Digital Computer Control Systems

Basing on lifting technology, this paper researches a design method for multirate sampled-data control system in the background of flight control system design, which consummates the theory of multirate sampled-date control system design for further steps, and provides a method to design multirate sampled-data controller. As the reason of uncertainty in the aircraft model and the need of different sampling frequencies in different control loops, H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</inf> -optimal multirate sampled-data control is considered. First, multirate sampled-data control system is outlined, and then the signal description are presented. Because of multirate sampled-data system is time-variant, the direct digital controller design becomes difficult. The equivalent discrete time-invariant systems can be converted from the linear time-variant systems through lifting technology. Then the H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</inf> discretization of multirate sampled-data systems is researched. After the sampled-data control system was lifted, the equivalent L <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> [0, h) -induced norm is proven. Base on the above, the method of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</inf> -optimal multirate sampled-data control is summarized. A height control is simulated using a simplified aircraft model to illustrate the design. The simulation shows that the multirate Sampled-data control system can achieve the satisfactory objective accurately and optimally.

This paper presents a study of multi-objective optimal design of a slide mode control for an under-actuated nonlinear system with the parallel simple cell mapping method. The multi-objective optimal design of the slide mode control involves 6 design parameters and 5 objective functions. The parallel simple cell mapping method finds the Pareto set and Pareto front efficiently. The parallel computing is done on a graphic processing unit (GPU). Numerical simulations and experiments are done on a rotary flexible arm system. The results show that the proposed multi-objective designs are quite effective.

This paper discusses a new design method for state feedback multirate control with current estimator. A computationally effective multirate digital control scheme, in which the control outputs are calculated based only on the state estimates at sampling instants, is presented. It is shown that the states of the redesigned state feedback multirate control system match the states of conventional state feedback multirate control system at every sampling instant. The redesigned method is applied to a HDD servo control systems. The experimental results show that the performance of the redesigned multirate system is similar to that of the conventional multirate design in terms of open loop bandwidth, phase margin and gain margin.

Architecture of a Dynamic Position Autonomous VesselAbstract This paper introduces the architecture of an autonomous floating vessel for real timeheading control and modeling. The vessel is a four by eight foot barge propelled by sixcommercial Minn Kota trolling motors. The automatic controller consists of a discrete timeLogic Proportional Integral Derivative (LPID). The LPID controller determines the motoroutputs necessary to correct the real time vessel’s heading angle. A Printed Circuit Board (PCB)designed by students is used to control each motor’s thrust by a computer. The controlleroutputs are combined and normalized by the computer before being sent to the microcontroller.An AIRMAR PB200 WeatherStation sensor is used to collect vessel data. All data are collectedin a database for the real time control and post analysis. This architecture is demonstrated byexperimental data collected from this vessel at the United States Coast Guard Academy for acapstone project in Electrical Engineering major. In this senior project, students used successful design architecture in performinglinearization, data collection, utilizes sensor, robust controller design, and the identification ofthe system dynamic. The first challenge was to build the vessel and collect initial data. Vesselheading (system output) and the motors trust (system input) as a function of time were recordedin a data base. Students used standard linear least squares system identification methods toidentify the vessel’s discrete-time step invariant equivalent transfer function. The open-loopsystem identification was performed from a random motors (4 motors) trust in order to maintainsome directional control during the data collection. After the system identification studentsdesigned a logic discrete time PID controller for the real time controller of the heading ofplatform. The real time heading controller for the vessel was based on the updating of discretetime PID controller coefficients.

This paper presents an optimization-based algorithm for state estimation of multirate digital control systems. The algorithm features a predictor estimator structure and it is derived by employing a time invariant modelling approach to multirate systems. Special care is taken to ensure the causality of the derived estimation algorithm and to reduce the dimensionality inherent in multirate system modelling while maintaining a reasonably simple implementation. The proposed algorithm is developed to ensure convergence in state estimation between base sampling instants as well as between model rate sampling instants.

Design of Consensus Controllers for Multi-rate Sampled-data Strict-Feedback Multi-agent Systems

This paper considers robust control design for large-scale uncertain systems with state, input and output overlapping decompositions. The extension principle, which is a generalized notion of overlapping decomposition, is investigated from a robust control viewpoint. It is shown that if a controller designed for the expanded system achieves robustness in the expanded spaces, then the contracted controller achieves required robustness of the original system. This paper also defines and develops a framework of the extension principle for multirate control systems with hybrid signals. An approach to robust performance design with the overlapping multirate control is proposed.

