Control of high frequency microactuators using active structures

A three phase PLL with a dynamic feed forward frequency estimator for synchronization of grid connected converters under wide frequency variations

This paper presents a robust distributed secondary control (DSC) scheme for inverter-based microgrids (MGs) in a distribution sparse network with uncertain communication links. By using the iterative learning mechanics, two discrete-time DSC controllers are designed, which enable all the distributed energy resources (DERs) in an MG to achieve the voltage/frequency restoration and active power sharing accuracy, respectively. In special, the secondary control inputs are merely updated at the end of each round of iteration, and thus, each DER only needs to share information with its neighbors intermittently in a low-bandwidth communication manner. This way, the communication costs are greatly reduced, and some sufficient conditions on the system stability and robustness to the uncertainties are also derived by using the tools of Lyapunov stability theory, algebraic graph theory, and matrix inequality theory. The proposed controllers are implemented on local DERs, and thus, no central controller is required. Moreover, the desired control objective can also be guaranteed even if all DERs are subject to internal uncertainties and external noises including initial voltage and/or frequency resetting errors and measurement disturbances, which then improves the system reliability and robustness. The effectiveness of the proposed DSC scheme is verified by the simulation of an islanded MG in MATLAB/SimPowerSystems.

An adaptive filters based PMU algorithm for both steady-state and dynamic conditions in distribution networks

The growth of distributed generation significantly reduces the synchronous generators' overall rotational inertia, causing large frequency deviation and leading to an unstable grid. Adding virtual rotational inertia using virtual synchronous generators (VSG) is a promising technique to stabilize grid frequency. Due to coupled nature of frequency and active output power in a grid-tied virtual synchronous generator (GTVSG), the simultaneous design of transient response and steady state error becomes challenging. This paper presents a duplex PD inertial damping control (DPDIDC) technique to provide active power control decoupling in GTVSG. The power verses frequency characteristics of GTVSG is analyzed emphasizing the inconsistencies between the steady-state error and transient characteristics of active output power. The two PD controllers are placed in series with the generator's inertia forward channel and feedback channel. Finally, the performance superiority of the developed control scheme is validated using a simulation based study.

RES penetration increase in power systems is beneficial in several aspects, such as the reduction of greenhouse gas emissions, cost of electricity, and energy dependence on fossil fuels. At the same time, the operation of electrical systems with high RES penetration results in several technical challenges, such as frequency deviations, due to the variability of their primary source of energy. Such issues are more evident in isolated power systems, like the Non-Interconnected Islands (NII) in Greece, where distortions in their power equilibrium lead to relatively large frequency deviations, due to the small inertia and lack of interconnections with larger power systems. In addition, RES development in island systems faces important restrictions, due to the inability to absorb the full potential of RES production during low load time periods. An efficient solution in increasing RES penetration in NIIs, without compromising their power quality, is the utilization of energy storage systems, such as battery energy storage systems or pump-hydro storage plants (PHSPs). This paper proposes fully controllable energy storage systems combined with RES units, which constitute the so-called "hybrid power stations", which can adequately replace the existing conventional units.

Large increase in wind and photovoltaics will lead to lower and more volatile grid inertia but also to the lack of primary frequency control, i.e. frequency containment reserve (FCR) providers in the Continental Europe Grid. This will therefore impact negatively the frequency dynamics. One potential solution for ensuring the frequency to stay in reasonable bounds is to take the dynamics of potential providers into consideration. From this observation, we develop a novel methodology for having a linear programming problem to select the most suited FCR providers. It is based on the minimization of the overall cost while respecting static and dynamic constraints which are respectively ensuring a sufficient amount of FCR and avoiding too large frequency deviations after a large disturbance. The methodology has been tested on a case with 200 potential FCR providers in function of various grid inertia and load damping factors.

