Alternative implementations of a fractional order control algorithm on FPGAs

Traditionally, microprocessor and digital signal processors have been used extensively in controlling simple processes, such as direct current motors. The Field Programmable Gate Arrays (FPGA) are currently emerging as an alternative to the previously used devices in controlling all sorts of processes. The fractional order proportional-integrative control algorithm has the advantage of enhancing the closed loop performance as compared to traditional proportional-integrative controllers, but the implementation requires a higher number of computations. Implementations of control algorithms on FPGAs are nowadays much faster than implementations on microprocessors. This allows for a more accurate digital realization of the fractional order controller. The paper presents nine alternative implementations of such control algorithm on two different FPGA targets. The experimental results, considering DC motor speed control, show that double, fixed-point and integer data representation may be used efficiently for control purposes

Theoretical analysis and experimental validation of a simplified fractional order controller for a magnetic levitation system

Fractional order (FO) controllers are among the emerging solutions for increasing closed-loop performance and robustness. However, they have been applied mostly to stable processes. When applied to unstable systems, the tuning technique uses the well-known frequency-domain procedures or complex genetic algorithms. This brief proposes a special type of an FO controller, as well as a novel tuning procedure, which is simple and does not involve any optimization routines. The controller parameters may be determined directly using overshoot requirements and the study of the stability of FO systems. The tuning procedure is given for the general case of a class of unstable systems with pole multiplicity. The advantage of the proposed FO controller consists in the simplicity of the tuning approach. The case study considered in this brief consists in a magnetic levitation system. The experimental results provided show that the designed controller can indeed stabilize the magnetic levitation system, as well as provide robustness to modeling uncertainties and supplementary loading conditions. For comparison purposes, a simple PID controller is also designed to point out the advantages of using the proposed FO controller

Fractional order modeling and control of a smart beam

Smart beams are one of the most frequently used means of studying vibrations in airplane wings. Their mathematical models have been so far solely based on classical approaches that ultimately involve integer order transfer functions. In this paper, a different approach towards modeling such smart beams is considered, an approach that is based on fractional calculus. In this way, a fractional order model of the smart beam is obtained, which is able to better capture the dynamics of the system. Based on this novel fractional order model, a fractional order PD mu controller is then tuned according to a set of three design constraints. This design leads to a closed loop system that exhibits a much smaller resonant peak compared to the uncompensated smart beam system. Experimental results are provided, considering both passive and active control responses of the smart beam, showing that a significant improvement of the closed loop behavior is obtained using the designed controller

Discrete-time implementation and experimental validation of a fractional order PD controller for vibration suppression in airplane wings

Vibrations in airplane wings have a negative impact on the quality and safety of a flight. For this reason, active vibration suppression techniques are of extreme importance. In this paper, a smart beam is used as a simulator for the airplane wings and a fractional order PD controller is designed for active vibration mitigation. To implement the ideal fractional order controller on the smart beam unit, its digital approximation is required. In this paper, a new continuous-to-discrete-time operator is used to obtain the discrete-time approximation of the ideal fractional order PD controller. The efficiency and flexibility, as well as some guidelines for using this new operator, are given. The numerical examples show that high accuracy of approximation is obtained and that the proposed method can be considered as a suitable solution for obtaining the digital approximation of fractional order controllers. The experimental results demonstrate that the designed controller can significantly improve the vibration suppression in smart beams

Structure and Dynamics of AMPA Receptor GluA2 in Resting, Pre-Open, and Desensitized States

SummaryIonotropic glutamate receptors (iGluRs) mediate the majority of fast excitatory signaling in the nervous system. Despite the profound importance of iGluRs to neurotransmission, little is known about the structures and dynamics of intact receptors in distinct functional states. Here, we elucidate the structures of the intact GluA2 AMPA receptor in an apo resting/closed state, in an activated/pre-open state bound with partial agonists and a positive allosteric modulator, and in a desensitized/closed state in complex with fluorowilliardiine. To probe the conformational properties of these states, we carried out double electron-electron resonance experiments on cysteine mutants and cryoelectron microscopy studies. We show how agonist binding modulates the conformation of the ligand-binding domain “layer” of the intact receptors and how, upon desensitization, the receptor undergoes large conformational rearrangements of the amino-terminal and ligand-binding domains. We define mechanistic principles by which to understand antagonism, activation, and desensitization in AMPA iGluRs

Fractional order control of unstable processes: the magnetic levitation study case

Although a considerable amount of research has been carried out in the field of fractional order controllers, the majority of the results deal with stable processes. Very little research has been reported regarding the design, analysis, and tuning of fractional order controllers for unstable processes. This paper proposes a methodology for designing and tuning fractional order controllers for a class of unstable second-order processes. The design is carried out using the stability analysis of fractional order systems, by means of Riemann surfaces and a proper mapping in the w-plane. The resulting fractional order controllers are implemented using graphical programming on industrial equipment and are validated experimentally using a laboratory scale magnetic levitation unit

Domain organization of photosystem II in membranes of the cyanobacterium Synechocystis PCC6803 investigated by electron microscopy

The supramolecular organization of photosystem II (PSII) complexes in the photosynthetic membrane of the cyanobacterium Synechocystis 6803 was studied by electron microscopy. After mild detergent solubilization, crystalline PSII arrays were extracted in which dimeric PSII particles associate in multiple rows. Image processing of the arrays shows that the PSII dimers are tightly packed at distances of 12.2 and 16.7 nm. The domains are considered to be an important type of association for preventing either spill-over energy from PSII towards photosystem I (PSI) or direct energy flow from phycobilisomes to PSI, because the latter can only be at periphery of the arrays.

Experimental results of fractional order PI controller designed for second order plus dead time (SOPDT) processes

The present paper presentes the tuning of a Fractional Order Proportional Integral (FOPI) controller for second-order-plus-time-delay (SOPDT) plants. The tuning procedure is based on imposing frequency domain constraints for the open loop system with the FOPI controller and the SOPDT plant. The gain crossover frequency, phase margin and the iso-damping property that guarantees a certain degree of robustness to gain variations are imposed in order to obtain the parameters of the fractional order controller. The proposed method is validated by real life implementation on a process whose dynamics are approximated to a SOPDT model. The settling time, steady state error, robustness and disturbance rejection capabilities are analyzed using experimental test cases