Recently, as a solution for earth-warming problem, the high voltage direct-current (HVDC) technology is growing in the world. An important issue of insulation for HVDC is space charge phenomena that would cause a severe influences on cable performance, then measurement methods of space charges also become more and more important. Here, space charge phenomena and their measurement techniques are looked over. About measurement techniques, not only recent progresses but international standardization of them are described.

Renewable energy sources are essential in a stand-alone hybrid system. Modeling and optimization of stand-alone hybrid microgrid systems based on solar, wind, and diesel with batteries are presented in this work. In a microgrid, frequency management is a major problem, and the primary aim is to reduce frequency variations under varying operating/load conditions. For this purpose, a PI controller is used in this work and its regulating parameters are optimized by using a Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Firefly (FF), and Cuckoo Search algorithms (CSA). Simulation results show a significant improvement in results.

This study evaluates the economic and environmental performance of several households with different PV power generation and power demand characteristics. The analysis was multidimensional, ranging from no PV and no battery energy storages to the installation of each device, further capacity expansion, and advanced control potential of battery energy storages. When evaluating the potential for advanced operation of battery energy storages, three different foresight periods; one day, two days, and one year are compared in the optimization calculation. The results demonstrate that 2-day planned operation yielded almost the same operational patterns and effects as those obtained with 1-year planned operation.

This study simulates supply-demand operation based on Electric Vehicle (EV) bus travel data and examined the impact of the amount of V2G controlled EV buses introduced on supply-demand operation. The evaluation of the effect of reducing supply-demand adjustment costs from a renewable energy ratio of 50-60% to the current amount of EV buses introduced, and from the case where all of the 70,000 EV buses in the Kanto region were converted to EVs to the case where no EVs were converted to EVs. In all cases, the introduction of EV buses was confirmed to reduce the demand-supply adjustment cost. In addition, the cost reduction effect seemed to converge to a certain value.

In recent years, the introduction of photovoltaic power generation systems has been increasing from the perspective of global warming countermeasures. However, there is a problem that it becomes difficult to adjust the supply and demand balance of electric power. Therefore, in this research, the inverter by using estimation signal estimates the load of the consumer, then we aim to adjust the supply-demand balance at the demand side. By the verification of experimental, three-phase inverter, which is assumed to be an industrial photovoltaic power generation system, estimates the load by using pseudo random binary sequence signal and two proposed methods. The load estimation results show that the error rate of the estimated resistance of each phase is within a few percent by using the two proposed methods, and the load estimation is achieved.