Design of smart autonomous solar panel with cascaded SEPIC-boost converter for high voltage renewable applications

ABSTRACT The most admired alternative to conventional energy sources is solar energy. In north-eastern regions of India, where availability of sun is unpredictable but irradiance level is high, special observation is needed to upgrade the solar collection systems. The main objective of the research work is to develop a renewable system, which can extract maximum voltage using dual axis movable surface and design a cascaded converter, which can further increase the voltage while maintaining high efficiency. The output of the smart independent self-regulating solar panel hardware model proposed in this paper is fed into a DC–DC cascaded Boost-SEPIC system for renewable-based applications. The newly created renewable system is built to move the panel so that the most voltage is extracted. The DC–DC cascaded converter receives power from the solar panel’s output. To assess the system’s effectiveness and voltage gain, a thorough circuit analysis is carried out. The converter is tested using various duty cycles. With a 50% duty ratio and 90% efficiency, the suggested converter produces a 40 V DC output from a 20 V DC input voltage from a solar panel. Results from an experimental prototype are used to verify the converter’s viability.


Introduction
The period of technological progress, which has been made possible by abundant energy resources, has had a profound quantitative and qualitative impact on humankind's level of living. However, the environment is being negatively impacted by the traditional power plant's large emissions. (Sanyal et al. 2022) states that major countries have adopted significant renewable energy sources (RES), according to the 2019 IRENA Renewable Statistics study. In (IRENA 2019) the total amount of renewable energy increased globally from 1135.6 GW in 2009 to 2356.4 GW in 2019, representing an increase of 107.5%. Since 2009, the total capacity and generation of RES have increased steadily. Despite the exceptional nature of this progress, there is still potential for improvement. Though (Sanyal et al. 2020) presented specific evidences that there have been significant climate changes at the UN summit held from September 21-27, 2019. Similar proofs were presented by Bessa, Trindade, and Miranda (2014), stating different climatic changes occurring in the present environment. Therefore, it is urgent to switch to renewable energy from conventional electricity in order to reduce greenhouse gas emissions, which will considerably help lower the carbon footprint. Adarsh, Anand, and Singla (2015) presented that the energy demand is currently being met by a variety of RES, including solar, wind, hydropower, biomass energy, and many others. Altin (2012) stated that one of the RES that is easy to utilize, maintenance and pollution-free for stand-alone applications is photovoltaic energy system According to (Mousazadeh et al. 2009), 0.16% of Earth's surface might be covered by 10% efficient solar conversion devices, producing 20 TW of power -nearly twice as much as the world currently consumes in terms of fossil fuels. This demonstrates the capacity of solar energy and, in turn, underlines the requirement for a suitable tracking mechanism in solar systems (Adarsh, Anand, and Singla 2015). To extract maximum power from the sunlight it is important to use a suitable solar tracking system. Munna et al. (2015). In his paper mentioned that to maximize the power output of the solar energy, it is very much desirable to increase its efficiency. Soltani and Kouhanjani (2017) mentioned in his work that there are two types of sunshine: the "direct beam," which contains roughly 90% of the solar energy, and the "diffuse sunlight," which contains the remaining 10%. On a clear day, the diffuse portion is the blue sky, and it grows correspondingly when it is clouded. The sun must be visible to the panels for as long as feasible in order to maximize collection because the majority of the energy is in the direct beam. PV systems are becoming increasingly popular source of clean energy. This can be only done if the panels are aligned to the sun.
As per Mustafa et al. (2018), an arrangement must be made so that solar radiation hits the panel at an angle of 90 degrees throughout the day in order to capture the most energy possible. As a result, portable solar panels are needed. Therefore, it is necessary to use a solar tracker that will follow the sun throughout the day, regardless of the season, to gather solar radiation perpendicular to the solar panel. Dual-axis tracking technology is required to precisely follow the movement of the sun. The continuous tracking technology precisely monitors the sun's changing light intensity (Al Nabulsi and Dhaouadi 2012). Consequently, this increases the system's overall power output (Rahman et al. 2013). However, the electricity produced by RES is erratic and unpredictable. Thus, (Elshaer et al. (2010) concluded that to serve as an interface between PV panels and loads, a DC-DC converter is needed. (Yaramasu and Wu 2011) states that a lot of work has been done in the last 10 years to design and build extremely effective DC-DC converters for a variety of applications. In the paper of Pallavee Bhatnagar and Nema (2013), large number of conventional MPPT techniques, have been reported. Each technique has its own advantage and disadvantages. The work created by Karthika et al. (2022) proposed the designs of a three level DC to DC Converter and a dual axis-based solar tracker. These converters comply with the MPPT technique whenever the load and climatic conditions tend to vary. Therefore, it employs Golden Section Search Algorithm in the highest power point tracking in conjunction with the microcontroller. This approach is for small range inductors. Jancarle et al. (2005) focuses on the design and experimental design of an MPPT tracker for a highly efficient dc/ dc boost converter working in CCM. To achieve high efficiency and lower EMI levels due to the soft switching operation, a non-dissipative passive turn-on turn-off snubber is used. Though snubber improves the overall efficiency, but makes the entire circuit more complex and bulkier.
