**1. Introduction**

The DC microgrid contains renewable energy sources and a hybrid energy storage unit. Hence, we are using Energy Management Methods to reduce power fluctuation on power quality [1]. We utilise many switching devices in renewable energy sources because high penetration occurs and switching losses or harmonics impact the utility grid's system reliability [2]. This paper presents an overview of microgrids' energy management strategies and grid integration technologies. To produce a clean energy future and minimize costs, renewable energy-based distributed generation is moving fast to meet the world's vital needs of utilizing clean energy sources [3]. By converting solar energy into electrical energy without environmental contamination photovoltaic system provides a direct method. PV systems convert solar power to electric power integrated with the grid if it meets the grid code [4]. The DC microgrid consists of a battery energy storage system, wind turbine, grid-connected converter system, and dc loads. Solar PV is one of the renewable energy technologies best suited for islands, hills, and forest areas such as,

	- ➣ Illiterate and Poor technical knowledge places.

Here power electronics blocks are required for grid integration to maximize the benefits of solar energy [5].

Solar PV and load require a suitable DC-DC converter to increase the system's efficiency. Multiple converters are typically designed for high voltage gain of solar PV applications [6]. In addition, better dynamic response and less ripple are obtained by multiphase interleaved DC-DC converters, preserving their efficiency. This study presents a SEPIC, CUK combination converter-based interleaved converter for connecting distributed generation to bipolar DC micro grids and power architecture [7]. Finally, switched inductors

**Citation:** Jagadeesh, I.; Indragandhi, V. Comparative Study of DC-DC Converters for Solar PV with Microgrid Applications. *Energies* **2022**, *15*, 7569. https://doi.org/ 10.3390/en15207569

Academic Editors: Alon Kuperman and Nicu Bizon

Received: 29 August 2022 Accepted: 10 October 2022 Published: 13 October 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

School of Electrical Engineering, Vellore Institute of Technology, Vellore 632014, India

and switched capacitors are used to provide a high gain. All semiconductor devices have the same voltage stress. Therefore, it is possible to utilize devices with uniform ratings and minimal internal resistance [8]. Finally, a multi-port isolated DC-DC converter replaced the traditional Buck/Boost circuit to ensure electrical isolation of the energy storage system's micro sources [9]. The boost DC-DC converter topology has the following demerits: large capacitors are needed, there is a <4:1 voltage gain, parallel devices are required at high power levels, and there is a high ripple rate [10,11]. Due to their high conversion efficiency, minimal size, and low production costs, the described DC-DC converter topology a significant role in the power-generating industry, including microgrids. The DC-DC converters in are separated into isolated and non-isolated topologies [12,13]. The general classification of DC-DC converters are depicted in Figure 1. uted generation to bipolar DC micro grids and power architecture [7]. Finally, switched inductors and switched capacitors are used to provide a high gain. All semiconductor devices have the same voltage stress. Therefore, it is possible to utilize devices with uniform ratings and minimal internal resistance [8]. Finally, a multi-port isolated DC-DC converter replaced the traditional Buck/Boost circuit to ensure electrical isolation of the energy storage system's micro sources [9]. The boost DC-DC converter topology has the following demerits: large capacitors are needed, there is a <4:1 voltage gain, parallel devices are required at high power levels, and there is a high ripple rate [10,11]. Due to their high conversion efficiency, minimal size, and low production costs, the described DC-DC converter topology a significant role in the power-generating industry, including microgrids. The DC-DC converters in are separated into isolated and non-isolated topologies [12,13]. The general classification of DC-DC converters are depicted in Figure 1.

plications [6]. In addition, better dynamic response and less ripple are obtained by multiphase interleaved DC-DC converters, preserving their efficiency. This study presents a SEPIC, CUK combination converter-based interleaved converter for connecting distrib-

*Energies* **2022**, *15*, x FOR PEER REVIEW 2 of 22

**Figure 1.** Types of DC-DC converters. **Figure 1.** Types of DC-DC converters.

When the traditional boost converter is preferred in PV systems, it has to be operated at a duty cycle of 0.88, making it difficult in practical application due to the limitation of semiconductor devices. Moreover, the boost converters suffer the drawback of high switching voltage stress and reverse recovery issues [14]. The applications of smart grid system are summarized in Figure 2. When the traditional boost converter is preferred in PV systems, it has to be operated at a duty cycle of 0.88, making it difficult in practical application due to the limitation of semiconductor devices. Moreover, the boost converters suffer the drawback of high switching voltage stress and reverse recovery issues [14]. The applications of smart grid system are summarized in Figure 2.

