# On Transient Stability Problems in DC Microgrids
## 1 Introduction  
The rapid advancement and widespread deployment of solar photovoltaic (PV) generation and grid-scale energy storage systems are significantly accelerating the global transition towards a more sustainable energy landscape. In contrast to conventional synchronous generators (SGs), which produce alternating current (AC) power, PV generators and energy storage devices such as batteries and ultracapacitors generate direct current (DC) outputs. This DC characteristic enhances power-transfer efficiency in specific scenarios by reducing the need for conversion stages [1; 2]. By integrating power converters, DC generators, DC loads, and storage units, these components can form DC microgrids (as illustrated in Figure 1). These microgrids offer versatility, enabling both autonomous operation in remote areas and connection to the main grid [3; 4], therefore contributing to a more flexible and resilient energy infrastructure. Ensuming system stability is of utmost importance in both large-scale traditional grids and smaller-scale AC or DC microgrids. Stability can be broadly classified into two aspects: Small-signal stability and large-signal stability. The primary distinction between these lies in the magnitude of disturbances, which determines the applicability of system linearization [5]. Small-signal stability issues have been extensively investigated using various methods, such as transfer functions and state-space models [6; 7], providing valuable insights into system behavior under minor perturbations. In contrast, significant attention has been given to addressing large-signal stability problems involving more substantial disturbances since the pioneering work by [PERSON] et al. in the 1980s [8; 9]. Researchershave dedicated considerable efforts to comprehending and tackling these challenges to ensure robust and reliable operation of both traditional and microgrid systems [10; 11; 12; 13]. Currently, several potential factors contributing to large-signal instabilities in DC microgrids have been identified. These factors encompass the interaction between duty cycles and state variables [8], the presence of constant power loads [14], and the maximum power point tracking of photovoltaic (PV) panels [15]. Each of these elements can introduce nonlinear dynamics that pose challenges to system stability. In both AC grids and microgrids, transient stability issues arise when the active power transfer between synchronous generators (SGs) or grid-forming converters exceeds their capacity limits [5; 16]. This situation can lead to a counterintuitive effect where a further increase in the power angle actually reduces active power injection, creating an undesirable positive feedback loop [5; 16; 17]. The practical implications of transient stability problems are significant in both AC and DC microgrids. In AC microgrids, transient instability can cause loss of synchronization among generating units, resulting in power oscillations, voltage fluctuations, and potentially system collapse [18]. These issues lead to power supply interruptions, equipment damage, and safety hazards. Similarly, in DC microgrids, transient instability manifests as voltage instability, power fluctuations, and system breakdown [19]. However, the unidirectional nature of power flow in DC microgrids presents unique challenges in maintaining stability, particularly under high penetration of constant power loads and rapid load changes [20]. Transient instability in DC microgrids can disrupt critical loads, damage sensitive electronic devices, and hinder the reliable integration of renewable energy sources. Recent studies have made significant progress in stability analysis of DC microgrids. [PERSON] et al. [21] investigated the inertia issue in power electronics-dominated power systems and its impact on stability, proposing potential solutions. However, their focus was primarily on general power systems, not specifically on DC microgrids. [PERSON] et al.