Mingwei Sun

On Low-Velocity Compensation of Brushless DC Servo in the Absence of Friction Model

Friction compensation is usually realized based on a friction model; however, the induced undercompensation or overcompensation, which can lead to steady-error or limit-cycle phenomenon, respectively, is inevitable. A novel straightforward reference compensation scheme for the brushless dc servo system independent of the friction model is presented to reject the aftereffect caused by the friction instead of its original mechanics. Neither the accurate friction model nor any estimation of some specific characteristic parameters is needed in this design. Moreover, the inexact velocity estimation information is not as crucial as it is in the traditional compensation methods. A linear control law is proposed based on a reduced-order observer, which could be readily implemented in low-cost embedded fixed-point chips. Two guidelines for the selection of control parameters are presented in terms of delay sensitivity and limit-cycle avoidance. The approach can be applied to the cases with multiple disturbance torque sources except the friction one, where the friction-model-based strategy is difficult to take effect. Finally, comparative mathematical simulation and practical experiment results are used to validate the effectiveness of the proposed method. Substantial low-velocity performance improvements are achieved in the hardware experiments.

A novel disturbance-observer based friction compensation scheme for ball and plate system.

Friction is often ignored when designing a controller for the ball and plate system, which can lead to steady-error and stick-slip phenomena, especially for the small amplitude command. It is difficult to achieve high-precision control performance for the ball and plate system because of its friction. A novel reference compensation strategy is presented to attenuate the aftereffects caused by the friction. To realize this strategy, a linear control law is proposed based on a reduced-order observer. Neither the accurate friction model nor the estimation of specific characteristic parameters is needed in this design. Moreover, the describing function method illustrates that the limit cycle can be avoided. Finally, the comparative mathematical simulations and the practical experiments are used to validate the effectiveness of the proposed method.

Practical Wind-Disturbance Rejection for Large Deep Space Observatory Antenna

The wind-load disturbance is the major factor that affects the pointing and tracking accuracy of a large deep space observatory antenna. An antenna position control scheme is proposed based on the most popularly used proportional-integral-derivative controller. The wind-load torque and other uncertain mechanical dynamics are treated as external and internal disturbances, respectively. All disturbances considered as a whole can be estimated and compensated based on an extended state observer, which can attenuate the adverse effects caused by the wind. The mechanism of electric motor is used to simplify the design procedure and reduce the required order of the observer. In addition, only minor control software modifications are required for the existing control system of the antenna. At first, the effectiveness of the proposed approach was illustrated by mathematical simulations. Then, this methodology was applied to a practical installation. In the experiment, a 65.2% reduction of overshoot and a remarkable amelioration in the capacity of wind-disturbance rejection were achieved, whereas the tracking precision was also improved significantly. In addition, the proposed method can also reduce the possibility of wearing and tearing of the installation.

Practical solution to attitude control within wide envelope

Purpose – This paper aims to present a fast, economical and practical attitude control design approach for flight vehicles operating within wide envelopes. Design/methodology/approach – Based on a linear disturbance observer, an enhanced proportional-derivative (PD) control scheme is proposed. Utilizing the data from the onboard gyro, the observer can treat the entire response of the system, with the exception of the control term, as a disturbance, and use the estimation of the disturbance to cancel out this response and thereby to effectively simplify the control channel. Using the stability margin tester, the explicit graphical tuning rules are given in a consistent way for the longitudinal dynamics based on the induction method. Mathematical simulations are performed for a highly maneuverable flight vehicle to test the proposed method, which are compared with the traditional PD and H8 control algorithms. Findings – The proposed strategy for attitude control can be reformulated as a static-dynamic contr...

Stability margin-based PD attitude control tuning for unstable flight vehicle

Proportional-derivative (PD) attitude control is widely used for the flight vehicles, especially in boost phase. Some of the flight dynamics are open-loop unstable, which often limits the achievable closed-loop performance. Based on the intrinsic characteristics of the linear model obtained from the small perturbation theory, simple numerical analytical tuning formulae of PD attitude control are derived to meet the gain and phase margin specifications. According to Routh stability criterion, the decreasing gain margin is obtained by using the approximation of delay amid low frequency with the established tuning rule. Some numerical polynomial solving approaches are employed to seek the feasible stability margin region, which is explicitly plotted in the 2-D plane. Taking engineering practice into account, the maximum gain constraint is also imposed. Finally, several numerical examples are presented to validate the analysis result.

