Improve System Stability Research Articles

Stability Analysis of Delayed Tumor-Antigen-ActivatedImmune Response in Combined BCG and IL-2Immunotherapy of Bladder Cancer

We use a system biology approach to translate the interaction of Bacillus Calmette-Gurin (BCG) + interleukin 2 (IL-2) for the treatment of bladder cancer into a mathematical model. The main goal of this research is to predict the outcome of BCG + IL-2 treatment combinations. We examined whether the delay effect caused by the proliferation of tumor antigen-specific effector cells after the immune system destroys BCG-infected urothelium cells after BCG and IL-2 immunotherapy influences success in bladder cancer treatment. To do this, we introduce a system of differential equations where the variables are the main participants in the immune response after BCG installations to fight cancer: the number of tumor cells, BCG cells, immune cells, and cytokines involved in the tumor-immune response. The relevant parameters describing the dynamics of the system are taken from a variety of biological, clinical literature and estimated using the mathematical models. We examine the local stability analysis of non-negative equilibrium states of the model. In theory, treatment could improve system stability, and we analyze the stability of all equilibria using the method of Lyapunov functionals construction and the method of linear matrix inequalities (LMIs). Our results prove that the period for the proliferation of tumor antigen-specific effector cells does not influence to the success of the non-responsive patients after an intensified combined BCG + IL-2 treatment.

Application of Neuro-Fuzzy Controller to Replace SMIB and Interconnected Multi-Machine Power System Stabilizers

In this research, an effective application and performance assessment of the Neuro-Fuzzy Controller (NFC) damping controller is designed to replace a single machine infinite bus (SMIB) power system stabilizer (PSS), and coordinated multi PSSs in large interconnected power systems are presented. The limitation of the conventional PSSs on SMIB and interconnected multi-machine test power systems are exposed and disclosed by the proposed NFC stabilizer. The NFC is a nonlinear robust controller which does not require a mathematical model of the test power system to be controlled, unlike the conventional PSSs’ damping controller. The Proposed NFC is designed to improve the stability of SMIB, an interconnected IEEE 3-machine, 9-bus power system, and an interconnected two-area 10-machine system of 39-bus New England IEEE test power system under multiple operating conditions. The proposed NFC damping controller performance is compared with the conventional PSS damping controller to confirm the capability of the proposed stabilizer and realize an improved system stability enhancement. The conventional PSSs’ design problem is transformed into an optimization problem where an eigenvalue-based objective function is developed and applied to design the SMIB-PSS and the interconnected multi-machine PSSs. The time-domain phasor simulation was done in the SIMULINK domain, and the simulation results show that the transient responses of the system rise time, settling time, peak time, and peak magnitude were all impressively improved by an acceptable amount for all the test system with the proposed NFC stabilizer. Thus, the NFC was able to effectively control the LFOs and produce an enhanced performance compared to the conventional PSS damping controller. Similarly, the result validates the effectiveness of the proposed NFC damping controller for LFO control, which demonstrates more robustness and efficiency than the classical PSS damping controller. Therefore, the application and performance of the NFC has appeared as a promising method and can be considered as a remarkable method for the optimal design damping stabilizer for small and large power systems.

Modeling and Performance Improvement of Direct Power Control of Doubly-Fed Induction Generator Based Wind Turbine through Second-Order Sliding Mode Control Approach

