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The port-Hamiltonian form (PHF) of nuclear reactor dynamics is first given with the corresponding Hamiltonian function determined by the shifted-ectropies of neutron kinetics and reactor thermal-hydraulics. Then, a passivity-based control (PBC) is proposed by adding extra damping injections to the PHF, and it is shown by theoretical analysis that satisfactory closed-loop stability can be guaranteed. The newly designed control law is applied to a nuclear heating reactor, and the simulation results not only verify the theoretical analysis but also show the satisfactory reactor power-level control performance. [ABSTRACT FROM AUTHOR]

This brief concerns the problem of false data injection (FDI) attacks against partial sensor measurements of a networked stochastic system. For a Kalman filter based output tracking control system with a residual-based anomaly detector, a partial FDI attack strategy is presented to deteriorate the system performance by injecting false signals into the feedback communication channel to tamper partial sensor measurements. The stealthiness condition of the attack as well as its impact on the closed-loop system is derived, which are quite different from those of the FDI attack against all sensor measurements given in the existing work. This may be helpful for guaranteeing the secure control of a networked system by protecting partial critical sensor measurements from FDI attacks. Two numerical examples are included to verify the theoretical results. [ABSTRACT FROM AUTHOR]

Stability is one of the most important characteristics of the potentiometric urea biosensors; however, it has rarely been discussed in previous literature. In this article, the stability of the potentiometric urea biosensor based on the urease-Ag NPs/RuO2 sensing film was studied. Using the voltage–time ($V$ – $T$) measurement system, the stability was verified by analyzing the biosensor’s reproducibility, repeatability, long-term measurement, and effect of temperature. Based on the results of this study, the proposed potentiometric urea biosensor had good reproducibility [relative standard deviation (RSD) was 2.23%] and repeatability (RSD was 1.16%). The urease-Ag NPs/RuO2 sensing film still has 90% initial sensitivity after 15 days of storage at room temperature. Moreover, the proposed urea biosensor was integrated into the microfluidic system and the remote measurement system. The sensing characteristics of the potentiometric urea biosensor under different flow rates (1.4–7.0 $\mu \text{L}$ /min, 0–30 $\mu \text{L}$ /min) were studied. In the remote measurement, the average sensitivity was 45.75 mV/decade and the linearity was 0.986. [ABSTRACT FROM AUTHOR]

A proportional–integral extended state observer (PI-ESO) of nuclear reactors is proposed for disturbance estimation, driven by the measurement errors of neutron flux, primary coolant temperatures at reactor inlet and outlet, as well as their integrations. This PI-ESO can provide a globally asymptotically bounded estimation for not only the reactor process variables, including normalized neutron flux and precursor concentrations as well as average temperatures of fuel assemblies and primary coolant, but also the total disturbances in channels of neutron kinetics and coolant thermal hydraulics. Furthermore, the newly built PI-ESO is applied to reconstruct both the unmeasurable state variables and the total disturbances of a nuclear heating reactor (NHR). Numerical simulation results verify the theoretical result, showing both the satisfactory performance and the influence of observer parameters. [ABSTRACT FROM AUTHOR]

In this work, we used radio frequency (RF) system and screen printing technology to fabricate urea biosensor based on urease-maghemite nanoparticles (γ-Fe2O3 NPs)/graphene oxide (GO)/nickel oxide (NiO) sensing membrane on silver conductive wire printed polyethylene terephthalate (PET) substrate. The V – T measurement system was used to investigate the sensing characteristics of urea biosensors based on GO/NiO sensing membrane modified by γ-Fe2O3 NPs. The sensing membrane was modified by adding different contents of γ-Fe2O3 NPs. The concentration of γ-Fe2O3 NPs was 1 mg/mL. When the volume ratio of urease/γ-Fe2O3 NPs was 1/1, it had the best sensitivity. The average sensitivity, the linearity, and the limit of detection of (LOD) of the best urea biosensor in this work were 52.36 mV/decade ± 0.22 mV/decade, 0.996, and $7.91~μM, respectively. The effect of temperature on the urea biosensor was investigated from 25 °C to 65 °C. The stability of urea biosensors was evaluated by the effect of hysteresis and long-term storage stability. After 29 days, the average sensitivity remained 80.62% of the initial value. Compared with other urea biosensors, our urea biosensor based on urease-γ-Fe2O3 NPs/GO/NiO sensing membrane has better average sensitivity. [ABSTRACT FROM AUTHOR]

For a conventional islanded microgrid, each distributed generation (DG) unit usually equips with an LC filter and a closed-loop filter capacitor voltage control is applied to ensure an accurate tracking of DG voltage. In this article, a cost reduction microgrid and DG units configuration is developed via the following two steps. First, an L-type filter is adopted by each DG unit and a centralized shunt capacitor is placed at point of common coupling (PCC). Then, the inherent synchronization feature of droop control is further exploited as an inherent synchronizer to identify the carrier angle relationships between parallel inverters, but without any communications between them. With the carrier information obtained, a decentralized interleaving pulsewidth modulation (PWM) among parallel inverter can be easily achieved via a slow proportional integral (PI) regulation of each DG unit relative carrier. Accordingly, the high-frequency switching harmonics of PCC voltage are suppressed even with simplified and size reduced DG output chokes. Second, a virtual impedance control is applied to DG units to cancel the voltage drops on the DG feeder in a direct PWM manner. Accordingly, mitigating the low-order harmonic PCC voltages is obtained without using any closed-loop voltage tracking at DG unit local processor. Comparative experimental results have been provided to validate the correctness of the proposed method. [ABSTRACT FROM AUTHOR]

Reactor power-level control is a key technique of enhancing the safety, stability, and efficiency of nuclear plants. Currently, nearly all the power-level control methods are based on the scheme of inducing reactivity directly via control rods. However, the reactivity can also be injected indirectly via the negative temperature feedback effect, which results in the opportunity to develop indirect nuclear reactor power-level control methods. Motivated by this, a cascaded power-level control of high-temperature gas-cooled reactor, which is composed of a helium temperature controller and a neutron flux controller, is proposed based on only regulating the primary helium flow rate. The temperature controller, which is in the inner loop, regulates the primary helium flow rate according to the setpoint of helium temperature. The flux controller, which is in the outer loop, revises the setpoint of the inner-loop controller so as to eliminate the error of reactor neutron flux. It is proved that the closed-loop system can be guaranteed to be globally asymptotically stable. Finally, numerical simulation results corresponding to the application to the high-temperature gas-cooled reactor pebble-bed module (HTR-PM) plant verifies the theoretical result while showing the satisfactory performance as well as the influence of the controller parameters. [ABSTRACT FROM AUTHOR]

A simple decentralized interleaving PWM approach is proposed for parallel grid-tied converters, in order to achieve significant reduction of switching current ripples at the point of common couplings (PCC). First, the remote PCC voltage phase angle information is calculated through only the local measurement of a distribution generation (DG) unit converter and the estimation of the corresponding feeder voltage drops. With simple interpolations, the discretized PCC voltage angle information at a DG local controller is used as a novel synchronizer to effectively identify the carrier angle of DG units at the exact time instant of the PCC voltage phase angle zero crossing. Then, the relative digital carrier phase angles of parallel DG units are adaptively adjusted in a high-resolution manner until they are properly interleaved. It has been validated that the proposed modulation approach is effective under adverse situations with mismatched feeder impedances, processor crystal oscillator frequency deviations, and notable grid voltage frequency/magnitude disturbances. [ABSTRACT FROM AUTHOR]