The DC-DC converter topologies that are to be used in a PV-based power supply should meet the conditions given in the subsequent paragraphs. A typical layout of DC microgid is depicted in Figure 4. Without increasing the stack size, we can obtain the desired DC voltage value with the help of the DC-DC converter. For example, the DC output from the polymer electrolyte membrane (PEM) FC stack is mostly around several tens of volts. Therefore, the ripple current value observed across the PV due to the DC-DC converter switching should be low. Most importantly, a sharp rise or a fall in the current and high-frequency current ripple of a large magnitude should be avoided [16].

An overview of the present-day technology in isolated DC-DC converters for PV-based power generation is presented in Table 1. The study includes an analysis of literature to understand current achievements and viewpoints. While many papers on the subject have been published, many of them do not include details on the achieved efficiency or the complexity of the converter when operating a greater number of devices, and issues with power density maximization are mentioned. Within the limited information available, a comparison of published literature for high voltage gain DC-DC converters is attempted, and an overview of each solution is provided.

This section enumerates the published solutions of coupled inductor topology DC-DC converters possess high gain, as shown in Figure 5, Figure 6, Figure 7 and Figure 8. Each published technique explains the topology used, the converter V_in and V_out range, and the power range of the experimental setup are given to validate the interfacing with FC for power generation. In [17] the authors proposed a DC-DC converter with soft switching exhibits continuous input current and a high voltage gain. Experimentally, a 200 W prototype having V_in = 24 V, and V_out = 360 V gives 96.4% efficiency at full load. The advantages of derived interleaved boost converter having Winding-Cross-Coupled Inductors (WCCIs) and passive-lossless clamp circuits are increased voltage gain, reduced switching voltage stress, and reduced reverse recovery problem due to the leakage inductance when compared with conventional interleaved boost converters [18]. An interleaved boost converter rated 1 kW, 40 V to 380 V experimental findings show an efficiency of 90.7% at full load, which is 5% better than a typical interleaved boost converter. [19]. A three-winding coupled inductor produced a high voltage gain. The energy in the leakage inductor is released to the output directly, reducing the switch stress. The output diode’s reverse recovery current is evaluated using a coupled inductor. A closed loop control method is used, which overcomes the power source voltage drift problem. The converter is used with a FC which gives a P_o = 300 W V_out = 400 V, V_in = 27 V–36.5 V and F_s = 100 kHz. It gives a maximum efficiency of 95.2% at 220 W. A 200 W boost converter having coupled inductors, and buck-boost active clamps for low V_in applications is proposed in [20]. The V_in range is 25–40 V, V_out is 200 V and output current of 1A with a switching frequency of 66 kHz. ZVS turns on the main and auxiliary switches, and the boost diode is turned on DC-DC ZCS. Thus, the switching losses are chopped. The converter efficiency is 92%, and the output power is 200 W. A high voltage gains 250 W non-isolated DC-DC converter having a three-stage switching cell and voltage multiplier is proposed and demonstrates the V_in range is 30–45 V, and V_out is 400 V. The three-stage switching cells reduce the converter’s size and conduction losses while efficiency is 97% [20].

A high step-up DC-DC converter is required to boost the voltage value generated through the 400 V DC bus voltage PV. Passive loss clamped technology is used to improve efficiency and limit voltage stress. Recycling of leakage energy is possible with the help of passive losses clamped technology. The basic boost converters’ main disadvantages include problems with the electromagnetic interface, high voltage stress and hard switching on the semiconductor elements [21]. Coupled inductor DC-DC buck-boost converter is used for a step up and down by non-inverting voltage, this also offers high efficiency, control and regulation of input and output currents smoothly and immediately [22].

The structure of the DC-DC boost converter consists of two hybrid, multiple voltage cells, and three winding coupled inductors. Using two multiple voltage cells, parallelly charged and discharged series, can provide very high voltage gain under the appropriate turns of ratio and duty cycle [28].

This section listed the published solutions of high gain interleaved non-isolated DC-DC converter topology. The voltage multiplier technique is used to the non-isolated DC-DC converters to possess a high step-up static gain, is presented in [29]. The V_in is 24 V, and the output V_out is 400 V. The output power is 400 W. The converter operated with a switching frequency of 40 kHz. The converter efficiency was 95%. Low electromagnetic interference production and commutation losses are attained. Without a power transformer, high static gain operation is possible. The V_in is 48 V and V_out is 380 V with an operating frequency of 100 kHz. The measured efficiency at 1 kW is 94.1%. The voltage doubler circuits increase the operating range of the converter by reducing the transformer’s parasitic capacitor’s effects. The interleaved Inductor-Inductor-Capacitor (LLC) converter for high gain is shown in Figure 9. This converter operates in two modes: independently and simultaneously. At the same frequency, both the interleaving converters are operated in the simultaneous mode. The single converter only operates in the independent mode.

The wider V_out range is possible only with frequency control and combined mode changing [30]. The phase-shedding technique is used to improve the efficiency of the interleaved switched capacitor DC-DC converter. The high voltage gain is achieved in the converter with modular characteristics and an interleaved configuration [31]. Using the lower voltage rating, the MOSFETs in the converter reduce the conduction losses [32]. The typical schematic layout is shown in Figure 10.

All diodes and switches operate on ZVS and ZCS techniques in the interleaved full soft-switching DC-DC converter. To reduce the power loss and to increase the efficiency of the DC-DC converters, the ZVS and ZCS are used. Finally, the auxiliary circuit is placed out of the main power path to avoid the switches’ high current and voltage stress [33]. The schematic circuit diagram of interleaved high step-up converter is depicted in Figure 11. A highly efficient power system always insists a reliable DC-DC converter. An interleaved boost converter is required to convert the high-current low-voltage to low-current high-voltage.

Classical boost converter deemed to be less advance then interleaved boost converter which offers high efficiency, low input ripple current, fast transient response, high reliability and less electromagnetic emission. Interleaved boost converters are suitable for the design of a highly efficient FC power system. To improve the system efficiency three-phase directly coupled interleaved boost converter using CoolMOS transistor and silicon carbide diode is used. Analysis based on the performances of interleaved converters are summarized in Table 2.