Low Inertia Research Articles

A Novel Master-Slave Interventional Surgery Robot with Force Feedback and Collaborative Operation.

In recent years, master-slave vascular robots have been developed to address the problem of radiation exposure during vascular interventions for surgeons. However, the single visual feedback reduces surgeon immersion and transparency of the system. In this work, we have developed a haptic interface based on the magnetorheological fluid (MRF) on the master side. The haptic interface can provide passive feedback force with high force fidelity and low inertia. Additionally, the manipulation of the master device does not change the operating posture of traditional surgery, which allows the surgeon to better adapt to the robotic system. For the slave robot, the catheter and guidewire can be navigated simultaneously which allows the two degrees of action on the catheter and axial action of a guidewire. The resistance force of the catheter navigation is measured and reflected to the user through the master haptic interface. To verify the proposed master-slave robotic system, the evaluation experiments are carried out in vitro, and the effectiveness of the system was demonstrated experimentally.

Force control of lightweight series elastic systems using enhanced disturbance observers

This paper analyzes the control challenges associated to lightweight series elastic systems in force control applications, showing that a low end-point inertia can lead to high sensitivity to environment uncertainties. Where mainstream force control methods fail, this paper proposes a control methodology to enhance the performance robustness of existing disturbance observers (DOBs). The approach is validated experimentally and successfully compared to basic control solutions and state of the art DOB approaches.

A Second-Order Cone Programming Model of Controlled Islanding Strategy Considering Frequency Stability Constraints

Controlled islanding is an important defense mechanism for avoiding blackouts by dividing the system into several stable islands. Sustainable systems that incorporate a high proportion of renewable energy are prone to frequency instability or even severe blackout events due to extreme weather conditions. Thus, it is critical to investigate controlled islanding considering frequency stability constraints to reduce the risk of a sustainable system collapse in extreme weather conditions. Here, the frequency constraint of islands is derived based on the law of energy conservation, and the island connectivity constraint is proposed based on the idea of network flow. A controlled island second-order cone programming model with frequency stability constraints is proposed for the islanding strategy. The consideration of frequency constraints can help to avoid islands with too low inertia generated by the islanding strategies, ensuring that the frequency nadir of the island remains within a safe range after disturbance. Connectivity constraints can ensure connectivity within the island and no connectivity between different islands. The model also meets the reactive power balance and voltage limits in the system. Simulations of the three test systems show that this island model, which takes frequency stability into account, is effective in reducing the risk of sustainable power system collapse in extreme weather conditions.

Distributed energy frequency–voltage support technology

With the development of distributed energy, the penetration rate of power electronic devices is increasing, and the dominance of thermal power generation will be slowly replaced by it. Synchronous generators, which are mainly thermal power generation, will also be slowly reduced with the development of new energy. It leads to the trend of power system with reduced inertia and weakened system strength, and the stability problem becomes serious. When the system is disturbed, the low inertia of the system will lead to power quality failure, which seriously affects the production as well as the life of the customer side. Therefore, in order to solve the power quality problem under the access of distributed energy with high penetration rate, this paper designs a distributed energy frequency–voltage support method. Firstly, the secondary frequency regulation of distributed energy is designed on the basis of the primary frequency regulation. Furthermore, for voltage support, this paper analyzes the quantitative relationship between voltage active and voltage reactive in the distribution network, and the voltage support is carried out to minimize network loss with the consideration of distributed energy inverters’ capacity characteristics and tidal current constraints. Finally, the effectiveness of the proposed strategy is verified through Matlab/simulink simulation.

Comparative Study of the Transmission Capacity of Grid-Forming Converters and Grid-Following Converters

The development trend of high shares of renewables and power electronics has increased the demand for new energy converters in the power system, but there is a lack of systematic research on the stability of different types of converters when transmitting power, which is worth exploring in depth. In this study, the power transfer capabilities of grid-forming and grid-following converters are investigated separately through an equivalent circuit diagram and phasor diagram when connected to the grid, and a quantitative relationship between converters’ power transmission limit and short circuit ratio under static stability conditions is obtained, leading to the conclusion that, in terms of power transmission, grid-forming converters are more suitable for weak grids with high damping and low inertia, whereas grid-following converters are more suitable for strong grids with high inertia. The conclusions are further verified by constructing the converter grid-connected models for different grid strengths through the PLECS simulation platform and the real-time simulation RTBOX1 and F28379D launchpad platform.