A second-order sliding mode (SOSM)-based direct power control (DPC) of a doubly-fed induction generator (DFIG) is introduced in this research paper. Firstly, the DFIG output powers are regulated with the developed SOSM controller-based DPC scheme. The Super Twisting Algorithm (STA) has been used to reduce the chattering phenomenon. The proposed strategy is a combination of the Lyapunov theory and metaheuristics algorithms, which has been considered to identify the optimal gains of the STA-SOSM controllers. The Lyapunov function method is employed to define the stability regions of the controller parameters. On the other hand, the metaheuristics algorithms are mainly employed to select the fine controllers’ parameters from the predefined ranges. A Thermal Exchange Optimization (TEO) method is used to compute the optimal gain parameters. To prove the superiority of the proposed TEO, its obtained results have been compared with those obtained by other algorithms, including particle swarm optimization, genetic algorithm, water cycle algorithm, grasshopper optimization algorithm and harmony search algorithm. Moreover, the results of the introduced TEO-based SOSM controller have been also compared with the Proportional-Integral (PI)-based vector control and the conventional sliding mode control-based DPC. Moreover, an empirical comparison is carried out to investigate the indication of every metaheuristics method by employing Friedman’s rank and Bonferroni tests. The main findings indicate the effectiveness of STA-SOSM control for system stability and power quality improvement. The ripples in the active and reactive powers are minimized and the harmonics’ distortions of stator and rotor currents are improved. Besides, the STA-SOSM controller shows a superior performance of control in terms of chattering phenomenon elimination.

Power system stability improvement using Battery Energy Storage System (BESS) in isolated grid

Rural areas and islands distant from main power grids mostly rely on diesel fuel for electricity generations, which assembles an isolated network. In eastern Indonesia, these isolated grids began to hybridize with solar photovoltaic (PV) systems to reduce the generation costs. However, the penetration of solar PV systems has risen one crucial problem related to the power system stability due to its output intermittency and variability. The Battery Energy Storage System (BESS) can be utilized as a frequency regulator so that the system stability can be maintained well. Besides, BESS can also function as an energy arbitrage so that the target of generation costs saving can also be achieved. This study analyzes the effectiveness of BESS utilization to reduce the stability issues of an isolated grid consisting of diesel generators and PV systems in eastern Indonesia by using PowerFactory software. The scenario of the daily operating pattern of each component is simulated as well by considering the optimal solar PV system and BESS capacity.

Disturbance-Observer-Based Terminal Sliding Mode Control for Linear Traction System With Prescribed Performance

In this article, a terminal sliding mode control (SMC) strategy based on the nonlinear disturbance observer (NDO) and prescribed performance method is proposed to deal with the speed tracking problem for permanent-magnet linear synchronous traction systems in urban rail transit. First, to improve the dynamic and static performances, a prescribed performance control characterizing the tracking performance employed for error transformation. This limits the tracking error of the original system to a prescribed bound if the transformed system is stable. Then, a terminal SMC is designed with backstepping, which guarantees the states converge to equilibrium point in finite time, realizing fast transient response of the system. Considering the existence of the uncertain disturbance, an NDO is utilized to estimate perturbations, and then, the estimation is used for the feedforward compensation, further improving system stability. Finally, the effectiveness and advantages of the proposed scheme are illustrated by computer simulations and experiments in dSPACE.

Controller parameter tuning of a single machine infinite bus system with static synchronous compensator using antlion optimization algorithm for the power system stability improvement

AbstractThe improvement of power system stability by damping oscillations in the system states is presented in this paper. An antlion optimization (ALO) algorithm is adopted to tune the damping device controller parameters. The ALO algorithm performance is investigated on the benchmark functions, and the same has been compared with the traditional particle swarm optimization (PSO) technique. The statistical analysis on the fitness achieved with the considered algorithms has been demonstrated using best, worst, mean, and SD values on the benchmark functions over 30 individual runs. Here power system stabilizer (PSS) and static synchronous compensator are considered as oscillation damping devices in the test power network. The analysis has been carried out in a sample power system network, and the proposed technique is compared with the conventional PSS and PSO. The results obtained from the designed test system recommends the superior performance characteristics of ALO in applying to the practical power system.

