# Influence of Load Dynamics on Converter-Dominated Isolated Power Systems
## 1 Introduction
The occurrence of short circuits in networks operating with a high percentage of constant torque IM could lead to a delayed voltage recovery due to the IM stalling. In such cases, the stalled IM will draw a large amount of reactive power from the network (five to six times its steady-state reactive power regime), precluding successful voltage recovery [22]. The specific effects resulting from the load dynamic behavior in the network transient stability must be taken into account. Nonetheless, the works presented in [16; 17; 18; 19; 20; 21] do not address the relevance of this specific issue, particularly in converter-dominated systems where grid-forming-type converters have a major role. In this paper, the operation of an isolated power system with 100% converter-based renewable generation is addressed, where a BESS connected to the grid with a grid-forming-type power converter is responsible for providing voltage and frequency regulation capabilities. Regarding the load modeling, exponential and IM load model types are considered as representative of the main loads' dynamics, in line with recent works such as [11] and [20], while also evidencing scenarios where IM-type loads still have a high relevance in global load composition. BESS power converter sizing usually neglects loads dynamics [23; 24]. However, it is demonstrated that different factors associated with dynamic load modeling largely affect the need for oversizing its power capacity when conventional control solutions are adopted in these units. This is of high relevance in order to assure the successful recovery of all of the IM load following a network fault, since it is recognized as the most severe frequency stability contingency in converter-dominated and isolated systems [25]. On the other hand, voltage-sensitive (active and reactive) current injection during faults has been pointed out as a fundamental requirement in isolated systems with high penetration of CI-RES [26]. In this work it is shown that such requirements are not suitable for specific network operating scenarios with high shares of IM loads. Emerging from the identified gaps in the literature survey, two novel control strategies are proposed to be integrated in the power electronic interfaces of the available converter-based generators in order to support the successful recovery of IM loads following a network fault. The first approach consists of implementing an appropriate voltage/reactive current control strategy at the CI-RES (operating as grid-following units) during faults. The second approach consists of a dynamic modulation strategy for the reference voltage of the grid-forming unit during the post-fault recovery period. Both strategies intend to increase the electromagnetic torque of the IM loads during the post-fault period and hence contribute to its reacceleration. Finally, it is shown that the coordinated implementation of these two control solutions is beneficial in operating scenarios with very large shares of IM loads. It is worth noting that the positive relevance of the contribution of this work is naturally more notable as far as the share of IM load increase. In cases with a low share of IM loads, the need for the proposed solution is less relevant but still does not jeopardize system dynamics.