Worsening of power system transient stability is concerned in a power system where renewable energy resources increase and synchronous generators (SG) decrease. One of the measures to enhance transient stability is synchronous condensers (SC). We showed that SC decreases acceleration energy by the kinetic energy storage function of inertia and increases deceleration energy area by voltage control function. SC can enhance transient stability by these two effects. However, since the rotor speed of SC is fixed, SC cannot control kinetic energy. So, we turned our attention to adjustable speed synchronous condensers (ASSC) capable of controlling kinetic energy. This paper proposes a control method of ASSC for the enhancement of transient stability utilizing the controllability of kinetic energy of ASSC in the situation where ASSC exists between a large SG and load. A simulation result shows that ASSC increases the active power output of the SG during a fault and after clearing the fault by the proposed method compared with SC. As a result, the method can decrease the acceleration energy of the SG, increase the deceleration area of the SG and enhance transient stability.

For safe operation of a photovoltaic generating system, an insulation monitoring function, which can immediately detect deterioration of insulation between photovoltaic module strings and the earth, is indispensable. This function requires accurate measurement, low leakage current and suppression of rising voltage against the earth. In this paper, a new insulation monitoring method of photovoltaic module strings is proposed by the improved existing self-biased method that has an inevitable voltage rise under measurement. In this new method, both terminals of photovoltaic module strings are always connected to the ground with appropriate resistors. Theoretical discussion and experiments for this new method showed precise measurement, and acceptable leakage current under various outdoor conditions. In addition, it was confirmed that this method could sufficiently decrease in the voltage rise compared with the existing self-biased method.

In an electric power system featuring an abundance of renewable energy sources (RES), such as photovoltaic generators (PVs) and wind farms (WFs), the need for curtailing RES output arises to maintain supply-demand balance during periods of anticipated excess generation across the electric power system. Ensuring equitable treatment among RES units regarding curtailment and minimizing overall curtailed energy become pivotal. This paper introduces a method to equitably establish upper output limits for each RES. The effectiveness of these methods is substantiated through numerical simulations. It was found that the key to achieving fairness is to uniformly improve the output control performance of RESs.

In Japan, power utilities have been divided into generation, retail, and transmission sectors, following the electricity system reform that began in 2016. In recent years, the Japanese electricity market has been improved. Generation and retail companies use the capacity, spot, and balancing markets to buy and sell electricity. Power generation companies must estimate profits from the electricity trades in the various markets to make their long-term business plans. As the first step, it is important to evaluate the sustainability of the long-term business plan throughout the entire power system. In this study, we propose a generation expansion planning evaluation method based on the generator unit commitment schedules considering the capacity, spot, and balancing markets. The proposed method can be used to check the sustainability of the power generation companies in the entire power system. The simulation results show that the design of the electricity market impacts on the profitability of power sources and can even enhance the economies of those with high operating costs.

The paper examines the relation between the short-circuit ratio (SCR) and voltage stability for offshore wind farms. Considering the capacitance of submarine transmission cables as well as the short circuit capacity at the onshore substation, it derives the equations for SCR by applying the Thevenin's theorem to the four-terminal circuit. The obtained equations reveal that, in case of low SCR at the onshore bus, the SCR at offshore bus can be greater than that at the onshore bus and can increase as the capacity of the wind farms increases. However, studies with a metric for voltage stability show that the voltage stability is deteriorated with the increase of the offshore wind farm. The results indicate that SCR—a widely-used metric to evaluate voltage stability—can bring misleading results for the voltage stability of offshore wind farms.

The introduction of renewable energy whose power outputs fluctuate depending on the weather causes uncertainties in power generation operations. To prevent effects by the uncertainties such as surplus or shortage of fuel tank and maximize the operational profitability, power generation companies require economic fuel risk management. As this risk management, a new power generation planning that maximizes the expected profitability under the uncertainties modeled by numerous scenarios is developed. To reduce the computation time to optimize the plan, the proposed method only considers the effective scenarios affecting the results of the optimization and applies progressive hedging which is a fast optimization method. To evaluate the performance of the proposed method, a weekly plan, which assumes 56 uncertainty scenarios and 27 generators, is constructed. As a result, we confirmed that the computation time can be reduced by 92% compared to a method which only applies the optimization solver, while mitigating the error of the objective function at 0.42%. In three - month plan assumed 14 uncertainty scenarios, the proposed method can optimize less than an hour with parallel processing in a computer.

To introduce ICT to the fisheries industry, it is important to secure a power supply. To supplement solar power generation at night, on rainy days, and on cloudy days, we have devised a rocking electric power generator that generates electricity from the rocking motion of waves.

We report on the building up a rocking electric power generator. The generator can generate electricity by rocking motion. It achieved to 1.28VA rotational speed of 0.78rps, and the maximum output current is 40mA. The load resistance is available 240Ω or more. We clarified the relationship between rocking motion and power generation in a rocking power generator, using evaluation sensors each of motion and electricity.

As a result of increasing the power generation efficiency of the air gap generator, the load current also flows to the coil, which causes the electromagnetic brake to work more strongly. Due to the influence of the electromagnetic brake, it was not possible to increase the generated voltage. It was found that a driving torque by the pendulum load was required that exceeded the braking force produced by the electromagnetic brake. To increase the pendulum load, the float becomes to lose its balance because the center of gravity becomes higher. The relationship between the pendulum load and balance is important for stable levitation.