An Autonomous Control Scheme of Global Smooth Transitions for Bidirectional DC-DC Converter in DC Microgrid

In dc microgrid, energy storage system (ESS) plays a crucial role to provide short-or-long term and high-quality electric energy. The different control strategies for bidirectional dc-dc converter (BDC) of ESS in grid-tied and islanded modes pose challenges to the coordination control of the dc microgrid. This paper proposes an autonomous control scheme for the BDC in dc microgrid. The proposed control scheme is based on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V^2-P$</tex-math></inline-formula> droop control and unifies bus voltage regulation and power regulation in a single control structure. Thus, global smooth transition between various operation modes can be achieved without any control strategy changes, which avoids various mode switch detection mechanisms and improves system stability. Furthermore, the proposed control scheme is fully decentralized which reduces the reliance on communication, and enhances the reliability of the microgrid. On the other hand, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V^2-P$</tex-math></inline-formula> droop approach eliminates the negative effect of widespread constant power loads (CPLs) in dc microgrid. The stability of the proposed control method is illustrated, and the design guideline of some critical control gains is addressed. Finally, the effectiveness of the proposed control scheme is validated by the real-time hardware-in-loop (HIL) platform.

Perbaikan CCT Pada Multi Machine Infinite Bus Dengan Supercapacitor Energy Storage Menggunakan Critical Trajectory

Transient stability is an important aspect in maintaining the continuity and reliability of the electrical power system when a sudden large disturbance occurs. However, there is a time operation's limitation of the protection system to eliminate disturbance before the system becomes unstable and loses its synchronization. Critical Clearing Time (CCT) is the toleration time to eliminate the fault to keep the system stable. To improve system stability, installing Supercapacitor Energy Storage (SCES) can be one of the methods for extending the CCT values. SCES absorb large amounts of electricity simultaneously when a fault occurs. This paper proposed a determination of SCES' controller effect in extending the CCT. SCES becomes a dummy load and extends the CCT value depending on the controller's ability to respond to a fault. Controller modeling is applied to SCES, which is installed at the bus generator with determined capacity. The modified Fouad and Anderson 9-bus 3-machine system with a single machine to an infinite bus is used to validate the proposed method. Moreover, the critical trajectory method, which is known as a faster calculation and better accuracy than the time domain simulation method, is used to obtain the CCT value. The result shows that the faster controllers work against fault, the higher the CCT value improvement of system CCT. The highest improvement occurs when the controller works at 0.001s.

Design and Implementation of a Multifunction Wearable Device to Monitor Sleep Physiological Signals.

We present a wearable device built on an Adafruit Circuit Playground Express (CPE) board and integrated with a photoplethysmographic (PPG) optical sensor for heart rate monitoring and multiple embedded sensors for medical applications—in particular, sleep physiological signal monitoring. Our device is portable and lightweight. Due to the microcontroller unit (MCU)-based architecture of the proposed device, it is scalable and flexible. Thus, with the addition of different plug-and-play sensors, it can be used in many applications in different fields. The innovation introduced in this study is that with additional sensors, we can determine whether there are intermediary variables that can be modified to improve our sleep monitoring algorithm. Additionally, although the proposed device has a relatively low cost, it achieves substantially improved performance compared to the commercially available Philips ActiWatch2 wearable device, which has been approved by the Food and Drug Administration (FDA). To assess the reliability of our device, we compared physiological sleep signals recorded simultaneously from volunteers using both our device and ActiWatch2. Motion and light detection data from our device were shown to be correlated to data simultaneously collected using the ActiWatch2, with correlation coefficients of 0.78 and 0.89, respectively. For 7 days of continuous data collection, there was only one instance of a false positive, in which our device detected a sleep interval, while the ActiWatch2 did not. The most important aspect of our research is the use of an open architecture. At the hardware level, general purpose input/output (GPIO), serial peripheral interface (SPI), integrated circuit (I2C), and universal asynchronous receiver-transmitter (UART) standards were used. At the software level, an object-oriented programming methodology was used to develop the system. Because the use of plug-and-play sensors is associated with the risk of adverse outcomes, such as system instability, this study heavily relied on object-oriented programming. Object-oriented programming improves system stability when hardware components are replaced or upgraded, allowing us to change the original system components at a low cost. Therefore, our device is easily scalable and has low commercialization costs. The proposed wearable device can facilitate the long-term tracking of physiological signals in sleep monitoring and related research. The open architecture of our device facilitates collaboration and allows other researchers to adapt our device for use in their own research, which is the main characteristic and contribution of this study.

