Radio Network Forensic with mmWave Using the Dominant Path Algorithm

For the last two decades, cybercrimes are growing on a daily basis. To track down cybercrimes and radio network crimes, digital forensic for radio networks provides foundations. The data transfer rate for the next-generation wireless networks would be much greater than today’s network in the coming years. The fifth-generation wireless systems are considering bands beyond 6 GHz. The network design of the next-generation wireless systems depends on propagation characteristics, frequency reuse, and bandwidth variation. This article declares the channel’s propagation characteristics of both line of sight (LoS) and non-LOS (NLoS) to construct and detect the path of rays coming from anomalies. The simulations were carried out to investigate the diffraction loss (DL) and frequency drop (FD). Indoor and outdoor measurements were taken with the omnidirectional circular dipole antenna with a transmitting frequency of 28 GHz and 60 GHz to compare the two bands of the 5th generation. Millimeter-wave communication comes with a higher constraint for implementing and deploying higher losses, low diffractions, and low signal penetrations for the mentioned two bands. For outdoor, a MATLAB built-in 3D ray tracing algorithm is used while for an indoor office environment, an in-house algorithmic simulator built using MATLAB is used to analyze the channel characteristics.

Common-Mode Frequency in Inverter-Penetrated Power Systems: Definition, Analysis, and Quantitative Evaluation

<p>As synchronous generators (SGs) are extensively replaced by inverter-based generators (IBGs), modern power systems are facing complicated frequency stability problems. Conventionally, the frequency nadir and the rate of change of frequency (RoCoF) are the two main factors concerned by power system operators. However, these two factors heavily rely on simulations or experiments, especially in a power system with high-penetration IBGs, which offer limited theoretical insight into how the frequency response characteristics are affected by the devices. This paper aims at filling this gap. Firstly, we derive a formulation of the global frequency for an IBG-penetrated power system, referred to as common-mode frequency (CMF). The derived CMF is demonstrated to be more accurate than existing frequency definitions, e.g., the average system frequency (ASF). Then, a unified transfer function structure (UTFS) is proposed to approximate the frequency responses of different types of devices by focusing on three key parameters<a>, which dramatically reduces the complexity of frequency analysis. </a>On this basis, we introduce two evaluation indices, i.e., frequency drop depth coefficient (FDDC) and frequency drop slope coefficient (FDSC), to theoretically quantify the frequency nadir and the average RoCoF, respectively. Instead of relying on simulations or experiments, our method rigorously links the system’s frequency characteristics to the characteristics of heterogeneous devices, which enables an in-depth understanding regarding how devices affect the system frequency. Finally, the proposed indices are verified through simulations on a modified IEEE 39-bus test system. </p>

Common-Mode Frequency in Inverter-Penetrated Power Systems: Definition, Analysis, and Quantitative Evaluation

<p>As synchronous generators (SGs) are extensively replaced by inverter-based generators (IBGs), modern power systems are facing complicated frequency stability problems. Conventionally, the frequency nadir and the rate of change of frequency (RoCoF) are the two main factors concerned by power system operators. However, these two factors heavily rely on simulations or experiments, especially in a power system with high-penetration IBGs, which offer limited theoretical insight into how the frequency response characteristics are affected by the devices. This paper aims at filling this gap. Firstly, we derive a formulation of the global frequency for an IBG-penetrated power system, referred to as common-mode frequency (CMF). The derived CMF is demonstrated to be more accurate than existing frequency definitions, e.g., the average system frequency (ASF). Then, a unified transfer function structure (UTFS) is proposed to approximate the frequency responses of different types of devices by focusing on three key parameters<a>, which dramatically reduces the complexity of frequency analysis. </a>On this basis, we introduce two evaluation indices, i.e., frequency drop depth coefficient (FDDC) and frequency drop slope coefficient (FDSC), to theoretically quantify the frequency nadir and the average RoCoF, respectively. Instead of relying on simulations or experiments, our method rigorously links the system’s frequency characteristics to the characteristics of heterogeneous devices, which enables an in-depth understanding regarding how devices affect the system frequency. Finally, the proposed indices are verified through simulations on a modified IEEE 39-bus test system. </p>