Frequency prediction after disturbance of grid-connected wind power systems based on WOA and Attention-LSTM

Under the guidance of the goal of the “carbon peaking and carbon neutrality”, due to the high proportion of renewable energy and the high proportion of power electronic equipment, the power system will bring strong randomness, low inertia and other characteristics, causing a large number of frequency stability problems. In order to solve the problems of traditional power system frequency prediction methods, such as difficulty in modeling and poor prediction accuracy, and to determine whether the frequency stability problem will occur after the wind power grid-connected system is disturbed, the Lasso algorithm is first used to reduce the dimension of the input data, and then the attention mechanism based long and short memory (attention LSTM) neural network is used to predict the output frequency curve, The network parameters are optimized by the global search algorithm Whale Optimization Algorithm (WOA). Finally, the accuracy of the algorithm is verified by taking the improved wind power grid-connected 39 bus as an example. The results show that this method has a good guiding significance for evaluating the frequency stability of the wind power grid-connected system after interference, and can effectively predict the frequency curve of the system after interference, and evaluate the frequency stability of the system after topology change.

Home Chimney Pinwheels (HCP) as Steh and Remote Monitoring for Smart Building IoT and WSN Applications

Smart, and ultra-low energy consuming Internet of Things (IoTs), wireless sensor networks (WSN), and autonomous devices are being deployed to smart buildings and cities, which require continuous power supply, whereas battery usage has accompanying environmental problems, coupled with additional maintenance cost. We present Home Chimney Pinwheels (HCP) as the Smart Turbine Energy Harvester (STEH) for wind; and Cloud-based remote monitoring of its output data. The HCP commonly serves as an external cap to home chimney exhaust outlets; they have very low inertia to wind; and are available on the rooftops of some buildings. Here, an electromagnetic converter adapted from a brushless DC motor was mechanically fastened to the circular base of an 18-blade HCP. In simulated wind, and rooftop experiments, an output voltage of 0.3 V to 16 V was realised for a wind speed between 0.6 to 16 km/h. This is sufficient to operate low-power IoT devices deployed around a smart city. The harvester was connected to a power management unit and its output data was remotely monitored via the IoT analytic Cloud platform "ThingSpeak" by means of LoRa transceivers, serving as sensors; while also obtaining supply from the harvester. The HCP can be a battery-less "stand-alone" low-cost STEH, with no grid connection, and can be installed as attachments to IoT or wireless sensors nodes in smart buildings and cities.

Modelling, Analysis and Performance of a Low Inertia AC-DC Microgrid

In a world where the energy crisis is becoming overwhelming, demand for integrating renewable energy sources is increasing and forming microgrids is becoming an essential solution. The new microgrid systems, which depend mainly on renewable energy sources instead of conventional synchronous generators, come with a low inertia concern. This paper proposes a virtual inertia controller based on a high-pass filter (HPF) to support the frequency of the AC microgrid while maintaining the DC voltage of the DC microgrid within the nominal ranges in cases of contingencies. The proposed system encounters an AC-DC microgrid with a renewable energy source on the DC microgrid alongside constant power load and resistive loads, while on the AC microgrid side, a synchronous generator is used to present the low inertia of the grid with dynamic loads and static loads. The state-space linearized model of the system is developed and verified using Matlab Simulink. The dynamic response of the proposed controller is compared to the low-pas filter (LPF)-based controller. Moreover, the effect of changing the system’s parameters on eigenvalues is investigated.

Fast Frequency Support Through LED Street Lighting in Small Non-Synchronous Power Systems

Small-sized non-synchronous islands, which are inherently characterized by low system inertia, will face in the next years the challenge of integrating larger and larger amount of renewable energy sources, leading to further reduction of inertia. Several means to support inertia and frequency transients have been proposed in the literature, including energy storage systems, distributed generation, and demand response. LED street lighting systems are widespread control resources, which in a smart grid scenario, can be regulated by means of local or remote control signals. This article investigates the possibility to regulate the power consumption of LED street lighting to provide frequency support in a system characterized by reduced total inertia. Tests are carried out integrating the simulation of the non-synchronous power system of an Italian small island with the response of an actual LED street lamp, in a Power Hardware-in-the-Loop testing environment. Both synthetic inertia and fast frequency response approaches are tested and discussed.

