## 2 Virtual Power Plant (VPP) Communication Architecture  
### VPP Communication Architecture  
Information and communication technology (ICT) is indispensable for VPPs. The VPP communication architecture is divided into three layers based on their respective functions as shown in Figure 1. Its three layers include the VPP platform communication layer, the remote communication layer, and the local communication layer. The communication architecture enables the VPP to monitor the various DERs. From the perspective of the uplink direction, it provides real-time data transmissions of the collected device status to the VPP control platforms. A large quantity of energy storage, controllable loads, and electric vehicles are connected to the VPP control platforms through the communication architecture. From the perspective of the downlink direction, the instructions are generated by the VPP control platforms. For example, the power dispatching instructions and frequency regulation instructions are distributed to the corresponding VPPs and their aggregation control gateways through the communication architecture. The end devices perform the instructions to maintain the stability of the power grid system. The local communication layer enables the communications inside the VPP, while the remote communication layer connects the VPPs to the VPP control platforms. The three-layer VPP communication architecture divides the communication functions based on their different communication requirements. In addition, both wireline and wireless communications are considered in the design to provide heterogeneous access for various end devices. The VPP platforms include the VPP control platform, the power dispatching cloud platform, and the power trading market operation platform. They perform the functions of power control, power dispatching, and power trading, respectively. The power dispatching cloud platform communicates with the VPP control platform by exchanging the power dispatching information and responding information. The VPP control platform sends the power transaction confirmation information to the power trading market platform, while it provides the corresponding settlement information to the VPP control platform. The communications among them are named VPP platform communications. They are enabled by the remote wireline and wireless communication technologies. The three VPP platforms are considered as one large VPP control platform from the perspective of the various end devices. The remote communication layer consists of wireline and wireless communication networks to connect the large VPP control platform and various end devices through VPP aggregation control gateways. Traditional remote communication technologies include Ethernet, optical networks, 4G LTE (long-term evolution), and dedicated wireless networks for power systems. Ethernet is a cost-effective communication solution thanks to its wide deployment and commercial maturity. But Ethernet cannot guarantee the packet delay and packet loss performance resulting from network congestion. Optical networks provide a large capacity and reliable data transmissions. However, they lack flexibility in network access and they increase the cost of network deployment. The dedicated wireless networks for power systems operate at the frequencies of 230 MHz and 1800 MHz. They are only deployed in some cities and they lack the performance guarantee in terms of delay and reliability. The 4G LTE has been deployed in almost all cities. It is suitable for status data collection in VPP systems. However, LTE technology has limited capabilities to guarantee the transmission of the critical data and the large volume of collected data at the same time. The local communication layer connects the VPP aggregation control gateways with the various VPP end devices, such as various DERs (e.g., wind power and photovoltaic generation), energy storage, controllable loads, and electric vehicles. It enables communication among them inside the VPPs.