Ryoichi Hara

Testing the technologies

The penetration of photovoltaic (PV) systems in Japan has been on the rise. Two factors have been promoting the increase: improved generation efficiency of PV modules and governmental subsidies for the initial cost of residential PV generation systems. As a result, the cumulative installed PV capacity has increased exponentially; however, the cumulative installed PV capacity by 2007 was only about 40% of the target for 2010 (4,820 MW). Reaching the target and promoting larger installation capacities in the future will require further installation in the residential sector and the construction of large-scale PV systems. The New Energy and Industrial Technology Development Organization (NEDO) of Japan has conducted several demonstration projects to investigate technological issues regarding the large penetration of PV generation systems and to develop new technologies for using PV generation systems effectively. One of NEDOs demonstration grid-connected PV projects is the Ohta Project, a cluster of PV systems in a residential development. Another is the Wakkanai Project, the largest central-station PV system in Japan.

Estimation of battery capacity for suppression of a PV power plant output fluctuation

Demonstration project named “Verification of Grid Stabilization with Large-scale PV Power Generation” has been conducted by the New Energy and Industrial Technology Development Organization (NEDO). In the Wakkanai PV power station, Sodium-Sulfur battery system is introduced to realize some additional functions. Since fluctuation in output of MW-class PV system may disturb the stable operation of power station, it is important to develop a fluctuation suppression technology. The authors have developed a fluctuation suppression using a battery system. In this paper, the relation between available battery capacity and fluctuation suppression performance is analyzed by computational simulation. This paper also estimates and discusses required battery capacity for fluctuation suppression.

Voltage regulation in distribution system utilizing electric vehicles and communication

Challenges for the low carbon society has brought a spread of electric vehicles (EVs). Most of EVs could be charged at night simultaneously. That could cause severe voltage drop along the feeder. On the other hand, EVs are able to inject/absorb reactive power by using interfacing inverter in principle. This paper proposes active and reactive power management which can regulate feeder voltages in the distribution system avoiding short in charged energy. This paper also proposes a communication scheme among EVs and distribution system operators to realize more effective voltage regulation in the distribution system.

Development of energy management system for DC microgrid for office building:-Day Ahead operation scheduling considering weather scenarios-

In recent years, distributed generators (DG) with renewable energy (RE) are introduced to electric power systems for saving CO2 emission. Installation of DGs in user-side leads to the local demand and supply system, called microgrids (MGs). Since the some of DGs work in DC, advantages of DC supply system over the AC might be emphasized The authors are investigating the merits of DC microgrid (DCMG) using the actual DCMG for an office building. Operation of the DCMG is organized by an energy management system (EMS). This paper proposes an optimal scheduling algorithm implemented in the EMS. Simulation using the actual demand data shows that the proposed scheduling algorithm can save 0.3 % CO2 emission during the simulation terms.

Risk-based voltage stability monitoring and preventive control using wide area monitoring system

nowadays, power system tends to be operated in heavily stressed load, which can cause voltage stability problem. Moreover, occurrence probability of contingency is increasing due to growth of power system size and complexity. This paper proposes a new preventive control scheme based on voltage stability and security monitoring by means of wide area monitoring systems (WAMS). The proposed control scheme ensures voltage stability under major N-1 line contingencies, which are selected from all possible N-1 contingencies considering their occurrence probability and/or causing load curtailment. Some cases based on IEEE 57-bus test system are used to demonstrate the effectiveness of the proposed method. The demonstration results show that the proposed method can provide important contribution in improving voltage stability and security performance.

Voltage stability-based PMU placement considering N− 1 line contingency and power system reliability

New PMU placement algorithm considering network connectivity, zero injection bus, reliability of N-1 line contingency and voltage stability performance (enhancing Voltage Stability Index) are proposed in this work. Reliability and voltage stability level are selected to determine the security level of Wide Area Monitoring System and priority bus. Optimization problem is formulated by minimizing the number PMU installed and maximizing the coverage N-1 contingency and solved using Binary Integer Linear Programming. For showing the performance of proposed method, IEEE 57-Bus test bus system is used as test system, which shows flexible result of PMU number and location depending on the desired reliability and voltage stability level.

The effects of the transfer switching on the low voltage side of quality control center in FRIENDS

The authors have proposed FRIENDS as a concept of the future electric power system. In order to realize FRIENDS, it is necessary to design the concrete interior structure of quality control centers (QCC) which are newly installed between distribution substation and customers, and develop a method for controlling QCC appropriately. QCC is divided into two parts; high voltage side and low voltage side. Up to now, the authors have designed each part of QCC independently. This paper investigates the performance of QCC in more detail by integrating these two parts. Further, two kinds of novel method for transferring the power to be supplied from one feeder to the other feeder are presented. The effectiveness of the proposed method is ascertained through numerical simulation using the PSCAD/EMTDC.

Cooperation of energy storage systems and biogas generator for stabilization of renewable energy power plants

The Ministry of the Environment of Japan has promoted the demonstration project named “wide-area operation systems for multiple renewable energy power plants”. The purpose of wide-area operation system is to stabilize the total generation output of photovoltaic (PV) power plants and wind farms using energy storage systems (ESSs) and a controllable renewable energy (RE) generator based on the weather forecasts and online synchronized generation output monitoring. In this paper, detailed control strategy for ESSs and a controllable RE generator is proposed considering the energy/power ratios. The efficacy of proposed control strategy is ascertained through chronological computation simulations using actual observed and forecasted solar irradiance data at Wakkanai PV power plant.

Study on Voltage Regulation in a Distribution System Using Electric Vehicles - Optimal Real and Reactive Power Dispatch by Centralized Control -

A surge of needs for the low carbon society promotes a spread of electric vehicle (EV). EVs could be charged at night simultaneously. That could cause severe voltage drop. Typical charger for EV employs the self-commutated inverter, which can control both active and reactive powers in principle. The authors have investigated potential availability of EVs for the distribution system operation qualitatively, and have concluded that the utilization of reactive power from EV charger could provide great potential for voltage regulation in the distribution system without loss of EV owners convenience. The authors have proposed some voltage regulation algorithms using EVs. This paper proposes a new algorithm - a centralized control method in which the distribution system operator collects information of each EV in the distribution system and controls them.

A Method for Balancing the Supply and Demand in an Isolated System Consisting of Voltage Control Type Inverters in FRIENDS

The authors have proposed Flexible, Reliable and Intelligent ENergy Delivery System (FRIENDS) as a future power distribution system. In the FRIENDS, new facilities called quality control centers (QCCs), which consist of power electronics devices, distributed generators (DGs), energy storage systems (ESSs), etc., are installed between distribution substations and customers. By controlling and operating those devices in QCCs adequately, various functions can be realized. Particularly, when a power supply from the transmission network is interrupted, isolated local networks which consist of some QCCs are composed in order to realize uninterruptible power supply. In the isolated local network, the DG and ESS in QCCs are employed as backup generators. This paper proposes a novel distributed and autonomous method for balancing the supply and demand during isolated operation. This paper also investigates the effectiveness of the proposed method through some computational simulations using PSCAD/EMTDC.