A Discrete-Time Algorithm for Real Time Energy Management in DC Microgrids

A microgrid will often be characterized by very low embedded system inertia when operating fully islanded. In this state, management of the embedded stored energy in the microgrid over timescales of milliseconds is of critical importance as even short periods of mismatch between generation and consumption will cause voltage collapse on the network. This article proposes a discrete-time (sampling-based) energy management algorithm that uses the rapid controllability of power-electronics interfaced loads to manage the internal stored energy of loads with the aim of minimizing the use of bulk storage and dispatchable generation. Fast interconverter communication is used to balance storage demand across the network and to dispatch generation. A lab-scale microgrid with 10 nodes and a sampling time of 10 ms is used to investigate the effectiveness of the proposed energy management algorithm.

Energy Saving through Automation of the Lightweight Floor Heating System

The overview of the literature sources showed that over the last decade, the attention to the study of heat transfer processes with the automation and periodic use of underfloor heating systems has increased significantly. The aim of this study was to investigate the heat flux density from the surface of the lightweight floor heating system dependence on different parameters. These parameters are material of the finishing coating, average temperature difference between indoor air and heat carrier, heat carrier temperature and its flow rate, thickness of the thermal insulation layout under the lightweight floor heating system. The article shows results of both experimental and computational modelling studies of the lightweight floor heating system which was operated in different regimes and with different (ceramic tile and laminate) finishing coatings. A new experimental stand has been created in the thermophysical laboratory of the Institute of Engineering Thermophysics of the National Academy of Sciences of Ukraine for the purposes of experimental studies. For the purposes of comparison of different operational regimes as well as the determination of the energy saving through automation of the operation regimes of the lightweight floor heating system, the CFD modelling was conducted. The results showed that such systems have significant potential for automation and heat supply purposes of different premises since they have low thermal inertia due to the absence of the concrete screed monolith. On the other hand, the research showed that use of quantitative regulation of the lightweight floor heating system, by reducing the flow of the heat carrier is more effective in this case than qualitative with change of heat carrier temperature.

Adaptive Control Strategy for Frequency Support From MTDC Connected Offshore Wind Power Plants

Grid integration of large-scale power electronic interfaced renewable energy sources leads to a low inertia system, thus resulting in a high rate of change of frequency (RoCoF) and frequency deviations in the power system following a credible contingency. In this article, a realistic adaptive communication-independent control strategy for effective inertial and primary frequency support from multiterminal HVDC (MTDC) connected offshore wind farms (OWFs) has been proposed. The proposed strategy can identify and distinguish the grid under disturbance among the other healthy grids in the MTDC system by an adaptive droop frequency support (ADFS) scheme at each receiving end converter (REC). On the OWF side, the control system of wind turbine generators has been designed to coordinate with the ADFS scheme to comply with the grid code regulations (GCRs) for inertial and primary frequency support. The proposed ADFS control scheme ensures that while providing frequency support to the grid under disturbance, frequency deviation limits of the healthy neighboring grids are not breached. Moreover, the proposed strategy complies adequately with the maximum permissible limits of HVDC voltage deviation. Furthermore, the proposed strategy is dependent on only local measurements and can be easily customized to comply with any applicable GCR. The reliability and effectiveness of the proposed robust control strategy have been demonstrated on three power systems interconnected through the MTDC system to two OWFs.

Fast frequency response constrained electric vehicle scheduling for low inertia power systems