Tudorache and Kreindler (2010) described a dual tracking system with an electrical MPPT and a mechanical tracker that are both managed by different DSPs. Zeb et al. (2020) have worked on the interfacing of the DC converters with photovoltaic modules. To reduce voltage sag and swell, interruptions, and unbalanced outages in single-phase grids, a new topology of PV-based transformer less dynamic voltage restorer with high gain DC-DC boost converter is presented by Paramasivam et al. (2021). To improve the system's performance for grid-connected renewable applications, the suggested converter consists of one MOSFET switch, three inductors, and unit vector template control based on a second order generalized integrator (Raghavendra et al. 2020). Manickam et al. (2022) created selective harmonic elimination to correct the dominant harmonics, minimizing the lowerorder harmonics to provide a smaller THD and enhancing the quality of the output waveform. In this study, we propose a notion of selective harmonic elimination for dual voltage boosting nine-level inverter topology that has two times the voltage boosting capability than the traditional models (Ardi et al. 2018).
A step-up DC-DC converter with resonant voltage doubler is proposed by Antony et al. (2018). A DC-DC converter of 1.2 kW and 70 kHz switching frequency is used for the trials. An approach for increasing output voltage and power using solar tracking and a PIC microcontroller-controlled SEPIC was suggested by the authors of Asmita Jadhav et al. (2020). High-frequency DC/DC power conversion uses the multi-step buck converters that have been proposed extensively in Sun et al. (2016). High voltage ratio is also possible in typical boost converters without multistage cascading (Shyam Joseph Antony, Sangeetha, and Vimalika 2018). But the parasitic components and switching control employed in these set a limit on the voltage ratios (Gaikar, Jadhav, and Prof 2020).
But at larger conversion ratios, these conventional converters are unable to function (Fu, Ma, and Zhu 2014). Other traditional voltage boosting methods described by Kumari, Moumi Pandit, and Sherpa (2022), included coupled inductors, multilayer, interleaved, switching capacitors, have stability restrictions at their operating points. High voltage gain is possible with isolated converter structures in a cascaded topology (Triki et al. 2018). According to published research by Ardi, Ajami, and Sabahi (2018), even though the conventional single-switch boost converter may reach high voltage at unity duty cycle, complications, such as long switching turn-off times, would appear at extremely high duty cycles. Higher conversion ratios can be attained without the use of a transformer using a cascade connection (Kim and Lai 2008). The voltage gain is increased by integrating a straightforward boost converter with the SEPIC converter (Busquets-Monge, Alepuz, and Bordonau 2011). The ability of a boost converter to provide a high step-up voltage is taken into consideration while choosing one (Zhao et al. 2012). While the non-inverting output and low input current ripple of the SEPIC converter make it the preferred option by Ibrahim Alhamrouni et al. (2019) for the proposed structure of cascaded SEPIC-Boost Converter. The topology's voltage conversion ratio is D/(1-D) 2 . Table 1 presents the detailed comparison of the literature survey. It highlights the comparison and novelty of the current work.
The Sikkim Region is where the sunshine was tracked most closely for this report. Northeastern India's Sikkim is the country's 22nd state. Due to its Himalayan position, it has a variety of climates, varying between tundra in the north and subtropical regions in the south. Most of Sikkim's populated areas enjoy a moderate climate, with summertime highs rarely topping 28°C. The majority of this region experiences an annual average temperature of about 18°C as per (Baruah et al. 2021). If cascaded converters are employed, lower solar irradiation can be boosted. The dual-axis sun tracker and DC-DC cascaded BSC are used in this work to present a hardware architecture for maximizing solar energy harvesting.
The important contributions of this study are outlined below: (A) It demonstrates a double-axis PV system of tracking that uses the MPPT algorithm to collect the most solar light energy possible. (B) Use a cascaded BSC to convert the solar panel's output voltage to an appropriate amplitude for a range of applications. Practical findings were acquired after testing and implementing the designed cascaded converter utilizing a hardware setup.
The following is the breakdown of this paper structure: In section II, the solar panel's mechanical design is explained. Section III discusses the design study of the cascaded BSC. In Section IV, experimental findings for a solar panel with a 20 V DC as the input voltage and a 50% duty ratio are reported. The final section of this paper is Section V.

