive Control Scheme for Tracking Control of Magnetic Levitation System

Magnetic Levitation is a process in which an object is suspended with the support of the magnetic field. Despite being an unstable system, Magnetic Levitation Systems (MAGLEV) have profound applications in various fields of engineering. MAGLEV systems are sensitive, unstable, and nonlinear and uncertainties always pose a challenge in Controller Design. As a solution, adaptive controllers came into existence with adaptation mechanisms to cover the system uncertainties. In this study, a simple, novel, and an effective approach to the Enhanced Adaptive Control scheme is proposed for the ball position control and tracking of an unstable Magnetic Levitation System. The proposed Enhanced Model Reference Adaptive Scheme (EMRAC) follows the same phenomenon of the Model Reference Adaptive Scheme (MRAC) with a slight difference in its control strategy. The proposed scheme consists of Proportional-Integral-Velocity plus Feed Forward as the control structure and a modified version of the standard tuning rule is used as the adaptation mechanism. The control scheme is applied to a standard benchmark Magnetic Levitation System and the tracking performance of the scheme is tested by applying square and multi-sine pattern trajectories to the Magnetic Levitation System. The performance of the developed Enhanced MRAC performance is compared with that of the Proportional Integral Velocity with Feedforward Control (PIV+FF) scheme and the proposed control scheme is proven to be more suitable. The performance of the proposed scheme is also analyzed with Power Spectral Density and Root Mean Square Error to evaluate the ball position tracking control. It is inferred from the experimental results that Enhanced MRAC accommodates the changes and makes the system more reliable with good tracking ability.

Evaluation of Process Control Schemes for Sour Water Strippers in Petroleum Refining

For the sour water strippers in petroleum refinery plants, three prediction models were developed first, including the estimators of sour water feed concentrations using convenient online measurements, the minimum reboiler duty and the corresponding internal temperature at a specific location (Tstage,29). Feedforward control schemes were developed based on these prediction models. Four categories of control schemes, including feedforward, feedback, feedback with external reset, and feedforward-feedback, were proposed and evaluated by the rigorous dynamic simulation model of the sour water stripper for their dynamic responses to the sour water feed stream disturbances. The comparison of control performance, in terms of the settling time, integrated absolute error (IAE) of the NH3 concentration of the stripped sour water and IAE of the specific reboiler duty, reveals that FFT (feedforward control of Tstage,29) and FBA-DT3 (feedback control with 3 min concentration measurement delay) are the best control schemes. The second-best control scheme is FBAT (cascade feedback control of concentration with temperature).

The impact of static output nonlinearities on the control strategies that humans use in command-following tasks

The results of a human-in-the-loop experiment are used to investigate the control strategies that humans use to interact with nonlinear dynamic systems. Two groups of human subjects interact with a dynamic system and perform a command-following task. The first group interacts with a linear time-invariant (LTI) dynamic system. The second group interacts with a Wiener system, which consists of the same LTI dynamics cascaded with a static output nonlinearity. Both groups exhibit improved performance over the trials, but the average of the linear group’s performance is better on more than three-fourths of the trials. A new nonlinear subsystem identification algorithm is presented and used to identify the feedback and feedforward control strategies used by the subjects in both groups. The identification results for the linear group agree with prior studies suggesting that adaptive feedforward inversion is a primary control strategy used by humans for command-following tasks. The main results of this paper address an open question of whether a similar control strategy is used for nonlinear systems. The identification results for the nonlinear group suggest that those subjects also use adaptive feedforward inversion. However, the static output nonlinearity inhibits the human’s ability to approximate the inverse.

Docupling Control of High Power Factor Inverter without Electrolytic Capacitor SRM Driver Simulation

DC bus electrolytic capacitors influential on the life of Switched reluctance motor (SRM) due to their chemical properties. For the drive system without electrolytic capacitor SRM, the power decoupling type without electrolytic capacitor scheme is studied. The parallel bidirectional Buck/Boost compensation circuit is a power decoupling circuit, a feed-forward control strategy for output voltage fluctuations of the electrolytic capacitor PFC circuit. The inverter side uses the voltage hysteresis control to stabilize the DC bus voltage. During the two-phase adjacent commutation period, the measured DC bus voltage is compared with two predetermined high and low voltages, make the DC bus voltage fluctuate within a certain range. The effectiveness of the control strategy is verified by electrical tools. The grid-side power factor is 0.958, and the grid current harmonics meet the EN61000-3-2 standard.

Design and Implementation of a PV Generated Feed Forward Control Strategy of a Sepic Converter

Design and Implementation of a PV Generated Feed Forward Control Strategy of a Sepic Converter

Preisach-model-based position control of a shape-memory alloy linear actuator in the presence of time-varying stress

Tensioned shape-memory alloy (SMA) wires can repeatedly contract and extend, according to hysteretic loops defined by the shape-memory effect (SME), when subject to cyclic heating and cooling. Empirical evidence shows that these periodic hysteretic deformations are also a function of the loading stress applied to the tested wire. Therefore, to achieve accurate position control of an SMA wire-actuator, the SME hysteretic phenomenon in the presence of time-varying loading stress must be explicitly modeled in order to be compensated. To this end, we use a Preisach-model-based forward mapping that relates the time-varying exciting temperature and stress signals as inputs with the produced strain signal as the output, and whose parameters are experimentally estimated a priori through a series of steps in a nonlinear system identification process. Then, the identified parameters are employed by a Preisach-model-based inversion algorithm that is integrated into a feedforward inverse control scheme designed to mitigate the effects of hysteresis affecting the tested SMA wire. In the proposed scheme, the inverse controller reads two time-varying inputs, a strain reference and the known stress signal exciting the controlled SMA wire-actuator, and then it computes the corresponding temperature reference that, once enforced on the SMA material of the wire, generates the desired strain output. This approach to position tracking control can be realized using lightweight sensors and, as demonstrated in this paper through experimental results, is computationally efficient, which are the two most essential features required for the implementation of controllers on centimeter-scale autonomous robots. Using data obtained through real-time experiments, we demonstrate that the introduced position control scheme is highly effective and suitable to be used in future microrobotic applications. Furthermore, we show that the proposed methods for the system identification of the nonlinear hysteretic dynamics of SMA wires and for the synthesis of inverse controllers can be easily modified to be applied to the tracking control of SMA actuators thermally excited by means other than Joule heating.

An enhanced bulk-driven OTA with high transconductance against CMOS scaling

In this study, we propose a robust feed-forward control strategy to enhance the transconductance of bulk-driven (BD) operational transconductance amplifiers (OTAs), when working in weak inversion region. With the proposed control method, an enhanced bulk-driven OTA (EBD-OTA) is devised, whose gain bandwidth (GBW) and DC gain are both increased, with gmb/gm ratio displaying an inverse relation to the degree of CMOS scaling. The devised BD-OTA is fabricated with the SMIC 180 nm process, and experimental results demonstrate an unity 53 kHz GBW with a 0.6 V power supply, which verifies the proposed control approach.