Feedforward Branch Research Articles

FI-NPI: Exploring Optimal Control in Parallel Platform Systems

Typically, the current and speed loop closure of servo motor of the parallel platform is accomplished with incremental PI regulation. The control method has strong robustness, but the parameter tuning process is cumbersome, and it is difficult to achieve the optimal control state. In order to further optimize the performance, this paper proposes a double-loop control structure based on fuzzy integral and neuron proportional integral (FI-NPI). The structure makes full use of the control advantages of the fuzzy controller and integrator to improve the performance of speed closed-loop control. And through the feedforward branch, the speed error is used as the teacher signal for neuron supervised learning, which improves the effect of current closed-loop control. Through comparative simulation experiments, this paper verifies that the FI-NPI controller has a faster dynamic response speed than the traditional PI controller. Finally, in this paper, the FI-NPI controller is implemented in C language in the servo-driven lower computer, and the speed closed-loop test of the BLDC motor is carried out. The experimental results show that the FI-NPI double-loop controller is better than the traditional double-PI controller in performance indicators such as convergence rate and RMSE, which confirms that the FI-NPI double-loop controller is more suitable for BLDC servo control.

A New Approach for Solving the False Balance of a Closed-Loop Fluxgate Current Transducer

The closed-loop fluxgate current transducer (CFCT) is the only current sensor whose measurement accuracy can reach a level of the parts per million (ppm) at present. However, the false balance, which makes the CFCT unable to work, caused by an excessive offset current is the inherent flaw of the CFCT. The high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</i> (rate of current change) of the primary current is the main factor resulting in the offset current overload. Therefore, the CFCT is currently only applied for steady-state direct-current measurements. In this article, an approach is proposed to eliminate the false balance of the CFCT in the dynamic process by adding a feedforward branch, which provides a follow-up bias point for the CFCT to make the CFCT always work in a small-signal range, where a risk of magnetic saturation does not arise. The zero-flux state of the CFCT still only depends on the feedback branch, so its high measurement accuracy is maintained. The experiments prove that the CFCT can measure a flat-top pulsed current with an accuracy of the ppm level by this method.

Research on VSG Frequency Characteristics and Energy Storage Device Capacity and Charge-Discharge Characteristics Based on Feedforward Branch

Renewable energy is connected to the grid through the inverter, which in turn reduces the inertia and stability of the power grid itself. The traditional grid-connected inverter does not have the function of voltage regulation and frequency regulation and can therefore no longer adapt to the new development. The virtual synchronous generator (VSG) has the function of voltage regulation and frequency regulation, which has more prominent advantages than traditional inverters. Based on the principle of VSG, the relationship between the frequency characteristics and the energy storage capacity of the feedforward branch-based virtual synchronous machine (FVSG) is derived when the input power and grid frequency change. Reveal the relationship between the virtual inertia coefficient, damping coefficient, and frequency characteristics of VSG and energy storage capacity. An energy storage configuration method that meets the requirements of frequency variation characteristics is proposed. A mathematical model is established, and the Matlab/Simulink simulation software is used for modeling. The simulation results verify the relationship between the inertia coefficient, damping coefficient, and energy storage demand of the FVSG.

GARP transcription factors repress Arabidopsis nitrogen starvation response via ROS-dependent and -independent pathways.

Plants need to cope with strong variations of nitrogen availability in the soil. Although many molecular players are being discovered concerning how plants perceive NO3- provision, it is less clear how plants recognize a lack of nitrogen. Following nitrogen removal, plants activate their nitrogen starvation response (NSR), which is characterized by the activation of very high-affinity nitrate transport systems (NRT2.4 and NRT2.5) and other sentinel genes involved in N remobilization such as GDH3. Using a combination of functional genomics via transcription factor perturbation and molecular physiology studies, we show that the transcription factors belonging to the HHO subfamily are important regulators of NSR through two potential mechanisms. First, HHOs directly repress the high-affinity nitrate transporters, NRT2.4 and NRT2.5. hho mutants display increased high-affinity nitrate transport activity, opening up promising perspectives for biotechnological applications. Second, we show that reactive oxygen species (ROS) are important to control NSR in wild-type plants and that HRS1 and HHO1 overexpressors and mutants are affected in their ROS content, defining a potential feed-forward branch of the signaling pathway. Taken together, our results define the relationships of two types of molecular players controlling the NSR, namely ROS and the HHO transcription factors. This work (i) up opens perspectives on a poorly understood nutrient-related signaling pathway and (ii) defines targets for molecular breeding of plants with enhanced NO3- uptake.

