## 1 Introduction
Considering the requirements of power system operation, the regional supply-demand balance is met by the optimal VPP dispatch. A dispatch model has been established to optimize the performance of multi-energy VPPs, where the economic cost and power quality are taken as the optimization objectives [21]. Moreover, based on the decision area division method, a multi-objective optimization model for VPPs has been established, and the average daily cost, load characteristics, and degree of RES accommodation and aggregation have been compromised [22]. In addition, the comprehensive prices for active and reactive power have been designed, on which a bi-level programming approach is proposed for the collaborative management of multiple VPPs [23]. Considering the uncertainty of multi-energy VPP operation, a scenario-based optimization approach has been proposed, which is applied to an electricity-hydrogen VPP [24]. Regarding the architecture design of VPPs, the communication system is one of the key infrastructures, on which the data collection and command transmission can be performed. With the utilization of standard-based power system communications, a service-oriented VPP architecture has been designed for the seamless integration of DERs [25]. Moreover, the communication, information, and functional requirements of VPPs have been analyzed, and the IEC 61850 protocol has been used to realize the interaction between the VPP controller and DERs [26]. In addition, the IEC 60870-5-104 protocol has been applied to a VPP, whose communication quality is quantified as latency, packet loss, retransmissions, bandwidth, amount of traffic, and message patterns [27]. Besides, the VPP architecture using the OpenADR 2.0b protocol has been established to operate DERs securely and reliably and provide auxiliary services [28]. As mentioned above, there have been numerous researches on the optimal planning, bidding, dispatching, and communication architecture design of VPPs, which are mainly concentrated on economic efficiency and engineering realization. However, there are a few researches on how VPPs can take part in power system security and stability control. Because of the problems of energy accommodation and power system security and stability caused by RESs, the concept of grid-friendly has attracted more and more attention [29; 30; 31]. The grid-friendly technology is proposed to improve the grid-connection performance of RESs to decrease the influence of volatility, uncertainty, and low inertia, and enhance the control ability of power system to deal with large disturbances. Besides establishing VPPs for power markets and economic efficiency, the VPP can be designed with grid-friendly characteristics, and used as spinning reserve for power systems under contingencies. The grid-friendly VPP (GVPP) is promising to solve the problems of RES accommodation and power system security and stability simultaneously. In this paper, a GVPP-based dispatch and control architecture for the power system in China is proposed to accommodate RESs flexibly and securely. Although the architecture is proposed for the China state grid, it can be applied to any similar power systems with high penetration of RESs. The contributions of this paper are listed as below:  
* The challenges stemming from non-synchronous RESs to the dispatch and control system of the power system in China are analyzed. * The functional requirements, concept, and fundamental design of the GVPP are provided, which has grid-friendly characteristics and contributes to improve RES accommodation. * A bi-level dispatch and control architecture is established based on the GVPP, considering two objectives to reduce the curtailment of local RESs and provide emergency power support. * The key problems to be solved in the development of the GVPP-based architecture are summarized, which are helpful for further and important researches in this field. The remainder of the paper is organized as follows.