Takayuki Tanabe

Analysis Results of Output Power Loss Due to the Grid Voltage Rise in Grid-Connected Photovoltaic Power Generation Systems

This paper describes the connected photovoltaic (PV) power generation systems grid overvoltage protection function and summarizes the occurrence of the output power loss due to the grid voltage rise. Power injection from the PV system will raise the voltage at the power distribution line. A power conditioning subsystem (PCS) needs to regulate its output if the voltage becomes higher than the upper limit in order to avoid the overvoltage at the power grid. Thus, a PV system cannot generate electricity under the high grid voltage. There are 553 residential PV systems installed in Ota, Japan, for the demonstration research project of clustered PV systems. Measurement data of these 2.1-MW grid-connected PV systems are used for the analysis. Only the limited number of PV systems experienced a significant amount of output energy loss due to the high grid voltage in a particular day, whereas the other systems outputs also raise the grid voltage. The causes of this maldistribution of the output energy loss are the difference of the line impedance, the difference of the starting voltage of the PCSs grid overvoltage protection function, and the imbalance of the load in single-phase three-wire power distribution systems. The present control of the PCS successfully avoids the overvoltage on the grid but cannot share the loss.

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.

An autonomous agent for reliable operation of power market and systems including microgrids

This paper proposes a multi-agent approach to microgrid power system operation. The proposed method consists of several Loads Agents (LAGs) , Generator Agents (GAGs) and a single Microgrid Control Agent (MAG). The target of this study is to maximize revenue from the microgrid. To demonstrate its capability, the proposed electricity trading algorithm is applied to a model system. The simulation results show that the proposed multi-agent approach is promising.

Optimized operation and stabilization of microgrids with multiple energy resources

A microgrid supply/demand control system is proposed. In this control system, operation planning is realized based on generation and load forecasting by using artificial neural network and fuzzy systems. Unit commitment of generation includes start/stop of power generation and energy storage. Load following function is accomplished based on PI control scheme. To compensate for the power fluctuation in microgrid, power system stabilizer with EDLC is proposed.

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.

A loss minimum re-configuration algorithm of distribution systems under three-phase unbalanced condition

Many single phase distributed generators (DGs) - such as solar cells, small scale gas-engine CHP systems, etc. - are being installed in an electric power distribution system in recent years. These distributed generators are not always generating steady power due to the weather conditions or hot-water demand conditions, etc. Therefore, DGs could make ldquobalanced three-phase loadrdquo unbalanced. Unexpected load unbalance creates many unpredicted problems in power distribution systems: voltage unbalances, frequency deviations, etc. It is also known that the loss minimum normal open sectionalizing switch positions for three phase unbalanced conditions are not the same as the ones calculated by assuming three-phase balanced. Therefore, a method to find the optimal normal open sectionalizing switch positions that minimize both distribution loss and three phase unbalance is required. The problem is the multi-objective planning problem, and the palate solution must be found. In this paper, a solution algorithm for loss minimum re-configuration is explained and several numerical examples are shown.

The characteristics of higher harmonics in clustered PV systems

The PCS on the market approved by Japan Electrical Safety & Environment Technology Laboratory (JET) is satisfactory for the standards specified in the governments guideline of higher harmonics. So problems of higher harmonics are less serious than those of others in the present time. However the characteristics of higher harmonics are partially unknown if clustered PV systems are interconnected to the distribution line. In this research, higher harmonics voltage and higher harmonics current and phase are measured as for as 39 harmonics every one minute. We investigate quantity of generated higher harmonics and the transition. This investigation is carried out for PV-Systems made by main 4 manufacturers in Japan

An influence of voltage sag on nonutility generator shaft torque

An influence of the voltage sag on the shaft torque of the nonutility generator connecting to the utility system is investigated. During the oscillation of the generator electromagnetic torque, the mechanical shaft torque also oscillates according to the mechanical oscillation modes. In this situation, the shaft might be damaged. Three phase voltage sags are simulated by using ATP-EMTP, changing the fault point impedance and the short-circuit impedance of the utility system while the transformer impedance and the generator parameters are kept constant. The state equation of the generator mechanical system is investigated by using MATLAB/SIMULINK. Numerical simulation results show that the waveform of the electromagnetic torque is influenced not only by the fault point impedance but also by the short circuit impedance of the utility system, and thus a special condition of both impedances, in which the shaft torque has a maximum amplitude, could be found.

An active network control method using distributed energy resources in microgrids

An active network control method using distributed energy resources in microgrids is shown. Some features of the system were outlined. And also, power system stabilizer to compensate for the fluctuation of active power in microgrid is proposed. The microgrid with these new techniques can contribute to efficient operation of DGs and stable power supply for customers.