Solar panel description
The solar tracking is most effective during synchronization of the monthly variation of the sun and the tilt angle of the PV tracking system. While a perfect tracking compensates for changes in the sun's latitude angle and height, the solar modules can face the sun. Therefore, a single-axis finds it difficult to maximize the solar panel's efficacy, whereas double-axis tracking guarantees cosine effectiveness.
The designed system focuses on enhancing the performance of a dual axis PV tracking system through the usage of P&O technique. The system's overall effectiveness is increased when the MPPT algorithm is used in conjunction with a cascaded DC-DC cascaded BSC. Thus, by utilizing a cascaded converter to convert the PV's output voltage to an appropriate amplitude, the suggested system's maximum efficiency is determined. Both solar panels are supported by a mechanical framework. At each of the four corners, there are four actuators that support the mechanical support framework. The actuators allow the mechanical framework and solar panels to move at the microcontroller-set angle. The configuration of the dualaxis PV tracking panel is shown in Figure 1.
The following components make up the mechanical structure: Though the conventional SEPIC converter are superior than the buck-boost converter but they also fail to achieve high voltage gain at increasing duty ratios. The boost converter is unable to achieve a voltage gain of more than six times the applied voltage due to presence of parasitic components. The combined circuit topology of boost and SEPIC converters helps to extend the duty ratio further for various high voltage renewable applications. Thus, the maximum efficiency is derived from the solar panel by using two combines.

3.
A real-time MPPT-based perturbation and observation algorithm for solar systems with dc/ dc boost converters working in continuous conduction mode is designed and experimentally tested. Due to the soft switching action, a passive nondissipative turn-on turn-off snubber is used to achieve high efficiency and lower EMI levels. There is no usage of snubber circuit in the proposed topology. This makes the circuit simple and less complex. Usage of conventional boost converter would tend to be drastically reduce the efficiency as the voltage gain is increased. In comparison to a traditional boost converter, the integration of a simple boost converter with a SEPIC converter results in a 10-fold improvement in voltage gain.

4.
The alternate topology of cascading non-isolated boost, buck, buck-boost, and Cuk converters is suggested in this work. To analyse the effectiveness of each topology and assess the advantages of rising cost and complexity. MATLAB simulations are employed.

(Walker and Sernia 2004)
Buck-boost and Cuk converters are adaptable in terms of voltage ranges but always have a cost or efficiency penalty. This study offers data from actual experiments, which improves its applicability and suitability for high voltage applications.

5.
This paper discusses the boost-buck converter used with a Permanent Magnet Synchronous Motor drive for a refrigeration system's variable speed compressor. (Spier 2017) The main issue associated with Buck-Boost converter is that the output is inverting and usage of transformer would result in noninverting output.

6.
The work discusses about the variable voltage control at the PV panel with less voltage stress across the boost-buck converter switches, provided the necessary voltage gain and system efficiency are fulfilled. (Dubey et. al 2020) Addition of transformer to the circuit increases the complexity, cost, space and also making it high loss and less efficient. Also, the switch of buckboost is not grounded. This complicates the driving circuitry. Whereas, the combination of Boost and SEPIC converter overcome these drawbacks.
• Actuators: To supply the necessary movement of the mechanical setup, a movable joint set is used to connect four actuators at each of its four corners. As shown in Fig. 2, the actuators are coupled with a stepper motor to provide a 10 mm extension. • Jolt Connector: In order to enable free 360° rotation of the system, the nut bolt connector set is specifically designed.
For maximizing energy, two PV panels of 12 V and 100 W each has been connected in series. A solar charge controller with inbuilt MPPT algorithm is used to track the maximum solar power from the panel. Total four numbers of actuators managed by the microcontroller spin along the two axes. One servo motor control the horizontal axis, and the other is used to control the vertical axis. These two servo motors control the movement of the solar panel to create the perfect angle between solar panel and solar radiation. The microprocessor delivers the signal to the servo motors for the proper angle of rotation after calculating the desired angle of horizontal and vertical rotation based on the direction of sun radiation sensed by the four LDRs. The control technique relies on the variance of the LDR-received signals. The panel does not move if there is no difference. The panel can be put back into its original position at a 40-degree incline by pressing the reset button. Throughout movement, the control programme continuously measures the generated voltage at various angles. In order to  generate the most voltage, the solar panel is then placed at an angle that receives the most solar radiation. As depicted in Figure 3, the procedure is repeated after a predetermined amount of time.