Input-output linearized spacecraft formation control via differential drag using relative orbital elements

The derivation, implementation, and performance assessment of a differential drag based algorithm, designed for spacecraft formation control using a relative orbital elements formulation, is presented. In contrast to similar approaches found in literature, the underlying motion dynamics model used to derive the control law includes J 2 perturbation as well as atmospheric drag perturbation based on a nonlinear density model. The basic idea of the control algorithm is to algebraically transform the nonlinear plant into a linear substitute. The resulting control law can be interpreted as combined feedforward and feedback PID control, applied to the linear substitute model. Motion dynamics and perturbations are accounted for in a feedforward branch while a PID feedback branch undertakes the cancellation of errors caused by model uncertainties and unmodeled physics. For linearized plant models, the computation of a feedforward branch is straight forward from the state transition matrix. In the nonlinear case proposed in this paper, the inclusion of a feedforward signal is achieved using the input-output linearization technique, yielding a nonlinear and globally valid control law. Sample numerical simulations are presented to support the validity of the controller and to demonstrate its performance compared to a simple PID controller. Simulation results show enhanced tracking performance of the mean along-track separation reference signal and reduced control effort. Moreover, input–output linearization enables the control of a large set of operating points using one set of control parameters.

Temperature Dependence of Hippocampal Short‐term Facilitation (STF) in Syrian Hamsters, a Hibernating Species

Studies on non‐hibernating mammals have identified short‐term facilitation (STF) as a form of cellular neural plasticity that modulates information processing over a hippocampal neural network of CA3 and CA1 pyramidal neurons. The circuit has two branches: (1) a monosynaptic excitatory (E) feedforward pathway wherein CA3 axons directly excite CA1 neurons, and (2) a bi‐synaptic inhibitory (I) feed‐forward pathway. Pathway I includes a GABAergic inhibitory neuron such that CA3 axons excite GABAergic interneurons that in turn inhibit CA1 neurons. The present study evaluated the possibility that such a dual feedforward circuit supported STF in hibernating as well as in non‐hibernating Syrian hamsters (Mesocricetus auratus). We tested the hypotheses that: (1) at temperatures at (or above) 25° C, the hamster’s circuits support STF as in non‐hibernating species, and (2) as temperature declines from 25° to 20° (simulating brain temperatures encountered during entry into torpor), STF is attenuated. For this, we evaluated responses in 400μ hamster hippocampal slices, using tungsten stimulating electrodes placed to excite CA3 axons (Schaffer collaterals/commissural fibers) and a glass electrode positioned to record CA1 neuron evoked responses (fEPSPs). Paired‐pulse stimulation (with an interpulse interval of 30 msec and an interval between pairs of 60 sec) evoked a pair of responses – i.e., fEPSP1 followed fEPSP2. With bath temperature at (or above) 25° C, the initial slope of fEPSP2 was greater than that of fEPSP1. This finding supports the presence of a hamster facilitating circuit with at least an E feedforward pathway linking CA3 and CA1 neurons. To determine if the hamster circuit also has a bi‐synaptic inhibitory branch, paired‐pulse experiments were repeated in the presence and absence of picrotoxin, a non‐competitive GABA receptor antagonist. Picrotoxin altered fEPSP1 and fEPSP2 slopes (e.g., when GABAergic interneurons were blocked, fEPSP1 slope increased), indicating the hamster circuit also had an inhibitory feedforward branch. Additionally, paired‐pulse experiments with bath temperature lowered to 20° C resulted in a decreased ratio of fEPSP2/fEPSP1, marking a decline in STF. Nonetheless, at 20° C (and even at 15° C), single‐shock CA3 stimulation still evoked action potentials (population spikes) in CA1 neurons, showing that, despite a loss in facilitation, the circuit continued to relay signals from CA3 to CA1 neurons. Taken together, our data are consistent with the proposal that awake and behaving hamsters have a dual feed‐forward neural circuit supporting STF, as in non‐hibernating mammalian species, but when the hamsters are hibernating, STF is muted.