Reduction in System Inertia (SI) and Primary Frequency Response (PFR) driven by the large-scale integration of uncertain and variable Renewable Energy (RE) sources disturbs the post-fault frequency dynamics. This necessitates the identification of potential solutions that can restrict high Rate of Change of Frequency (RoCoF). Electric vehicles (EVs), due to their fast response capability and instantaneous power delivery, are a viable source for the Fast Frequency Response (FFR) service. Potential assessment of EVs for FFR service is required to restrict high RoCoF and maintain secure and reliable system operation in real-time. The main contribution of this work is to assess the potential of EVs for FFR support through both Grid-to-vehicle (G2V) and Vehicle-to-grid (V2G) modes. In this work challenges like EVs aggregation, related netload uncertainty characterization, and post-fault frequency dynamics are modelled in a stochastic security-constrained scheduling framework. Further, a case study is carried out to investigate the role of EVs and their techno-economic impact on the overall system: (a) only in dumb charging mode and (b) participating in FFR service by scheduling aggregated EVs for both G2V and V2G with different level of RE integration. Numerical results indicate that the aggregated EVs scheduling can provide FFR support of around 71%, by simultaneously reducing system operating cost by 62% and 87% reduction in RE curtailment.

Frequency and Voltage Compliance Capabilities of Grid-Forming Wind Turbines in Offshore Wind Farms in Weak AC Grids

Weak grid conditions challenge the grid integration of offshore wind farms. Especially grids with low inertia and large grid impedance questions frequency and voltage compliance capabilities. Grid-forming wind turbines are a promising technology for weak grids due to the nature of their control strategy. This paper explains the difference in how weak grid conditions are described in the literature and shows how the voltage stability margin changes with the short-circuit ratio and X/R ratio. With that knowledge, the frequency and voltage compliance capabilities of three grid-forming controls in an offshore wind farm are investigated and benchmarked. These three controls are a droop control, a virtual synchronous machine, and a synchronverter. This was done by quantifying their performance during a frequency disturbance with sensitivity to the short-circuit ratio, X/R ratio, and the inertia constant, H. It is concluded that the virtual synchronous machine is the most compliant grid-forming control and that DC-link modeling is of great importance when testing compliance during frequency disturbances.

Control and Optimisation of Power Grids Using Smart Meter Data: A Review.

This paper provides a comprehensive review of the applications of smart meters in the control and optimisation of power grids to support a smooth energy transition towards the renewable energy future. The smart grids become more complicated due to the presence of small-scale low inertia generators and the implementation of electric vehicles (EVs), which are mainly based on intermittent and variable renewable energy resources. Optimal and reliable operation of this environment using conventional model-based approaches is very difficult. Advancements in measurement and communication technologies have brought the opportunity of collecting temporal or real-time data from prosumers through Advanced Metering Infrastructure (AMI). Smart metering brings the potential of applying data-driven algorithms for different power system operations and planning services, such as infrastructure sizing and upgrade and generation forecasting. It can also be used for demand-side management, especially in the presence of new technologies such as EVs, 5G/6G networks and cloud computing. These algorithms face privacy-preserving and cybersecurity challenges that need to be well addressed. This article surveys the state-of-the-art of each of these topics, reviewing applications, challenges and opportunities of using smart meters to address them. It also stipulates the challenges that smart grids present to smart meters and the benefits that smart meters can bring to smart grids. Furthermore, the paper is concluded with some expected future directions and potential research questions for smart meters, smart grids and their interplay.

Local Power Distribution—A Review of Nanogrid Architectures, Control Strategies, and Converters

Environmental issues and the global need to extend sustainable access to electricity have fostered a huge amount of research in distributed generation by renewables. The challenges posed by the widespread deployment of distributed generation by renewables, such as intermittent power generation, low inertia, the need for energy storage, etc., call for the development of smart grids serving specific local areas or buildings, referred to as microgrids and nanogrids, respectively. This has led in the last decades to the proposal and actual implementation of a wide variety of system architectures and solutions, and along with that the issue of the power converters needed for interfacing the AC grid with DC micro- or nanogrids, and for DC regulation within the latter. This work offers an overview of the state of the art of research and application of nanogrid architectures, control strategies, and power converter topologies.

An experience-sampling study on the relevance of affect dynamics to paranoid ideation.