This paper is concerned with control design for a generalized discrete-time Takagi-Sugeno fuzzy system. The Takagi-Sugeno fuzzy system generally describes nonlinear systems by employing local linear system representations. It is a great tool to analyze a nonlinear system and to design a stabilizing controller for it. However, there is a case where a controller design for a nonlinear system based on the Takagi-Sugeno fuzzy system becomes difficult due to its representation. A generalized fuzzy system to be considered in this paper describes even a wider class of nonlinear systems by representing locally nonlinear systems, and gives a different representation from the standard Takagi-Sugeno fuzzy system, which leads to a rather easy controller design. For such a generalized system, a stabilizing controller design method is proposed by introducing a new class of nonlinear controllers. Then, the resulting closed-loop system becomes a fuzzy system with linear system structures locally, which makes the control design easier. Stabilizing controller design conditions are given in terms of a set of linear matrix inequalities(LMIs), which are easily numerically solvable. A relaxation method is used to reduce the conservatism of design conditions. Finally, numerical examples are given to illustrate our nonlinear control design and to show the effectiveness over other existing results.

Control design in the longitudinal-vertical channel is studied for tilt-rotor aircraft at low speed flight. The famous XV-15 tilt-rotor aircraft is used as a prototype. A model predictive control (MPC) design is developed based on a state-space model in a cascaded architecture. The MPC algorithm considers a terminal cost in its objective function so as to ensure close-loop stability, and an error-rate term is introduced in order to improve transient performance. By transforming constraints, the controller designed based on a linearized model at single operating point is applied to the whole stage at low speed flight. It means that there is not switching as gain scheduling in the realization of the longitudinal control. The simulation results show that the flight control system presents satisfied performance and robustness.

This paper describes an experimental study on H∞ control for vibration in multi-degree-of-freedom systems. An H∞ controller designed by using the reduced-order model makes a closed loop system, not only causing no spillover phenomena, but also controlling the vibration on the four-degree-of-freedom experimental model. The experimental results are very similar to the simulation results, and the efficiency of the H∞ control system is confirmed. Also experiments on frequency-shaped cost function LQG (H2) control design are performed in comparison with the H∞ optimal control. Because the H∞ optimal control has strong robust stability against the parameter variations, it can construct a more useful control system than H∞ control for a real control object.

A modal H∞-norm-based performance requirement for damage-tolerant active controller design

This paper presents a design of power factor correction (PFC) stage for a dimmable electronic ballast system to feed a T5 HE 28 W fluorescent lamp. The proposed topology is composed of a Single-Ended Primary Inductance Converter (SEPIC) used as a PFC stage with variable output voltage in order to supply a half-bridge inverter with an LCC filter controlled by a dedicated IR21592 integrated circuit. A novel dimming method based on controlling the output voltage of the PFC stage together with the variation of the half-bridge switching frequency in a narrow range is proposed and evaluated. A digital compensator design is presented in order to control the SEPIC output voltage. Experimental results for the PFC system are presented in order to test the operation of the entire illuminating system.

With the information technology development of the modern ship, integrated management platform system (IPMS) has received great attention. The IPMS network architecture has the advantages of low cost, easy maintenance and great flexibility. But it inevitably introduces network delay, packet loss and other issues, so the networked control system modelling and controller design over the IPMS network becomes more and more important. In this paper, a new sliding mode networked controller, based on the T-S fuzzy model, is proposed to deal with the problems of uncertainty and disturbances in networked control system (NCS). Firstly, we choose the time delay as premise variables of the fuzzy system, so that the system with control time delay is transformed into one with no time delay based on the fuzzy fusion technology. And then, the global sliding surface is designed by the parallel distributed compensation technique. Adaptive reaching law and disturbances prediction methods are researched. The stability of IPMS networked sliding mode control system is analysed. Finally, with a certain variable time delay, the simulation results illustrate that the proposed networked controller is effective.

A critical step in the design of multi-objective control systems is the selection of the control structure. This paper presents a multiple-degrees-of-freedom control structure for optimal controller design for infinite-dimensional systems. The approach for design of the controllers uses the internal model control design method that is applicable to infinite-dimensional systems, which alleviates the need for finite-dimensional approximation of partial differential equations. The control structure enables the multi-objective controllers to effectively deal with input saturation nonlinearities when the manipulated inputs saturate. A multi-objective infinite-dimensional control system is designed for a distributed parameter system motivated by tissue engineering. The control system is shown to remain optimal when controllers are taken off-line in the event of component failures, without redesigning any of the on-line controllers.

A new model for networked control systems (NCSs) with structured uncertainties and multiple state time-delays is presented, In view of multi-input and multi-output (MIMO) NCSs with many independent sensors and actuators, a continuous time model of NCSs with distributed time-delays and uncertainties are proposed. A method of delay-estimation online is also given. Then a scheme based on LQG controller is designed to achieve desired Real-time performance. The result illustrate that the effectiveness of the proposed control design and the satisfactory performance of the system.