A Robust Power Regulation Controller to Enhance Dynamic Performance of Voltage Source Converters

This paper presents a novel power regulation controller for grid-connected voltage source converter (VSC). The proposed controller is usually applied to achieve smooth active and reactive power dynamics against the variation of parameters. The dynamic performance of grid-connected VSC is sensitive to parameter variation, threatening the safe operation especially when the relative stability is low. Moreover, there is no possibility to modify the dynamic response without the loss of power regulation precision or output voltage and frequency accuracy. In this paper, an improvement in the dynamic response is achieved by introducing feedforward branches into the VSC power regulation controller. Owing to the model reduction mechanism, the VSC provides smooth dynamic response and robustness against the variation of parameters. Simulation and experiment results are presented to prove the effectiveness of this approach, which shows excellent performance as opposed to the conventional controller paradigm.

Maximum Power Point Tracking Strategy for a New Wind Power System and Its Design Details

This study presents two methods to improve the maximum power point tracking strategy for a new wind power system that consists of a planetary gear, two permanent magnet synchronous machines, and loads. The generator, the electric motor, and the wind turbine are connected to the sun gear, ring gear, and carrier of planetary gear, respectively. With the aid of an electric motor, the system can track the maximum power without the full-power converter for generator because of its special operating principle. Conventional optimum torque (COT) control method with a torque error feed forward branch is proposed to obtain faster response compared with COT control method. Moreover, considering that the actual power cannot reach the theoretical optimum point due to the loss torque of the system, the COT control with torque loss compensation is described. A method is also proposed to estimate loss torque. Finally, the theoretical analysis is verified by simulation and experiment results.

Analysis and design of vector control for VSC-HVDC connected to weak grids

Voltage source converter based high voltage direct current transmission (VSC-HVDC) is considered one of the most suitable technologies to integrate renewable energies. However, connecting VSC to a weak grid is challenging since traditional vector control tends to become unstable under high power demand conditions. In this paper, an improved vector control method is proposed wherein a feed forward branch based on steady state and small signal analysis of the VSC system is added under weak grid situations. The feed forward branch promotes faster reactive power response, thus enhancing the stability of the VSC system. Since the improved vector control uses the same inner loop as traditional vector control, the proposed method allows for the ability to retain fault current suppression capabilities. Furthermore, the control parameters of the outer loop of the improved vector control need not vary according to the variation of the operating points, which makes it easy to implement. The feed forward branch is implemented by solving a nonlinear equation or through use of a look-up table. The influence of the estimation errors of short circuit ratio (SCR) on the control performance is also studied. The effectiveness of the improved vector control is demonstrated through small signal model analysis and time domain simulations.

High-Precision Repetitive Motion Control in Permanent Magnet Synchronous Motor Using a Periodic Adaptive Extended State Observer

This paper focuses on estimating and compensating the lumped disturbances in the repetitive motion control system of permanent magnet synchronous motor. A Periodic Adaptive Extended State Observer (PAESO) consisting of a normal Extended State Observer (ESO) and a refined ESO is proposed. The normal ESO is designed to capture the approximate range of the disturbances, and the refined ESO is developed to optimize the quantity of the estimated lumped disturbances by integrating real-time position tracking error. Based on PAESO, a hybrid controller, including a feedback branch and a feedforward branch, is presented to make the overall system stable and the position tracking error convergent towards zero. The effectiveness of the proposed PAESO is verified through three real-time experiments. Experimental results show that a high-precision tracking performance is obtained by the proposed PAESO.

Potiskivanje utjecaja vjetra u projektiranju autopilota

Environmental conditions affects ship’s course. Hence, it affects velocity, and efficiency of fuel consumption, which is an important research topic nowadays. Therefore, it is important to take it into account in the design of ship’s autopilots. In this paper a method is proposed to compensate for wind’s influence, which is based on wavelet transform by introducing the so called wavelet anti-filter. The anti-filter is added to the feed-forward branch of the classic autopilot design scheme, which consists of feedback loop and PID controller. The anti-filter branch represents a modification of the classic scheme.

