Simple Tuning Rules for Feedforward Compensators Applied to Greenhouse Daytime Temperature Control Using Natural Ventilation

In this work, simple tuning rules for feedforward compensators were applied to design a control strategy to regulate the inside air temperature of a greenhouse during daytime by means of a natural ventilation system. The developed control strategy is based on a PI (Proportional-Integral) controller combined with feedforward compensators to improve the performance against measurable external disturbances such as outside air temperature, solar radiation, and wind velocity. Since the greenhouse process dynamics is very complex and physical non-linear models are mathematically complicated, a system identification methodology was proposed to obtain simpler models (high-order polynomial and low-order transfer functions). Thus, an easier procedure was completed to tune the PI controller parameters and to obtain the feedforward compensators expressions by following a series of modern and simple tuning rules. Simulations with real data were executed to compare the control performance of a PI controller with or without the addition of feedforward compensators. Moreover, real tests for the developed control strategy were carried out in an experimental greenhouse. Results demonstrate an enhanced control performance with the presence of the feedforward compensators under different weather conditions.

Class of Stabilizing Parallel Feedforward Compensators for Nonminimum-Phase Systems

In this work, the properties of the class of parallel feedforward compensators to stabilize linear closed-loop systems are studied. The characteristic equation and its root locus behavior, including its asymptotes, are investigated to leave out the compensators that will not result in a stable closed-loop system. Even though there have been numerous studies relevant to parallel feedforward compensation that result in the optimal integration of squared errors (ISE), the broader view of all possible compensators has not been of much interest in the literature. Nevertheless, this study is important because, in the presence of noise and disturbance, an optimal ISE control design for the nominal plant may perform poorly while a finite ISE design may have a robust and efficient performance. One of such class compensators is parallel feedforward compensator with derivative effort (PFCD) that for a vast number of processes can have impressive properties such as no branch comebacks to the right half plane (RHP) of the root locus plot (LHP black hole effect). The example in this paper shows how effectively PFCD can contract the root locus branches into the LHP.

Analytical Statistical Study of Linear Parallel Feedforward Compensators for Nonminimum-Phase Systems

In this work, a new parallel feedforward compensator for the feedback loop of a linear nonminimum-phase system is introduced. Then, analytical statistical arguments between the existing developed methods and the innovated method are brought. The compelling arguments suggest the parallel feedforward compensation with derivative (PFCD) method is a strong method even though at its first survey it seems to be optimistic and not pragmatic. While most of the existing methods offer an optimal integral of squared errors (ISE) for the closed-loop response of the nominal plant, the PFCD offers a finite ISE; in reality, typically, the nominal plant is not of main concern in the controller design and the performance in the presence of mismatch model, noise, and disturbance has priority. In this work, there are several arguments brought to bold the importance of the innovated PFCD design. Also, there is a closed-loop design example to show the PFCD effectiveness in action.

SUPERHEATED STEAM TEMPERATURE CONTROL FOR BOILER USING ADAPTIVE DYNAMIC FEEDFORWARD COMPENSATORS

This paper proposes a new control strategy for improving the performance of the superheated steam temperature control system in thermal power plants. Based on the analysis of the limitations of the static feedforward compensators (SFC) for temperature and boiler load disturbances in the existing control system of the auxiliary boiler in Dung Quat refinery, two adaptive dynamic feedforward compensators (ADFC) for temperature and boiler load disturbances were proposed to replace the SFCs. In addition, a method for predicting the tube wall temperature of the superheater using an autoregressive moving average (ARMA) model was also proposed. The simulation results for the two typical cases of the boiler load change indicate that the control system incorporated with the proposed ADFCs improves significantly the performance of the control system

Trajectory control of aggressive maneuver by agile autonomous helicopter

In this paper, a new state-dependent coefficient parameterization of an agile helicopter dynamics is derived to deal effectively with the optimal trajectory control of aggressive maneuver such as the infinity maneuver with agility. The angular velocity of the main rotor and engine throttle as state and input, respectively, are involved in the dynamic model to improve the maneuvering capability of helicopter. Since the presented six degrees-of-freedom helicopter model is highly nonlinear and nonaffine, particularly nonlinear in actuator, the state-dependent Riccati equation is implemented in the presence of saturation bounds for actuators to achieve precision trajectory control and conquer the challenge of aggressive maneuver tracking control. In addition, new helicopter dynamic representation results in the conventional state-dependent Riccati equation to be applied without prevalent simplifications within dynamic and actuators and also certain augmentations on controllers such as trim or feedforward compensators. Indeed, the proposed controller structure is verified by simulations for both regulation and trajectory tracking problem.

Nonlinear Compensators of Exhaust Gas Recirculation and Variable Geometry Turbocharger Systems using Air Path Models for a CRDI Diesel Engine

This paper investigates the design of model-based feedforward compensators for exhaust gas recirculation (EGR) and variable geometry turbocharger (VGT) systems using air path models for a common-rail direct injection (CRDI) diesel engine to cope with the nonlinear control problem. The model-based feedforward compensators generate set-positions of the EGR valve and the VGT vane to track the desired mass air flow (MAF) and manifold absolute pressure (MAP) with consideration of the current engine operating conditions. In the best case, the rising time to reach 90% of the MAF set-point was reduced by 69.8% compared with the look-up table based feedforward compensators.