A Combined RMS Simulation Model for DFIG-Based and FSC-Based Wind Turbines and Its Initialization

Reconstructable dynamic simulation models of modern variable-speed wind turbines (WTs), which are integrable into any simulation software, are crucial to the scientists investigating the contribution of WTs to counteracting the current power system stability issues. The structural similarity between a doubly fed induction-generator-based (DFIG-based) WT model and a full-scale-convertor-based (FSC-based) WT model using induction generator offers the possibility of integrating them into a combined modular model with little effort and the same used parameter set. This article presents a combined root mean square (RMS) WT model, which contains a DFIG-based WT and a FSC-based WT using induction generator. The model is designed based on fundamental machine and converter equations and can be applied for classical network stability analyses. Furthermore, analogous well-performing initialization procedures for both DFIG-based and FSC-based WT models are also introduced. As an example, to demonstrate the performance of the WT model in frequency stability studies, the model is extended with a droop-based fast frequency response (FFR) controller and is implemented in a MATLAB-based RMS simulation tool. The results of the case studies confirmed a solid functionality of initialization procedures. Furthermore, they illustrate feasible and comparable general behavior of both WT models as well as their plausible responses in the event of a frequency drop in a 220 kV test system.

Torque Limit-Based Inertial Control of a DFIG for Rapid Frequency Stabilization

With the increasing penetration of renewable energy generation, the frequency stability of a power grid can be significantly threatened. A doubly-fed induction generator (DFIG) participates in the frequency support of a power grid by releasing kinetic energy (KE) to boost the frequency nadir (FN). However, during rotor speed restoration, it is difficult to counterbalance the size of a second frequency drop (SFD) and the rotor speed recovery duration. This paper proposes an improved torque limit-based inertial control (TLBIC) to raise the FN by releasing less kinetic energy while guaranteeing rapid frequency stabilization with reduced SFD. To this end, when detecting a disturbance, the DFIG enhances the active reference power to the torque limit, and then the active power reduces smoothly based on an exponential function until the maximum power point tracking (MPPT) curve is met, and the rotor speed reverts to the initialization operating condition along the MPPT curve. A simulation system model with various wind power penetrations is established in EMTP-RV. Results show that the proposed scheme boosts the FN at a high level with less KE and guarantees rapid frequency stabilization.

Dynamic Behavior Analysis of the Sandwich Beam Structure with Magnetorheological Honeycomb Core under Different Magnetic Intensities: A Numerical Approach

In this article a sandwich beam structure with honeycomb core filled of MRE (magnetorheological elastomer) with different ratios of Elastomer and iron particles is proposed. Modal response for structures with Nylon and Resin8000 honeycomb core filled with MRE and sandwiched between aluminum face sheets were analyzed and compared for two different ratios of MRE by placing magnets at free end and center of the structure. The force generated by magnets on the sandwich beam structure was calculated using ANSYS EDT and the modal response of the structure was then observed under generated magnetic force using ANSYS Workbench. The results showed that the resonance frequency of the structure decreased as the magnetic intensity was increased for all the cases specially for the first mode. Secondly structure with Nylon honeycomb core showed lower frequency drop and higher deformation than the structure with Resin8000 honeycomb core.