An 80-dB DR, 7.2-MHz Bandwidth Single Opamp Biquad Based CT $\Delta \Sigma$ Modulator Dissipating 13.7-mW

A novel low power compact loop filter using a single amplifier biquad (SAB) network is presented for continuous-time (CT) delta-sigma (ΔΣ) modulators. This new technique reduces power consumption and die area by minimizing the number of active elements and simplifying the modulator topology. The new SAB network has a transfer function (TF) zero, which implements a local feedforward (FF) path in system-level diagram. By having a local FF branch embedded in the SAB network, the FF branches to the summing block in the SAB based feedforward modulator topology is reduced to half the number of FF branches in the conventional topology. Consequently, the SAB based modulator utilizes a switch-capacitor (SC) adder replacing the commonly used CT adder and the sample & hold blocks in the conventional architecture. The SAB based loop filter with reduced FF branches simplifies the design and implementation of the high-order continuous-time ΔΣ modulator. The proposed loop filter is a general filter, which can be used for both high and low oversampling ratios (OSRs). A 4th-order low pass continuous-time ΔΣ modulator is designed and implemented in 130 nm process to confirm the effectiveness of the proposed techniques. Within a 7.2 MHz signal bandwidth, the measured dynamic range and SFDR of this prototype IC are 80 dB and 83.1 dB, respectively, and the total power consumption of 13.7 mW.

Model-Based Evolution of a Fast Hybrid Fuzzy Adaptive Controller for a Pneumatic Muscle Actuator

Pneumatic artificial muscle-based robotic systems usually necessitate the use of various nonlinear control techniques in order to improve their performance. Their robustness to parameter variation, which is generally difficult to predict, should also be tested. Here a fast hybrid adaptive control is proposed, where a conventional PD controller is placed into the feedforward branch and a fuzzy controller is placed into the adaptation branch. The fuzzy controller compensates for the actions of the PD controller under conditions of inertia moment variation. The fuzzy controller of Takagi-Sugeno type is evolved through a genetic algorithm using the dynamic model of a pneumatic muscle actuator. The results confirm the capability of the designed system to provide robust performance under the conditions of varying inertia.

Dynamic Optimization of a Slab Reheating Furnace With Consistent Approximation of Control Variables

A dynamic optimization method is developed for temperature control of steel slabs in a continuous reheating furnace. The work was stimulated by the need for furnace control concepts that are computationally undemanding, robust, accurate, and capable of non-steady-state operating scenarios, where the properties and the temperature goals of slabs may vary significantly. The proposed hierarchical control structure is based on a continuous-time switched nonlinear model and uses the furnace zone temperatures as intermediate control variables. Consistent approximation is applied to obtain a parametric optimization problem that can be efficiently solved with the quasi-Newton method. Constraints on system states and control variables are considered by penalty terms in the cost function and saturation functions, respectively. The optimization method plans temperature trajectories for both the furnace and the slabs, which may be useful for open-loop control and feedforward branches of two-degrees-of-freedom control structures. The capabilities of the method are demonstrated in an example problem.

Design Techniques for Wideband Discrete-Time Delta-Sigma ADCs With Extra Loop Delay

Novel implementation techniques, such as the use of direct-charge-transfer stage, noise coupling, and dynamic element matching can improve the performance of wideband ΔΣ ADCs. However, they introduce extra loop delay, which compromises the low-distortion property and even the loop stability. This paper shows how the addition of independent feedback and feed-forward branches to the loop filter can compensate the extra loop delay, and restore the desired signal and noise transfer functions. The design methodology is then generalized for different kinds of ΔΣ ADCs, and the low-distortion property is analyzed. Two wideband delta-sigma ADCs have been designed and simulated to verify the theory.

Feedforward Control of Electrical Drives - Rules and Limits

Nowadays, there are several application in the field of position controlled electric drives, such as high speed cutting, where traditional cascade control structures provide insufficient accuracy. Therefore, it is necessary either to completely change the control structure (e.g. sliding mode control) or to modify and extend the basic cascade structure. One of those modifications can be feedforward direct branches. Feedforward increase order of astatism without stability influencing but on the other hand it brings other problems regarding to the feedforward technique implementation, system parameters changing or neglecting particular system behavior. This paper describes basic control structures, their features and several mentioned problems related to feedforward control of electric drives.

