The photovoltaic-powered elevator (PVPE) promises to be the invention of the next few years due to its several advantages and characteristics. It is pollution-free and needs less maintenance after installation. It does not need any fuel to be powered up, and its source of power is renewable, clean, and environmentally friendly. The source of power is renewable, clean, and environmentally friendly. It is estimated that in (Cronshaw, 2015) the solar-powered apparatus is going to play the most significant role in human life. As of now, the most important equipment is motors, which utilize non-renewable energy as the main source. We are badly in need of an alternate energy source that would be renewable and reliable—none other than solar PV systems.

One easier way of making electrical energy available during calamities is solar energy. Nevertheless, the solar-powered system available traditionally is too expensive, and most of the energy is lost in conversion. If a few steps were taken to minimize these aspects, then this kind of energy would become a cheaper and maintenance-free system for several years (Caracas et al., 2013; Meghni et al., 2017). In (Raghavendra et al., 2019), the authors propose a unique converter for solar water-pumping assemblies that do not require a battery (Antonello et al., 2016; Raghavendra et al., 2019; Meena and Singh, 2023b; Fekik et al., 2023; Thanikanti et al., 2023). Then, new high-voltage-boosting converters are designed in (Hwu et al., 2012; Hwu and Yau, 2013).

When sunlight intensity crosses 1000 W/m ², which is roughly equivalent to midday in summer in Germany, for example, or when solar irradiation approaches 1000 W/m ² at lower temperatures, a module’s real power may rise above its nominal power (Sontake and Kalamkar, 2016).Two popular configurations usually employed for PV-powered systems are (i) battery-coupled and (ii) direct-coupled methods. The former approach uses the battery to increase supply over a longer period by acting as a constant voltage source for the system. But for elevators, the longer utilization period will be only during the day, when the Sun shines brightly. Though battery utilization aids in some aspects, it has its own drawbacks, as discussed below. The batteries minimize the performance of the system as the voltage is decided by the battery and not by the solar panel. Therefore, when the Sun’s luminosity is high, the nominal power can exceed 1000 W/m ² (roughly during midday), but the battery lays an obstacle to the maximum utilization of power by the system. Furthermore, the batteries have a 2-year life duration when compared to the PV module’s life span of 20 years. In addition, the cost of battery maintenance and replacement is significant. As a result, the total efficiency of the system is diminished, while the PVPE system installation cost is increased. As a result, the battery-coupled system is not employed (Eker, 2005; Meah et al., 2008; Chunting et al., 2010; Tschanz et al., 2010; Vitorino et al., 2010; Malla et al., 2011; Meena and Singh, 2022; Arun et al., 2024; Jagan et al., 2024).

In (Lee et al., 2000), interleaved operation of two or more boost converters is presented in this study for high-power applications to increase output power and reduce output ripple (Lee et al., 2000; Kengne et al., 2023). Two structures, a switched-capacitor (SC)-based boost converter and a two-level inverter, are connected in cascade in this article (Axelrod et al., 2005). To meet safety standards and make maximum use of the PV-generated power, a recent research trend in residential power generation systems is to adopt the PV parallel connected configuration rather than the series-connected design (Li and He, 2010; Meghni et al., 2018; Radwan et al., 2018; Suresh et al., 2019; Sethuraman et al., 2020). This work includes thorough mathematical analysis, detailed converter design, parameter analysis and comparison with other existing converters, and a new hardware prototype with expanded hardware results (Sathyan et al., 2015; Periyanayagam et al., 2020; Kalaiarasi et al., 2021; Meena and Singh, 2023a; Reddy et al., 2023; Meena et al., 2024; Bharatiraja et al., 2016a; Bharatiraja et al., 2016b). From the analyses made above, it is evident that an efficient and low-cost PVPE can be set up if a suitable boost converter is designed while still minimizing the conduction and switching losses for improved performance.

In this paper, we propose a detailed study of four high-step-up boost converters. Then, the most suitable topology is chosen after a careful analysis of the simulation results. In Figure 1, the overall block diagram of the proposed system is shown for better understanding of the proposed topology. The design of four types of high-step-up bootstrap converters and a multilevel inverter energizing the switched reluctance motor (SRM) according to the prevailing necessity are considered the main contributions of the work claimed in this research. The cost-reducing factor has already been discussed adequately.

The rest of this paper is organized as follows: The Section 2 elaborates on the design and selection part of the optimal bootstrap DC-DC converter and its reliable features. The multilevel-inverter-fed SRM drive is designed to provide a dynamic speed response during source variations as well as load surges in the Section 3. Section 4 shows the photovoltaic supply comparison with and without the maximum power point tracking (MPPT) controller that excites the DC-DC converter. Numerical results and hardware implementation are depicted in Section 5, while the paper’s conclusions and justifications are briefly highlighted in Section 6.