The grid functions today are the same as when there were minor improvements, and the energy cost was relatively low. There is currently no heavy electricity storage technology available. Therefore, if we use this power during off-peak hours, we will build an effective system. However, we may adjust load consumption to increase grid efficiency, which is how the Smart grid differs from a traditional grid.

These converters require a higher power transformer, as higher power converters cannot use a single switch topology. For example, Half-bridge, push-pull and Full-bridge converters comes under another DC-DC isolated converters which use a minimum of multi-switch. Figure 3 represents a simplified hybrid microgrid charging station for batterypowered electric vehicles.

*Energies* **2022**, *15*, x FOR PEER REVIEW 3 of 22

**Figure 2.** The architecture of smart grid management system applications. **Figure 2.** The architecture of smart grid management system applications. mum of multi-switch. Figure 3 represents a simplified hybrid microgrid charging station

for battery-powered electric vehicles.

The grid functions today are the same as when there were minor improvements,

**Figure 3.** The battery-based electric vehicle's charging station with the hybrid microgrid model. **Figure 3.** The battery-based electric vehicle's charging station with the hybrid microgrid model.

The PV technologies can be employed in various applications, including electric vehicles, domestic, and microgrid applications [15]. The different operating voltages of the DC-DC converters linked to the PV system are described. In addition, in grid-connected mode converters, suitable load types are identified along with their corresponding voltage gain and conversion efficiency. This review elucidates the operation of 14 types of DC-DC converters for grid-connected PV applications. This is followed by comparing the converters performance for different grid-connected PV systems operating modes along with discussed distributed energy sources. At last, each converters parametric analysis and

**Figure 3.** The battery-based electric vehicle's charging station with the hybrid microgrid model.

components sizing comparison are critically examined to further identify the drawbacks in each converter for a particular source application for a specific mode of operation. identify the drawbacks in each converter for a particular source application for a specific mode of operation.

The PV technologies can be employed in various applications, including electric vehicles, domestic, and microgrid applications [15]. The different operating voltages of the DC-DC converters linked to the PV system are described. In addition, in grid-connected mode converters, suitable load types are identified along with their corresponding voltage gain and conversion efficiency. This review elucidates the operation of 14 types of DC-DC converters for grid-connected PV applications. This is followed by comparing the converters performance for different grid-connected PV systems operating modes along with discussed distributed energy sources. At last, each converters parametric analysis and components sizing comparison are critically examined to further

#### **2. Requirements for the Selection of DC-DC Converter Topology 2. Requirements for the Selection of DC-DC Converter Topology**

*Energies* **2022**, *15*, x FOR PEER REVIEW 4 of 22

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]. 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].

**Figure 4.** Layout of DC microgrid **Figure 4.** Layout of DC microgrid.

An overview of the present-day technology in isolated DC-DC converters for PVbased 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. 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.

#### **3. Survey of DC-DC Converter Topologies**

#### *3.1. Coupled Inductor Converter Topology*

This section enumerates the published solutions of coupled inductor topology DC-DC converters possess high gain, as shown in Figures 5–8. Each published technique explains the topology used, the converter Vin and Vout 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 Vin = 24 V, and Vout = 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<sup>o</sup> = 300 W Vout = 400 V, Vin = 27 V–36.5 V and F<sup>s</sup> = 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 Vin applications is proposed in [20]. The Vin range is 25–40 V, Vout 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 Vin range is 30–45 V, and Vout is 400 V. The three-stage switching cells reduce the converter's size and conduction losses while efficiency is 97% [20]. 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 threewinding 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<sup>o</sup> = 300 W Vout = 400 V, Vin = 27 V–36.5 V and F<sup>s</sup> = 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 Vin applications is proposed in [20]. The Vin range is 25–40 V, Vout 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 Vin range is 30–45 V, and Vout is 400 V. The three-stage switching cells reduce the converter's size and conduction losses while efficiency is 97% [20].

This section enumerates the published solutions of coupled inductor topology DC-DC converters possess high gain, as shown in Figures 5–8. Each published technique explains the topology used, the converter Vin and Vout 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 Vin = 24 V, and Vout = 360 V gives 96.4% efficiency at full load. The advantages of derived interleaved boost converter having Winding-Cross-Coupled Inductors (WCCIs) and

*Energies* **2022**, *15*, x FOR PEER REVIEW 5 of 22

**3. Survey of DC-DC Converter Topologies** *3.1. Coupled Inductor Converter Topology*

**Figure 5. Figure 5.**  Coupled inductor 1. Coupled inductor 1.

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 buckboost 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 im-

**Figure 6.** Coupled Inductor 2. **Figure 6.** Coupled Inductor 2.

**Figure 7.** Coupled Inductor 3.

**Figure 8.** Coupled inductor 4.

mediately [22].