Adaptive iterative working state prediction based on the double unscented transformation and dynamic functioning for unmanned aerial vehicle lithium-ion batteries

In lithium-ion batteries, the accuracy of estimation of the state of charge is a core parameter which will determine the power control accuracy and management reliability of the energy storage systems. When using unscented Kalman filtering to estimate the charge of lithium-ion batteries, if the pulse current change rate is too high, the tracking effects of algorithms will not be optimal, with high estimation errors. In this study, the unscented Kalman filtering algorithm is improved to solve the above problems and boost the Kalman gain with dynamic function modules, so as to improve system stability. The closed-circuit voltage of the system is predicted with two non-linear transformations, so as to improve the accuracy of the system. Meanwhile, an adaptive algorithm is developed to predict and correct the system noises and observation noises, thus enhancing the robustness of the system. Experiments show that the maximum estimation error of the second-order Circuit Model is controlled to less than 0.20V. Under various simulation conditions and interference factors, the estimation error of the unscented Kalman filtering is as high as 2%, but that of the improved Kalman filtering algorithm are kept well under 1.00%, with the errors reduced by 0.80%, therefore laying a sound foundation for the follow-up research on the battery management system.

Direct control method for improving stability and reliability of nonlinear stochastic dynamical systems

Optimal control for improving the stability and reliability of nonlinear stochastic dynamical systems is of great significance for enhancing system performances. However, it has not been adequately investigated because the evaluation indicators for stability (e.g. maximal Lyapunov exponent) and for reliability (e.g. mean first-passage time) cannot be explicitly expressed as the functions of system states. Here, a unified procedure is established to derive optimal control strategies for improving system stability and reliability, in which a physical intuition-inspired separation technique is adopted to split feedback control forces into conservative components and dissipative components, the stochastic averaging is then utilized to express the evaluation indicators of performances of controlled system, the optimal control strategies are finally derived by minimizing the performance indexes constituted by the sigmoid function of maximal Lyapunov exponent (for stability-based control)/the reciprocal of mean first-passage time (for reliability-based control), and the mean value of quadratic form of control force. The unified procedure converts the original functional extreme problem of optimal control into an extremum value problem of multivariable function which can be solved by optimization algorithms. A numerical example is worked out to illustrate the efficacy of the optimal control strategies for enhancing system performance.

Mechanism and quantified criteria of stability characteristics of hydropower plants with surge tanks during regulation

The dynamic processes of the coupled hydro-turbine-governor system and water diversion system are complex. An inappropriate design and regulation may result in poor regulating quality and even unstable operation. This study focused on the stability characteristics of the ultra-low frequency oscillation of hydropower plants caused by the water level oscillation in surge tanks during regulation. The coupled system was divided into the turbine-governor-penstock subsystem (TGPS) and surge tank-headrace tunnel subsystem (STHS) and their magnitude-frequency characteristics were presented respectively. Based on the two subsystems, the stability mechanism of the coupled system was explained by using the oscillation superposition method and a physically based and quantified criteria “superimposed magnitude” was proposed. Then, the influence mechanism of some dominant factors on the regulating stability were analyzed. The results indicated that the stability characteristics depended on the superimposed magnitude of the coupled system. When the superimposed magnitude of the combined TGPS and STHS is greater than 1, the oscillation continuously enlarges and results in instability. Meanwhile, the value of the superimposed magnitude can quantify the regulation quality. Furthermore, increasing the surge tank area or head loss coefficient of the headrace tunnel can reduce the superimposed magnitude, resulting in the improvement of system stability.

