**3. System Design**

### *3.1. Physical Model and Operation Principle*

Based on the analysis of the atmospheric conditions, we designed the standalone renewable energy system. As shown in Figure 3, the proposed renewable energy system in this study is equipped with a power generator, an energy storage system, an end-user and a control station. The power generator consists of the PV arrays and wind turbines (WT), which can complete the conversion of wind energy and solar energy to electric energy. The energy storage system includes low-temperature batteries. The end-user is various loads at Zhongshan Station, which includes instruments for scientific research, electricity for daily use, heating, etc. The control station includes a control system, which has functions of controlling the process of charging and discharging of hybrid wind–solar power system. The rotation of wind turbines can produce AC currents. A three-phase rectifier circuit in the control system is designed to convert the three-phase alternating currents into stable direct currents. A DC chopper circuit is also designed to implement the control strategy for the renewable energy system to complete maximum power output. The control system is used to monitor voltage and current of PV and WT, battery voltage and charging current. This proposed system would be a reliable and sustainable energy supply and guarantee the load demand of Zhongshan Station for 24 h a day.

### *3.2. Mathematical Modeling of the Power System*
