## 1 Introduction
Meanwhile, an active network management (ANM) framework is proposed in order to operate this hybrid network to its fullest potential. The ANM framework optimises the operation of multiple VSCs within the network and takes advantage of schemes such as flexible demand shifting and renewable energy curtailment to minimise operational costs and maintain a continuity of supply to all loads even after contingencies. The concept of steady-state operational security is well known for transmission networks. However, a similar concept has received little attention for distribution networks, mostly due to the radial configuration of distribution feeders. Notwithstanding this, the problem of operational security in distribution networks has been introduced in [20]. The work in [20] proposed a distribution system security region (DSSR), based on the concept of total supply capability (TSC) [21]. In this way, all operating points were determined, satisfying the \(N-1\) security criteria. The approach considered the capacities of substation transformers, network topology, and operational constraints. This concept was also applied in [22] at a varying load using network reconfiguration techniques to reduce total load shedding. Recently, a quantitative maximum DG output assessment was used in [23] based the concept of DSSR to guarantee the \(N-1\) secure operation of distribution networks. The work in [24] incorporated the situation awareness that involved three steps: Perception (i.e., data collection), comprehension (i.e., data analysis), and projection (i.e., data prediction) to carry out preventive actions toward any contingency events. However, the studies allow load interruptions during contingencies and lack of involvement from other network devices to react toward undesirable events. In our ANM framework, however, using the MVDC interface in conjunction with flexible demand and renewable energy curtailment entails that the operating of loads and grid supply points can be planned in advance (i.e., day-ahead) in such a way to keep the continuity of supply at contingency conditions given a \(N-1\) criterion in place. We, therefore, introduce a new distribution security constrained optimal power flow (D-SCOPF) that contains three stages, namely pre-contingency, short-term, and long-term post-contingencies to distinguish from the DSSR. The short-term contingency period is introduced in order to take advantage of the fast control of VSCs connected to the MVDC interface and distinguish from other slow reaction devices such as the tap changer in the long-term contingency period. Our contributions in this paper are three-fold: (1) A day-ahead distribution network management framework with flexible demand and DG curtailment to uphold the secure operation during contingencies, (2) an extended security constrained, which covers three stages, pre-contingency, short-term, and long-term post-contingencies, is used to highlight the different remedial action capabilities between slow response (i.e., load tap changer) and fast response (i.e., VSCs) control devices, and (3) a multi-terminal configuration of MVDC is introduced to alleviate the limitations of back-to-back (BTB) or point-to-point (P2P) configurations used in [7; 8; 9; 10; 11; 12; 13] and thus a more flexible network operation can be achieved. The MVDC interface works as a platform for renewable energy integrations at the end of distribution feeders that uses the same number of VSCs as in P2P configuration. This paper is organised as follows: A new active network management by adopting the flexible demand and non-firm distributed generation for security operational is presented in Section 2, Section 3 describes a mathematical model of the hybrid AC/DC network for a possible application within the ANM framework, Section 4 discusses case studies and comparison results of applying the ANM framework to the hybrid network, and finally, a conclusion is drawn in Section 5.