Previous neurofeedback research has shown training-related frontal theta increases and performance improvements on some executive tasks in real feedback versus sham control groups. However, typical sham control groups receive false or non-contingent feedback, making it difficult to know whether observed differences between groups are associated with accurate contingent feedback or other cognitive mechanisms (motivation, control strategies, attentional engagement, fatigue, etc.). To address this question, we investigated differences between two frontal theta training groups, each receiving accurate contingent feedback, but with different top-down goals: (1) increase and (2) alternate increase/decrease. We hypothesized that the increase group would exhibit greater increases in frontal theta compared to the alternate group, which would exhibit lower frontal theta during down- versus up-modulation blocks over sessions. We also hypothesized that the alternate group would exhibit greater performance improvements on a Go-NoGo shooting task requiring alterations in behavioral activation and inhibition, as the alternate group would be trained with greater task specificity, suggesting that receiving accurate contingent feedback may be the more salient learning mechanism underlying frontal theta neurofeedback training gains. Thirty young healthy volunteers were randomly assigned to increase or alternate groups. Training consisted of an orientation session, five neurofeedback training sessions (six blocks of six 30-s trials of FCz theta modulation (4-7 Hz) separated by 10-s rest intervals), and six Go-NoGo testing sessions (four blocks of 90 trials in both Low and High time-stress conditions). Multilevel modeling revealed greater frontal theta increases in the alternate group over training sessions. Further, Go-NoGo task performance increased at a greater rate in the increase group (accuracy and reaction time, but not commission errors). Overall, these results reject our hypotheses and suggest that changes in frontal theta and performance outcomes were not explained by reinforcement learning afforded by accurate contingent feedback. We discuss our findings in terms of alternative conceptual and methodological considerations, as well as limitations of this research.

A control method has been developed to always excite a multi-degree-of-freedom system efficiently at a resonance frequency. When an excitation point corresponds to a vibration detection point in the multi-degree-of-freedom system, a phase lag at a resonance frequency and a phase lead at an anti-resonance frequency alternately appear in the vibration characteristics, and the phase lag becomes 90° at all the resonance frequencies. Therefore, if a controller that has a phase lag of 90° and a constant gain in a wide frequency range is used, self-excited vibration is generated at all the resonance frequencies. The self-excited vibration mode in the multi-degree-of-freedom system with local feedback control can be freely switched by dynamic stimulation. However, it can be also disadvantage in the point of changing against the desire. In this paper, a cross feedback control is added to the local feedback control to excite and stabilize the self-excited vibration modes. The cross feedback control mutually exchanges control signal between adjacent local feedback controllers. Giving the sign of the cross feedback gain corresponding to natural vibration modes can assist formation of the self-excited vibration modes. At first, we verified all the natural vibration modes are excited by adding cross feedback control. Additionally, we verified the desired natural vibration can be maintained against a disturbance. Finally, we verified amplitude of the vibration is maintained against changing mass and dumping.

A control method has been developed to always excite a multi-degree-of-freedom system efficiently at a resonance frequency. When an excitation point corresponds to a vibration detection point in the multi-degree-of-freedom system, a phase lag at a resonance frequency and a phase lead at an anti-resonance frequency alternately appear in the vibration characteristics, and the phase lag becomes 90° at all the resonance frequencies. Therefore, if a controller that has a phase lag of 90° and a constant gain in a wide frequency range is used, self-excited vibration is generated at all the resonance frequencies. The self-excited vibration controller can be expressed as the sum of the positive velocity feedback control with a high gain in a high frequency domain and the integral control of the displacement with a high gain in a low frequency domain. A local feedback controller for each actuator consists of a self-excited vibration controller, a saturation element that limits excitation force, and a negative velocity feedback controller that provides damping. A driving at a resonance point system using many actuators with local feedback control, that is, decentralized control, is excellent in its adaptability to the environment, in its extendibility, and in its fault tolerance. In addition, the self-excited vibration mode can be freely switched on by changing the frequency of the sine wave that causes the self-excited vibration.

Two-photon annihilation quanta are emitted in a pure quantum state and when detected in coincidence, the photon pairs possess orthogonal polarizations. We propose that this polarization correlation can be exploited in Positron Emission Tomography (PET), which relies crucially on accurate coincidence detection of photon pairs. In this proof of concept study, we investigate how photon polarization information can be exploited in PET imaging by developing a method to discern true coincidences using the polarization correlation of annihilation pairs. We demonstrate that the unique identification of true photon pairs with their polarization correlation can dramatically enhance overall PET image quality, especially for high emission rates, when conventional, energy- based coincidence detection methods become increasingly unreliable. Our results suggest that polarization-based coincidence detection offers new prospects for in vivo molecular imaging with next-generation PET systems.