Current limiting characteristics of a magnetic shielding type Superconducting Fault Current Limiter of REBCO pancake coils

Superconducting Fault Current Limiters (SFCLs) are installed in the electric power system, and expected to limit fault current and improve system stability. In this paper, we focus on the transformer magnetic shielding type SFCL made of REBCO wires. This SFCL limits fault current mainly with reactance for small fault current. When fault current gets larger, resistance component is added and a larger impedance is generated. In this time, we fabricated the transformer type SFCL composed of pancake coils and investigated the basic characteristics. The pancake coil type has the advantage that the amount of superconducting wire is less and the size of SFCL becomes smaller than solenoid coil type. As the results of experiment, it was confirmed that SFCL limits fault current with reactance and resistance properly. Regarding the current limiting impedance, it almost agreed with the designed value, and confirmed the current limiting operation as expected.

Analysis of distributed power sources impact on distribution network voltage and reactive power optimization

The grid connection of distributed power sources will greatly change the initial electrical state of the system. Therefore, it is necessary to do scientific research on the impact of grid connection of distributed power sources and take appropriate measures to improve system stability. Two evaluation indexes of average voltage change rate and average voltage fluctuation rate are established to describe the impact of different distributed power grids on voltage. The IEEE 33-node power distribution network is used as a model. The distributed power source is connected to the power distribution network with different capacities and different locations. Based on the calculation results of the power flow, the voltage distribution diagrams of the system under different states are drawn, and a comprehensive analysis is performed according to the formulated quantitative indicators. A genetic algorithm was used to search for the optimal reactive power output of a single power supply connected to the grid.

Characterisation of microalgae-based monocultures and mixed cultures for biomass production and wastewater treatment

Microalgae-based systems have been increasingly considered to remediate wastewater, while producing valued biomass. While microalgal monocultures are difficult to maintain in wastewater, mixed cultures have the potential to offer improved system stability and robustness. This research aims to provide a detailed comparison of microalgal monoculture and mixed culture photobioreactors (PBRs) in terms of microalgae growth, biomass harvesting potential, nutrient removal and organic characteristics. Some of the PBRs were further tested for their responses to the presence of wastewater-derived bacteria. Monocultures (containing species from Chlorophyta, Cyanophyta and Eustigmatophyta, respectively) and mixed cultures (mixing two or three species) were evaluated using advanced characterisation techniques including flow cytometry, liquid chromatography – organic carbon detection and excitation−emission matrix fluorescence spectroscopy. The impact of bacteria on system performance was explored by co-culturing some of the cultures with activated sludge. In general, mixed culture systems showed more stable biomass growth and improved nutrient removal uptake (by 20%), as compared to monocultures. However, overyielding (higher biomass production) was not observed in the mixed cultures. Mixing different microalgae tended to increase the concentrations of soluble extracellular materials (e.g. biopolymers) that were able to retain water within the biomass, leading to a lower biomass harvesting potential, as indicated by the capillary suction time. Adding activate sludge significantly increased reduction of measurable dissolved organic carbon concentration (particularly biopolymers and low molecular weight compounds) and nitrogen by >250%. However, wastewater-derived bacteria reduced the yield of all the cultures substantially (by 63–76%) and lowered the dewaterability of the cultures.

Integration of STATCOM and ESS for power system stability improvement

The power system enters a state of voltage instability due to the inability of the power system to meet the demand for active power and reactive power due to the increase of system load. In order to stabilize the power system, the installation of STATCOM and ESS needs to be performed. The main objective of this study is to identify the suitable size and location of STATCOM and ESS for power system stability improvement. First, the IEEE 14 bus system was simulated using DIgSILENT software in ideal condition. Then, the system loadability was increased up to 200% of initial value to locate the weakest bus. This study includes the applicable location and sizing of STATCOM and ESS towards improving power system stability. The results showed that the application of STATCOM and ESS with the most reliable size can increase the bus voltage (p.u and kV) of IEEE 14 bus system thus improving the power system stability. For recommendation, the power system stability can be improved by installing multiple STATCOM and ESS at other load buses and applying a controller to both STATCOM and ESS to improve the effectiveness of generating and absorbency of active and reactive power in the power system.

