Although the number of pieces of equipment that emit harmonic currents has increased, harmonic voltages in Japan have gradually decreased since about 1999. In addition, harmonic voltages are generally lower during the daytime when there is greater usage of different types of equipment that emit harmonic currents. As a first step, we showed the reason for these strange phenomena qualitatively. The phase angles of the fifth harmonic current emitted by three-phase equipment of consumers using a 6.6kV or higher voltage power supply and those by the other equipment are almost opposite and they cancel each other out. As a second step, we classified equipment of all consumers into six different groups depending on the number of phases (i.e., single-phase or three-phase) and consumers' supply voltage and the ratio of the contribution of each group to the fifth harmonic voltage was then quantitatively clarified. As a third step, in this paper, we analyzed the seventh harmonic current in the same way as the fifth harmonic current. Time trends of the fifth and the seventh harmonic voltages are different but the estimated results of effective power of each group are almost same.

Variable renewable energy sources, such as photovoltaic (PV) and wind generator, would create the need for more flexibility to the existing power system. Concerning the unit commitment of dispatchable generators, the start-stop frequency of generators would increase if more PV or wind generation integrates in the power system. This paper discusses how much increment of the start-stop frequency is expected due to PV and wind power integration by using real data of the demand, the PV power, and the wind power in the north-east area of Japan for seven years (2008-2014 fiscal years). Two different types of approach, ‘the simulation method’ and ‘the demand wrinkle stretching method’ are used for evaluating the start-stop frequency of dispatchable generators, and results are around 30% increment of start-stop frequency for the 30% PV integration and around 40% increment for the 20% wind power integration.

This study aims to quantitatively clarify the effects of storage battery introduced to districts where large variable renewable energy (VRE) is implemented. Such districts will have difficulties in balancing between power demand and supply, and to keep the load frequency control (LFC) ability, and will be forced to curtail much VRE without storage battery. Authors developed a simulation model to optimize generation mix and hourly operation of thermal power, pumped hydro generation, and storage battery considering partial load efficiency, LFC supply and demand, and power transmission between districts. With this model, the authors obtained the following results on Japan's power system in 2030. (1) Some capacity of battery can decrease VRE curtailment rates as well as total power generation costs. However unit generation costs increase by the drop in thermal power capacity factors. (2) The curtailment rates can decrease to zero by having extremely large capacity of battery though this is a very expensive way. (3) The required battery capacity decreases when VRE ratios to power system size are averaged among districts.

This paper proposes a self-contained voltage control method for distribution line feeders. The proposed system consists of two types of agent: feeder agent (F_AG) and bus agent (B_AG). The F_AG plays as an important role, which decides the power factors of all distributed generators by executing the load flow calculations repeatedly. The voltage control strategies are implemented as the class definition of Java into the system. In order to verify the performance of the proposed method, it has been applied to a distribution model system. The simulation results show that the system is able to control very violent fluctuation of the demands and the photovoltaic generations (PVs).

The installed capacity of photovoltaic (PV) systems has been increasing rapidly due to the enforcement of the feed-in tariff scheme in Japan. However, reverse power flows from the roof-mounted PV systems cause voltage-rises in distribution networks. PV output can be separated into two fluctuation components, short-period and long-period. Long-period fluctuation is compensated by SVR (Step Voltage Regulator) with low response speed, and short-period fluctuation is stabilized by reactive power compensation with high response speed. As for the reactive power compensation, installing SVC (Static Var Compensator) in high-voltage lines has been studied. On the other hand, the idea of installing reactive power compensators in low-voltage lines has been proposed as a promising alternative. This paper proposes a method for analyzing the cost-effectiveness of the reactive power compensators, considering SVR and the constant power factor control of PCS (Power Conditioning System). The proposed method calculates the break-even cost of pole-mounted equipment to SVC, and analyzes the changes in the break-even cost under various power system conditions.

Because of significant change in environmental policies and electric power deregulation in the last decade, a lot of photovoltaic (PV) generations have so far been installed to the power system in Japan. When a huge amount of PVs generation is installed into the power system, we are very much concerned that disconnection of the PVs due to a system fault has a big impact on the power system stability and transient voltage stability. So it is important to equip the PV with Fault Ride Through (FRT) function in order to maintain power supply-demand balance. In addition, Dynamic Voltage Support (DVS) function of the PV is effective to recover the voltage after the system fault. However, it is unclear how the PVs which are equipped with the FRT and DVS functions affect transient stability and voltage stability. In this paper, how power factor of the PV power output affect the power system after a system fault is analyzed using P-δ curve. Then, a new PV power factor control method for improving the transient stability is proposed and its effectiveness is shown by digital simulations on a simple power system model.

Various evolutionary computation techniques have been applied to voltage and reactive power control. High penetration of renewable energies and deregulation of power systems require to shorten an interval of the control. One of the practical solutions for this problem is applications of parallel and distributed computing with dependability, which is an ability to keep sustainable control against various faults. This paper presents dependability evaluations of parallel differential evolutionary particle swarm optimization (DEEPSO) for voltage and reactive power control. Simulation results with IEEE118 bus systems indicate high dependability of the method, compared with parallel PSO and parallel differential evolution.

The trend of renewable energy integration, power system size and complexity growth, occurrence of line contingencies, and more stressed loading conditions for power systems increase the threat of voltage stability, which has recently been among the main problems in power systems. This paper proposes a multistage preventive scheme based on voltage stability and security monitoring and control. A stochastic security-constrained optimal power flow considering voltage stability and renewable energy generation uncertainty, reactive power compensator tap re-operation minimization, and load-shedding minimization problems are hierarchically implemented in the proposed method. This method ensures voltage stability under the uncertainty of renewable energy generation and selected line contingencies considering their occurrence probability and/or voltage instability severity level for the upcoming time-slot. Several cases based on a modified IEEE 57-bus test system are used to demonstrate the effectiveness of the proposed method. The simulation results show that the proposed method can make an important contribution to improve voltage stability and security performance under severe conditions, especially to handle the uncertainty.

This study examines meteorological conditions associated with ramp events of wind farms in the Hokkaido and Tohoku area in the eastern Japan using phenomenological and statistical analysis. The result of the analysis for the area-integrated wind power generation shows clear seasonal and diurnal variations of the occurrence rate of the wind ramps. The ramp events mainly occur in cold season. The occurrence rate of ramp-up (down) increases in the daytime (night) as the diurnal variation. It could be conceivable that the diurnal variation is mainly related to development/decay of atmospheric boundary layer. As a common result of phenomenological and statistical analysis focusing on the sea level pressure pattern around the areas, we identify that there are dominant surface pressure patterns. The major weather patterns of the ramp-up events are corresponding with the strengthening of (or transition to) the winter monsoon and approaching of an extratropical cyclone to the area. On the other hand, the major patterns for the ramp-down are weakening of the winter monsoon and that the area is covered by the high-pressure system.

The 27th Power and Energy Society Annual Conference was held on September 7 - 9, 2016 at Kyushu Institute of Technology in Kita-Kyushu. The total number of technical papers was 471, and technical sessions were 49 (48 oral sessions and 1 poster session). A special lecture and a panel discussion were organized. All events were very well attended and the final enrollment attained to 1073 registrations. The conference was successfully closed by the great contribution of all participants. The outline of the conference is reported in this article.