Affective functioning is compromised in people who develop persecutory delusions, but the specifics of these affective disturbances remain unclear. To better understand the precise nature of affective disturbances in this group, it could prove helpful to focus not only on average or momentary affect intensities but also on the dynamic properties of affect, that is, the patterns and regularities with which affect fluctuates over time. This study used experience-sampling in a community sample with varying levels of paranoid ideation (n = 144) to capture different aspects of temporal affect dynamics in the two affective dimensions of valence and arousal. Specifically, we aimed to elucidate whether paranoid ideation is associated with high affective instability (i.e., both high affective variability and low inertia) or only with high affective variability or low affective inertia and whether these effects would be maintained when mean affect levels are controlled for. Results showed that the intensity and frequency of paranoid ideation were significantly associated with high variability of affective arousal, but for paranoia frequency, the effect was not robust against controlling for average arousal levels. Paranoia frequency was also associated with low inertia in affective valence, and paranoia intensity was associated with high valence variability. We discuss the implications of these findings for future research and clinical practice. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

A Supplementary Damping Control for MMC-HVDC System to Mitigate the Low-Frequency Oscillation Under Low Inertia Condition

With the increasing penetration of renewable energy, the inertia of AC system gradually decreases. When modular multilevel converter (MMC) based high voltage DC transmission (HVDC) system is connected to a low inertia AC system, the low-frequency oscillation may occur due to the interaction between MMC and synchronous generator (SG). To investigate this issue, a detailed small-signal model considering the dynamics of MMC and SG is developed and the corresponding eigenvalue analysis is conducted. Based on the developed model, the impact of the inertia on the low-frequency oscillation of MMC-HVDC system is studied, and the dominant low-frequency mode is investigated by participation factor and control parameter sensitivity analysis. From the results, it is found out that there exists close control interaction between SG and MMC under low inertia condition. To damp the low-frequency oscillation of MMC-HVDC system under low inertia condition, a supplementary damping control (SDC) approach is proposed, the parameters of the SDC approach are tuned by pole-assignment approach. Finally, the damping effect of the SDC approach is validated by theoretical analysis and simulation study in PSCAD.

The Effect of the Fast Frequency Response of the Solar Energy System on the Power System Dynamic Frequency Evolution

The existence of a large-scale photovoltaic power generation system without any rotational inertia can deteriorate the frequency stability of the power system. The solar energy storage system consisted of photovoltaic power generation and the energy storage device with fast charge and discharge can provide fast frequency responses to the grid through the power electronics controls, and therefore improve the dynamic frequency security of the low-inertia system. This paper discusses the modeling and fast frequency controls, namely virtual inertia and droop control. The modified WSCC 9-bus system with high photovoltaic power penetration and low inertia serves to show the effects of the solar energy storage system’s fast frequency responses on the frequency evolutions of the new power system. The results show that in the low inertia system with large-scale photovoltaic power generation, the active power droop control of the solar energy storage system can decrease the frequency deviations, but may introduce low-frequency oscillations during the frequency evolution following a contingency; the virtual inertia control can depress both the rate of change of frequency as well as the oscillations during the frequency evaluation.

Mid-IR Observations of IRAS, AKARI, WISE/NEOWISE, and Subaru for Large Icy Asteroid (704) Interamnia: A New Perspective of Regolith Properties and Water Ice Fraction

(704) Interamnia is one of the largest asteroids located in the outer main-belt region, which may contain a large amount of water ice underneath its surface. We observe this asteroid using 8.2 m Subaru telescope at mid-infrared wave bands and utilize a thermophysical model for realistic surface layers to analyze mid-infrared data from Subaru along with those of IRAS, AKARI, and Wide-field Infrared Survey Explorer (WISE)/NEOWISE. We optimize the method to convert the WISE magnitude to thermal infrared flux with temperature-dependent color corrections, which can provide significant references for main-belt asteroids at a large heliocentric distance with low surface temperature. We derive best-fitting thermal parameters of Interamnia—a mean regolith grain size of μm, with a roughness of and rms slope of deg, thereby producing thermal inertia ranging from 9 to 92 Jm−2 s−1/2 K−1 due to seasonal temperature variation. The geometric albedo and effective diameter are evaluated to be and , respectively, being indicative of a bulk density of 1.86 ± 0.63 g cm−3. The low thermal inertia is consistent with typical B/C-type asteroids with D ≥ 100 km. The tiny regolith grain size suggests the presence of a fine regolith on the surface of Interamnia. Moreover, the seasonal and diurnal temperature distribution indicates that thermal features between the southern and northern hemispheres appear to be very different. Finally, we present an estimation of volume fraction of water ice of 9%–66% from the published grain density and porosity of carbonaceous chondrites.