## 1 Introduction
For Europe, Spain implements a scheme of selectively shedding load based on a pre-determined criterion when imbalance of supply and demand is critical. Norway determines the load shedding amount based on offline analysis. The installed capacity of DERs has increased significantly in industrialized countries in the last decade. High penetration of DERs could affect the power grid during system emergencies, potentially causing DVR events. One of the most important renewable power technologies is wind generation. A certain number of Type-1 induction generators are still operating in conventional wind farms. As a result, the dynamic behavior of induction machines has a significant impact on stability [28; 29]. Wind generation facilities to DVR events are possibly exposed in the systems with a large amount of IM loads [30]. In [31], the effect of this problem was analyzed for the doubly fed induction generator (DFIG). The recent blackout event in South Australia clearly illustrated the catastrophic impact of DVR on a high-level wind energy penetrated power system [32]. A DVR problem was detected in [33] by a photovoltaic (PV) panel connecting to the power system, considering the impact of fault ride through (FRT) and dynamic reactive power support of large-scale PV systems on short-term voltage stability [34]. This paper analyzes the two aspects of modeling IM loads and countermeasures mitigating DVR, as well as the impact of IM loads on power systems. Since the proportion of IM loads is gradually increasing in today's power systems, transient voltage collapse due to short-term voltage instability might occur, and this can be a major threat to system security. The driving force of the problem is the tendency of aggregated IM loads to restore power consumption [23]. Thus, adequate IM modelling is very important to capture DVR phenomenon associated with short-term voltage stability (STVS). The DVR is directly related to the degree of IM-load penetration, especially that of residential air conditioning (AC) in the power system. The U.S. Department of Energy (DOE) recognized the concerns of DVR events because of the increasing penetration of AC loads and started to deal with it as a national issue [35]. In the Republic of Korea, the demand for AC loads has grown significantly over the last few years, especially in summer seasons. The AC load in Korea occupies about 30% of the total load, and because of this the Korean power system might suffer from insufficient compensation of reactive power, possibly leading to an unacceptable voltage recovery after faults and critically to voltage collapse under summer peak load conditions. The purpose of this study is to improve the understanding of IM load impacts and to identify the appropriate countermeasures to ensure stability of the power system. The widely used composite load model (ZIP + IM) is adopted in this paper for the system loads. This paper analyzes the sensitivity of the IM load parameters, and uses data from the statistical system to estimate the proportion of IM loads on the summer peak condition. In this paper, a multi-phase UVLS (MUVLS) scheme is proposed to improve the voltage stability. In the UVLS mitigation scheme, the dynamics of IM loads are considered, utilizing voltage stability determination conditions to determine the most efficient load shedding strategy. Employing MUVLS can mitigate the DVR caused by IM load power consumption characteristics, and it can improve system security in the most economical way.