*Energies* **2022**, *15*, x FOR PEER REVIEW 6 of 22

**Figure 7.** Coupled Inductor 3. **Figure 7.** Coupled Inductor 3. **Figure 7.** Coupled Inductor 3.

**Figure 6.** Coupled Inductor 2.

**Figure 6.** Coupled Inductor 2.

**Figure 8.** Coupled inductor 4. **Figure 8.** Coupled inductor 4. **Figure 8.** Coupled inductor 4.

mediately [22].

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 buckboost 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 im-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 buckboost 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 im-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].




**Table 1.** *Cont.*

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].

#### *3.2. Interleaved Non-Isolated Topology*

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 Vin is 24 V, and the output Vout 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 Vin is 48 V and Vout 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. *Energies* **2022**, *15*, x FOR PEER REVIEW 8 of 22

**Figure 9.** Interleaved non-isolated topology. **Figure 9.** Interleaved non-isolated topology.

verter.

The wider Vout 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. The wider Vout 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.

**Figure 10.** Non-isolated high voltage gain ratio interleaved coupled-inductor type DC-DC con-

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

The wider Vout 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

**Figure 9.** Interleaved non-isolated topology.

[32]. The typical schematic layout is shown in Figure 10.

**Figure 10.** Non-isolated high voltage gain ratio interleaved coupled-inductor type DC-DC con-**Figure 10.** Non-isolated high voltage gain ratio interleaved coupled-inductor type DC-DC converter.

verter. 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 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. *Energies* **2022**, *15*, x FOR PEER REVIEW 9 of 22 [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

silicon carbide diode is used. Analysis based on the performances of interleaved con-

) (

) (

This section lists the published solutions of isolated push-pull boost converter topology for high-gain DC-DC converters [38]. The proposed converter is a push-pull type hard switched isolated boost converter. The proposed converter is implemented along with a voltage clamp circuit on the isolation transformer's primary and secondary sides. After the front end, the push-pull converter H-bridge DC-AC converter follows. The range of converter input Vin is taken as 25–45 V and Vout as 350–400 V. For the 900 W power level, the maximum calculated efficiency is 91%. Utilizing the resonant converter gives an advantage of a 1.5 kW front-end converter for FC applications, which is presented in [39]. On the secondary side of isolation transformer, a voltage doubler concept was introduced to tune the current resonance to minimize the diode losses (recovery).

0 4

2( + 1) 1 −

) (

) <sup>2</sup> + (

0 3 )

(23+2−) 1−

)

**Figure 11.** High step-up interleaved converter. **Figure 11.** High step-up interleaved converter.

( 0 6

2 ( + 2) 1 −

The voltage stress on the switches (*n* = 1)

Voltage gain (

verters are summarized in Table 2.

) (

) (

*3.3. Isolated Push-Pull Boost Converter*

**Table 2.** Performance analysis of the interleaved converters. **Parameter [34] [35] [36] [37]** Input ripple current Low Low Low Moderate Number of diodes 4 8 4 6

> 0 4

3 + 1 1 −

Number of windings 4 6 4 6

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.


**Table 2.** Performance analysis of the interleaved converters.

#### *3.3. Isolated Push-Pull Boost Converter*

This section lists the published solutions of isolated push-pull boost converter topology for high-gain DC-DC converters [38]. The proposed converter is a push-pull type hard switched isolated boost converter. The proposed converter is implemented along with a voltage clamp circuit on the isolation transformer's primary and secondary sides. After the front end, the push-pull converter H-bridge DC-AC converter follows. The range of converter input Vin is taken as 25–45 V and Vout as 350–400 V. For the 900 W power level, the maximum calculated efficiency is 91%. Utilizing the resonant converter gives an advantage of a 1.5 kW front-end converter for FC applications, which is presented in [39]. On the secondary side of isolation transformer, a voltage doubler concept was introduced to tune the current resonance to minimize the diode losses (recovery). Switching active clamp circuits' blocking voltage is used on both sides to clamp the peak. The proposed converter follows with an H-bridge DC-AC converter. Overall, a calculated system efficiency of 92.5% is achieved with an Vin range of 30 V and an Vout of 350 V for 700 W power level. *Energies* **2022**, *15*, x FOR PEER REVIEW 10 of 22 Switching active clamp circuits' blocking voltage is used on both sides to clamp the peak. The proposed converter follows with an H-bridge DC-AC converter. Overall, a calculated system efficiency of 92.5 % is achieved with an Vin range of 30 V and an Vout of 350 V for 700 W power level.

