In this chapter, we describe a plan for comprehensive evaluation of a satellite communications (SATCOM) system with frequency flexibility. To cope with the more and more increasing demand of the SATCOM system, next-generation high-throughput satellites (HTS) will install a frequency flexibility function that can change the frequency assignment flexibly. To control this HTS, the flexible channel assignment method has been proposed. Under the time-varying traffic, this method performs higher throughput and reduces the number of control actions that change the frequency assignment. In the next step, comprehensive evaluation of the HTS system with the frequency flexibility is required. We summarize our previous results and describe a plan for the comprehensive evaluation of the HTS system in terms of performance index, communication traffic, and link assignment schemes. Finally, we suggest operations strategy of the HTS system including the predictive control.

For high-speed space communications, future needs of space optical communication technologies are further increasing to provide operation services of intersatellite links and direct links in the field of remote sensing and space explorations. However, cloud blockage of direct communication links is one of the issues in space optical direct communications, while the atmospheric effect on the communication links is also an important issue on the link quality in a given satellite path connected with optical ground stations. Space optical communication experiments have been performed and results have also been reported internationally, but many of them are mainly focused on communication link evaluations for stable optical direct links under atmosphere, while experiments of optical ground systems for avoidance of cloud blockage with ground network switching controls have not been sufficiently reported. For the network switching controls among optical ground stations based on cloud blockage on a given satellite path over stations, JAXA developed ground network systems. First, the laser ground network planning system is explained. Next, our optical ground stations and the infrared cloud monitoring and discrimination system for lower cloud blockage are explained. Finally, our planned network switching testings are explained.

In this chapter, we investigate a DVB-RCS2-based satellite communication system consisting of a gateway, a satellite, and a return channel satellite terminal (RCST). We formulate an optimization problem to maximize the transmission rate of the system. To solve the problem, we propose an adaptive coding and modulation (ACM) and power control scheme for return link transmission based on the return channel condition and power headroom of the RCST. Simulation results show that the proposed ACM and power control scheme increases the transmission rate as the transmit power of RCST and satellite increases or the power headroom of RCST increases.

Inverter-side current feedback control (ICFC) has been extensively adopted in distributed generation systems because of its simple implementation and better consistency with actual operating conditions. At the same time, when there are a large number of background harmonics in the grid, capacitor voltage feedforward (CVF) is usually added to the system for its suppression. This method could make the system keep the first-order characteristics under the analogue control. However, under digital control, due to the digital control delay, a reverse resonance peak will be generated in the loop gain, which makes the system unstable in the weak grid. In order to solve the aforementioned problems, this study proposes a feedforward phase compensation method of LCL grid-connected inverter based on the all-pass filter (AF). By introducing AF into the CVF channel, the phase lag in the range of reverse resonance peak frequency is compensated, so as to enhance the robustness of the system in the weak grid. At the same time, this study gives the detailed design process of the proposed method. Experimental results on a 3-kW prototype are provided, and the effectiveness of the proposed control method is verified..

Local blackout occurs when the transient stability limit is exceeded after a transmission line fault. As to global blackout, a recording of the 10 August 1996-WECC blackout shows that it was accompanied negative damping. A turbine-generator swinging against an infinite bus is used to approximate the dynamics leading to the WECC blackout. There is no analytic solution when non-linearity is included. Small-signal linearisation shows that negative damping can occur but cannot produce the waveform recorded in the WECC blackout. Therefore, the graphical phase-plane method, which is easy to use, is resorted to. The study shows that the kernel of non-linearity consists of the gradients which produce limit cycles. Positive or negative damping is produced by shifting the gradients of the limit cycles to the right or left in the direction of the trajectory. The study makes a contribution by showing that phase plane can be used to study the impact of multiple independent controllers. A worked example shows when transient stability limit is exceeded, local blackout occurs. The swing equation of local blackout is applied to the WECC blackout. As proof that negative damping was due to non-linearity, a waveform having the frequency of the recorded WECC blackout is presented.

