## 2 Advantages and Design Procedure of Capacitive Isolated Series Resonant Converter  
This section, along with Section 3, forms the core methodology of the proposed system and covers the converter design and control strategy in detail. In most resonant converters, a high-frequency transformer is used to either step up or step down the voltage level, which is suitable for grid-connected applications. Transformers also provide galvanic isolation for the system to separate grounds and enhance electrical safety. However, the high-frequency transformer introduces copper and core losses, and to keep them within acceptable limits, the core size of the transformers will be constrained. Even with an optimized design, the converter will still require multiple magnetic elements. In standalone applications, the PV panel voltage and battery voltage can be scaled to match or closely align. In fact, even if the voltage levels differ by up to a factor of two, a transformer-less converter can still be realized to handle the interface. In addition, the galvanic isolation can be achieved by splitting the capacitor of the resonant tank into two capacitors and facing one in the outgoing path and the other in the incoming path. Figure 1 shows the possible choices for PV battery charging using a series resonant converter in standalone applications. If a series resonant converter is used in this system, its nominal operating point could be carefully chosen to charge the battery with minimal voltage changes, even with extreme irradiation levels affecting the PV panel. This is due to the fact that the maximum power point (MPP) voltage of the PV panel varies only slightly from maximum irradiation to very low irradiation. The battery voltage also varies slightly between low and nominal voltage to full charge levels. These factors make a series resonant converter very suitable for this type of application. Figure 2 shows the variation in the MPP voltage of the PV panel with respect to irradiation level. The normalized voltage gain curve of a series resonant converter of a configuration similar to the one in Figure 1a can be seen in Figure 3; it shows a possible region of operation  
Figure 1: Different configurations for using a series resonant converter without a transformer: (**a**) The output voltage could be matched close to the input voltage. (**b**) The output voltage could be matched up to double the input voltage. (**c**) The output voltage could be less than half the input voltage. for the converter to operate nominally and it also shows that if the nominal operating point is placed at a middle point, the converter will be able to increase or decrease the voltage by a considerable percentage more than required for the PV MPP voltage at different irradiance levels. In addition to the PV voltage change, the battery voltage changes with respect to its state of charge. Figure 4 shows a typical characteristic curve for the battery voltage versus its state of charge (SOC). While this study focuses on maximum power point tracking using ESC, it is acknowledged that optimal and safe battery charging requires adherence to profiles such as Constant Current (CC) and Constant Voltage (CV). The ESC algorithm does not inherently enforce these profiles, as its primary objective is to maximize power transfer from the PV panel. In real-world systems, such functionality is typically handled by a dedicated battery management system (BMS), which monitors parameters like temperature, state of charge (SOC), and terminal voltage, and can coordinate with or override the MPPT loop if needed. It can be seen from these curves that a series resonant converter with capacitive galvanic isolation is more than capable of handling the interface between the PV and the battery without the need for a transformer. By removing the transformer, a major part of the converter losses (copper and core) is eliminated or at least reduced.