# A Review on Distribution System State Estimation Algorithms
## 5 Technical Requirements and Applications
### Applications  
Having discussed all the basic theory and technical requirements regarding DSSE, this sub-Section is dedicated to applications as well as actual projects where DSSE has been implemented.  
Regarding the applications of DSSE in distribution systems, research is mostly focused on RES penetration and \"green\" technologies, due to the ongoing energy transition. In this sense, it is quite common to find studies where DSSE is performed on distribution systems with high PV penetration. For example, the authors of [134] have performed DSSE in a distribution system with PVs using a typical WLS algorithm. Similar concepts have been studied by [51; 135], with the use of a variation of WLAV and a variation of EKF, respectively. Moreover, ref. [136] has performed DSSE in a distribution system that includes not only PVs but also Wind Turbines (WTs). In this case, the DSSE utilizes a DNN. In a more interesting scenario, ref. [137] has performed DSSE in a hybrid AC/DC system including PVs, WTs and diesel generators. The estimation is performed with the use of WLS, supported by a DNN. Finally, in a slightly different direction, the authors of [50] perform DSSE in a distribution system that is used to charge Electric Vehicles (EVs). For this purpose, a variation of the EKF is deployed.  
The various applications and methodologies found in literature are summarized in Table 6. It is noted that all sorts of algorithms that were discussed in sub-Section 3.2 have been used, meaning that there is no unique, optimal solution when it comes to actual implementation.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Application** & **Approach** \\ \hline PV [134; 135; 134] & Model based, such as WLS [134], WLAV [135] but also \\  & FASE, such as EKF variations [51]. \\ \hline PV and WT [136] & Data-driven DSSE, with DNN [136]. \\ \hline PV, WT and diesel generator [137] & Model-based WLS DSSE coupled with DNN [137]. \\ \hline EV charging [50] & FASE DSSE, with a variation of EKF [50]. \\ \hline \hline \end{tabular}
\end{table}
Table 6: Applications of DSSE [50; 134; 135; 51; 136; 137].  
Furthermore, there are many research and innovation projects, pilot use cases, Horizon 2020 programs, etc., where DSSE is applied on real smart grids. A map of the most well-known cases is presented in Figure 5, indicating the sort of algorithm that was deployed. More specifically, in the context of EVOLVDSO, DSSE was implemented in a 74-node LV distribution system in Portugal and a 77-node LV distribution system in France [138]. In both cases, the overall approach was based on ANN. Furthermore, the French DSO, Enediis, applied WLS DSSE in a MV system called the VENTEEA smart grid demonstrator [120]. A WLS DSSE was also applied on a MV smart grid in the UK in the context of the Low Carbon London project [139]. The Swiss DSO applied WLS DSSE as well, in a LV 102-node distribution system located in Switzerland [140]. For the purpose of SuSTAINABLE project, a WLS DSSE was demonstrated in a MV/LV distribution system in Portugal [141]. The Slovenian Research Agency funded the development of an EKF-based DSSE in a 97-node LV distribution system in Slovenia [50]. In Denmark, a WLS DSSE supported by an ANN for the generation of pseudo-measurements was demonstrated in a MV 52-node distribution system [142]. The SmartSCADA project demonstrated a WLS DSSE in a LV distribution system in Germany [143]. The LV SCADA project developed an ANN DSSE and demonstrated it in a LV system in Portugal [144]. Finally, the largest contribution regarding actual DSSE application is the one of INTERPRETER, which is a Horizon 2020 program with three demo-sites, in Belgium, Spain, and Denmark, where WLS DSSE is implemented by the current research group [145,146].  
Judging by the real-life applications, it can be concluded that the main option in DSSE remains WLS. This is mostly attributed to the fact that it constitutes an easy, fast, and tested-in-time algorithm.  
Figure 5: DSSE pilot project implementation [50,120,138,139,140,141,142,143,144,145].