Over the last few years, the dramatic proliferation of emerging viruses such as Zika has resulted in a pressing need to develop inexpensive point-of-care diagnostic devices for rapid, sensitive, and accurate screening of patients. The ability to diagnose active infections on-site can improve patient compliance, allow physicians to tailor treatment options, and help prevent transmission to uninfected people. While commercially available point-of-care tests exist for bacterial infections, there are currently no approved point-of-care diagnostic assays for use in health clinics or in the field that detect viral infections. We are developing a point-of-care diagnostic device for viral detection that is inexpensive and can carry out all assay steps in an automated format. Our earlier work characterized electrochemical paper-based analytical devices (ePADs) coupled with metallic microwire electrodes as a disposable sensing system suitable for this application.1,2 Toward development of virus particle sensors, we have functionalized the electrodes with bioaffinity reagents to drive specific analyte binding, optimized electrode-integrated paper-based microfluidic platforms, and employed electrochemical impedance spectroscopy (EIS) to detect low levels of virus-sized particles. As shown in the figure, the functionalized electrode enables the binding of analyte to its surface and forms an insulating layer, increasing the impedance at the surface. In a proof of concept study, biotin-modified electrodes were incubated with streptavidin conjugated beads of size similar to viruses and investigated as a representative specific binding system. Two different electrode systems have been investigated. In the first, freestanding Au microwires were used because they can be easily modified with specific recognition elements using well-established coupling techniques prior to incorporation into the ePAD. As an alternative, Au nanoparticles were electrodeposited on screen-printed carbon electrodes, functionalized via the same chemistry, and compared for detection limits, sensitivities, and linear ranges. Preliminary optimization tests were achieved in a paper-based wax-confined static well fabricated as previously described.1 After demonstrating detection in static solutions, we tested the system using a flow-through ePAD system2 for improved sensitivity. To create steady-state flow, a fan-shaped passive pump was connected to the channel inlet and the microwire electrodes were embedded between two paper layers for electrochemical analysis. The two layers of paper create a channel and generate relatively high flow rates and more effective mass transport to the electrode surfaces. Key elements of flow rate, paper/electrode geometry, and number of electrodes were optimized for the method. Furthermore, multiple wires modified with the same affinity group were added in an overlapping, parallel configuration to increase surface area and enhance the signal. Sensor response was characterized with EIS using ferri/ferrocyanide as the mediator before and after analyte incubation. EIS provides significantly lower detection limits compared to traditional colorimetric lateral flow devices, while being inexpensive to manufacture and readily multiplexed for multiple analyte detection. The optimized electrochemical affinity assay makes ePAD particularly promising to rapidly detect virus-size particles in a multiplexed sample with high sensitivity, selectivity, and stability. (1) Adkins, J. A.; Henry, C. S. Analytica Chimica Acta 2015, 891, 247-254. (2) Adkins, J. A.; Noviana, E.; Henry, C. S. Anal Chem 2016, 88, 10639-10647. Figure 1

Conventional and novel control designs for direct driven PMSG wind turbines

Since the deregulation of the electrical energy market, the technical realisation of power transactions based on energy market contracts often effects large stepwise power programme changes - especially at the change of the hour. Originating from the current market boundaries and system rules, these stepwise power programme changes lead to remarkable power imbalances within the European Power System causing large unintended frequency deviations with a negative impact on the control performance of power plants and power system. Within the framework of this paper, a cause study to establish an understanding of the origins of the power imbalances is presented. Subsequently, counteractive measures for an improvement of the performance of scheduled stepwise power programme changes are proposed.

This paper concerns the feasibility of Fast Active Power Regulation (FAPR) in renewable energy hubs. Selected state-of-the-art FAPR strategies are applied to various controllable devices within a hub, such as a solar photovoltaic (PV) farm and an electrolyzer acting as a responsive load. Among the selected strategies are droop-based FAPR, droop derivative-based FAPR, and virtual synchronous power (VSP)-based FAPR. The FAPR-supported hub is interconnected with a test transmission network, modeled and simulated in a real-time simulation electromagnetic transient (EMT) environment to study a futuristic operating condition of the high-voltage infrastructure covering the north of the Netherlands. The real-time EMT simulations show that the FAPR strategies (especially the VSP-based FAPR) can successfully help to significantly and promptly limit undesirable large instantaneous frequency deviations.

An open-loop digital receiver performing simultaneous carrier phase/frequency estimation and block (two-bit) detection is proposed for MSK signaling in Gaussian channels affected by Doppler frequency shift. Phase estimation and symbol detection are provided by a parallel bank of matched estimators (each one comprising a phase rotation block and a stochastic nonlinear filter) and by a decision algorithm based on the nonlinear filters' innovations processes. The Doppler frequency shift, estimated by a Kalman-Bucy (1968) filter coupled with a Kay (1989) estimator, is used for fine tuning of the nonlinear filters. The receiver exhibits a, fast phase/frequency acquisition capability and is able to withstand large carrier frequency deviations. These are essential features in LEO satellite burst communications.