Working principle of cascaded BSC
The typical SEPIC converter is unable to provide large voltage gain while operating at higher duty ratios. By adding a simple boost converter in between inductor L 1 and the regulated power semiconductor device, the gain of the SEPIC converter is raised. Figure 4 displays the cascaded BSC circuit diagram.
The revised SEPIC converter operates in both conducting and non-conduction mode. During CCM, the L 1 is first magnetized by the source voltage V in then the D 2 and S. Switch S magnetizes L 2 through. On the other hand, capacitor C 2 uses the semi-controlled device S to magnetize L 3 . The current via L 1 , L 2 , and L 3  grows linearly during the CCM. On the other hand, inductor currents decrease linearly in the nonconduction state. The C 1 , V in, and D 1 cause the demagnetization of the L 1 . As a result of C C 2 and C 3 , L 1 and L 3 are also demagnetized, followed byD 2 and D 3 in that order [34]. Fig. The suggested circuit is shown in conduction and nonconduction modes in Figure 5.
Switch S is turned on during CCM. The voltage across L 1 , L 2 , L 3 during on state is: (1) The voltage across inductor L 1 , L 2 , L 3 during off state is: Using the inductor L 1 volt-second balance approach Using the inductor L 2 volt-second balance approach Using the inductor L 3 volt-second balance approach From Eq. (3) Ignoring the circuit's internal resistances. Consequently, the suggested Converter's voltage gain is: -

Results from double axis PV tracking system
The PV statistics gathered on July 25, 2021, are shown in Table 2. Dual-axis observations of solar irradiance have been made in both of these circumstances, i.e., with as well as without a solar tracker. Figure 6, explains the precise studies comparing the valves of both fixed and tracking arrangements at various points utilizing graphical representation.
The information in Table 2 makes it obvious that solar irradiance with a tracker is more than it would be without one. The 20.75 V (from Table 2) input is taken into consideration when designing the DC-DC cascaded BSC. Based on the circuit's characteristics, which are listed in Table 3, this voltage has been chosen. The efficiency of a solar power system is improved by adding the MPPT algorithm. For optimal light energy absorption, the solar tracker continuously follows the movement of the sun in both the and horizontal and azimuth directions. The DC-DC cascaded BSC receives the output from the MPPT, which takes the most power possible from the panel

Experimental hardware model setup of cascaded BSC
The hardware configuration of the experimental model is shown in Figure 7. The suggested model's switching frequency and pulse were modified using a PWM and Duty ratio generator device. The characteristics in Table 2 constitute the foundation for the predicted converters. It has been compared to the produced voltage as measured on July 25, 2021. In both situations, i.e. with and without a tracker, the solar panel data is collected. The graphs in Figures 8 and 9 are depicted. The suggested model is tested using the data from Table 2. The cascaded converter can handle a maximum voltage of 50 V according to its rating. As a result, the converter input for validation has been the 17th output of Table 2.
Thus, the DC-DC cascaded BSC input has been deemed to equal the solar panel's 20 V output. 22 kHz is the switching frequency in use. The converter receives square pulses with a switching frequency of 22 kHz from a PWM generator. The square pulse sent to the MOSFET IRF540N's gate terminal is shown in Figure 8. The project's inductor values (L 1 , L 2 , and L 3 ) are 0.3 H. The chosen capacitor values (C 1 , C 2 ) have a rating of 47 F and a 63 V voltage tolerance. The output capacitor (C 3 ) has a 47-F capacity and a 200-V voltage tolerance. The resistive load chosen for the proposed converter has a rating of 400 ohms and 1.1 amps. The measured input current is 0.3 Amps. The output current, which was measured at 0.13 amps. 38 V for a 20 V input appears across the output capacitor C 3 at a 50% duty ratio. The 38 V output voltage waveform at 50% duty ratio is shown in Figure 9. At 50% of the rated output power, a 90% maximum efficiency was recorded. Efficiency is increased across the board of operation. A resistive load rated at 400 Ohms and 1.5 Amps is employed. The prototype-designed device has a maximum efficiency of 90% at 400Ω resistive load. 10% of the circuit's total energy is lost internally, including through switches, inductors, diodes and other elements.

Conclusion
This work successfully designs and tests dual axis autonomous solar tracking for cascaded BSC. The dualaxis tracker that was created successfully controlled the system to produce the most solar electricity possible. In comparison to a single solar tracking system, the results demonstrated in this paper proves that the proposed system is highly effective in terms of electrical power generation. A 20 V solar output is routed to the cascaded BSC in order to boost efficiency even more. We tested the converter utilizing a range of switching frequencies and duty cycles. With a 50% duty ratio, the suggested converter converts a solar panel's 20 V input into a 40 V DC output. The overall system output is 90% efficient. Losses across each component have an impact on efficiency to the tune of 10%. Efficiency is increased across the board of operation. Numerous high-voltage applications can effectively employ the acquired energy.

SEPIC
Single Ended Primary Inductor Converter

Disclosure statement
I declare that on behalf of all the participating authors there are no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. I declare that there are no following financial interests/personal relationships, which may be considered as potential competing interests

Data availability statement
There is no data availability in this paper

Future scope
The work can be further extended by applying more than one renewable source as the input to the cascaded BSC. The combination of dual inputs from the renewable sectors such as solar and wind energy together fed to the cascaded converter would help us to make a multi-input sustainable hybrid renewable system.