Figure 4 illustrates the general setup of a quadratic boost converter which comprises one switch, three diodes and four passive elements. A high step-up voltage gain can be obtained by using a quadratic converter
Figure 4 at a moderate duty cycle [
22,
32], but the main drawback of such converters is that the voltage stress on the power switch is equal to the output voltage. Therefore, efficiency is compromised. The conventional quadratic boost converter has a limited voltage gain and is thus unsuitable for high-step-up applications.
Figure 5(a) shows a quadratic boost converter with a modified VL cell [
33]; it achieves a high voltage gain at the output side. Furthermore, it reduces the voltage stress on the power switch, which is an issue with traditional quadratic boost converters. In the literature ref [
34,
35,
36,
37,
38,
39,
40,
41,
42,
43,
44,
45,
46,
47,
48,
49,
50,
51,
52], many DC/DC converters based on quadratic boost converters and modified quadratic boost converters have been proposed to inhibit the dominant constraints in conventional boost converters. A quadratic following boost converter (QFBC) is presented in [
38]. It consists of two switches, three capacitors, three diodes and two inductors, and it can step up the voltage gain at a moderate duty cycle. In the modified QFBC (MQFBC) proposed in [
39], a bootstrap network is integrated to improve the conventional boost converter. In
Figure 5(b), a high voltage gain and reduced voltage stress are achieved by using a quadratic boost converter with a coupled inductor [
40,
41]. However, the power switch suffers from a high voltage stress caused by the leakage inductance of the coupled inductor. Passive clamping circuits are adopted to reduce this high voltage stress. The quadratic boost converter and SEPIC topologies in
Figure 5(c), which are presented in [
42], increase the voltage conversion ratio without an extreme duty ratio. This converter takes advantage of two well-known DC/DC converters, namely, a quadratic boost converter, which has a high step-up capability, and a SEPIC converter which can reduce the input current ripple. A quadratic SEPIC with a switched-coupled inductor, shown in
Figure 5(d), is proposed in [
43] to increase the voltage gain. In [
44], a quadratic boost converter and a zeta converter are proposed for a high voltage gain and efficiency. Additionally, both the input and output current ripples are low (features of the quadratic boost converter and zeta converter, respectively). A quadratic boost converter and a Ćuk converter are combined in [
45] to provide a high step-up voltage. Two configurations of this proposed converter are shown in Figs.
Figure 5(e) and
Figure 5(f). The configuration in
Figure 5(e) is called hybrid QBC type I and its voltage stress is lower than the output voltage of the converter. The configuration in
Figure 5(f) is called hybrid QBC type II, and its voltage gain is higher than that of hybrid QBC type I. A novel quadratic boost converter with low inductor currents is proposed in [
46]; it can increase the voltage gain as well as the conventional quadratic boost converter can. Furthermore, it has a non-pulsating input current and low voltage stress on the power switch. The main drawback of this converter is its use of two switches. A hybrid cascaded DC/DC converter usually consists of a quadratic boost converter and voltage multiplier circuits. A high voltage gain in [
47] is achieved by using a quadratic boost converter and a coupled inductor with an extended voltage doubler cell. Quadratic boost with a voltage multiplier cell was proposed in [
48], the output voltage is much higher under the same duty cycle of the traditional quadratic boost converter. Moreover, the input current ripple is low, and the voltage stress is reduced.