Microgrid inverters in the presence of faults, unavoidable modelling uncertainties, disturbance and harmonic current resulting from nonlinear loads should have small steady state tracking error, small THD and high robustness hence this subject has turned one of the motivations of this investigation. To achieve the stated goals, fractional adaptive sliding mode controller (FASMC) is proposed in this paper. The proposed controller increases the robustness, flexibility and degree of freedom. As far as in practice it is not easy to define the bounds of disturbances and guarantee the system stability, hence in next step, to overcome this challenge the adaptation laws are suggested. Then for the problem of determining the controller parameters, Particle Swarm Optimization (PSO) algorithm is used. The performance of the proposed technique is investigated for an islanded microgrid under different disturbances, also to verify the advantages of the proposed controller, the results are compared with other controllers. Finally, the proposed controller and PID controller are implemented experimentally on Arduino mega 2560 microcontroller.

In this study, a novel predictive event-triggered load frequency control has been developed for a hybrid power system with renewable energy sources (RESs) to deal with denial-of-service (DoS) attacks, where the DoS duration (the time attack lasts) are boundless. A predictive event-triggered transmission scheme is built for the multi-area hybrid power systems under DoS attacks to reduce the load of network bandwidth while maintaining adequate levels of performance. Therefore, an observer-based predictive controller is developed in the presence of both external disturbances and DoS attacks by formulating the LFC problem as a disturbance attenuation issue. In the proposed method, a hybrid power system with RESs is used to achieve novel and better security strategies. Based on the new model, sufficient conditions are obtained using the Lyapunov stability theory to ensure a stable multi-area hybrid power system with a prescribed performance. Moreover, an algorithm is provided to obtain the control strategy of DoS attacks. Finally, the simulation of a hybrid power system with RESs is presented to demonstrate the effectiveness of the proposed method in dealing with the DoS attacks.

A tool to visualise real-time phasor measurement unit (PMU) data of a transmission line is proposed, named PQ chart. It is a simple and intuitive visualisation aid for operator situational awareness. The use of PMU data helps in capturing both steady-state and dynamic behavioural aspects of the transmission line. The tool is based on basic active and reactive power equations of a transmission line. The locus of active and reactive power flow corresponds to a circle in which the radius depends on voltage regulation. If the circle is imagined as a wheel, then the spokes of it correspond to the voltage angular difference across the transmission line. The PMU data is plotted on this canvas and its progression in time is observed. The occurrence of power swings, angular and voltage instabilities lead to a trajectory on the chart. A system operator can be alerted when any such movement occurs. The tool provides a single view from which deciphering active power flow, reactive power flow, voltage regulation, and voltage angle difference across a line becomes easy for the operator. Case studies with PMU data of 400 kV transmission lines in the Indian grid are presented to illustrate the tool's capabilities.

The controlled islanding problem is typically considered only for pure ac power systems, with the ultimate objective of either minimising power imbalance or power-flow among islands. However, as ac/dc hybrid power systems are becoming popular worldwide, current controlled islanding schemes should be redesigned to take into account the presence of high-voltage dc (HVDC) links, possibly connecting different islands. Accordingly, in this study, the authors solve the classic islanding problem combining HVDC power modulation with the conventional ac cutset search. The flexibility of the HVDC allows the authors' strategy to jointly capture the previously mentioned objectives, and provides even lower power imbalances than the minimum imbalance strategy, at a relatively small cost of increasing power-flow impact. Then, the optimisation problem is formulated as a mixed-integer linear programming problem, which can be conveniently solved with existing commercial solvers. Finally, they validate their proposed strategy in two case studies, corresponding to a modified IEEE-118 system and to the China Southern Power Grid system. In both cases, dynamic simulations show that their proposed approach outperforms classic algorithms where the presence of HVDC power modulation is not explicitly taken into account.

A microgrid (MG) is a cyber-physical system that facilitates integration of several distributed renewable energy resources. In the last decade, several efforts were made to standardise the framework of a cyber-physical MG network and its control structure. In this perspective, various studies discussing the different control techniques are reported in the literature. However, a comprehensive and systematic review of a cyber-physical MG is discussed rarely. In this study, a comprehensive review of a MG architecture and hierarchical control structure in both islanded and grid-connected modes are presented. The hierarchical control of the MG includes primary, secondary, and tertiary control. Recent studies provide significant opportunities in dividing the control task among various layers resulting in a distributed framework. This study analyses the cyber and physical networks separately while discussing the primary, centralised, and distributed secondary control levels with their merits, demerits, and typical applications. A Venn diagram analysis is also presented that clearly distinguishes the primary control scheme in different research sub-areas. Furthermore, the MG communication structure, protocols, design, constraints, and cyber security are also reviewed systematically. Finally, future trends are summarised based on the state-of-the-art MG research.