DC-DC converters are necessary for electric vehicles (EVs), transportation, microgrids powered by renewable energy, etc. DC-DC converters are essential interfaces for effective energy management.

Classification of DC-DC Converter

There are two types of DC-DC converter topologies:

● Isolated converter

● Non-isolated converter

Isolated Converter

The high-frequency transformers that separate the load and input source are the primary components of isolated topologies. Sensitive loads may need this kind of isolation. This isolation shields the load from input-side failures that may occur.

The turn ratio of the windings is the primary factor that increases the voltage ratio in isolated converters. It is important to note that the suggested factor has significant negative impacts, including

● EMI noises

● Residual current that necessitates the use of energy recovery circuits

● Increase in loss

● A fall in power density as a result of this component's magnetic basis

Non-Isolated Converter

It is not essential to isolate the input source and the load while using non-isolated topologies. As a result, most applications, including high-intensity discharge lights (HIDs) and renewable energy sources, use non-isolated converters.

The voltage range needed for HID lighting is 100 V to 250 V. The car's batteries, whose maximum voltage is 12 V, can supply such a voltage, though. Vehicles cannot handle the increased weight that results from using isolated topologies. Consequently, the use of non-isolated converters is necessary.

Photovoltaic panels and other forms of renewable energy are the subject of the second case study. The voltage between 15 V and 65 V is the output of the converter.

Types of Non-Isolated DC-DC Converters

The conventional non-isolated DC-DC converters that have the ability to raise their input voltage are

● Boost

● Buck-Boost

● Cuk

● SEPIC topologies

Challenges Faced By Non-Isolated Topologies

Out of all the topologies described, the boost topology can raise the input voltage level by every duty cycle value. Its input current is also continuous, as for SEPIC and Cuk topologies.

It is important to note that the Cuk and Buck-Boost converters have lost both the common ground and the load from the input source. All the discussed topologies have the same deficiencies. Apart from a low duty cycle % and adequate efficiency, they are unable to deliver a high voltage gain value. The proposed solution to this problem is the use of Luo converters.

Positive Output Super Lift Luo (POSLL) converter

By using smaller duty cycle percentages, the voltage lift technique raises the voltage gain to a larger amount. The converters are described as the Positive Output Super Lift Luo (POSLL) converter.

This topology has a low count. Its design includes

● One inductor

● One switch

● Two diodes

● Two capacitors

Limitations

This converter has a larger voltage gain than the traditional ones. The voltage gain of the POSLL converter increases to 3 as the duty cycle approaches 50%. In contrast, this value is 1 in the Buck-Boost, SEPIC, and Cuk topologies and 2 in the Boost topology.

Based on the aforementioned ideas, alternative topologies must be provided because the voltage gain of the POSLL converter is not as great as anticipated.

Proposed Topology

The article proposes a modified quadratic DC-DC converter. The redesigned connection between the Cuk and POSLL converters makes up the converter's topology. As such, the voltage gain of the suggested converter features the voltage lift approach and quadratic topologies.

Fig. 1(a) shows an illustration of the suggested converter, which is made up of

● Two inductors (L1 and L2)

● Three capacitors (C1, C2, and Co)

● Three diodes (D1, D2, and D3)

● Two switches (S1 and S2)

Fig. 1: The proposed converter topology Source: IEEE Access

The provided topology, as shown in Fig. 1(b), is the result of combining the initial portions of the Cuk and POSLL topologies. It is noteworthy to notice that the output of the boost converter and the voltage of the first capacitor in the Cuk converter are the same. As a result, the voltage at the first step has been raised enough.

The second component has received the voltage from the first capacitor, as shown in Fig. 1(b). This section, which is red in color, relates to POSLL. The input source voltage has increased in two steps due to the indicated architecture.

When the converter is in its continuous conduction mode (CCM), it operates in two modes. Simultaneous activation of the second diode and switches occurs. The remaining semiconductors are also inactivated.

The converter's early use of the Cuk topology was successful in ensuring the continuity of the input current, according to a thorough examination of its topology. Furthermore, the absence of a common ground issue with the traditional Cuk topology has been resolved by the manner in which Cuk's topology is explained.

It is necessary to take certain factors into account in order to extract the converter's core relationships. The converter's structure is studied in the ideal mode and in the steady-state mode.

Conclusion

The voltage gain that a 50% duty cycle provides in the suggested topology is six times greater. In addition to the high voltage gain, there has been input current continuity. Furthermore, compared to the cascaded connection of the Cuk and POSLL converters, the resulting topology has a better voltage gain and fewer components.

Several of the semiconductors in the recently proposed converters have greater voltage and current stress values. Moreover, the voltage and current stress of both semiconductors in the proposed topology have decreased. The topology of the proposed converter produced a better level of voltage gain with fewer components.

Summarizing the Key Points

● DC-DC converters are vital for energy management in electric vehicles, transportation, and renewable energy applications, serving as essential interfaces for effective energy management.

● The article provides a comprehensive classification of DC-DC converters into isolated and non-isolated topologies, emphasizing their respective benefits and limitations.

● It is suggested that the Cuk and POSLL topologies be combined into a new quadratic DC-DC converter topology that will have a higher voltage gain and fewer parts.

● Non-isolated converters are indispensable for various applications, including high-intensity discharge lights and renewable energy sources, due to their ability to handle increased voltage levels.

● The article discusses the voltage lift technique as a solution to enhance voltage gain in non-isolated topologies, addressing challenges and improving overall efficiency.