## 3 Establishment of the GVPP
### Design of the GVPP  
In order to realize the grid-friendly function, the resources of a virtual unit should be evaluated and controlled to promote the accommodation of RESs in the inner level, operate as spinning reserves for power support under contingencies, and respond to commands from the system level. Because of the spatial distribution of aggregated DERs, the GVPP virtualize all the DERs into a single point, which is represented as a virtual PCC (VPCC). In the system level, the output characteristics of a single VPCC rather than the numerous PCCs of inner DERs are detected and controlled. The proposed GVPP is demonstrated in Figure 6.  
Considering the types of consumers, the GVPP can be classified into three types with residential, industrial, and commercial loads, respectively. GVPP can incorporate the uncontrollable loads, traditional generators, RESs, ESSs, and controllable loads, and so on. More specially, the crucial loads, such as government, hospital, and precision production, in the region of a GVPP are uncontrollable, of which the forced outage may lead to great loss. The output power of RESs, such as WTGs and PV panels, can be adjusted by adding strategies to their control systems. But the control performances of RESs are restricted by their primary energy resources. Thus, the high-controllable generators and ESSs are necessary to establish a GVPP. In addition, the controllable loads, such as EVs, air conditioners, and water heaters, can be used to enhance the controllability of GVPPs, whose interruption results in little cost. In order to realize the operation, the inner architecture of a GVPP is provided based on multi-agent technologies, as shown in Figure 7. The two layers of the GVPP and state grid are included. The GVPP layer is the main part of the architecture, which consists of the energy assets in Figure 6, inner network topology, and the corresponding control systems. Moreover, the GVPP layer interacts with the state grid layer through VFCCs. In the state grid layer, the agents and entities corresponding to the dispatch and control system, and other infrastructures, such as centralized power plants, transmission network, and network network, are incorporated. In addition, the physical, communication, and control agents are deployed and integrated to realize the operation of a GVPP. The physical agents abstract the energy assets of GVPPs, so as to depict and estimate the state of these assets. Considering the spatial distribution of aggregated energy assets, the communication agents are necessary, which  
Figure 6: Schematic diagram of the proposed grid-friendly virtual power plant (GVPP). Figure 7: Multi-agent architecture of a GVPP. exchange information among agents, and transfer data and commands between the GVPP and state grid layers. Moreover, the control agents operate to manage the states of energy assets, of which the output power and on-off status are adjusted. From Figure 7, the control agents consist of the optimal dispatch agent, emergency response agent, RES control agent, ESS control agent, flexible load management agent, and load shedding agent. More specially, the optimal dispatch agent provides the operation strategies of the GVPP under normal condition. In addition, the emergency response agent is activated when the power system is subjected to large disturbances. The emergency response agent will displace the optimal dispatch agent and take over the control of the GVPP to provide grid-friendly power support for the power system. The RES control agent determines the operation strategies of RESs, such as the distributed WTGs and PV panels. Additionally, the charging and discharging power of ESSs is managed by the ESS control agent. The flexible load management agent is deployed to carry out the flexible demand response of EVs, air conditioners, water heaters, and so on. Furthermore, the load shedding agent is utilized to deal with the extreme contingencies and prevent power system collapse.