*6.3. Charging Circuit*

The solar/wind charging circuit is shown in Figure 14. The three-phase input of wind turbine converts AC to DC through a three-phase rectifier bridge, and mixes with the input of the PV array. In this circuit, freewheeling diodes are replaced to reduce rectification losses and the current sharing effect is significantly enhanced. The electric energy generated by wind and solar is very unstable. The electric energy is converted into a stable and usable DC through the interleaved Buck circuit. The choice of MOS tube considers the following elements: (1) Withstand voltage greater than or equal to 3 times DC bus voltage; (2) The current value is less than 1/4 of the rated current; (3) Low on resistance.

**Figure 14.** The solar/wind charging circuit.

As shown in Figure 14, MOSFET RU190N08 (Ruichips Semiconductor, Shenzhen, Guangdong, China) is selected as the power device of the interleaved Buck circuit, which has a withstand voltage of 80 V and a withstand current of 190 A. Relevant parameters of the power supply circuit can be seen in Table 11.

The inductance of interleaved Buck circuit can be obtained as follows.

$$L\_{\text{Buck}} = V\_0 (1 - D) / (rI\_L f\_s) \tag{25}$$

where *LBuck* is the inductance of interleaved Buck circuit; *V*0 is DC bus voltage (24 V); *D* is the minimum duty cycle of the PWM control method (0.57); *r* is inductor current ripple peak-to-peak factor (0.4); *IL* is inductor rated current (40 A); *fs* is switching frequency of PWM control signal (20 KHz). Thus the inductance of interleaved Buck circuit *LBuck* is 32 μH.


**Table 11.** Relevant parameters of the solar/wind charging circuit.

### **7. A case Study in Antarctica**

### *7.1. Existing Power Supply System in Zhongshan Station*

At present, there are three sets of diesel generator in Zhongshan Station. In the process of power generation, the on-duty personnel should be arranged to record and maintain the relevant parameters of the generators. Based on the data provided by the Chinese National Antarctica Research Expeditions, we aggregated the data of the existing diesel power supply system at Zhongshan Station in Antarctica in 2013, 2014 and 2015. The average monthly power supply and monthly fuel consumption of Zhongshan Station are obtained. The actual monthly load power and fuel consumption are shown in Figure 15.

**Figure 15.** Actual monthly load power, air temperature and fuel consumption in Zhongshan Station.

As can be seen from Figure 15, the annual power consumption of Zhongshan Station is closely related to climatic conditions. The trend of monthly load power has a good correlation with the monthly average air temperature. The peak annual power consumption of Zhongshan Station is concentrated in May, June, July and August. At this time, it is the winter and polar night in Antarctica, which the air temperature in these months is the lowest in one year. However, scientists would continue to conduct scientific investigations near Zhongshan Station. At the same time, the outside temperature is low and the demand of indoor heating is increasing. Therefore, the power consumption of Zhongshan Station will also increase. As shown in Figure 2b, the annual radiation intensity and day lengths are the lowest in this period. The power supply of Zhongshan Station mainly depended on the wind turbine and the battery. Zhongshan Station has a total load of 100 KW. The monthly average power consumption is 72,516 KW h, the monthly average fuel consumption is above 20 t. Polar day occurs from December to January in Zhongshan Station, and it can make full use of solar power to generate electricity. The

power consumption of the load in February, March, April, September, October, and November basically maintain the average power consumption of Zhongshan Station, which both wind and solar energy resources can generate electricity, and batteries have electricity reserves.

### *7.2. Analysis of Simulation Operation Results*

The power generation of the standalone renewable energy system in Zhongshan Station from 2014 to 2015 is presented in Figure 16.

**Figure 16.** The power generation of the standalone renewable energy system in Zhongshan Station from 2014 to 2015.

The results of Zhongshan Station load were previous monitoring data. The power generated by wind energy and solar energy was calculated by mathematical models of the standalone renewable energy system. If the power generated by the standalone renewable energy system cannot meet the requirement of load, the battery will act as an energy storage system to supply the load of the Zhongshan Station to maintain the normal operation. Accordingly, battery capacity can be also derived from the simulation. The observed wind speed data were selected to complete simulation calculation. The values of radiation intensity from NASA were used to calculate power generation by PV array. As can be seen in Figure 16, the monthly average load of Zhongshan Station remained basically stable within one year. The annual load of Zhongshan Station was 870,196 KW h. The minimum and maximum values of the load were 56,175 KW h in November and 87,743 KW h in July, respectively. The average value of the load of Zhongshan Station was 72,516 KW h. Wind power production dominated the power supply of the standalone renewable energy system and generated 747,858.4 KW h in a year, which was 86% of the load. The monthly average maximum and minimum values of wind power were 74,400 KW h in March, May, July, August, October and 8455.4 KW h in January. In March, April, October and November, only the energy generated by wind can meet the load of Zhongshan Station. The solar power was shown strong seasonal fluctuations owing to the polar night (June and July) in Antarctica. The annual solar power of Zhongshan Station was 97,361 KW h. The monthly average solar power of polar day in January and December were larger, which were 19,659.9 KW h and 21,779.7 KW h, respectively. The minimum value of monthly average solar power in a year appeared in June (0 KW h) and July (34 KW h). In January, February, May, June and July, wind and solar energy were less than the load required for the month, thus, the energy storage system also provided power to the load.

Especially in August, the sum of the power of wind, solar, and battery (75,712.83 KW h) was less than the load (82,938 KW h), and fuel was used to complete the power supply (7225.17 KW h) to the load.