There are two types of converters available for modifying the power obtained from the solar cells, which are meant for consumer-friendly use. The first is an inverter, which converts the DC into AC at the desired frequency to supply AC appliances. The other one is a DC-to dc converter, which already possesses numerous applications via DC motors for solar water pumping systems and other emerging areas like solar-powered electrical vehicles. In this proposed system, the preferred PVPE is driven by SRM; therefore, we have opted for designing a suitable boost converter and PWM inverter. As a result, various boost converters, starting from the basic conventional converter to newly proposed topologies like interleaved converters, quadruple converters, hybrid interleaved-quadruple converters, and finally bootstrap converters, were designed and simulated in this paper. The results were compared to choose the best converter according to the motor requirements.

The multilevel-inverter-fed SRM drive is designed to provide a dynamic speed response during source variations as well as load surges in this section. Figure 8 illustrates the energy flow diagram of the proposed multilevel inverter topology (Phase A) at various levels. When the DC supply is given to the circuit, all three capacitors C1, C2 and C3 get charged. The DC voltage across the capacitors is equally divided, i.e., V C 1 = V C 2 = V C 3 = V d c 3 (1)

To attain the first level in the positive cycle, the switches SA and X1 are excited, and the energy flows through C1 − D1 − X1 − D3 − RL − SA − C1. For the second level, the current flows through C2 − D5 − X2 − D7 − SA − C1 − C2 and C3 − SC − RL − SA − C1 − C2 − C3 for the third level. In the negative cycle, for the first level, the current flows from C3 − SD − RL − D6 − X2 − D8 − C1, for the second level, the current flows from C2 − C1 − SD − RL − D2 − X1 − D4 − C2; and C1 − C2 − C3 − SD − RL − SB − C1.

In terms of the switching conditions provided in Table 2, the gating pulses for each switch are graphed in Figure 9. In one full cycle of operation, the seven-level output is divided into 16 regions with respect to the firing angle (α _n ). For a seven-level switched capacitor-based symmetric multilevel inverter (SCBSMLI), the three positive half cycle levels are triggered at α ₁, α ₂, and α ₃, which lie between 0 and π/2, and the negative half cycle levels are triggered at α ₉ (=π + α ₁), α ₁₀ (=π + α ₂), and α 11 = π + α 3 , which lies between π and 3π/2. The zero level occurs during α ₀ (=0) to α ₁, α ₇ to α ₉, and α ₁₅ to α ₁₆ (=2π).

The switches are turned on in the following regions: S A : α 1 < ω t < α 7 S B : α 11 < ω t < α 13 S C : α 3 < ω t < α 5 S D : α 9 < ω t < α 15 X 1 : α 1 < ω t < α 2 α 6 < ω t < α 7 α 10 < ω t < α 11 α 13 < ω t < α 14 (2) X 2 : α 2 < ω t < α 3 α 5 < ω t < α 6 α 9 < ω t < α 10 α 14 < ω t < α 15 (3) The above switching conditions (2) and (3) are rewritten in the term of α ₁, α ₂ and α ₃ S A : α 1 < ω t < π 2 + α 3 S B : π + α 3 < ω t < 3 π 2 + α 1 S C : α 3 < ω t < π 2 + α 1 S D : π + α 1 < ω t < 3 π 2 + α 3 X 1 : α 1 < ω t < α 2 π 2 + α 2 < ω t < π 2 + α 3 π + α 2 < ω t < π + α 3 3 π 2 + α 1 < ω t < 3 π 2 + α 2 (4) X 2 : α 2 < ω t < α 3 π 2 + α 1 < ω t < π 2 + α 2 π + α 1 < ω t < π + α 2 3 π 2 + α 2 < ω t < 3 π 2 + α 3 (5)

From the above (4) and (5), the AC output voltage of the SCBSMLI is calculated using the Fourier Half Sine series as given in the (6), since the desired output is ultimately as f ω t = V C 1 , i f α 1 < ω t < π − α 1 V C 2 , i f α 2 < ω t < π − α 2 V C 3 , i f α 3 < ω t < π − α 3 (6) f ω t = ∑ n = 1 ∞ b n s i n n ω t (7) where b n = 2 π ∫ 0 π f ω t s i n n ω t d ω t (8) writing (8) in terms of voltage V a c = 2 π ∫ 0 π V m s i n ω t d ω t (9) Substituting (5) in (8) V a c = 2 π ∫ α 1 π − α 1 V C 1 s i n ω t + ∫ α 2 π − α 2 V C 2 s i n ω t + ∫ α 3 π − α 3 V C 3 s i n ω t (10) Substituting (2) in (9) V a c = 2 π ∫ α 1 π − α 1 V d c 3 s i n ω t + ∫ α 2 π − α 2 V d c 3 s i n ω t + ∫ α 3 π − α 3 V d c 3 s i n ω t (11) V a c = 2 V d c 3 π ∫ α 1 π − α 1 s i n ω t + ∫ α 2 π − α 2 s i n ω t + ∫ α 3 π − α 3 s i n ω t (12)