Model-based trajectory planning, optimization, and open-loop control of a continuous slab reheating furnace

Abstract A temperature control method is developed for reheating steel slabs in an industrial furnace. The work was motivated by the need for mathematically simple furnace control schemes that feature accuracy, robustness, applicability to online control, and capabilities of non-steady-state operating scenarios, where the temperature goals and other properties of the slabs may vary considerably. The proposed hierarchical control concept computes desired heat inputs for each individual slab based on a discrete-time nonlinear model. Then, a quadratic program is solved to plan reference trajectories of furnace temperatures which optimally realize the desired heat inputs into the slabs. The iterative algorithm accounts for constraints on system inputs as well as states and may be used for open-loop control or as a feedforward branch in two-degrees-of-freedom control structures. The feasibility and the limitations of the approach are demonstrated by means of an example problem.

Self-sensing High Speed Controller for Piezoelectric Actuator

This study proposes an effective scheme for high speed positioning control of a piezoelectric actuator. The proposed approach is based on the combination of a feedforward branch and a proportional integral derivative (PID) feedback controller. The feedforward branch consists of an inverse model of the actuator that includes hysteresis compensation, inverse mechanical transfer function, and electrical losses compensation. In order to avoid using a bulky and costly displacement sensor, a detection model has been developed to compute the displacement of the piezoelectric actuator as a function of the current. This approach has been compared with a regular PID feedback control scheme, and with a feedforward/feedback controller using a sensor. Experiments have been carried out for a 2ms pulse excitation of the actuator. It is shown that the proposed approach allows to combine feedforward advantages (quickness and hysteresis compensation) and feedback advantages (static error and creep cancellation). Moreover, it is shown that the detection model allows to smartly avoid using any mechanical sensor.

Novel topologies for time-interleaved delta-sigma modulators

An elegant way to decrease the operation speed or equivalently to increase the conversion bandwidth of /spl Delta//spl Sigma/ modulators is via exploitation of the time-interleaving approach. Recently, we have proposed a novel method to obtain efficient architectures for time-interleaved /spl Delta//spl Sigma/ modulators. In this paper, we extend this method to a sub-class of modulators containing cascaded integrators with weighted feedforward summation and cascaded integrators with distributed feedback as well as feedforward branch topologies. A new time-interleaving concept based on zero-insertion interpolation is also proposed, which eliminates the high-sampling-rate multiplexer at the input stage, resulting in a further significant simplification in hardware complexity. In this approach, the input signal is sampled at the operation frequency of the channels and applied only to the first channel, whereas all other channels are fed with zeros all the time. The low-pass filter at the output of the modulator serves two purposes: 1) it rejects the spectral replicas of the input signal and 2) it attenuates the out-of-band quantization noise.

Modelling, Identification and Control of Thermal Deformation of Machine Tool Structures, Part 5: Experimental Verification

Machining accuracy is more often governed by thermal deformation of the machine tool structure than by static stiffness and dynamic rigidity. Since thermally induced errors cannot completely be eliminated at the design stage, the use of control and compensation systems is an inevitable course of action. Existing control systems are based on two different approaches; the use of empirical compensation function, and on-line execution of numerical simulation models. To overcome the limitations of these methods, a new control system has recently been proposed by the authors. This system, which is based on the concept of generalized modelling, incorporates a realtime inverse heat conduction problem IHCP solver to estimate the transient thermal load applied to the structure. With this information, the relative thermal deformation between the tool and the workpiece is estimated and used as a feedback control signal. In previous parts of this series, computer simulation test cases were carried out to examine the dynamic response, accuracy and stability of the system. In the present study, the performance of various components of the control system, specifically, the IHCP solver, the thermal deformation estimator, and the feedback controller are verified experimentally using a three-component structure. The results showed that the derived generalized thermoelastic transfer functions and algorithms are indeed quite accurate in predicting and controlling the transient thermoelastic response behaviour of a predominantly linear structure. The results showed that the a IHCP solver is inherently stable even when the temperature measurements are contaminated with random errors. The excellent computational efficiency of the integrated system is shown to be well suited for real-time control applications involving multi-dimensional structures, achieving a control cycle of less than 0.5 second. The experimental results showed that in real structures higher modes can be present, and therefore, a fourth order deformation model should be used to improve the prediction accuracy. The proposed PID control system, with feedforward branches, was capable of reducing thermal deformations of the order of 200 μm to levels below ±8 μm. These results also demonstrated the effectiveness of artificial heat sources as a control actuation mechanism, in spite of their inherent limitations, namely, thermal inertia, coupledness, and unidirectionality.