## 1 Introduction  
Green energy includes solar, wind, thermal, hydro, tidal, biomass, thermal, etc. Although green energy is a clean and inexhaustible source, there are still many problems to overcome, such as the low voltage generated by green energy, the susceptibility to unstable voltages or currents due to external environmental influences, and the tendency for voltages or currents to fluctuate with load changes. To solve these problems, a step-up converter is usually connected to the back end of the thermoelectric generator (TG), with maximum power point tracking (MPPT) to extract energy steadily for the back-end equipment, or to a step-up or step-down inverter to convert DC power to AC power in parallel with the mains or for other loads [1, 2], as shown in Figure 1.  
Concerning multi-input single-output (MISO) converters, the topology proposed by [3] is a switched capacitor (SC) converter, which uses the superposition of capacitor voltages to improve the boost ratio. The circuit presented by [3] is a modification of the circuit [4] with a two-stage interleaved structure, which allows for a higher boost ratio for high currents but increases the number of elements. The structures proposed by [5, 6] are simple and are derived from the conventional interleaved boost converter such that they use fewerelements to improve the boost ratio. Consequently, the corresponding boost ratios are limited. The dual-input isolated high-boost structure proposed in [7] incorporates an active clamp circuit to reduce the voltage stress on the switches. The circuit presented by [8] is a dual-input converter derived from the interleaved structure of [9], and therefore is not suitable for systems with multiple MPPTs because this circuit has automatic balance of the input currents. The structure proposed by [10] is a dual-input converter derived from the quasi-Y-source structure. The circuit proposed by [11] is a modification of the conventional buck-boost converter into two inputs. The topology presented by [12] adopts a transformer to enable a full-bridge converter to possess multiple inputs. By doing so, it is not possible to extend more inputs due to the size limitation of the transformer. In [13], one of the inputs of the multi-input converter is connected to batteries, which have bidirectional operation of charging and discharging circuits. Because of the need to consider the circuit path of the battery, the battery charging and discharging circuitry is more complex than normal. The circuit shown in [14] is composed of two interleaved boost circuits and employs two switches instead of two diodes to reduce conduction losses. In [15], a transformer and an interleaved boost circuit with switched capacitors are utilized to improve the boost ratio. In addition, an active clamping circuit is added to obtain ZVS turn-on of the switch. The topology presented by [16] adopts an interleaved structure with switched inductors to form a three-port circuit and active clamping circuits to ensure all the switches have ZVS turn-on. In [17], a dual-input boost converter modified from the conventional boost converter possesses a simple structure and a wide input voltage range. However, the second input voltage needs to be of opposite polarity to the output voltage. Consequently, this structure cannot be extended with more inputs. In [18], a converter with a three-port circuit and bidirectional operation is proposed. In [19], a modification of the conventional buck-boost circuit is presented, whose duty cycle can be regulated so that the converter can operate in buck, boost, and buck-boost modes. In [20], a thermal energy harvesting converter with two inputs and an isolated output is proposed. In addition, the number of inputs can be extended. As shown in Figure 2a, the MISO circuit modified from Figure 2b is applied to two heat sources [21]. Staggering the timing for the two maximum power traces solves the problem of two heat sources not being able to carry out individual MPPTs.