PID pitch attitude control for unstable flight vehicle in the presence of actuator delay: Tuning and analysis

Abstract In the realm of flight control, proportional–integral–derivative (PID) control is still widely used in practice due to its simple structure and efficiency. The robustness and dynamic performance of PID controller can be evaluated by stability margins. Based on the empirical knowledge about the unstable flight dynamics, the analytical tuning formulas of the PID pitch attitude control with actuator delay are derived with the help of several proper approximations. These tuning formulas can meet the increasing gain and phase margins (iGPM) requirement and avoid time-consuming trial-and-error tuning process. The feasible iGPM area is established in 2-D plane subject to several conditions, especially taking the decreasing gain margin into account, wherein the numerical polynomial solving approaches are employed. The relationship between an existing PD tuning scheme and the proposed PID tuning method is also revealed. The applicable area of the tuning rule is then investigated on the basis of a crucial assumption. Furthermore, the achievable decreasing gain and phase margins (dGPM) area is obtained when the decreasing gain margin is critical; and another tuning rule is derived according to the dGPM specifications. The effect of the actuator delay on the achievable GPM area is demonstrated in a straightforward manner such that the reasonable criteria can be specified. Finally two numerical paradigms are presented to validate the proposed method; and the robustness and dynamic performance of the PID control are also reexamined for unstable flight dynamics.

Proportional–integral–derivative attitude control subject to dynamic rate saturation of elevator through explicit command reshaping: An engineering approach

In this article, an explicit pitch command governor for a kind of proportional–integral–derivative attitude control system is proposed based on the model predictive control philosophy to avoid the dynamic rate saturation in the elevator. In this command governor, the control horizon of the model predictive controller is selected as 1 such that the predicted saturations can be represented by a set of linear inequalities, which can significantly reduce the computational complexity, and the optimal solution can be calculated in real-time. The effectiveness of the proposed method is validated via numerical simulations. In addition, the limitations of this pitch governor are also revealed through investigating its scope of application in terms of uncertainties, nonlinearities and coupling effects.

ADRC Based Attitude Control of a Quad-rotor Robot

In this paper, active disturbance rejection control (ADRC) technique is described in detail. Typical algorithms for each component are given as well. In order to control the attitudes of a quad-rotor robot as we desired, two kinds of continuous ADRC controllers are designed. The satisfactory real-time control experimental results indicate that the continuous ADRC can not only meet the control accuracy requirement but also can achieve rapid and effective response for the nonlinear coupled systems. Eventually, the advantages and scopes of application of the two controllers are summarized.

Receding Horizon Trajectory Optimization with Terminal Impact Specifications

The trajectory optimization problem subject to terminal impact time and angle specifications can be reformulated as a nonlinear programming problem using the Gauss pseudospectral method. The cost function of the trajectory optimization problem is modified to reduce the terminal control energy. A receding horizon optimization strategy is implemented to reject the errors caused by the motion of a surface target. Several simulations were performed to validate the proposed method via the C programming language. The simulation results demonstrate the effectiveness of the proposed algorithm and that the real-time requirement can be easily achieved if the C programming language is used to realize it.

Neural Networks Based Formation Control of Anti-ship Missiles with Constant Velocity

On the basis of nonlinear model predictive control, a formation controller is designed for a group of missiles by regulating the flight path angles in a proper manner. According to the formation requirement and the practical location of the leader missile, a dynamic virtual guidance point is generated for each follower missile. The formation control of follower missiles is considered as a dynamic optimization problem. The performance index is presented in a quadratic form. The optimization problem is reformulated as a static one. The active set method is used to obtain the optimal solution in terms of three key factors offline. Therefore, a solution table is established and used to train the neural network guidance model. The online control is achieved using the real-time state measurements as model inputs. Simulation results show the effectiveness of the proposed method.