Virtual Power Plant System Integration Technology

The history of commercial power system traces back to 1881 with Thomas Edison’s electric lighting company in New York; soon after that, his company installed hydroelectric power generation facility effectively in 1882. However, unlike present power systems, the first commercial power system employed direct current (DC) transmission and distribution. Those systems could not stay alive because the voltage could not easily converted to the high voltage with the available technology at that time. Besides voltage conversion constraint, protection and safety issues in distribution networks and consumer facilities were also concerned. Additionally, massive current flow was there due to low-voltage transmission (thereby causing resistive power losses). Hence, distant power transmission was unfeasible due to consequent voltage drop because of significant resistance of longer transmission lines for greater distances.

In previous chapter, we mentioned that the basis of the commercial power system is the accurate operation of the AC synchronous generators. In this chapter, we will explain the relationship between the precise operation of the AC synchronous generators and the instantaneous supply–demand balance.

As described in the proceeding chapters, in present power system, the demand and supply are controlled only by generation side, according to the fluctuation of the power consumption on the demand side. However, if the number of renewable power generation facilities such as solar power generation and wind power generation increases, the proportion of the amount of supply that can be controlled by governor control or LFC control described in the Chap. 2 decreases relatively and control according to the demand side becomes difficult.

Chapter 1 explained that the fluctuations in renewable energy generation is a major cause of the imbalance between supply and demand. By connecting the battery system as a power source to the grid, it is possible to reduce the fluctuations of the renewable energy generation. That is, if the power supply is insufficient, the battery can be discharged to reduce the power demand. And if the power supply is excessive, the battery can be charged to increase the power demand, thereby contributing to the balance between supply and demand (IEEJ JEC Technical report, "Standard specifications for energy service by storage battery system JEC-TR-59002", 2018).

According to the literature, the power batteries can be broadly divided into the following three categories as their usage. The first is a system frequency fluctuation suppression measure, which has been used mainly in thermal and hydroelectric power plants, but in recent years, demand and supply adjustment with a fast responsive power storage battery system has come to be expected. Secondly, it is used as a measure against surplus power, and surplus power is generated during the daytime due to the recent large-scale integration of photovoltaic power generation. In order to avoid the wastage of such natural energy, it is useful method that charges the battery with surplus energy like a pump in a pumped storage hydropower plant. Third, it is used as a virtual power plant, which is the theme of this book. Charge and discharge capacity of batteries installed in a distributed manner is centrally controlled by advanced ICT network technology. This is a convenient method that controls the charge and discharge power as a single power plant by remotely controlling the grid-connected power conditioner of the power storage battery system group.

Building multi-type air-conditioning is considered to be promising as a negawatt generation load of FastADR by power control among a number of power customer facilities. There are two reasons for this. First is the high penetration of building multi-type air-conditioning and the high power consumption. In general office buildings, in case of Japan, the power consumption of air-conditioning accounts for about 50% of the entire building, and in particular, building multi-type air-conditioning is installed in large quantities in small and medium-sized office buildings. Second, the equipment does not have a serious adverse effect on occupant compared to other consumer equipment (such as lighting).

The refrigerant compressor accounts for 90% of the power consumption of building multi-type air-conditioning. Therefore, in this chapter, the power consumption of the refrigerant compressor is modeled based on the principle of the refrigeration cycle.

Data such as demand response events in OpenADR is exchanged in XML format and messages are defined in XML Schema Definition Language (XSD) [W3C standard, XML Schema Definition Language (XSD) 1 Part 1: Structures. W3C Proposed Recommendation (2012). http://​www.​w3.​org/​TR/​2012/​PR-xmlschema11-1-20120119/​]. There are two query method PUSH type and PULL type. The difference between PUSH type and PULL type is the communication protocol corresponding to the subject when the message is transmitted from VTN to VEN. In the case of PULL, VEN is main component, and message notification is periodically requested (polled) to the VTN, and HTTP is used as the communication protocol. In the case of the PUSH type, the VTN is the main component, the message is directly notified to the VEN, and HTTP or XMPP (Extensible Messaging and Presence Protocol) [P. Saint-Andre, Extensible Messaging and Presence Protocol (XMPP): Core. RFC61020 (2011)] is used as the communication protocol.

Taking Japan as an example, the number of installed building multi-type air-conditioners in Japan estimated to be 1.52 million outdoor units. Here, the building multi-type air-conditioner is not an entire commercial air-conditioner, but a part of a packaged air-conditioner in which multiple indoor units are piped to an outdoor unit. There are about 5–10 indoor units per outdoor unit of a building multi-type air-conditioner, the order of indoor units is estimated to be 10 million units. There are various types of outdoor units with different air-conditioning capacities, but 10 H.P class, which is the representative model, that is, the rated cooling capacity is about 28 kW, the rated power consumption per unit is about 10 kW. It can be said that the total installed power is about 15 million kW. Of course, since it is partly operated on a daily basis and the average power consumption is less than the rated value, it goes without saying that only a few percent can be used as negative wattage resources. However, there is no doubt that the installed capacity is a useful load type.