## 2 Network Attacks in Distributed Photovoltaic Microgrids
### Network Attacks in Photovoltaic Microgrids  
False Data Injection Attack (FDIA): The objective of FDIA [25] is to disrupt the normal operation of the system by injecting erroneous data into it. Attackers can manipulate sensor data or data packets in communication channels to provide the control center with incorrect system state information, leading to erroneous decision-making and control operations. In photovoltaic microgrids, attackers may tamper with data related to photovoltaic generation, energy storage status, or grid connection status, causing the system to incorrectly schedule and allocate power resources. Specifically, attackers may launch FDIA against sensors monitoring current, voltage, and power within the photovoltaic array and converters. These sensors utilize the Electromagnetic Interference (EMI) method. As described in [26], the attack model is represented by Equation (1).  
\[\begin{cases}V_{A}=a_{V}(V_{o}+A_{V})\\ I_{A}=a_{I}(I_{o}+A_{I})\\ P_{A}=a_{P}(P_{o}+A_{P})\end{cases} \tag{1}\]  
In this context, \(V_{A}\), \(I_{A}\), and \(P_{A}\), respectively, represent the measured values of voltage, current, and power output within the target device by the attacked sensors. \(a_{V}\), \(a_{I}\), and \(a_{P}\) denote arbitrary attack multipliers for the measurements of different sensors. \(A_{V}\), \(A_{I}\), and \(A_{P}\) represent arbitrary attack additions for the measurements of different sensors. This amplification and biasing result in the malicious manipulation of the original measured values \(V_{o}\), \(I_{o}\), and \(P_{o}\) of voltage, current, and power, respectively. As a consequence, sensor monitoring is manipulated, leading to the disruption of normal operations, and, potentially, the direct shutdown or damage to the equipment. However, FDIA is subject to intensity constraints and must be carefully designed to maintain stealthiness. The values and rates of change of the attack signal must fall within acceptable ranges; otherwise, the attack will fail to evade defense mechanisms and lead to failure. It is worth noting that stealthy FDIA poses challenges to detection tasks. For example, for voltage sensors, the attack must satisfy the constraints described in Equation (2) as described in [26].  
\[\begin{split}\mid V_{A}\mid<V_{MAX}\\ \left|\frac{dV_{A}}{dt}\right|<R_{MAX}\end{split} \tag{2}\]  
where \(V_{MAX}\) represents the acceptable magnitude of the attacked voltage measurement, and \(R_{MAX}\) is the maximum value of the rate of change.  
Denial-of-Service Attack (DoS): A DoS attack [26] aims to disrupt the normal functioning of a system by rendering certain parts of it inaccessible. Attackers achieve this by flooding the system with a large volume of useless data packets or exploiting vulnerabilities to overload critical components (such as sensors or communication networks), rendering them unable to function properly. In a photovoltaic microgrid, a DoS attack may prevent  
Figure 1: Framework of photovoltaic microgrid energy storage systems and their network attack threats.  
the control center from obtaining real-time data, thereby impacting the overall operational efficiency and stability of the system. This type of attack can be represented by Equation (3), as described in [26].  
\[x(k)=\begin{cases}x(k)&k\leq k_{a}\\ x(k_{a})&k\geq k_{a}\end{cases} \tag{3}\]  
where \(x\) represents the data of monitoring or control commands. \(k\) is the time index, and \(k_{a}\) is the time index when the DoS attack begins. In the field of photovoltaic microgrids, DoS attacks may pose a serious threat to the operational safety of damaged equipment. For instance, interruptions in voltage sensors within the photovoltaic array and corresponding inverters can disrupt MPPT control, significantly impacting photovoltaic power output and causing deviations in DC bus voltage. Consequently, efficient detection and defense mechanisms need to be researched and developed to safeguard the secure operation of photovoltaic microgrids against common network attacks such as FDIA and DoS.