## 3 MG-Based BTS Operation  
### MG-Based BTS Measurements and Control Electronics  
In this subsection, the parameters to monitor and the electronics required to accomplish the stated objectives are described. The relationship between the elements that measure the electrical parameters and control the flow of energy in the MG-based BTS is shown in Figure 3. In the following paragraphs, these elements will be explained. Figure 3: Measurement and control electronics of the MG-based BTS. Firstly, the DC currents are measured using the ACS758 LCB-100B-PFF-T and the ACS758 LCB-100U-PFF-T sensors [36] (Figure 4). The range and the sensitivity of these sensors are \(\pm\)100 A and 40 mV/A, respectively. Regarding the currents, these values are enough for an expected maximum BESS current of \(\pm\)60 A and a maximum single load current of 20 A. As for the sensitivity, at a full scale, the sensors will output ideally a DC voltage signal between 0 V and 5 V, covering the dynamic range of the ADC used. The conditioning circuits for the current sensors consist of low pass filters with a cutting frequency of 50 Hz. They are used to eliminate possible coupled noise from the grid. Finally, the typical output noise of the sensor, in measured current units, will be 0.33 A, which is acceptable for this application. The BESS voltage is measured using a voltage divider to scale the voltage to the dynamic range of the ADC (Figure 4). The ADC used to convert the DC currents and voltage measurements is the ADS1115 [37]. This low-cost four-channel 16-bit IEC ADC has an input range from 0 V to 5 V, a maximum sampling frequency of 860 Hz and features low power consumption. Furthermore, to measure the ambient parameters (temperature, humidity and pressure), the IEC BME680 sensor [38] is used due to its low cost and low power consumption. Once the measurements are obtained, the BESS SoC is estimated. This is an important parameter for the management of the MG-based BTS. In [39], a complete state of the art analysis of different algorithms for lead acid batteries SoC estimation can be found. Among them, the current integration or Coulomb counter method has been used in this paper. This method, along with the manufacturer's specifications of the batteries, are merged to provide an accurate estimation of the SoC, through the floating voltage of the BESS and the dynamic capacity depending on the discharge current rate [40]. The MPPT solar charger provides several parameters related to the PV installation through the Modbus protocol [41]. For the sensing strategy proposed in this paper, the following parameters are required: (i) the output voltage of the MPPT solar charger; (ii) the output current provided by the charger; and (iii) the voltage, current and power of the PV modules. All these parameters are collected in the SBC. The loads are connected or disconnected through low cost off-the-shelf MOSFET-CSD18536 KCS 60 V N-Channel transistors [42]. Their maximum drain-source voltage is 60 V, over the maximum voltage of the DC bus 58 V, which is imposed by the rectifier of the RF equipment at the dedicated output for the BESS [43]. Furthermore, for the connection of  
Figure 4: Electronics for the measurement of currents and voltages in BESS, non-critical and critical loads. the different parts of the installation, EW60-1A3 12 VDC 60 A [44] latching relays have been included in the hardware architecture. Figure 5 briefly depicts the conditioning circuits of the transistors and relays of the SBC driver. Regarding the power supply for the electronics, there are three isolated sources: (i) the SBC power supply; (ii) the power supply for the main board of the SBC Driver and the transistor-based switches for the critical loads; and (iii) the power source for transistor-based switches for the non-critical loads.