## 2 Recent Trends in DC & Hybrid Microgrids
The fourth paper [4], entitled \"Improved Control of Forest Microgrids with Hybrid Complementary Energy Storage\", by [PERSON] et al. is also from China, particularly from the School of Technology, Beijing Forestry University. The paper proposes a hybrid complementary energy storage control method to improve the power quality and the fault ride-through capability of islanded forest microgrids. In the paper, mode-based sectional coordinated control is adopted as the basic control scheme, whereas control of the hybrid energy storage adopts the improved strategy. The hybrid energy storage system contains a battery and a supercapacitor coupled to a wind turbine subsystem. Given the different characteristics of the energy storage units, the adaptive control of battery and supercapacitor are adopted in the paperto smooth the low-frequency power fluctuation in the long term and to suppress the high-frequency component separately. It is to be noted that a predictive control of the converters is adopted to achieve rapid regulation. The wind power unit is also investigated as third energy storage unit. The idea involves utilizing the large rotating kinetic energy of the wind turbine to temporary suppress huge power disturbances and to avoid load shedding. The paper show simulations of the islanded DC microgrid in forest areas, performed with MATLAB/Simulink, to validate the effectiveness of the proposed coordination control with hybrid complementary energy storage. The achieved results show that the transient operation characteristics of the system were effectively enhanced by utilizing the improved control method. The fifth paper [5], entitled \"An AC/DC Distribution Network DG Planning Problem: A Genetic-Ant Colony Hybrid Algorithm Approach\", is by [PERSON] et al. from the School of Electrical Engineering, Southeast University, Nanjing, China and the College of Energy and Electrical Engineering, Hohai University, Nanjing, China. The paper addresses the topic of the planning problem of distributed generators (DG) accessing the AC/DC distribution network. The paper presents a location and volume model of a DG that considers several DG costs, such as operation and maintenance costs, investment costs, system network loss costs, fuel costs, pollution compensation costs, and environmental protection subsidies. Voltage and power constraints are also considered in the model. A hybrid algorithm that combines the ant colony algorithm (ACO) and the genetic algorithm (GA) is proposed to solve the model presented, resulting in a GA-ACO technique. The IEEE-33 node distribution network is taken as example to verify the rationale of the proposed approach and its effectiveness. The simulation results show that the proposed model is aligned with reality and the hybrid algorithm is effective in solving the model, with advantages in both convergence speed and convergence results, if compared to single ACO and/or GA techniques. The sixth paper [6], entitled \"A Stability Preserving Criterion for the Management of DC Microgrids Supplied by a Floating Bus\", by [PERSON] et al. is from Italy, from the Department of Engineering and Architecture, University of Trieste and the Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano in Milan. One of the most important enabling technologies for the future development of microgrids is DC distribution. This is due to the easier interfacing with many DC components of a modern smart grid, such as batteries, photovoltaic systems, and native DC loads. The large use of controlled power converters suggests the need for a careful analysis of system stability in these power systems, as the stability can be impaired in particular conditions. For example, a destabilizing effect can arise in DC power systems due to the presence of inductor/capacitor (LC) filtering stages installed for power quality requirements. Other stability problems can arise due to high-bandwidth controlled converters that behave as constant power loads (CPLs).