## 1 Introduction
A residential-level fast load-control scheme is proposed, where the starting point and the power deficit of the disturbance event are estimated by the distribution-level phasor measurement [24]. A hierarchical control architecture for distribution network VPP to manage the inverter and deferrable loads is proposed to provide a fast frequency response to the bulk power system, where the resources coordination strategy is solved online after a frequency event occurs [25]. EVs installed in distribution networks are grouped into VPP, and a frequency-dependent absorbed power control scheme for EV clusters is proposed to provide a fast frequency response to the transmission network [26]. The above works mainly focus on one type of DERs for frequency control and cannot be directly utilized to coordinate multiple resources for event-driven EFC. An online coordinated control of emergency demand response and HVDC modulation is proposed, where the emergency demand response aggregation model is simplified as a delayed step function by ignoring the difference in response speed between DER devices [27]. With the diverse device types and the large number of devices in VPP, it is critical to determine the response priority of DERs [28]. Several indicators that need to be considered to build priorities are given, which include load importance, frequency dependence, control cost, energy efficiency, and customer satisfaction [29]. The controllable characteristics of DERs are restricted by user behavior, so the priority index needs to consider user comfort [30]. An OFF-time priority-based control method for fridges to provide secondary frequency control is given, where the fridge with the longer OFF time has the higher priority [31]. A temperature-priority-list method for AC participating in primary frequency regulation is adopted, where the device with a low room temperature will have a high priority to be turned off [32]. A dynamic criteria of EV priority is proposed for load shedding, where the priority parameters include state of charge (SOC), slack time, and completed charging intervals [33]. A priority list considering willingness and charging power for EVs participating in under-frequency load shedding is expressed [34]. The above works mainly focus on presenting quantitative indicators for the priority of single-type DERs. With the help of the Internet of Things and low-latency communication such as 5G, VPP can realize high-precision condition monitoring and low-latency transmission of control instructions with massive DER devices [35; 36; 37]. VPP aggregates devices that guarantee user comfort to participate in EFC, reducing the impact of the ELS on residents, so its control cost is lower than the ELS. The response speed and control cost of ELS and VPP are complementary. However, few works have been focused on the coordination of VPP emergency power regulation (VEPR) with the existing control resources for EFC. Moreover, DERs are dispersed, and their communication means can be diverse. Therefore, the difference in communication delay and response speed of different DER devices should be considered when constructing the VPP response process for EFC decision-making. Meanwhile, there are several DERs types in VPP, and the response priority of DERs needs to consider the differences in the flexible duration between different devices. To further reduce the EFC control cost for the receiving-end power grid and make full use of the massive controllable DERs on the demand side, this paper manages and controls the demand-side DERs in the form of VPP to provide VEPR and proposes an EFC strategy with the coordinating multiple control resources. The main contributions of this paper are three-fold. Firstly, an EFC strategy with multiple resources coordination for dealing with a HVDC blocking disturbance at the receiving-end power grid is proposed to minimize the total control cost while meeting constraints on rotor angle stability and frequency deviation security.