According to “PV2030+,” a roadmap to photovoltaic (PV) generation dissemination announced by NDEO, 10% of the total electric energy and 50% of the total electric power in Japan, which equals to 102GW, will be covered by a large penetration of PV in a few years ahead of the original plan of 2030. This makes an approach to install a large amount of PV generation to reduce CO2 emission gaining momentum. Therefore, developing a new structure of control technologies to achieve a stable electric power supply using PV generation forecasts is urgent. In addition, there are needs to fundamentally review frameworks of the entire system to achieve the supply and demand balance. Electric power supply systems will be renewed after the separation of electrical power production from power distribution and transmission, and the deregulation of electricity. Developments of new mechanisms, such as demand response, from advancements in information infrastructures and home battery technologies also cause the necessity to review the frameworks.

To begin with our research, we evaluated numerically, in each case of 28~64GW, 102GW, and 330GW of PV generation installed, the power generating conditions of thermal power generation equipments under a power source composition which uses current thermal power generation equipments as the main power source for adjustment, and PV-prediction error distribution caused by the current prediction techniques. The following is the summary on ingredients to be considered in electric power system under a large penetration of PV:

• (i) Advanced control based on PV generation predictions is essential under a large penetration of PV generation, however, countermeasures to non-uniform prediction errors like outliers are necessary. For example, cooperated control techniques spatiotemporally integrating control techniques at various steps like UC, EDC, and LFC should be developed.
• (ii) A large penetration of PV systems based on the practical use of batteries will reduce the number of rotator types of generators, and appearance of aggregators, balancing groups of suppliers, and xEMS from the electricity deregulation is expected to drastically change the current generation composition. Therefore, the role of conventional power sources will change, and thermal generators will devote on only operation responsibility for example. There will be also a necessity to effectively integrate such system control with many different markets such as one-hour ahead markets and regulation markets.

The goal of this research, as shown in Fig. 1, is to develop a system theory for the more advanced generation electric power system control by fully exploiting demand/PV predictions and focusing on properties and functions of a middle layer (called here a harmonized aggregator). The middle layer is expected to take many different forms such as demand-side energy management systems (FEMS, CEMS, etc.), cooperative power conditioners (PE-AG), demand response aggregators (AG), and balancing groups of suppliers (BG). In particular, as a basic theory and technology to be the core of harmonized electric power systems control to enable PV introduction of 102GW, and further towards PV introduction of 330GW, we aim to develop the following fundamental theories and technologies:

1. Electric Power System Design: A system design theory composed of supply layer, middle layer, and consumer layer.
2. Prediction Technology: A PV generation prediction technology adapted to power system control techniques that achieves a stable power supply.
3. Control Technology: A power system control theory and technology to realize a harmonized stable power supply from the perspectives of fairness and comfort as well as the economics and environmental friendliness, by fully exploiting PV generation predictions.

Fig. 1 Framework of the more advanced generation electric power system control

As a result of our research, we expect to develop a basis theory to realize electric power system control that harmonizes the entire system in terms of economy, environmental friendliness, fairness, and comfort even under uncertainty in PV generation predictions. With this expectation, we can provide a fundamental framework of a future power control system that allows us to continuously introduce up to 102GW of PV, setting 64GW, the target set by the Japanese government, as a checkpoint, and that can be further developed towards a stable supply under introduction of more than 102GW. In addition to the above, we aim the following:

• Development, management, and operation of a collaboration room:
  By developing a collaboration room that realizes powerful collaborative research through electric power simulations, we can offer a new collaborative research method for developing new cooperative control techniques of electric power systems.
• Workshops involving related enterprises:
  Throughout this kind of workshops, we can develop a basic theory and technology adapted to practical implementation.
• Development, management, and operation of an electric power portal site:
  Developing a portal site allows us to open our research results and data such as electric power to the public, and to offer information and data necessary for related researches.

1. The basic theory of system control that this research develops focuses on PV generation in terms of introduced renewable energy. This research also constructs a basis system theory based on universal principles on integrity, spatial-temporal resolution, global vs. local characteristics, efficiency, risk and resilience, etc., in order to efficiently manage uncertain and different distributed energy. Therefore, this research will provide a basis leading to various system design theories that efficiently manage different sources of energy including other renewable energy, thermal and gas.
2. Not only for electric power systems and energy systems, results of this research will lead to a development of theories for building social systems such as the next generation or the more advanced generation traffic systems, physical distribution/transportation systems, economic systems, and communication systems, and the entire system that unifies these social systems. We hope that this research will provide a basis for a system theory that optimizes socials systems in which multiple large-scale complicated networks interact with each other.

To accomplish the goal of this research, we perform researches centered on the following two main topics:

• （A） (Harmonized electric power system control using PV generation predictions) Development of electric power system control theory and technology based on PV generation predictions including huge errors, to achieve a harmonized electric power stable supply from the social system points of view such as economy, environmental friendliness, fairness, and comfort.
• （B） (Electric power system design composed of supply layer, middle layer, and consumer layer) Development of a system design theory to optimize the entire electric power system by focusing on the role of various aggregators in the middle layer. Aggregators, the third function not included in the supply layer and the consumer layer, are originated from with reference to changes in electric system structures such as a large penetration of PV and batteries, the electricity deregulation, and the separation of electrical power production from power distribution and transmission.

Especially in (A), in addition to developing the technology of PV prediction and analyzing large prediction errors, it is of importance when corresponding to a large unexpected error to develop a completely new cooperation system control including the demand-side. This new cooperation system control will reform the conventional control structure, which is divided based on time-spatial resolutions such as UC, EDC, LFC, and GF. In (B), in addition to constructing frameworks to integrate system control and markets under the electricity deregulation, the role of the middle layer involving balancing groups in the supply-side, DR aggregators in the demand-side, and cooperative power converter in distribution systems is clarified to optimize its system and to evaluate its efficiency.

To promote this research from the above two points of view, it is executed according to the following five units, as shown in Fig. 2:

• PV Prediction Unit:
  Develops high precision PV generation forecasting and estimation technology for the entire spatial-temporal region, merging large scale generation data and variety of weather resources.
• Supply and Demand Control Unit:
  Clarifies the roles of conventional power sources under supply and demand control/operation of the more advanced generation, and realizes cooperative control techniques with the conventional and the other regulating power resources.
• Demand-Side Control Unit:
  Develops basic theory and technology for cooperatively utilizing the flexibilities of consumers having PV generations and batteries under ensured comfort and fairness. This achieves the demand-side control in order to contribute the maintenance of the system supply and demand balancing.
• Control of Transmission and Distribution Grids Unit:
  Develops theory and technology to solve the stabile operation problem of transmission and distribution grid (synchronized stability, overload, voltage, etc.), taking account of spatial output fluctuation characteristics of PV generation and its possibility to forecast.
• Basic System Theory Unit:
  Develops basic system theory and technology for optimally designing the entire system composed of supply layer, middle layer, and consumer layer, from the various points of view such as system, integrity, and stability.

Fig. 2 Two main research topics and five units