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  • 1.
    Samaranayake, Lilantha
    KTH, School of Electrical Engineering (EES).
    Distributed Control of Electric Drive Systems via Ethernet2006Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    This thesis is on adapting standard Switched Ethernet for distributed control applications in electric drive systems. The critical issue of Ethernet here is to provide services to real-time applications. The architectural construction of Ethernet is described, where the objective is to summarize the state of the art and indicate the causes of delays. This results in a network configuration suitable for distributed control applications, with no modifications to the protocols, but introducing the correct placement for the Ethernet Switch. A timing analysis on the Switch itself results in useful conclusions on the causes of non-deterministic nature of delays. Further, the delay measurements are taken on a real Switched Ethernet network, which are used to characterize the network.

    The delays are addressed also in the control systems perspective, as they trigger unwanted performance issues. They set limitations on the performance that can be achieved, even with the best possible controller. The architectures for connecting the nodes of a distributed control system is also studied, which are categorized according to the triggering mechanism.

    Both the networking and control system perspectives are extended for the delay compensation, where standard delay compensation techniques are experimentally verified on a speed control of a Brushless DC motor drive setup. The Proportional Integral controller with robust tuning techniques and Smith Predictor delay compensation, modified with the algebraic design techniques as well as State Feedback controller deploying on-line delay compensation have been verified. The latter technique proved to be promising but at the cost of time stamped measurements, which require synchronization of clocks at the nodes. This is presently cumbersome with most of the cost effective sensor actuator modules with Ethernet connectivity.

    Therefore the state feedback method is further improved using a plant model based predictor, where it eliminates the need of time stamped measurements. The stability has been studied and the design methodology is derived, which is proved to be better in simulations. However, the methodology expects the control delay not to exceed the sampling period. The thesis introduces an adaptive sampling scheme to cope with this situation, in which the sampling period is varied on-line depending on the current control delay. Further this methodology is experimentally verified using distributed position control of an XY board via Ethernet. The network connectivity for the motors of the XY board are obtained through Ethernet Ready Sensor Actuator (ERSA) modules designed and manufactured in the course of studies.

    Finally the general aspects of design, simulation and applications of distributed control systems have been presented.

  • 2.
    Samaranayake, Lilantha
    KTH, School of Electrical Engineering (EES).
    Speed synchronized control of permanent magnet synchronous motors with field-weakening capability2014In: International Review of Aerospace Engineering, ISSN 1973-7459, Vol. 7, no 3, p. 108-115Article in journal (Refereed)
    Abstract [en]

    A vast amount of attentions has been given to permanent magnet synchronous motors (PMSM) in a variety of automotive applications as these motors present higher efficiency, power factor and better dynamic performance than asynchronous motors without sacrificing reliability. It has also been shown that they can be operated over a wide constant power speed range (CPSR) with the field weakening capability. This paper presents a theoretical study on speed synchronized control of the PMSMs in both the constant torque and the field-weakening (or constant power) operation regions. Promising applications of this can be found in aero dynamic, naval, material processing etc., industries.

  • 3.
    Samaranayake, Lilantha
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Alahakoon, Sanath
    KTH, Superseded Departments, Electrical Systems.
    Leksell, Mats
    KTH, Superseded Departments, Electrical Systems.
    Control and Scheduling Co-design of Distributed Real-Time Control Systems2004Conference paper (Refereed)
    Abstract [en]

    Closing control loops over networks is becomingincreasingly popular in embedded applications because of itsflexibility, but it also introduces many new problems. From acontrol perspective, the computer system will introduce (possiblyrandom) delays in the control loop. There is also the potentialproblem of lost measurement signals or control signals. Froma real-time perspective, the first problem is figuring out thetemporal constraints (deadlines, etc.) of the different tasks in thesystem, and then scheduling the CPUs and the network such thatall constraints are met during runtime. As a recurring example,a DC servo, whose position control-loop that is closed over aSwitched Ethernet communication network is studied. It is thenextended to three such systems running parallel sharing the CPUtime and the network bandwidth. Hence different schedulingpolicies with subtask scheduling is investigated.

