**6. Conclusions 6. Conclusions**

A hybrid complementary energy storage control method in forest DC microgrid is proposed, in which wind turbine energy storage, the battery, and the supercapacitor coordinate under different working conditions. Firstly, according to the characteristics of batteries and supercapacitors, batteries are adopted as a long-term energy reserve to bear the low-frequency fluctuation, while supercapacitors are used to suppress the corresponding high-frequency component. In addition, predictive control of the converters is adopted to reduce control delay and ensure the effectiveness of the energy storage converters. Furthermore, the inertia enhancement control strategy of the wind turbine system was studied by utilizing the large rotating kinetic energy of wind turbines to suppress power disturbance in a timely way and improve the fault ride-through capacity. A hybrid complementary energy storage control method in forest DC microgrid is proposed, in which wind turbine energy storage, the battery, and the supercapacitor coordinate under different working conditions. Firstly, according to the characteristics of batteries and supercapacitors, batteries are adopted as a long-term energy reserve to bear the low-frequency fluctuation, while supercapacitors are used to suppress the corresponding high-frequency component. In addition, predictive control of the converters is adopted to reduce control delay and ensure the effectiveness of the energy storage converters. Furthermore, the inertia enhancement control strategy of the wind turbine system was studied by utilizing the large rotating kinetic energy of wind turbines to suppress power disturbance in a timely way and improve the fault ride-through capacity.

smoothing can be achieved so that power quality is improved compared with methods using traditional PI control or fixed droop control. In addition, fault ride-through capability was effectively enhanced compared with microgrid with single energy storage by inertia control of the wind power

unit that utilizes the kinetic energy in wind turbine.

Through simulations of the DC microgrid in forest area conducted in MATLAB/Simulink, conclusions can be drawn that by utilizing the hybrid complementary energy storage, fast power smoothing can be achieved so that power quality is improved compared with methods using traditional PI control or fixed droop control. In addition, fault ride-through capability was effectively enhanced compared with microgrid with single energy storage by inertia control of the wind power unit that utilizes the kinetic energy in wind turbine.

**Author Contributions:** M.Y. proposed the algorithm; M.Y. and J.Z. conceived and designed the experiments; M.Y. and J.Z. performed the experiments; M.Y. and H.L. wrote the paper.

**Funding:** Project supported by funding for fundamental research business expenses of central universities (Grant No. BLX201716).

**Conflicts of Interest:** The authors declare no conflict of interest.