Fiber Optic Particle Plasmon Resonance-Based Immunoassay Using a Novel Multi-Microchannel Biochip.

A novel multi-microchannel biochip fiber-optic particle plasmon resonance (FOPPR) sensor system for the simultaneous detection of multiple samples. The system integrates a novel photoelectric system, a lock-in module, and an all-in-one platform incorporating optical design and mechanical design together to improve system stability and the sensitivity of the FOPPR sensor. The multi-microchannel FOPPR biochip has been developed by constructing a multi-microchannel flow-cell composed of plastic material to monitor and analyze five samples simultaneously. The sensor system requires only 30 μL of sample for detection in each microchannel. Moreover, the total size of the multi-microchannel FOPPR sensor chip is merely 40 mm × 30 mm × 4 mm; thus, it is very compact and cost-effective. The analysis was based on calibration curves obtained from real-time sensor response data after injection of sucrose solution, streptavidin and anti-dinitrophenyl (anti-DNP) antibody of known concentrations over the chips. The results show that the multi-microchannel FOPPR sensor system not only has good reproducibility (coefficient of variation (CV) < 10%), but also excellent refractive index resolution (6.23 ± 0.10 × 10−6 refractive index unit (RIU)). The detection limits are 2.92 ± 0.28 × 10−8 g/mL (0.53 ± 0.01 nM) and 7.48 ± 0.40 × 10−8 g/mL (0.34 ± 0.002 nM) for streptavidin and anti-DNP antibody, respectively.

Investigation into optimal control of terminal unit of air conditioning system for reducing energy consumption

In the operation of central air conditioning systems, the phenomenon of large flow and small temperature difference is often seen. Due to great differences in user cooling loadings, the terminal temperature difference between the supply and return water is considerable. Thus, the performance of the system is insignificant when using a variable frequency to control the chilled water pump. In order to find a more effective approach, this paper presents a deep analysis of the terminal surface heat exchange performance under wet conditions. By building a simulation model, the effects of the chilled water flow and air flow on the surface heat exchange performance were determined, and an optimal energy-saving control strategy based on a fixed-temperature-difference surface cooler was proposed. This strategy not only maintains the good alignment of the temperature difference between the supply and return chilled water, but also improves system stability and decreases chilled water transfer loss. Based on this strategy, the system prioritises the utilisation of air flow to meet the cooling load disturbance and reduce energy consumption of the fan. The total energy saved is up to 12.5%. The control strategy was validated by experimental results. This strategy is benefit for reducing energy consumption.

Improvement of Power System Stability by using FLC based PID Controller

Improvement of Power System Stability by using FLC based PID Controller

Higher order sliding mode STATCOM control for power system stability improvement

The objective of this research is to design a higher order Sliding Mode Controller (SMC) for a Static Synchronous Compensator (STATCOM) and investigation of its implication on power system stability improvement. The theory of Super-Twisting–Sliding-Mode-Control (STSMC) is applied to determine the nonlinear control law of a STATCOM. The STSMC based control combines 2-sliding control and Robust Exact Differentiator (RED) which can efficiently mitigate the effect of external disturbance to the system The purpose of the application of the STSMC based control method is that it not only solves the chattering problem of classical SMC but also the derived control law is independent of system parameters. The efficacy of the design of the proposed STATCOM controller has been investigated in comparison to both the nonlinear (via exact linearization) and conventional (via approximate linearization) Linear Quadratic Regulator (LQR) based STATCOM controller. An IEEE type 14 bus multi-machine system has been taken into consideration to study the simulation results with regard to the transient stability improvement in multiple operating scenarios. It has been revealed from the simulation results that the proposed control scheme based on STSMC is more effective with respect to both the exact linearization based as well as approximately linearization based approach for the design of STATCOM controller. Furthermore, it has been abstracted that the STSMC based nonlinear STATCOM controller is competent to mitigate the dynamic instability of an electric power system even under contingency and different loading conditions.