  • 4.
    Samaranayake, Lilantha
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Leksell, Mats
    KTH, Superseded Departments, Electrical Systems.
    Output feedback predictor compensating time-delays in distributed real-time systems2004In: Proceedings of the Sixth IASTED International Conference on Intelligent Systems and Control / [ed] Hamza, MH, CALGARY: ACTA PRESS , 2004, p. 162-167Conference paper (Refereed)
    Abstract [en]

    Inherent time-delays in distributed real-time control systems can deorade the performance or unstable the system unless treated properly. Standard delay compensation schemes usually include time stamped measurements, which require clock synchronization at different nodes. This needs periodic re-synchronization to minimize the impact of clock drift. consuming additional bandwidth. Further, the controller to actuator delay is unknown prior to the controller calculation, where probability distribution based complicated methods are required, to know it in advance. In this paper, a plant model based predictor is cascaded to the state observer to predict the states corresponding to the next sample. These states are then used in the controller to derive the next control signal, which is released C just after reading the next sample. This completely eliminates clock synchronization and complications in delay compensation. The proposed method is implemented in simulation in a real-time environment for open loop stable and unstable systems.

  • 5.
    Samaranayake, Lilantha
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Alahakoon, S
    Distributed control of an XY board via Ethernet2005In: Proceedings of the Eighth IASTED International Conference on Intelligent Systems and Control, CALGARY: ACTA PRESS , 2005, p. 216-221Conference paper (Refereed)
    Abstract [en]

    With the recent IPv6, Power over Ethernet (PoE) and robust hardware designs, Switched Ethernet technology is currently reaching the status of a complete fieldbus system for harsh factory floor applications. However, the investors still hesitate on its field level operation for time critical applications, due to the non-deterministic delays in the closed world of a switched network. The objective of this paper is to practically prove an adaptive sampling scheme to handle network delays and to highlight the potential of Switched Ethernet in implementing time critical real-time distributed control system applications. Experiments are carried out on a distributed XY board, in which the speed and position control loops on each axis, are closed through a 100Mbps Switched Ethernet network.

  • 6. Samaranayake, Lilantha
    et al.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Alahakoon, S
    Relating sampling period and control delay in distributed control systems2005In: Eurocon 2005: The International Conference on Computer as a Tool, Vol 1 and 2 , Proceedings, NEW YORK: IEEE , 2005, p. 274-277Conference paper (Other academic)
    Abstract [en]

    The control delay in distributed control systems may be compensated on-line or off-line depending on the required quality of the output, available computational power of the controller node, time stamping and clock synchronizing facilities etc. Irrespective of the compensation technique, there is an upper bound to the constant or variable control delay, which is decided by the plant, controller and the selected sampling period of the distributed computer controlled system. It is shown that in general, if the control delay exceeds the sampling period, the system becomes multi-rate; deteriorate performance as the plant updates do not correspond to the output samples. This paper introduces an adaptive sampling scheme to ensure the control delay is less than the sampling period in steady state and uses the maximum tolerable delay of the system at a particular sampling interval to ensure stable transform from one sampling period to another.

  • 7.
    Samaranayake, Lilantha
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Leksell, Mats
    KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
    Vijayananda, T
    Alahakoon, S
    Ethernet ready sensor actuator module for distributed control applications2005In: Eurocon 2005: The International Conference on Computer as a Tool, Vol 1 and 2 , Proceedings, NEW YORK: IEEE , 2005, p. 342-345Conference paper (Refereed)
    Abstract [en]

    Ethernet today is the most widely used information carrier and the service provider for many important applications in the routine life such as e-mail, voice-image data and web based information. It is also emerging strongly into the area of industrial communication covering even sensors and actuators at the factory floor level. However, obtaining network connectivity for existing machinery is still an open question on which many research interests are being focused. This paper presents the hardware development of a general purpose Ethernet Ready Sensor Actuator (ERSA) module and its usage in closing the speed control loop of a Brushless DC motor over a standard Switched Ethernet network. The module is subsequently used to compare connection oriented TCP with connectionless UDP for the same Distributed Control Application under constant network traffic but at different sampling rates.

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