#### *3.4. Fly Back Converter Topology 3.4. Fly Back Converter Topology*

This section lists the published solutions of Fly-back converter topology for high-gain DC-DC converters as shown in Figures 12 and 13. A 300 W isolated high step-up ratio DC-DC converter that uses a voltage multiplier on the secondary side and active clamp on the transformer main side is proposed in [40]. The Vin range is 25–35 V, and Vout is 400 V. The circulating current through the active clamp is reduced due to the resonant phases between transformer leakage inductances and diode parasitic capacitances, which also lowers the conduction losses. This section lists the published solutions of Fly-back converter topology for highgain DC-DC converters as shown in Figures 12 and 13. A 300 W isolated high step-up ratio DC-DC converter that uses a voltage multiplier on the secondary side and active clamp on the transformer main side is proposed in [40]. The Vin range is 25–35 V, and Vout is 400 V. The circulating current through the active clamp is reduced due to the resonant phases between transformer leakage inductances and diode parasitic capacitances, which also lowers the conduction losses.

The converter's efficiency of 92% to 94% for the entire Vin range and 300 W output power. A 300 W high step-up ratio converter for low-voltage and high-current energy sources is proposed [41]. The clamping diode integrated with boost-flyback (IBF) topology that naturally clamps parasitic oscillations. Resonance caused by the parasitic components helps to increase the voltage gain. The Vin range is 25–35 V, and Vout is 400 V. Various parameter has been evaluated and summarized in Table 3 for various converters. A simple design of asymmetrical forward cells of stacked multiple output topology

**Figure 12.** Boost fly-back converter topology. **Figure 12.** Boost fly-back converter topology.

**Figure 13.** Active clamp boost fly-back converter.

is depicted in Figure 14.

Switching active clamp circuits' blocking voltage is used on both sides to clamp the peak. The proposed converter follows with an H-bridge DC-AC converter. Overall, a calculated system efficiency of 92.5 % is achieved with an Vin range of 30 V and an Vout of 350

This section lists the published solutions of Fly-back converter topology for highgain DC-DC converters as shown in Figures 12 and 13. A 300 W isolated high step-up ratio DC-DC converter that uses a voltage multiplier on the secondary side and active clamp on the transformer main side is proposed in [40]. The Vin range is 25–35 V, and Vout is 400 V. The circulating current through the active clamp is reduced due to the resonant phases between transformer leakage inductances and diode parasitic capaci-

V for 700 W power level.

*3.4. Fly Back Converter Topology*

tances, which also lowers the conduction losses.

**Figure 13.** Active clamp boost fly-back converter. **Figure 13.** Active clamp boost fly-back converter.

**Figure 12.** Boost fly-back converter topology.

The converter's efficiency of 92% to 94% for the entire Vin range and 300 W output power. A 300 W high step-up ratio converter for low-voltage and high-current energy sources is proposed [41]. The clamping diode integrated with boost-flyback (IBF) topology that naturally clamps parasitic oscillations. Resonance caused by the parasitic components helps to increase the voltage gain. The Vin range is 25–35 V, and Vout is 400 V. Various parameter has been evaluated and summarized in Table 3 for various converters. A simple design of asymmetrical forward cells of stacked multiple output topology The converter's efficiency of 92% to 94% for the entire Vin range and 300 W output power. A 300 W high step-up ratio converter for low-voltage and high-current energy sources is proposed [41]. The clamping diode integrated with boost-flyback (IBF) topology that naturally clamps parasitic oscillations. Resonance caused by the parasitic components helps to increase the voltage gain. The Vin range is 25–35 V, and Vout is 400 V. Various parameter has been evaluated and summarized in Table 3 for various converters. A simple design of asymmetrical forward cells of stacked multiple output topology is depicted in Figure 14.

is depicted in Figure 14. **Table 3.** Parameter analysis of various DC-DC converters.


The converter efficiency is about 94% for a 100 kHz frequency of operation, and the output power is 300 W. The conventional isolated converter with N-outputs requires 2 N primary switches. The above circuit requires *N* + 1 primary switches to independently regulate the secondary side N output voltages [45].