Fast Stepwise Inertial Control Scheme of a DFIG for Reducing Second Frequency Drop

With the fast growth in the penetration of wind power, doubly fed induction generators (DFIGs) are recommended for their ability to enforce grid codes that provide inertial control services by releasing rotational energy. However, after supporting the system frequency, a second frequency drop (SFD) is prone to occurring to regain the rotor speed caused by the sudden reduction in output. In this article, we propose a torque limit-based fast stepwise inertial control scheme of a DFIG using a piecewise reference function for reducing the SFD while preserving the frequency nadir (FN) with less rotor energy released. To achieve the first objective, the power reference increases to the torque limit and then decays with the rotor speed toward the preset operating point. To achieve the second objective, the power reference smoothly lessens over time based on the exponential function. The performance of the proposed stepwise inertial control strategy was studied under various scenarios, including constant wind speed and ramp down wind speed conditions. The test results demonstrated that the frequency stability is preserved during the frequency support phase, while the second frequency drop and mechanical stress on the wind turbine reduce during the rotor speed restoration phase when the DFIG implements the proposed stepwise inertial control scheme.

Cooperative Synthetic Inertia Control for Wind Farms Considering Frequency Regulation Capability

To fully utilize the frequency regulation (FR) capability of wind turbines (WTs) and to avoid a secondary frequency drop caused by the rotor speed recovery, this paper firstly proposes an FR capability evaluation method for wind farms based on the principle of equal rotational kinetic energy of WTs, and analyses the essence of cooperative rotor speed recovery for WTs. Based on these, a cooperative synthetic inertia control (CSIC) for wind farms considering FR capability is proposed. By introducing the cooperative coefficient, the CSIC can fully utilize the FR capability of WTs, maintain the fast response of WTs with synthetic inertia control, and reduce communication requirements for the wind farm control center. By directly compensating the auxiliary FR power of WTs, the CSIC realizes the cooperative rotor speed recovery for WTs between different wind farms, avoiding a secondary frequency drop and a complex schedule of rotor speed recovery for multiple WTs. Finally, the simulation results verify the effectiveness and feasibility of the proposed control.

Damage Detection on a Beam with Multiple Cracks: A Simplified Method Based on Relative Frequency Shifts

Identifying cracks in the incipient state is essential to prevent the failure of engineering structures. Detection methods relying on the analysis of the changes in modal parameters are widely used because of the advantages they present. In our previous research, we found that eigenfrequencies were capable of indicating the position and depth of damage when sufficient vibration modes were considered. The damage indicator we developed was based on the relative frequency shifts (RFS). To calculate the RFSs for various positions and depths of a crack, we established a mathematical relation that involved the squared modal curvatures in the healthy state and the deflection of the healthy and damaged beam under dead mass, respectively. In this study, we propose to calculate the RFS for beams with several cracks by applying the superposition principle. We demonstrate that this is possible if the cracks are far enough from each other. In fact, if the cracks are close to each other, the superposition method does not work and we distinguish two cases: (i) when the cracks affect the same beam face, the frequency drop is less than the sum of the individual frequency drops, and (ii) on the contrary, cracks on opposite sides cause a decrease in frequency, which is greater than the sum of the frequency drop due to individual damage. When the RFS curves are known, crack assessment becomes an optimization problem, the cost function being the distance between the measured RFSs and all possible RFSs for several vibration modes. Thus, the RFS constitutes a benchmark that characterizes damage using only the eigenfrequencies. We can accurately locate multiple cracks and estimate their severity through experiments and thus prove the reliability of the proposed method.

A comparative analysis of the performance of centralized inverter and parallel inverter based hybrid microgrid system for distributed generation

In this paper, the performance and reliability of the hybrid microgrid system is analyzed with the two different configurations where multiple distributed energy sources supplied the power to the loads through centralized inverter and parallel inverter. The power quality, power sharing, power exchange and voltage and frequency drop parameters are evaluated by applying 1.1 kVA load on the centralized and parallel inverter hybrid systems with LL and LLG faults. The hysteresis current controller in the centralized inverter hybrid system is assuring the accurate power exchange between the grid and hybrid system during abnormal conditions. The droop controller in parallel inverter hybrid system is effectively sharing the load among the inverters during normal and abnormal conditions. The comparative analysis of these energy systems is made based on control aspects, power quality, reliability and economics.