Integrating and simplifying (10) using trigonometric functions, the AC output voltage is for seven-level SCBSMLI given as V a c = 4 V d c 3 π c o s α 1 + c o s α 2 + c o s α 3 (13) DC machine-like performance can be achieved for a permanent magnet synchronous motor (PMSM) drive when vector-control or field-oriented control (FOC) is used to achieve decoupling control. It is mentioned that the vector-control decouples the excitation component (i _d ) and torque segment (i _q ) in PMSM by applying the instant space-vector hypothesis (Pillay and Krishnan, 1989; Bharatiraja et al., 2016a; Bharatiraja et al., 2016b). A high-precision and servo-controlled industrial robot driven by PMSM-Direct Torque Control utilizing composite active vectors is designed in (Yuan et al., 2019). The conceptual framework of antecedents to trends on permanent magnet synchronous generators for wind energy conversion systems has been briefed in (Chokkalingham et al., 2018; Padmanathan et al., 2019; Fekik et al., 2021).

The PMSM-PUMP drive comprises five primary parts: the PMSM, inverter, control unit, temperature sensor, and pump as load. The schematic representation of the drive system is shown in Figure 10. The inverter receives DC supply from the PV panel with a constant-voltage MPPT controller. Thus, the pump receives constant voltage during the day even when fluctuations are experienced in the Sun’s radiance insolation.

The proposed system is simulated, and the results are compared with the system simulated without MPPT. The MPPT-controlled bootstrap converter drives the SVM inverter to run the PMSM-PUMP assembly block diagram, as shown in Figure 11. The comparison between the proposed system without MPPT and with MPPT is done after introducing a step change in the insolation from 1,000 to 950, as exhibited in Figure 12.

Following the insolation graph, the other parameters like V _pv , P _pv , V _out , and speed of the motor are obtained and compared with the system without MPPT to show the superiority of the proposed system.

A comparison of output voltage and motor speed with and without MPPT is delineated in Table 3. By using the MPPT controller, the output voltage is enhanced from 385V to 415V, and motor speed is also enhanced from 1200 RPM to 1415 RPM. The panel voltage and power also seem to be improved in the MPPT-controlled system.

From Table 3, it is evident that the system with MPPT is showing better results than the system without MPPT. Also, the desired values are obtained, and the response is stable for the system with the MPPT technique.

Thus, after the design of the proposed system, the implementation of the prototype model is carried out. Its results are validated with the proposed topology, and the challenges of implementation are summarized. Figure 13 shows the hardware setup of the proposed topology. The bootstrap converter is designed, and its output is shown in the DSO. The solar panel supplies the DC voltage for the bootstrap converter, and the constant voltage MPPT technique is employed to offer the required output as per the motor ratings. The motor speed response is converted into serial input, and then it is sent to the COM-8 port of the computer, where it is displayed on the monitor. The hardware parameters of the bootstrap are given in Table 4.

Figure 14 shows the output of the bootstrap converter from the hardware implemented for the purpose of giving constant dc voltage equal to 23.7 V and current of 142 mA to the inverter which drives the SRM. Then Figure 15 gives the speed response of the SRM to deliver a constant speed to the ELEVATOR load even if any disturbance occurs.

This work has introduced four architectures of DC-DC converters for possible application in low-cost PVPEs. Results and comparisons from simulations show that the proposed bootstrap converter provides an enhanced output and small voltage pressure on the switches. In the projected topology, only two inductors are used for high-voltage output applications. In different operations, the converter just handles two duty ratios. Thus, we can minimize the overall cost of the solar-powered water elevator system by reducing processes like battery installation, maintenance, and further switching losses due to the DC-AC alteration stage. The direct DC-DC boost converter coupled configuration might also provide additional cost reduction. In our solution, the SRM is used as the drive for the elevator. The speed response of the SRM is guarded by a multilevel inverter controller, which ensures the stability of the whole system. The bootstrap converter supplying DC to the inverter that excites the SRM to drive the prototype is finally implemented.

Future work will focus on refining the proposed bootstrap converter architecture to optimize its efficiency and performance further. Additionally, research will explore integrating advanced control strategies to enhance the overall stability and reliability of the solar-powered water elevator system.